Composition control mixing

Cotton linters or wood pulp are nitrated using mixed acid followed by treatment with hot acidified water, pulping, neutralization, and washing. The finished product is blended for uniformity to a required nitrogen content. The controlling factors in the nitration process are the rates of diffusion of the acid into the fibers and of water out of the fibers, the composition of mixed acid, and the temperature (see Cellulose esters, inorganic esters). 

Spencer R. J. and Hardie L. A. (1990) Control of seawater composition by mixing of river waters and mid-ocean ridge hydrothermal brines. In Fluid-Mineral Interactions A Tribute to H. P. Eugster. Special Publication 2 (eds. R. J. Spencer and I.-M. Chou). Geochemical Society, San Antonio, TX, pp. 409-419. 

The materials used in this study were fabricated following two different techniques (figure 1). The WCyCo graded samples were fabricated by a stepwise compositional control. It consists on layering the mixed powders with different composition ratios in a die. Then, they were... 

The mixed alloy arsenides are important to a wide range of optoelectronic applications. The addition of A1 to GaAs allows for compositional control of the bandgap and formation of heterojunctions from various alloys written as Al Gai- As. In turn, a great variety of devices may be fabricated. A difficulty in fabricating these alloys is the reactivity of Al. A1 and its primary sources TMAl and TEAl are very reactive to oxygen. TMAl is the most popular reactant. Oxygen incorporation readily occurs because AlyO precipitates are involatile (GaO which readily evaporates from the deposition... 

A full exposition of diffusion theory and diffusion mechanisms is beyond the scope of this chapter but the reader is referred to McDougall and Harrison (1999). Many observations show that argon diffusion rates in natural and laboratory experiments follow an Arrhenius relationship. There are however, important departures where fast track diffusion dominates in nature (Kramar et al. 2001 Reddy et al. 2001b) and laboratory analysis of hydrous minerals (Gaber et al. 1988 Lee 1993 Lo et al. 2000). Even in natural cases which might earlier have been identified as volume diffusion effects, careful compositional control shows that phase mixing can mimic argon loss profiles (e g., Onstott and Peacock 1987 Wartho 1995). In such cases the data can not easily be inverted to produce thermal histories. 

The best precursors are obtained using the sol-gel technique for they require lower calcination temperatures, allow better microstructural and compositional control plus the flexibility to produce a variety of shapes. Chandler et al. (1993) have reviewed the chemical aspects of solution routes to produce mixed oxides. The thermal decomposition of heterobinuclear complexes reported by Skaribas et al. (1991) leads to the production of perovskite oxides. More recently, Moreau et al. (1996) synthesized binuclear complexes of La-Ni, La-Co and La—Cu. Upon calcination at 973 K, the former two complexes yielded LaNiC>3 and LaCoC>3 perovskites while the latter yielded La2CuC>4. The main limitation in this and related methods is the complicated synthesis of the binuclear complexes that makes their application for large scale processing very unlikely. 

It is only rarely possible to probe the composition or structure of secondary solvation shells. One situation where this is possible is [Cr(NCS)6] in solution in aqueous acetonitrile, described in Section 3 of Chapter 4. Control over solvent shell composition in mixed solvents is most readily achieved by the use of mixtures of co-ordinating and non-co-ordinating solvents. Examples of applications of this include the study of DMSO exchange at nickel(ii) in DMSO-nitromethane and DMSO-methylene chloride mixtures, and of aquo-ions in methylene chloride. ... 

Details are given of an experimental technique, (the PLS2 method), which has been developed to determine the composition of mixed polymers using the NIR technique as a tool for the quality control of recycled plastics. PP/ polystyrene blends were quantitively analysed, and the effects of aluminium and paper contaminants were evaluated. 9 refs. 

Sol-gel Lower crystallization temperature, lower cost, better control of mixing of precursors, quickly produce new materials Lack of phase and composition control, morphology, reproducibility... 

The bulk shear viscosity of the polymer blend at a given composition must be measured to understand the non-isothermal, non-Newtonian flow behavior of a polymer melt to control mixing and reaction at the interface during a melt blending process to manufacture polymer blends with desired properties. 

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