Determination of the H2O content in minerals, especially zeolites, from their refractive indices based on mean electronic polarizabilities of cations
Determination of the H2O content in minerals, especially zeolites, from their refractive indices based on mean electronic polarizabilities of cations
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DOI：
10.5194/ejm-32-27-2020
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发表时间：
2020-01
影响因子：
2.1
通讯作者：
R. Fischer;M. Burianek;Robert D. Shannon
中科院分区：
文献类型：
--
作者：
R. Fischer;M. Burianek;Robert D. Shannon
抽象的。结果表明，用平均折射率可以准确地测定含水矿物的水含量。当只有小单晶可用时，这一点尤其重要。这种小晶体通常不适合热分析或其他可靠的测量H2O量的方法。为了确定H2O分子对光学性质的贡献，使用阳离子和阴离子的单个电子极化率的加和规则从化学组合物的无水部分计算总电子极化率。然后将这种无水贡献与使用Anderson-Eggleton关系从含水化合物的平均折射率计算的总观察到的电子极化率进行比较。两个值之间的差值代表H2O的贡献。该量可通过求解方程α calc = ∑ i n i α i cat + ∑ j α j o × 10 - N j V m 1.2 × n j + n W 1.2 + n w × α W得出，其中每个分子式单位（pfu）的H2O分子数nw为阳离子的电子极化率αcat，值N和αo描述阴离子极化率，阳离子和阴离子的数量n，和摩尔体积Vm，用αW= 1.62A3表示H2O的电子极化率。用数值方法求解该方程，得到每个分子式单元的H2O分子数nw。结果进行了比较，观察到的水含量评价157沸石型化合物和770非沸石含水化合物，表现出良好的协议。对于大多数化合物，该一致性通过将计算值与观察值相关的因子表示为接近1。沸石与闭塞的阴离子或中性物种（SO 3，SO 4，CO2，或CO 3）显示出异常高的偏差之间的计算值和观察到的量的H2O，这表明这些物种的极化率应被不同的沸石和沸石型化合物。
Abstract. It is shown here that the H2O content of hydrous minerals can be determined from their mean refractive indices with high accuracy. This is especially important when only small single crystals are available. Such small crystals are generally not suitable for thermal analyses or for other reliable methods of measuring the amount of H2O . In order to determine the contribution of the H2O molecules to the optical properties, the total electronic polarizability is calculated from the anhydrous part of the chemical composition using the additivity rule for individual electronic polarizabilities of cations and anions. This anhydrous contribution is then compared with the total observed electronic polarizability calculated from the mean refractive index of the hydrous compound using the Anderson–Eggleton relationship. The difference between the two values represents the contribution of H2O . The amount can be derived by solving the equation α calc = ∑ i n i α i cat + ∑ j α j o × 10 - N j V m 1.2 × n j + n W 1.2 + n w × α W for the number nw of H2O molecules per formula unit (pfu), with the electronic polarizabilities αcat for cations, the values N and αo describing the anion polarizabilities, the number n of cations and anions, and the molar volume Vm , using a value of αW=1.62 A 3 for the electronic polarizability of H2O . The equation is solved numerically, yielding the number nw of H2O molecules per formula unit. The results are compared with the observed H2O content evaluating 157 zeolite-type compounds and 770 non-zeolitic hydrous compounds, showing good agreement. This agreement is expressed by a factor relating the calculated to the observed numbers being close to 1 for the majority of compounds. Zeolites with occluded anionic or neutral species ( SO3 , SO4 , CO2 , or CO3 ) show unusually high deviations between the calculated and observed amount of H2O , indicating that the polarizabilities of these species should be treated differently in zeolites and zeolite-type compounds.