Zinc Oxide Topical pasteWhat is this medicine?ZINC OXIDE (zingk OX ide) is used to treat or prevent minor skin irritations such as burns, cuts, and diaper rash. Some products may be used as a sunscreen.How should I use this medicine?This medicine is for external use only. Do not take by mouth. Follow the directions on the prescription or product label. Wash your hands before and after use. Apply a generous amount to the affected area. Do not cover with a bandage or dressing unless your doctor or health care professional tells you to. Do not get this medicine in your eyes. If you do, rinse out with plenty of cool tap water.Talk to your pediatrician regarding the use of this medicine in children. While this drug may be prescribed for selected conditions, precautions do apply.What side effects may I notice from receiving this medicine?There have been no side effects reported this medicine. If you experience any unusual effects while using zinc oxide, contact your doctor or health care professional right away.What may interact with this medicine?Interactions are not expected. Do not use other skin products at the same site without asking your doctor or health care professional.What if I miss a dose?If you miss a dose, use it as soon as you can. If it is almost time for your next dose, use only that dose. Do not use double or extra doses.Where should I keep my medicine?Keep out of reach of children.Store at room temperature. Keep closed while not in use. Throw away an unused medicine after the expiration date.What should I tell my health care provider before I take this medicine?They need to know if you have any of these conditions: an unusual or allergic reaction to zinc oxide, other medicines, foods, dyes, or preservatives pregnant or trying to get pregnant breast-feedingWhat should I watch for while using this medicine?Tell your doctor or health care professional if the area you are treating does not get better within a week. SEMISOLID DOSAGE FORMS

SyllabusOintment bases: oleaginous bases, hydrocarbon and silicon containing bases.Absorption bases, emulsion bases, water soluble bases.Preparation and preservation of these ointments with industrial equipment used for processing.

Questions:1.Define and differentiate between Ointment and creams, lotion and liniment. (98) [4+4]2.Give different ointment bases with examples. (98)[8]3.Discuss various methods for manufacturing of ointments. [8]4.Write a note on different types of raw materials that are used in the manufacture of semisolid dosage forms. What are the factors that affect skin penetration of drugs from semisolids (96)[16]5.Preservative in ointment. (95) [4]6.How do you select the ointment base for a water soluble and insoluble drug to be incorporated for a medicinal preparation. Discuss on the selection of ointment base (94) [16]7.Discuss on the importance of packing materials for ointments. What is the influence of packing materials for ointment storage? (94) [16]8.Write in brief the factors governing the selection of ointment bases. (93) [6]9.Give the characteristics and examples of oleaginous bases. (93)[6]10.Discuss the different methods of ointment preparations. (93) [4]

INTRODUCTIONPharmaceutical semisolid dosage preparations include ointments, pastes, cream, emulsions, gels and rigid foams.

Ointmentsare soft semisolid preparations meant for external application to the skin or mucous membrane. They usually contain medicament, which is either dissolved or suspended in the base.They have emollient and protective action.Creamsare semisolid emulsions for external application and are generally of softer consistency and lighter than ointments.They are less greasy and are easy to apply.Pastesare semisolid preparations for external application that differs from similar products in containing a high proportion of finely powdered medicaments. They are stiffer and are usually employed for their protective action and for their ability to absorb serous discharges from skin lesions.Thus when protective, rather than therapeutic action is desired, the formulation pharmacists will favor a paste, but when therapeutic action is required, he will prefer ointments and creams.Jelliesare transparent or translucent, non-greasy, semisolid preparation mainly used externally.In these systems the liquid phase is entrapped within a three-dimensional polymeric matrix in which a high degree of physical cross-linking has been introduced.The polymers (gelling agents) used include:Natural Polymers : Tragacanth, pectin, carageenan, agar, alginic acid nd gelatin.Synthetic and Semisynthetic polymers: Methyl cellulose, hydroxymethyl cellulose, carboxymethyl cellulose and Carbopols.

STRUCTURE OF SKINThe skin has three main layers: the epidermis, dermis and hypodermis.Epidermisis the outermost layer. It consists of:(a)Thebasal layer(innermost) is one cell thick layer. Its cells divide constantly and the daughter cells are steadily pushed towards the surface.(b)Theprickle cell layer: The cells in this region are linked by tiny bridges or prickles.(c)Thegranular layer: When they reach this region, the upwardly moving cells become granules and begin to synthesize the inert protein keratin.(d)Thehorny layer(stratum corneum). This is the outermost layer and the cells are heavily keratinized and dead. The dead cells sloughs off gradually.Dermisis the middle and the main part of the skin. The dermis is made up of protein collagen and elastin. The collagen is in the form of gel that is reinforced by a framework of elastin.Dermis contains the following structures:(a)Blood vessels, lymphatics and nerves.(b)Epidermal appendages e.g. hair follicles, sebaceous glands and sweat glands.Hypodermis, the innermost layer, consists of adipose tissues. It gives physical protection and thermal insulation to underlying structures.N.B.Epidermis is non-granular but is penetrated by hair follicles, sebaceous glands and sweat glands.Sebum is the secretion of sebaceous glands. Sebum is a mixture of fatty substances and emulsifiers; it mixes with water producing a fluid of pH 5.5 that covers the skin surface and permeates the upper layer of keratinized cells this is called the acid-mantle of skin.Keratin is hydrophillic, the stratum corneum normally contains about 20% w/w of water, the amount varying with atmospheric humidity. This moisture keeps the skin supple and if its level falls below about 12% the cells becomes dry and brittle and then shrink and curl at the edges, making the skin feel rough.Cracking may follow, causing discomfort. Loss of water may be the result of excessive evaporation, over-usage of detergents (which removes sebum) and cold weather (which inhibits sebum production).

PERMEABILITY OF DRUG THROUGH EPIDERMISMost dermatological preparations belong to one of tw classes:1.Preparation intended to remain on the surface e.g. products for penetration or for emollient action.2.Preparations intended to penetrate the skin but will not enter into blood streamDrugs penetrate the epidermis by two man routes:(a)Through the keratinized cells of the stratum corneum.The keratinized cells are fused together so drug molecules directly diffuse through them. These cells contains keratin which is hydrophilic and phospholipids which is hydrophobic, so drug molecules having solubility in both water and oil have good permeability through this route.(b)Via hair folliclesAlthough the hair follicles occupy only a small area of the total epidermis, they provide a very important route of penetration. The fat soluble drugs dissolve in sebum, diffuses in to the sebum-filled follicles and passes to dermis.

