Vitrification

The glass transition of a polymer is reduced by the presence of an additive, i.e.a solvent or nonsolvent. This glass transition depression can been described by various theories fiom which the one of KeUey-Bueche is widely used [28] (see chapter EL, eq. II - 6). A schematic phase diagram of the system PPO/trichloroethylene/methanol is shown in figure in - 34. Four regions can be observed  

a two-phase region where liquid-liquid demixing occurs. In the figure only one tieline is given in which the polymer rich phase has entered the vitrification area. On the leftside of this tieline (II) the (equilibrium) system is still a liquid whereas at the right side (III) vitrification of the polymer rich phase has been occurred. 

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Cryoinnnobilization procedures tiiat lead to vitrification (immobilization of the specimen water in the amorphous state) are the sole methods of preserving the interactions of the cell constituents, because the liquid character of the specimen water is retained (reviewed in [25]). 

Sartori N, Richter K and Dobochet J 1993 Vitrification depth can be increased more than 10-foid by high pressure freezing J. Microsc. 172 55-61... 

When we speak of the solidification of the extruded polymer, we use the term in the broadest sense It includes crystallization, vitrification, or both. The extent of the drawing of the fibers and the rate and temperature of the drawing affect the mechanical properties of the fiber produced. This conclusion should be evident from a variety of ideas presented in the last three chapters ... 

Poly(ethylene oxide). The synthesis and subsequent hydrolysis and condensation of alkoxysilane-terniinated macromonomers have been studied (39,40). Using Si-nmr and size-exclusion chromatography (sec) the evolution of the siUcate stmctures on the alkoxysilane-terniinated poly(ethylene oxide) (PEO) macromonomers of controlled functionahty was observed. Also, the effect of vitrification upon the network cross-link density of the developing inorganic—organic hybrid using percolation and mean-field theory was considered. 

To recovery and recycle or vitrification and disposal in deep geologic repository... 

Some of the most common stabilization—soHdification processes are those using cement, lime, and pozzolanic materials. These materials are popular because they are very effective, plentiful, and relatively inexpensive. Other stabilization—soHdification technologies include thermoplastics, thermosetting reactive polymers, polymerization, and vitrification. Vitrification is discussed in the thermal treatment section of this article and the other stabdization—soHdification processes are discussed below. 

Vitrification is effective at destroying and immobilizing hazardous materials, but it is very energy intensive and thus expensive. Consequently, it is used primarily where wastes are difficult to treat or destmction—immobilization of contaminants is very important such as with radionucHdes. 

Binders. To create needed physical strength in catalysts, materials called binders are added (51) they bond the catalyst. A common binder material is a clay mineral such as kaolinite. The clay is added to the mixture of microparticles as they are formed into the desired particle shape, for example, by extmsion. Then the support is heated to remove water and possibly burnout material and then subjected to a high temperature, possibly 1500°C, to cause vitrification of the clay this is a conversion of the clay into a glasslike form that spreads over the microparticles of the support and binds them together. 

Because clays (rocks) usually contain more than one mineral and the various clay minerals differ in chemical and physical properties, the term clay may signify entirely different things to different clay users. Whereas the geologist views clay as a raw material for shale, the pedologist as a dynamic system to support plant life, and the ceramist as a body to be processed in preparation for vitrification, the chemist and technologist view clay as a catalyst, adsorbent, filler, coater, or source of aluminum or lithium compounds, etc. 

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). 

When used for ceramic heating, furnaces are called Idlus. Operations include drying, oxidation, c cination, and vitrification. These Idlus employ horizontal space burners with gaseous, hquid, or solid fuels. If product quahty is not injured, ceramic ware may be exposed to flame and combustion gases otherwise, muffle Idlus are employed. Dutch ovens are used frequently for heat generation. 

As the system continues to crosslink, vitrification occurs which can result... 

Rotary kilns, as described previously, can be used to incinerate materials which can be excavated and fed into the kiln. Vitrification is a process which can be used without removing the soil and is described below. 

Applicability Limitation Vitrification was originally tested as a means of solidification/immobilization of low level radioactive materials. It may also be useful for forming barrier walls. This latter use needs testing and evaluation to determine how uniform the wall would be and to evaluate the stability of the material over a period of time. 

Major categories of industrial waste solidiflcation/stabilization systems are cement-based processes, pozzolanic processes (not including cement), thermoplastic techniques, organic polymer techniques, surface encapsulation techniques, and self-cementing techniques (for high calcium sulfate sludges). Vitrification (discussed previously) can also be considered a solidification process. 

Vitrification processes are being developed in several countries in which the dried waste is calcined and heated with ground glass frit to produce a borosilicate glass which can be stored or disposed of more permanently if there is agreement on suitable sites. 

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. 

Fitzpatrick, V. F. Timmerman Buelt, J. L., In situ vitrification - A candidate process for in situ destruction of hazardous waste Pacific West Laboratory, PNL-SA-14065 (1986)... 

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