SILICON NITRIDE CERAMIC

SILICON NITRIDE CERAMIC Group 5 :Desy Akmalia (333413)M. Fakih Hasbi (333413)Rafa Muadz (333413)Rizki Novid (333412)Sukma Suci Friandani (3334131140)TRI ALIF Shandy (333413)

Silicon Nitride CeramicsSilicon nitride (Si3N4) was developed in the 1960s and '70s in a search for fully dense, high strength and high toughness materials. A prime driver for its development was to replace metals with ceramics in advanced turbine and reciprocating engines to give higher operating temperatures and efficiencies.Crystal Structure

Crystal Structure

Si-N Phase Diagram

Types Of Silicon NitrideReaction-Bonded Silicon Nitride (RBSN)

RBSN is made by carefully nitriding a silicon (Si) dough or compact at about 1450C. During the Reaction, the Si3N4 grows in the porosity in the compact. This results in little dimensional change accompanied by an increase in density. A consequence of this reaction is that the final product contains porosity. However, the material is relatively cheap to produce and has found application particularly as kiln furniture.

Hot Pressed Silicon Nitride (HPSN)

HPSN was developed in the 1960s and 1970s. HPSN is made by adding a flux (usually magnesia) to a fine Si3N4 powder and then pressing the powder in a graphite die typically at 1800C and 40MPa of pressure. The resultant body is fully dense with excellent mechanical properties. These HPSNs have found application as cutting tools for example. HPSN parts tend to be expensive.

Sintered Reaction-Bonded Silicon Nitride (SRBSN)

SRBSN is a development on RBSN aimed at reducing the final porosity of the product and therefore improving its mechanical properties. This is achieved by adding sintering additives to the starting powder mix which allows the material to be sintered after the reactionbonding stage. SRBSN is therefore cheaper to manufacture than both HPSN and SSN. Applications of SRBSN include cutting tools and wear components.

Sintered Silicon Nitride (SSN)

SSN covers silicon nitride materials which are densified by pressureless sintering in anitrogen atmosphere at around 1750C. In order to aid densification, various combinations of sintering additives such as yttrium oxide, magnesium oxide and aluminium oxide are used.Sialon

Where there is an addition of an aluminium containing additive the sintered material can be classed as a sialon. Sialons are ceramic alloys based on the elements silicon (Si), aluminium (Al), oxygen (O) and nitrogen (N).

SSN and sialon generally offer the best mechanical properties available for a silicon nitride and are the most widely used in industrial applications such as molten metal handling, industrial wear, metal forming, the oil and gas industries and the chemical and process industries. Comparison of Physical Property Data for RBSN, HPSN, SRBSN, SSN and Syalon 101

Lightweight (60% Lighter Than Steel) Excellent Wear Resistance Low Coefficient Of Friction Contact Fatigue Resistant High Fracture Toughness Low Surface Porosity Electrical Insulator Non Magnetic High Strength Excellent Chemical Stability. Thermal Stability. High Strength Over A Wide Temperature Good Thermal Shock Resistance Good Chemical Resistance

PROPERTIES Silicon Nitride Engineering Properties

Additional

Additional Properties

Manufacturing Process Of Silicon Nitride Ceramic The process steps in the manufacturing of advanced ceramics such as silicon nitride are summarised in the flow diagram below:

Each of these stages in the manufacturing process (with the exception of the inspection step) influences the properties of the final product

Raw Material ProcessesThe raw materials for manufacturing advanced ceramics come in powder form.MethodsCeramic Dough FeedstockAqueous SlipSpray Dried Powder*Spray Dried Powder

Spray drying is a method of producing a free flowing, uniform,granulated powder which is the ideal feedstock for a variety of pressing processes such as uniaxial pressing and wet and dry-bag isostatic pressing. The raw material blend is firstly milled in a ball mill in a solvent, such as water, using ceramic balls. At this stage up to 5% of organic binder can be added to the slurry feedstock prior to spray drying. The binder, which can include a lubricant and pressing aids, helps give the material good green strength in the subsequent pressing stage. The slurry and additives is spray dried by atomizing it in a hot air stream.*Aqueous Slip

Aqueous slip is prepared by milling together the raw material blend in a ball mill in water along with an organic dispersant to produce a fluid, highly concentrated slurry, which is used for slip and pressure casting to produce a high green density part.*Ceramic Dough Feedstock

Ceramic dough feedstock is prepared by mixing the ceramic raw material blend with a solvent (usually water) and a blend of organic binder and plasticizer to produce a clay-like plastic body that is deformable under pressure, for example by extrusion.The quality of these raw material feedstocks becomes critical in the next stage of manufacture the forming process. The better the feedstock, the better the green density achieved during consolidation and consequently the lower the sintering shrinkage in the sintering stageForming ProcessesThe forming process involves a consolidation stage and an optional machining stage, as shown in the flow diagram below:

Consolidation techniques used by include uniaxial pressing, isostatic pressing, slip casting and extrusion.

*Uniaxial PressingUniaxial or die pressing is a medium to high volume consolidation method for parts ranging from the simple (for example discs or plates) to relatively complex (for example parts with holes or recesses). This shaping method is inexpensive and suitable for high-volume production of simple shapes (limited geometrical possibilities). The uniformity of compaction is not very high.