FACTOR AFFECTING PERMEABILITY OF A DRUG THROUGH SKINA.Factor associated with the skin(a)Hydration of the horny layerThe hydration of keratinized cells is raised by covering the area with a moisture-proof plastic film to prevent evaporation of perspiration. Hydration increases the drug penetration.(b)Thickness of the horny layerThe horny layer is thickest on palms and soles and thinnest on the face; penetration rate increases with decreased thickness of horny layer.(c)Skin conditionThe permeability of the skin is affected by age, disease, climate and injury. For xample, absorption occurs rapidly in children and if the dermis is exposed by a wound or burn.B.Factors associated with the medicament(a)Solubility of the drugHighly lipid soluble molecules enters through hair follicles. Moderately lipid soluble molecules penetrates directly across the horny layer.(b)Dissociation constant (pKa)If a drug is ionized in the surrounding pH of the dermis then the penetration of the ionic species are restricted by electrostatic interactions. Degree of ionization depends on the pKa of the drug.e.g. Methyl salicylate and methyl nicotinate penetrate much faster than salicylic acid and nicotinic acid respectively.(c)Particle sizeReducing the particle size increases the dissolution of a poorly soluble drug in suspension and thus increases the release rate from the vehicle.(d)Crystal structureThe metastable polymorph is much more soluble than its stable form, so the release of drug in metastable state is much more faster than stable form.C.Factors associated with vehiclesThe rate of release of a drug from a vehicle to stratum corneum is governed byvehicle-to-stratum corneum partition coefficient. The thermodynamic activity of the drug in the vehicle is the product of the concentration of the drug and the activity coefficient () of the drug in the vehicle. Drugs held firmly by the vehicle exhibit low activity coefficient, hence slow rate of release from that drug-vehicle combination. Drug held loosely by the vehicle shows higher activity coefficient, hence shows faster rate of release.The vehicles may enhance the penetration of a drug in one or more of the following ways:-a)By ensuring good contact with the surface of the bodyb)By increasing the degree of hydration of the stratum corneumc)By penetrating the epidermisd)By directly altering the permeability of the skin(a)Contact with body surfaceSticky bases such as soft paraffin, Paraffin ointment B.P.C., Simple ointment B.P. etc. adheres well to the skin but are difficult to apply evenly and remove completely.Creams are easier to apply and remove. Oil in water (o/w) creams mix with sebum and are more suitable for weeping or wounded surface.(b)Hydration of stratum corneumAn occlusive layer reduces evaporation of water from skin, increasing hydration of the horny layer and, therefore, promotes penetration of medicament.e.g. hydrocarbons, wool fat and isopropyl myristate containing ointments produce occlusive films on the skin. Water in oil (o/w) type creams have some occlusive effects.Humectants like glycerols are not good for retaining water because at low atmospheric humidities, because they tend to increase loss of water by absorbing it from the skin.(c)Penetration of the epidermisBases miscible with the sebum penetrate into the regions of the skin in which sebum is found.e.g. Woolfat (originating from sebaceous glands of sheep) penetrates into the skin.Vegetable oils penetrate more slowly and liquid paraffin does not penetrate at all.(d)Alteration of skin permeabilityPenetration can be improved by dissolving the medicament in an organic liquid such as ethanol, dimethylformamide(DMF), dimethyl acetamide, dimethylsulfoxide (DMSO) and propylene glycol. They increases the hydration of skin.

OINTMENTDefinition: Ointments are semisolid preparations for application to the skin or mucosae. The ointment bases are almost always anhydrous and generally contains one or more medicaments in suspension or solution.

Characteristics of an ideal ointment:1.It should be chemically and physically stable.2.It should be smooth and free from grittiness.3.It should melt or soften at body temperature and be easily applied.4.The base should be non-irritant and should have no therapeutic action.5.The medicament should be finely divided and uniformly distributed throughout the base.

Classification of ointmentsAccording to their therapeutic properties based on penetration of skin.(a) Epidermic, (b) Endodermic, (c) Diadermic

(a) Epidermic ointmentsThese ointments are intended to produce their action on the surface of the skin and produce local effect.They are not absorbed.They acts as protectives, antiseptics and parasiticides.(b) Endodermic ointmentsThese ointments are intended to release the medicaments that penetrate into the skin. They are partially absorbed and acts as emollients, stimulants and local irritants.(c) Diadermic ointmentsThese ointments are intended to release the medicaments that pass through the skin and produce systemic effects.

OINTMENT BASESThe ointment base is that substance or part of an ointment preparation which serves as carrier or vehicle for the medicament.An ideal ointment base should be inert, stable, smooth, compatible with the skin, non-irritating and should release the incorporated medicaments readily.Classification of ointment bases:1.Oleaginous bases2.Absorption bases3.Water-miscible bases4.Water soluble bases

OLEAGINOUS BASESThese bases consists of oils and fats. The most important are theHydrocarbonsi.e. petrolatum, paraffins and mineral oils.Theanimal fatincludes lard.The combination of these materials can produce a product of desired melting point and viscosity.(a) Petrolatum (Soft paraffin)This is a purified mixture of semi-solid hydrocarbons obtained from petroleum or heavy lubricating oil.Yellow soft paraffin (Petrolatum; Petroleum jelly)This a purified mixture of semisolid hydrocarbons obtained from petroleum. It may contain suitable stabilizers like, antioxidants e.g.-tocopherol (Vitamin E), butylated hydroxy toluene (BHT) etc.Melting range : 38 to 560C.White soft paraffin (White petroleum jelly, White petrolatum)This a purified mixture of semisolid hydrocarbons obtained from petroleum, and wholly or partially decolorized by percolating the yellow soft paraffin through freshly burned bone black or adsorptive clays.Melting range : 38 to 560C.Use:The white form is used when the medicament is colourless, white or a pastel shade. This base is used inDithranol ointment B.P.Ammoniated Mercury and Coal tar ointment B.P.C.Zinc ointment B.P.C.(b) Hard paraffin (Paraffin)This is a mixture of solid hydrocarbons obtained from petroleum.It is colourless or white, odorless, translucent, wax-like substance. It solidifies between 50 and 570C and is used to stiffen ointment bases.(c) Liquid paraffin(Liquid petrolatum,; White mineral oil)It is a mixture of liquid , hydrocarbons obtained from petroleum. It is transparent, colourless, odourless, viscous liquid.On long storage it may oxidize to produce peroxides and therefore, it may contain tocopherol or BHT as antioxidants.It is used along with hard paraffin and soft paraffin to get a desired consistency of the ointment. Tubes for eye, rectal and nasal ointments have nozzles with narrow orifices through which it is difficult to expel very viscous ointments without the risk of bursting the tube. To facilitate the extrusion upto 25% of the base may be replaced by liquid paraffins.Advantages of hydrocarbons bases:(i)They are not absorbed by the skin. They remain on the surface as an occlusive layer that restricts the loss of moisture hence, keeps the skin soft.(ii)They are sticky hence ensures prolonged contact between skin and medicament.(iii)They are almost inert. They consist largely of saturated hydrocarbons, therefore, very few incompatibilities and little tendency of rancidity are there.(iv)They can withstand heat sterilization, hence, sterile ophthalmic ointments can be prepared with it.(v)They are readily available and cheap.Disadvantages of hydrocarbon bases;(i)It may lead to water logging followed by maceration of the skin if applied for a prolonged period.(ii)It retains body heat, which may produce an uncomfortable feeling of warmth.(iii)They are immiscible with water; as a result rubbing onto the surface and removal after treatment both are difficult.(iv)they are sticky, hence makes application unpleasant and leads to contamination of clothes.(v)Water absorption capacity is very low, hence, these bases are poor in absorbing exudate from moist lesions.

ABSORPTION BASEThe term absorption base is used to denote the water absorbing or emulsifying property of these bases and not to describe their action on the skin.These bases (some times calledemulsifiable ointment bases) are generally anhydrous substances which have the property of absorbing (emulsifying) considerable quantity of water yet retaining its ointment-like consistency. Preparations of this type do not contain water as a component of their basic formula but if water is incorporated a W/O emulsion results.Wool Fat (anhydrous lanolin)It is the purified anhydrous fat like substance obtained from the wool of sheep.It is practically insoluble in water but can absorb water upto 50% of its own weight. Therefore it is used in ointments the proportion of water or aqueous liquids to be incorporated in hydrocarbon base is too large.Due to its sticky nature it is not used alone but is used along with other bases in the preparation of a number of ointments.e.g. Simple ointment B.P. contains 5% and the B.P. eye ointment base contains 10% woolfat.Hydrous Wool Fat (Lanolin)It is a mixture of 70 % w/w wool fat and 30 % w/w purified water. It is a w/o emulsion. Aqueous liquids can be emulsified with it.It is used alone as an emollient.Example:- Hydrous Wool Fat Ointment B.P.C., Calamine Coal Tar Ointment.Wool AlcoholIt is the emulsifying fraction of wool fat. Wool alcohol is obtained from wool fat by treating it with alkali and separating the fraction containing cholesterol and other alcohols. It contains not less than 30% of cholesterol.Use:-It is used as an emulsifying agent for the preparation of w/o emulsions and is used to absorb water in ointment bases.It is also used to improve the texture, stability and emollient properties of o/w emulsions.Examples:- Wool alcohol ointment B.P. contains 6% wool alcohol and hard, liquid and soft paraffin.BeeswaxIt is purified wax, obtained from honey comb of bees.It contains small amount of cholesterol. It is of two types: (a) yellow beeswax and (b) white beeswax.Use:-Beeswax is used as a stiffening agent in ointment preparations.Examples:-Paraffin ointment B.P.C. contains beeswax.CholesterolIt is widely distributed in animal organisms. Wool fat is also used as a source of cholesterol.Use:- It is used to increase the water absorbing power of an ointment base.Example:- Hydrophilic petroleum U.S.P. contains: Cholesterol 3% Stearyl alcohol 3% White beeswax 8% White soft paraffin 86%Advantages of absorption bases:(i)They are less occlusive nevertheless, are good emollient.(ii)They assist oil soluble medicaments to penetrate the skin.(iii)They are easier to spread.(iv)They are compatible with majority of the medicaments.(v)They are relatively heat stable.(vi)The base may be used in their anhydrous form or in emulsified form.(vii)They can absorb a large quantity of water or aqueous substances.Disadvantages:Inspite of their hydrophilic nature, absorption bases are difficult to wash.

