【作者】 严俊；

【导师】 盛嘉伟；

【作者基本信息】 浙江工业大学 ， 应用化学， 2012， 博士

【摘要】 叶腊石(pyrophyllite)为一含水层状铝硅酸盐粘土矿物,化学式为Si4Al2O10(OH)2。因其优异的耐化学腐蚀、耐高温、较低的导电与导热及低膨胀等特性,而被广泛应用于陶瓷、涂料、塑料、橡胶、传压介质、耐火材料、填料、医药及吸附材料等领域。本课题研究中首先采用粉晶R射线衍射(XRD)、高分辨透射电镜(HRTEM)、选区电子衍射(SAED)、场发射扫描电镜(FESEM)、X射线荧光光谱(XRF)、傅立叶红外光谱(FTIR)等测试方法对浙江青田叶腊石的矿物学特征进行了较系统的研究；其次,分别就在热处理过程中叶腊石呈色的改变机制及机械力研磨过程中其微观形貌、物相变化特征进行了较深入的探讨。与此同时,对叶腊石草酸酸洗浸出液的析晶体的热处理后产物微结构及热相变进行了初步探讨；再次,采用高能球磨的方法结合喷雾干燥工艺制备出了分散的单层纳米板片与球形的叶腊石粉体；最后,采用机械力化学法制备了Ti02/叶腊石基复合颜料,并研究了复合配比、机械力球磨时间强度、物料颗粒粒径与复合颜料性能之间的相互关系。通过上述工作取得了以下主要结果：1.叶腊石矿物颗粒微结构中最基本的构成单元为纳米板片,且该板片多呈聚集态,单层板片面积大小不一,厚度约为(8±2)nm。原矿粉体的XRF分析结果表明青田叶腊石原矿混合物中SiO2与Al2O3的分子个数比为6.2,明显高于理想叶腊石中Si02与A1203的分子个数比4.0。HRTEM对叶腊石晶体结构的研究证实青田叶腊石具有典型的单斜晶系特征,该结论与叶腊石粉晶X射线衍射结论一致,且叶腊石原矿粉体的XRD结论证实其伴生矿为石英,该结论与XRF所获得的青田叶腊石的“富硅”特征吻合。此外,HRTEM结果表明叶腊石晶格结构中存在着较明显的晶体缺陷。同时,在高能电子束辐照作用下,叶腊石晶体结构发生了明显的结构破坏,并在辐照下最终转变为非晶态结构。2.叶腊石粉体在热处理过程中,随着煅烧温度的提高,叶腊石粉体的呈色出现由灰白色至淡红色并最终呈现雪白色的颜色渐变特征。相比于叶腊石原粉的片层状形貌结构特征,不同温度下煅烧后粉体微结构无明显改变,粉体在热处理条件下的呈色改变机制与粉体微结构及其中所含有机物成分无直接联系。笔者初步推测叶腊石中杂质元素Fe为该矿物致色的主要因素,且热处理温度决定Fe在叶腊石晶体结构中的赋存状态或者Fe3+/Fe2+量比,进而决定该矿物在不同温度下的呈色。3.在研磨过程中,叶腊石微粉颗粒粒径在逐渐减小,但随着研磨强度的进一步加大,粉体颗粒因其表面能的增大而出现团聚。不同研磨强度下,研磨后粉体的形貌存在明显差异。较大研磨强度下小颗粒粉体因团聚而呈“准球形”的团聚体,且随着研磨的进行团聚颗粒粒径逐渐增大。较低研磨强度下粉体随着研磨时间的延长呈粒径减小行为,但是叶腊石片层状形貌特征并不改变。4.在研磨过程中叶腊石粉体(原矿混合物)中的叶腊石红外光谱的变化表现出显著的惰性特征,该矿物中游离态二氧化硅是导致该叶腊石在研磨过程中出现红外惰性的直接原因。与此同时,在研磨过程中,叶腊石结构中的化学键的破坏也存在一先后的顺序,表现为：在研磨的最初阶段,叶腊石的1120cm-’处的特征谱带强度较迅速的减小,该现象表明硅氧四面体中Si-O键的破坏；随着研磨的进一步进行,连接在铝氧八面体中心原子A1上的-OH,其特征谱带为3673,948,854和835cm-1逐渐消失,该特征表明铝氧八面体结构在机械力作用下逐渐破坏；最后,在叶腊石研磨的最终阶段,代表Si-O-Al化学键的518cm-1谱带强度慢慢减小,上述现象表明,在机械力作用下,硅氧四面体与铝氧八面体框架结构在研磨的最终阶段受到破坏。5.研磨后叶腊石粉体的XRD与HRTEM测试表明,研磨作用使得叶腊石晶体结构发生明显改变,且由初期的叶腊石相生成偏叶腊石相,终产物为石英和无定形态铝硅氧化物,其中终产物中的晶态的石英源白叶腊石原矿中的伴生相。6.叶腊石原矿的草酸酸洗浸出液的析晶产物由铁、氧及少量的铝元素组成,上述析晶体产物的XRD结果表明其成份主要为FeOOH与H2C2O4·2H2O的混合相。浸出液蒸馏析出产物在焙烧过程中,随着焙烧温度的升高,铁氧体经历了由FeOOH→γ-Fe2O3→α-Fe2O3的物相转变。特别值得注意的是,HRTEM与SAED对析出晶体在不同温度下焙烧产物的物相分析与同一样品的XRD分析的结果存在极其明显的差异,该差异应归因于HRTEM中高能电子束对样品晶体结构的辐照影响所致。7.高能球磨、喷雾干燥联用工艺制备了干燥分散的单层纳米板片与球形叶腊石粉体。叶腊石粉体在初步研磨后,经喷雾干燥可得到分散的叶腊石纳米板片,板片厚度为(8士2)nm,其长轴粒径大小为0.2-1.2μm。粉体在较长时间的研磨并喷雾干燥后,可获得均匀粒径的准球形的叶腊石聚集体,其中单个球形微粒的直径约2.5μm,经进一步的FESEM观察,球形颗粒由直径为100nm左右的叶腊石纳米板片团聚形成。8.以叶腊石微粉为基底材料、金红石型钛白粉为包覆基质,利用内核化学表面改性与机械研磨的协同效应,实现叶腊石、钛白粉的类核壳包覆结构,制备得到新型的复合钛白粉体。HRTEM、EDX、粉体白度以及遮盖力测试结果表明钛白粉与叶腊石基质达到较好的包覆,复合粉体可实现颜料级别钛白粉的替代。更多还原

【Abstract】 Pyrophyllite (Al2Si4O10(OH)2), which exhibits good physicochemical characteristics, such as low thermal and electrical conductivity, low expansion coefficient, low reversible thermal expansion and excellent reheating stability, has been widely used in many industries, principally in ceramic, plant, plastic, rubber, pressure transmission medium, refractory material, filler, medical carrier and adsorption material.In the present work, the mineralogical characterizations of pyrophyllite from Qingtian were firstly investigated by using X-ray diffraction (XRD), high-resolution transmission electron microscopy (HR-TEM), X-ray Fluorescence (XRF) and Fourier transform Infrared spectroscopy (FTIR) and field emission-scanning electronic microscope (FE-SEM). Secondly, the efforts of grinding on structural alteration and phase transformation of pyrophyllite were discussed. At the same time, the phase transformation and crystal microstructure during heat-treatment for the leachate of pyrophyllite precipitation by oxalic acid were investigated. Next, Using spray drying technique combined with high energy ball milling for the preparation of dispread