Swapnil Roll no. 15 NPC, Visnagar

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Seminar onThermogravimetric analysis (TGA)

AndDifferential thermal analysis (DTA)

Presented By:Swapnil M. SanghaviRoll no. 15M. Pharm.- sem IDept. Of Pharmaceutics,Nootan Pharmacy College, Visnagar.

Swapnil Roll no. 15 NPC, Visnagar

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THERMOGRAVIMETRIC ANALYSIS

CONTENTS

INTRODUCTIONTYPESPRINCIPLE & METHODOLOGYINSTRUMENTATIONFACTORS AFFECTING RESULTSAPPLICATIONS

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INTRODUCTION

- CONCERNED WITH AN ANALYSIS OF SAMPLE WEIGHT CHANGE CURVE.

-INVOLVES CHANGE IN WEIGHT OF A SYSTEM UNDER EXAMINATION AS THE TEMPERATURE IS INCREASED AT A PREDETERMINED RATE (PREFERABLY LINEAR)

-USING THERMOBALANCE, CURVE OF WEIGHT CHANGE OF SAMPLE VS. SAMPLE TEMPERATURE CAN BE OBTAINED DIRECTLY

- VERY RELIABLE, RUGGED AND VERY ACCURATE

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TYPES OF TGA

•DYNAMIC TGA: Sample is subjected to conditions of continuous increase in temperature usually linear with time

•ISOTHERMAL (STATIC) TGA: Sample is maintained at a constant temperature for a period of time during which any changes in weight are noted

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METHODOLOGY

*Described by ‘thermogram’ of calcium oxalate monohydrate (CaC2O4.H2O)

2017.514

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weight

100

250

400

500

700

850

H2O

(2.46mg)

CO(3.84mg)

CO2 (6.02mg)

Temperature-

Thermogravimetric analysis of calcium oxalate monohydrate heated at rate of 6̊̊ c/ min

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STAGE I: The water of crystallization (or hydration) is lost which corresponds to 2.46 mg(12.3%) eqlt. to 1 mole of H2O in temp range 100-250 c.12.3% wt loss corresponds to 12.3% of the original formula wt of CaCO3H2O(fw=146), hence the product being lost has has a formula wt of 0.123*146=18, which corresponds to H2O.

STAGE II: 1 mole of carbon monoxide is evolved corresponding to 3.84 mg (19.2%) in temp. range 400-500 c. Again, 0.192*146=28, which corresponds to carbon monoxide.

STAGE III : Finally a mole of CO2 is evolved calcium carbonate that corresponds to 6.02mg (30.1%) in temp range 700-850 c. The wt loss is 0.301*146= 44, which corresponds to CO2.

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INSTRUMENTATION

1)A Recording Balance

2) A Furnace

3) Furnace programmer or controller

4) A Recording Device

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Swapnil Roll no. 15 NPC, Visnagar

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RECORDING BALANCE

Deflection type

helical Cantilever beam

Torsion wire Beam

Null type

RECORDING BALANCE

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NULL-POINT TYPE:Makes use of a sensing element which aptly detects any slightest deviation of the balance beam & provides the application of restoring force, directly proportional to the change in weight, thereby returning the beam to its original null point. The restoring point is subsequently recorded.

DEFLECTION TYPE:Essentially based on either a conventional analytical balance consisting of helical spring, cantilever beam, and strain gauze or a torsion analytical balance involving the conversion of deviation directly into a record of wt change

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Sample holders:This is most important in accurate thermogravimetric analysis.

Depending upon the nature of sample, its weight and quantity to be handled, different size and shape of sample holders known as crucibles are employed.

These are constructed from various materials like glass, quartz, aluminium, stainless steel, platinum etc.

These generally are of two types:(a) Shallow pan for holding samples which eliminates gas, vapours or volatile matter by diffusionduring heating or.(b) Deep crucible for general purpose.

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Furnace Must be designed in such a fashion so as to incorporate an

appropriate smooth input thereby maintaining either a fixed temp. or predetermined linear heating program. (e.g.- 6 c/min)

Temperature control is achieved via a thermocouple mounted very close to the furnace-winding.

Maximum operational temp. may be obtained using different thermocouple as indicated below:

SR. NO.

SPECIFICATION MAX. TEMP.

1 Nickel-chrome(nichrome)

1100

2 Platinum-rhodium 14503 Graphite- tube furnace >1500

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Furnace temperature programmer:

o These are the controller which can provide gradual rise of temperature at a fixed rate.

o This device has a coarse and fine control knobs through which desired temperature with respect to rate/ time can be obtained.

o This controlling is done by increasing voltage through the heated element by motor driven variable transformer or by different thermocouples.

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Factors affecting Thermogravimetric Results:

(I)Instrumental factors:These include various aspects of instruments like furnace heating (its temperature and rate), recording of changes on charts (its speed), furnace atmosphere (its rate of cooling and maintaining temperature), sample holder and its geometry and the sensitivity of balance

(II)Characteristics of sample:The important factors about the sample are: weight of sample, particle size of sample, nature of evolved gas or volatile matter, thermal conductivity of sample and the heat of decomposition of the reaction.

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Applications of Thermogravimetry

o Determining the purity and thermal stability of both primary and secondary standards.

o Investigating the correct drying temperatures and the suitability of various weighing forms for gravimetric analysis

o Direct application to analytical problems

o Determining the composition of alloys and mixtures.Thermogravimetry is a valuable technique for assessing the purity of materials

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o Analytical reagents, especially those used in titrimetric analysis as primary standards, e.g. Na2CO3, KHP have been examined. Many primary standards absorb appreciable amounts of water when exposed to moist atmospheres. TG data can show the extent of this absorption, hence the most suitable drying temperature for a given reagent may be determined.

o The thermal stability of EDTA as the free acid and also as the more widely used disodium salt. Na2EDTA .2H2O has been reported. According to that the dehydration of the disodium salt commences at between 110 and 125 c , which confirmed the view that Na2EDTA.2H2O could be safety heated to constant weight at 80 C.

