Final Flashcards
(22 cards)
viscous sintering
used for amorphous materials like glass. powder is heated up and gets soft and flowy like honey. there are no grain boundaries because it is amorphous, and it just flows.
1st way to 3d print
material extrusion. like regular printing but with a paste made from ceramic powder and a glue binding agent. this is pushed through a nozzle and laid in layers. good for simple shapes, low cost and no waste.
2nd way to 3d print
vat photopolymerization. ceramic powder is mixed with photosensitive (UV or heat) resin. a laser or projector is pointed at the resin and cures/solidifies the part layer by layer. when the part is complete it is lifted from the resin. the resin is burned out during firing, so left with the pure ceramic part. high precision and the waste is the resin that can’t be reused. smooth finishes, good for tiny or complex parts.
3rd way to 3d print
binder jetting. like an inkjet printer spraying glue instead of ink onto flour. ceramic powder is spread out, a thin layer, then a glue binding agent is sprayed onto the ceramic powder. the part is formed layer by layer and then sintered so it stays solid. good for large parts with no need for support structures. average precision and low waste.
4th way to 3d print
laser based powder fusion. a laser melts a small amount of ceramic powder to fuse it together, very high precision and high energy but low waste. needs special materials that can partially melt.
2nd method to make zirconia crystals from a single melt
verneuil method (flame fusion). zirconia powder is dropped through a very hot flame where it melts and then lands on a rotating seed crystal below. as the drops cool they form into a single crystal rod. this is cheaper and simpler than skull melting. it is good for producing small crystals or gem-quality zirconia.
how zirconias conductivity is used in sensors
lamda oxygen sensor in car exhausts. a small zirconia tube is coated with platinum electrodes. one side is exposed to gas and the other air(oxygen). because of the difference in oxygen levels, ions NOT ELECTRONS move through the zirconia and generate a voltage. the ECU monitors the voltage and tells the engine whether the fuel is rich or lean. this helps reduce emissions. if the mix is rich the fuel is reduced. this is fully stabilized zirconia that has the oxygen conductivity.
how zirconias conductivity is used in fuel cells
solid oxide fuel cell. zirconia is used as the electrolyte and oxygen ions travel through the solid electrolyte to react with fuel (hydrogen) which generates electricity. it is high efficiency and works at high temperatures
how zirconias conductivity is used in oxygen concentration
oxygen concentrator/separator. when you apply voltage across zirconia, oxygen ions more from one side to the other. this lets you pump oxygen ions from air, concentrating it. this is used for high-purity gas production or medical oxygen devices.
clay refractory
made from alumina and silica clays. cheaper but limited to lower temps (1400c). example is fireclay bricks
non-clay refractory
made from zirconia or magnesia. these are purer materials than used for clay refractories. these can handle much higher temps and harsh environments. example is magnesia bricks for steel furnaces
monolithic refractory
installed in a paste, slurry or powder form on-site and hardened. fewer joints = fewer weak spots. example is spray lining inside furnaces
cast/molded refractory
pre-shaped bricks or blocks, made in molds. these are easier to handle and replace
application of refractory in first scenario
basic oxygen steelmaking vessel. uses magnesia-based bricks, must resist extremely high heat (1600) and chemical attack from slag. Magnesia-Carbon bricks are un-fired refractory products
application of refractory in second scenario
jet engine thermal barrier coating. thin ceramic coating (fully stabilized zirconia) on turbine blades which shields metal parts from hot combustion gasses (1200-1400)
application of refractory in third scenario
nuclear fuel rod/pellet. the fuel is uranium dioxide which is a ceramic refractory. it must handle extreme heat, radiation, and provide structural stability. refractory cladding (like zirconium alloys) surrounds the pellets to contain radiation and fission products.
why is it difficult to prepare large ceramic single crystals by solidification from a bulk melt
during cooling, temperature gradients create thermal stresses which often cause cracks or defects that prevent single crystal growth. some ceramics have phase changes when cooling, which disrupts the formation of single crystals.
three ways to overcome challenges of growing large single ceramic crystals
controlled crystal growth technique (czochralski method), flux growth technique, hydrothermal or vapor phase methods.
czochralski method
a single crystal is grown from a molten material by dipping and slowly pulling a seed crystal from the melt while rotating.
flux growth technique
ceramic is dissolved into a molten flux (solvent with lower melting point). crystals grow slowly from this lower-temperature solution, reducing thermal stress and avoiding decomposition
hydrothermal or vapor phase method
growth occurs from vapor or high-temperature aqueous solutions under pressure, which allows single crystals to grow without melting the ceramic.
producing single crystal elongated ceramics using the czochralski method with edge defined film fed growth (EFG).
the efg die is positioned at the surface of the molten ceramic. a seed crystal touches the molten film at the die edge, and the crystal is slowly pulled upward. this produces high-quality single crystals, typically cylindrical shape. common in growing silicon, sapphire, and yttria aluminum garnet. like in CZ controlled pulling and rotating ensure a single crystal grows with minimal defects. there is little need for post-processing since the crystal is shaped during growth thanks to EFG.
