【作者】 陈玮；

【导师】 尹周澜； 李旺兴；

【作者基本信息】 中南大学 ， 冶金物理化学， 2010， 博士

【摘要】 α-Al2O3是重要的无机非金属材料,煅烧是制备α-Al2O3的必备过程,该过程消耗大量能量。降低煅烧温度,降低能耗,提高产品中α-Al2O3含量,制备不同显微结构的α-Al2O3,为下游产品提供优质原料是该领域科研工作者孜孜以求的目标。由于显微结构对α-Al2O3的性能有重大影响,因此,揭示α-Al2O3形成过程显微结构的演变规律对于制备性能优良的α-Al2O3产品具有重要的理论及实际意义。本文采用X-射线衍射、扫描电子显微镜等分析测试手段,对氢氧化铝煅烧过程中的相变规律及氧化铝显微结构演变进行了系统研究；采用X-射线衍射定量分析方法,研究了添加剂对氧化铝相变的影响；结合扫描电子显微镜及激光粒度分析,研究了α-Al2O3晶体生长动力学；提出了α-Al2O3显微结构控制方法,由此制备了片状及类球状晶体结构的α-Al2O3,制备了低温烧结α-Al2O3及其陶瓷材料。主要研究结果如下：1.氢氧化铝脱水过程分步完成,脱水过程与氢氧化铝样品的粒度相关,粒度越小,脱水速率越快。过渡相氧化铝之间的物相转变属于位移型相变,形成α-Al2O3过程属于重建型相变。过渡相氧化铝之间转变时,显微结构基本不发生变化；当转变为α-Al2O3时,氧化铝发生明显的收缩。煅烧过程中,真密度随温度的升高而升高；松装密度随温度的升高而降低,氧化铝的比表面积在400℃左右达到最大值,然后随温度的升高而下降,氧化铝的孔径在900℃左右达到最大值,然后随温度的升高而下降。2.过渡相氧化铝到α-Al2O3的物相转变需在1300℃才能完成；Na2O和MgO对过渡相氧化铝到α-Al2O3的物相转变过程有抑制作用,含有Fˉ和Clˉ的添加剂、粉碎和加入晶种均可以促进相变过程；过渡相氧化铝与α-Al2O3含量之间存在一个相界面；样品中α-Al2O3含量随煅烧温度的提高而提高,存在一个最高相变速率点Tm。Tm大致在1150℃左右,此时样品中α-Al2O3的含量大致为20-45%。3.粉碎结合激光粒度检测是一种简单易行测定α-Al2O3一次晶体大小的方法。以固相物质输送为主要传质方式时,α-Al2O3一次晶体为蠕虫状空间网状结构；以气相为主要传质形式生长的α-Al2O3具有特定的显微结构。添加剂对α-Al2O3晶体生长的作用顺序为：NH4F> AlF3> H3BO3> MgF2> None> MgO添加剂可以影响a-Al2O3的理论成核温度,影响的顺序为：NH4F> AIF3> None>H3BO3>MgO通过粉碎、加入NH4Cl和Mg(HCO3)2添加剂等工艺,抑制a-Al2O3晶粒生长,制备了约20m的纳米晶a-Al203。4.煅烧后a-Al2O3继承了氢氧化铝的基本颗粒形貌。提高煅烧温度不改变a-Al2O3的结晶习性,Na2O和MgO可以抑制a-Al2O3晶体生长；H3BO3及含有F-、Cl-、NO3-的添加剂可以促进a-Al2O3的一次晶体生长,H3BO3促进形成蠕虫状a-Al2O3结晶,含F添加剂促进形成片状a-Al2O3结晶。添加剂对a-Al2O3显微结构的影响顺序为：AlF3>H3BO3>NH4Cl>MgO5.基于a-Al2O3显微结构的演变规律,通过改变添加剂的品种及其配比,可以制备出不同显微结构的a-Al2O3晶体。采用晶体模板导向剂,并选择合理的添加剂,制备了类球状、柱状、大晶体片状等特殊显微结构的a-Al2O3。通过选择合适的添加剂及烧结温度,制备了一次晶体小于0.5微米的a-Al2O3粉体。最佳的添加剂条件是0.4%MgO+0.3%NH4Cl,最佳的煅烧温度是1350℃；开发了低温氧化铝陶瓷烧结技术,最佳烧结温度为1580℃,体积密度达到3.92g/cm3。更多还原

