本文選題：負熱膨脹　切入點：鎢酸鋯　出處：《上海交通大學(xué)》2015年碩士論文

【摘要】：近年來,鎢酸鋯作為負熱膨脹系數(shù)大、負熱膨脹溫度范圍大、且具有各向同性等優(yōu)點的負熱膨脹材料,在航空航天、精密儀器等對材料的熱穩(wěn)定性要求極高的領(lǐng)域獲得了廣泛的關(guān)注與應(yīng)用。然而,鎢酸鋯晶須和不規(guī)則的顆粒作為增強相制備復(fù)合材料可能影響材料的機械性能,同時鎢酸鋯較大的密度制約了其在追求輕量化的航空航天等領(lǐng)域的應(yīng)用。而納米材料,尤其是空心結(jié)構(gòu)納米材料,由于其自身的特殊性能,可以顯著降低復(fù)合材料的熱膨脹系數(shù),并有效降低復(fù)合材料密度。因此如何制備納米尺寸、低密度、并具有幾何均勻性的鎢酸鋯空心球,是本文研究的重點。本文探討了鎢酸鋯空心微納米結(jié)構(gòu)的液相合成、表征、反應(yīng)機理以及其負熱膨脹性能,通過選擇適當(dāng)?shù)闹苽浞椒�、對液相合成中溶液酸堿性的控制、選擇合適的前驅(qū)體反應(yīng)物與表面添加劑等,制備了三種不同的鎢酸鋯結(jié)構(gòu),包括一維納米棒包覆空心球結(jié)構(gòu)、零維納米空心球與零維納米實心球,分析了反應(yīng)機理,并對后續(xù)熱處理過程的結(jié)晶動力學(xué)進行了分析。1.一維納米鎢酸鋯包覆空心球結(jié)構(gòu)的制備利用水熱反應(yīng)制備了單分散膠體碳微球作為模板,采用模板法-溶膠凝膠法相結(jié)合,制備了鎢酸鋯納米棒包覆的空心球殼結(jié)構(gòu),并對其進行了系統(tǒng)的表征與負膨脹性能測試。產(chǎn)物具有較高的結(jié)晶度與純度,制備過程簡單、清潔,所得鎢酸鋯空心球密度為2.8g/cm3,較理論值降低約45%;具有良好的負熱膨脹性能,在室溫-200°C溫度區(qū)間的平均熱膨脹系數(shù)為-11.4×10-6K-1,較理論值有所降低,這是由于溶膠-凝膠法制備得到納米棒,提高了負熱膨脹性能。2.零維鎢酸鋯納米球的制備通過對水熱合成反應(yīng)過程、影響因素與反應(yīng)機理的研究,實驗采用了在水熱條件下改變礦化劑鹽酸與金屬的摩爾比,控制了水熱合成過程,觀測到了依賴于反應(yīng)反應(yīng)酸堿度的形貌演化過程,并利用這一方法分別制備得到納米級別鎢酸鋯空心球與實心球,產(chǎn)率高、尺寸小、分布較為均勻,并具有良好的負熱膨脹性能。同時分析了不同條件下,得到不同形貌的水熱合成機理,分別為溶解-再結(jié)晶機制與原位轉(zhuǎn)化機制。實驗所得鎢酸鋯空心球密度為3.6g/cm3,較理論值降低約29.1%;具有良好的負熱膨脹性能,在室溫-200°C溫度區(qū)間的平均熱膨脹系數(shù)為-9.15×10-6K-1。3.鎢酸鋯前驅(qū)體結(jié)晶動力學(xué)的研究鎢酸鋯在燒結(jié)過程中的結(jié)晶動力學(xué)不僅受到固相轉(zhuǎn)變過程中外部因素的影響,也受到反應(yīng)前驅(qū)體形貌與尺寸的制約。利用KJMA方程對不同形貌前驅(qū)體的結(jié)晶過程進行分析,對于實心納米球,740°C時反應(yīng)級數(shù)為0.54,反應(yīng)活化能為489 kJ/mol遵循D3擴散機制�？招募{米球,反應(yīng)級數(shù)為0.96,在900°C時為一級反應(yīng),由于尺寸較小且表面存在細微結(jié)構(gòu),因此反應(yīng)活化能僅為63 kJ/mol。晶須的熱處理溫度為610°C,所需時間最長為2h,該溫度下的反應(yīng)級數(shù)為0.62,D1擴散模型,活化能353kJ/mol。
[Abstract]:In recent years, zirconium tungstate as negative thermal expansion coefficient, negative thermal expansion temperature range, and has a negative thermal expansion material isotropy, in aerospace, precision instruments and other materials on the thermal stability of high demand areas get extensive attention and application. However, zirconium tungstate whiskers and irregular preparation of composite particles as may affect the mechanical properties of reinforced materials is made, and the density of zirconium tungstate greatly restricted its application in pursuit of lightweight aerospace and other fields. And nano materials, especially the hollow structure of nano material, because of its special properties, can significantly reduce the thermal expansion coefficient of the composites. And effectively reduce the density of the composites. So how to prepare nano size, low density, and has a hollow spherical zirconium tungstate geometric uniformity, is the focus of this paper. This paper discusses the zirconium tungstate hollow The micro nano structure of liquid phase synthesis, characterization, reaction mechanism and the expansion properties of negative heat, by choosing proper preparation methods, the pH of the solution phase control in the synthesis of liquid, suitable precursor reactants and surface additives, three kinds of zirconium tungstate structure were prepared, including nanorods coated hollow spherical structure, zero dimensional nano hollow spheres with