Calcium Lanthanoid Sulfide Ceramics for LWIR Windows
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Solution Overview
Problem
Current materials used for Long Wave Infrared (LWIR) sensor windows, such as single crystal ZnS, ZnSe, and Ge, suffer from poor environmental weatherability, low mechanical strength, and high absorption coefficients, making them unsuitable for various applications, especially in military and industrial settings.
Innovation Solution
A method for forming ultrafine, high-purity calcium lanthanoid sulfide powders through spraying soluble salts into a precipitating solution, followed by oxidation and sulfurization, which allows for the creation of transparent ceramic materials with high mechanical strength and improved environmental durability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If single crystal ZnS, ZnSe, or Ge are used for LWIR sensor windows, then transparency in the LWIR range is achieved, but mechanical strength and environmental weatherability are poor
Solution Approach 1:
The patent employs calcium lanthanoid sulfide ceramic composite materials that combine the transparency required for LWIR applications with enhanced mechanical strength and environmental durability. The composite ceramic structure integrates multiple crystalline phases and grain boundary characteristics that simultaneously provide optical transmission and structural integrity, resolving the contradiction between strength and weatherability while maintaining transparency.
2Strength
If ceramic polycrystalline materials are produced to increase strength, then mechanical strength improves, but transparency in the LWIR range deteriorates
Solution Approach 1:
The patent applies local quality control by optimizing specific microstructural features including grain size distribution, phase composition, and grain boundary characteristics. By controlling the local microstructure to have finer grains and specific phase arrangements, the material achieves both high mechanical strength and maintained LWIR transparency, as the local structural features are tuned to minimize light scattering while maximizing strength.
Solution Approach 2:
The patent utilizes parameter changes in the ceramic processing including sintering temperature, pressure, and atmosphere composition to transform the material properties. By adjusting these parameters during fabrication, the ceramic achieves an optimal balance between mechanical strength and optical transparency, where controlled densification and phase formation enable simultaneous improvement of both properties.
3Ease of manufacture
If conventional single crystal materials are used, then ease of manufacture is maintained, but mechanical strength and environmental durability are insufficient
Solution Approach 1:
The patent replaces the conventional single crystal growth process with a ceramic powder processing route that involves mechanical mixing, pressing, and sintering. This substitution of the manufacturing approach enables production of materials with superior mechanical properties while maintaining manufacturing simplicity, as the ceramic process avoids complex crystal growth equipment and procedures.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The resulting ceramic materials are significantly stronger and more environmentally durable than existing materials, enabling the production of transparent ceramic bodies suitable for LWIR and MWIR sensor windows with reduced sulfur loss and porosity, maintaining transparency and strength across a wide temperature range.
Implementation Method 1
spraying soluble calcium and lanthanoid salts into at least one precipitating solution to form a precipitate comprising insoluble calcium and lanthanoid salts
Implementation Method 2
oxidizing the precipitate comprising insoluble calcium and lanthanoid salts
Implementation Method 3
sulfurizing the optionally oxidized precipitate to form a fine powder of calcium lanthanoid sulfide
Implementation Method 4
flame pyrolyzing a liquid comprising calcium and lanthanoid salts to form a mixture comprising oxides of calcium and the lanthanoid
Data Source
AI summary
A method of preparing a fine powder of calcium lanthanoid sulfide is disclosed. The method includes spraying soluble calcium and lanthanoid salts into at least one precipitating solution to form a precipitate comprising insoluble calcium and lanthanoid salts, optionally, oxidizing the precipitate comprising insoluble calcium and lanthanoid salts, and sulfurizing the optionally oxidized precipitate to form a fine powder of calcium lanthanoid sulfide. An alternative method for forming the powder is by flame pyrolysis. The calcium lanthanoid sulfide powder produced by either method can have an impurity concentration of less than 100 ppm, a carbon concentration of less than 200 ppm, a BET surface area of at least 50 m2/g, and an average particle size of less than 100 nm.