WATER MISCIBLE BASESThey are miscible with an excess of water. Ointments made from water-miscible bases are easily removed after use.There are three official anhydrous water-miscible ointment bases:-Example:- Emulsifying ointment B.P. contains anionic emulsifier.Cetrimide emulsifying ointment B.P.contains cationic emulsifierCetomacrogol emulsifying ointment B.P. contains non-ionic emulsifierUses:they are used to prepare o/w creams and are easily removable ointment basese.g. Compound Benzoic Acid Ointment (Whitfields Ointment)used as antifungal ointment.Advantages of water miscible bases:(i)Readily miscible with the exudates from lesions.(ii)Reduced interference with normal skin function.(iii)Good contact with the skin, because of their surfactant content.(iv)High cosmetic acceptability, hence there is less likelihood of the patients discontinuing treatment.(v)Easy removal from the hair.

WATER SOLUBLE BASESWater soluble bases contain only the water soluble ingredients and not the fats or other greasy substances, hence, they are known as grease-less bases.Water soluble bases consists of water soluble ingredients such as polyethylene glycol polymers (PEG) which are popularly known as carbowaxes and commercially known as macrogols.They are a range of compounds with the general formula: CH2OH . (CH2OCH2)nCH2OHThe PEGs are mixtures of polycondensation products of ethylene and water and they are described by numbers representing their average molecular weights. Like the paraffin hydrocarbons they vary in consistency from viscous liquids to waxy solids.Example:- Macrogols 200, 300, 400viscous liquids Macrogols 1500greasy semi-solids Macrogols 1540, 3000, 4000, 6000waxy solids.Different PEGs are mixed to get an ointment of desired consistency.Advantages of PEGs as ointment base:(a)They are water soluble; hence, very easily can be removed from the skin and readily miscible with tissue exudates.(b)Helps in good absorption by the skin.(c)Good solvent properties. Some water-soluble dermatological drugs, such as salicylic acid, sulfonamides, sulfur etc. are soluble in this bases.(d)Non-greasy.(e)They do not hydrolyze, rancidify or support microbial growth.(f)Compatibility with many dermatological medicaments.Disadvantages:(a)Limited uptake of water. Macrogols dissolve when the proportion of water reaches about 5%.(b)Reduction in activity of certain antibacterial agents, e.g. phenols, hydroxybenzoates and quaternary compounds.(c)Solvent action on polyethylene and bakelite containers and closures.

Certain other substances which are used as water soluble ointment bases include tragacanth, gelatin, pectin, silica gel, sodium alginate, cellulose derivatives, etc.

FACTORS GOVERNING SELECTION OF AN IDEAL OINTMENT BASE1. Dermatological factors2. Pharmaceutical factors1. Dermatological factors(a) Absorption and Penetration:Penetration means passage of the drug across the skin i.e. cutaneous penetration, and absorption means passage of the drug into blood stream.Medicaments which are both soluble in oil and water are most readily absorbed though the skin.Whereas animal and vegetable fats and oils normally penetrate the skin.Animals fats, e.g. lard and wool fat when combined with water, penetrates the skin.o/w emulsion bases release the medicament more readily than greasy bases or w/o emulsion bases.(b) Effect on the skinGreasy bases interfere with normal skin functions i.e. heat radiation and sweating. They are irritant to the skin.o/w emulsion bases and other water miscible bases produce a cooling effect due to the evaporation of water.(c)Miscibility with skin secretion and sebumSkin secretions are more readily miscible with emulsion bases than with greasy bases. Due to this the drug is more rapidly and completely released to the skin.(d)Compatibility with skin secretions:The bases used should be compatible with skin secretions and should have pH about 5.5 because the average skin pH is around 5.5. Generally neutral ointment bases are preferred.(e)Non-irritantAll bases should be highly pure and bases specially for eye ointments should be non-irritant and free from foreign particle.(f)Emollient propertiesDryness and brittleness of the skin causes discomfort to the skin therefore, the bases should keep the skin moist. For this purpose water and humectants such as glycerin, propylene glycol are used. Ointments should prevent rapid loss of moisture from the skin.(g)Ease of application and removalThe ointment bases should be easily applicable as well as easily removable from the skin by simple washing with water. Stiff and sticky ointment bases require much force to spread on the skin and during rubbing newly formed tissues on the skin may be damaged.2. Pharmaceutical factors(a)StabilityFats and oils obtained from animal and plant sources are prone to oxidation unless they are suitably preserved. Due to oxidation odour comes out. This type of reactions are calledrancidification. Lard, from animal origin, rancidify rapidly. Soft paraffin, simple ointment and paraffin ointment are inert and stable. Liquid paraffin is also stable but after prolonged storage it gets oxidized. Therefore, an antioxidant liketocopherol(Vit -E) may be incorporated. Other antioxidants those may be used arebutylated hydroxy toluene(BHT) orbutylated hydroxy hydroxy anisole(BHA).(b)Solvent propertiesMost of the medicaments used in the preparation of ointments are insoluble in the ointment bases therefore, they are finely powdered and are distributed uniformly throughout the base.(c)Emulsifying propertiesHydrocarbon bases absorbs very small amount of water.Wool fat can take about 50% of water and when mixed with other fats can take up several times its own weight of aqueous solution.Emulsifying ointment, cetrimide emulsifying ointment and cetomacrogol emulsifying ointment are capable of absorbing considerable amount of water, forming w/o creams.(d)ConsistencyThe ointments produced should be of suitable consistency. They should neither be hard nor too soft. They should withstand climatic conditions. Thus in summer they should not become too soft and in winter not too hard to be difficult to remove from the container and spread on the skin.The consistency of an ointment base can be controlled by varying the ratio of hard and liquid paraffin.

PREPARATION OF OINTMENTSA well-made ointment is(a)Uniform throughouti.e. it contains no lumps of separated high melting point ingredients of the base, there is no tendency for liquid constituents to separate and insoluble powders are evenly dispersed.(b)Free from grittiness, i.e. insoluble powders are finely subdivided and large lumps of particles are absent. Methods of preparation must satisfy this criteria.Two mixing techniques are frequently used in making ointments:1.Fusion, in which ingredients are melted together and stirred to ensure homogeneity.2.Trituration, in which finely-subdivided insoluble medicaments are evenly distributed by grinding with a small amount of the base or one of its ingredients followed by dilution with gradually increasing amounts of the base.1.Ointments prepared by Fusion method:When an ointment base contain a number of solid ingredients such as white beeswax, cetyl alcohol, stearyl alcohol, stearic acid, hard paraffin, etc. as components of the base, it is required to melted them. The melting can be done in two methods:Method-IThe components are melted in the decreasing order of their melting point i.e. the higher m.p. substance should be melted first, the substances with next melting point and so on. The medicament is added slowly in the melted ingredients and stirred thoroughly until the mass cools down and homogeneous product is formed.Advantages:This will avoid over-heating of substances having low melting point.Method-IIAll the components are taken in subdivided state and melted together.Advantages:The maximum temperature reached is lower than Method-I, and less time was taken possibly due to the solvent action of the lower melting point substances on the rest of the ingredients.