zero dimension nano solid ball, the reaction mechanism was analyzed and the crystallization kinetics of the subsequent heat treatment of.1. one-dimensional nano zirconium tungstate coated hollow spherical structure was prepared by hydrothermal reaction to prepare monodisperse colloidal carbon spheres as template by template method sol gel method, spherical shell coated zirconium tungstate nanorods were prepared, and the characterization of the system with negative expansion performance test. The crystallinity and purity of the product is high, the preparation process. Simple, clean, the zirconium tungstate hollow ball density is 2.8g/cm3, lower than the theoretical value of about 45%; with negative thermal expansion performance good, the average heat ambient temperature -200 C temperature range expansion coefficient is -11.4 * 10-6K-1, lower than the theoretical value, this is because the sol-gel prepared nanorods, improved negative thermal expansion properties of zero dimensional.2. zirconium tungstate nanospheres were prepared by hydrothermal synthesis reaction process, reaction mechanism and influence factors of the experiment, by changing the molar ratio of hydrochloric acid and metal mineralization agent under hydrothermal conditions, controlled hydrothermal synthesis process, observed the morphology dependent reaction pH the process of evolution, and using this method respectively to prepare nano level zirconium tungstate hollow spheres and solid spheres, high yield, small size, uniform distribution, and has a negative thermal expansion performance good. At the same time is analyzed under different conditions, By hydrothermal synthesis mechanism of different morphologies, respectively, recrystallization mechanism and transformation mechanism of in situ dissolution. The zirconium tungstate hollow ball density is 3.6g/cm3, lower than the theoretical value of about 29.1%; with negative thermal expansion performance good, the average thermal expansion coefficient at room temperature of -200 DEG C temperature range for the crystallization kinetics of -9.15 * 10-6K-1.3. zirconium tungstate precursor crystallization kinetics of zirconium tungstate in the sintering process is not only influenced by external factors in the process of solid phase transition, is constrained by the precursor morphology and size were analyzed. The crystallization process of different morphology of the precursor using the KJMA equation for the solid nanoparticles, 740 C reaction order 0.54, the activation energy of the reaction follows the D3 diffusion mechanism is 489. KJ/mol hollow nanospheres, the reaction order is 0.96, in 900 ~ C is a first-order reaction, due to the small size and surface fine structure, therefore The activation energy of reaction is only 63 kJ/mol., the heat treatment temperature of whisker is 610 degree C, the longest time is 2h, the reaction order at this temperature is 0.62, D1 diffusion model and activation energy 353kJ/mol..

【學(xué)位授予單位】：上海交通大學(xué)
【學(xué)位級別】：碩士
【學(xué)位授予年份】：2015
【分類號】：TB383.1;TQ134.12

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