Al_2O_3超微粉体的制备、改性及其α相变控制的研究
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摘要
本文首先以NH_4Al(SO_4)_2和NH_4HCO_3为原料，用沉淀法制备了一种氧化铝的新型前驱体—碳酸铝铵(AACH)，对其制备工艺进行了研究。接着对碳酸铝铵进行了焙烧实验，研究了其在升温过程中的相变行为，结果表明：纯AACH在1200℃保温1.5h的情况下才能100％转变为α氧化铝，而在这样高的温度下，粒子之间会形成烧结颈，从而使粉体产物在形貌上出现所谓“树枝状”结构，给粉体使用时的分散带来了困难。
为了消除这种“树枝状”结构，本文通过掺杂TiO_2、MgO、ZnO等物质来降低氧化铝α相变温度，从而抑制“树枝状”结构的形成，控制粉体颗粒的粒径。结果表明：这三种物质均有明显的降低氧化铝α相变温度，促进氧化铝α相变的作用，得到的焙烧产物中基本上没有“树枝状”结构。
用作催化剂载体的氧化铝粉体需要有良好的热稳定性。本文研究了SiO_2、ZrO_2这两种物质对氧化铝的热稳定性能的影响。结果表明SiO_2优于ZrO_2：5％SiO_2添加的样品在1200℃焙烧2h后粒子粒径仍然保持在10nm左右。
A new precursor of Al2O3 has been synthesized by precipitation method, using NH4A1 (SO4) 2 and NH4HCO3 as raw materials. Some research work has been done on the preparation process. The phase transformation behavior during heat-treatment has been studied. The results show that the a -phase-transformation of pure AACH can be completed by heating at 1200 癈 for two hours. But under this temperature, the alumina particles will be sintered together, which can lead to the formation of bough-like structures. And these bough-like structure will make the powder difficult to be dispersed.
To resolve this problem , TiO2, MgO, ZnO have been used as doping materials. The results show that these three kind of materials are effective to reduce the a -phase-transformation temperature and accelerate the a -Phase-Transformation process. No bough-like structure was found in the doping production of heat-treatment.
As far as alumina powder is concerned ,on the contrary, the excellent thermal stability is needed as catalyst carrier. The effects of SiO2 and ZrO2 on the thermal stability of alumina powder has been studied. The. results show that SiO2 is effective to stablize Al2O3 powder, which can be drawn from the fact that the particle size of the sample with 5%Si02 doped can be kept around 10nm after calcined at 1200℃ for two hours.
为了消除这种“树枝状”结构，本文通过掺杂TiO_2、MgO、ZnO等物质来降低氧化铝α相变温度，从而抑制“树枝状”结构的形成，控制粉体颗粒的粒径。结果表明：这三种物质均有明显的降低氧化铝α相变温度，促进氧化铝α相变的作用，得到的焙烧产物中基本上没有“树枝状”结构。
用作催化剂载体的氧化铝粉体需要有良好的热稳定性。本文研究了SiO_2、ZrO_2这两种物质对氧化铝的热稳定性能的影响。结果表明SiO_2优于ZrO_2：5％SiO_2添加的样品在1200℃焙烧2h后粒子粒径仍然保持在10nm左右。
A new precursor of Al2O3 has been synthesized by precipitation method, using NH4A1 (SO4) 2 and NH4HCO3 as raw materials. Some research work has been done on the preparation process. The phase transformation behavior during heat-treatment has been studied. The results show that the a -phase-transformation of pure AACH can be completed by heating at 1200 癈 for two hours. But under this temperature, the alumina particles will be sintered together, which can lead to the formation of bough-like structures. And these bough-like structure will make the powder difficult to be dispersed.
To resolve this problem , TiO2, MgO, ZnO have been used as doping materials. The results show that these three kind of materials are effective to reduce the a -phase-transformation temperature and accelerate the a -Phase-Transformation process. No bough-like structure was found in the doping production of heat-treatment.
As far as alumina powder is concerned ,on the contrary, the excellent thermal stability is needed as catalyst carrier. The effects of SiO2 and ZrO2 on the thermal stability of alumina powder has been studied. The. results show that SiO2 is effective to stablize Al2O3 powder, which can be drawn from the fact that the particle size of the sample with 5%Si02 doped can be kept around 10nm after calcined at 1200℃ for two hours.
引文
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