Chemical discontinuities

Products of partial He-burning they are visible only in WC and WO stars. C and 0 appear prominently at the stellar surfaces. The appearance of these elements is predicted to be quite fast because there is usually a large chemical discontinuity at the edge of the He-burning core (cf. 3). 

Goodwin, A. M. Smith, J. E. M. 1980. Chemical discontinuities in Archaean volcanic terrain and the development of Archaean crust. Precambrian Research, 10, 301-311. 

However, SPS grades suffered from poor mechanical properties relative to other ETPs. Glass-reinforced grades were handicapped by no interfacial attraction between the glass fiber and the nonpolar, nonfunctional SPS. Besides lower strength and stiffness, the weld lines were very poor. In 2005, Dow Chemical discontinued the SPS product line. SPS plastics are available from Indemitsu Kosan, Co. and LG Chemicals under the Xarec SPS and LUSEP SP trade names, respectively. 

It is generally assumed that isosteric thermodynamic heats obtained for a heterogeneous surface retain their simple relationship to calorimetric heats (Eq. XVII-124), although it may be necessary in a thermodynamic proof of this to assume that the chemical potential of the adsorbate does not show discontinu-... 

The integral under the heat capacity curve is an energy (or enthalpy as the case may be) and is more or less independent of the details of the model. The quasi-chemical treatment improved the heat capacity curve, making it sharper and narrower than the mean-field result, but it still remained finite at the critical point. Further improvements were made by Bethe with a second approximation, and by Kirkwood (1938). Figure A2.5.21 compares the various theoretical calculations [6]. These modifications lead to somewhat lower values of the critical temperature, which could be related to a flattening of the coexistence curve. Moreover, and perhaps more important, they show that a short-range order persists to higher temperatures, as it must because of the preference for unlike pairs the excess heat capacity shows a discontinuity, but it does not drop to zero as mean-field theories predict. Unfortunately these improvements are still analytic and in the vicinity of the critical point still yield a parabolic coexistence curve and a finite heat capacity just as the mean-field treatments do. 

Taking advantage of the intrinsic physical and chemical differences of surfaces introduced by the discontinuity of the bulk enviromuent. Specifically, most solids display specific structural relaxations and reconstructions, surface... 

For both first-order and continuous phase transitions, finite size shifts the transition and rounds it in some way. The shift for first-order transitions arises, crudely, because the chemical potential, like most other properties, has a finite-size correction p(A)-p(oo) C (l/A). An approximate expression for this was derived by Siepmann et al [134]. Therefore, the line of intersection of two chemical potential surfaces Pj(T,P) and pjj T,P) will shift, in general, by an amount 0 IN). The rounding is expected because the partition fiinction only has singularities (and hence produces discontinuous or divergent properties) in tlie limit i—>oo otherwise, it is analytic, so for finite Vthe discontinuities must be smoothed out in some way. The shift for continuous transitions arises because the transition happens when L for the finite system, but when i oo m the infinite system. The rounding happens for the same reason as it does for first-order phase transitions whatever the nature of the divergence in thennodynamic properties (described, typically, by critical exponents) it will be limited by the finite size of the system. 

Another successor to OCCS was SECS [35], which was further developed into the GASP system by a consortium of German and Swiss chemical companies. The development of both the CASP and the SECS systems was discontinued in the early 1990. 

The expansion process consists of three steps creating small discontinuities or cells in a fluid or plastic phase causing these cells to grow to a desired volume and stabilizing this cellular stmcture by physical or chemical means. 

When water activity is low, foods behave more like mbbery polymers than crystalline stmctures having defined domains of carbohydrates, Hpids, or proteins. Water may be trapped in these mbbery stmctures and be more or less active than predicted from equiUbrium measurements. As foods change temperature the mobiUty of the water may change. A plot of chemical activity vs temperature yields a curve having distinct discontinuities indicating phase... 

