Porcelain firing

Porcelain, fired Berlin Porcelain, green Berlin Porcelain, fired earthenware Porcelain, green earthenware... 

V Vitrified A glass or porcelain fired to a high temperature. 

Solder melting range 1 Porcelain firing temp... 

The high point, before the introduction of modem electrical and oil- or gas-fired kilns, was the development in China of the dragon kiln, a tunnel kiln built against a hillside, with a draft which resulted in the temperatures needed for the firing of porcelain ware. 

Alloys suitable for castings that ate to be bonded to porcelain must have expansion coefficients matching those of porcelain as well as soHdus temperatures above that at which the ceramic is fired. These ate composed of gold and palladium and small quantities of other constituents silver, calcium, iron, indium, tin, iridium, rhenium, and rhodium. The readily oxidi2able components increase the bond strength with the porcelain by chemical interaction of the oxidi2ed species with the oxide system of the enamel (see Dental materials). 

Ceramics. In ceramics, talc is widely used in wall tile and hobbyware bodies, in electrical porcelains, and in cordierite formulations. Wall tile and hobbyware ate talc—clay bodies that ate pressed and fast-fired to a high porosity (bisque) and then glazed and tefired to produce the final product. Talc containing tremolite and carbonate is preferred to ensure good porosity. 

In a fire-assay method used at the smelters, a weighed quantity of concentrate is mixed with sodium cyanide in a clay or porcelain cmcible and heated in a muffle furnace at red heat for 20—25 min. The tin oxide is reduced to metal, which is cleaned and weighed. Preliminary digestion of the concentrate with hydrochloric and nitric acids to remove impurities normally precedes the sodium cyanide fusion. 

The resistance of these materials to firing temperature is definitely limited. They can be fired to about 1000°C. Hence, they are limited to use in porcelain enamels and in low firing artware gla2es. 

Veneering Investments. These are phosphate bonded and contain finely ground quart2, 2irconium oxide, and/or titanium oxide to produce highly refractory, low expansion dies of fine detail. The dies are formed within impressions taken of teeth that the dentist has prepared in anticipation of covering the front surface with an aesthetic ceramic veneer. Porcelain or ceramic powders are shaped to detail on the dies and these are fired at high (- 1000° C) temperatures to produce the veneers. The veneers are then cemented to the front surface of the previously prepared teeth. 

Special low fusing porcelain veneers are appHed to pure (unalloyed) titanium dental castings. It is important that firing be done either in a vacuum or inert atmosphere to protect the metal surface from excessive oxidation. The strength of the metal-ceramic bond is apparently adequate although the bonding is thought to involve primarily a mechanical rather than a chemical component. 

Enamel Defects. Characterization of defects in porcelain enamel surfaces frequently requites detailed examination via microscopy to determine the sources of the defects. Defects ate divided into processing and material defects. The greatest number of defects result from processing bhsters, pinholes, black specks, dimples, tool marks, and chipping. Defects often occur from unobserved sources at almost every stage of the enameling process, but they ate not recognizable until the ware is fired. Conscientious process control helps to minimize the incidents of unacceptable finishes. 

Chemical-Porcelain Pipe Made of dense, nonporous material and fired at 1230°C (2250°F), chemical-porcelain pipe, fittings, and valves are inert to all acids except hydrofluoric but are not usually recommended for alkalies. Surfaces, except when ground for gasketing, are usually glazed for easy cleaning. Working pressures of 0.3 to 0.7 MPa (50 to 100 Ibftin") are recommended for valves and piping. Temperatures of 200°C (400°F) or more can be used, but sudden thermal shocks must be avoided. 

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