pyrophyllite particles with lamellar or spheroidal structure. Finally, the composite powder was prepared by using pyrophyllite and futile titanium oxide powder as the substrates and outer covered material respectively, and the relations between the quaitly of pigment and some facts, for example, milling time, particle size of pyrophyllite and futile titanium, the rate of pyrophyllite and futile titanium were investiged.Based on the above works, the main conclusions were drawn as following:1. A composite laminal structure of pyrophyllite is found, and the thickness of the lamina with irregular surface area is about (8±2) nm. The result of XRF shows the SiO2/Al2O3molar ratio is6.2, which is higher than that calculated for an ideal pyrophyllite (ratio=4.0). The crystal system of pyrophyllite from Qingtian deposit is monoclinic by powder HR-TEM analysis, and the monoclinic pyrophyllite is corroborated well by X-ray diffraction (XRD) analysis. Meanwhile, quartz is the associated phase in raw ore, and the fact is according with the characteristic of rich-silicon by XRF analysis. In addition, it is clearly found that the crystal defect exists in the microstructure of pyrophyllite. The high energy electron beam irradiation induces the changes in morphology of clay mineral particles, and that results in phase transformation from crystalline to amorphous.2. The coloring mechanism of pyrophyllite before and after heating were investigated by reflection spectra, chemical analysis, differential thermal analysis (DTA), Fourier transform Infrared spectroscopy (FTIR) and field emission-scanning electronic microscope (FE-SEM). The results show that the color of pyrophyllite powder is variable from grayish white to light pink and turns to the color of snow-white finally with increasing firing temperature. Compared to the original pyrophyllite, the laminal microstructure of pyrophyllite has no changed after high-temperature heating, and the microstructure and organic pigment do not play a role in the coloring of the pyrophyllite.3. The mechanical treatment by grinding produces a decrease in the particle size of original pyrophyllite with increasing time. With the increase of grinding intensities, the powder appears re-aggregation due to the high surface energy of active particle. The morphologies of pyrophyllite powder are different after grinding under different grinding intensities. The particles gradually have the characteristic of "torispherical" under high grinding intensitie, and the agglomerates are constituted by a greater number of welded particles with the increasing grinding intensity. On the other hand, the original lamellar structure does not changed as the gradual size reduction.4. The perverse characteristics of IR spectra reappear by intensive grinding, and the phase of quartz takes a mainly role in affecting the structural alteration. The rate of destruction of chemical bonds in pyrophyllite structure is not the same. It is shown as below, in the first step of milling, the peak at1120cm-1shows a rapid decrease in the intensity during the first step min of grinding and is absent from the IR spectrum of the sample, indicating breakdown of the Si-O bonds, namely, destruction of the tetrahedral sheets. As the grinding goes, the disappearance of the bands at3673,948,854and835cm-1indicates that OH groups, coordinating central atoms (mainly Al) in the octahedral, are released