Imperial Chemical Industries (ICI) operated a coal hydrogenation plant at a pressure of 20 MPa (2900 psi) and a temperature of 400—500°C to produce Hquid hydrocarbon fuel from 1935 to the outbreak of World War II. As many as 12 such plants operated in Germany during World War II to make the country less dependent on petroleum from natural sources but the process was discontinued when hostihties ceased (see Coal conversion PROCESSES,liquefaction). Currentiy the Fisher-Tropsch process is being used at the Sasol plants in South Africa to convert synthesis gas into largely ahphatic hydrocarbons at 10—20 MPa and about 400°C to supply 70% of the fuel needed for transportation. 

Commercial VPO of propane—butane mixtures was in operation at Celanese Chemical Co. plants in Texas and/or Canada from the 1940s to the 1970s. The principal primary products were acetaldehyde, formaldehyde, methanol, and acetone. The process was mn at low hydrocarbon conversion (3—10%) and a pressure in excess of 790 kPa (7.8 atm). These operations were discontinued because of various economic factors, mainly the energy-intensive purification system required to separate the complex product streams. 

The interface region in a composite is important in determining the ultimate properties of the composite. At the interface a discontinuity occurs in one or more material parameters such as elastic moduli, thermodynamic parameters such as chemical potential, and the coefficient of thermal expansion. The importance of the interface region in composites stems from two main reasons the interface occupies a large area in composites, and in general, the reinforcement and the matrix form a system that is not in thermodynamic equiUbhum. 

For pipelines in service in chemical plants, it is not usually convenient to place a radiation source inside the pipe and position it to irradiate each welded joint. The radioisotope source container maybe placed on the outer surface of the pipe. The radiation beams then pass through two pipe wall thicknesses to expose films placed diametrically opposite the radiation source, also on the outside of the pipe wall. Other methods, such as magnetic particle inspection of welds in steel pipe, or ultrasonic inspection of welds in pipes of all materials, supplement x-rays in many critical appHcations. The ultrasonic tests can often detect the thin, laminar discontinuities parallel to the pipe surface or the incomplete fusion discontinuities along the weld... 

Although numerous mud additives aid in obtaining the desired drilling fluid properties, water-based muds have three basic components water, reactive soHds, and inert soHds. The water forming the continuous phase may be fresh water, seawater, or salt water. The reactive soHds are composed of commercial clays, incorporated hydratable clays and shales from drilled formations, and polymeric materials, which may be suspended or dissolved in the water phase. SoHds, such as barite and hematite, are chemically inactive in most mud systems. Oil and synthetic muds contain, in addition, an organic Hquid as the continuous phase plus water as the discontinuous phase. 

At Great Salt Lake Minerals Corporation (Utah), solar-evaporated brines are winter-chilled to —3° C in solar ponds. At this low temperature, a relatively pure Glauber s salt precipitates. Ponds are drained and the salt is loaded into tmcks and hauled to a processing plant. At the plant, Glauber s salt is dissolved in hot water. The resulting Hquor is filtered to remove insolubles. The filtrate is then combined with soHd-phase sodium chloride, which precipitates anhydrous sodium sulfate of 99.5—99.7% purity. Great Salt Lake Minerals Corporation discontinued sodium sulfate production in 1993 when it transferred production and sales to North American Chemical Corporation (Trona, California). 

Economic Aspects. The price of thionyl chloride in mid-1995 was 1.21/kg. As of late 1996 there was only one U.S. producer, Bayer Chemical (Baytown, Texas). Oxychem discontinued production in 1992. 

New technology and development of brine reserves are increasing each year in the United States and abroad. This affects the uses and price of brine chemicals. For example, development of the Salar de Atacama in Chile in the 1980s as the largest producer of brine lithium in the world has affected lithium production and prices worldwide. Lithium production from Seades Lake brine has been discontinued, and the Silver Peak operation in Nevada is in a slow production decline caused by weaker brine grades. 

The reaction of lithium with methyl chloride in ether solution produces a solution of methyllithium from which most of the relatively insoluble lithium chloride precipitates. Ethereal solutions of halide-free" methyllithium, containing 2-5 mole percent of lithium chloride, were formerly marketed by Foote Mineral Company and by Lithium Corporation of America, Inc., but this product has been discontinued by both companies. Comparable solutions are also marketed by Alfa Products and by Aldrich Chemical Company these solutions have a limited shelf-life and older solutions have often deteriorated... 

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