Dielectric ceramic wearproof coverings

Dielectric ceramic wearproof coverings allow to provide necessary electroinsulating properties of a surface at high wear resistance. Dielectric coverings put by means of a plasma dusting. We apply ceramic electroinsulating coverings from various materials: Oxide _{of Al2O3 aluminum} can exist in three main crystal modifications:

• and — forms represent pure oxides.
• and - the form represents a symbol of group of aluminates with the high content _{of Al2O3}.
• Except them, some more crystal modifications, the majority of which at 1200 °C is passed in - a form (corundum), are recorded. As the main structural motive in corundum serves the alyumokislorodny octahedron. In nature only the form in the form of a mineral of corundum, a ruby, sapphire meets.

Hardness of corundum on Moos's scale — 9, on Rockwell's scale — 90. Corundum density depending on availability of impurity in it fluctuates from 3980 to 4010 ^kg/m3. Temperature of melting makes 2050 °C, an enthalpy of formation of 1, 7 Mdzhmol. Conductivity at ^{a temperature of 20O °C of 10-16}, at ^{a temperature of 1300 °C of 10-6 of Om-1m-1}.

The ceramics containing more than 95% - _Al2O3 is called corundum ceramics. As additives — mineralizers use MGO, _MnO2, _TiO2, _ZrO2. If the additive leads to distortion of a crystal lattice of corundum as, for example, at introduction _{of TiO2}, then conductivity of corundum increases yttrium Oxide to 2300 °C does not show polymorphic transformations. _Tpl = 2410 — 2415 °C. Density of crystals — 5030 ^kg/m3, specific heat makes 0, 105 kJ/kg. To, an enthalpy of formation of N =-1910 kJ/mol, Gibbs's potential of G =-1820 kJ/mol. In the oxidizing atmosphere (air) oxide of yttrium is stable up to _Tpl. Resistance to thermal shocks of the baked ceramics is low. It is caused by small heat conductivity (8, 5 W / m*k) and rather high TKLR = ^{8 — 9*10-6 K-1}. On electric properties the yttric ceramics belongs to good insulators: conductivity at 500 °C makes 8 * ^{10-10 Om-1m-1}.