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Mechanisms of Polyacrylate Modified Sodium Oxalate Crystallization from Highly Alkaline Solutions

机译：高碱性溶液中聚丙烯酸酯改性草酸钠的结晶机理

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摘要

The shape changes of sodium oxalate (Na2C2O4) crystals in the presence of polyacrylic acids (PAA) with different molecular weights (1800, 5100, 450 000, 1 250 000 g/mol) and propionic acid (74 g/mol) was investigated hi a highly alkaline solution (5 M NaOH), Over the entire concentration range tested (0-100 mg/L), propionic acid had no influence on Na2C2O4 shape, indicating hat the number of carboxylate functional groups is not the vital factor for Na2C2O4 shape control, despite: playing a role in the adsorption. In contrast, with increasing PAA concentrations, Na2C2O4 crystals were significantly modified through distinct shape changes proceeding through a coexisting family of rods, bundles, flower-like structures, irregular spherulites, and eventually spherulites. PAA anions with medium molecular weights (1800; 5100 g/mol) were the most effective in promoting the spherulitic shape. Thus, the mechanisms of Na(2)C(3)G(4) shape changes can be attributed to PAA adsorption on Na2C2O4 surfaces and their subsequent incorporation into the Na2C2O4 crystal matrix. PAA adsorption is responsible for the inhibition of step train growth on prismatic {110} and {200} faces and nuclei propagation on their top {001} faces, PAA incorporation can lead to multistep-branching growth based on a noncrystallographic crystal branching model.
机译：研究了存在不同分子量（1800、5100、450 000、1250000 g / mol）和丙酸（74 g / mol）的聚丙烯酸（PAA）时草酸钠（Na2C2O4）晶体的形状变化碱性溶液（5 M NaOH），在整个测试浓度范围（0-100 mg / L）中，丙酸对Na2C2O4形状没有影响，表明帽子羧酸盐官能团的数量不是Na2C2O4形状的重要因素控制，尽管：在吸附中起作用。相反，随着PAA浓度的增加，Na2C2O4晶体通过不同的形状变化而显着改性，这些变化通过并存的棒，束，花状结构，不规则球晶以及最终球晶共存。中等分子量（1800; 5100 g / mol）的PAA阴离子最有效地促进了球形。因此，Na（2）C（3）G（4）形状变化的机制可以归因于PAA在Na2C2O4表面上的吸附及其随后并入Na2C2O4晶体基质中。 PAA吸附负责抑制棱柱形{110}和{200}面上的阶梯形增长以及核在其顶部{001}面上的扩散，PAA的掺入可导致基于非晶体晶体分支模型的多步分支生长。

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