Abstract Silicic melts in magma chambers below active volcanoes typically contain several wt% H2O. The dissolved water has drastic effects on the chemical and physical properties of the melts and, hence on processes like magma differentiation, ascent and degassing. But interaction of water with glasses and melts is also of great importance for the production and application of glasses. The effect of water is closely related to its speciation. OH groups bond to tetrahedral cations and H2O molecules are predominant species in polymerized melts. In strongly depolymerized melts “free” OH groups may also be present. In this paper we review the data on water speciation in oxide melts, considering new data for hydrous silica and basaltic melts. SiO2 glasses containing up to 4 wt% H2O were produced at temperatures of 1573–1673 K and pressures of 100–200 MPa in an internally heated gas pressure vessel. Water speciation in the quenched glasses was determined by near-infrared spectroscopy. The set of samples used for the calibration of the absorption coefficients for the combination bands of OH and H2O also included a natural hyalite and water-poor commercial silica glasses. Fictive temperatures of the glasses were estimated based on viscosity and cooling rate. The derived K values (=[OH]2/([O]∙[H2O]),) indicate, at given melt temperature, higher abundance of molecular H2O for hydrous silica melts than for other oxide melts. For tholeiitic basalt melts, water speciation was inferred using speciation data for glasses from Shishkina et al. (2010) , and Tf was estimated using the viscosity model of Giordano et al. (2008) . Some general trends can be derived by considering literature data for water speciation in oxide melts. At constant p,T, little variation of K values is observed for melts of the pseudo join from rhyolite to basalt, implying that composition has minor effect for most natural aluminosilicate melts. However, this applies only to melts with Al/Si ≪ 1. The network can be hydrolyzed much more easily if alternating Al-O-Si bonds are present, i.e. when Al/Si approaches 1. K values are higher for silicate melts than for aluminosilicate melts, implying that non-bridging oxygen support the dissociation of H2O. The type of network former also has a strong influence on the dissociation of H2O in the melt as well. Replacement of Al by B favors the formation of OH groups, and OH contents are particularly high in borate and phosphate melts. This can be explained by easy hydrolysis of P O and B O bonds.

中文翻译：

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氧化物玻璃和熔体中的水形态

摘要 活火山下方岩浆房中的硅熔体通常含有几个重量百分比的 H2O。溶解的水对熔体的化学和物理性质有很大的影响，因此对岩浆分异、上升和脱气等过程有很大影响。但是水与玻璃和熔体的相互作用对于玻璃的生产和应用也很重要。水的作用与其物种形成密切相关。OH 基团与四面体阳离子键合，而 H2O 分子是聚合熔体中的主要物质。在强烈解聚的熔体中，也可能存在“游离”OH 基团。在本文中，我们回顾了氧化物熔体中水形态的数据，考虑了含水二氧化硅和玄武岩熔体的新数据。在 1573-1673 K 的温度和 100-200 MPa 的压力下，在内部加热的气体压力容器中生产含有高达 4 wt% H2O 的 SiO2 玻璃。淬火玻璃中的水形态通过近红外光谱测定。用于校准 OH 和 H2O 组合带的吸收系数的一组样品还包括天然透明玻璃和缺水的商业二氧化硅玻璃。基于粘度和冷却速率估计玻璃的假想温度。导出的 K 值 (=[OH]2/([O]∙[H2O]),) 表明，在给定的熔体温度下，含水二氧化硅熔体的分子 H2O 丰度高于其他氧化物熔体。对于拉斑玄武岩熔体，使用来自 Shishkina 等人的玻璃的物种形成数据推断水的物种形成。(2010) , 和 Tf 是使用 Giordano 等人的粘度模型估计的。(2008)。通过考虑氧化物熔体中水形态的文献数据，可以得出一些一般趋势。在恒定的 p,T 下，观察到从流纹岩到玄武岩的假连接熔体的 K 值变化很小，这意味着成分对大多数天然铝硅酸盐熔体的影响很小。然而，这仅适用于 Al/Si ≪ 1 的熔体。如果存在交替的 Al-O-Si 键，网络可以更容易水解，即当 Al/Si 接近 1 时。硅酸盐熔体的 K 值高于铝硅酸盐熔化，这意味着非桥连氧支持 H2O 的解离。网络形成剂的类型对熔体中 H2O 的解离也有很大影响。B 取代 Al 有利于形成 OH 基团，硼酸盐和磷酸盐熔体中的 OH 含量特别高。这可以通过 PO 和 BO 键的容易水解来解释。