聚碳硅烷的改性及其抑晶行为研究
发布时间：2018-10-23 13:25
【摘要】：采用陶瓷先驱体转化法制备碳化硅(SiC)陶瓷纤维具有拉伸强度高、模量高、纤维直径小等优点,广泛应用于航天、航空、以及其它耐高温应用领域。但是通过该方法制备出的Si C陶瓷在耐高温性能上的表现通常很难达到使用预期。主要是因为SiC陶瓷中存在的富余C和富余O对其高温结晶会产生不利影响,无定形结构Si—C—O会分解为SiO、CO和C,其中SiO和C会进一步发生反应生成新的β-SiC相,新生成SiC相会在已结晶的β-SiC晶界处结晶长大,从而撑破晶界,导致材料的热稳定性低于理论值。本论文的主要研究内容有:1)使用低温等离子体处理技术,改性聚碳硅烷的反应活性,采用红外光谱(FT-IR)对反应产物进行结构表征,并通过热重分析(TGA)对改性产物进行陶瓷产率分析;2)引入具有抑晶作用的异种元素B、Al,改善SiC先驱体聚碳硅烷(PCS)的高温热稳定性,以频那醇硼烷(PIN-BH)为硼源,以乙酰丙酮铝(Al(AcAc)3)为铝源,在N2气氛下,以二甲苯为溶剂,分别与PCS进行缩合反应,合成了化学性质稳定的含B、Al聚碳硅烷(B-PCS、Al-PCS),将PCS、PIN-BH以及PCS、Al(AcAc)3在不同工艺条件下进行回流反应,研究并确定其最佳改性工艺;3)着重研究B改性PCS,为除去反应物PIN-BH,对B-PCS进行300℃热处理,并在Ar气氛下烧结成为SiC陶瓷,通过FT-IR和核磁共振氢谱(1H-NMR)表征了B-PCS分子结构中的含B基团,通过凝胶渗透色谱(GPC)表征了B-PCS的交联行为以及分子量及其分布,通过X射线衍射仪(XRD)表征了B-PCS陶瓷产物的抑晶行为。研究结果表明,1)低温等离子处理使PCS中Si—H键的含量增加;2)B改性PCS的最佳工艺为:PIN-BH投料配比10%wt,反应时间5h,反应温度110℃,陶瓷产率为相较于PCS从78.7%上升至90.1%,数均分子量(?)从4818上升至5123,分子量分布变宽;3)B-PCS分子侧链中存在含B基团;B-PCS在1400℃的烧结产物存在无定形SiC结构,而PCS烧结产物中并不存在,说明B元素起到了对SiC的高温抑晶作用。
[Abstract]:Sic (SiC) ceramic fibers prepared by ceramic precursor transformation have many advantages such as high tensile strength, high modulus and small fiber diameter. They are widely used in aerospace, aviation and other high temperature resistance applications. However, the performance of Si C ceramics prepared by this method in high temperature resistance is difficult to meet the expectations of use. The main reason is that the existence of surplus C and O in SiC ceramics will have a negative effect on the crystallization at high temperature. The amorphous Si-C-O will be decomposed into SiO,CO and C, in which SiO and C will react further to form a new 尾-SiC phase. The newly formed SiC phase will grow up at the crystalline 尾-SiC grain boundary, thus breaking through the grain boundary, resulting in the thermal stability of the material being lower than the theoretical value. The main contents of this thesis are as follows: 1) the reaction activity of polycarbosilane modified by low temperature plasma treatment was studied. The structure of the product was characterized by infrared spectroscopy (FT-IR). The ceramic yield of the modified product was analyzed by thermogravimetric analysis (TGA). 2) introducing the dissimilar element Bnl with inhibitory effect to improve the high temperature thermal stability of SiC precursor polycarbosilane (PCS), using PIN-BH as boron source and acetylacetone aluminum (Al (AcAc) 3 as aluminum source. In N _ 2 atmosphere, PCS,PIN-BH and PCS,Al (AcAc) _ 3 were refluxed under different conditions by condensation reaction with PCS in N _ 2 atmosphere. The optimum modification process was studied and determined. 3) the heat treatment of B-PCS by B modified PCS, to remove the reactant PIN-BH, was carried out at 300 鈩，
本文编号：2289387
[Abstract]:Sic (SiC) ceramic fibers prepared by ceramic precursor transformation have many advantages such as high tensile strength, high modulus and small fiber diameter. They are widely used in aerospace, aviation and other high temperature resistance applications. However, the performance of Si C ceramics prepared by this method in high temperature resistance is difficult to meet the expectations of use. The main reason is that the existence of surplus C and O in SiC ceramics will have a negative effect on the crystallization at high temperature. The amorphous Si-C-O will be decomposed into SiO,CO and C, in which SiO and C will react further to form a new 尾-SiC phase. The newly formed SiC phase will grow up at the crystalline 尾-SiC grain boundary, thus breaking through the grain boundary, resulting in the thermal stability of the material being lower than the theoretical value. The main contents of this thesis are as follows: 1) the reaction activity of polycarbosilane modified by low temperature plasma treatment was studied. The structure of the product was characterized by infrared spectroscopy (FT-IR). The ceramic yield of the modified product was analyzed by thermogravimetric analysis (TGA). 2) introducing the dissimilar element Bnl with inhibitory effect to improve the high temperature thermal stability of SiC precursor polycarbosilane (PCS), using PIN-BH as boron source and acetylacetone aluminum (Al (AcAc) 3 as aluminum source. In N _ 2 atmosphere, PCS,PIN-BH and PCS,Al (AcAc) _ 3 were refluxed under different conditions by condensation reaction with PCS in N _ 2 atmosphere. The optimum modification process was studied and determined. 3) the heat treatment of B-PCS by B modified PCS, to remove the reactant PIN-BH, was carried out at 300 鈩，
本文编号：2289387
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