Ceramics Flashcards
What are Ceramics?
Typically composed of silicates, oxides, nitrides, and carbides.
Insulate against electricity and heat flow.
More resistant to high temperatures and harsh environments compared to metals and polymers.
Hard and very brittle.
Properties of Ceramics
High Hardness & Wear Resistance: Ceramics are very hard and resist scratching and wear caused by friction.
Heat Resistance & Insulation: They can withstand high temperatures without melting and are poor conductors of heat (thermal insulators).
Corrosion Resistance: Ceramics are generally resistant to chemical attack and degradation.
Brittle & Low Ductility: They are strong under compression but break easily upon impact (brittle) and cannot be easily bent or stretched (low ductility).
Low Electrical Conductivity: Most ceramics are electrical insulators, meaning they don’t conduct electricity well.
Low Thermal Expansion: They expand minimally with increasing temperature compared to some other materials.
Poor Thermal Shock Resistance: Sudden temperature changes can cause cracking due to uneven expansion/contraction.
Low Density: Some ceramics are lightweight due to pores within their structure. (Porosity can also affect other properties.)
High Strength at Elevated Temperatures: Ceramics can maintain their strength even at high temperatures.
What are refractory ceramics used for?
High-temperature applications like furnace linings and kilns due to their heat resistance.
What materials are commonly used in refractory ceramics?
Silica (SiO2) - Alumina (Al2O3) system is a common base. Silica refractories are rich in silica with small additions of alumina.
How does alumina help in refractory ceramics?
While it increases refractoriness slightly, alumina’s main benefit is lowering the melting temperature of silica, allowing for stronger bonds at lower firing temperatures.
What are some applications of ceramic cutting tools?
Grinding glass, tungsten carbide, ceramics, cutting silicon wafers, and oil drilling (blades and bits).
What materials are used in ceramic cutting tools?
Manufactured single crystal or polycrystalline diamonds embedded in a metal or resin matrix. Polycrystalline diamonds can be resharpened through microfracturing.
How does a zirconia oxygen sensor work?
Adding calcium (Ca) impurity to ZrO2 increases oxygen vacancies, allowing faster oxygen ion diffusion. This rapid diffusion creates a voltage difference based on the oxygen concentration around the sensor.
List some advantages of using advanced ceramics in engines.
Operate at high temperatures for better efficiency, reduce frictional losses, eliminate the need for a cooling system, and offer lighter weight compared to traditional engines.
What are the two main components of ceramic armor?
Outer facing plates (hard and brittle for projectile fracture) made of materials like alumina (Al2O3), boron carbide (B4C), silicon carbide (SiC), and titanium diboride (TiB2). Backing sheets (soft and ductile for absorbing remaining energy) made of aluminum or synthetic fiber laminates.
List some challenges of using advanced ceramics in engines.
Brittleness of the material, difficulty in removing internal voids that weaken the structure, and challenges in forming and machining complex ceramic engine parts.
What is glass?
State of Matter: It refers to an amorphous (non-crystalline) solid material. This means its atoms are not arranged in a regular, repeating pattern like crystals.
Type of Ceramic: Glass is also a type of ceramic. However, unlike most ceramics that form a crystalline structure upon cooling from a molten state, glass doesn’t have enough time for crystals to form during cooling, resulting in its unique amorphous structure.
Why is SiO2 (silicon dioxide) so important in glass?
Excellent Glass Former: SiO2 is the primary glass former because it readily forms a glassy state when cooled from a molten state.
High Content in Glass Products: Silica makes up 50% to 75% of most glass due to its role as the main building block.
Natural Glass Formation: Unlike most ceramics that crystallize upon cooling, SiO2 inherently transforms into a glassy state during solidification. This makes it ideal for glass production.
What are other ingredients besides SiO2 used in glass and their functions?
Sodium Oxide (Na2O), Calcium Oxide (CaO): Act as fluxes, lowering the melting temperature of SiO2 (promoting fusion during heating) and making the molten glass more fluid for easier processing.
Aluminum Oxide (Al2O3), Magnesium Oxide (MgO): Improve the chemical resistance of glass against attack by acids, bases, or water.
Potassium Oxide (K2O): Can also act as a flux and improve chemical durability.
Lead Oxide (PbO): Traditionally used to create a more brilliant and refractive glass, but its use is being phased out due to health concerns.
Boron Oxide (B2O3): Improves the workability of molten glass and can also influence the index of refraction for optical applications.`
What is Slip Casting?
Slip casting is a ceramic forming technique that uses a liquid mixture called slip to create a shaped object.
Here’s how it works:
Slip Preparation: A ceramic powder is mixed with water and other additives to create a pourable slurry called slip.
Mold Preparation: A mold, typically made of plaster of Paris (CaSO4·2H2O), is used to form the desired shape of the ceramic piece.
Casting: The slip is poured into the mold. Water in the slip is drawn out by the porous plaster mold walls through capillary action, leaving a layer of ceramic particles on the mold surface.
Solidification: Once a sufficient layer thickness is achieved (depending on the desired final wall thickness of the ceramic piece):
In drain casting, the remaining liquid slip is poured out.
In solid casting, more slip is added to form a solid piece.
Drying and Firing: The cast piece (still wet) is removed from the mold and allowed to dry. Then, it’s fired at high temperatures to harden the ceramic permanently.
