Chemical properties consolidation

Calcines are products obtained by removing the volatile components of the waste, i.e., water and nitrate, at temperatures between 400 and 900° C. The result is a mixture of oxides of fission products, actinides, and corrosion products in particulate form with a specific surface of 0.1 to 5 ra /g. The plain calcine is not very stable chemically because of its large surface area and the chemical properties of some of the oxides, and it is highly friable. To improve the properties of calcines, advanced forms are developed. One such product is the so-called multibarrier waste form, a composite consisting of calcine particles with inert coatings, such as pyrocarbon, silicon carbide, or aluminum, embedded in a metal matrix. Another advanced calcine is the so-called supercalcine. This is essentially a ceramic obtained by adding appropriate chemicals to the HLW to form refractory compounds of fission products and actinides when fired at 1200°C. Supercalcine requires consolidation by embedding in a matrix but does not need to be coated, as the material is supposed to have inherent chemical stability. 

Surface area of a powder increases geometrically with decreasing particle size, so that the volume fraction of the outermost layer of ions on the surface increase significantly, which has a significant effect on properties of the powder. With the development of nanotechnology, it is readily to synthesize powders with nanosized particles (1-100 nm). Therefore, characterization of surface properties becomes more and more important. Specifically for ceramics or transparent ceramics, the consolidation of fine ceramic powders with liquid suspensions to produce more uniform green bodies has been shown to play an important role in the fabrication ceramics, especially when special or complex structures are required. Because the quality of microstructure of the consolidated body is determined by the dispersion behavior of the powder and the interaction between the particles in the suspension, which is closely related to the surface properties of the particles, controlling the physical and chemical properties of particles is a critical to ceramics fabrication. 

In this section, we report our recent results on the synthesis of Mg-based amorphous alloys in ribbon, bulk and powder forms by various preparation techniques such as melt spinning, metallic mold casting, high-pressure die casting and high-pressure gas atomization, and on their thermal, mechanical and chemical properties. This review also deals with the microstructure and mechanical properties of Mg-based alloys produced by warm consolidation of the atomized powders. 

In addition, detailed analysis of the chemical and physical properties of different oils used in the plant can, in some cases, allow consolidation or reduction of the number and types of lubricates required to maintain plant equipment. Elimination of unnecessary duplication can reduce required inventory levels and therefore maintenance costs. 

On the basis of this assessment of the current literature and on comments received on the first edition of this book, this volume has been written to focus on these details. With this new information, additional classes of agents have been added. Where it provided clarity, multiple classes have been consolidated into a single class. The information in existing classes has been updated and expanded. There is a significant increase in the number of agents described, as well as in the number of components, precursors, and decomposition products. There is more information on health effects and on the chemical, physical, and biological properties of these materials. 

Similar to cleaning operations, consolidation and adhesion treatments are usually under analytical control. Measurements of the chemical, morphological, and physical properties of the consolidated material are indispensable to assure the efficiency of the operation. Changes in mechanical strength, color, and gloss, as well as chemical composition are assessed. Studies of stability of consolidants are frequently performed by means of namral and accelerated aging trials. 

The use of ion exchange resins and natural or synthetic inorganic exchange materials in the nuclear industry is well documented ( ). In the waste solidification application, the titanates or niobates offer no unique sorption properties. They do, however, provide a relatively high overall sorption capacity for a variety of nuclides in materials which can be converted into a stable ceramic host for the sorbed ions. After the sorption process, the column bed must be consolidated to reduce surface area. The project emphasis was directed toward a stable waste form and a considerable effort was devoted to producing and characterizing a highly dense form with favorable physical, chemical and thermal properties (l ). 

All of the chemical evidence that can be marshalled indicates that wood fiberboard manufacture exploits the thermoplastic properties of lignin. Defibering is effected by the thermal softening of lignin in the middle lamella at saturated steam pressures above 130C. Interfelted fiber mats are consolidated with or without densification pressure by the thermoplastic fusion of lignin-rich fiber surfaces at high board conversion temperatures. 

The major chemical changes in wood caused by fiberboard manufacture are secondary side reactions which are both beneficial and detrimental to the final properties achieved. Defibering is accomplished by hydrolytic breakdown of lignin and hemicelluloses under wet acidic conditions combined with high process temperatures. Board conversion and consolidation is attended by pyrolytic reactions which... 

Table 8.1 describes the steps of the methodology in more detail. The procedure starts with the Problem definition production rate, chemistry, product specifications, safety, health and environmental constraints, physical properties, available technologies. Then, a first evaluation of feasibility is performed by an equilibrium design. This is based on a thermodynamic analysis that includes simultaneous chemical and physical equilibrium (CPE). The investigation can be done directly by computer simulation, or in a more systematic way by building a residue curve map (RCM), as explained in the Appendix A. This step will identify additional thermodynamic experiments necessary to consolidate the design decisions, mainly phase-equilibrium measurements. Limitations set by chemical equilibrium or by thermodynamic boundaries should be analyzed here. 

So, some trends seem to be selection of a few systems (either by market consolidation or users who rely on a database they are comfortable with) that include multiple databases or a combination of bibliographic and property and chemical data and linking programs that tie primary literature with other forms of data or secondary and tertiary literature. 

The earliest cast, composite binder was studied by Jet Propulsion Laboratories (JPL) and made use of molten asphalt (7). This material was heated until it formed a fluid melt, was mixed with oxidant, and the heated mixture cast into a motor cavity and allowed to cool. This system was poor because of the limited temperature range, the low solids content which could be formulated, and the poor mechanical properties of highly loaded asphalt. A chemically cured system was then introduced when acrylate monomers were mixed with oxidizer and curative (8). The mixture eould be cast, heated to cure temperature, and the acrylate polymerized to give a well consolidated grain. The basic deficiencies encountered... 

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