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China Precision Optics Corporation successfully developed a 4m silicon carbide mirror for aerospace Hay:B01ZKCC

Space telescope is the most important and direct tool for human research and exploration of the universe. Its development is related to the speed and progress of human research on the universe. It is an important scientific method for human development and progress and understanding of the natural world. Compared with ground-based telescopes, it has a good observation environment and observation conditions, and is favored by astronomers. Large-aperture space mirrors are the most important part of space telescopes, and they are also a key factor restricting the development of space telescopes. Carrying out research on the design and manufacturing of large-aperture space mirrors can solve major technical bottlenecks in space telescope technology and promote the development of space science in my country. It is a research work of great significance.

The mirror is so important, what material should be used to make it? From the optical glass of the first refraction lens, to the aluminum alloy and copper alloy of the first-generation reflective lens, to the second-generation metal beryllium, ULE, and Zerodur, these materials have more or less shortcomings in terms of mechanical and thermal properties. Later, developed countries in the West turned their attention to silicon carbide ceramics with excellent comprehensive properties.


Mirror optical material performance requirements

(1) The high mechanical strength can avoid the mechanical deformation of the lens body, so the material is required to have the highest possible elastic modulus, specific stiffness and as small as possible Poisson's ratio.

(2) Good thermal performance can avoid thermal deformation caused by temperature changes. Therefore, the base material of the reflector should have a small thermal expansion coefficient and as large a thermal conductivity as possible.

(3) Machinability. The base material of the reflector is required to be optically polished to obtain excellent surface roughness.

(4) High chemical stability. During processing, or long-term storage in a natural environment, the material is not corroded by water vapor or other atmospheres to ensure that the quality of the optical mirror is not damaged.

(5) The base material of the reflector must have a high degree of uniformity. This uniformity includes density, mechanical properties, and thermal properties. The unevenness of any aspect will have a serious impact on the processing and use of the mirror.

(6) Other requirements, such as low manufacturing cost, non-toxic and environmentally friendly, etc.

Comparative analysis of several mirror materials

Currently, mirror materials mainly include glass materials, low-expansion metal materials, ceramic materials, and composite materials. The glass material is the first-generation mirror material, and the commonly used ones are ULE and Zerodur. The thermal expansion coefficient of glass material is very low, and the optical processing performance is excellent, but the thermal conductivity of glass material is low, and the specific rigidity is poor.

The second-generation mirror material is a low-expansion metal material, mainly including Al and Be, etc. The metal material has excellent thermal conductivity, but its thermal expansion coefficient is relatively large, and its surface shape accuracy is easily affected by temperature. At the same time, the specific rigidity of Al is low, while the metal Be, although the specific rigidity is higher, is toxic and can cause fatal damage to the human body. Therefore, strict safety measures are required in the production process.

Silicon carbide materials belong to the third generation of mirror materials. The material has good chemical stability, excellent resistance to space particle radiation, low thermal expansion coefficient, high elastic modulus, and good thermal conductivity.

Silicon carbide material has the highest rigidity, good thermal conductivity, low linear expansion coefficient, and can manufacture large-size mirror blanks. With silicon carbide materials in mirror blank manufacturing, modification, optical processing, coating and other complete optical The processing methods of parts are gradually mature, and they are especially favored in large-aperture spatial optical systems.

Sintering process of silicon carbide mirror

The preparation process methods of SiC ceramic materials mainly include: hot pressing sintering process, reaction sintering process, atmospheric sintering process and chemical vapor deposition process (CVD). Among them, the hot-pressing sintering process is not suitable for preparing mirror blanks with complex shapes due to the limitation of the process; the shrinkage rate of the mirror blanks in the sintering process of the atmospheric pressure sintering process reaches 10%~15%, which is nearly clean for the preparation of precise dimensions. Unfavorable size molding.

The CVD technology to prepare SiC mirrors is to introduce a gas containing a silicon source (SiCl4) and a carbon source (CXHY) into the reaction furnace, and then synthesize SiC and deposit it on the substrate. The lens body prepared by this process has the best quality, but also the highest cost. This technology can only be used in special circumstances.

The reaction sintering process can prepare large-size and complex-shaped SiC mirror mirror blanks, and the preparation temperature of reaction sintering is relatively low, the sintering time period is short, the manufacturing cost of the mirror blank is low, the sintered structure is compact, comprehensive mechanical properties, and thermal characteristics It is better and meets the application requirements of super large-aperture mirrors.

Properties of SiC materials in different sintering processes

The world's largest silicon carbide mirror

According to the major national strategic needs and the development trend of silicon carbide ceramic materials, ZKCC began to carry out research on the preparation technology of silicon carbide mirrors at the end of the twentieth century. The founder of the team, Dr. Wenxing Zhao, led the project team through more than ten years of hard work, breaking through the core technologies of complex-structure silicon carbide ceramic preposition molding, blank connection, densification reaction sintering, etc., and successively developed 0.5-2m level Silicon carbide mirrors have been successfully used in commercial remote sensing, "Tianwen No. 1" payloads, and "high scores" and other model tasks.

Silicon carbide mirror with a diameter of 4m


Silicon carbide mirror with a diameter of 4m.jpg


In order to further expand its technological leadership, the project team proposed a research goal of 4m silicon carbide mirrors in 2009. In the following eight years, the research team experienced hundreds of experimental verifications and four failed sintering tests. Finally, the fifth mirror blank was successfully developed in March 2016, becoming the world's largest silicon carbide mirror with a diameter of 4.03m and a weight of 1.7t.


The optical processing and coating of the mirror blank were completed in 2018, and its surface shape accuracy and reflectivity fully met user requirements, and it has been applied to engineering projects. The successful development of 4m silicon carbide mirrors broke the foreign monopoly, marking that China's large-aperture optical manufacturing technology has entered the international advanced ranks, further consolidating China's leading advantage in the field of advanced optical system manufacturing, and promoting the realization of China's new optical remote sensing technology Leaping Development.

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