【作者】 江红涛；

【导师】 王秀峰；

【作者基本信息】 陕西科技大学 ， 材料学， 2013， 博士

【摘要】 硅酸铋（BSO）及含铋（Bi）氧化物系统具有一系列独特的声光、光电、介电等性能，可以用来制备发光材料、闪烁材料、电介质材料等高新材料，在材料、化工、国防、工业等领域有着广泛的应用。目前对于该系统的研究主要集中在晶体生长、性能改善、粉体制备等方面，而对于该系统在熔融及冷却过程中熔体结构和性质的研究却相对较少。探明硅酸铋熔体的结构和性质对了解硅酸铋晶体生长机理以及改进和提高硅酸铋晶体生长速度和质量无疑具有重要意义。而硅酸铋粉体是制备适合熔体的先决条件。因此，研究硅酸铋粉体制备对掌握硅酸铋熔体结构和性质有着重要的意义。本文主要研究了硅酸铋粉体制备和熔体性能。通过固相法和熔盐法分别制备了Bi₄Si₃O₁₂粉体和Bi₂SiO₅粉体，研究了相关的工艺参数，并探讨了形成机理。研究了熔体密度、表面张力等熔体性能以及熔体结构。在以下几方面获得了创造性成果：（1）采用固相法制备了较纯的Bi₄Si₃O₁₂粉体。以氧化铋和二氧化硅为原料，在乙醇中球磨5h，在830℃煅烧3h制得较纯Bi₄Si₃O₁₂粉体。在均匀实验中因素主次关系可知，煅烧温度对杂相数目的影响显著，其余因素为不显著。（2）采用NaCl-KCl熔盐制备了较纯的Bi₄Si₃O₁₂粉体，颗粒微观形貌主要以颗粒状与片状为主，同时利用NaCl-Na₂SO₄熔盐制备了纯相Bi₄Si₃O₁₂粉体，颗粒微观形貌主要为多面体。在NaCl-KCl熔盐系统中，以氧化铋和二氧化硅为原料，盐含量为40wt%，Bi₂O₃过量5wt%，在780℃煅烧4h制得较纯Bi₄Si₃O₁₂粉体。Bi₄Si₃O₁₂粉体的激发光谱和发射光谱分别位于266nm和457.6nm，和晶体材料相比，激发光谱和发射光谱显示蓝移。采用NaCl-Na₂SO₄系统用熔盐法制备Bi₄Si₃O₁₂粉体时，以氧化铋和二氧化硅为原料，盐含量40wt%，在850℃煅烧3h制得纯相Bi₄Si₃O₁₂粉体。Bi₄Si₃O₁₂的禁带宽度为2.44eV，Bi₄Si₃O₁₂粉体的激发光谱和发射光谱分别位于270nm和462nm，和晶体材料相比，激发光谱和发射光谱显示蓝移。通过比较两种熔盐系统中制备Bi₄Si₃O₁₂粉体的表观活化能可知，在NaCl-Na₂SO₄熔盐体系下较易形成Bi₄Si₃O₁₂粉体。通过比较固相法和熔盐法制备Bi₄Si₃O₁₂粉体的纯度和微观形貌可知，熔盐法更易制得纯相Bi₄Si₃O₁₂粉体，颗粒的形状和尺寸更容易控制。（3）采用NaCl-KCl熔盐和NaCl-Na₂SO₄熔盐制备了较纯的Bi₂SiO₅粉体，颗粒形貌为片状。在NaCl-KCl熔盐体系下，以氧化铋和二氧化硅为原料，盐含量30wt%，690℃下煅烧0.5h制得较纯的Bi₂SiO₅粉体。SEM观察表明Bi₂SiO₅粉体分散性较好，片状长度大约为1-4μm。采用NaCl-Na₂SO₄系统用熔盐法制备Bi₂SiO₅粉体时，以氧化铋和二氧化硅为原料，盐含量40wt%，625℃下煅烧1h制得较纯的Bi₂SiO₅粉体。通过比较两种熔盐系统中制备Bi₂SiO₅粉体的表观活化能可知，在NaCl-Na₂SO₄熔盐体系下较易形成Bi₂SiO₅粉体。（4）采用高温热台配合偏光显微镜对Bi₁₂SiO₂0多晶粉体的熔融过程进行原位实时观察。熔融过程大致可分为以下三个阶段：多晶粉体熔化阶段、分相阶段（亚稳分相阶段和不稳定分相阶段），均一性阶段。在亚稳分相阶段，熔体中广泛分布着大量黑色斑点状结构，其结构随着熔体温度升高会越来越明显；在不稳定分相阶段，随着温度的变化熔体中主要存在两类不同的结构，一类为环状互锁结构，另一类为蠕虫状的滴状结构，且在分相过程中熔体中两相存在着明显的随温度运动的分界线。更多还原

