本文選題：先驅(qū)體轉(zhuǎn)化法 + 氮化硼　； 參考：《國防科學(xué)技術(shù)大學(xué)》2011年博士論文

【摘要】：隨著新型高馬赫數(shù)導(dǎo)彈天線罩對材料防熱、承載和透波性能的要求不斷提高,現(xiàn)有的透波纖維增強陶瓷基復(fù)合材料已經(jīng)成為天線罩技術(shù)發(fā)展的瓶頸。氮化硼(BN)纖維具有工作溫度高、高溫?zé)g率低、工作性能穩(wěn)定、介電常數(shù)和節(jié)電損耗小等優(yōu)點,是新型陶瓷基透波復(fù)合材料增強體的理想候選材料。在此背景下,本文開展了聚合物先驅(qū)體轉(zhuǎn)化法制備BN纖維的基礎(chǔ)研究。 在溫和條件下分別以共取代和分步取代法合成了三種不同結(jié)構(gòu)、可溶可熔的聚硼氮烷先驅(qū)體,合成過程均不需極低溫度,簡化了操作,降低了成本。分別采用NMR、FTIR、XPS、TGA和元素分析等手段對三種先驅(qū)體進(jìn)行了表征。 由三氯化硼和甲胺合成了PTMB,PTMB的分子中含有B3N3六元環(huán)、C-H、B-N、N-H和C-N等化學(xué)鍵;PTMB可溶于甲苯和二甲苯等溶劑,典型的PTMB的元素組成為(wt%):B(24.5), C(32.8), N(29.9)和H(10.2),其化學(xué)式可表示為BC1.20N0.94H4.5。在NH3中的處理可以提高PTMB的陶瓷產(chǎn)率,在NH3中的無機(jī)化可以除去碳元素;失重主要發(fā)生在600℃以下,900℃基本完成無機(jī)化;PTMB的分子結(jié)構(gòu)和較低的陶瓷產(chǎn)率不適宜用于制備BN纖維,但可能用作制備其它BN材料;經(jīng)1600℃處理的產(chǎn)物為t-BN,該BN在空氣中900℃時的失重小于3.0wt%,表現(xiàn)出了較好的抗氧化性能。 由三氯環(huán)硼氮烷和異丙胺合成的PTPiAB具有一定的熔融加工性能,PTPiAB的分子中含有B3N3六元環(huán)、C-H鍵、B-N鍵、N-H鍵和C-N鍵等特征結(jié)構(gòu);PTPiAB可溶于甲苯、二甲苯等常見有機(jī)溶劑;典型的PTPiAB的化學(xué)組成為(wt%):B (12.4)、N(35.8)、C(37.2)、H(9.3),其化學(xué)式可表示為BC2.7N2.2H8.1。1000℃時,PTPiAB在NH3中的陶瓷產(chǎn)率低于在Ar中的陶瓷產(chǎn)率;在NH3中的失重主要發(fā)生在800℃以下,800℃先驅(qū)體中的有機(jī)基團(tuán)基本消失,接近無機(jī)化;NH3的除碳效果明顯,600℃時已有94.0wt%的碳被除去;1400℃以上為晶粒長大的主要區(qū)間,1800℃熱解產(chǎn)物的(002)晶面間距為0.334nm,密度為2.03g·cm-3,在空氣中900℃以下的增重小于0.3wt%,抗氧化性能隨結(jié)晶程度的增加而增強。 由正丙胺/甲胺和三氯環(huán)硼氮烷合成了PPAB。通過調(diào)控原料的比例,控制合成溫度和時間等參數(shù),能得到可以熔融的PPAB先驅(qū)體,軟化點隨聚合反應(yīng)溫度的增加和保溫時間的延長而升高;優(yōu)化的合成工藝參數(shù)為n-PA?MA?TCB=2?1?1(摩爾比),聚合溫度為150~170℃,保溫時間為5~7h,所合成PPAB的軟化點為90~100℃;典型的PPAB含有B、N、C和H元素,元素組成為(wt%):B(22.28)、C(23.24)、N(44.75)、H(7.78),其化學(xué)式可近似表示為BC0.94N1.55H3.75;PPAB分子中含有N-H、C-H、B-N和C-N等化學(xué)鍵,B3N3六元環(huán)通過-B-(NCH3)-B-連接;典型PPAB的數(shù)均分子量為1002(相對于聚苯乙烯標(biāo)樣),重均分子量為1359,分散系數(shù)為1.50,可溶于甲苯和二甲苯等溶劑,在Ar中1000℃的陶瓷產(chǎn)率約為50wt%。 對三種先驅(qū)體進(jìn)行的熔融挑絲實驗表明,PPAB具有更好的成絲性,更適合用于制備BN纖維。PTMB和PTPiAB可用于制備其它形式的BN材料。 對PPAB在空氣中的穩(wěn)定性研究表明,PPAB在空氣中極易水解,水解程度隨溫度、濕度和時間的增加而增大;PPAB對少量的O2不敏感,水解主要是由于H2O引起的;PPAB的水解引入了大量氧元素,生成B-O鍵,形成不溶不熔的三維網(wǎng)狀結(jié)構(gòu),不能熔融加工;水解的PPAB在Ar中的主要熱解產(chǎn)物為BN和B2O3。比較了以PTPiAB和PPAB兩種不同分子結(jié)構(gòu)先驅(qū)體所制備BN的異同,結(jié)果表明:得到的BN均具有近化學(xué)計量比,不含碳雜質(zhì),具有類似的組成和結(jié)構(gòu);兩種BN的結(jié)晶程度不同,具有對稱結(jié)構(gòu)的分子單體TPiAB得到的BN結(jié)晶程度更高,氧化性能優(yōu)于由非對稱結(jié)構(gòu)單體PAB得到的BN。 考察了PPAB的軟化點、紡絲溫度和紡絲壓力等工藝參數(shù)對熔融紡絲的影響,當(dāng)軟化點在93~112℃,紡絲溫度高于軟化點20~70℃,紡絲壓力為0.4~0.6MPa,可以得到連續(xù)長度大于200m的PPAB纖維。 