Chemicals segregation

Cavani et al. [61], who reviewed this area extensively in 1991, emphasize that all the stages of preparation of a catalyst with a HT-type precursor need precise chemical control to avoid inhomogeneities and chemical segregation. 

This paper describes chemical analyses at points across individual zeolite crystals in the size range 0.1-2.0pm. The technique employed was x-ray emission spectroscopy in the scanning transmission electron microscope (STEM). Two ZSM-5 preparations were made with Si Al ratios about 10 and 40. Many particles were examined carefully to detect chemical segregation. To check the analysis procedure, particles of NaA zeolite were examined as a control. 

In its simplest form, steel is an alloy of iron and carbon. In general, there are other alloying elements present. Steel wires can vary in composition enormously, from simple C-Mn steel to alloy steels containing more than ten alloy additions. Control of impurities (mostly nonmetallic inclusions), chemical segregation,... 

The solvent is removed by vacuvim sublimation being carefvil not to form any liquid phase that could cause chemical segregation. 

As we have noted in Chapter 6, some salts have a solubility that decreases with decreasing temperature. In this case these salts will crystallize during the freezing process, which can lead to chemical segregation into different salt crystals within the droplet. When the solubility increases with decreasing temperature, a more homogeneous mixing of the various metal salts is found. 

It is well known [59] that among the main elements of an ingot structure which are inherited by a deformed metal are grain and dendritic cell sizes and chemical segregation in the ingot volume. 

Indium occurs in widespread association with both zinc and tin ores. It seems improbable that this can be due to chemical segregation, for isomorphism of indium and tin compounds, for example, appears to be ruled out by their difference both in valency and atomic radius. It has been suggested that the tin isotope 115 has gradually been transmuted into iftdium 115 by loss of an electron and a neutrino. The process is presumed to take place extremely slowly so that in finite time it escapes observation. Tin has eleven natural isotopes of these Sn 115 constitutes 0-44 per cent. Indium comprises In 115, 95 5, and In 113, 4-5 per cent. The high percentage of isotope 115 in natural indium is in harmony with the above suggestion. 

METALLURGICAL FACTOR - The condition of the metal, such as inclusions, chemical segregation s, cold work and others, which have an impact upon the rate of electrochemical corrosion rates. 

In the materials with DBDI (Fig. 2.14(b)) the overall etched texture is much flatter. The regions of chemical segregation are more or less equally attacked. The material with DBDI does not show the precipitated crystals. A more detailed SEM description on the morphology of MDI and DBDI based PUs and mixtures of them, is made in section 2.3.2.2. where the materials are characterized and compared from two perspectives (a) effect of the SS macrodiol nature (polyester or polyether) (b) effect of type, and number of diisocyanates (crystallizing or not) and their order of introduction in the reaction synthesis. 

Homogenization (Soaking) A high temperature heat treatment intended to eliminate or decrease chemical segregation by diffusion. 

Here no chemical segregation occurs due to the polymorphic transformation into the amorphous state. This transformation is fast in time compared to the nucleation and growth of the two crystalline phases where diffusion of the metal atoms is necessary. The low diffusivity of the metal atoms compared to the high mobility of the hydrogen atoms connected with the attractive interaction between one metal species and the hydrogen gives the basic understanding of the SSR process. 

Light microscope images of the deposits from untreated artificial synovial fluid confirm that simple chemical segregation of HA and protein mixtures is inadequate for reduction of interferences from proteins. A few concentric rings are observed, but only protein spectra are seen in all of them. Small molecule impurities are still easily segregated from HA. 

Varying the kinetics of decomposition of the precursors was profitable for the controlled synthesis of RuPt NPs. Whilst the co-decomposition of [Ru(COD(COT)] and [Pt(dba)2] in the presence of polyvinylpyrrolidone as stabilizer led to a RuPt alloy with a fee structure, core-shell RuPt NPs were obtained in PVP, using [Pt(CH3)2(COD)] (i.e., [dimethyl(l,5-cyclooctadiene) platinum (II)]) instead of [Pt(dba)2] [91]. This is related to the slower rate of decomposition of [Pt(CH3)2(COD)]. In summary, the chemical order can be controlled via the choice of the precursor. The chemical segregation leading to core-shell RuPt results from kinetic (decomposition rate of the metal precursors) and thermodynamic (preferred location of each metal in the particle) parameters as well as from the steric... 

The corrosion problems commonly associated with welding of anstenitic stainless steels are related to precipitation effects and chemical segregation. These problems can be eliminated or minimized through control of base metal metallurgy, control of the welding practice, and selection of the proper filler metal. 

Other Appiications Nuclear fuel reprocessing operations generate different types of effluents. Chemical segregation of most or all the radioactive components from the inactive bulk constituents of the waste can reduce the... 

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