Fluxes, melt solidification

For reversible transformations such as melting/solidification or the Q to (3 quartz inversion in silica, heat flux DSC and power compensated DSC can each be equivalently precise in determining the latent heat of transformation. Transformations of... 

Molten solutions can also be used for crystallization. Fluxes are selected that have a high solubility of the to-be crystallized material. Borate fluxes are used for some oxide systems, sodium sulfide fluxes are used for sulfide systems, and molten metal fluxes are used for carbide and nitride systems. In both the melt and flux systems, the solubility is highly temperature dependent. The solubility in flux systems is not particularly well known except for a few systems. The general solubility behavior is like that in liquid phase precipitation, which was discussed in Chapter 6. In melt solidification, the supersaturation, S, is given by... 

The appearance of the post-braze surfaces predominantly depends on initial flux loading and uniformity of coating. Once the flux melts, it is completely liquid. In its molten state, the flux has no particles. Once the flux is liquid, it immediately spreads out and wets the surfaces. Upon cooling and solidification, the amount of flux residue and its distribution on the surface of the work-piece is related entirely to the initial flux loading, and not particle size. 

Applications of PCM cover many diverse fields. As mentioned before, the most important selection criterion is the phase change temperature. Only an appropriate selection ensures repeated melting and solidification. Connected to the melting and solidification process is the heat flux. The range of heat flux in different applications covers a wide range from several kW for space heating with water or air, domestic hot water and power plants to the order of several W for temperature protection and transport boxes (Figure 124). 

The melting process for a resin is complex and depends on many parameters, including screw speed, screw geometry, barrel temperatures, and channel pressures. Moreover, the compression ratio and compression rate also affect the pressure in the channel. The melting flux is known to increase with increasing pressure in the channel [1,12]. A series of Maddock solidification experiments were performed at... 

When studying the growth kinetics of the intermetallic layers, after the run the crucible, together with the flux, the melt and the solid specimen, was shot into cold water to arrest the reactions at the transition metal-aluminium interface. Note that the solid specimen continued to rotate until solidification of the melt, ft is especially essential in examining the formation of the intermetallic layers under conditions of their simultaneous dissolution in the liquid phase (with undersaturated aluminium melts). The time of cooling the experimental cell from the experimental temperature down to room temperature did not exceed 2 s. 

Fig. 22. A brief classification of R123 crystal growth techniques on a basis of different phenomena taking place at various interfaces between solid, liquid and gaseous phases participating in the solidification process (a) possible interface boundaries and phenomena connected with the presence of such interfaces (b) different interfaces present in the self-flux method note that numbers in brackets correspond to the general scheme of classification (a) (c) a number of interfaces and phenomena of some importance for the unidirectional solidification method note that (crystal-high-temperature phase and melt-high-temperature phase) interfaces are close to each other (d) different interfaces and phenomena to be considered in the SRL-CP pulling technique of bulk crystal production note that solute transport and nudeation can be controlled in order to achieve a desired morphology of the crystal.

Heat flux is described as the ability of exporting the heat released by steel solidification on the entire face of copper plates of the mold. The mean heat flux is derived from the temperature of melt, the flow rate and temperature difference of cooling water, and is given by... 

An alternate approach is to use a fusion technique. The samples are dissolved in a molten flux such as LiBO, Na COj, or other appropriate salts. Spike additions of the analyte elements can be added to the molten sample and flux in varying concentrations. The fused melt is solidified by pouring the molten flux onto a flat surface (aluminum or stainless steel plate), where it cools, forming a uniform glassy specimen suitable for direct laser ablation analysis. Ablation of the fluxed material, after solidification, is used to establish calibration curves for quantitation or for standard addition analysis. 

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