Cautions:(i)Melting time is shortened by grating waxy components (i.e. beeswax, wool alcohols, hard-paraffin, higher fatty alcohols and emulsifying waxes) by stirring during melting and by lowering the dish as far as possible into the water bath so that the maximum surface area is heated.(ii)The surface of some ingredients discolors due to oxidation e.g. wool fats and wool alcohols and this discolored layers should be removed before use.(iii)After melting, the ingredients should be stirred until the ointment is cool, taking care not to cause localized cooling, e.g. by using a cold spatula or stirrer, placing the dish on a cold surface (e.g. a plastic bench top) or transferring to a cold container before the ointment has fully set. If these precautions are ignored, hard lumps may separate.(iv)Vigorous-stirring, after the ointment has begun to thicken, causes excessive aeration and should be avoided.(v)Because of their greasy nature, many constituents of ointment bases pickup dirt during storage, which can be seen after melting. This is removed from the melt by allowing it to sediment and decanting the supernatant, or by passage through muslin supported by a warm strainer. In both instances the clarified liquid is collected in another hot basin.(vi)If the product is granular after cooling, due to separation of high m.p. constituents, it should be remelted, using the minimum of heat, and again stirred and cooled.

Example:(i)Simple ointment B.P. contains Wool fat 50g Hard paraffin 50g Cetostearyl alcohol 50g White soft paraffin 850gType of preparation: Absorption ointment baseProcedure:Hard paraffin and cetostearyl alcohol on water-bath. Wool fat and white soft paraffin are mixed and stirred until all the ingredients are melted. If required decanted or strained and stirred until cold and packed in suitable container.(ii) Paraffin ointment baseType of preparation:Hydrocarbon ointment base(iii) Wool alcohols ointment B.P.Type of preparation: Absorption base(iv) Emulsifying ointment B.P.Type of preparation:Water-miscible ointment base.(v) Macrogol ointment B.P.CType of preparation:Water soluble ointment baseFormula: Macrogol 4000 Liquid Macrogol 300Method:Macrogol 4000 is melted and previously warmed liquid macrogol 300 is added. Stirred until cool.

2. OINTMENT PREPARED BY TRITURATIONThis method is applicable in the base or a liquid present in small amount.(i)Solids are finely powdered are passed through a sieve (# 250, # 180, #125).(ii)The powder is taken on an ointment-slab and triturated with a small amount of the base. A steel spatula with long, broad blade is used. To this additional quantities of the base are incorporated and triturated until the medicament is mixed with the base.(iii)Finally liquid ingredients are incorporated. To avoid loss from splashing, a small volume of liquid is poured into a depression in the ointment an thoroughly incorporated before more is added in the same way. Splashing is more easily controlled in a mortar than on a tile.Example:(i)Whitfield ointment(Compound benzoic acid ointment B.P.C.)Formula: Benzoic acid, in fine powder 6gm Salicylic acid, in fine powder 3gm Emulsifying ointment 91gmMethod:Benzoic acid and salicylic acid are sieved through No. 180 sieves. They are mixed on the tile with small amount of base and levigated until smooth and dilute gradually.(ii) Salicylic acid sulphur ointment B.P.C.

3. OINTMENT PREPARATION BY CHEMICAL REACTIONChemical reactions were involved in the preparation of several famous ointments of the past, e.g. Strong Mercuric Nitrate Ointment, of the 1959 B.P.C.(a)Ointment containing free iodineIodine is only slightly soluble in most fats and oils but readily soluble.Iodine is readily soluble in concentrated solution of potassium iodide due to the formation of molecular complexes KI.I2, KI.2I2, KI.3I2etc.These solutions may be incorporated in absorption-type ointment bases.e.g.Strong Iodine Ointment B.Vet.C(British Veterinary Pharmacopoeia) is used to treat ringworm in cattle. It contains free iodine. At one time this type of ointments were used as counter-irritants in the treatment of human rheumatic diseases but they were not popular because:They stain the skin a deep red color.(i)Due to improper storage the water dries up and the iodine crystals irritate the skin, hence glycerol was some times added to dissolve the iodine-potassium iodide complex instead of water.Example:Strong Iodine Ointment B. Vet.C. Iodine Woolfat Yellow soft paraffin Potassium iodide WaterProcedure:(i)KI is dissolved in water. I2is dissolved in it.(ii)Woolfat and yellow soft paraffin are melted together over water bath. Melted mass is cooled to about 400C.(iii)I2solution is added to the melted mass in small quantities at a time with continuos stirring until a uniform mass is obtained.(iv)It is cooled to room temperature and packed.Use: - Ringworm in cattle.(b) Ointment containing combined iodineFixed oils and many vegetable and animal fats absorb iodine which combines with the double bonds of the unsaturated constituents, e.g.CH3.(CH2)2.CH = CH.(CH2)7.COOH + I2CH3.(CH2)2.CHI CHI.(CH2)7.COOH Oleic acid di-iodostearic acidExample:Non-staining Iodine Ointment B.P.C. 1968 Iodine Arachis Oil Yellow Soft ParaffinMethod:(a)Iodine is finely powdered in a glass mortar and required amount is added to the oil in a glass-stoppered conical flask and stirred well.(b)The oil is heated at 500C in a water-bath and stirred continually. Heating is continued until the brown color is changed to greenish-black; this may take several hours.(c)From 0.1g of the preparation the amount of iodine is determined by B.P.C. method and the amount of soft paraffin base is calculated to give the product the required strength.(d)Soft paraffin is warmed to 400C. The iodized oil is added and mixed well. No more heat is applied because this causes deposition of a resinous substance.(e)The preparation is packed in a warm, wide-mouthed, amber color, glass bottle. It is allowed to cool without further stirring.4. PREPARATION OF OINTMENTS BY EMULSIFICATIONAn emulsion system contain an oil phase, an aqueous phase and an emulsifying agent.For o/w emulsion systems the following emulsifying agents are used: (i) water soluble soap (ii) cetyl alcohol (iii)glyceryl monostearate (iv) combination of emulsifiers: triethanolamine stearate + cetyl alcohol (v) non-ionic emulsifiers: glyceryl monostearate, glyceryl monooelate, propylene glycol stearateFor w/o emulsion creams the following emulsifiers are used: (i) polyvalent ions e.gmagnesium, calcium and aluminiumare used. (ii) combination of emulsifiers:beeswax + divalent calcium ionThe viscosity of this type of creams prevent coalescence of the emulsified phases and helps in stabilizing the emulsion.Example:Cold cream:Procedure:(i)Water immiscible components e.g. oils, fats, waxes are melted together over water bath (700C).(ii)Aqueous solution of all heat stable, water soluble components are heated (700C).(iii)Aqueous solution is slowly added to the melted bases with continuous stirring until the product cools down and a semi-solid mass is obtained.N.B. The aqueous phase is heated otherwise high melting point fats and waxes will immediately solidify on addition of cold aqueous solution.

MANUFACTURE OF OINTMENTS / CREAMS IN INDUSTRIAL SCALE1. Preparation of oil and aqueous phaseOils + Fats Water soluble ingredients + Purified water Equipment: Steam jacketed kettle Equipment: Mechanicalstirrer Melted and mixed Dissolved Strained through several layers of cheese Filteredcloths to remove foreign matter Heated to the melting point of oil phaseCakes, flakes or powdered waxes are directly weighed in a physical balance.Semisolid petrolatum is melted in the container supplied by an immersion heater, the liquid petrolatum is then transferred by ametering pumpthroughmetal reinforced inert plastic hoses and insulated pipes.

2. Mixing of oil and water phasesMixing temperature is 70720C for proper mixing.Three methods of mixing are there:(A)Simultaneous blending

For continuous or large batch operationEquipmentsProportioning pumpContinuous mixer(B)Addition of disperse phase to continuous phase

For an emulsion having low volume of dispersed phase.Equipment:Simple metering pump(C)Addition of continuous phase to disperse phase

For an emulsion formed by phase inversion method.Equipment:Simple metering pump.

Batch sizes are on weight basis. For weighing ahydraulic load cellis fitted under one of the leg of the mixing kettle.

