Refractory cement

Cements and Ceramics. Refractory cements and ceramics (qv) are prepared from slurries of siUca, 2irconia, alumina, or magnesia and a prehydroly2ed siUcate (see Cement). Calcining at 1000°C yields cured refractory shapes (48,49). 

Refractories and Molds. Citric acid is used as a binder for refractory cements, imparting volume stabiUty and strength in ceramic materials for electrical condensers, foundry and glassmaking molds, and sand molds for metal castings (219—223). 

Fuller treatments of the phase relations and structures of polyphosphates, and their uses as glasses, ceramics, refractories, cements, plasters and abrasives, are available. 

One example is silicate cement where orthosilicic acid, chemically generated in solution, condenses to form a silicic acid gel. Another is refractory cement where a cementitious product is formed by the heat treatment of an acid orthophosphate, a process which again involves condensation to form a polyphosphate. 

The most important of these are the refractory cements formed by the heat treatment of aluminium acid phosphate solutions. This subject has been well reviewed by Kingery (1950a), Morris et al. (1977), Cassidy (1977) and O Hara, Duga Sheets (1972). The chemistry of these binders is extremely complex as the action of heat on acid phosphates gives rise to polymeric phosphates, with P-O-P linkages, and these are very complex systems (Ray, 1979). 

Spaces between the coal block and the reactor walls are filled with refractory cement to prevent accumulation of combustible gases, and leaks are exhausted from the outer casing. Temperatures are measured with 1/8" Type K SS sheathed thermocouples, which are cemented Into the block at predetermined locations. 

After taking suitable coal samples for analysis, removing the blockage and filling the cavity with refractory cement, the thlrd burn test was carried out on the same channel. Figure 5 shows time-data plots for this burn. Because much of the moisture had been driven forward by the preceding burn, only a relatively low-BTU product gas was produced but by cyclical Injection of steam and air, heat values could be periodically Increased. 

The laboratory furnace, illustrated in Figure 1, has been described in detail elsewhere (19). The combustion chamber design is similar to that of Pershing and Wendt (20). It consists of a vertical cylinder 1.0 m long and 0.2 m inside diameter cast from alumina refractory cement. A series of convective heat exchangers, also 1.0 m long and 0.2 m inside diameter, are mounted directly below the combustor. The combustor is fired at a rate of 8 to 12 Kw, providing a residence time of 1 to 2 seconds in the combustion chamber. 

Solid State Reaction - Hexaaluminates have been long known as interesting materials for many applications (electrical ceramics, matrices for permanent immobilization of radioactive elements from nuclear wastes and refractory cement and concrete). For many years ceramists prepared hexaaluminates via solid state reaction for both crystallographic and application purposes.6... 

The proper location of couples in the furnace depends upon the particular process and use to which the furnace is put. The primary consideration must be to locate the hot junction at the point the temperature of which is required. A secondary consideration, however, is to locate the couple where the lead wires may be conveniently taken care of. The space between the protecting tube of the couple and the furnace wall should be tightly plugged with refractory cement, so that hot air cannot strike through the hole on to the head of the couple, nor cold air be drawn in thus cooling the hot junction of the couple. 

Firefrax [Carborundum], TM for a group of refractory cements made from kaolin or fireclay base materials for applications where aluminum silicate cements are best suited. 

Glasses and ceramics based on the Al203-based systems have important applications as ceramic materials, optical materials, and biomedical materials. Aluminate materials include alkaline earth aluminates, such as those in the CaO-A Cf system, which are refractory cousins of hydrous Portland cement [1-3]. Calcium aluminates have a role as both traditional ceramic and cement materials and are used for example as refractory cements however, calcium aluminates are also important for more novel applications... 

One very important niche application for calcium aluminate (cements) is as refractory castables. Key to the success of calcium aluminates in this application are their refractory properties that contrast with those of Portland cements. Although Portland cement maintains good strength when heated, reactive components (CaO) are liberated and can absorb moisture from the atmosphere when cooled, causing expansion and deterioration of, for example, kiln linings. CACs are not much susceptible and can be used to form monolithic castables and refractory cements [28, 29],... 

Radiative furnaces. A resistance wire is embedded in a refractory cement or ceramic with conical openings for accessibility to the sample. Furnaces are normally designed to operate in air, although the crystal itself may be sealed in a glass capillary. Some heaters operate either in vacuum or in a controlled atmosphere (especially for neutron diffraction). 

Castable (high alumina) screened refractory cements. 

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