纳米金属/石蜡复合相变蓄热材料的实验研究

以石蜡为相变材料基体、纳米金属铜、镍、铝、铁和锌为导热增强剂、油酸为分散剂,采用超声波震荡法制备纳米金属/石蜡复合相变蓄热材料体系。通过复合蓄热体系的步冷曲线分析,结果显示纳米铁为有效导热增强剂。对不同质量分数纳米铁/石蜡复合相变蓄热体系进行DSC和导热系数测试分析,结果表明:随着纳米铁质量分数的增加,复合材料的导热系数逐渐增大,相变潜热值逐渐降低,相变温度变化不大;纳米铁质量分数为0.1%时,复合材料的固态导热系数可增大2.8倍,相变潜热值下降1.1%。     

Thermal properties of a modified MOF-stearic acid composite phase change materials

以ZIF-67作为金属有机框架（MOF）,通过原位沉淀法生长在膨胀石墨片上对膨胀石墨进行改性,经过煅烧后形成Co₃O₄/EG分级多孔混合结构。为了优化硬脂酸的充放热性能,将Co₃O₄/EG与硬脂酸通过熔融共混和真空吸附法复合,制备出具有优异充放热性能的SA/Co₃O₄/EG复合相变材料。表征SA/Co₃O₄/EG复合相变材料的微结构、物相、相变焓值、相变温度和充放热时间等热物理性能,分析添加物Co₃O₄/EG的微结构对硬脂酸相变储热材料微结构和热性能产生的影响。添加物Co₃O₄/EG对SA/Co₃O₄/EG复合相变材料的相变温度影响较小,相变温度与Co₃O₄/EG添加量没有依赖关系。而复合储热材料的相变潜热随Co₃O₄/EG量的增加而减少,但与理论计算相差较少。Co₃O₄/EG分级多孔结构可以阻止Co₃O₄的团聚并提供高比表面积和孔体积吸附硬脂酸,多孔隙结构Co₃O₄和高热导率膨胀石墨（EG）的协同作用可以增加硬脂酸相变储热材料的热传递,缩短充放热时间,提高充放热效率。     

Fe3+交联的预包覆Fe3O4纳米粒子改性rGO自支撑膜的储锂性能

本工作采用Fe³⁺对含有氧化石墨烯(graphene oxide,GO)预包覆Fe₃O₄的GO自支撑膜进行改性处理制备Fe³⁺诱导交联的预包覆Fe₃O₄纳米粒子复合热还原型氧化石墨烯自支撑膜(Fe³⁺@Fe₃O₄/r GO)。采用扫描电镜(SEM)、透射电镜(TEM)、X射线衍射(XRD)、X射线光电子能谱(XPS)等测试手段表征材料组成、结构与形貌,并研究Fe³⁺@Fe₃O₄/r GO自支撑膜作为锂离子电池负极的储锂性能。结果表明球状Fe₃O₄纳米颗粒被GO片层紧密包裹,且经过Fe³⁺诱导交联的Fe³⁺@Fe₃O₄/r GO自支撑膜稳定性显著提高;电化学结果表明,在电流密度为100 m A/g恒...     

Fe3O4纳米颗粒对玉米秸秆光发酵产氢的影响

以HAU-M1光合菌群作为发酵细菌,以玉米秸秆为发酵底物,研究Fe₃O₄纳米颗粒对光发酵产氢过程的影响。结果表明:粒径60 nm的Fe₃O₄纳米颗粒浓度为100 mg/L时,比产氢量达到(46.68±1.00)mL/g VSS,与对照组的(35.07±0.56)mL/g VSS相比提升(33.11±0.01)%,此时的能量转化率也提高33.10%。产氢动力学分析结果也表明Fe₃O₄纳米颗粒对反应体系有明显的影响,粒径60 nm的Fe₃O₄纳米颗粒浓度为100 mg/L时,最大产氢潜能和最大产氢速率分别为46.97 mL/g VSS和1.06 mL/(g VSS·h)。适宜的Fe₃O₄纳米颗粒的粒径和浓度能显著促进光发酵产氢能力,而浓度过高则会产生抑制作用。     

铁基和硅基材料对有机垃圾厌氧发酵产沼气的促进作用研究

制备并考察3种功能材料（Fe₂O₃、Silicalite-1和Fe₂O₃@Silicalite-1）的3种投加量（50、100和150 mg）对有机垃圾（鸡粪）的厌氧发酵产气影响。结果表明：各功能材料组的日沼气产量和甲烷含量相比于空白组均得到有效提高,其中Fe₂O₃组分别提高31.07%和10.34%;Silicalite-1组分别提高23.98%和12.07%;Fe₂O₃@Silicalite-1组的产气效果最佳,其最高累计产气量和甲烷含量分别提高41.39%和17.24%。由此可见,将纳米Fe₂O₃分散负载在多孔材料（Silicalite-1）上可作为一种有效的厌氧发酵催化剂,该材料可避免传统方法中纳米颗粒的团聚造成的自身性能失活,从而通过厌氧发酵技术耦合复合材料实现有机垃圾处理工艺的能源效益和环境效益。     