3. Cooling the semisolidCooling should be slow to prevent crystallization of high m.p. waxes. Perfumes are added at 43 to 450C.Equipments: Kettle fitted with heating / cooling arrangements, agitator and sweep blades (for scrapping the wall).

Cooled to 43 to 450C Kettle with agitator and sweep blades Addition of perfumeAddition of drug powderDispersed or dissolved

4. Homogenization Creams or ointmentsEquipment: Low-shear gear pump androller mill / colloid mill / valve type homogenizer Homogenization

5. Storage of semisolids Stored before packaging. In the mean time Q.C. report comes. Stored in a tight-fitting stainless steel (SS#316) container.

6. Transfer of materials for packagingEquipment: Ointment filling machineWashing of the equipments with high-pressure (up to 1000psi), low-volume pumps and hot water and detergents should be done.To sterilize the equipments, containers, pumps and other accessories are flushed with chlorinated water or formalin followed by rinsing them with bacteria free water.

STABILITY OF OINTMENTS

The ointments should remain stable from the time of preparation to the time when the whole of it is consumed by the user.(i)To stop microbial growth preservatives are added. Preservatives for ointment includes : p-hydroxy benzoates, phenol, benzoic acid, sorbic acid, methyl paraben, propyl paraben, quaternary ammonium compounds, mercury compounds etc.(ii)The preservatives should not react with any of the component of the formulation. Plastic containers may absorb the preservative and thereby decreasing the concentration of preservative available for killing the bacteria.(iii)Some ingredients like wool fat and wool alcohols are susceptible to oxidation. Therefore, a suitable antioxidant may be incorporated to protect the active ingredients from oxidation.(iv)Incompatible drugs, emulsifying agents and preservatives must be avoided. The drugs which are likely to hydrolyze must be dispensed in an anhydrous base.(v)Humectants such as, glycerin, propylene glycol and sorbitol may be added to prevent the loss of moisture from the preparation.(vi)Ointment must be stored at an optimum temperature otherwise separation of phases may take place in the emulsified products which may be very difficult to remix to get a uniform product.

Preservatives in ointments

DOWN LOAD------ORIGINAL------SEMISOLID DOSAGE FORM

FOR PHARMACEUTICS THEORY

Email ThisBlogThis!Share to TwitterShare to FacebookHomeSubscribe to:Posts (Atom)Contact FormTop of FormName

Email*

Message*Bottom of Formwell,here is some details:1-Pastes:paste is a substance that behaves as a solid until a sufficiently large load or stress is applied,at which point it flows like a fluid,paste typically consists of a suspension of small particles in a background fluid,the small particles are jammed together like grains of sand on a beach,forming a disordered,glassy or amorphous structure, and giving pastes their solid-like character,in pharmacology,paste is basic pharmaceutical form,it consists of fatty base (e.g. petroleum jelly) and at least 25% solid substance (e.g. zinc oxide).2-Ointments:an ointment is a viscous semisolid preparation used topically on a variety of body surfaces.these include the skin and the mucus membranes of the eye (an eye ointment),vagina,glans and nose,an ointment may or may not be medicated.3-creams:Cream is semi-solid emulsion,that is mixtures of oil and water,they are divided into two types:oil-in-water (O/W) creams which are composed of small droplets of oil dispersed in a continuous aqueous phase,and water-in-oil (W/O) creams which are composed of small droplets of water dispersed in a continuous oily phase.Viscosity?

Paste - Thick, almost solid form.

Ointment - Not as thick, like grease

Cream - Even less thick, like a thick oil.definitions - zinc oxidezinc oxide(n.)1.oxide of zinc; a white powder used as a pigment or in cosmetics or glass or inks and in zinc ointmentZinc Oxide(n.)1.(MeSH)A mild astringent and topical protectant with some antiseptic action. It is also used in bandages, pastes, ointments, dental cements, and as a sunblock.definition (more)definitionof WikipediaAdvertizing synonyms - zinc oxideZinc Oxide(n.)(MeSH)Lassar's Paste(MeSH)zinc oxide(n.)flowers of zinc,philosopher's wool,philosophers' woolAdvertizing analogical dictionaryInorganic Chemicals-Anions-Oxygen Compounds[Hyper.]Zinc Compounds-Oxides[Hyper.]Zinc Oxide(n.)[MeSH]

oxide; hydroxide[ClasseHyper.]compos d'oxygne (fr)[Classe](enamel)[termes lis]chemistry[Domaine]CompoundSubstance[Domaine]chemical compound, compound-pigment[Hyper.]oxidate, oxidise, oxidize[Driv]oxide[Hyper.]Chinese white, cover white, zinc white[Element]zinc oxide(n.)

WikipediaZinc oxideupdate Zinc oxide

Other namesZinc white, Calamine, philosopher's wool, Chinese white, flowers of zinc

Identifiers

CAS number1314-13-2

PubChem14806

ChemSpider14122

EC number215-222-5

ChEBICHEBI:36560

ChEMBLCHEMBL1201128

RTECS numberZH4810000

ATCvet codeQA07XA91

InChI InChI=1S/O.ZnKey: XLOMVQKBTHCTTD-UHFFFAOYSA-N

Properties

Molecular formulaZnO

Molar mass81.408 g/mol

AppearanceWhite solid

Odorodorless

Density5.606 g/cm3

Melting point1975 C (decomposes)[1]

Boiling point2360 C

Solubilityinwater0.16 mg/100 mL (30 C)

Band gap3.3 eV (direct)

Refractive index(nD)2.0041

Thermochemistry

Std enthalpy offormationfHo298-348.0 kJ/mol

Standard molarentropySo29843.9 JK1mol1

Hazards

MSDSICSC 0208

EU Index030-013-00-7

EU classificationDangerous for the environment (N)

R-phrasesR50/53

S-phrasesS60,S61

NFPA 704120W

Flash point1436 C

Related compounds

OtheranionsZinc sulfideZinc selenideZinc telluride

OthercationsCadmium oxideMercury(II) oxide

(verify)(what is:/?)Except where noted otherwise, data are given for materials in theirstandard state (at 25C, 100kPa)

Infobox references

Zinc oxideis aninorganic compoundwith theformulaZnO. ZnO is a white powder that is insoluble in water, which is widely used as an additive in numerous materials and products including plastics, ceramics, glass, cement, lubricants[2], paints, ointments, adhesives, sealants, pigments, foods (source of Znnutrient), batteries, ferrites, fire retardants, and first aid tapes. It occurs naturally as the mineralzincitebut most zinc oxide is produced synthetically.[3]Inmaterials science, ZnO is a wide-bandgap semiconductor of theII-VI semiconductor group(sinceoxygenwas classed as an element of VIA group (the 6th main group, now referred to as 16th) of theperiodic tableandzinc, a transition metal, as a member of the IIB (2nd B), now 12th, group). The nativedopingof the semiconductor (due to oxygen vacancies) is n-type. This semiconductor has several favorable properties, including good transparency, highelectron mobility, widebandgap, and strong room-temperatureluminescence. Those properties are used in emerging applications for transparentelectrodesinliquid crystal displays, in energy-saving or heat-protecting windows, and in electronics as thin-filmtransistorsandlight-emitting diodes.Contents 1Chemical properties 2Physical properties 2.1Structure 2.2Mechanical properties 2.3Electrical properties 3Production 3.1Indirect (French) process 3.2Direct (American) process 3.3Wet chemical process 3.4Laboratory synthesis 3.5Nanophase ZnO 4Applications 4.1Rubber manufacture 4.2Concrete industry 4.3Medical 4.4Cigarette filters 4.5Food additive 4.6Pigment 4.7Coatings 4.8Corrosion prevention in nuclear reactors 5Potential applications 5.1Electronics 5.2Zinc oxide nanorod sensor 5.3Spintronics 5.4Piezoelectricity 6History 7Safety 8In popular culture 9See also 10References 11Reviews 12External links

