火星富氯（氯化物、高氯酸盐）卤水体系低温水化学模型研究

Chlorine, which is known mainly as chloride and perchlorate, is wide-spread in the soil on Mars. Strong hygroscopicity and freezing point depression of chloride and perchlorate are of significance on the present transient liquid water. Cold aqueous chemistry model is an important tool on the prediction of Mars brine properties and crystallization path. In this proposal, a cold aqueous chlorine chemistry model will be developed based on the chloride parameters, i.e., the parameters in the Na,Mg,Ca//Cl-H2O system, in ISLEC model, which was constructed by the applicant in previous studies. The extention of the available chloride model in ISLEC to perchlorate systems needs to determine the binary and tenrary perchlorate parameters. Binary perchlorate parameters can be regressed from various type of thermodynamic data, e.g., solubility, osmotic coefficient, water activity, enthalpy of dilution and heat capacity, reported in literature. However, the ternary experimental data for the perchlorate systems are still lack at subzero temperatures. To obtain reliable ternary perchlorate parameters, the ternary solubility and aqueous heat capacity data are necessary. As a key part of the proposal, solubility and aqueous heat capacity will be measured for the perchlorate(chloride) ternary systems at subzero temperatures using isothermal method, DSC heating-cooling curve method and DSC sapphire approach in the temperature range of -100 C to 0 C. From the ternary data obtained in this proposal at subzero temperatures and these reported in literature especially at 25 C, the perchlorate ternary parameters will be determined. Combining the chloride parameters in ISLEC and perchlorate parameters newly determined, a cold aqueous chlorine model for the quinary Na,Mg,Ca//Cl,ClO4-H2O system will be constructed. Using the model, the stability of chloride and perchlorate hydrates and thermodynamic properties of the Mars chlorine aqueous can be predicted accurately. The model generated thermodynamic properties of the chlorine aqueous and minerals can be used for revealing the formation condition of Mars chloride and perchlorate and evaluating the probability of Mars as a habitant for life.

氯在火星土壤中广泛存在，氯化物和高氯酸盐强烈的吸湿性和凝固点降低作用对于火星表面液态水的形成具有重要意义。低温水化学模型是研究火星卤水性质及其成盐过程的重要工具。本项目拟以申请人前期开发的ISLEC模型中多组分氯化物体系（Na,Mg,Ca//Cl-H2O）低温参数为基础，建立火星富氯（氯化物、高氯酸盐）卤水体系低温水化学模型。采用等温溶解平衡法、升降温曲线法和DSC蓝宝石法，测定含高氯酸盐三元体系低温溶解度和比热容数据；利用多性质综合参数化方法，确定高氯酸盐二元和三元体系的低温模型参数，结合已有氯化物参数，建立Na,Mg,Ca//Cl,ClO4-H2O体系可靠低温水化学模型（-100 ℃～25 ℃）；预测氯化物和高氯酸盐矿物及卤水的低温性质，为认识火星氯化物和高氯酸盐的形成条件、评价火星低温富氯卤水的生物适应性提供重要理论依据。

氯在火星土壤中广泛存在，氯化物和高氯酸盐强烈的吸湿性和凝固点降低作用对于火星表面液态水的形成具有重要意义，并且明确氯化物/高氯酸盐混合盐的潮解（或与冰共融）液化条件能够有助于理解火星气候（如温度-湿度变化）对于形成的混合卤水中ClO4/Cl比值的变化范围的影响程度，进而从化学热力学角度约束火星表面高氯酸根母盐矿物种类与高氯酸盐的富集规律。低温水化学模型是研究火星卤水性质及其成盐过程的重要工具，然而含高氯酸盐低温溶解度数据的缺乏、以及现有单一溶解度模型较差的温度外推能力成为了构建该模型最为主要的瓶颈。本项目：1）测定了NaCl+NaClO4+H2O、Mg(ClO4)2+MgCl2+H2O、Ca(ClO4)2+CaCl2+H2O、NaClO4+Mg(ClO4)2+H2O、NaClO4+Mg(ClO4)2+H2O和Mg(ClO4)2+Ca(ClO4)2+H2O共6个含高氯酸盐和氯盐三元体系的低温（-40 °C至0 °C）溶解度数据、以及Mg(ClO4)2+Ca(ClO4)2+H2O、Mg(ClO4)2+MgCl2+H2O和Ca(ClO4)2+CaCl2+H2O混合溶液的比热容；2）完成了3个高氯酸盐二元体系NaClO4+H2O、Mg(ClO4)2+H2O和Ca(ClO4)2+H2O以及上述6个三元体系的低温多温模型化工作，确定了所有体系的变温混合参数以及体系中出现的所有高氯酸盐及其水合物的标准Gibbs自由能，并与研究团队前期开发的ISLEC软件中已有的氯化物体系模型相融合，建立了可靠Na,Mg,Ca//Cl,ClO4-H2O体系低温水化学模型，适用温度范围为-100 °C~50 °C；3）借助构建的低温水化学模型，构筑了上述3个高氯酸盐二元体系和6个三元体系的完整低温相图；并确定了最低共晶物的组成、温度和水活度；并且利用模型预测了水合高氯酸盐的温度-湿度稳定区、以及高氯酸盐-高氯酸盐和高氯酸盐-氯化物混合的潮解/风化条件；借助模拟计算，充分研究了凤凰号着陆点高氯酸盐的超常规富集机制，并借助相图探讨了高氯酸盐/氯盐分异程度与火星表面气候的密切联系，借助火星全球气候数据，圈定了火星表面高氯酸盐可能出现高度富集的区域。