【Abstract】 Bismuth silicate （BSO） and Bi-contained oxide have many uniqueproperties such as acousto-optic, photoelectric, dielectric, and piezoelectric,which are widely used as luminescent, scintillant and dielectric materials indifferent kinds of industrial fields. In recent years, the aspects such as crystalgrowth, property improvement and powder preparation are mainly studied.However the structures and properties for melt during the process of melting andcooling are less researched.The structures and properties of bismuth silicate melt are important factorsinfluencing the crystal growth, which is significant to understand the mechanismof crystal growth and to improve the growth rate and quality of crystals. Bismuthsilicate powders are prerequisite of preparation for appropriate melt. Therefore, itis very important to study synthesis of bismuth silicate powders for commandingstructures and properties of melt.In this paper the powder preparation and melt properties of bismuth silicatewere mainly studied. By solid phase method and molten salt method, Bi₄Si₃O₁₂powders and Bi₂SiO₅powders were separately prepared. Relevant processparameters were researched. The formation mechanisms were discussed. Themelt properties such as densities and surface tensions and melt structures werestudied. The innovative achievements were obtained:（1） By solid phase method, high purity Bi₄Si₃O₁₂powders were synthesized.Bi₄Si₃O₁₂powders were produced at830℃for3h using Bi₂O₃and SiO₂as rawmaterials after the raw materials were milled for5h in ethanol. Throughanalyzing the relation among primary and secondary factors in uniformexperiment, the calcination temperature had significant effects on the number ofimpure phase, and the rest of the factors were not significant.（2） High purity Bi₄Si₃O₁₂powders were produced in NaCl-KCl molten salts.The microstructures of powders were mainly grains and sheets. And pure Bi₄Si₃O₁₂powders were prepared using NaCl-Na₂SO₄molten salts. The shapesof powders were polyhedrons. High purity Bi₄Si₃O₁₂powders were obtained at780℃for4h by reaction in NaCl-KCl molten salts using Bi₂O₃and SiO₂as rawmaterials with40wt%salts and5wt%excessive content of Bi₂O₃. Excitationspectra and emission spectra of Bi₄Si₃O₁₂powders respectively lay at266nm and457.6nm. Compared to crystalline materials, excitation spectra and emissionspectra showed blue shift. Pure Bi₄Si₃O₁₂powders were synthesized at850℃for3h under40wt%NaCl-Na₂SO₄molten salts, and the best combination of rawmaterials was bismuth oxide and silicon dioxide. The forbidden band width ofBi₄Si₃O₁₂was2.44eV. Excitation spectra and emission spectra of Bi₄Si₃O₁₂powders were separately at270nm and462nm. Compared to crystallinematerials, excitation spectra and emission spectra indicated blue shift. Bycomparing apparent activation energy for synthesizing Bi₄Si₃O₁₂powders underthe two kinds of molten salt systems, Bi₄Si₃O₁₂powders were more easilyformed using NaCl-Na₂SO₄molten salt system. By making a comparisonbetween the purity and microstructures of Bi₄Si₃O₁₂powders by solid phasemethod and by molten salt method. Pure Bi₄Si₃O₁₂powders were more easilyprepared by reaction in molten salts. The shapes and sizes of grains werefurthermore easily controlled.（3） High purity Bi₂SiO₅powders were produced under molten salts（NaCl-KCl and NaCl-Na₂SO₄）. The micrographs of powders were sheets. InNaCl-KCl molten salt system, high purity Bi₂SiO₅powders were obtained at690℃for0.5h. Bi₂O₃and SiO₂with30wt%salts were acted as raw materials.SEM images indicated that powders had preferable dispersity and the sizes ofsheets were about1-4μm. High purity Bi₂SiO₅powders were prepared byreaction at625℃for1h in40wt%NaCl-Na₂SO₄molten salts, and Bi₂O₃andSiO₂were selected as the best combination of raw materials. By comparingapparent activation energy for synthesizing Bi₂SiO₅powders under the two sortsof molten salt systems, Bi₂SiO₅powders were more easily produced byNaCl-Na₂SO₄molten salt system.（4） The melting processes of Bi₁₂SiO₂0polycrystalline powders were insitu observed by hot-stage combined with polarizing microscope. The meltingprocess could divide into three stages: powder melting, phase splitting （metastable phase splitting and unstable phase splitting）, and melt homogenizing.During metastable phase splitting, numerous black punctate structures werewidely distributed in the melt. As the melt temperature rose, the structures wouldbe more and more obvious. During unstable phase splitting, with the change oftemperature, two different types of structures mainly existed in melt. One wasannular interlocking structure. The other was vermiform structure. And duringthe process of phase splitting obvious dividing line between two phases in themelt appeared with temperature movement.更多还原