Chemical and Radiation Stability

There are notions that ion-exchange membranes based on polystyrene and polyethylene are stable in 30% HCl and 25% NaOH as well. But it has been reported that membrane selectivity decreased monotonically during heating in water at 80 °C, which may be explained by expansion of membrane pores filled with external solution. 

During exposure of ion-permeable membranes to radiation, their mechanical firmness and flexibihty decreases. Ion-exchange capacity, crosshnking, conductivity and selectivity decrease as well. 

Interestingly, perfluorinated membranes have superior chemical stability, but their radiation stability is worse than that of membranes with a hydrocarbon matrix. 

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Inorganic membranes of good radiation and chemical resistance available Separation of dissolved salts from particulate and colloidal material Inorganic membranes available with good chemical and radiation stability can also operate at elevated temperatures Pressure <1 MPa... 

High thermal conductance Low leachability Chemical and radiation stability Mechanical ruggedness Noncorrosiveness to container Minimum volume Minimum cost... 

Inorganic membranes available with good chemical and radiation stability can also operate at elevated temperatures. 

Ceramic membranes are proposed as advantageous with respect to resistance toward fouling as compared to organic polymer-based membranes. In this category, zeolite membranes have received considerable attention because of their superior characteristics of thermal, mechanical, chemical, and radiation stability. 

The polysulfone Victrex represents amorphous thermoplastic con-stmctional polymer differing by high heat-resistance, dimensional staunchness, low combustibility, chemical and radiation stability. It can easily be reprocessed on standard equipment at 340-3 80°C and temperature of press-form 100-150 °C. It is dried at 150 °C for 1, 08 10" sec before casting [167, 168]. 

Although each of these cyclic siloxane monomers can be polymerized separately to synthesize the respective homopolymers, in practice they are primarily used to modify and further improve some specific properties of polydimethylsiloxanes. The properties that can be changed or modified by the variations in the siloxane backbone include the low temperature flexibility (glass transition temperature, crystallization and melting behavior), thermal, oxidation, and radiation stability, solubility characteristics and chemical reactivity. Table 9 summarizes the effect of various substituents on the physical properties of resulting siloxane homopolymers. The... 

Boron carbide is used in the shielding and control of nuclear reactors (qv) because of its neutron absorptivity, chemical inertness, and radiation stability. For this application it may be molded, bonded, or the granular material may be packed by vibration. 

Good chemical and physical stability toward heat and radiation. 

Thorium phosphate-diphosphate Th4(P04)4P207 (TPD, Pcam) is an actinide host phase due to its very high chemical durability and radiation stability [165-167]. TPD is synthesized by drying of thorium nitrate and phosphorus acid or ammonium phosphate solution, cold pressing at 300-800 MPa, and sintering of pellets at 1100-1250 for 10-30 hours. Th" in the TPD structure may be replaced by other tetravalent actinides but its isomorphic capacity is reduced with decreasing cationic radii in the following sequence > Np" > Pu". ... 

As for the physical-chemical properties, radiation stability and thermal stability are most important. Irradiation does not appear to pose great problems. Elevated temperatures may cause dehydration processes in the host rock, resulting in large quantities of free water. Rock salt formations are frequently interspersed with camallite (KChMgClj 6H2 0), which will probably be dehydrated when heated above llO C and may even develop hydrochloric acid above 16S°C. In addition it is of low strength and easily soluble in water. 

In addition to band-gap and band-edge positions, some criteria for the selection of a good semiconductor include its chemical and photochemical stability and its environmental impact. Ti02 is the most popular semiconductor because of its resistivity to strong acids and bases and its stability under illumination [15,17,18]. ZnO, although its band-edge positions are very similar to those of Ti02 [30], is less desirable due to photocorrosion induced by self-oxidization. CdS has limited potential for practical use despite its attractive spectral response to solar radiation because CdS decomposes to release environmentally harmful Cd " [15]. 

The chemical and mechanical stability of poly(n-butyl acrylate)(PnBA) to weathering, especially to solar radiation, is of interest for possible use of this material as an encapsulant/ pottant for silicon cell solar energy arrays. This application requires that the material retain an acceptable level of its desirable properties, such as transparency, elastic modulus, etc., over several years of exposure to intermittent moisture, temperatures ranging from -10 to 50 C, solar radiation, and other norms and extremes of exposure conditions. Knowledge of the dependence of changes in properties and composition of the material on exposure conditions is a requisite for establishing reasonable estimates of its prospective performance lifetime characteristics. 

Oxide fuels have demonstrated very satisfactory high-temperature, dimensional, and radiation stability and chemical compatibility with cladding metals and coolant in light-water reactor service. Under the much more severe conditions in a fast reactor, however, even inert UO2 begins to respond to its environment in a manner that is often detrimental to fuel performance. Uranium dioxide is almost exclusively used in light-water-moderated reactors (LWR). Mixed oxides of uranium and plutonium are used in liquid-metal fast breeder reactors (LMFBR). 

Ethylene-propylene rubbers are the important class of elastomers and are widely used in many branches of industry due to their unique properties, in particular good stability to environmental effects, good physical-chemical and elastic characteristics, chemical and ozone-stability, radiation, oils, acids and alkalis stability, etc. [78,79,176,207,253]. 

The chemical nature of the base polymer is an important aspect in membrane development. There has been preference for the thermally stable fluorinated polymers over hydrocarbon polymers. Fluorine-containing polymers, characterized by the presence of carbon-fluorine bonds, are widely used as the base matrices owing to their outstanding chemical and thermal stability, low surface energy, and the ease of modiflcation of various properties by the grafting method. Per fluorinated polymers and partially fluorinated polymers combining hydrocarbon and fluorocarbon structures are excellent candidates as base polymers. For instance, fluorinated FEP has drawn wide attention due to its reasonably good radiation stabiUty [58]. 

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