A study on the technological parameters' influence on the properties, polishing and microstructure of corundum ceramic discs for water taps
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2015-01-01
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Abstract
Some of corundum ceramics properties like high chemical resistance, hardness and mechanical strength make it an extremely suitable material for water tap gaskets and regulators. Solid fragments that normally get into the water, like sand, rust and limestone, cannot damage corundum ceramics. The latter stability allows these products to remain perfectly smooth even when exposed to varying levels of pressure and extreme water temperature fluctuations. The corundum ceramics properties depend mainly on the purity of the starting powder, the production method and the microstructure. This work investigates how the pressure applied during the semidry pressing, the firing temperature and the source materials composition (percentage of Al<inf>2</inf>O<inf>3</inf>) affect the apparent density, the coefficient of abrasion, the polished surface (the degree of polishing) and the microstructure of corundum ceramic water taps discs. Four types of a corundum powder were used as a source material for the process of semidry pressing. Five different pressures (100 MPa 150 MPa, 200 MPa, 250 MPa, 350 MPa) and three firing temperature values (1600°C, 1650°C, 1680°C) were applied in addition to the subsequent procedures of lapping and polishing in the course of production of corundum ceramic discs for water taps. The fired corundum samples underwent characterization aimed to determine the apparent density (using the method of Archimedes), the coefficient of abrasion (determined by the loss of mass in percentage points), as well as the degree of surface polishing. Using SEM and optical microscopy we proved that the technological parameters determine to a large extent the appearance of a microstructure which in turn affects the properties and the degree of polishing of corundum ceramics. Water taps of a homogeneous structure having the highest density, the smallest pores, the lowest coefficient of abrasion and the highest degree of polishing were made from a starting powder containing 98 % of Al<inf>2</inf>O<inf>3</inf> and a glass phase containing CaO, MgO and SiO<inf>2</inf>. A firing temperature of 1650°C and pressing pressure 350 MPa were applied.