基于模板法制备氧化铝纤维及其石蜡复合相变材料热性能

石蜡是一种高储热密度的有机相变材料,但是热导率低和易泄漏的缺点限制其进一步发展。为提高石蜡的导热和防泄漏性能,本研究以天然纤维为模板制备了具有高导热性的纤维状氧化铝导热填料,通过真空浸渍混合法制备了氧化铝纤维/石蜡复合相变材料,并对其形貌、热导率、相变循环稳定性、防泄漏性能以及热响应性能进行测试。结果表明,随着填料含量的增加,复合相变材料的导热系数近似线性增加。1200℃高温烧结形成的α型Al₂O₃比1000℃低温烧结γ型Al₂O₃具有更高的导热性能,且α型氧化铝纤维填充量达到45%(质量分数,余同)时,导热系数达到最高值为0.69 W/(m·K),是纯石蜡的2.9倍。通过对3种不同填充量Al₂O₃纤维进行100次的热循环测试,复合相变材料的相变焓值基本不变,说明了其具有良好的热循环稳定性。同时对复合相变材料的防泄漏性能以及热响应性能进行测试,结果显示30%和45%填料的α型Al₂O₃纤维均具有较好的防泄漏以及快...     

一种新型复合相变蓄热材料的制备与表征

相变蓄热材料是太阳能高效利用的基础与关键。文章选用54%KNO_3-46%NaNO_3作为太阳能高温热电站的蓄热材料,并选用膨胀石墨作为添加剂,分别制备了膨胀石墨(EG)质量分数为1%和2%的新型太阳能复合相变蓄热材料KNO_3-NaNO_3/EG。然后利用同步热分析仪(SDT-Q600)测量上述蓄热材料的相变温度、潜热,利用扫描电子显微镜(SEM)观测上述蓄热材料的微观结构。分析结果表明:太阳能复合相变蓄热材料KNO_3-NaNO_3/EG的相变温度为224.28℃,相变潜热为105.8 J/g;添加膨胀石墨能够明显地增强蓄热材料的导热性能,石墨对蓄热材料的熔点影响较小。     

Preparation and characterization of KF-KCl/SiO2 composite materials

采用混合烧结工艺将相变材料KF-KCl和陶瓷材料SiO₂进行复合,并添加聚乙烯醇作为黏结剂、B₂O₃作为烧结助剂,成功制备出一种陶瓷基复合结构储热材料。通过试验,确定了复合材料的烧结程序以及最佳的烧结温度。XRD分析表明,由KF-KCl/SiO₂构成的复合结构储热材料各物质之间具有良好的化学相容性;TG-DSC分析表明,复合材料在591.7 ℃时出现吸热峰,相变潜热是157.4 J/g。该复合材料具有储热密度高、无需容器盛装等特点,可以实现高温储热。     

石墨/Ba(OH)_2·8H_2O复合相变材料的制备及热性能

以BaCO_3、CaCl_2、NaCl为成核剂,进行Ba(OH)_2·8H_2O的成核剂筛选实验。采用超声波震荡法,制备不同质量分数的石墨/Ba(OH)_2·8H_2O复合相变蓄热材料体系。对该复合相变蓄热材料体系进行步冷曲线、DSC、导热系数测试和红外成像表征,结果表明:添加1%~2%的BaCO_3不仅可使Ba(OH)_2·8H_2O的过冷度小于1℃,并可延长相变潜热放热时间;石墨粉可有效提高Ba(OH)_2·8H_2O的导热系数和相变稳定性,但添加量应小于0.3%,过量会导致相变潜热值下降和石墨粉在基体材料中的团聚。     

铁钴修饰镍基复合载氧体化学链重整制氢研究

采用浸渍法制备Fe₂O₃-NiO-CeO₂/γ-Al₂O₃和CoO-NiO-CeO₂/γ-Al₂O₃复合载氧体,研究了不同复合载氧体对化学链重整制氢反应性能的影响。固定床活性测试实验表明,在镍铈载氧体中加入质量分数为5%的Fe₂O₃复合载氧体(5%Fe-Ni-Ce)的H₂选择性和H₂体积分数最大;在镍铈载氧体中加入CoO后,其复合载氧体的反应性能下降。循环实验表明,5%Fe-Ni-Ce复合载氧体在经过20次循环后仍保持高活性。X射线衍射(XRD)结果表明,5%Fe-Ni-Ce复合载氧体中有固溶体形成,进一步的XRD分析发现5%Fe-Ni-Ce晶粒粒径较小。扫描电子显微镜分析发现,反应前5%Fe-Ni-Ce复合载氧体的颗粒分散度最优,在经过20次循环后复合载氧体仍能保持较好的形貌。进一步的固定床实验研究表明,5%Fe-Ni-Ce...     

