Gibbsite在工業上主要做為生產氧化鋁產品的重要原料。然而隨著其粉末粒徑越小以及片狀外型的具備，在複合材料上有更高的應用層面與效果，單價也隨之大幅提高。如能突破現今技術，以低成本生產出較目前商業上次微米級產品更細的奈米級片型gibbsite粉末，勢必能成為更高階應用與高單價的產品。因此本研究欲以χ-Al2O3為原料，利用熱水溶液法來合成奈米級的片狀gibbsite粉末。
本研究藉由攪拌、球磨、珠磨以及珠磨+離心四種不同細化方式取得不同粒度的χ-Al2O3，調配成pH～4.5，固含量1 wt%的漿料作為原料，在100℃熱水溶液環境中合成gibbsite晶體。探討gibbsite生成與原料粒徑、熱水處理時間的關係，試著找出生成機制並觀察合成粉末的外型。研究結果顯示：（1）Gibbsite的生成量有隨原料粒徑減小而增加的趨勢，且主要受小粒徑（＜200 nm）χ-Al2O3的多寡影響。生成量與熱水處理時間呈一指數成長的關係。（2）此環境下χ-Al2O3原料以一類似熱水法中溶解-析出的機制生成gibbsite。（3）此法可合成結晶性良好且單離的gibbsite晶體，以scherrer formula計算出其（002）晶面厚度為31 nm。整體粉末具片狀外型，片面直徑約300～600 nm，厚度在50 nm左右。

Traditionally, gibbsite (Al(OH)3) is the most important raw material for producing alumina powders in industry. Moreover, it has more advanced applications in composite materials and higher price when the particle size was reduced and the plate-like shape was possessed. It is going to be higher level application and higher unit price powders if the low-cost ways that can manufacture gibbsite platelets with particle size thinner than the submicron-scaled commercial powders.
In this study, χ-Al2O3 was used as raw material to synthesis nano-scaled gibbsite platelets by hydrothermal treatment. Four kinds of χ-Al2O3 slurries with different particle size were obtain by different fining treatments: stirring, ball milling, pearl milling, and pearl milling + centrifuge treatment. After dilution, χ-Al2O3 slurries with pH~4.5 and solid contain 1 wt% were obtained as the starting materials. And then, gibbsite crystallites were synthesized under hydrothermal conditions at 100℃. The relationship among the formation of gibbsite crystallites, particle size of the raw materials and duration of the hydrothermal treatment were discussed. Further, the particle size and shape of the produced powders were investigated and the synthesized mechanism was tried to find out. The results showed that: (1) The formation of gibbsite crystallites tended to increase with the reduction of the particle size of starting materials, and it was mainly dominated by the amount of theχ-Al2O3 crystallites with small particle size (＜200 nm). The formation of gibbsite crystallites showed a exponential increase with the durations of the hydrothermal treatment. (2) Under the hydrothermal treatments, the mechanism of gibbsite crystallites synthesis from χ-Al2O3 is similar to the mechanism of dissolution-precipitation. (3) Mono-dispersed and well crystallized gibbsite crystallites with mean crystallite size 31 nm calculate from the (002) XRD reflection by Scherrer formula can be synthesized in this study. From the investigations of TEM and SEM micrographs, the synthesized gibbsite powders possess plate-like shape and whose crystallite size in diameter and in thickness are 300～600 nm and about 50 nm, respectively.

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