【Abstract】 a-Al2O3 is an important inorganic non-metallic material. The energy consumption is huge in the preparation process of a-Al2O by sintering. Reduction of the calcination temperature and energy cost is the main target inα-Al2O3 industry. As the properties ofα-Al2O3 are mainly depending on its microstructure characteristics, it is of great theoretical and practical significance to study on the microstructure evolution during the phase transformation ofα-Al2O3.The phase transformation of aluminum hydroxide and the microstructure evolution of aluminum oxide have been studied using XRD and SEM measurements. The influence of additives on the phase transformation has been studied using XRD quantitative analysis. The crystal growth kinetics of a-Al2O3 has been studied using laser particle size analysis and SEM technique. The method of microstructure control of a-Al2O3 has been proposed based on above studies. As a result of that, plate and near-spherical a-Al2O3 have been successfully obtained. Sinterable a-Al2O3 has been made by adjusting the microstructure ofα-Al2O3. The research results are mainly as follows:1. The dehydration process from aluminum hydroxide to aluminum oxide proceeds in steps. The smaller the particle size of the sample, the faster the dehydration process. The phase transformation between different transition alumina belongs to displacement, while the formation of a-Al2O3 from transition alumina belongs to reconstruction. There is no obvious change of microscope between transition alumina. But apparent shrinkage appears whenα-Al2O3 was formed. In the calcination process, the real density of alumina rises and the bulk density of alumina decreases with the increase of temperature. The specific surface area of alumina reaches its maximum at about 400℃, the aperture of alumina reaches the maximum at about 900℃.2. The phase transformation from transition alumina toα-Al2O3 completes above 1300℃. Na2O and MgO can depress the phase transformation, while the addition of additives containing F-, and Cl-grinding and the addition of crystal seeds can promote the phase transformation process. Due to heat conduction, there is a phase interface between transition alumina andα-Al2O3.The percent of a-Al2O3 rises with the increase of the calcination temperature. There is a maximum rate of phase transformation at Tm when the percent of a-Al2O3 is about 20-45%.3. Grinding combined with laser particle analysis is a suitable way to determine the crystal size ofα-Al2O3. a-Al2O3with worm-like structure was formed by solid-phase mass transfer. a-Al2O3 with a specific microstructure was formed by gas-phase mass transfer. Additives could influence the crystal growth of a-Al2O3 in the following order:NH4F> AIF3> H3BO3> MgF2> None> MgOAnd additives could change the nucleation temperature ofα-Al2O3 in the order as follows:NH4F> AIF3> None>H3BO3>MgONanocrystallineα-Al2O3 of about 20nm has been successfully made by grinding and the addition of such additives as NH4Cl and Mg(HCO3)2 because NH4Cl can restrict the process of phase transformation and Mg(HCO3)2 can depress the crystal growth ofα-Al2O34.The morphology of a-Al2O3 particles is similar to that of aluminum hydroxide. The crystallization habits of a-Al2O3 do not change with the increase of calcination temperature. Na2O and MgO can inhibit the crystal growth of a-Al2O3. H3BO3, and additives containning F-, Cl- and NO3" can accelerate the crystal growth ofα-Al2O3. H3BO3 can promote the formation of worm-like a-Al2O3 crystal, while additives containing F-can promote the formation of flake a-Al2O3 crystal. The influence of additives to the microstructure ofα-Al2O3 is in the order as follows:AlF3>H3BO3>NH4Cl>MgO5. a-Al2O3 with different microstructure can be made by the addition of different additives.α-Al2O3 with specific microstructure such as spherical, columnar, large flake crystal have been successfully obtained by the addition of seed crystal or additives. By selecting the appropriate additives and sintering temperature, the original crystal less than 0.5 microns has been acquired with the addition of additive 0.4%MgO+0.3%NH4Cl at 1350℃. The sintering technology for the preparation of lower temperature alumina ceramic with the bulk density of 3.92g/cm3 has been developed at the optimum sintering temperature of 1620℃.更多还原