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specialized ceramic products
Transcript of specialized ceramic products
*FERROELECTRIC AND FERROMAGNETIC CERAMICS
scove kilns Periodic Kilns tunnel kilns
roller hearth kiln
Continuous Kilns Cermets comprise one of a group of composite materials consisting of an intimate mixture of ceramic and metallic components. These are compacted and sintered in order to obtain certain physical properties not found solely in either of the components. CERAMIC COMPOSITES
Reaction bonded ceramic-metal composites are formed by a chemical reaction that bonds the materials when heated below the melting point of either. The ceramic acts as a catalyst to cause corrosion of the metal to a metal oxide. As the metal oxide is formed, crystals of the oxide grow into the crystal structure of the ceramic. The bond is extremely strong and permanent and forms quickly, although for optimum strength the two materials are usually kept hot for several hours while clamped together.
Strongest bonds are formed between the noble metals:
*oxides of ceramics of alumina, magnesia, zirconia and beryllia.
Resources * In purchasing, a metal sheet should meet a definite specification.
*The surface must be thoroughly cleaned of all foreign matter.
- Sheet metal is cleaned by pickling in dilute hydrochloric or sulfuric acid at 60degC after the iron has been annealed. Preparation of Metal Parts How are ceramic composites formed? Applications:
*gold-coated ceramic wafers for semiconductor chips
*zirconia-lined steel for corrosion-resistant uses
*ceramic-capped gold dental crowns
SPECIALIZED CERAMIC PRODUCTS FERROELECTRIC AND FERROMAGNETIC CERAMICS
-exhibit unusual properties useful in electrical applications, the most important
of which involves high capacity at various frequencies.
-have been responsible for important advances in the design of equipment. They are used in television sets, computers, magnetic switches, wideband transformers, recorders and memory devices.
-mechanically strong dense materials, unlike refractories which are usually porous. Most high-alumina ceramics are used to take advantage of their wear resistance, corrosion resistance and dimensional stability rather than their ability to resist temperatures.
Vitreous enamel, also porcelain enamel in US English, is a material made by fusing powdered glass to a substrate by firing, usually between 750 and 850 °C (1,382 and 1,562 °F). The powder melts, flows, and then hardens to a smooth, durable vitreous coating on metal, or on glass or ceramics Long valued as a material of great beauty in the field of decorative arts, it has come into general commercial use because it provides a product of great durability and wide application, it is easy to clean and resist corrosion. Raw Materials refractories
Refractories include such material as quartz, feldspar, and clay which contribute to the acidic part of the melt and give body to the glass. Fluxes include such products as borax, soda ash, cryolite and fluorspar, which are basic in character and react with the acidic refractories to form the glass. They tend to lower the fusion temperature of enamels. Opacifiers are compounds added to the glass to give it the white opaque appearance of vitreous enamels. insoluble opacifiers
Color materials may be oxides,elements, salts, or frits, and may act either as refractories or as fluxes. Floating agents such as clay and gums are chosen to suspend the enamel in water To peptize the clay and properly suspend the enamel, electrolytes are added, such as borax, soda ash, magnesium sulfate, and magnesium carbonate. * The raw materials are mixed in the proper proportions and charged into a melting furnace maintained near 1370degC, from 1 to 3hrs.
* After the batch has been uniformly melted, it is allowed to pour from the furnace into a quenching tank of cold water, shattering the melt into millions of friable pieces. This material is called frit.
* Enamel is normally made in a wet process by grinding the ingredients, principally a mixture of frit and clay in a ball mill and then passing through a 200-mesh screen. Manufacture of the Frit Application of the Enamel * Dipping
- The requirements for succesful firing of a good enamel are:
*proper firing temperature from 750degC to 800degC
*time-1 to 15 minutes
*proper support of the ware
*uniform heating and cooling of the ware
*an atmosphere free from dust Firing KILNS Tunnel Kilns
-used for the firing of brick, tile, porcelain, tableware and refractories * direct-fired type
* indirect type Roller Hearth Kiln
- This type of kiln is particularly suited for the production of electronic parts that must meet exacting specifications. Chamber Kiln
- This type of kiln is used to burn brick and tile. Periodic Kilns Downdraft Kilns
- These are used in burning face brick, sewer pipes, stoneware tile and common brick. Updraft Kilns - These are used in burning potteryware. Scove Kilns - Common bricks are burned in this type of kiln. THE END