Chemical propertiesZnO occurs as a white powder. The mineralzinciteusually contains manganese and other impurities that confer a yellow to red color.[4]Crystalline zinc oxide isthermochromic, changing from white to yellow when heated and in air reverting to white on cooling.[5]This color change is caused by a small loss of oxygen to the environment at high temperatures to form the non-stoichiometric Zn1+xO, where at 800 C, x = 0.00007.[5]Zinc oxide is anamphoteric oxide. It is nearlyinsolublein water, but it is soluble in (degraded by) mostacids, such ashydrochloricacid:[6][7]ZnO + 2 HCl ZnCl2+ H2OBases also degrade the solid to give soluble zincates:ZnO + 2 NaOH + H2O Na2[Zn(OH)4]ZnO reacts slowly with fatty acids in oils to produce the correspondingcarboxylates, such asoleateorstearate. ZnO forms cement-like products when mixed with a strong aqueous solution ofzinc chlorideand these are best described as zinc hydroxy chlorides.[8]This cement was used in dentistry.[9]

HopeiteZnO also forms cement-like products when treated withphosphoric acid; related materials are used in dentistry.[9]A major component of zinc phosphate cement produced by this reaction ishopeite, Zn3(PO4)24H2O.[10]ZnO decomposes into zinc vapor and oxygen only at around 1975 C, reflecting its considerable stability. Heating with carbon converts the oxide into the metal, which is more volatile than the oxide.[11]ZnO + C Zn + COZinc oxide can react violently withaluminiumandmagnesiumpowders, with chlorinated rubber andlinseed oilon heating causing fire and explosion hazard.[12][13]It reacts withhydrogen sulfideto give thesulfide. This reaction is used commercially in removing H2S using ZnO powder (e.g., as deodorant).ZnO + H2S ZnS + H2OWhen ointments containing ZnO and water are melted and exposed toultravioletlight,hydrogen peroxideis produced.[7]Physical properties

Wurtzite structure

A zincblende unit cellStructureZinc oxide crystallizes in two mainforms, hexagonalwurtzite[14]and cubiczincblende. The wurtzite structure is most stable at ambient conditions and thus most common. The zincblende form can be stabilized by growing ZnO on substrates with cubic lattice structure. In both cases, the zinc and oxide centers aretetrahedral, the most characteristic geometry for Zn(II).In addition to the wurtzite and zincblende polymorphs, ZnO can be crystallized in therocksaltmotif at relatively high pressures about 10 GPa.[15]Hexagonal and zincblende polymorphs have noinversion symmetry(reflection of a crystal relative to any given point does not transform it into itself). This and other lattice symmetry properties result inpiezoelectricityof the hexagonal and zincblende ZnO, andpyroelectricityof hexagonal ZnO.The hexagonal structure has a point group 6mm (Hermann-Mauguin notation) or C6v(Schoenflies notation), and thespace groupis P63mc or C6v4. The lattice constants area= 3.25 andc= 5.2 ; their ratioc/a~ 1.60 is close to the ideal value for hexagonal cellc/a= 1.633.[16]As in mostgroup II-VImaterials, the bonding in ZnO is largelyionic(Zn2+O2) with the corresponding radii of 0.074 nm for Zn2+and 0.140 nm for O2. This property accounts for the preferential formation of wurtzite rather than zinc blende structure,[17]as well as the strongpiezoelectricityof ZnO. Because of the polar Zn-O bonds, zinc and oxygen planes are electrically charged. To maintain electrical neutrality, those planes reconstruct at atomic level in most relative materials, but not in ZnO its surfaces are atomically flat, stable and exhibit no reconstruction. This anomaly of ZnO is not fully explained yet.[18]Mechanical propertiesZnO is a relatively soft material with approximate hardness of 4.5 on theMohs scale.[2]Its elastic constants are smaller than those of relevant III-V semiconductors, such asGaN. The high heat capacity and heat conductivity, low thermal expansion and high melting temperature of ZnO are beneficial for ceramics.[19]ZnO's most stable phase being wurtzite, ZnO exhibits a very long lived optical phonon E2(low) with a lifetime as high as 133 ps at 10 K[20]Among the tetrahedrally bonded semiconductors, it has been stated that ZnO has the highest piezoelectric tensor, or at least one comparable to that ofGaNandAlN.[21]This property makes it a technologically important material for manypiezoelectricalapplications, which require a large electromechanical coupling.Electrical propertiesZnO has a relatively largedirectband gapof ~3.3eV at room temperature. Advantages associated with a large band gap include higher breakdown voltages, ability to sustain large electric fields, lowerelectronic noise, and high-temperature and high-power operation. The bandgap of ZnO can further be tuned to ~34eV by its alloying withmagnesium oxideorcadmium oxide.[15]Most ZnO hasn-typecharacter, even in the absence of intentionaldoping.Nonstoichiometryis typically the origin of n-type character, but the subject remains controversial.[22]An alternative explanation has been proposed, based on theoretical calculations, that unintentional substitutional hydrogen impurities are responsible.[23]Controllable n-type doping is easily achieved by substituting Zn with group-III elements such as Al, Ga, In or by substituting oxygen with group-VII elementschlorineoriodine.[24]Reliablep-typedoping of ZnO remains difficult. This problem originates from low solubility of p-type dopants and their compensation by abundant n-type impurities. This problem is observed withGaNandZnSe. Measurement of p-type in "intrinsically" n-type material is complicated by the inhomogeneity of samples.[25]Current limitations to p-doping does not limit electronic and optoelectronic applications of ZnO, which usually require junctions of n-type and p-type material. Known p-type dopants include group-I elements Li, Na, K; group-V elements N, P and As; as well as copper and silver. However, many of these form deep acceptors and do not produce significant p-type conduction at room temperature.[15]Electron mobilityof ZnO strongly varies with temperature and has a maximum of ~2000cm2/(Vs) at 80 K.[26]Data on hole mobility are scarce with values in the range 530cm2/(Vs).[27]ProductionSee also:Zinc smeltingFor industrial use, ZnO is produced at levels of 105tons per year[4]by three main processes:[19]Indirect (French) processMetallic zinc is melted in a graphite crucible and vaporized at temperatures above 907 C (typically around 1000 C). Zinc vapor reacts with the oxygen in the air to give ZnO, accompanied by a drop in its temperature and bright luminescence. Zinc oxide particles are transported into a cooling duct and collected in a bag house. This indirect method was popularized by LeClaire (France) in 1844 and therefore is commonly known as the French process. Its product normally consists of agglomerated zinc oxide particles with an average size of 0.1 to a few micrometers. By weight, most of the world's zinc oxide is manufactured via French process.Direct (American) processThe direct process starts with diverse contaminated zinc composites, such aszinc oresor smelter by-products. The zinc precursors are reduced (carbothermal reduction) by heating with a source of carbon such asanthraciteto produce zinc vapor, which is then oxidized as in the indirect process. Because of the lower purity of the source material, the final product is also of lower quality in the direct process as compared to the indirect one.Wet chemical processA small amount of industrial production involves wet chemical processes, which start with aqueous solutions of purified zinc salts, from whichzinc carbonateorzinc hydroxideis precipitated. The precipitate is then filtered, washed, dried and calcined at temperatures around 800 C.Laboratory synthesis

