【作者】 沈毅；

【导师】 姚书振； 李珍；

【作者基本信息】 中国地质大学 ， 矿物学、岩石学、矿床学， 2012， 博士

【摘要】 钨是一种高熔点、高硬度的稀有金属,至18世纪以来,钨的探索和应用就一直引起了广泛关注。钨和钨合金具有高强度、高密度、低热膨胀系数,抗腐蚀性以及机械加工性良好等综合性能,因而在航空航天,船舶,原子能,电子、电气工业、军事装备、汽车工业及化学工业等多个领域具有广泛地应用。除钨及其合金外,钨的氧化物以其独特的物理化学性能,在缓蚀剂和催化剂等多个方面具有很大的利用价值而成为长期的研究热点。因此,钨资源对于一个国家来说,具有十分重要的战略意义。我国有丰富的钨资源,保有储量、产量以及出口量均居世界第一。世界上主要的钨矿有十多种,而我国主要的钨矿品种有两种,即黑钨矿((Mn,Fe) WO4)和白钨矿(CaWO4).虽然我国储量组成为白钨矿居多,黑钨矿比较少,但是长期以来,我国钨矿开采的对象大多是黑钨矿。而在钨矿产资源的高端产品的研发和利用领域,白钨矿的应用价值及可能性要明显高于黑钨矿。在这种背景之下,对于如何有效地控制钨产品的供给,科学而有效的建立产业发展模式显得格外的重要。而白钨矿具有大量有益而特殊的性能已成为目前的研究热点。白钨矿(scheelite),是一种简单岛状的钨酸盐矿物,其中钨和钼可以呈同象置换,因而实际白钨矿晶体,主要是由钨酸盐(MeWO4,Me: Ba、Sr、Ca)和钼酸盐(MeMoO4, Me: Ba、 Sr、Ca)晶体组成,属于四方晶系。白钨矿晶体结构非常稳定,具有耐高温、高压的突出优点。这也为其在某些应用领域上成为首选材料,提供了重要的科学的依据。白钨矿,也是一类自激活荧光材料,具有十分优良的发光性能。在闪烁计数器、激光、探测、发光和显示等多个领域都有很大的应用潜力。此外,白钨矿型的钼酸盐、钨酸盐晶体,大多都是重要的闪烁体或是X射线发光体,会在紫外光的作用下发出从浅蓝到黄色的光谱。在荧光、激光等光电材料中起着十分重要作用,已经在超大屏幕显示和器发光二极管等多个方面获得了应用,在气敏元件、显色材料以及变色材料等方面也存在着广阔的应用空间。应当指出的是,目前真正广泛应用于高附加值功能材料的白钨矿多为人工合成,所以大量的研究仍然集中于白钨矿的合成领域。而天然的白钨矿因选矿困难,且精选纯度低等缺陷的影响导致其在高端功能材料领域的应用并不乐观。因此,为了有效拓宽我国白钨矿资源在高端功能材料的应用领域,促进我国钨资源的有效利用,深入研究天然白钨矿成为研究的热点。天然白钨矿粗选后的精矿中仍存在有大量的细粒萤石、方解石等脉石矿物。因此目前大量的研究集中于对白钨矿精矿提纯的研究,其中典型的方法有“彼得罗夫法”、常温浮选等,并且也有大量的研究者们对传统的精选选矿法做出了一定的改进,但在目前的常规方法下,白钨矿的纯度仍然不足以应用于高附加值的功能材料中。若要继续提纯天然白钨矿,则要采取特殊的化学的方法和仪器设备。目前已有的深入提纯的化学方法可以进一步提高天然白钨矿中的钨含量,但是这些方法将破坏白钨矿的化学组成及晶体结构而形成新的高纯钨的氧化物。同时,需要注意到的是：虽然白钨矿具有前文所述多种优点,但是由于白钨矿晶体结构对称性较好,在光／电激发条件下之下,其相关受激性能活性较低,使其在高附加功能材料的使用上有较大的困难和局限。鉴于上述现状,进一步提纯白钨矿精矿,再以白钨矿为前驱体制备氧化钨(WO3)的研究逐渐进入研究者们的视野。而且目前这方面的研究已经有了一定的进展,例如：张永安等采用活性炭吸附和乙二醇净化法成功地制备出了高纯三氧化钨。这一全新的白钨矿研究视角的出现,为扩展了白钨矿将来的发展与应用方向注入了新的希望。WO3是一种禁带宽度约为3.25eV的n型半导体材料,其结构可看作是钨氧八面体以角氧相连,构成的三维网状结构。是目前备受关注的一种典型的宽禁带半导体,由于其具有优良的光电化学性能,因而在变色、催化、敏化等领域具有非常广泛的应用范围。而目前白钨矿精矿进行酸化处理提高钨纯度的产物是有可能形成WO3的,冈此,将天然白钨矿精矿进行深入提纯,转而制成WO3不仅能有效解决天然白钨矿精矿在高附加值功能材料的利用范同局限这一现状,也能提高我国向钨矿资源的利用效率。WO3具有多种优秀的功能特性,而其中光致变色性是最近该类材料山现的新的研究方向,WO3的光致变色性能使之在变色窗、信息存储、汽车反光、镜人面积信息显示屏等多个领域都有着十分广泛的应用前景,因而成为了研究的热点。某些物质在一定波长的光的辐照下会发生颜色的变化,然后又会在光、热的作用或避光的情况下恢复原来的颜色,物质这种在光的作用下颜色发生可逆性变化的现象,称为光致变色性。光致变色现象最早是在生物体内被发现的,距今己有一百多年。上世纪40年代就发现了有机化合物的光致变色现象。随着研究的深入,光致变色材料的独特优势使它快速的朝着实崩化、产业化的方向进展。近年来,在全球范围内,将光致变色材料用于光调控、光信息存储、光学器件材料、光开关、修饰基因芯片材料、光信息基因材料等领域已成为关注焦点之一。WO3具有三斜,单斜,正交,四方,六方及立方六种品型,其中只有某些介稳晶型并且具备特殊形貌的WO3才可能具有光致变色性能。目前,有关WO3光致变色性能的研究尚不多见,而且很难制备出具有较为良好光致变色性能的WO3材料,因此,如何有效提高WO3材料的光致变色性能是研究的热点之一。WO3材料分为粉体材料与薄膜材料两大类,目前涌现出大鼙繁杂的制备方法,来获取良好性能的WO3材料。其中水热法因其经济、易操作、产物形貌可调控等优点而广为使川。WO3材料所具有的光致性能很人程度上取决丁其纳米结构单元的尺寸、形貌及其组装的特殊结构。冈此,特殊分级结构和形貌氧化钨材料的制备与性质研究一直是倍受人们关注的内容。在具有光致敏感性能的WO3粉体材料的研究领域,具有空心球结构的WO3材料,一直都是国内外学者研究的热点所在,这是由于空心结构不仅具有比表面积较人、密度低等十分显著的优点,而且该结构具有的内部空间还可以用来容纳一定尺寸人小的分子,这种内部部分封闭的空间将对受激光源形成光路谐振,增强光吸收效率,改善光致性能,像这种结构类似于微观包裹,往往会具备一些新性能。而这些优点也使得具有空心结构的氧化钨粉体颗粒成为了一种具有十分广泛的应用前景的新型光致材料。但是迄今为止,基本上人多数用于空心球的合成方法都是依赖牺牲模板的方法,例如硬模板法、软模板法。这也就使得要想产生内部具有空心结构的材料,需要用锻烧或溶解的方法来去除模板,又由于钨基氧化物因为价态的复杂性使得在模板的去除过程中会导致壳层的不稳定,而到合成后期往往会使已成型的空心球结构发生坍塌。因此对于W03微纳米球的制备上仍存在一定的难度,关于W03空心微球的报道也并不多。论文中采用钼离子调控法,以白钨矿为钨源,钼酸钠为钼源,经简易的酸化提纯和水热合成过程,成功获得了空心球结构的WO3粉体,由于无机离子能在析晶前构造一个有组织的微反应环境,该环境有决定了无机物成核的位置和形成晶体的功能,故采用无机离子修饰可能成为合成具有空心球特殊形貌的WO3粉体有效策略。经测试分析发现,空心球的W03粉体为六方相W03,且表面呈现刺球状结构,比表面积为101.8m2g-1是基础样的3.5倍,且带隙和能级间距变窄。除此之外,软模板法合成中空心结构实验方法简单,条件温和。通常软模板法需要先引入表面活性物质分子,然后通过有机溶剂或氧化等手段取核,以得到微纳米空心球结构。而气泡在具有普通软模板法的优点之外,同时避免了表面活性剂的引入和去除。据此,我们还提供了另一条有效制备空心球结构的WO3粉体的途径：白钨矿为钨源,双氧水和草酸为添加剂,采用H202分解产生的O2气泡作为模板,经水热合成之后也成功制备出了W03空心球,经XRD研究显示,该产物同样为六方相氧化钨,而且气泡为模板合成的样品结晶性优于基础样,这可能是由于气泡的引入减缓了其成核过程,有利于晶体的长大所致。SEM照片显示加入H2O2后合成粉体为大量直径约为0.7μm且大小均一的微球,从进一步放大的照片可以发现空心结构颗粒由长度约为200nm左右的纳米棒堆积而成。空心球结构的WO3的比表面积为基础样品的2倍左右,且吸收带发生明显的红移。两种途径所制备的WO3空心结构颗粒均具有更加优异的光致变色性能,这可能是由于空心球结构特殊的光子限域作用,样品比表面积的增加,以及WO3空心球带隙的减少有效的增加了光生电子空穴的数目所致。以白钨矿精矿为前驱,合成光致变色WO3薄膜材料是另一类应用形态,在WO3薄膜材料的研究领域,制备不同分级结构的WO3薄膜,以提高其相关性能是研究关键点之一。论文中采用白钨矿精矿为钨源,酸化纯化后水热沉积法在玻璃基片上生长WO3薄膜,并通过调整水热反应体系的环境实现对W03薄膜形貌结构的调控。因此实施方案一：仍然以白钨矿为钨源,以盐酸、硫酸和硝酸为诱导剂,合成了三种由棱柱组装而成的不同形貌的W03分级结构薄膜,经XRD和SAED结果分析,产物为六方相W03。薄膜表面空隙的产生,可能是由于通过含氧酸引入了氧基团。氧基团被吸附在WO3薄膜表面使得四方棱柱具有较大的极性,造成了棱柱间的排斥生长。且由于拱桥效应,WO3薄膜的比表面积会显著地增加。尤其HN03的加入会给W03薄膜提供更高的成核位垒。进而用硝酸合成的W03薄膜表面空隙更大,结构单元排列更松散。具有更优异的光致变色性能。实施方案二：在上述的基本基础之上,把不同的酸诱导剂改成小分子有机物来作为体系的诱导剂,从而调控薄膜的形貌结构,最终达到优化WO3薄膜光致变色性能的目的。采用乙醇与草酸这两种常见的小分子有机物为诱导剂,来制备样品。XRD结果显示添加诱导剂与未添加诱导剂的WO3薄膜均为六方相W03。SEM结果显示,无诱导剂的W03薄膜为有序纳米杆阵列结构,乙醇和草酸作诱导剂分别合成了“桔瓣”和“花椰菜”状分级结构的WO3薄膜,这种新颖的分级结构WO3薄膜以其疏松多孔结构、大的外露面积等优点,而具有更加优良的光致变色性能。更多还原

