Using Dubrovsk kaolin in porcelain manufacture

Abstract

The use of local raw materials means more rational and effective use of raw material resources. These include materials for the factories in the Ukrainian Porcelain Industry Association, such as kaolin from the Dubrovsk area, which is a complex raw material and which can be used in porcelain manufacture. It contains such components as feldspar, quartz, kaolinite. The Dubrovsk deposit is located in the Zhitomirsk oblast, 25 km from the Baranovsk porcelain factory. This factory first began to use Dubrovsk kaolin raw material (70%) in its porcelain bodies. Then the Dovbyshsk and Polonskii porcelain factories, and also the Polonsk decorative ceramics factory, changed over to the porcelain technology, using 30-70% of this kaolin. The technology and body recipes of these factories were developed by the Institute. The Dubrovsk raw kaolin is also used for making porcelain glazes; it is added to them in amounts of 25-50%. The chemical composition of Dubrovsk kaolin (wt. content %) is 68.88-74.61 SiO2; 15.13-20.37 AI20~; 0.13-0.54 Fe203; 0.05-0.20 TiO2; 0.14-0.84 CaO; 0.09-0.49 MgO; 0.04-0.98 Na20~ 3.62-5.40 K20; 1.42-5.95 loss on ignition. The mineral composition is (%): 25-40 kaolinite, 22-33 feldspar, 33-47 quartz, 1-2 mica and small amounts of ore minerals, carbonates, montmorillonite, etc. Dubrovsk beneficiated kaolin has a high mechanical strength compared with Prosyanovsk kaolin: 1.6-2 MPa in the air-dried state and 2.5-3.7 MPa after drying at I05-II0~ The mechanical strengths of Prosyanovsk beneficiated kaolin are respectively 0.5-0.8 and 1-1.5 MPa. The presence of montmorillonite in the Dubrovsk kaolin positively affects the strength of the unfired ware. However, in the presence of excessive amounts, to avoid loss, the total content of clay components in the body should be reduced by 2-3%. The inconsistency of the composition of Dubrovsk kaolin material creates a number of difficulties in body preparation. In order to stabilize the body composition the Institute has developed a rapid method of calculating and correcting the recipe for the porcelain body with the use of raw materials from the Dubrovsk deposit [i]. The most difficult process is grinding, since the Dubrovsk kaolin contains 37% particles measuring more than 40 ~m, and also mica. The presence of mica and the coarse, badly rolled grains of quartz measuring more than i0 mm prolongs the milling time of the nonplastics and hinders the determination of the end of the milling process for the body and glaze. In order to determine the optimum milling fineness of the body we studied the chemical and mineralogical composition of the residues of the suspensions of porcelain body from the factories of the "Porcelain" association after passing it through screens of the vibration type with different degrees of milling in ballmills. For comparison a study was made of the mineral composition of the residues of a suspen