长白山硅藻土热处理相变及方英石形成机制探讨  

HIGH-TEMPERATURE TRANSFORMATION OF CHANGBAISHAN DIATOMITE AND THE FORMATION MECHANISM OF CRISTOBALITE

作　　者：肖万生[1] 陈晋阳[1] 翁克难[1] 彭文世[1] 王冠鑫[1] 王辅亚[1] 

机构地区：[1]中国科学院广州地球化学研究所,广东广州510640

出　　处：《矿物学报》2005年第1期20-26,共7页Acta Mineralogica Sinica

基　　金：中国科学院知识创新工程重要方向项目(No.KJCX2 SW N03);国家自然科学基金(批准号:40302012)

摘　　要：在常温到1250℃温度范围对吉林长白山硅藻土和非晶态SiO2进行热处理,并对热处理后的样品进行红外光谱和X射线衍射测试,结果表明长白山硅藻土在1100℃开始转变成方英石,非晶态SiO2在1200℃开始形成方英石,它们的转变温度均处于鳞石英的热力学稳定区。方英石这种热力学亚稳态形成机制与硅藻土和非晶态SiO2的中程有序结构与方英石结构类似有关,这种结构相似性有利于降低了方英石成核所需的活化能从而有利于方英石成核作用的发生,因而在硅藻土(非晶态SiO2)→方英石→鳞石英的系列转变反应中,硅藻土→方英石的反应占主导,而在相应的温度条件下,方英石→鳞石英的相变几乎是被禁止的。长白山硅藻土与非晶态SiO2转变成方英石存在大约100℃的温度差异,主要与硅藻土独特的结构缺陷及Na、Al等杂质元素存在有关。高温下Si OH基团的脱水反应使硅藻土结构中以OH-形式存在的非桥氧变成桥氧,原来的结构缺陷消失,有利于降低方英石的形成温度;而Na、K、Ca、Fe等杂质元素与SiO2形成多组份体系,导致SiO2结晶温度降低,它们强的扩散特性,还有利于提高孤立Si OH基团的脱失速率和缺陷迁移速率,并增加方英石的稳定性。The samples of Changbaishan diatomite and amorphous silica (99.9% purity) were thermally treated at 1250 ℃. The products were analyzed by X-ray diffraction and FTIR. The results showed that Changbaishan diatomite was transformed to cristobalite at about 1100 ℃ and amorphous silica at about 1200 ℃, which are in the thermodynamic stable condition of tridymite. The authors proposed that the metastable formation mechanism of cristobalite is controlled by dynamical process and is related to the similarity in the intermediate range order structure between diatomite/amorphous silica and cristobalite, which lowed the nucleation activation energy of cristobalite so that the nucleus of cristobalite was easy to form. In the serial reactions of diatomite/amorphous silica→cristobalite→tridymite, the reaction of diatomite/ amorphous silica that is transformed to cristobalite is dominant to the reaction of cristobalite to tridymite, and the latter transformation reaction is almost prohibited under experimental temperature conditions. The temperature difference of about 100 ℃ between Changbaishan diatomite and pure amorphous silica is possibly related to the defects and impure elements such as Na, Al in diatomite. An essentially large amount of water in diatomite is propitious to lower the transformation temperature of amorphous silica to cristobalite. The dehydration of Si-OH group under high temperature led to the transformation of abridging oxygen of OH to bridging oxygen, which caused the disappearance of structure defects and formed the long-range order structure of cristobalite. Impure elements such as Na, K, Ca, Fe formed the multi-component system with SiO_(2), which lowered the crystalline temperature of SiO_(2). On the other hand, the strong diffusion property of impure elements is favorable to promoting the dehydration velocity of Si-OH group and defects transfer ratio, and also increasing the structural stability of cristobalite.

关 键 词：硅藻土 非晶态SiO2 方英石 相变机制 长白山 热处理 扩散特性 

分 类 号：P578.94[天文地球—矿物学]