【Abstract】 Tungsten is a kind of rare metal that possessing high melting point and high hardness. From the18th century, large attention has been paid on the exploration and application of tungsten. Tungsten and tungsten alloy show wide application in the aerospace, marine, atomic energy, electronics, electrical industry, military equipment, automobile industry, chemical industry, and other fields, ascribed to their good comprehensive performances including high strength, high density, low thermal expansion coefficient, corrosion resistance and good machinability. In addition, tungsten oxide has also draw much attention in a long time because of its great utilization value in corrosion inhibitor, catalyst and many other fields. As a consequence, it can be conclude that the tungsten resources are of important strategy significance for a country.Tungsten resources are extremely rich and of highly centralized distribution in our country, the reserves, production and exports of which are all ranked first in the world. Although there are ten kinds of tungsten ores in the world, our country mainly owns two of them, that is, wolframite ((Mn, Fe) WO4) and scheelite (Ca (WO4)). Although reserve of scheelite is larger than wolframite in our country, mining object of tungsten ores major is wolframite for a long time due to the much rich ore and facile mining and beneficiation. However, as high-end products of tungsten ores, the application value and research feasibility of scheelite are much higher than wolframite. Therefore, it is very significant to efficiently control the supply of tungsten products and establish an industrial development pattern. Scheelite has stimulated great interest due to the large number of valuable and special performances.Scheelite (CaWO4) is an island of tungstate mine, and the tungsten can be replacement as isomorphism by molybdenum. As a result, scheelite crystal is composed of tungstate crystals (MeWO4, Me:Ba、Sr、Ca) and molybdate crystals (MeMoO4, Me:Ba、Sr、Ca), which belongs to tetragonal system. The crystalline nature of scheelite is very stable, which can resistance to high temperature and high pressure. Indeed, this advantage provides vital scientific evidence for scheelite as a preferred material in some application. Scheelite is also a self-activation fluorescent material and bears excellent luminescence property, which shows great potential application in scintillation counter, laser, detection, luminous and display, and other fields. Moreover, most tungstate crystals and molybdate crystals from scheelite are important scintillator or X ray illuminant, which can give out many spectrum from shallow blue to yellow under the UV light excitation. Thereby, scheelite plays an important role in fluorescence and laser photoelectric material, and has been widely applied in large screen display and light emitting diode. Besides, scheelite has also broad application space in gas sensitive element, color materials and off-color material, etcIt should be pointed out that almost all scheelite is artificially synthesized which is really used in high value-added functional materials, so that there are many researches have been focus on the synthesis of scheelite at present. While natural scheelite is seldom applied