Synthetic ZnO crystals. Red and green color are associated with different concentrations of oxygen vacancies.[28]A large number of specialised methods exist for producing ZnO for scientific studies and niche applications. These methods can be classified by the resulting ZnO form (bulk, thin film,nanowire), temperature ("low", that is close to room temperature or "high", that is T~1000C), process type (vapor deposition or growth from solution) and other parameters.Large single crystals (many cubic centimeters) are usually grown by the gas transport (vapor-phase deposition),hydrothermal synthesis,[18][28][29]or melt growth.[1]However, because of highvapor pressureof ZnO, growth from the melt is problematic. Growth by gas transport is difficult to control, leaving the hydrothermal method as a preference.[1]Thin films can be produced bychemical vapor deposition,metalorganic vapour phase epitaxy,electrodeposition,pulsed laser deposition,sputtering,sol-gelsynthesis,atomic layer deposition, spray pyrolysis, etc.Ordinary white powdered zinc oxide can be produced in the laboratory by electrolyzing a solution of sodium bicarbonate with a zinc anode. Zinc hydroxide and hydrogen gas are produced. The zinc hydroxide upon heating decomposes to zinc oxide.Zn + 2 H2O Zn(OH)2+ H2Zn(OH)2 ZnO + H2ONanophase ZnONanophaseZnO can be synthesized into a variety of morphologies including nanowires, nanorods, tetrapods, nanobelts, nanoflowers, nanoparticles etc. Nanostructures can be obtained with most above-mentioned techniques, at certain conditions, and also with thevapor-liquid-solid method.[18][30]Rodlike nanostructures of ZnO can be produced via aqueous methods, which are attractive for the following reasons: They are low cost, less hazardous[citation needed], and thus capable of easy scaling up; the growth occurs at a relatively low temperature, compatible with flexible organic substrates; there is no need for the use of metal catalysts, and thus it can be integrated with well-developed silicon technologies. In addition, there are a variety of parameters that can be tuned to effectively control the morphology and properties of the final product. Wet chemical methods have been demonstrated as a very powerful and versatile technique for growing one dimensional ZnO nanostructures.[31]The synthesis is typically carried out at temperatures of about 90 C, in an equimolar aqueous solution of zinc nitrate andhexamine, the latter providing the basic environment. Certain additives, such as polyethylene glycol or polyethylenimine, can improve the aspect ratio of the ZnO nanowires.[32]Doping of the ZnO nanowires has been achieved by adding other metal nitrates to the growth solution.[33]The morphology of the resulting nanostructures can be tuned by changing the parameters relating to the precursor composition (such as the zinc concentration and pH) or to the thermal treatment (such as the temperature and heating rate).[34]Aligned ZnO nanowires on pre-seededsilicon,glassandgallium nitridesubstrates have been grown in aqueous solutions using aqueous zinc salts such asZinc nitrateandZinc acetatein basic environments.[35]Pre-seeding substrates with ZnO creates sites for homogeneous nucleation of ZnO crystal during the synthesis. Common pre-seeding methods include in-situ thermal decomposition ofzinc acetatecrystallites, spincoating of ZnO nanoparticles and the use ofphysical vapor depositionmethods to deposit ZnO thin films.[36][37]Pre-seeding can be performed in conjunction with top down patterning methods such aselectron beam lithographyand nanosphere lithography to designate nucleation sites prior to growth. Aligned ZnO nanowires can be used indye-sensitized solar cellsand field emission devices.[38][39]ApplicationsThe applications of zinc oxide powder are numerous, and the principal ones are summarized below. Most applications exploit the reactivity of the oxide as a precursor to other zinc compounds. For material science applications, zinc oxide has highrefractive index, high thermal conductivity, binding, antibacterial and UV-protection properties. Consequently, it is added into materials and products including plastics, ceramics, glass, cement, rubber, lubricants,[2]paints, ointments, adhesive, sealants, pigments, foods, batteries, ferrites, fire retardants, etc.[40]Rubber manufactureAbout 50% of ZnO use is in the rubber industry. Zinc oxide along withstearic acidis used in thevulcanizationof rubber[19][41][42]ZnO additive also protect rubber from fungi (see medical applications) and UV light.Concrete industryZinc oxide is widely used forconcretemanufacturing. Addition of ZnO improves the processing time and the resistance of concrete against water.[41]MedicalZinc oxide as a mixture with about 0.5%iron(III) oxide(Fe2O3) is calledcalamineand is used in calamine lotion. There are also two minerals,zinciteandhemimorphite, which have been historically calledcalamine. When mixed witheugenol, aligand,zinc oxide eugenolis formed, which has applications as arestorativeandprosthodonticindentistry.[9][43]Reflecting the basic properties of ZnO, fine particles of the oxide have deodorizing and antibacterial[44]properties and for that reason are added into materials including cotton fabric, rubber, and food packaging.[45][46]Enhanced antibacterial action of fine particles compared to bulk material is not intrinsic to ZnO and is observed for other materials, such assilver.[47]This property is due to the increased surface area of the fine particles.Zinc oxide is widely used to treat a variety of other skin conditions, in products such asbaby powderandbarrier creamsto treatdiaper rashes,calaminecream, anti-dandruffshampoos, andantisepticointments.[48][49]It is also a component in tape (called "zinc oxide tape") used by athletes as a bandage to prevent soft tissue damage during workouts.[50]Zinc oxide can be used in ointments, creams, andlotionsto protect againstsunburnand other damage to the skin caused byultraviolet light(seesunscreen). It is the broadest spectrum UVA and UVB reflector that is approved for use as a sunscreen by the FDA,[51]and is completely photostable.[52]When used as an ingredient insunscreen, zinc oxide sits on the skins surface and is not absorbed into the skin, and blocks bothUVA(320400nm) andUVB(280320nm) rays ofultraviolet light. Because zinc oxide (and the other most common physicalsunscreen,titanium dioxide) are not absorbed into the skin, they are nonirritating, nonallergenic, and non-comedogenic.[53]Many sunscreens use nanoparticles of zinc oxide (along with nanoparticles of titanium dioxide) because such small particles do not scatter light and therefore do not appear white. Although there has been concern that they might be absorbed into the skin,[54][55]comprehensive reviews of the medical literature have not uncovered any risk.[56]Cigarette filtersZinc oxide is a constituent ofcigarette filtersfor removal of selected components from tobacco smoke. A filter consisting of charcoal impregnated with zinc oxide and iron oxide removes significant amounts ofHCNandH2Sfrom tobacco smoke without affecting its flavor.[40]Food additiveZinc oxide is added to many food products, includingbreakfast cereals, as a source of zinc,[57]a necessarynutrient. (Zinc sulfateis also used for the same purpose.) Some prepackaged foods also include trace amounts of ZnO even if it is not intended as a nutrient.PigmentZinc white is used as a pigment[58]inpaintsand is more opaque thanlithopone, but less opaque thantitanium dioxide. It is also used in coatings for paper. Chinese white is a special grade of zinc white used in artists'pigments. It is also a main ingredient of mineral makeup.[59]CoatingsPaints containing zinc oxide powder have long been utilized as anticorrosive coatings for metals. They are especially effective for galvanized iron. Iron is difficult to protect because its reactivity with organic coatings leads to brittleness and lack of adhesion. Zinc oxide paints retain their flexibility and adherence on such surfaces for many years.[40]ZnO highly n-type doped with Al, Ga, or In is transparent and conductive (transparency~90%, lowestresistivity~104cm[60]). ZnO:Al coatings are used for energy-saving or heat-protecting windows. The coating lets the visible part of the spectrum in but either reflects the infrared (IR) radiation back into the room (energy saving) or does not let the IR radiation into the room (heat protection), depending on which side of the window has the coating.[4]Plastics, such aspolyethylene naphthalate(PEN), can be protected by applying zinc oxide coating. The coating reduces the diffusion of oxygen with PEN.[61]Zinc oxide layers can also be used onpolycarbonate(PC) in outdoor applications. The coating protects PC form solar radiation and decreases the oxidation rate and photo-yellowing of PC.[62]Corrosion prevention in nuclear reactorsMain article:Depleted zinc oxideZinc oxide depleted in thezinc isotopewith theatomic mass64 is used in corrosion prevention in nuclearpressurized water reactors. The depletion is necessary, because64Zn istransformedinto radioactive65Zn under irradiation by the reactor neutrons.[63]Potential applicationsElectronicsZnO has widedirect band gap(3.37 eV or 375nm at room temperature). Therefore, its most common potential applications are in laser diodes andlight emitting diodes(LEDs).