【作者】 赵涛涛；

【导师】 冯小平；

【作者基本信息】 武汉理工大学 ， 建筑材料与工程， 2011， 硕士

【摘要】 碳酸钙晶须是一种环境友好型材料。其长径比较大,类似于短纤维,是一种优良的增强增韧材料；同时,其长度较短,具有优良的加工流动性,所得的制件表面光洁度高,而且原料来源广泛、价格低廉,因此在塑料、造纸和涂料等领域中都拥有广阔的应用前景。本文以活性氧化钙为原料,以六水氯化镁作为晶型控制剂,采用气液反应合成法制备碳酸钙晶须,并利用偏光显微镜、X射线衍射仪和扫描电镜等测试手段对产物形貌和结构进行观察分析。实验结果表明：当反应温度为80℃,镁钙比为2,CO2气体的通气量为70ml.min-1,搅拌速度为100r.min-1时,可以获得长度在30μm左右,长径比约为25的碳酸钙晶须。在此基础上,通过优化工艺参数来提高碳酸钙晶须的纯度和长径比。研究结果表明：改变氧化钙的消化方式,能够有效的提高氢氧化钙溶液的纯度,相应的增加反应溶液的镁钙比,进而提高碳酸钙晶须的纯度,当把11.2g的氧化钙缓慢消化至80℃,与氯化镁溶液混合后,可制得纯度在98.7%以上的碳酸钙晶须,较之优化工艺前的97.5%有所提高；同时,利用数显pH/mV计检测反应溶液的pH值,通过补加氢氧化钙溶液控制反应过程中镁钙比的变化,抑制由于镁离子浓度升高而对碳酸钙晶须生长产生的不利影响。结果表明：当碳化反应进行1h后,补加625ml 0.16mol.L-1的氢氧化钙溶液,碳酸钙晶须的长径比能够提高到30以上,较之优化前的25有所增加。通过考虑资源的再回收利用,来节约成本。由氯化镁溶液的回收利用对碳酸钙晶须的影响可知：当反应的初始镁钙比为1.7时,能够有效的降低晶核增多对碳酸钙晶须生长的不利影响,提高碳酸钙晶须的长径比,此时碳酸钙晶须的长度为27.7μm、长径比可达26.6；为了废料的再生利用,需精致氢氧化钙溶液,步骤为：将25g的废料放置于烧杯中,用2L80℃注入其中,快速搅拌使其充分消化,降至室温时,用200目的标准筛过滤,将滤液陈化2-3天即可,利用上述的制备工艺参数,反应后即可获得长度约为53℃m、长径比在31.5左右的碳酸钙晶须。氯化镁是合成碳酸钙晶须常用的晶型控制剂之一,但就其作用机理而言,依然有很多的未明之处。本文从反应动力学的基础上,阐述了氯化镁溶液可以有效的降低反应溶液的过饱和度,促进碳酸钙晶须的成核生长；当反应的镁钙比小于1时,通过比较氢氧化镁和氯化镁两种不同的Mg2+状态对合成碳酸钙晶须的影响,结果表明：絮凝状的氢氧化镁颗粒可以起到晶核聚集的作用,使得碳酸钙晶须可以在其表面迅速的生长,但所得晶须多呈树枝状分布；同时,通过比较分析反应时间对碳酸钙晶须的影响可知：Mg2+不仅可以抑制碳酸钙晶须向方解石转化,提高产物的纯度,也能够抑制碳酸钙晶须直径的过快增长,提高其长径比。以此为据,推断碳酸钙晶须的生长是螺旋位错生长理论作用的结果。更多还原

【Abstract】 Calcium carbonate whisker is a kind of environmental-friendly materials. Similar to short fibers, which have high ratio of length to diameter, it is a kind of excellent enhancing toughening materials. On the other hand, as having a short length leads to the good processing properties, available products have a highly smooth surface. Thanks to the widely existence of raw material and low price, it has a broad application prospect in industrial areas such as plastic, papermaking and painting. This thesis used industrial calcium oxide as a raw material, and magnesium chloride hexahydrate as crystal control agent, uses Gas-liquid reaction synthesis method to form the calcium carbonate whiskers. Through polarizing microscopy, X-ray Diffraction and Scanning Electron Microscopy and other tools to observe and analysis the appearance and crystalloid structure of whiskers. The result indicated that calcium carbonate whiskers with a length of 30μm and length-diameter ratio of 25 can be got when the react temperature is 80℃, the ratio of magnesium and calcium is 2,the flow of CO2 is 70 ml.min-1, and stirring speed is 100r.min-1.On the basis, we can improve the purity and length-diameter ratio of calcium carbonate whiskers by optimizing the parameters design. The result indicated that the purity of calcium carbonate whiskers by changing the digestion of calcium oxide, because it can improve the purity of calcium hydroxide solution and increase the ratio of magnesium and calcium. The content of calcium carbonate whiskers in product 97.5% increased to 98.7% when 11.2g calcium oxide digested slowly to 80℃and mixed with magnesium chloride solution. At the same time, using digital pH/mV meter to test the pH value of reaction solution. We can restrain the adverse effects of calcium carbonate whiskers by adding calcium hydroxide solution. It can manage the ratio of magnesium and calcium and reduce the concentration of Mg2+.The aspect of calcium carbonate whiskers can increase from 25 to 30 when one-time additional 625ml 0.16mol.L-1 calcium hydroxide after the reaction of 1h.Furthermore, we can cost saving by recycling resource. Studying of recycling of magnesium chloride solution on the synthesis of calcium carbonate whiskers, the result indicated that we can increase the length-diameter ratio of it by reducing the ratio of magnesium and calcium suitably. When magnesium to calcium ratio is 1.7, calcium carbonate whiskers with length 27.7μm and aspect ratio 26 can be acquired. To recycle the waste materials, we should refine the calcium hydroxide solution. The 25g waste materials dissolve in 2L80℃water and stirring fast make its digesting fully. Using 200# standard sieve to filter the reaction solution after it drops to room temperature.The filtrates are then aged 2-3 days in a beaker. Through refining the calcium hydroxide solution can gain length 53μm and aspect ratio 31.5 of calcium carbonate whiskers.As one of the most common crystal control agent, many mechanisms of magnesium chloride still remain unknown. Based on the kinetics of reaction, we know that magnesium chloride can decrease effectively the supersaturation of reaction solution, and accelerate the nuclei growth of calcium carbonate whiskers.When the ratio of calcium and magnesium involved in the reaction is less than 1,through analyzing the effect on the synthesis of calcium carbonate whiskers by the state of Mg2+ in magnesium hydroxide and magnesium chloride, the result indicated that flocculation magnesium hydroxide could gather the crystal nucleus, which could prompted the growth of arborization calcium carbonate whiskers on its surface, at the mean time, through comparison and analysis effects to calcium carbonate whiskers caused by the react time, we could know that the Mg2+ not only restraining the calcium carbonate whiskers transform into calcite, and improving the purity of the products, but also increasing the length-diameter ratio by restraining the over-fast growth of diameter of the calcium carbonate whiskers. Due to evidence above, it could get the conclusion that the growths of calcium carbonate whiskers is the result of screw dislocation induced growth mechanism.更多还原