Bulk refractories

Specialty Refractories. Bulk refractory products include gunning, ramming, or plastic mixes, granular materials, and hydrauhc setting castables and mortars. These products are generally made from the same raw materials as their brick counterparts. 

In 1991, the average value per metric ton of lime in bulk was reported to be 78.44 for agricultural lime, 68.12 for constmcfion lime, 54.90 for chemical lime, and 82.62 for refractory lime. The average value for total lime was 57.02/t. 

Type Bulk density. Apparent 20°C 1260°C Refractoriness Linear reheat... 

The most important properties of refractory fibers are thermal conductivity, resistance to thermal and physical degradation at high temperatures, tensile strength, and elastic modulus. Thermal conductivity is affected by the material s bulk density, its fiber diameter, the amount of unfiberized material in the product, and the mean temperature of the insulation. Products fabricated from fine fibers with few unfiberized additions have the lowest thermal conductivities at high temperatures. A plot of thermal conductivity versus mean temperature for three oxide fibers having equal bulk densities is shown in Figure 2. 

Activated Sludge. There are several generic activated sludge processes presendy available. Complete Mix (CMAS) is appHcable to refractory-type wastewaters in which filamentous bulking is not a problem. This process has the advantage of dampening ductuations of induent wastewater quaUty. 

Because of the larger surface area (compared with solid-ceramic refractories) the chemical resistance of fibers is relatively poor. Their acid resistance is good, but they have less alkah resistance than solid materials because of the absence of resistant aggregates. Also, because they have less bulk, fibers have lower gas-velocity resistance. Besides... 

So far, few of the commercially operated diffusion processes have been applied to the lower-melting-point metals. While they are being used to an increasing extent for protection of nickel, cobalt and refractory alloys, the bulk of present-day applications is still concerned with the treatment of ferrous materials. 

While it is inherently probable that product formation will be most readily initiated at sites of effective contact between reactants (A IB), it is improbable that this process alone is capable of permitting continued product formation at low temperature for two related reasons. Firstly (as discussed in detail in Sect. 2.1.1) the area available for chemical contact in a mixture of particles is a very small fraction of the total surface (and, indeed, this total surface constitutes only a small proportion of the reactant present). Secondly, bulk diffusion across a barrier layer is usually an activated process, so that interposition of product between the points of initial contact reduces the ease, and therefore the rate, of interaction. On completion of the first step in the reaction, the restricted zones of direct contact have undergone chemical modification and the continuation of reaction necessitates a transport process to maintain the migration of material from one solid to a reactive surface of the other. On increasing the temperature, surface migration usually becomes appreciable at temperatures significantly below those required for the onset of bulk diffusion within a product phase. It is to be expected that components of the less refractory constituent will migrate onto the surfaces of the other solid present. These ions are chemisorbed as the first step in product formation and, in a subsequent process, penetrate the outer layers of the... 

Optical systems can be used in multiphase flows at a very low volume fraction of the dispersed phase. Through a refractory index matching of hquid-liquid or liquid-solid systems, it is also possible to measure at high void fractions. However, it is not possible to obtain complete refractory index matching since the molecules at the phase boundary have different optical properties than the molecules in the bulk. Consequently, it is possible to measure at a higher fraction of the dispersed phase with larger drops and particles because of the lower surface area per volume fluid. 

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