Vitrification range

Clays composed of mixtures of clay minerals having from 20—50% of unsorted fine-grain nonclay materials are most satisfactory. Large amounts of iron, alkaHes, and alkaline earths, either in the clay minerals or as other constituents, cause too much shrinkage and greatiy reduce the vitrification range thus, a clay with a substantial amount of calcareous material is not desirable. Face bricks, which are of superior quaHty, are made from similar materials but it is even more desirable to avoid these detrimental components (see Building materials, survey). 

There are thus three fixed points to consider in the testing of fireclays or for that matter in the examination of refractories in general, viz., the vitrification temperature at which the mass becomes dense and practically impervious, the point at which it becomes overfired and vesicular and the softening temperature. The difference between the vitrification and overfiring temperature constitutes the vitrification range which is of considerable technical importance from the manufacturing standpoint. 

Bloating. The permanent expansion exhibited by some clays and bricks when heated within their vitrification range it is caused by the formation, in the vitrifying clay, of gas bubbles resulting either from entrapped air or from the breakdown of sulphides or other impurities in the clay (cf. exfoliation and intumescence). 

A vitrification range during which liquid phases are produced from the crystalline components exists in most clay materials. A long vitrification range is commercially desirable. Results from equilibrium systems of pure oxides may be significantly different from those produced from natural materials. It is, therefore, important to characterize raw materials at each plant location for most industrial applications. 

Amorphous alloys stable at ambient and higher temperatures consist of at least two components without any long-range atomic order. They are produced by a variety of constituents from the gas, liquid and aqueous phases. Vitrification of metal surfaces is also caused by destruction of the long-range atomic order in the surfaces of solid metals. 

We thus see that the RFOT theory provides a rather complete picture of vitrification and the microscopies of the molecular motions in glasses. The possibility of having a complete chart of allowed degrees of freedom is veiy important, because it puts strict limitations on the range of a priori scenarios of structural excitations that can take place in amorphous lattices. This will be of great help in the assessment of the family of strong interaction hypotheses mentioned in the introduction. To summarize, the present theory should apply to all amorphous materials produced by routine quenching, with quantitative deviations expected when the sample is partially crystalline. The presence and amount of crystallinity can be checked independently by X-ray. It is also likely that other classes of disordered materials, such as disordered crystals, will exhibit many similar traits, but of less universal character. 

According to the vendor, this project could provide a compact, low-cost reactor to treat aqueous mixed waste streams containing nitrates or nitrites, eliminate the need for chemical reagents, and minimize or eliminate secondary wastes such as nitrous oxide and secondary products such as ammonia, H2, and O2 that are prevalent with other nitrate destruction processes. By removing nitrates and nitrites from waste streams before they are sent to high-temperature thermal destruction and vitrification, production of NO can be decreased with the attendant decrease in off-gas system requirements. Biocatalytic nitrate destruction is applicable to a wide range of aqueous wastes with a highly variable composition. All information is from the vendor and has not been independently verified. 

In 1995, Battelle PNL estimated that the cost of processing wastes using the Terra-Vit vitrification system would range from 50 to 300 per wet ton. This estimate may not include all indirect... 

Various sources estimate vitrification costs as ranging from under 100/ton to over SlOOO/ton for units treating hazardous waste. These estimates are assumed to be for treatment only, not... 

The vendor states that costs for Cold Top vitrification would generally range from 50 to 147 per ton. The primary factor determining costs is power requirements, which will vary with the material treated. The vendor states that dumping the waste in a hazardous waste landfill... 

The temperature range (240-220 K) of the unusual behavior of the process rate (increase of the rate with decrease in T) appears to correspond to the temperature range of vitrification of the solution. The increase in the decay rate of P700+ upon transition from a liquid solution to a vitreous sample has been explained on the assumption that the decay of P700+ proceeds by reactions with two types of reduced primary acceptors A and A, ... 

In an isothermal cure process, vitrification will be always observed if Tc is selected in the range between Tgo and Tgco. So, vitrification was not observed when the epoxy-anhydride formulation was cured at Tc= 130°C(> Tgoo). 

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