PPAB纖維在NH3中的不熔化過程伴隨著凝膠含量變化、失重和碳含量下降,碳含量的下降主要由烷基基團(tuán)的脫去引起,C-N鍵未參與反應(yīng);合適的不熔化工藝為,以0.5℃/min的升溫速率升溫至70~80℃并保溫80min,由此得到的PPAB不熔化纖維的凝膠含量大于90wt%。 PPAB在N2中熱解得到含碳的BN,而在NH3中熱解會脫除碳元素,得到近化學(xué)計量比的BN;在N2中的陶瓷產(chǎn)率高于NH3中陶瓷產(chǎn)率,NH3中的熱解產(chǎn)物具有更好的結(jié)晶性能、抗氧化性能和介電性能。 采用NH3作為熱解氣氛,考察了溫度、NH3濃度、保溫時間和升溫速率等參數(shù)對PPAB不熔化纖維無機(jī)化過程的影響和無機(jī)化纖維組成、結(jié)構(gòu)的影響,結(jié)果表明:在800℃基本完成無機(jī)化,在NH3/N2=1:1(vol)的混合氣氛中即可實現(xiàn)脫碳。較優(yōu)的無機(jī)化工藝為:在NH3濃度為50vol%的NH3/N2熱解氣氛中,以4℃/min的升溫速率升至800℃并保溫2h,由此得到的無機(jī)纖維碳含量小于0.5wt%。 對無機(jī)化纖維進(jìn)行高溫處理有利于獲得性能更優(yōu)異的BN纖維,研究了處理溫度對纖維結(jié)晶性能、密度、力學(xué)性能以及抗氧化性能的影響規(guī)律。結(jié)果表明:1200℃以下是纖維密實性增加的主要階段, 1800℃得到BN纖維具有較好的抗氧化性,密度為1.92g·cm-3,(002)晶面間距和晶粒尺寸分別為0.337nm和6.50nm,拉伸強度為850MPa,在頻率為10GHz處的介電常數(shù)為3左右、損耗角正切為10-3量級。
[Abstract]:With the requirements of the new high Maher number missile radome to prevent heat, load and wave performance, the existing permeable fiber reinforced ceramic matrix composites have become the bottleneck of the development of the radome technology. Boron nitride (BN) fiber has high working temperature, low high temperature ablative rate, stable working performance, low dielectric constant and power saving loss. In this context, the basic research on the preparation of BN fibers by polymer precursor conversion method is carried out in this context.
Three different structures, soluble and melted polyboranane precursors were synthesized by CO substitution and stepwise substitution under mild conditions. The synthesis process was not very low, the operation was simplified, and the cost was reduced. The three precursors were characterized by NMR, FTIR, XPS, TGA and elemental analysis respectively.
PTMB is synthesized from three boron chloride and methylamine, and the molecules of PTMB contain chemical bonds of six membered rings of B3N3, C-H, B-N, N-H and C-N, and PTMB can be dissolved in toluene and xylene. The typical PTMB elements are (wt%): B (24.5), C (32.8), 29.9 and 10.2. The carbon element can be removed by the inorganic chemical production in NH3; the weight loss is mainly below 600 C, and the inorganic is basically completed at 900 C; the molecular structure of PTMB and the lower ceramic yield are not suitable for the preparation of BN fiber, but it may be used for the preparation of other BN materials; the product treated at 1600 C is t-BN, and the weight loss of the BN in the air is less than 3 .0wt% shows good antioxidant properties.