[64]Some optoelectronic applications of ZnO overlap with that ofGaN, which has a similar bandgap (~3.4 eV at room temperature). Compared to GaN, ZnO has a larger exciton binding energy (~60 meV, 2.4 times of the room-temperature thermal energy), which results in bright room-temperature emission from ZnO. ZnO can be combined with GaN for LED-applications. For instance as TCO layer and ZnO nanostructures provide better light outcoupling.[65]Other properties of ZnO favorable for electronic applications include its stability to high-energy radiation and to wet chemical etching.[66]Radiation resistance[67]makes ZnO a suitable candidate for space applications. ZnO is the most promising candidate in the field ofrandom lasersto produce an electronically pumped UV laser source.The pointed tips of ZnO nanorods result in a strong enhancement of an electric field. Therefore, they can be used asfield emitters.[68]Aluminium-doped ZnO layers are used as a transparentelectrodes. The constituents Zn and Al are much cheaper and less poisonous compared to the generally usedindium tin oxide(ITO). One application which has begun to be commercially available is the use of ZnO as the front contact for solar cells or ofliquid crystal displays.[69]Transparent thin-filmtransistors(TTFT) can be produced with ZnO. As field-effect transistors, they even may not need a pn junction,[70]thus avoiding the p-type doping problem of ZnO. Some of the field-effect transistors even use ZnO nanorods as conducting channels.[71]Zinc oxide nanorod sensorZinc oxide nanorod sensorsare devices detecting changes inelectrical currentpassing through zinc oxidenanowiresdue toadsorptionof gas molecules. Selectivity to hydrogen gas was achieved by sputtering Pd clusters on the nanorod surface. The addition of Pd appears to be effective in the catalytic dissociation of hydrogen molecules into atomic hydrogen, increasing the sensitivity of the sensor device. The sensor detects hydrogen concentrations down to 10 parts per million at room temperature, whereas there is no response to oxygen.[72][73]SpintronicsZnO has also been considered forspintronicsapplications: if doped with 110% of magnetic ions (Mn, Fe, Co, V, etc.), ZnO could becomeferromagnetic, even at room temperature. Such room temperatureferromagnetismin ZnO:Mn has been observed,[74]but it is not clear yet whether it originates from the matrix itself or from secondary oxide phases.PiezoelectricityThepiezoelectricityintextilefiberscoatedin ZnO have been shown capable of fabricating "self-powered nanosystems" with everyday mechanical stress from wind or body movements.[75][76]In 2008 theCenter for Nanostructure Characterizationat theGeorgia Institute of Technologyreported producing an electricity generating device (called flexible charge pump generator) delivering alternating current by stretching and releasing zinc oxide nanowires. This mini-generator creates an oscillating voltage up to 45 millivolts, converting close to seven percent of the applied mechanical energy into electricity. Researchers used wires with lengths of 0.20.3mm and diameters of three to five micrometers, but the device could be scaled down to smaller size.[77]HistoryIt is hardly possible to trace the first usage of zinc oxide zinc compounds were used by early humans, in processed and unprocessed forms, as a paint or medicinal ointment, but their composition is uncertain.The use ofpushpanjan, probably zinc oxide, as a salve for eyes and open wounds, is mentioned in theIndianmedical text theCharaka Samhita, thought to date from 500 BC or before.[78]Zinc oxide ointment is also mentioned by theGreekphysicianDioscorides(1st century AD.)[79]Avicennamentions zinc oxide inThe Canon of Medicine(1025 AD), which mentioned it as a preferred treatment for a variety ofskin conditions, includingskin cancer. Though it is no longer used for treating skin cancer, it is still widely used to treat a variety of other skin conditions, in products such asbaby powderand creams againstdiaper rashes,calaminecream, anti-dandruffshampoos, andantisepticointments.[48]The Romans produced considerable quantities ofbrass(an alloy ofzincandcopper) as early as 200 BC by a cementation process where copper was reacted with zinc oxide.[80]The zinc oxide is thought to have been produced by heating zinc ore in a shaft furnace. This liberated metallic zinc as a vapor, which then ascended the flue and condensed as the oxide. This process was described byDioscoridesin the 1st century AD.[81]Zinc oxide has also been recovered from zinc mines at Zawar inIndia, dating from the second half of the first millennium BC. This was presumably also made in the same way and used to produce brass.[79]From the 12th to the 16th century zinc and zinc oxide were recognized and produced inIndiausing a primitive form of the direct synthesis process. From India, zinc manufacture moved toChinain the 17th century. In 1743, the first European zinc smelter was established inBristol,United Kingdom.[82]The main usage of zinc oxide (zinc white) was again paints and additive to ointments. Zinc white was accepted as a watercolor by 1834 but it did not mix well with oil. This problem was quickly solved by optimizing the synthesis of ZnO. In 1845, LeClaire in Paris was producing the oil paint on a large scale, and by 1850, zinc white was being manufactured throughout Europe. The success of zinc white paint was due to its advantages over the traditional white lead: zinc white is essentially permanent in sunlight, it is not blackened by sulfur-bearing air, it is non-toxic and more economical. Because zinc white is so "clean" it is very valuable for making tints with other colors; however, it makes a rather brittle dry film when unmixed with other colors. For example, during the late 1890s and early 1900s, some artists used zinc white as a ground for their oil paintings. All those paintings developed cracks over the years.[83]In the recent times, most zinc oxide was used in the rubber industry (see applications above). In the 1970s, the second largest application of ZnO was photocopying. High-quality ZnO produced by the "French process" was added into the photocopying paper as a filler. This application was however soon displaced.[19]SafetyAs a food additive, zinc oxide is on the U.S. FDA's list ofgenerally recognized as safe, or GRAS, substances.[84]Zinc oxide itself is non-toxic; however it is hazardous to inhale zinc oxide fumes, as generated when zinc or zinc alloys are melted and oxidized at high temperature. This problem occurs while meltingbrassbecause the melting point of brass is close to the boiling point of zinc.[85]Exposure to zinc oxide in the air, which also occurs while welding galvanized (zinc plated)steel, can result in a nervous malady calledmetal fume fever. For this reason, typically galvanized steel is not welded, or the zinc is removed first.[86]A recent study has also raised a concern that zinc oxide nano-particles may cause cancer.[87]In popular culture Reflecting its many varied but relatively unobtrusive and unglamorous uses, zinc oxide was the theme of a spoof inThe Kentucky Fried Movieas a short educational filmZinc Oxide and You. InSpongeBob SquarePants, the lifeguards in Goo Lagoon use zinc oxide to make their noses white to show that they're a lifeguard.zinc oxidena white insoluble powder used as a pigment in paints (zinc white or Chinese white), cosmetics, glass, and printing inks. It is an antiseptic and astringent and is used in making zinc ointment. Formula: ZnO,(Also called)flowers of zinc, philosophers woolStarchoramylumis acarbohydrateconsisting of a large number ofglucoseunits joined byglycosidic bonds. Thispolysaccharideis produced by most greenplantsas an energy store. It is the most common carbohydrate in human diets and is contained in large amounts in suchstaple foodsaspotatoes,wheat,maize(corn),rice, andcassava.Pure starch is a white, tasteless and odorless powder that is insoluble in cold water or alcohol. It consists of two types of molecules: the linear andhelicalamyloseand the branchedamylopectin. Depending on the plant, starch generally contains 20 to 25% amylose and 75 to 80% amylopectin by weight.[1]Glycogen, the glucose store of animals, is a more branched version of amylopectin.Starch is processed to produce many of the sugars in processed foods. Dissolving starch in warm water giveswheatpaste, which can be used as a thickening, stiffening or gluing agent. The biggest industrial non-food use of starch is as adhesive in thepapermakingprocess. Starch can be applied to parts of some garments before ironing, tostiffen them.Petroleum jelly,petrolatum,white petrolatum,soft paraffinormulti-hydrocarbon,CAS number8009-03-8, is asemi-solidmixture ofhydrocarbons(withcarbonnumbers mainly higher than 25),[1]originally promoted as a topicalointmentfor its healing properties.After petroleum jelly became a medicine chest staple, consumers began to use it for myriad ailments and cosmetic purposes, includingtoenail fungus, male genital rashes (non-STD),nosebleeds,diaper rash, andchest colds. Its folkloric medicinal value as a "cure-all" has since been limited by better scientific understanding of appropriate and inappropriate uses (seeusesbelow). It is recognized by the U.S.Food and Drug Administration(FDA) as an approvedover-the-counter(OTC)skinprotectant, and remains widely used incosmeticskin care.