长波红外窗口材料γ-La2S3热压多晶的高温抗氧化机理及热压动力学

Cubic γ-La2S3 is an excellent 8～14μm long-wave infrared materials working in extremely adverse environmental condition, which has a wide application as the key dome materials for the imaging infrared guidance in defense field. However, the lower capacity to resistance of oxidation and the poor optical uniformity causing by some difficulties in hot-pressed sintering process are both obvious disadvantages to its development. In this research, γ-La2S3 polycrystal ceramics will be achieved through hot-pressed sintering. Na+ ions is firstly proposed to introduce into γ-La2S3 matrix as a selected dopant to improve its structure stability and antioxidative capacity due to its ion radius similar to La3+ and the higher active of Na than that of La metal. Based on the different effects caused by various dopants as Li+、K+ and Rb+ with larger difference in ion radius, the influence on the antioxidative capacity of γ-La2S3 of the lattice strain,distortion and defects caused by the ions radius diffrence between La3+ and dopant ions will be studied, so that the antioxidative mechanism of Na+ ion dopants can be revealed. Considering the chemical valance, we will vertify and improve the mechanism through intrducing Ca2+ into γ-La2S3 andγ-Pr2S3. Moreover, the sintering kinetics of γ-La2S3:Na+ polycrystals will be investigated to understand well the action of some factors such as the precursor morphlogies, the dopant dose, the density, the micro-morphology, the composition, and the closed space resulfurizing in improving IR transmission of sintered γ-La2S3 pellet. The sintering method and theories of γ-La2S3 bulk polycrystals as a key longwave infrared materials will be developed with higher antioxidative capacity and IR optical uniformity.

立方γ-La2S3是极端苛刻服役条件下的8～14μm长波红外材料,是高超音速下长波红外成像寻的/制导用窗口材料。易氧化导致的低红外透过、难烧结制备导致的均匀性差制约了其应用。本项目采用热压制备γ-La2S3多晶材料,提出与La3+半径最接近且较镧活泼的Na+掺入可提高其抗氧化能力,在与La3+半径差异较大的Li+、K+和Rb+掺入后的抗氧化效果相比较的基础上，研究掺入离子半径不同引起的晶格应力、畸变和缺陷等对目标多晶氧化性能的影响，对比揭示出Na+掺入目标多晶的抗氧化机理；并分析二价Ca2+掺入γ-La2S3或γ-Pr2S3的抗氧化效果来完善该机理。进而研究γ-La2S3多晶的热压晶粒长大动力学，揭示传质机理；在以上基础上,揭示前驱体形貌、离子掺入量、相组成、致密度、微观组织和密闭系统高压再硫化等对材料红外性能的影响;发展出高温抗氧化好、均匀性高的γ-La2S3红外多晶热压制备理论与方法。

项目采用自行设计建造的电磁感应气氛热压烧结炉成功制备了高透过率的γ-La2S3长波红外透明陶瓷，获得的最优γ-La2S3陶瓷的光学性能为平均透过率为61.3％@ 8～14μm，最大透射率为64.03％@13.1μm。项目解决了γ-La2S3红外陶瓷在热压制备和应用中的主要瓶颈问题：一是在材料制备中，镧的亲氧性导致的硫氧化物杂质难消除引起的红外吸收带和低红外透过率；二是γ-La2S3的高硬度和烧结性差导致的晶粒异常长大和光学均匀性低。通过研究不同离子稳定的γ-La2S3的高温稳定性，揭示了不同离子对γ-La2S3的抗氧化能力提升顺序为：Na+>Li+>Ca2+>K+，其归因于离子半径不同引起的晶格应力差异、阳离子化合价不同引起的缺陷类型和产物化学配比差异的能力不同，据此抗氧化机理，发展了高抗氧化γ-La2S3:Na+粉体制备方法；同时发现不同钠源如NaX (X=F、Cl、Br、I)与碱式碳酸镧前驱体原料混合硫化反应的产物成分存在NaX用量-物相依赖关系，该关系归因于X-离子半径与S2-离子半径差异导致NaX在硫化镧中的溶解度差异，由于F-离子半径小于S2-，NaF在空位型γ-La2S3中的溶解度较大，从而产物为NaLaS2，反之当X= Cl、Br、I时产物为仅为γ-La2S3，项目依此开发了抗氧化能力可控的γ-La2S3:Na+；Na0.5La2.5S4；NaLaS2粉体的制备方法，研究表明Na0.5La2.5S4具有最好的抗氧化性能，适用于在高温氩气气氛下烧结制备γ-La2S3红外陶瓷。同时选择NaCl作为烧结助添加剂，成功制备了在8～14μm波段高透过率的γ-La2S3长波红外透明陶瓷；进一步在研究NaCl添加剂对γ-La2S3陶瓷的微观结构、晶界成分、缺陷反应、晶粒长大和红外性能影响的基础上，采用NaCl纳米晶作为烧结助剂，有效解决了γ-La2S3多晶陶瓷难以烧结制备、晶粒易于异常长大和均匀性差等难点问题，在揭示NaCl添加剂的作用机理基础上设计工艺参数并制备出了高通过的γ-La2S3红外陶瓷；同时也成功制备出了NaLaS2光学陶瓷，并采用密封空间再硫化技术提高了其红外性能。项目也成功制备了γ-Pr2S3、NaPrS2和CaLa2S4光学陶瓷等，表明项目相关方法可拓展至其它稀土硫化物。本项目对发展飞行速度高于3马赫的下一代高速飞行器红外窗口材料具有重要意义。