Phase equilibrium analysis of the hottest solid-li

Phase equilibrium analysis of solid-liquid system

at a certain temperature, when any solid solute contacts the solution, if the solution is not saturated, the solute dissolves; When the dissolution process is carried out until the solution just reaches saturation, at this time, the solid and the solution are in phase equilibrium with each other. The solution at this time is called saturated solution, and its concentration is the solubility (equilibrium concentration) of the substance at this temperature; If the solution exceeds the solubility limit (supersaturation), at this time, the amount of dissolved substance contained in the solution exceeds the solubility of the substance, and the excess substance exceeding the solubility will crystallize out of the solution

the output of crystallization process depends on the equilibrium relationship between solid and solution, which can usually be expressed by the solubility of solid in solvent, that is, the mass of anhydrous salt solute that can be dissolved at most in 100g water or other solvents. The solubility of substances is related to their chemical properties, solvent properties and temperature. Solubility of certain substances in certain solvents preparation technology of ceramic structural parts for modern industry; Preparation technology of high-performance ceramic structural parts for special purposes; Preparation technology of ceramic matrix composites and superhard composites; Preparation technology of ceramic metal composites; Preparation technology of ceramic fiber reinforced composites; Special preparation technology of multi-functional, multi-layer structure multiphase ceramics and silicon carbide ceramics; Preparation technology of ultra-high temperature non oxide ceramic materials; Preparation technology of wear-resistant and high temperature resistant coating materials; Special coatings and coatings, special crystals, special functional ceramics, high-performance interfaces, especially important materials such as carbon fibers and silicon carbide fibers, and the preparation technology of their composite products; The preparation technology of superhard materials and products mainly changes with temperature, while the change with pressure is very small, which can often be ignored

solubility curve shows the relationship between the solubility of solute in solvent and temperature, as shown in Figure 14-1. The solubility curves of many substances are continuous without breaking in the middle, and the solubility of substances increases significantly with the increase of temperature, such as nan03, kn03, etc; However, the solubility curve of some hydrated salts (substances containing crystal water) has an obvious turning point (abnormal point) according to the manufacturer's introduction, which indicates that its composition has changed, such as na2s04 • 10h20 changing to na2s04 (abnormal point temperature is 32.4 ° C); In addition, the solubility of some substances decreases with the increase of temperature, such as na2s04; As for NaCl, temperature has little effect on its solubility

understanding the solubility characteristics of substances is conducive to the selection of crystallization methods. For substances whose solubility is sensitive to temperature change, the variable temperature method can be used for crystallization and separation; Substances whose solubility changes slowly with temperature can be separated by evaporation crystallization (removing part of the solvent)