A study of gas-liquid reactive crystallization for CO 2 -BaCl 2 -H 2 O system was performed in a continuous flow crystallizer. The influences of mixing on the crystallization kinetics of barium carbonate crystals were investigated. The mixing parameters are stirrer speed, feed concentration, gas-flow rate, pH of solution, addition rate of NaOH solution, and mean residence time. Under pH-stat operation, the crystallization mechanism can be assessed by the addition rate of NaOH solution, which acts as an indicator for the absorption rate of carbon dioxide. Assuming a size-independent agglomeration mechanism, the nucleation rate, growth rate and agglomeration kernel can be obtained, simultaneously, at steady state, by the method of moments. Evidence shows that feed concentration, feed rate, gas-flow rate, and stirrer speed have a significant influence on the nucleation rates and mean particle sizes. This shows the effect of micromixing. The crystallization mechanism tends to be reaction limited when the feed concentration of barium chloride solution is higher than 5 mM, while at lower stirrer speeds and feed concentrations, the mechanism tends to be both mixing and reaction controlled. The growth rate depends on the mean supersaturation value and the pH of the solution and the mass-transfer resistance cannot be completely eliminated in this work. For a monodispersal collision model, in the viscous sub-range of turbulence, the agglomeration kernel can be expressed as, showing a low efficiency of collision. The result is also demonstrated by the agglomeration kernel expression. Comparison with a liquid-liquid-mixing reactive crystallization system is also discussed.

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In this paper, the precipitation, recrystallization, and evolution of twins in Cu-Cr-Zr alloy strips were investigated. Tensile specimens were aged at three different temperatures for various times so as to bring the strips into every possible aging condition. The results show that the appropriate aging parameter for the 70% reduced cold-rolled alloy strips is 723 K for 240 min, with a tensile strength of 536 MPa and an electrical conductivity of 85.3% International Annealed Copper Standards (IACS) at the peak aged condition. The formation of fcc (face-centered cubic) ordered Cr-rich precipitates (β) is an important factor influencing the significant improvement of properties near the peak aged condition. In terms of crystallographic orientation relationships, there are basically two types of β precipitates in the alloy. Beyond the Cr-rich precipitates (β (I)) formed during the early aging stages, which mimic a cube-on-cube orientation relationship (OR) with the matrix, another Cr-rich precipitate (β (II)) is observed in the peak aged condition. β (II) is coherent with the matrix, with the following ORs: [111] β (II) //[100] Cu , {02-2} β (II) //{02-2} Cu and [011] β (II) //[211] Cu , {200} β (II) //{-111} Cu. These precipitates have a strong dislocation and grain boundary pinning effect, which hinder the dislocation movement and crystal boundary migration, and eventually delay recrystallization and enhance the recrystallization resistance of the peak aged strips. During the subsequent annealing process, the transition phase β gradually loses the coherence mismatch and grows into a larger equilibrium phase of chromium with a bcc (body-centered cubic) structure (β), resulting in the reduction of the pinning effect to dislocations and sub-grains, so that recrystallization occurs. Annealing twins are formed during the recrystallization process to release the deformation energy and to reduce the drive force for interface migration, eventually hindering grain growth.

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Purpose The purpose of this paper is to investigate the effect of Na2SiO3 concentration on the microstructure and corrosive properties of microarc oxidation (MAO) coating on Al-Mg-Sc alloy and explore microstructure evolution rule of Al substrate in the contact area. Design/methodology/approach The Na2SiO3 concentration in electrolytes influenced the microstructure and corrosion behavior of MAO coatings. Instantaneous high temperature and high pressure due to microarc discharge caused annealing treatment. The corrosive behavior of the MAO coating was featured with polarization curves and electrochemical impedance spectrum in 3.5 Wt.% NaCl solution. Findings The substrate in the contact area existed the instantaneous annealing treatment, which caused obvious recrystallization. The coating prepared in electrolyte containing 7 g/L Na2SiO3 exhibited the highest protective properties in 3.5 Wt.% NaCl solution. Originality/value MAO treatment could increase the corrosion resistance by producing a protective layer on the Al-Mg-Sc alloy surface at a suitable Na2SiO3 concentration and microstructure evolution rule of Al substrate in the contact area was obtained.

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