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Jon - Ceramic Intro - Coggle Diagram
Jon - Ceramic Intro
Mechanical Properties
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Fracture Toughness is critical stress intensity factor \(K_{IC}\), at which crack will propogate
Sintering
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Sintering variables:
Temperature - diffusion rate
Hold time - diffusion distance
Rate - critical temp for diffusion
Particle size - :arrow_down: gives :arrow_down: diffusion distances
System composition - Controls how much liquid is present, diffusion is quicker when
Atmosphere - Fraction of vacancies present therefore atomic diffusion rate
Pressure - :arrow_up: densification but :arrow_up: costs
Mechanisms
Vitrification: 20-30% liquid @ firing temp, turns to glass on cooling and glues particles. Rarely used for advanced ceramics
Liquid phase sintering: 5-10% liquid @ firing temp. Acts as diffusion route. Particle shape change is involved. ast densification but limited by the 5-10% glassy phase
Solid State Sintering: No liquid involved, slower diffusion, particle shape change is involved
Grain growth
Oxides: Pore boundary atoms in tension so atoms diffuse from high stress corners to low stress edges
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Formation
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3 Variations
Dry forming
Die Pressing: Pressure is applied to powder and binder (water) to cause particle fracture. Too much pressure causes :arrow_up: risk of disintergration
Cold Isostatic Pressing: Pressure from all directions, no temp. Dry bag gives faster production but more costs and more challenging design. Wet bag is simpler, cheaper and better tolerances but longer
Wet forming
Wet forming: stable suspension of ceramic in liquid, poured into a mould. Viscosity must be right ( :arrow_up: gives flabby casts, :arrow_down: gives brittle casts)
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Plastic forming
Injection Moulding: ~60% ceramic powder mixed with polymers. Rapid cycle times but polymer needs burning out which can take days
Three main factors:
Particle size distribution - affects ratio of polymer to ceramic
Die design - ensure polymer fills mould
Composition of polymer mix - maximise burn off speed
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