Chemical crystalline oxides

Flaws in the anodic oxide film are usually the primary source of electronic conduction. These flaws are either stmctural or chemical in nature. The stmctural flaws include thermal crystalline oxide, nitrides, carbides, inclusion of foreign phases, and oxide recrystaUi2ed by an appHed electric field. The roughness of the tantalum surface affects the electronic conduction and should be classified as a stmctural flaw (58) the correlation between electronic conduction and roughness, however, was not observed (59). Chemical impurities arise from metals alloyed with the tantalum, inclusions in the oxide of material from the formation electrolyte, and impurities on the surface of the tantalum substrate that are incorporated in the oxide during formation. 

The chosen combinations of these chemicals and metals depend on the requirements of the specific application. Gasless combustion prevents pressure increase in a closed combustion chamber. Some combinations of metal particles and metal oxide particles or of metal particles and crystalline oxidizers are chosen as chemical ingredients of gasless pyrolants. On the other hand, hydrocarbon polymers are used to obtain combustion products of low molecular mass, such as H2O, CO, CO2, and H2. High pressure is thus obtained by the combustion of hydrocarbon polymers. Table 10.6 shows the chemical ingredients used to formulate various types of pyrolants. 

Though the chemical potentials of ammonium perchlorate and potassium perchlorate are high compared with those of other oxidizers, hydrogen chloride is formed as a combustion product. Hydrogen chloride is known to generate hydrochloric acid when combined with water vapor in the atmosphere. The chemical potentials of crystalline oxidizers are dependent on the fuel components with... 

Polymeric materials used as fuel components of pyrolants are classified into two types active polymers and inert polymers. Typical active polymers are nitropoly-mers, composed of nitrate esters containing hydrocarbon and oxidizer structures, and azide polymers, containing azide chemical bonds. Hydrocarbon polymers such as polybutadiene and polyurethane are inert polymers. When both active and inert polymers are mixed with crystalline oxidizers, polymeric pyrolants are formed. 

Chemical effects also occur in crystalline oxides that is, impurity atoms diffuse at varying rates through oxides. In all cases, cation diffusion is much faster than oxygen diffusion, but similar cations, such as Ca and Mg, can behave very differently in different oxides. This is due to differences in chemical potential and activity, and mobility differences. 

The key to the successful application of high performance, pourable nitrocellulose plastisols lies in a reasonably priced, high quality source of fine-particle, at least partially colloided, spheroidal nitrocellulose. Here we are speaking of particles much finer than the well-known ball powder, produced by the Olin Mathieson Chemical Co. for small arms for over 30 years (7). Actually, particles on the order of 5-50/x diameter appear to be required to assure a reasonable continuum of uniformly plasticized nitrocellulose binder in a propellant containing 45% or more of combined crystalline oxidizer and powdered metal fuel. Such a continuum of binder is necessary to assure acceptable mechanical properties and reproducible burning characteristics of the finished propellant. Preincorporation of a certain content of the water-insoluble solids within the nitrocellulose microspheres is an effective means of helping to assure this continuum of binder and alleviates the requirements for extremely small ball size. The use of a total of 45% or more of crystalline oxidizer and (generally) metal fuel is essential if the propellant is to be competitive with other modern propellants now in service. 

A major development in fluoroplastics is the recent small scale production of Teflon AF, a noncrystalline (amorphous) fluorocarbon polymer with a high glass transition temperature (240 °C) This optically transparent TFE copolymer is soluble m certain fluorocarbons and has the same chemical and oxidative stability as crystalline TFE homopolymers [5]... 

Aeroplex Propellants are solid rocket propellants developed and manufd by the Aerojet Engineering Corp, Azusa, Calif. They consist of a finely divided crystalline oxidizer (such as Amm or K perchlorate)dispersed in a thermosetting resin(such as styrene, methyl acrylate, etc), acting as a fuel. In addition there are binders (such as resins) and other ingredients. Aeroplex propellants differ from the usual NC or NC-NG propellants not only in physical and chemical properties, but also in their methods of manuf... 

Approaches for the development of water-resistant surface treatments include application of inhibitors to retard the hydration of oxides or the development of highly crystalline oxides as opposed to more amorphous oxides. Standard chemical etching procedures, which remove surface flaws, also result in improved resistance to high humidity. 

Chemical stability - Ceramic membranes are not degraded by organic solvents and can withstand exposure to chlorine. Many crystalline oxides are relatively insoluble in acidic and alkaline media hence cercunic membranes coitposed of such oxides should be relatively inert under extreme pH conditions. 

Physical transformations (usually solid-state crystallization) are more often directly linked to molecular mobility and orientation than the most common chemical reactions (oxidation and hydrolysis) thus the major stability concern for amorphous materials is with their tendency to revert to the crystalline state. As with all crystallization processes, there are the normal nucleation and propagation (crystal growth) stages to consider, and procedures that increase the barrier to nucleation or slow the rate of crystal growth can be used to physically stabilize many amorphous materials. 

The first report was by Komameni and coworkers [179] using a microwave-hydrothermal process to catalyze the synthesis of crystalline oxides such as Ti02, Zr02 and Fc203, and binary oxides such as KNbOs and BaTiOs. The importance of this work was that this technique led to fine powders of these materials. The effect of different parameters, such as concentration of chemical species, time and temperature, on the crystallization kinetics of the above phases has been investigated under microwave-hydrothermal conditions using microwaves of 2.45 GHz frequency. 

For example, it is possible to find with the help of the STM images that the highly crystalline nature of the oxide film on the nickel surfaces is Ni(100) in the alkaline solutions [46]. At low potentials, a well-ordered rhombic structure is formed, which is resistant to reduction and is assigned to the irreversible Ni(OH)2 formation. At higher potentials, it is possible to see a quasi-hexagonal structure consistent with NiO(lll). In other words, a crystalline oxide is formed of the NiO(lll) order independently of the crystal orientation of nickel. Moreover, it is very useful and practical to obtain a reduced surface by the cathodic treatments, where the hydrogen evolution produces the chemical and electrochemical reductions of nickel. However, this has to be done with careful attention and in light alkaline solutions to avoid nickel dissolution. When this is performed, monoatomic steps mostly oriented in the (100) and (111) directions are observed [47]. 

Various types of polymers are used to formulate propellants and explosives. The nature of polymers is identified by their chemical bond structure. Two types of copolymers are used to formulate modern propellants and explosives (1) polyurethane copolymer and (2) polybutadiene copolymer. The chemical bond structures of polyether and polyester are used for polyurethane copolymers. Since the molecular concentration of oxygen is relatively high for polyurethane binder, this class of binder is used to achieve high combustion efficiency with low oxidizer concentration of crystalline materials. On the other hand, the heat of formation of polybutadiene copolymer is high and the molecular concentration of oxygen is low when compared with polyurethane copolymer. This class of binder is used to achieve a high combustion temperature when mixed with crystalline oxidizer particles. 

Microporous, crystalline oxides (alumina, silicates, phosphates, etc.) are used as catalyst is in the petroleum and in the chemical technologies in large volume to carry out cracking, isomerization, alkylation, and many other important hydrocarbon conversion reactions [198, 199, 203]. Discuss the structure of these so-called zeolites that have one-dimensional and two-dimensional micropores. How can the acidity of the catalysts be altered How do their acid strengths compare with concentration H2SO4 and HF ... 

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