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K22CaSi44O1010: A novel phase in the ternary system K22O–CaO–SiO22and member of the litidionite group of crystal structures
【文件类型】 【消费金额】0.3 【文章页数】1 【会员操作】  
【文章作者】Schmidmair Daniela;Kahlenberg Volker;Grie?er Anja
【文章摘要】      Abstract

The main goal of this work was to verify whether a phase with composition K2CaSi4O10exists in the ternary system K2O‐CaO‐SiO2. Therefore, a series of solid‐state reactions of stoichiometric mixtures of K2CO3, CaCO3and SiO2was performed at 800 and 900?C which, indeed, resulted in the formation of this previously unknown potassium calcium silicate. More detailed characterizations of this compound were based on single‐crystal X‐ray diffraction experiments. Basic crystallographic data are as follows: triclinic symmetry, space groupP‐1,a= 7.0915(7) ?,b= 8.4211(9) ?,c= 10.2779(12) ?, α = 104.491(10)°, β = 100.570(9)°, γ = 113.738(9)°,V= 515.26(10) ?3,Z= 2. Structure solution was performed by direct methods. Subsequent refinement calculations using anisotropic displacement parameters for all atoms converged to a residual ofR(|F|) = 0.0355 for 1889 independent reflections withI> 2σ(I). From a structural point of view K2CaSi4O10belongs to the so‐called litidionite family of A′AMSi4O10compounds for which several natural and synthetic representatives have been described in the literature. Actually, it is the first member where the A′‐ and A‐positions are exclusively occupied by K‐ions. Following the nomenclature for oxosilicates K2CaSi4O10can be allocated to the group of the tubular chain silicates. Fundamental building units are loop‐brancheddreierdouble chains (running parallel to [100]) which can be described using the following structural formula: {lB,21}[3Si8O20]. Ca‐ions are coordinated by 5 nearest oxygen neighbors in form of distorted trigonal bipyramids. By sharing a common edge two adjacent bipyramids are linked into [Ca2O8]‐dimers providing linkage between consecutive tubes in the direction of thec‐axis. Charge compensation is achieved by the incorporation of the larger potassium ions into cavities of the heteropolyhedral network. Powder X‐ray diffraction patterns of the bulk material of the synthesis products revealed that, additionally to K2CaSi4O10, the 800°C ‐sample contained K8CaSi10O25and at least one further, yet unknown crystalline phase. This unidentified so‐called 22‐? compound was also present in the 900 °C‐specimen together with K2CaSi4O10and K2Ca4Si8O21. Our proof of existence of K2CaSi4O10is a further step towards a better understanding of the ternary system K2O‐CaO‐SiO2and provides a basis for identification and quantification of this compound in phase analysis. It corrects earlier phase‐analytical studies on this system which is of relevance for applied and technical mineralogy including different types of residual materials such as slags or ashes from biomass combustion. The results of our investigation show that even comparatively simple ternary oxide systems are not as well understood as expected.

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【卷】101【ISSUE】2【ISSUEID】815B0005    【文章期份】2018    【发布日期】2018/8/28 16:25:10    点击率:0    打印    关闭
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