*Isostatic PressingIsostatic pressing is a small to medium volume consolidation technique of which there are 2 variations: wet-bag pressing and dry-bag pressing. In both cases a spray dried is contained in a flexible (usually rubber or polyurethane) bag which is subjected to an isostatic pressure. Wet-bag pressing is primarily for simple stock shapes such as rods whereas dry-bag pressing can produce more complex shapes such as nozzles.

*Slip Casting

Slip casting, also known as drain casting, is a small to medium volume consolidation method for generally simple shapes such as tubes and crucibles but also for more complex shapes such as ladles.*Extrusion

Extrusion is a medium to high volume consolidation technique for producing simple shapes such as small diameter tubes. The dough feedstock deforms under pressure and the binders in the mix help retain the extruded form as it dries.

Green MachiningGreen machining is the machining of an unfired green or raw body. This needs to be done when the consolidation method used cannot produce the required shape. Not only is green machining quick, it is also cheaper than diamond grinding and the dust from the machining process can be collected and recycled.SinteringSintering is the process during which the consolidated green ceramic part is fired to give a dense, advanced technical ceramic. Just before or during this stage any organic binder additives need to be removed. This is best done in an air atmosphere.During sintering the ceramic is heated to below its melting point. At high temperatures the fine ceramic powders undergo several changes from particle rearrangement to grain growth and finally pore elimination. SinteringCeramics such as silicon nitride are more difficult to densify and often use sintering mechanism called liquid-phase sintering. In this case a small volume of additives in the mix form a liquid at sintering temperatures in which the primary particles (for example silicon nitride) firstly rearrange due to capillary forces, giving better packing. Then at the points of contact between particles some of the solid particles begin to dissolve in the liquid and are re-precipitated at the neck areas between the particles. Eventually the pores are eliminated and the ceramic reaches full densitySinteringSintering takes place in a different atmosphere depending on the material being sintered. For example silicon nitrides are sintered in a nitrogen atmosphere. During sintering advanced ceramics typically shrink approximately 20-25%. It is vitally important to obtain good, uniform green density during the forming stage to have a controlled, uniform shrinkage.

Diamond GrindingDiamond grinding is a machining process which is carried out on a sintered part that needs to be tightly tolerance, needs an improved surface finish or to remove surface flaws and as such is an optional process.

Final machining processes include grinding, cutting, honing and lapping and polishing. Each of these processes requires diamond tooling due to the high hardness of dense advanced ceramics. The rate of material removal is very slow as care must be taken not to cause surface damage. These are therefore relatively expensive processes InspectionInspection is the final stage of the ceramic manufacturing process and generally involves a visual inspection of the part and dimensional inspection to a drawing.

Visual inspection involves looking for cracks or flaws in the part and to ensure the part is clean. Dimensional inspection can be done using a variety of equipment such as Vernier calipers, micrometers, coordinate measuring machine (CMM), shadow graph etc. Automotive Aerospace Metal Forming Mineral Processing Molten Metal Processing Oil & Gas Petrochemical SemiconductorApplication *Automotive Engine Components Cam Rollers Fuel Pump Components Engine Valves Check Valves EGR Valves Valve Seats Valve Guides

* Aerospace Applications Electrical Insulators Radomes Bearings Seal Rings Wear Plates

*Oil & Gas Severe Environments

Logging Tools Drilling Components Measuring Wheels Check Valves Proprietary Down Hole Components* Industrial Wear Applications

*Molten Metal Processing Molten Metal Processing Melting and Holding Furnaces Casting Furnaces Metal Dosing Chemical Processing

*Metal working

Silicon nitride due to its excellent thermal shock behaviour, high strength, hardness and toughness shows improved service time and product quality in both, at cold and even at hot rolling with temperatures up to 1050C in rolling of stainless steel, titanium and aluminium alloys.

The advantage of silicon nitride in welding is the improved strength, thermal shock capability and the non wetting for sparks created through the welding processWelding Rolling Hazard

Summary Silicon nitride is a very important engineering ceramic which is available in several forms, each with their own unique properties. These include high strength, toughness and hardness, excellent wear resistance, corrosion resistance to many acids and alkalis and outstanding thermal shock resistance. These properties are enabling silicon nitride to find use in many industrial applications.Referenceshttp://www.ceradyne.com/uploads/Brochures/SiN_Brochure.pdfhttp://www2.lbl.gov/ritchie/Library/PDF/ZieglerSi3N4.pdfhttps://www.ceramtec.com/ceramic-materials/silicon-nitride/http://www.azom.com/article.aspx?ArticleID=53http://www.syalons.com/resources/guides/manufacturing.phphttp://www.syalons.com/resources/downloads/manufacturing.pdfhttp://www.fcti.de/de/download/AST_Silicon-Nitride-Ceramics-forProduct-and-process-Innovations.pdfhttp://www.syalons.com/resources/downloads/siliconNitride.pdfhttp://accuratus.com/silinit.htmlhttp://www.designinsite.dk/htmsider/p1006.htmhttp://www.azom.com/properties.aspx?ArticleID=53http://accuratus.com/silinit.html