periclasechromite refractories; articles produced from a mixture of magnesite (periclase) powder (65-80 percent) and ground chromite (35-20 percent).
In order to increase the heat resistance of magnesite-chromite refractories, the chromite or some of the periclase is added to the initial material in relatively coarse-grained form (0.5-3 mm) and the remainder in finely pulverized form. After the addition of 1-2 percent organic binder (for example, a sulfite-alcohol vinasse), the mass is compacted under a pressure of 100-150 meganew-tons (MN) per sq m, or 1,000-1,500 kilograms force (kgf) per sq cm. The products are then roasted in tunnel furnaces at 1650°-1750°C.
Magnesite-chromite refractories exhibit the following properties: apparent density, 3,000-3,300 kg/m3; open porosity, 14-20 percent; compressive strength, 40-60 MN/m2 (400-600 kgf/ cm2); temperature at onset of deformation under a load of 200 kilonewtons (kN) per sq m (2 kgf/cm2), 1500°-1630°C; and heat resistance, in excess of 6-10 thermal cycles (1300°C—water). They are also highly resistant to basic and ferrous melts.
Denser products made from masses containing a finely pulverized mixture of magnesite and chromite are known as periclasespinelid refractories. The roasting of pure initial materials at higher temperatures yields products containing a “direct bond” between the crystals of the periclase and the spinelids. These products exhibit still higher stability. Reinforced products and products prepared from a chemical binder base without roasting are also manufactured. Magnesite-chromite refractories are used primarily in the crowns of open-hearth, electric-arc, cement-roasting, and copper-smelting furnaces.
A. K. KARKLIT