Ceramics Flashcards
(19 cards)
Why do we not use tensile test to measure stress stain behaviour of ceramics
-Difficult to prefer a specimen with required geometry
-Difficult to grip brittle material without fracturing them
-ceramics fail at very low strain so specimen would need to be perfectly aligned to avoid bending stresses
What is used to measure stress strain behaviour of ceramics
Three or four point loading technique
Flexural strength
Stress at fracture
How does volume of specimen Impact flexural strength
Increase in volume p, decrease in flexural strength due to increase in probability of a crack producing flaw
Glasses
Non crystalline materials containing other oxides. Choose materials with optical transparency and ease to be fabricated.
Glass ceramics
Fine grained polycrystalline materials
Properties of glass ceramics
Relatively high mechanical strengths, low coefficient of thermal expansion, relatively high temp capability, good dielectric properties (for electronic packing) and good illogical compatibility. Some transparent, some opaque. Easily fabricated
Refractory ceramics
Ones that can withstand high temps. Unreavive and inert in severe environments. Thermal insulation
Why does firing increase strength of ceramic
Fine particles form binding phases, phase may be predominantly either glassy or crystalline
Abrasive ceramics
Used to wear, grind or cut away other materials.
Properties needed for abrasive ceramics
Hard and wear resistant.High degree of toughness so the abrasive particles do not fracture. Refractoriness as high temp may be produced from frictional forces
What are the different forms of abrasives
Bonded to grinding wheels, coated abrasives and as loose grains
How are abrasives bonded to a wheel structured
Bonded by glassy ceramics or organic resin. Surface has some porosity for flow of air around grains to prevent excessive heating
Structure of coated abrasives
Abrasive powder coated in some type of paper or cloth material
Usefulness of cement
When mixed with water, forms a paste that sets and hardens to form solid rigid structures
How is Portland cement produced
Process called calcination. Grinding and mixing clay with lime beating minerals and heating to about 1400 degrees in a rotary kin. The resulting clinker product is the. Ground into a very fine powder which is added a small amount of gypsum to retard the setting process.
Why is Portland cement termed a hydraulic cement
It hardness develops by chemical reactions with water.
What is meant by non hydraulic and give example
Lime is non hydraulic. It hardens by reacting with other compounds than water
How to recycle thermoset or thermoplastic matrix composite,
Shredding/grinding. Sometimes theses ground particles are used as filler materials that are blended with a polymer before fabrication into consumer products. Other processes allow for separating of fibres and matrix materials. With some the matrix is volatized, with others it is recovered as a monomer. Recovered frisbees have short lengths and experience reduction of mechanical strength
