Common knowledge of coating: new silicon polymer (1)

Core tips: Chapter 9 new silicon polymer In recent 20 years, the silicon-containing polymers developed include: polysilane with silicon as the main chain; Polycarbosilane with silicon carbon as the main chain; polysilazane with silicon nitrogen as the main chain These polymers have special properties They can be used as ceramic precursor, high temperature resistant fiber, high temperature resistant coating, optical material, photoresist, liquid crystal material, initiator of olefin polymerization, etc We mainly introduce the silicon polymer used in C / C composite for oxidation resistance Section I oxidation resistance of C / C Composite C / C composite is a kind of composite material, its reinforcing phase Paint knowledge | precautions for wall paint color selection Recommended introduction: when painting the wall, the owner sometimes has difficulty in choosing what color of the wall paint to paint In fact, there is no ugly color in the wall paint, only the disharmonious color matching The use of wall color contains the knowledge of health Too strong color will stimulate people's perception, make people have a sense of fidgety, affect people's mental health Grasp the basic principles of wall color and paint a colorful space 1、 Wall paint color selection notice 1 Light color is generally used for the top surface Light colors make people feel light, dark colors make people feel heavy Usually, the treatment of rooms is from top to bottom, from shallow to deep For example, the ceiling and walls of rooms are white and Home of coatings: in Chapter 9, the new silicon-containing polymers developed in recent 20 years include polysilane with silicon as the main chain, Polycarbosilane with silicon carbon as the main chain, and polysilazane with silicon nitrogen as the main chain These polymers have special properties They can be used as ceramic precursor, high temperature resistant fiber, high temperature resistant coating, optical material, photoresist, liquid crystal material, initiator of olefin polymerization, etc We mainly introduce the silicon polymer used in C / C composite for oxidation resistance Section 1 oxidation resistance of C / C composite C / C composite is a kind of composite material Its reinforcement phase and matrix phase are carbon fiber and carbon respectively The carbon matrix can be resin carbon, deposited carbon or a combination of the two It is a kind of all carbon heterogeneous material C / C composite has some special properties: 1) the density is small (< 2.0g / cm - 3), only 1 / 4 of high temperature nickel base alloy, 1 / 2 of ceramic material 2) With the increase of temperature (up to 2200 ℃), its strength is not only not decreased, but also higher than that of room temperature This unique performance is incomparable to other materials such as metal materials, resin matrix composites, metal matrix composites, ceramics, etc 3) It has good anti ablation performance, even ablation, and can reach a high temperature higher than 3000 ℃ It is used in the environment of short-term ablation, such as rocket engine nozzle and throat lining used in aerospace industry, and has unparalleled advantages 4) It has excellent friction and wear resistance, small friction coefficient and stable performance, and is the best candidate material for various wear-resistant and friction parts It has the characteristics of other composite materials, such as high strength, high modulus, high fatigue strength and creep properties 1、 Although C / C composite is the most heat-resistant material at present (about 2300K), the oxidation of C / C composite begins at 400 ℃, and is serious at 450-500 ℃, even at low oxygen partial pressure, it can be mixed with H2O, O2, Co 2 Co reacts in an oxidizing atmosphere, resulting in weight loss, which leads to the change of the material size, and also destroys the fiber and reduces its mechanical properties, thus affecting its reinforcement effect It is very harmful to the material of missile throat lining and end cap and other thermal structural parts For example, the material size change caused by oxidation of missile throat lining and end cap will affect the thrust, range and life of missile Therefore, countries attach great importance to solving the oxidation problem of C / C Composite, which is also the hot and difficult problem in the research of C / C composite at present 1 Fiber / matrix interface: the micro analysis shows that the surface of carbon fiber is not smooth, but micro groove or step groove along the axis Taking CVI Process as an example, in this process, pyrolytic carbon is deposited on the surface of the fiber preferentially at the steps with high surface activity, forming strong bonding, while weak bonding is formed in the grooves During the subsequent high-temperature treatment of 2000-3000 ℃, these weak bonding places are easy to break and form pores, thus becoming the diffusion channel of oxidation atmosphere That is to say, the fiber / matrix interface is the sensitive area of oxidation Because the fiber and matrix have different coefficient of thermal expansion, cracks are produced at the interface of fiber / matrix during the cooling process after heat treatment, thus forming the diffusion channel of oxidation atmosphere 2 Oxidation of different deposited carbon structures: generally, the deposited carbon is divided into smooth layer (SL), rough layer (RL) and isotropic layer (ISO) according to the results observed by polarizing microscope The anisotropy of SL layer is larger than that of ISO and RL layer, and it is easier to oxidize The RL layer has good comprehensive properties and high graphitization rate, but the mixed structure is often obtained because of the difficult control of technological conditions 3 Influence of reinforcement structure on C / C composite: reinforcement structure not only has influence on the mechanical properties of C / C composite, but also on its oxidation behavior The oxidation behavior of different reinforcement structures (carbon felt and carbon cloth) has been proved in the literature Because the pore size and distribution of carbon felt and carbon cloth are different, the inner surface area of carbon felt and carbon cloth will be affected, and then the adsorption behavior of gas will be affected, so the oxidation order will be affected Only by studying the influence of fiber arrangement structure and subsequent treatment process on the oxidation behavior of C / C composite, can the structure and process be optimized 4 The influence of carbon fiber impurities on C / C composites: Carbon fiber contains about 0.01-0.1% Mo, V, O, N, Cr, Na, Ca and other impurities, which are brought in during the production of carbon fiber precursor, or introduced during the impregnation of asphalt and resin, and can not be completely removed even after high temperature treatment, and become the catalyst for oxidation If these elements are not evenly distributed in the fiber dimension, the fiber will be oxidized unevenly, resulting in fiber defects and affecting its reinforcement effect 。 Home of coatings is specialized in coatings, diatom mud, paint coating, coating technology, fire retardant coating news and coating, diatom mud, paint coating, coating technology, fire retardant coating decoration knowledge and decoration renderings,