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Chapter 32. Processes Used to Condition Ceramic Materials. Objectives. Types of sintering used in producing ceramic products Dehydrating before firing ceramic products. Primary Processing.
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Chapter 32 Processes Used to Condition Ceramic Materials
Objectives • Types of sintering used in producing ceramic products • Dehydrating before firing ceramic products
Primary Processing • Primary processing operations (crushing and grinding) are used to separate the desired minerals from undesired components (impurities and organics). • Most traditional and advanced ceramic processes require the use of high purity products. • Clay with high iron content causes discoloration.
Densification • The process of increasing the density of a ceramic part is called densification. • Sintering transforms the loosely bonded green compact formed by dry pressing into a dense ceramic product. • Reducing or eliminating pores in ceramics is essential if the full strength of the ceramic is to be realized.
Calcination • Calcination is a high temperature heat treating process for ceramics. • Calcining prior to sintering results in improved densification. • A calcined part is more desirable for many electrical applications. • Calcining can also be used to dehydrate materials as is done when producing plaster from gypsum.
Firing • Ceramic products that have been dried and finished are called greenware. • Firing consists of heating the part to an elevated temperature in a carefully controlled environment. • It is common to fire some ceramic products twice. • The first firing is done without a glaze (coating) applied to the product. This firing solidifies and fuses the body, so it can be handled without problems in glazing. • In the second firing the clay body is sintered and the glaze develops.
Vitrification • Selecting the correct sintering temperature is important in product applications such as brick making. • If the firing temperature is too low, the bricks will be too porous and fragile. • If the temperature is too high they will be too dense and brittle.
Vapor Deposition Coating Process • Chemical Vapor Deposition: The chemical vapor reacts when it contacts the heated part. • This results in a coating that is harder than most other ceramic fabrication processes. • Sputtering: Sputtering is done by placing the part to be coated next to a flat plate of coating material inside an evacuated chamber. • The plate is bombarded by a beam of electrons. Atoms break off the target and are deposited on the part.
Ion Implantation • Ion implantation is a process that introduces ions into the surface of the part to improve hardness, wearability, and corrosion resistance. • Doping involves adding alloys to liquid metal to produce unique properties. • The addition of impurities (dopants) is necessary to give the materials their desired electrical properties.
Annealing & Tempering • Annealing is a process that relieves the strains in ceramic or glass products through reheating and gradual cooling, just as it does in metals. • Tempering is a heat treating process used with glass products. It gives the product 3 to 5 times the annealed strength. Glass cannot be cut or drilled after tempering.
Summary • Primary processing operations (crushing and grinding) are used to separate the desired minerals from undesired components (impurities and organics). • Calcination is a high temperature heat treating process for ceramics. • Selecting the correct sintering temperature is important in product applications such as brick making. If the firing temperature is too low, the bricks will be too porous and fragile. If the temperature is too high they will be too dense and brittle. • Chemical Vapor Deposition: The chemical vapor reacts when it contacts the heated part. This results in a coating that is harder than most other ceramic fabrication processes. • Ion implantation is a process that introduces ions into the surface of the part to improve hardness, wearability, and corrosion resistance. • Tempering is a heat treating process used with glass products. It gives the product 3 to 5 times the annealed strength.
Home Work • 1. What happens if the firing temperature for bricks is too low or too high? • 2. What is the advantage of the chemical vapor deposition process? • 3. What is the advantage of tempering with glass products?