PTPiAB, synthesized by three chloro-boranonanane and isopropyl amine, has certain melting processing properties, PTPiAB molecules contain B3N3 six membered ring, C-H bond, B-N bond, N-H bond and C-N bond, and PTPiAB can be dissolved in the common organic solvents such as toluene, xylene, etc.; typical PTPiAB is composed of (wt%): B (35.8), N (37.2), 9.3), and its chemistry When the formula can be expressed as BC2.7N2.2H8.1.1000 C, the ceramic yield of PTPiAB in NH3 is lower than that in Ar; the weight loss in NH3 is mainly below 800 C, and the organic groups in the 800 C precursor are basically disappearing and close to the inorganic; the carbon removal effect of NH3 is obvious, and the carbon of 94.0wt% has been removed at 600 C, and the grain growth above 1400 degrees C is the grain growth. In the main section, the (002) surface spacing of the pyrolysis product at 1800 C is 0.334nm, the density is 2.03g cm-3. The weight gain below 900 C in the air is less than 0.3wt%, and the oxidation resistance increases with the increase of the degree of crystallization.
The PPAB precursor which can be melted can be obtained by controlling the proportion of the raw material and controlling the parameters such as temperature and time by controlling the proportion of the raw material and controlling the temperature and time of the synthetic PPAB.. The softening point increases with the increase of the polymerization temperature and the prolongation of the heat preservation time. The optimized synthetic parameters are n-PA? MA? TCB=2? 1? 1 (mole ratio) and polymerization temperature The softening point of the synthesized PPAB is 150~170 C and 5~7h, and the softening point of the synthesized PPAB is 90~100 C; the typical PPAB contains B, N, C and H elements, and the element composition is B (22.28), C (44.75), 7.78. The average molecular weight of the typical PPAB is 1002 (relative to the standard polystyrene), the weight average molecular weight is 1359, the dispersion coefficient is 1.50, the solvent is soluble in toluene and xylene, and the yield of ceramics at 1000 C is about 50wt%. in Ar.
The experiment of three kinds of precursor melt wire pick - up shows that PPAB has better filaments and is more suitable for the preparation of BN fiber.PTMB and PTPiAB for the preparation of other forms of BN material.
The stability of PPAB in air shows that PPAB is very easy to hydrolyze in the air, and the degree of hydrolysis increases with the increase of temperature, humidity and time; PPAB is insensitive to a small amount of O2, and the hydrolysis is mainly caused by H2O; the hydrolysis of PPAB has introduced a large number of oxygen elements to form a B-O bond, forming an insoluble and unmelted three-dimensional network structure that can not be fused added. The main pyrolytic products of the hydrolyzed PPAB in Ar compare the similarities and differences of BN produced by two different molecular structural precursors of PTPiAB and PPAB, and the results show that the obtained BN has a near stoichiometric ratio, no carbon impurities, similar composition and structure, and the two BN has different crystallinity and a symmetrical structure of molecular single. The crystallization degree of BN obtained by bulk TPiAB is higher and the oxidation property is better than that of BN. obtained by asymmetric structure monomer PAB.
The effects of the softening point of PPAB, spinning temperature and spinning pressure on the melt spinning are investigated. When the softening point is at 93~112 C, the spinning temperature is higher than the softening point 20~70 C, the spinning pressure is 0.4~0.6MPa, and the continuous length of PPAB fiber with a continuous length greater than 200m is obtained.
The melting process of PPAB fiber in NH3 is accompanied by the change of the gel content, the weight loss and carbon content decrease, the decrease of carbon content is mainly caused by the removal of the alkyl group, the C-N bond is not involved in the reaction; the appropriate melting process is that the heating rate of 0.5 C /min is heated to 70~80 and 80min, thus the gel of the PPAB non melting fiber is obtained. The content is more than 90wt%.
PPAB is pyrolyzed in N2 to get carbon containing BN, and the pyrolysis of NH3 will remove the carbon element and get a near stoichiometric BN; the ceramic yield in N2 is higher than the ceramic yield in NH3, and the pyrolysis products in NH3 have better crystallization properties, antioxidant properties and dielectric properties.
The influence of temperature, NH3 concentration, heat preservation time and heating rate on the inorganic process of PPAB fiber and the inorganic fiber composition and structure are investigated by using NH3 as the pyrolysis atmosphere. The results show that the inorganic chemical can be accomplished basically at 800 C and can be decarbonization in the mixed atmosphere of NH3/N2=1:1 (Vol). The better inorganic chemical industry can be achieved. The art is: in the NH3/N2 pyrolysis atmosphere of 50vol% with the concentration of NH3, the temperature rising to 800 C at 4 centigrade /min and thermal insulation 2h, the carbon content of the inorganic fiber is less than 0.5wt%.
The high temperature treatment of inorganic fibers is beneficial to obtaining better performance of BN fibers. The effects of temperature on the crystalline properties, density, mechanical properties and antioxidant properties of the fibers are studied. The results show that the main phase of fiber density increases below 1200 C, and the BN fiber has better oxidation resistance and density at 1800. For 1.92g. Cm-3, (002) the crystal space and grain size are 0.337nm and 6.50nm respectively, the tensile strength is 850MPa, the dielectric constant at the frequency of 10GHz is about 3, and the loss angle tangent is 10-3.

【學(xué)位授予單位】：國防科學(xué)技術(shù)大學(xué)
【學(xué)位級別】：博士
【學(xué)位授予年份】：2011
【分類號】：TQ343

【引證文獻(xiàn)】

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本文編號：1807348