【作者】 孟庆芬；

【导师】 高胜利； 陈三平；

【作者基本信息】 西北大学 ， 材料化学， 2011， 博士

【摘要】 本文比较系统地研究了制备硼酸三钴晶须的方法,筛选出合适的原料、助熔剂、助熔剂含量和反应条件,对所制备的晶须进行了XRD、SEM、TEM和SAED等表征,通过查阅文献和对实验现象的观察,对硼酸三钴晶须的生长机理做了初步探索,研究的主要内容和结论如下：(1)通过单因素实验,钴源、硼源分别选定氯化钴和硼砂,且二者的配比为3：2-3：3；助熔剂选定氯化钾,且助熔剂的含量为钴原料和硼原料质量和的0.75-1.25倍,反应温度850℃-900℃,反应时间2-3 h,该条件可制备出高长径比的硼酸三钴晶须。(2)通过正交试验,利用极差、方差分析法对生长硼酸三钴晶须的反应条件进行了优化,找出了制备硼酸三钴晶须的最佳工艺条件：Co：B为3：2.25,助熔剂的含量为钴硼原料质量的0.75倍,反应温度为900℃,反应时间为4h；因素影响的主次顺序为反应温度>助熔剂含量>钴硼配比>反应时间。(3)借助XRD、SEM、TEM和SAED等测试手段对所制备的晶须进行了分析和表征。结果表明：制备的晶须为正交晶系的硼铁矿系Co3BO5；晶须长度平均在500μm以上,直径在0.5-5μm,个别直径10μm,长径比平均在100以上,为单晶结构,沿[231]方向生长。(4)通过对前驱体产物的判断,初步探讨了硼酸三钴晶须的生长机理,认为该方法制备的硼酸三钴晶须坩埚内、外壁上的生长机理为气相反应,烧结块内部晶须可以用溶解-析出机理来解释。根据制备硼酸三钴晶须筛选出的条件,进行小范围调整制备出二硼酸三钴晶须和二硼酸二钴晶须,试剂仍选择氯化钴和硼砂,助熔剂为氯化钾,优化的条件为反应温度850℃,反应时间为1.5 h,钴硼配比为1：2时,可得到夹杂着少量黑色晶须的紫色二硼酸三钴晶须；当钴硼配比1：3至1：4,可制得浅紫色二硼酸二钴晶须。其中制备的二硼酸三钴晶须强度较差,有缺陷,晶体表面有熔槽、裂痕、断痕,晶须长度平均在500μm以上,直径在10-100μm；二硼酸二钴晶须质量好于二硼酸三钴晶须,为大量的长纤维状,少量棒状,部分晶体表面有裂痕、断痕,晶须长度平均在200μm-300μm,个别可达500μm,直径一般在2-20μm。在制备硼酸三钴晶须的过程中,发现了层状六角片Co3O4,为该化合物的新的形貌,对该六角片状Co3O4的合成原料、合成条件进行了优化,确定最终的实验条件为CoCl2·6H2O:NaOH:H3BO3=1:5:1,反应温度为750℃,反应时间2h。XRD结果显示最终产物为C0304；SEM显示六角片形状规整,表面干净平整无裂痕和其它缺陷,边长范围为2-10μm,侧面图像显示为层状结构；TEM可以看出,产物为六角片状的单晶,结晶很好,表面平整无孔洞,测得HRTEM图中的条纹间距离为0.24 nm,对应于[311]晶面。更多还原

【Abstract】 This dissertation has systematically studied the preparation and growth mechanism of CO3BO5 whiskers. Appropriate materials, flux, the flux ratio and the reaction conditions were optimized. The whiskers were characterized by XRD, SEM, TEM and SAED, the growth mechanism of the whiskers was explored. The main contents are as following:(1) Through Single factor experiments, cobalt chloride and borax were selected as cobalt source, boron source, respectively, and the ratio of the materials is in the range of 3:2-3:3; potassium chloride was selected as the flux, and the ratio of the flux is 0.75-1.25 of the summation quantity of cobalt salts and borate materials; the reaction temperature is between 850℃-900℃, and the reaction time is between 2-3 h. High length ratio of CO3BO5 whiskers can be prepared under these conditions.(2) Through orthogonal experiments, the range and variance analysis, the optimum prepartion conditions of Co3BO5 whiskers were determined as:the ratio of Co:B is 3:2.25, the ratio of flux is 0.75, the reaction temperature is 900℃, and the reaction time is 4 h; the order of the factors affecting the reactions is:temperature> content of flux> ratio of Co:B> reaction time.(3) The prepared whiskers were analyzed and characterized by XRD, SEM, TEM and SAED et al. The results showed that:the whiskers are orthorhombic Co3BO5, the average length of the whisker is more than 500μm, most diameters are between 0.5-5μm with a few diameters up to 10μm, the average length ratio is above 100 within high ratio. It is a single crystal structure that grows along the [231] direction.(4) Through estimating the precursor product, the growth mechanism of the CO3BO5 whiskers was explored. The Co3BO5 whiskers prepared by the crucible outer wall was considered as the gas phase reaction growth, and after sintering, the dissolved whiskers within a block can be explained by dissolving-depositing mechanism.Based on the selected preparation conditions of Co3BO5 whiskers, Co3B2O6 and Co2B2O5 whiskers were obtained. Reagents were chosen as cobalt chloride and boric acid, flux is potassium chloride, the optimized conditions are:reaction temperature is 850℃, reaction time is 1.5 h, the ratio of cobalt:boron is 1:2 and 1:3 to 1:4 respectively. The prepared Co3B2O6 whiskers are brittle and have some defects. The crystals’surfaces have taken on some cracks and ruptures, and the average length of the whiskers is more than 500μm, most diameters are between 10-100μm. Contrasted with Co3B2O6 whiskers, the quality of Co2B2O5 whiskers was improved. The fibriform crystals are increased and the clavas are reduced. The cracks and ruptures are reduced also.The average length of the whiskers are 200-500μm, most diameters are between 2-20μm.During the preparation of Co3BO5 whiskers, a hexagonal plate Co3O4, a new morphology, was discovered surprisingly. The synthetic material, conditions of the hexagonal plate Co3O4 were optimized and the final experimental conditions are:the material ratio is CoCl2·6H2O: NaOH:H3BO3= 1:5:1; the reaction temperature is 750℃, the reaction time is 2 h. XRD results show that the final product is Co3O4; SEM results show that their shapes are regular hexagonal piece, the surface is clean, smooth, no cracks and other defects, the side range is between 2-10μm, the side image shows a layer structure. TEM results show that the product is hexagonal plate single crystal, crystal is perfect, the surface is smooth with no holes. SAED and HRTEM figures show that the distance between the strips is 0.24 nm, corresponding to the [311] crystal face.更多还原