We describe a simple hydrothermal process for synthesizing vaterite-type CaCO₃ microparticles with a hexagonal bipyramidal shape using seawater. Vaterite with a spherical morphology is synthesized at room temperature relatively frequently, and a few high-temperature synthetic methods have been reported. However, the majority of these procedures require specific conditions, such as the use of detrimental surfactants, ultrasonication, and microwave irradiation. In this study, we successfully synthesized vaterite in Mg-free seawater using Ca(NO₃)₂ and urea, which do not require surfactants/organic additives or complex experimental conditions. The obtained vaterite hexagonal bipyramids had sharp edges and facets and a purity of 96%. We investigated the effects of the solvent type, reaction temperature, reaction time, and the ratio of Ca²⁺ and CO₃²⁻, on the crystallization and morphology of the CaCO₃ polymorph. The phase and morphology of the vaterite were primarily determined by the synergistic effects of seawater and the ammonium ions from urea.

我们描述了一种使用海水合成具有六角双锥形状的球霰石型CaCO _{3微粒的简单水热工艺。}具有球形形态的球霰石在室温下合成比较频繁，并且已经报道了一些高温合成方法。然而，这些程序中的大多数都需要特定的条件，例如使用有害的表面活性剂、超声波处理和微波照射。在这项研究中，我们使用 Ca(NO ₃ ) _{2在无镁海水中成功合成了球霰石。}和尿素，它们不需要表面活性剂/有机添加剂或复杂的实验条件。得到的球霰石六方双锥体具有锋利的棱边和刻面，纯度为96%。我们研究了溶剂类型、反应温度、反应时间以及Ca ²⁺和CO ₃ ^{2-的比例对CaCO} ₃多晶型物的结晶和形态的影响。球霰石的相和形貌主要由海水和尿素中的铵离子的协同作用决定。