A Novel method for the Large-Scale Production of Calcium Lanthanum Sulfide (CLS) Nanopowders for Optical Ceramic Applications

Calcium lanthanum sulfide (CaLa2S4 or CLS) is a refractory ternary sulfide that possesses the cubic thorium phosphate structure. It has been developed as a material for infrared ceramic windows since the 1980s. CLS is considered a promising candidate to replace traditional sulfides as infrared optical ceramics for applications in harsh environments due to its dual IR transmittance wavelength, excellent mechanical strength, and high resistance to rain erosion. Current manufacturing processes involve high-temperature and high-pressure equipment, long processing times, and give low yields leading to high costs. To address this problem, Bhawin, LLC has invented a novel environmentally benign technology and demonstrated its proof-of-concept during the Phase I project and feasibility to scale-up the synthesis process during the Phase II project. Key results demonstrated our ability to consistently reproduce CLS nanopowders of ~200 nm in size. Consolidation of this ultra-high purity (99.9%) CLS nanopowders produced ultra-high density optical ceramics showing nano-grained structures with a mechanical strength two times that of existing ZnS and CLS products. In the proposed Phase II Sequential (PIIS) project, processes will be scaled-up to produce multi-kilogram quantities of metal-sulfide powders (CLS, ZnS, and Ga2S3) with the above-mentioned properties to engineer next-generation missile sensor windows, lenses, and domes. Bhawin LLC in collaboration with Raytheon IDS will sinter larger windows and lenses of CLS. Nanocomposites of CLS-ZnS and CLS-Ga2S3 will also be sintered to enhance the thermal shock resistance of CLS windows, domes, and lenses. Collaboration with a leading Medium Wavelength Infrared (MWIR) and Long Wavelength Infrared (LWIR) manufacturer is established to evaluate samples and provide technical guidance. Their input described under Phase II Sequential tasks and the letter of support attached demonstrates their intention to become a commercialization partner leading to near-term technology utilization potential.