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o Thermogravimetry may be used to determine the composition of binary mixtures. E.g. for Ca and strontium binary mixture. Here the decomposition temperature for CaCO3 is 650 to 850 C. Where for strontium carbonate the decomposition temperature is 950 to 1150C. Both carbonates decompose to their oxides with the evolution of carbon dioxide. Hence the amount of calcium and strontium present in a mixture may be calculated from the weight losses due to the evolution of carbon dioxide at the lower and higher temperature ranges respectively.o This method can also be extended to the analysis of a three component mixtures.o The most important applications of thermogravimetry is in examining the thermal stability of polymers.

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References

1) Instrumental Methods of Chemical Analysis

B.K.Sharma Page No. – m-3082) Pharmaceutical Drug Analysis

Ashutosh KarPage No. - 194

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DIFFERENTIAL THERMAL ANALYSIS

CONTENTS

Theory Instrumentation Methodology Application

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THEORY

The difference of temp. under estimation & a thermally inert reference material is continuously recorded as a function of furnace temp. in DTA.

The measurement of changes in heat content is carried out by heating the two material at elevated temp. or cooling to subnormal temp. at a predetermined rate.

The thermal effect may either be endothermic or exothermic and are caused by physical phenomena such as fusion, crystalline structure inversion, boiling, vapourisation, sublimation or others. Some enthalpic effect are also caused by chemical reaction. In this manner, endo- and exothermal bands and peaks appearing on thermogram give info, regarding the detection of enthalpic changes.

The range of phenomena measurable during a DTA-run is much larger than in a TGA-run.

TGA & DTA are complementary techniques, because the information obtained by the application of one approach is often enhanced by the application of other method.

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METHODOLOGYA. Insert a very thin thermocouple into a disposable sample tube

2mm in diameter and containing 0.1-10 mg of sample.B. Another identical tube is either kept empty or filled with

reference substance, such as quartz, sand, alumina or alundum powder.

C. The two tubes are simultaneously inserted into a sample block and subsequently heated(or cooled) at uniform predetermined programmed rate. And

D. DTA- being a dynamic process, it is extremely imp that all aspects of the technique must be thoroughly standardized so as to obtain reproducible results. Such aspects are,

-pretreatment of specimen, -particle size & packing of specimen, -dilution of the specimen, -nature of inert diluent, -crystalline substances must be powdered and sieved thru 100 mesh sieve, -micelle size is critical for colloidal particle and – adequate control of atmosphere.

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INSTRUMENTATION

1)Sample holder with built-in thermocouple assembly2)Flow-control system3)Furnace assembly4)Preamplifier & Recorder5)Furnace power programmer and controller

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(1)Sample Holders:

Both metallic as well as non-metallic materials are employed for the fabrication of sample holders.Metallic materials generally include nickel, stainless steel, platinum and its alloys.Non- metallic material generally includes glass, vitreous silica or sintered alumina.Metallic holders give rise to sharp endotherms and flat endotherms.On the other hand non-metallic holders yield relatively sharp endotherms and flat exotherms.

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o In DTA apparatus, one always prefers a tubular furnace.o This is constructed with an appropriate material (wire or ribbon) wound on a refractory tube.o Such furnaces possess the desired characteristics for good temperature regulation and programming.o These are fairly inexpensive. Generally, the choice of the resistance material as well that of refractory is decided from the intended maximum temperature of operation and gaseous environments.

(2)Furnace:

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Temp. controller In order to control temperature, the three basic elements are required.-Theses are sensor, control element and heater.

On-off Control- In this device, if the sensor-signal indicates the temperature has become greater than the set point, the heater is immediately cut off.Not used in DTA.

Proportional control – In on-off controllers there occurs fluctuatations of temperature around the set value. These can be minimized if the heat input to the system is progressively reduced as the temperature approaches the desired value. Such a controller that anticipates the approach to the set value is known as a proportional controller.

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(4) Recorders –

In thermo analytical studies, the signal obtained from the sensors can be recorded in which the signal trace is produced on paper or film, by ink, heating stylus, electric writing or optical beam.

There are two types of recording devices similar to the TG.- one is deflection type and other is null type.

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APPLICATION(a) Identification of substances – We know that the DTA curve for two substances is not identical. Therefore, these serve as finger prints for various substances. Particularly, DTA has become an established technique for the identification of clays.(b) Identification of products – When a substance reacts with another substance, the products is identified by their specific DTA curves. Therefore, this technique has been termed ‘reaction DTA’.(c) Melting points – As melting points can be easily determined by DTA, it means that this technique can be used as a direct check of the purity of the compound.(d) Quantitative Analysis – We know that the area of DTA peak is proportional to the total heat of reaction and hence to the weight of the sample. Therefore, the quantitative analysis is possible with the help of standard curves of peak area vs. weight.(e) Quality control – DTA technique has been widely used for the quality control of a large number of substances like cement, glass, soil, catalysts, textiles, explosives, resins etc.

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References1) Instrumental Methods of Chemical

Analysis B.K.Sharma Page No. – m-3182) Pharmaceutical Drug Analysis

Ashutosh KarPage No. - 198

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THANK YOUWhat the caterpillar calls the end, Butterfly calls it the beginning