- 14.4 Processing of Ceramics
- Fiberoptics Fundamentals (MIT Video)
- Engineering Ceramics (Book preview)
- Fundamentals of Ceramics (Book preview)
- Properties of Glass-Forming Melts (Book preview)
- Fiberglass and Glass Technology (Book preview)
- Fibre Optics: Principles and Practices (Book preview)
- Video: Prince Rupert’s Drops
Crystalline, few free electrons, hard, brittle stiff, stronger in compression than tension.
Complex compounds and solutions that contain both metallic and nonmetallic elements.
Highly resistant to abrasion, heat and staining.
Susceptible to spalling (thermal cracking)
Typically heated to incandescence during processing.
Typically hard and brittle, high strength, high melting points, low thermal and electrical conductivity.
Properties of Ceramics
- High Electrical Resistance
- Used in electrical industry
- Withstand High Temperatures
- Refractory Material
- Melting Points up to 7000F
- Resist Wear
- Cutting tool applications
- Hard, Brittle, High Melting-point
- Low Thermal Conductivity
- Low Thermal Expansion
- Good Chemical and thermal Stability
- Good Creep Resistance
- High Modulus of Elasticity
- High Compressive Strength
- Glass products
- Laboratory Glassware
- Window Glazing
- Wired glass
- Tempered glass (pre-stressed)
- Laminated glass
- Fiber Optics
- Advanced Ceramics
- Cutting Tools
- Orthopedic Implants
- Aerospace Components
- Structural Ceramics
- Silicon Carbide
- Aluminum Oxide
- Cubic Boron Nitride
- Electrical and Magnetic ceramics
Nature and Structure
- Clay, silica, feldspar
- Bricks, sewer pipe, tile, china, porcelain
- Oxides, carbides, nitrides
- Amorphous, can be somewhat crystalline. Glasses are distinct from both liquids and crystals.
- Glasses lack a clear phase transition, but are in most ways are like solids
- Types of glass
- Silica glass
- Soda-lime glass (cheapest; windowpanes bottles, etc.)
- Borosilicate glass (pyrex)
- Lead oxide glass (decorative cut crystal, optics)
- Aluminosilicate glass (high temperature applications)
- High-content silica glass& fused silica glass (same properties as quartz) expensive. Scientific applications.
History of Ceramics
Naturally occurring glasses
- Libyan desert glass
Man made glass
- Dates to ca.5000 B.C.
- Core formed
- Blown glass
Stone and Structural Ceramics
- One of the oldest building materials
- Types of rock and stone
- Igneous rock – (L. ignis = fire) formed by solidification of magma. e.g., granite.
- Sedimentary rock – small particles cemented together. E.g., limestone
- Metamorphic rock – changed by heat, pressure, and water to produce a more compact and highly crystalline form (slate and marble
Types of Brick
- Common & Face brick
- Face brick
- Darker, denser, stronger, tighter tolerances
- Used on exterior of buildings
- Absorbs more water by weight
- Basic building of structures
- Grades SW, MW, NW (frost/no frost resistance)
- Also glazed brick, paving brick, and tile
- Lower density, more porosity
- Little or No mortar used
- Fired at higher temperatures
Slip Casting (Drain Casting)
Slip is a clay suspension in water (aqueous ceramic slurry)
- talc (reduces shrinkage, prevent cracking)
- And Deflocculants (keep the slip from settling).
Slip Casting Process
First, molds are cleaned, assembled, and clamped together (often with elastic bands). Slip is prepared and poured into plaster of paris molds. The molds absorb water from the slip, which solidifies on the inside surface of the mold. When the slip has dried to create a sufficient wall thickness, the remaining liquid slip is poured out of the mold. The mold is opened and the “green” part is removed. The plaster molds must dry before they are used to mold another component.
The “green” part is air dried, optionally coated with a vitreous glaze, and then sintered (fired) in a furnace.
Making the Plaster Molds
Molds are made from a pattern that is somewhat oversized to allow for shrinkage. They are made from plaster, wood, clay or plastic. The shape of the pattern must allow for part shrinkage to avoid breakage. Molds are considered permanent, but usually only last for 20-50 cycles.
Similar to slip casting, with the major difference being that all of the slip is allowed to solidify in the mold. Often extra slip is supplied to make up for shrinkage.
This process uses a rotating mold into which some ceramic material has been placed. In true centrifugal casting, the internal diameter of the component is controlled only by the amount of slurry introduced into the mold. Centrifugal casting at different RPMs can affect the porosity of the components.
The RAM Process is the mechanical hydraulic plastic pressing of ceramic shapes with permeable dies. Gypsum cement (plaster) is commonly used, but more permanent materials have been developed and are being used where applicable. Instant release of the pressed shape is obtained by means of fluid pressure forced through the permeable die.
Granular powder or die pressed compacts are loaded into a flexible air-tight container, typically polyurethane, placed in a closed pressure vessel filled with liquid and compacted by increasing the pressure within the vessel.
The pressure change takes place throughout the liquid, thus exerting a uniform applied pressure over the entire surface area of the air-tight container. In this way, the material is uniformly compacted and will retain the general shape of the flexible container, and any internal tooling profile. www.dynacer.com
Auger Fed Extrusion
Piston Fed Extrusion
Float glass (video – PPG 6:57)
Glass bottle blow molding (video – how it’s made 5:32)