Full
JIANG Tianxing (1995-), male, Doctoral candidate. E-mail: 1258295612@qq.com
Outline
Ultra-high temperature ceramics are a new type of heat-resistant materials that could withstand extreme service environments such as long periods of ultra-high sound speeds, atmospheric flight, and re-entry. It usually refers to advanced ceramics with a melting point above 3 000 ℃ and the ability to resist ablation in an oxidizing atmosphere above 2 000 ℃, mainly including carbides, nitrides, and borides of transition metals in the IVB and VB groups. As thermal protection materials used in extreme environments, single-phase ultra-high temperature ceramics exhibit extremely poor antioxidant performance in extreme environments. In this paper, the development of ultra-high temperature ceramics is moved towards diversification and multiphase, and ultra-high temperature ceramic matrix composites are formed by compounding with fibers and other materials.
Polymer conversion methods mainly include two types: the first type is metal hybrid polymer method, which use alcohol oxides (such as alcohol organic compounds, acetate, acetylacetone, salicylic acid, etc.) to modify and obtain polymer precursors with M (Ti, Zr, Hf, Ta, Nb, etc.) and O acted as the main chains; The second type is the metal organic polymer method, which choose alkyl, alkenyl, alkynyl or aryl ligands to realize the chemically modified organic metal compounds (such as metallocene compounds, methylamine metal compounds, etc.) to obtain polymer precursors containing M and C or B bonds. With the diversification and multiphase development of ultra-high temperature ceramics, the multi-component nanocomposite ceramics obtained by reacting metal with polycarbosilane, polysilazane, polyborosilicate, etc. were significantly better than those obtained by traditional ultra-high temperature ceramics. The polymer conversion ultra-high temperature ceramic technology could realize the control of the composition, microstructure, properties, etc., which could exhibit a revolutionary significance in the preparation of structure function integrated ceramics.
The preparing process of ceramics and composites via PDCs becomes more and more sophisticated. The oxygen-containing system requires a carbon thermal reduction process to obtain ultra-high temperature ceramics, resulting in a lower yield of ultra-high temperature ceramics with more pores and cracks, which leads to excessive PIP times, long densification time, and poor mechanical properties. Therefore, the development of oxygen free ultra-high temperature ceramic precursors is one of the important direction for the future development. Moreover, compared to single-phase ultra-high temperature ceramics, diversified and multiphase ultra-high temperature ceramics exhibite superior performance. Therefore, the development of precursors that could achieve a diversified ultra-high temperature multiphase ceramics was also an important direction to develop in the future. Polymer precursors can also be used in new application fields such as preparing ultra-high temperature thermal protective coatings, ultra-high temperature binders, and ultra-high temperature ceramic fibers. Polymer precursors would have extremely wide applications in the future.
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| 科 Family | 属数 Number of genus | 种数 Number of species | 占总种数比例 Percentage of total species (%) | 属 Genus | 种数 Number of species | 占总种数比例 Percentage of total species (%) |
|---|---|---|---|---|---|---|
| 鹅膏菌科Amanitaceae | 2 | 11 | 5.26 | 鹅膏菌属 Amanita | 10 | 4.78 |
| 小菇科 Mycenaceae | 2 | 12 | 5.74 | 丝盖伞属 Inocybe | 5 | 2.39 |
| 多孔菌科 Polyporaceae | 8 | 14 | 6.70 | 蜡蘑属 Laccaria | 5 | 2.39 |
| 红菇科 Russulaceae | 3 | 23 | 11.00 | 小皮伞属 Marasmius | 6 | 2.87 |
| 小菇属 Mycena | 11 | 5.26 | ||||
| 光柄菇属 Pluteus | 5 | 2.39 | ||||
| 红菇属 Russula | 17 | 8.13 | ||||
| 栓菌属 Trametes | 5 | 2.39 |
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