氮化硅材料由于具有诸多优异性能而被广泛地应用在航空航天、高温器件等多个领域。氮化硅常呈现α相和β相两种晶型。其中，α-Si3N4粉体的应用领域相对更多，发展前景十分广阔。然而，商业α-Si3N4粉体的高成本和高售价极大地限制了氮化硅材料的应用和发展。尤其在国内，高质量α-Si3N4粉体产品几乎全部来自进口，国外企业对该行业形成了技术和产品的双重垄断。燃烧合成法是一种利用反应自身放热来维持反应自发进行的快速合成工艺，具有设备工艺简单、能耗极低、反应速度快、产物纯度高等突出优势，非常适用于规模化、低成本生产高质量陶瓷粉体。然而，燃烧合成法规模化制备α-Si3N4仍然存在着重大的技术瓶颈。首先，燃烧合成反应温度常高达1800℃以上。而α-Si3N4可在低至1300℃下向β-Si3N4发生不可逆的相转变。因此，使用燃烧合成法制备α-Si3N4似乎是“天方夜谭”。另一个更大的问题是，燃烧合成过程中必须使用一些自制的成品α-Si3N4粉体作为稀释剂加入到下一轮生产的原料中，如此往复循环，实现低成本的迭代生产。目前，随着迭代的进行，产物的α相含量常常持续降低，燃烧合成反应常在迭代数次后无预兆地中断，原料无法继续引燃，大大影响了生产的稳定性和连续性。为解决这些行业难题，工业界和学术界的普遍工艺思路是降低燃烧合成过程的反应温度，通过机械活化预处理、低压反应等方法，促使燃烧合成反应在α-β相变温度附近甚至以下发生。但仍未能实现α-Si3N4的无限次稳定迭代燃烧合成。本课题即旨在解决“燃烧合成迭代式制备高α相Si3N4粉体”的行业难题。本论文深入研究了α-Si3N4的燃烧合成生长机制，推翻了 “低温反应才能制备α-Si3N4”的传统思路，创新性提出了“硅颗粒蒸发时间”和“高温持续时间”对产物α相含量的联合决定作用。并系统研究了不同杂质元素对燃烧合成Si3N4的不同影响机制。在上述理论的指导下，通过针对性调整合成参数，最终实现了高α相Si3N4粉体的燃烧合成稳定迭代式制备。该技术在天津纳德科技有限公司完成了成果转化，目前已经建立了高质量α-Si3N4粉体的工业化产线，实现了其低成本、规模化的制备。本论文还对α-Si3N4产品的后续应用进行了探索。其中，实验证实了陶瓷烧结用粉体产品具有较高的烧结活性；脱模剂产品经企业实际使用后，发现其具有良好的脱模效果；本文中还利用高纯α-Si3N4为原料，使用燃烧合成制备了不同性能的SiAlON系荧光粉体，为LED荧光粉体的低成本制备提供了实验基础。
Si3N4-based materials can be used in numerous fields such as aerospace, aviation and high-temperature devices, benefiting from its outstanding comprehensive properties. As well known, α-phase and β-phase are two common phases of Si3N4 in crystallography. Among them, the Si3N4 powders with high α-phase contents can be applied in more kinds of fields and possess more significant prospect. However, the high-cost and high-price of commercial α-Si3N4 powders have limited the application and development of Si3N4 greatly. Especially, the vast majority of α-Si3N4 powders with high quality are imported. In other words, the oversea companies monopolize the industry of α-Si3N4 with high quality both on the technology and the product.Combustion Synthesis (CS) relies on the ability of highly exothermic reactions to be self-sustaining. This synthesis approach possesses lots of appealing advantages including simplicity of equipment, low energy consuming, high production rate and high purity of products, making it appealing for the large-scale synthesis of refractory ceramic powders with low cost. However, there are still some significant problems in the industrialized combustion synthesis of α-Si3N4 powders. Firstly, the combustion temperature during the CS reaction is usually higher than 1800℃. It is well-known that α-Si3N4 is a metastable polymorph at low temperature and the α?β phase transformation is believed to occur at temperatures as low as 1300℃ through a liquid assisted “dissolution-precipitation” process. Thus, it seems that the achievement of α-Si3N4 by the CS method is impossible. Secondly, a more difficult problem is encountered in the synthesis process of α-Si3N4. In the CS process, some self-synthesized α-Si3N4 powders, acting the role of diluent, need to be incorporated in the reaction mixtures of next round of synthesis, which is called the iterative synthesis of α-Si3N4 powders. In the current research work and industrialized production, with the conduction of the iterative synthesis, the α phase content usually tend to be decreased continuously. What’s more, the CS reaction commonly stops without any omens after iteratively synthesizing for several times, which results in the interruption of continuous production. For purpose of solving these aforesaid problems, the researchers proposed the synthetic strategy with low reaction temperature, in which the temperature of CS reaction was lowered close to that of α?β phase transformation by some means including the mechanical activation process and the reduction of N2 pressure. Unfortunately, the unlimited iterative-synthesis of α-Si3N4 through CS method has not been achieved. Herein, the industry problem of the unlimited iterative-CS of α-Si3N4 has been focused and solved. In this paper, the inherent growth mechanism of Si3N4 in CS reaction was rationally proposed. It turned out that the conventional synthetic strategy with low reaction temperature was proved to be unreasonable. And we innovative put forward that the vaporization process of Si particles and the residual time under high-temperature period would synergistically affect the α phase content of product. Moreover, the influencing mechanisms of different impurity elements on the CS process was investigated. Based on the aforesaid theories, we improved the technological parameters accordingly and achieved the unlimited iterative-CS of α-Si3N4 in a stable way. This synthesis route for α-Si3N4 was successfully applied by the Tianjin Nitride Co. Ltd. to set up the industrialized production line in low cost. In addition, the application of the self-synthesized α-Si3N4 products has been explored in this work. The α-Si3N4 powders, which used as the raw materials for the sintering of Si3N4 ceramics, was proved to present high sintering activity. The α-Si3N4 powders applied as mold release coatings was confirmed by some photovoltaic companies to be beneficial to the separation between the silicon ingot and silica crucible during the fusion and recrystallization process of polycrystalline silicon. The SiAlON-based phosphor powders with distinct properties were successfully synthesized by CS method by employing the α-Si3N4 powders with high-purity as one of the raw materials, which laid fundament for the synthesis of SiAlON-based phosphors with low cost.
