Porcelain types

The various porcelain types fall into three regions of the phase diagram and will be discussed in turn typical properties are summarized in Table 5.3 and examples of components are illustrated in Fig. 5.19. 

A) Filtration on the Buchner Funnel. The Biichner funnel is used for large-scale filtrations. If the quantity of material is small (<2 g), the Hirsch funnel can be used. Properly matched Buchner funnels, filter paper, and flasks are shown in Fig. 6. The Hirsch funnel shown in the figure is an old-style porcelain type. 

FIG, 1S2, The effect of temperature on the sintering of porcelain-type materials. The dashed line indicates the actual porosity, the full line represents apparent porosity. 

Conventional porcelain types require tunnel kiln transit times of 24 to 72 h. Firing times of 1 to 3 h are attainable with the recently developed rapidly fired porcelains. With such short firing times the furnace throughput can be kept high even when the articles are mounted as a single layer... 

Energy saving field transmission lines are being planned to carry very high tensions of up to lOOOkV, and only this type of insulator is usable because the heavy porcelain type would require excessively large pylons to support them. 

This type of filtration is almost invariably performed with the aid of a Buchner flask and funnel, by means of which a rapid and almost complete separation can be obtained. The Buchner flask A (Fig. 4) consists of a simple thick-walled conical flask with a short side-arm for connection to a water-pump. Into the neck of the flask is fitted the Buchner funnel B which consists usually of a cylindrical porcelain funnel, the bed of which is pierced by a... 

The furnace and thermostatic mortar. For heating the tube packing, a small electric furnace N has been found to be more satisfactory than a row of gas burners. The type used consists of a silica tube (I s cm. in diameter and 25 cm. long) wound with nichrome wire and contained in an asbestos cylinder, the annular space being lagged the ends of the asbestos cylinder being closed by asbestos semi-circles built round the porcelain furnace tube. The furnace is controlled by a Simmerstat that has been calibrated at 680 against a bimetal pyrometer, and the furnace temperature is checked by this method from time to time. The furnace is equipped with a small steel bar attached to the asbestos and is thus mounted on an ordinary laboratory stand the Simmerstat may then be placed immediately underneath it on the baseplate of this stand, or alternatively the furnace may be built on to the top of the Simmerstat box. 

Another large appHcation is as an ingredient in the production of charcoal briquettes. The amount of sodium nitrate used in charcoal briquette manufacture depends on the type and amount of wood and coal used. Typically charcoal briquettes contain up to almost 3% sodium nitrate. Sodium nitrate is also used in the manufacture of enamels and porcelain as an oxidizing and fluxing agent. In porcelain—enamel frits used for metal coating, the amount of sodium nitrate in a batch varies with the various metal bases to be coated, typically from about 3.8 to 7.8 wt %. 

The uses of boric oxide relate to its behavior as a flux, an acid catalyst, or a chemical iatermediate. The fluxing action of B2O2 is important ia preparing many types of glass, gla2es, frits, ceramic coatings, and porcelain enamels (qv). 

Tuberculocidal Test. The tubercle bacillus is resistant to disinfectants because the cells are protected with a waxy coating that is not readily penetrated. The tuberculocidal test is a use dilution practical type test that employs porcelain cylinders. The bacteria are different from those in the use dilution method (Table 10), the incubation time is longer, and the details of the procedure are different. For example, in the tuberculocidal test the test is divided into two parts, a presumptive test and a confirmatory test. The former employs Mycobacterium smegmatis and the latter employs Mycobacterium bovis (BCG). For the presumptive test the incubation time is 12 days, as against 48 hours for other bacteria used in the use-dilution method. For the confirmatory test the incubation time is 60 days, with an additional 30 days in case there is no growth. As shown in Table 10, the concentrations of the phenol standard are higher than used with other bacteria. 

Hydrocyclones are available in numerous sizes and types ranging from pencil-sized 10-mm diameters of plastic to the 1.2-m (48-in) diameter of rubber-protected mild or stainless steel. Porcelain units 25 to 100 mm (1 to 4 in) in diameter are becoming popular, and in the 150-mm (6-in) size the starch industry has standardized on special molded nylon types. Small units for fine-size separations are usually manifolded in multiple units in parallel with up to 480 ten-mm... 

Unglazed usual type specified except special requirement of low adsorption on surface. Special ceramics available for mild caustic. Porcelain stronger and more resistant than stoneware. 

As stoneware and porcelain can be given a glazed finish on both interior and exterior surfaces, articles made from these materials can be very easily cleaned, even after years of use. The glaze also has an effect on the strength of the ware, increasing it by up to 20%, but certain types of body are difficult to glaze satisfactorily. 

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