The real structure of tobermorite 11Å:: normal and anomalous forms, OD character and polytypic modifications
The real structure of tobermorite 11Å:: normal and anomalous forms, OD character and polytypic modifications
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DOI：
10.1127/0935-1221/2001/0013-0577
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发表时间：
2001-05-01
影响因子：
2.1
通讯作者：
Armbruster, T
中科院分区：
文献类型：
--
作者：
Merlino, S;Bonaccorsi, E;Armbruster, T
通过X射线衍射研究了南非Wessel矿的11埃雪硅钙石样品（一种“异常”雪硅钙石）和俄罗斯乌拉尔Bascenov的11埃雪硅钙石样品（一种“正常”雪硅钙石）。它们的结构紊乱，由k奇数反射的扩散性证明，已经通过OD方法处理，这使我们能够导出可靠的结构模型，以定义两个主要的多型体（MDO结构），随后进行了改进，揭示了两个标本的独特结构细节。来自Weschromine的11埃雪硅钙石的MDO 1多型[正交晶系，空间群F2dd，a = 11.265（2），B = 7.386（1），c = 44.970（9）埃]被细化为R = 0.128，而对MDO 2多型[单斜晶系，空间群B11 m，a = 6.735（2），B = 7.385（1），c = 22.487（4）埃，γ 123.25（1）度]收敛到R = 0.051。对来自乌拉尔的样品的MDO 2多型进行了两次改进[空间群B11 m，a = 6.732（2），B = 7.368（1），c = 22.680（4）埃，伽马= 123.18（1）度]，数据采用常规源采集（R = 0.089）和同步辐射（R = 0.110）。共同的结构特征是平行于（001）的钙多面体的无限层，硅灰石型的四面体链沿着B延伸并附着在这些层的两侧。复合材料层沿c方向沿着堆积，并通过形成双四面体链连接，在Wavelimine和Urals样品中分别具有“理想”组成[Si_6O_（15）（OH）（2）]和[Si_6O_（16）（OH）]。最鲜明的功能：两个样品中最重要的成分是结构空腔的含量：而在来自Weasels矿的样品中只发现了水分子，在来自乌拉尔的样品中发现了“沸石”钙阳离子和水分子。这些结构方面进行了比较，并在解释不同的热行为的两种类型的雪硅钙石11埃表示其相关性。
Specimens of tobermorite 11 Angstrom from Wessels mine, South Africa, an 'anomalous' tobermorite, and from Bascenov, Urals, Russia, a 'normal' tobermorite, have been studied through X-ray diffraction. Their structural disorder, evidenced by the diffuseness of the reflections with k odd, has been dealt with through an OD approach, which allowed us to derive a reliable model of the structure, to define the two main polytypes (MDO structures), which were subsequently refined, revealing the distinctive structural details of the two specimens.The MDO1 polytype of tobermorite 11 Angstrom from Wessels mine [orthorhombic, space group F2dd, a = 11.265(2), b = 7.386(1), c = 44.970(9) Angstrom] was refined to R = 0.128, whereas the refinement carried on the MDO2 polytype [monoclinic, space group B11m, a = 6.735(2), b = 7.385(1), c = 22.487(4) Angstrom, gamma 123.25(1)degrees] converged to R = 0.051. Two refinements were carried out for the MDO2 polytype of the specimen from the Urals [space group B11m, a = 6.732(2), b = 7.368(1), c = 22.680(4) Angstrom, gamma = 123.18(1)degrees] with data collected with conventional source (R = 0.089) and with synchrotron radiation (R = 0.110).Common structural features are the infinite layers of calcium polyhedra, parallel to (001), with tetrahedral chains of wollastonite-type running along b and attached on both sides of these layers. The composite layers are stacked along c and connected through formation of double tetrahedral chains, with 'ideal' composition [Si6O15(OH)(2)] and [Si6O16(OH)] in the specimens from Wessels mine and Urals respectively. The most distinctive feature: of the two specimens is the content of the structural cavities: whereas only water molecules were found in the specimen from Weasels mine, 'zeolitic' calcium cations and water molecules were found in that from Urals. These structural aspects are compared and their relevance in explaining the different thermal behaviour of the two types of tobermorite 11 Angstrom is indicated.