The structural role and homogeneous redox equilibria of iron in peraluminous, metaluminous and peralkaline silicate melts
The structural role and homogeneous redox equilibria of iron in peraluminous, metaluminous and peralkaline silicate melts
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铁在过铝、偏铝和过碱硅酸盐熔体中的结构作用和均匀氧化还原平衡
DOI：
10.1007/bf00375294
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发表时间：
1986
影响因子：
3.5
通讯作者：
Paul C. Hess
中科院分区：
文献类型：
--
作者：
M. Dickenson;Paul C. Hess
实验测定了K_2 O-Al_2 O_3-SiO_2-Fe_2 O_3-FeO（KASFF）和K_2 O-CaO-Al_2 O_3-SiO_2-Fe_2 O_3-FeO（KCASFF）硅酸盐熔体中氧化还原比（FeO/FeO_（1.5））与组成的关系。组合物在1,450° C下在空气中用78摩尔% SiO2平衡。KASFF熔体具有1至5摩尔%的Fe 2 O3，并且包括两种过铝（K2 OAl 2 O3）组合物。KCASFF熔体具有1摩尔%的Fe 2 O3，包括过铝、偏铝（CaO+ K2 O> Al 2 O3）和过碱性成分。过碱性KASFF熔体与1摩尔%的Fe 2 O3具有低的和恒定的值的氧化还原比，而在过铝熔体的氧化还原比增加（K2 O/Al 2 O3）。增加总铁浓度增加过铝熔体中的氧化还原比，并略有降低过碱性熔体中的氧化还原比。在固定的总铁（1摩尔%）的CaO取代K2 O增加过铝和metaluminous KCASFF熔体的氧化还原比，但是，在过碱性KCASFF熔体的氧化还原比不受此交换。这些数据表明，Fe 3+是在四重协调，与K+或Ca 2+提供局部电荷平衡。四面体铁物种是最稳定的过碱性熔体和最不稳定的过铝熔体，由于在后者熔体中的电荷平衡阳离子之间的竞争Al 3+和Fe 3+。当Ca 2+提供局部电荷平衡时，四面体Fe 3+也不太稳定。这些数据与熔体中Fe ~（2+）的网络修饰作用相一致，反映了熔体组成对K ~+、Ca ~（2+）和Fe ~（3+）、Al ~（3+）在熔体中各组分间分配的影响。这些关系进行了讨论，在各种含铁和无铁熔体物种之间的均匀平衡。结果还反映了液体组成对交换电位μ Fe 3 + Al−1和μ Ca 0.5K −1的影响。在过碱性熔体中，交换势相对恒定，而在过铝质和偏铝质熔体中，交换势随着（CaO+ K2 O）/（CaO+ K2 O + Al 2 O3）和K2 O/CaO的减小而减小。这些定性观察意味着，表现出这些交换的矿物也将受到类似的影响，作为液体成分的变化。
The compositional dependence of the redox ratio (FeO/FeO1.5) has been experimentally determined in K2O-Al2O3-SiO2-Fe2O3-FeO (KASFF) and K2O-CaO-Al2O3-SiO2-Fe2O3-FeO (KCASFF) silicate melts. Compositions were equilibrated at 1,450° C in air, with 78 mol % SiO2. KASFF melts have from 1 to 5 mol % Fe2O3 and include both peraluminous (K2OAl2O3) compositions. KCASFF melts have 1 mol % Fe2O3 encompassing peraluminous, metaluminous (CaO+K2O>Al2O3) and peralkaline compositions. Peralkaline KASFF melts with 1 mol % Fe2O3 have low and constant values for the redox ratio, whereas in peraluminous melts the redox ratio increases with increasing (K2O/Al2O3). Increasing total iron concentration increases the redox ratio in peraluminous melts and slightly decreases the redox ratio in peralkaline melts. Substituting CaO for K2O at fixed total iron (1 mol %) increases the redox ratio in both peraluminous and metaluminous KCASFF melts; however, the redox ratio in peralkaline KCASFF melts is not affected by this exchange. These data indicate that Fe3+ is in four-fold coordination, with K+ or Ca2+ providing local charge balance. The tetrahedral ferric species is most stable in peralkaline melts and least stable in peraluminous melts, due to the competition between Al3+ and Fe3+ for charge balancing cations in the latter melt. Tetrahedral Fe3+ is also less stable when Ca2+ provides local charge balance. The data are consistent with a network modifying role for Fe2+ in the melt.The data are interpreted to reflect the effects of melt composition on the partitioning of K+ and Ca2+ and Fe3+ and Al3+ between various species in the melt. These relationships are discussed in terms of homogeneous equilibria between various iron-bearing and iron-free melt species. The results also reflect the effect of liquid composition on the exchange potentials μFe3+ Al−1 and μCa0.5K−1. The exchange potentials are relatively constant in peralkaline melts, but decrease in metaluminous and peraluminous melts as both (CaO+K2O)/(CaO+K2O+Al2O3) and K2O/CaO decrease. These qualitative observations imply that minerals exhibiting these exchanges will also be similarly affected as liquid composition changes.