sic 探究 research

September 06, 2021

 

SiC俗称金刚砂,一般是用硅石和焦炭混合后通电反应制成的。碳化硅是一种共价键化合物,具有玻璃光泽,密度为3.17~3.47g/m3。莫氏硬度9.2,在还原气氛下2600℃开始分解;抗拉强度71.5MPa、耐压强度为1029MPa。原子间结合力强,具有高熔点、高硬度、高强度和低膨胀性、高热导性、高导电性、强化学稳定性,因此是良好的耐火材料原料。但是,在氧化气氛下,SiC易氧化,只有形成SiO2保护膜时,方能减缓氧化。

SiC具有热传导高、热膨胀低、与炉渣难以反应等许多通常氧化物原料所没有的特性。为此,从很早开始就被作为炉渣反应和高温剥落严重部位的耐火材料的主要原料使用。在不定形耐火材料中也是一样,从以捣打料和可塑料为主的时代到以低水泥浇注料为主的现在,SiC的重要性没有改变。SiC抗氧化气氛较弱,伴随着氧化生成固相的SiO2和碳以及气相的CO和COs气体。当温度超过1823K时,SiC不稳定,转变为SiO2。使ASC系转变成Al2O3-SiO2-C系。但如果该系统不是封闭系统,ASC质工作衬与外界接触时,CO分压有可能低于0.1Mpa,此时,SiC即是最稳定的。

 

碳具有不和渣铁反应、热膨胀率低等特点,因此碳材料具有耐渣侵蚀性强、不易粘渣的特性,且在一定温度条件下,基质中的Si与C发生反应,生成非常细小的(直径约为0.1~0.5μm)的纤维状SiC,形成SiC的补强效应。所以在研制ASC质耐火材料时,应选用挥发较少,固定碳相对较多的含碳材料,并按一定比例加入防氧化剂和分散剂。石墨材料具有很高的热稳定性,升华温度为3800℃,在铁水中很容易达到饱和,所以石墨具有抗铁水侵蚀的优点。常用的石墨材料有无定性石墨、人造石墨、球状石墨和鳞片状石墨。石墨材料含有部分挥发物,本身又易被氧化,所以,在追求材料致密化时不易添加石墨材料。然而,石墨的导热系数大,能使浇注料内部热量均匀分布,热应力相应减少,能提高浇注料的热震稳定性和耐剥落性。在浇注料中,石墨和沥青都可以作为碳添加剂引入。在浇注料混合物中,石墨难以稳定,当浇注料中加入水时,由于其结构,在施工中大部分石墨到达表面并很容易消失。由于其较差的可润湿性、可分散性和铝质抗氧化剂的水化趋势,会产生许多新问题,这些问题己经妨碍了含碳浇注料的发展及应用。为了在浇注料混合物中配有石墨,石墨应用一定的改性剂进行处理,以提高其粘附性。

以沥青为C源则可以避免上述缺点,沥青是煤焦油或石油经过蒸馏处理或催化裂化提取沸点不同的各种馏分后的残留物,是以芳香族和脂肪族结构为主体的混合物,呈棕黑色,不溶于水,组成和性能随原料来源、蒸馏方法和加工处理方法不同而异。

SiC, commonly known as diamond sand, is generally made of silica after mixing and coke.Silicon carbide is a covalent bond compound with a glass luster at a density of 3.17~3.47g/m3. Mo hardness is 9.2,2600℃ in reducing atmosphere; tensile strength 71.5MPa, is 1029MPa.The interatomic binding force is strong, has a high melting point, high hardness, high strength and low expansion, high heat conductivity, high conductivity, strong chemical stability, and therefore is a good refractory raw material.However, in an oxidative atmosphere, SiC is prone to oxidation, only when the SiO2 protective membrane is formed.

SiC has properties not found in many usual oxide raw materials such as high heat conduction, low thermal expansion and difficulty to react with slag.To this end, it was used as a primary raw material from early on for refractory to severe slag reaction and high temperature peeling sites.The same is true in indefinite refractory, and the importance of SiC remains unchanged from the era of tamping and plastic to the present era of low cement pouring.The SiC antioxidant atmosphere is weak, accompanied by oxidation of solid phase SiO2 and carbon as well as gas phase CO and COs gases.At temperatures above 1823K, the SiC is unstable and converted to SiO2. Turn the ASC line into the Al2O3-SiO2-C line.However, if the system is not a closed system, the ASC mass working lining in contact with the outside world, the CO partial pressure may be less than 0.1Mpa,, SiC is the most stable.

Carbon has the characteristics of incompatible slag iron reaction and low thermal expansion rate, so carbon material has the characteristics of strong slag corrosion resistance and easy adhesion, and under certain temperature conditions, Si in the substrate reacts with C to generate very small (about 0.1~0.5 μm diameter) fibrous SiC, to form the tonic effect of SiC.Therefore, in developing ASC quality refractory materials, less volatile and relatively more fixed carbon-containing materials should be selected, and antioxidants and dispersants should be added according to a certain proportion.Graphite materials have very high thermal stability, with a sublimation temperature of 3,800℃, which can easily reach saturation in iron water, so graphite has the advantage of resisting ferrowater erosion.Commonused graphite materials have qualitative, artificial, spherical and squamous graphite.Graphite materials contain some volatiles, which are easy to be oxidized, so it is not easy to add graphite materials in the pursuit of material compaction.However, the large thermal conductivity of graphite can make the uniform distribution of heat inside the pouring material, and reduce the thermal stress accordingly, and improve the thermal shock stability and peeling resistance of the cast material.In pouring materials, both graphite and asphalt can be introduced as carbon additives.In the pouring mixture, the graphite is difficult to stabilize, and when water is added to the pouring, most of the graphite reaches the surface and easily disappears during construction due to its structure.Due to its poor weidability, dispersability and the hydration trend of aluminum antioxidants, there are many new problems that have hindered the development and application of carbon pouring materials.To include graphite in the poured mixture, the graphite was treated with a certain modifier to improve its adhesion.

Bitumen as a C source can avoid the above disadvantages. Aspumen is a residue of coal tar or oil. It is a mixture of aromatic and aliphatic structure and is brown-black and insoluble in water. Its composition and performance vary with raw material source, distillation method and processing treatment method.

 

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