Rice industrialization generates large amounts of rice husk, and when this husk is burned, substantial volumes of ash are produced as a result. The lack of a sustainable application for these ashes constitutes a serious environmental liability. Employing rice husk ash as a starting material to manufacture higher-value products fulfills both environmental and economical purposes. Particularly, the presence of silica and carbon in intimate contact makes rice husk ash an attractive precursor for carbothermal reduction and nitridation processes. In the present work, a pre-treatment was applied to a locally sourced industrial rice husk ash, aiming to render not only a more appropriate starting material for carbothermal reduction and nitridation, but also precipitated silica as a by-product. This process involved a simple alkaline digestion step followed by filtering and acid precipitation of the solubilized silica. For carbothermal reduction and nitridation, the treated ash was introduced in graphite crucibles with graphite lids and held at soaking temperatures between 1200 °C and 1400 °C under a nitrogen atmosphere for 3 h. The pretreatment imposed on the ash permitted the adjustment of the carbon-to-silica ratio, producing a substantial improvement in the carbothermal reduction and nitridation results, and enabling the simultaneous obtention of precipitated silica. α- and β silicon nitride, and silicon oxynitride whiskers were obtained through carbothermal reduction and nitridation of the treated rice husk ash. The whiskers obtained had lengths in the millimeter range with cross-sections ranging from about 100 nm up to 500 nm.

中文翻译：

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工业稻壳灰联产氮化硅、氮氧化物晶须和沉淀二氧化硅

水稻工业化产生大量稻壳，当稻壳燃烧时，会产生大量灰烬。这些骨灰缺乏可持续的应用构成了严重的环境责任。使用稻壳灰作为原材料来生产更高价值的产品可以实现环保和经济的目的。特别是，二氧化硅和碳的紧密接触使得稻壳灰成为碳热还原和氮化过程的有吸引力的前体。在目前的工作中，对当地来源的工业稻壳灰进行了预处理，目的不仅是为碳热还原和氮化提供更合适的起始材料，而且还沉淀二氧化硅作为副产品。该过程包括简单的碱消化步骤，然后是过滤和溶解的二氧化硅的酸沉淀。对于碳热还原和氮化，将处理后的灰分放入带有石墨盖的石墨坩埚中，并在氮气气氛下在 1200 °C 至 1400 °C 的均热温度下保持 3 小时。对灰分进行预处理可以调整碳与二氧化硅的比例，从而显着改善碳热还原和氮化结果，并能够同时获得沉淀二氧化硅。对处理后的稻壳灰进行碳热还原和氮化，得到α-氮化硅、β-氮化硅和氮氧化硅晶须。获得的晶须长度在毫米范围内，横截面范围从约100纳米到500纳米。