in high functional materials in fact, result from difficile beneficiation and low purity. For this reason, in order to effectively broaden the application in high-end functional materials field of scheelite resources and promote the utilization of resources of our country, the in-depth study of natural scheelite is going to be a focus. Many gangue minerals such as fine grained fluorite and calcite still exist in the natural scheelite after rough concentration. Accordingly, at present a lot of researches have focused on concentrate purification, such as Petrov’s method and Plants.the flotation. Despite of the certain improvement on the traditional method made by a lot of researchers, the purity of scheelite still is not meet the needs to be used high value-added functional materials. Continue to purify natural scheelite requires some special chemical methods and instruments. The existing further purification methods can further improve tungsten content from the natural scheelite, but these methods would desdroy chemical composition and crystal structure of scheelite. Meanwhile, it is noted that although scheelite has many advantages mentioned above, the related performance activities are still relatively low under the light/electric excitation, because the crystal structure symmetry of scheelite is good, which results in great limitations on the use of the high additional functional materials.Based on the present situation, a research strategy about further purifying scheelite and then preparing another kind of high-end product of tungsten resources, tungsten oxide, with scheelite as precursor gradually come into the researchers view. At the same time, the research of this aspect has certain progress at present. For example, Zhang et al. using scheelite for tungsten source successfully prepared the high purity tungsten trioxide by activated carbon adsorption and ethylene glycol purification method. This study injected new hope to expand future of development direction and application of the scheelite.WO3is an n-type semiconductor material, band gap is about3.25eV. The structure of WO3can be regarded as [WO6] octahedral linked together by corner-sharing, and results in a three-dimensional network structure. As a typical wide bandgap semiconductor, WO3has attracted much attention due to the excellent photoelectric properties, which makes it for wide applications in color, catalysis, sensitization, etc. At present, it is possible to prepare WO3by acidifying the scheelite to achieve improvement of tungsten content. Accordingly, further purifying scheelite and then turning it to WO3, not only can effectively solve the limited application of natural scheelite in high value-added functional materials, but also can improve the utilization efficiency of scheelite resources of our country.WO3has many excellent performances. Among them, photochromic property recently is the new research direction of this material. WO3has been regarded as promising applications in the smart window, information storage media, automobile reflective mirror, large area information display and so on, which makes it become the research focus. The photochromism refers such a phenomenon that materials can change color in a reversible way by electromagnetic radiation. The reverse process can take place by the effect of heat and light in the dark. The photochromism was first phenomenologically observed in organisms, which dates back to more than one hundred years. In the1940s, photochromic phenomenon has already been found in the organic compounds. As research continues, photochromic materials are fast developed towards the practical direction and industrialization because of their unique advantages. In