and octahedral sheets are damaged. Finally, the intensity of the band at518cm-1decreased partly with grinding time, indicating breakdown of the Si-O-Al bonds, namely, destruction of the linkages between the octahedral and the tetrahedral sheets.5. To our surprised, a sequential phase transformation from pyrophyllite, through the anhydride phase, eventually to amorphous alumina-silicate aggregates was firstly observed. Meanwhile, it is found that the quartz-containing pyrophyllite was resistant to the mechanical destruction. Furthermore, dry grinding can cause the lattice dilatation and some stacking faults, and the influence by grinding was more significant along the c-axis of silicate crystal structure.6. The characetristic of phase transformation and the crystal microstructure during heat-treatment for the leachate of pyrophyllite precipitation by oxalic acid were investigated by using high resolution transmission electron microscopy (HRTEM) coupled with energy dispersive X-ray microanalysis (EDX) techniques, selecting area electron diffraction (SAED) and X-ray powder diffraction (XRD). The following results are obtained:The crystallization consists of Fe, O and a little Al, and the constituents of that are mainly FeOOH and H2C2O4·2H2O, which is the heated product of the leachate of pyrophyllite precipitation by oxalic acid. A sequential phase transformation from FeOOH, through the y-Fe2O3, eventually to a-Fe2O3is observed as the temperature increasing. In addition, the crystal phases after annealing at the same temperature revealed by HRTEM are different from that obtained from XRD ananlysis. It is induced clearly that high energy electron-beam irradiation induced crystal structural change.7. The present study is focused on the procedure of spray drying technique combined with high energy ball milling for the preparation of dispread pyrophyllite particles with lamellar or spheroidal structure. To get the desired pyrophyllite particles but not amorphous alumina-silicon aggregates, the effect of grinding time by high energy ball milling (HEBM) on the resulting particles is studied. The products are characterized in terms of their crystalline phase, particle size, particle morphology, specific surface area and structural modifications. It has been observed that the dispersed pyrophyllite particles with lamellar or spheroidal structure are achieved using spray drying technique combined with high energy ball milling. Meanwhile, after ground for a certain time, pyrophyllite particle retains the same structural and crystalline character as original one after the composite treatment technologies. Furthermore, it is indicated that spray drying treatment coupled with HEBM yields smaller dispread particles with different physical characteristics, while the spray drying does not induce the crystal structure change.8.Using pyrophyllite and futile titanium oxide powder as the substrates and outer covered material respectively, the compound powder was got with using the cooperative efects of chemical and the mechanical surface modification, which had the characteristic of quasi-nuclear shell structure. The high resolution transmission electronic microscope, energy dispersion X-ray Spectrum, whiteness and hiding test results indicated the pyrophyllite surface was coated with titanium oxide better,the compound powder might take place ofthe pigment level titanium oxide powder.更多还原