Solidification preferential

The disadvantage of lasers with nanosecond-picosecond pulse duration for depth profiling is the predominantly thermal character of the ablation process [4.229]. For metals the irradiated spot is melted and much of the material is evaporated from the melt. The melting of the sample causes modification and mixing of different layers followed by changes of phase composition during material evaporation (preferential volatilization) and bulk re-solidification [4.230] this reduces the lateral and depth resolution of LA-based techniques. 

When the equilibrium mixture is permitted to cool rapidly, the heavier salt phase settles and solidifies, thus leaving the lighter metal phase on top as a liquid. Inasmuch as calcium metal starts to precipitate and settle before the solidification point of the salt phase is reached, some of the calcium is trapped in the salt phase and, together with the calcium which is dissolved by the molten salt, is not recovered in the following synthesis. Once the sodium chloride-calcium chloride layer has solidified, however, the precipitating calcium remains trapped in the metal layer. When the metal layer freezes, its composition consists of calcium crystals embedded in a sodium matrix which may be removed by preferential reaction with a lower alcohol.9... 

Etchants will attack either concave or convex irregularities on the surface, such as formed by gas bubbles during solidification or at irregular growth steps. The pits left after a dislocation has been removed usually give results similar to a concavity (sections 2.1 and 2.2). The shape of these pits or hillocks are determined by the orientation of the surface and the type of attack of the etchant (i. e., preferential or non-preferential). There is no way at present to predict what planes will be revealed by a given etchant it is not yet even possible to predict whether a given solution will act preferentially or nonpreferentially. 

Austenitic alloys also make use of the concept of stabilization. Stainless types 321 and 347 are versions of type 304 stabilized with titanium and niobium, respectively. These elements will preferentially combine with carbon that comes out of solid solution during weld solidification. Rather than a loss of corrosion resistance associated with formation of harmful chromium carbides, the carbides of titanium and niobium are not detrimental to corrosion resistance. The austenitic family of stainless also prompted another approach to avoiding the effects of chromium carbide precipitation. Because the amount of chromium that precipitated was proportional to the carbon content, lowering the carbon could prevent sensitization. Maintaining the carbon content to below about 0.035% vs. 

But such action of cavitation can be realized when the cavitation region locates close to the solidification front. In most cases of ultrasonic treatment involving the developed cavitation, the other mechanism of increasing nucleation is preferential. 

We see from this example that heat transport is a key factor influencing stabiUty. In solidification of binary mixtures or alloys both heat and mass transport must be eonsidraed. If the solute is preferentially soluble in the hquid phase, for example, solute must diffuse from the interfaee to the bulk hquid as sohdification proeeeds. Sinee diffusion coefficimts are often mueh smalf than thermal diffu-sivities in liquids, the sohdification rate is often limited primarily by solute diffusion. By an argument similar to that given above for heat transport, we eonclude that solute (hffusion in the hquid is destabilizing and ean lead to dendritic growth. 

Gold and silver may be removed from soft lead by the Parkes process. This involves the preferential extraction of silver and gold into added molten zinc, which then rises to the surface of the lead and after solidification can be skimmed off. The final impurity of a little zinc can be removed either by air oxidation, or more recently by evaporation. 

Segregation of molybdenum in weld metal can be detrimental to corrosion resistance in some environments. In the case of boiling HCl solutions, the weld metal does not corrode preferentially. However, in H2SO4 -1- HCl and H2SO4 -1- H3PO4 acid mixtures, preferential corrosion of as-welded Alloy B-2 has been observed. No knifeline or HAZ attack was noted in these tests. During solidification, the initial solid is poorer in molybdenum and therefore can corrode preferentially. In such cases, postweld annealing at 1120 °C (2050 °F) will be beneficial. 

The hedgehogs in the centre of splay structures move to the edges (poles) with growing polymer network. With further polymerization, the polymer solidification quenches the growth and mobility of LC domains. The morphology remains more or less the same and at around 600 s, exhibits random optical axis orientations. It can be seen that the LC domains do not exhibit preferential alignment or orientation... 

The inadvertent presence of intermetallic compound particles in PbASn solder is most often a result of excessive base metal dissolution into molten solder. In most cases, the base metal is a single element such as Cu, Ni, or Au. In other applications, the base metal may be an alloy of several elements, in which case, some of the elements may exhibit preferential dissolution into the solder [27]. Intermetallic compound particles (e.g., Cu Sns, AuSri4, Ni3Sn4, PdSn4, etc.) precipitate upon solidification, when the base metal concentration exceeds its solid solubihty limit in either the Pb-rich or Sn-rich phases. The solubility limits are nearly zero for most Sn/base metal combinations as shown in Table 1 [28]. 

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