recent years, it has become the focus of attention that photochromic materials are applied in light regulation, optical information storage, optical device materials, optical switch, modification gene chip materials, optical information genetic material and many other fields around the world.WO3has six kinds of crystal type including triclinic, monoclinic, orthogonal, tetragonal, hexagonal and cubic phase. While only those WO3productions that possess some metastable crystal types and special morphologies may have photochromic properties. Since it is still a challenge to prepare WO3materials with good photochromic properties, pepole seldom do research in the photochromic property of WO3. Thus, how to effectively improve photochromic properties of WO3materials has attracted increasing interest. WO3materials contain powder materials and thin film material. Up till now, a large number of preparation methods have been explored to obtain WO3materials with improved properties. Among them, hydrothermal method is extremely popular because of its economic, operation facile, morphology controllable etc. features. Just as the photochromic properties of WO3materials depend not only on WO3units’shape and size, but also on their morphologies and arrangement. Therefore, it has drawn much attention about the preparation and properties of WO3with special hierarchical structure and morphologies.As for the investigation of photo-sensitive WO3powders materials, hollow ball structures have been favored. Because hollow ball structures usually have high surface area and low density, and the internal space of hollow ball can hold molecules with certain size, which conducive to the utilizing efficiency of luminous energy due to the effect of photons localization and improve the photochromic properties of WO3. These advantages make WO3hollow structure show a broad application prospect as a new type of optic material. However so far, most synthetic for obtaining hollow ball often need to remove template including hard template and soft template by dissolving or calcining. Meanwhile, the shell of hollow structure will be instable when the templates are removed due the multiple valence states of tungsten base oxide, which often results in the collapse of hollow ball structure with the synthesis proceeding. Therefore, it is still difficult to prepare WO3micro/nanospheres, and there is seldom report about the WO3hollow sphere.In this project, WO3hollow spheres were successfully obtain by molybdenum ion regulating method together with a simple acidification purification and hydrothermal synthesis process, which uses scheelite for tungsten source, sodium molybdate for molybdenum sources. Indeed, inorganic ions could construct an organized reaction environment before crystallization, which can play an important role on the nucleation position and the formation of crystal. Hence, it may be an effective strategy that using inorganic ions regulating method to synthesize WO3powder with hollow spherical structure. From the characterization results, it is revealed that as-prepared powder is urchin-like and the crystal belongs to hexagonal phase structure. The surface area of the hollow sphere sample is101.8m2g-1(3.5times as high as the standard sample) and the band gap is decreased.In addition, soft template synthesis method to synthesize hollow structure is simple and mild. In general, soft template synthesis method firstly needs to introduce surfactant molecules into reaction system, and then remove the core through organic solvent or oxidation, ultimately obtain micro/nano hollow sphere structures. Moreover, bubble not only possessing advantages of ordinary soft template synthesis method, but also avoided