Zircon refractories

Zircon Refractories. ASTM C545 classifies 2ircon refractories in two types. Types A and B have the same chemical requirements of not less than 60% and not less than 30% Si02. Type A (regular) must have a density of less than 3.85 g/cm and type B (dense) more than 3.85 g/cm. ... 

Zirconocenium cations, 76 95 Zircon pigments, 79 404-405 Zircon refractories, ASTM classifications and specifications for, 27 509-510 Zircon sands, 73 81 analysis of, 26 623t Zirpro Process, 26 404 Ziziphin, 24 246 Zn-Ag cartridges... 

Zirconia. Zircon (zirconium silicate), the most widely occurring zirconium-bearing mineral, is dispersed in various igneous rocks and in zircon sands. The main deposits are in New South Wales, Australia Travancore, India and Florida in the United States. Zircon can be used as such in zircon refractories or as a raw material to produce zirconia. The zircon structure becomes unstable after about 1650°C, depending on its purity, and decomposes into Zr02 and Si02 rather than melting (see Zirconiumand zirconium compounds). 

Zirconia. Zircon (zirconium silicate), the most widely occurring zirconium-bearing mineral, is dispersed in various igneous rocks and in zircon sands, Zircon can be used as such in zircon refractories or as a raw material to produce zirconia, ZrC>2. 

Corrosion of the glass-making melters must be maintained at an absolute minimum to increase the lifespan of the melter. Laboratory-measured corrosion rates indicate that melter lifetimes of several years can be achieved with high chrome oxide or zircon refractories metallic melters may have lifetimes of several months if alloys such as Inconel 690 are used. These conclusions have been reached on the basis of extrapolation of laboratory tests. Long-term tests, particularly with waste glasses in engineering-scale continuous melters, have not yet been made. 

Other studies have involved reactions of alkali salts with the minerals or raw materials used in making refractories. To a lesser extent, experiments have been conducted on unused brick, but these were primarily concerned with mullite or zircon refractories. 

Zircon is Zr02 -Si02. Zircon refractory bricks may contain 4% CaO. 

PZP. A zircon refractory ramming mix made by Savoie Refractaire, France. PZT. Lead zirconate-titanate, Pb(Zr,Ti)03 used as a ceramic component in piezoelectric transducers. Trade-name of Vernitron Ltd. 

Decomposition of Zircon. Zircon sand is inert and refractory. Therefore the first extractive step is to convert the zirconium and hafnium portions into active forms amenable to the subsequent processing scheme. For the production of hafnium, this is done in the United States by carbochlorination as shown in Figure 1. In the Ukraine, fluorosiUcate fusion is used. Caustic fusion is the usual starting procedure for the production of aqueous zirconium chemicals, which usually does not involve hafnium separation. Other methods of decomposing zircon such as plasma dissociation or lime fusions are used for production of some grades of zirconium oxide. 

Decomposition of Zircon. Zircon is a highly refractory mineral as shown by its geological stabiUty the ore is cracked only with strong reagents and high temperature. 

Other types of refractory that find use are forsterite, zirconia, and zircon. Acid-resisting bricks consisting of a dense body like stoneware... 

The elements for which the results can be underestimated because of an incomplete digestion of refractory accessory minerals such as zircon and garnet, and/or formation of insoluble fluoride complexes have been distinguished. Recommendations on the choice of the decomposition procedure for such samples are given. 

Other types of refractory that find use are forsterite, zirconia, and zircon. Acid-resisting bricks consisting of a dense body like stoneware are used for lining tanks and conduits in the chemical industry. Carbon blocks are used as linings for the crucibles of blast furnaces, very extensively in a number of countries and to a limited extent in the United States. Fusion-cast bricks of mullite or alumina are largely used to line glass tanks. 

In the drying of compound intermediates of refractory and reactive metals, particular attention is given to the environment and to the materials so that the compound does not pick up impurities during the process. A good example is the drying of zirconium hydroxide. After the solvent extraction separation from hafnium, which co-occurs with zirconium in the mineral zircon, the zirconium values are precipitated as zirconium hydroxide. The hydroxide is dried first at 250 °C for 12 h in air in stainless steel trays and then at 850 °C on the silicon carbide hearth of a muffle furnace. 

Zirconia Refractories. The most common zirconia-containing refractories are made from zircon sand and are used mosdy for container glass-tank subpaver brick. Refractory blocks made from a composition of zircon and alumina, used to contain glass melts, are generally electromelted and then cast. These exhibit excellent corrosion resistance but are subject to thermal shock. Refractories made from pure Zr02 are extremely expensive and are... 

Tests at 1000°C. After 1 hour of pumping the apparent leak rate of a mullite double-walled vessel is 1.7 X 10 8 l.-mm. of mercury per second or 2 X 10-8 cc. (N.T.P.) per second. In terms of permeability rates this value is equivalent to 3 X 10-10 cc./sq. cm./second/mm./cm. of mercury. Roeser (28) has studied a number of refractory procelain tubes from several manufacturers. His permeability values vary from 8.3 X 10 10 to 5 X 10-8 cc./sq. cm./second/mm./cm. of mercury. We have studied two double-walled vessels. These two tubes give nearly identical apparent leak rates although one is constructed of mullite and the other from zircon. It may be possible that more sensitive tests would show up differences in apparent leak rates. 

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