Applications of Si

Question 1

Grinding media

Answer 1

~ SiC is extensively used as an abrasive in bonded wheel shapes for grinding and honing (sharpening), coatings (sand paper), and in loose form (media for sand blasting)

~ it has a high hardness and exhibits colloidal fracture, which makes it a self-sharpening bound abrasive that’s highly effective at material removal

~ it used mainly for machining ceramics and non-ferrous metals; chemical rxn with ferrous metals increases the rate of attriteous wear

Question 2

Refractories

Answer 2

~ SiC is protected from oxidation by forming a passive silica surface coating
–> this is lost when SiC undergoes oxidative decomposition at
1800C: SiC + 2SiO2 = 3SiO + CO

~ SiC has a high temp thermal conductivity and a low CTE, together with undergoing no polymorphic phase transformations, means excellent thermal shock resistance

~ chemically inert and has low wetability by molten metals and slags

~ used in blast and other metal furnaces, and as support and shelving material in high temp kilns for firing ceramics and glasses

Question 3

Heating elements

Answer 3

~ SiC is a semiconductor and adequately conductive to be used as a heating element for furnaces in oxidative environments

~ used in either rod or spiral form, can heat furnaces up to 1600C

Question 4

Corrosive liquid handling and mechanical seals

Answer 4

~ sintered (hot-pressed and or post-HIPED) SiC is used in the chemical processing industry as pipework, heat-exchangers, and pump components for corrosive chemicals

~ a mechanical seal is used to seal the interface between a rotating shaft and a stationary housing (ex: centrifugal pumps) from leakage of process fluids

~ SiC is used because it conducts heat, is chemically inert, has a low coefficient of friction and good wear resistance

~ the seal faces are lapped flat to high precisoin; gap between the faces on a typical seal is ~1um

~ a thin film of process fluid is drawn in by capillary forces separates the two seal faces. This microgap keeps the mechanical seal from being totally leak free, however, the amount of liquide that leaks through is so small that it typically exits as un-noticed vapor

~ a SiC microstructure with enhanced graphite improves seal performance, the graphite either acts as a solid lubricant, or is eroded away, providing channels for capillary draw of liquid lubricant