introducing and removing the surfactant. Therefore, we provide another effective route to manufacture hollow sphere structure. Namely, the approach uses scheelite for tungsten source, hydrogen peroxide and oxalic acid for annexing agents, oxygen generated by hydrogen peroxide decomposition for template. In the consequence, we successfully obtained WO3hollow sphere with hydrothermal route. The analysis of XRD revealed that product is hexagonal structure of WO3as well, and crystallinity of samples synthetized with bubble as template is superior to standard sample. It is guessed that the nucleation process is slowed down due to the introducing of bubble, and it is beneficial to the growth of crystal. SEM patterns indicating that the synthetic powder is composed with a mass of microballoons whose diameter is0.7μm and sizes are uniform after the addition of H2O2. And from the further enlarged photograph, it could be found that particles with hollow structure are accumulated with nanorods whose length is near200nm. Specific surface area of WO3with hollow structures is twice larger than standard samples, and its absorption band occurred to an obvious red shift.The WO3hollow sphere structures prepared though this two approach bear improved photochromic properties, which may due to photons localization and large exposed area of the porous films together with the decreased band gap that is in favor of the production of electron-hole pairs.Using scheelite as precursor to synthesize photochromic WO3film material is another application approach. As for WO3film, it is attractive to prepare WO3film with various hierarchical structures, and as a result to improve the property. In this paper, scheelite was used as tungsten source and was acidified to purification. The WO3films were generated on the glass substrates, and we realized the controllable synthesis of morphologies of WO3films by modulating the hydrothermal reaction conditions. Method one:Three kinds of WO3hierarchical structure films assembled by tetragonal prisms were synthesized by using scheelite as tungsten source together with hydrochloric acid, sulfuric acid and nitric acid as inducer. The XRD and SAED results show that products are hexagonal WO3. Oxyacid introduced oxygen groups, which may result in generation of porous structure on surface of WO3films prepared with sulfuric acid and nitric acid. Because oxygen groups were absorbed on the surface of WO3films, which would makes tetragonal prisms to possess relative high polarity and be mutually exclusive assembled. As a result, surface area of WO3films was evidently increased due to bridge effect. Especially, WO3films prepared with nitric acid had higher nucleation barrier so that the pores on the surface of film were bigger, structure units were arranged more loosely. Thus WO3films prepared with nitric acid preformed better photochromic properties. Method two:The same preparation method was done using small molecule organics instead of inorganic acid to control the films’morphologies. Consequently, photochromic properties of WO3films were improved. In this route, ethanol and oxalic acid were using as inducer to in the preparation process of samples. Films prepared without capping agents were ordered nanorod arrays, while the ones obtained with ethanol and oxalic acid revealed peeled-orange-like and cauliflower-like hierarchical structure arrays, respectively. Both of the two hierarchical structures were composed of much thinner nanorods compared with the one obtained without capping agents. All the WO3films exhibited good photochromic properties and the two with inducers performed even better, which could be due to the loose porous structure and big exposed area.更多还原