多元碳酸盐相变储热材料改性研究

发布时间：2018-04-01 22:34

本文选题：碳酸盐　切入点：相变潜热　出处：《武汉理工大学》2015年硕士论文

【摘要】：太阳能热利用技术是能源领域的主要发展方向,但太阳能在时间和空间上都缺乏连续性,因此储热传热技术及材料的研究显得非常重要。本文在前期研究无机盐相变储热材料的基础上,对以K2CO3-Na2CO3-Li2CO3为基盐的多元碳酸盐添加不同种类不同含量的硝酸盐、碳酸盐以及高导材料,择优选择综合性能最佳的多元混合无机盐并研究其在600℃高温下与316L不锈钢和304不锈钢的相容性。利用差示扫描量热法(DSC)、热重分析(TG)、微量热仪法、电子扫描探针(EPMA)等测试方法,重点研究了多元碳酸盐的相变潜热、相变温度、分解温度、比热容及腐蚀性等。通过DSC测试添加10%、20%、30%的硝酸盐和碳酸盐的多元混合无机盐的相变潜热、相变温度。测试结果表明,与硝酸盐作为添加剂进行对比,碳酸盐作为添加剂能够更好的形成共晶、更大程度的提升基盐的相变潜热、降低基盐的熔点。添加剂的种类和含量都对相变潜热有影响,且随着含量的增加,相变潜热反而减小,从晶格能、静电作用力的角度对比分析硝酸盐和碳酸盐作为添加剂对相变潜热和相变温度的影响。择优选取综合性能较好的多元混合无机盐,通过TG分析测试其分解点,得出了不同试样的分解温度所在的温度范围,发现碳酸钡、碳酸锶、碳酸锰作为添加剂时,对基盐分解点的提高有更为明显的帮助,分解点最高的为添加10%BaCO3、10%SrCO3、和20%SrCO3的混合盐,均达到820℃。在此基础上计算多元碳酸盐在高温下可能会发生化学反应的吉布斯自由能变,分析了高温下影响熔盐不稳定性的主要因素。添加10%、20%和30%BaCO3到基盐K2CO3-Na2CO3-Li2CO3中,测试其比热容,结果表明,从100℃~300℃,随着温度逐渐的升高,无机混合盐的比热容曲线缓慢的上升,且比热容的稳定的平均值随着添加剂的增多而减少。在K2CO3-Na2CO3-Li2CO3-10%BaCO3基盐中添加5%、10%、20%、30%的膨胀石墨、粒状石墨和碳纤维及其混合物,测试其相变潜热、熔点以及热导率。测试结果表明,膨胀石墨、粒状石墨和碳纤维的加入降低了无机混合盐的相变潜热,但在很大的程度上提高了其热导率。添加膨胀石墨对热导率的提升幅度最明显,最大可以达到4.04W/(m·K)。利用静态腐蚀实验法研究了基盐K2CO3-Na2CO3-Li2CO3-10%BaCO3在600℃熔融态时与316L不锈钢和304不锈钢的相容性,利用光学显微法、电子扫描探针对经过192h浸蚀后的试样进行线扫描,发现两种不锈钢都只是被轻微腐蚀,腐蚀层并未出现坑或者凸起,也没有腐蚀产物的堆积。利用XRD分析可知浸蚀层仅有微弱的Li、O元素,其余的主要是奥氏体相和马氏体相。通过分析不锈钢浸蚀的动力学曲线可知,基盐K2CO3-Na2CO3-Li2CO3-10%BaCO3与316L不锈钢和304不锈钢的相容性较好。
[Abstract]:The use of solar thermal technology is the main development direction in the field of energy, but solar energy in time and space are lack of continuity, therefore it is very important to study the technology of heat transfer and heat storage materials. This paper based on the previous studies of inorganic salt phase-change material, adding different content of nitrate on multiple carbonate by K2CO3-Na2CO3-Li2CO3 as the base of salt, carbonate and high conductivity materials, compatibility selection the best comprehensive performance of mixed inorganic salt and study the stainless steel and 316L at 600 degrees Celsius and 304 stainless steel. By using differential scanning calorimetry (DSC), thermogravimetric analysis (TG), electronic scanning calorimetry method. Probe (EPMA) and other test methods, focusing on the latent heat, multiple carbonate phase transition temperature, decomposition temperature, specific heat and corrosion resistance. Through the test of DSC added 10%, 20%, 30% of nitrate and carbonate Latent heat, mixed inorganic salt phase change temperature. The test results show that compared with nitrate as additive, carbonate as additive can form eutectic better, enhance the latent heat based salt greater degree, reduce the base salt melting point. The kinds and contents of additives have the effect on the latent heat, and with the the increase of the content of latent heat decreases, the lattice energy, contrast analysis of electrostatic interaction effects of nitrate and carbonate as additive on the latent heat and phase transition temperature. The preferred mixed inorganic salt selected good comprehensive properties, through the TG analysis to test its decomposition, the decomposition temperature of the temperature range of different samples. Found, barium carbonate, strontium carbonate, manganese carbonate as an additive, has a more obvious help to improve the base salt decomposition point, the highest point for adding 10%BaCO3,10%Sr decomposition CO3, a mixture of salt and 20%SrCO3, have reached 820 degrees. On the basis of calculation of multiple carbonate under high temperature may occur chemical reaction Gibbs free energy, analyzes the main factors influencing the stability of high temperature molten salt is added. 10%, 20% and 30%BaCO3 to salt based K2CO3-Na2CO3-Li2CO3, to test the specific heat, the show that from 100 DEG ~300 DEG, with the temperature gradually increased, rising heat inorganic mixed salt volume curve slowly, and the average specific heat stable value decreases with the increase of additive. Adding 5%, in the K2CO3-Na2CO3-Li2CO3-10% BaCO3 based in salt 10%, 20%, 30% of the expanded graphite, graphite and carbon fiber and granular the mixture, test its latent heat, melting point and thermal conductivity. The test results show that the expanded graphite, granular graphite and carbon fiber decreased with the latent heat of inorganic salt mixture, but increased to a great extent The thermal conductivity. Adding the expanded graphite on thermal conductivity increases most obviously, the maximum can reach 4.04W/ (M - K). The compatibility between the static corrosion test method of salt based K2CO3-Na2CO3-Li2CO3-10%BaCO3 at 600 DEG C melting state and 316L stainless steel and 304 stainless steel, using optical microscopy, scanning electron microprobe of samples after 192h after etching of line scanning, found two kinds of stainless steel are slight corrosion, corrosion layer does not appear a pit or bulge, there is no accumulation of corrosion products. The analysis shows that the etching layer only weak Li, using the XRD O element, the rest is mainly austenite and martensite phases. The kinetic curves of stainless steel etching base, salt K2CO3-Na2CO3-Li2CO3-10%BaCO3 and 316L stainless steel and 304 stainless steel has good compatibility.

【学位授予单位】：武汉理工大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TB34

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