The preparation of Fe3O4/nanocellulose aerogel nanocomposite as anodes for lithium-ion batteries and electrochemical performance

纤维素因其环境友好、价格低廉等优点受到研究者的广泛关注,近年来作为碳材料广泛应用于电化学研究中。采用碳化后的纳米纤维素气凝胶为载体,六水合氯化铁为铁源,通过溶液热法合成了四氧化三铁/纳米纤维素气凝胶复合材料。通过XRD和SEM对产物进行了结构表征和微观形貌分析,并将其作为锂离子电池的负极材料,测试了一系列电化学性能,并与纯Fe₃O₄纳米颗粒的进行对比。结果表明,碳化后的纳米纤维素气凝胶保持着疏松多孔的三维网络结构,尺寸均一的Fe₃O₄纳米粒子均匀的分布于其中。该复合材料表现出优异的循环稳定性,在100 mA/g的电流密度下,首次放电比容量为1064 mA·h/g,100次循环后仍稳定在847 mA·h/g。相比于纯Fe₃O₄纳米颗粒,材料的电化学性能得到大幅度提高。本文有助于推动纤维素基碳材料在电化学领域中的进一步应用,为复合电极材料的发展提供一定的实验依据。     

石蜡/膨胀石墨复合相变储热材料的研究

以膨胀石墨为基体,石蜡为相变储热介质,利用膨胀石墨对石蜡良好的吸附性能,制备出了石蜡／膨胀 石墨复合相变储热材料。由于毛细作用力和表面张力的作用,石蜡在固-液相变时,很难从膨胀石墨的微孔中渗 透出来。实验结果表明,石蜡/膨胀石墨复合相变储热材料没有改变膨胀石墨的结构和石蜡的固-液相变温度, 且其结合了石墨高的导热系数和石蜡大的相变潜热,因而储热密度较高,导热性能好。其相变潜热与对应质量 分率下的石蜡相当,储/放热时间比石蜡明显减少。     

Thermal behavior of paraffin-nano-Al2O3 stabilized by sodium stearoyl lactylate as a stable phase change material with high thermal conductivity

A new kind of nano composite phase change material (NCPCM) was prepared using sodium stearoyl lactylate (SSL) as a surfactant to improve the dispersion of the Al₂O₃ nano-particles (with 2.5, 5, 7.5, and 10 wt.%) in paraffin with a SSL/Al₂O₃ mass ratio of 1:3.5. To evaluate the efficiency of the prepared PCMs, the melting rate of them at a temperature range of 50–60 °C and the effective thermal conductivity values in the solid and liquid states at a temperature range of 25–75 °C were measured using the k-type thermocouple and the transient hot wire technique, respectively. The heat storage behavior of the samples was investigated and their melting temperature, latent heat, and thermal reliability were determined using differential scanning calorimetry (DSC). Results showed that effective thermal conductivity enhancement ratios for the sample containing 10.0 wt.% nano-Al₂O₃ were 31% and 13% in the solid and liquid states, respectively, which are higher than those reported in similar studies. In addition, melting rate increased by 27%. As expected, all the PCMs showed good thermal reliability after 120 melting/freezing cycles. Based on our results, it may be concluded that the prepared PCMs can be regarded as effective heat storage materials for application in energy storage systems.     

Preparation and thermophysical properties of nanoparticle-in-paraffin emulsion as phase change material

In this study, phase change material (PCM) embedded by nanoparticles was prepared by emulsifying alumina (Al₂O₃) nanoparticles in paraffin (n-octadecane) by means of a non-ionic surfactant. The formulated nanoparticle-in-paraffin emulsions contain the nanoparticles of 5 wt.% and 10 wt.%, respectively; their effective thermophysical properties, such as latent heat of fusion, density, dynamic viscosity, and thermal conductivity, were investigated experimentally. The experimentally measured density of the emulsions agrees excellently with that predicted based on the mixture theory. The measured thermal conductivity and dynamic viscosity for the nanoparticle-in-paraffin emulsions formulated show a nonlinear increase with the mass fraction of the nanoparticles compared with that for the pure paraffin, depending on the temperature.     

Application of metal oxides-based nanofluids in PV/T systems: a review

Having the wide application of metal oxides in energy technologies, in recent years, many researchers tried to increase the performance of the PV/T system by using metal oxide-based nanofluids (NFs) as coolants or optical filters or both at the same time. This paper summarizes recent research activities on various metal oxides (Al₂O₃, TiO₂, SiO₂, Fe₃O₄, CuO, ZnO, MgO)-based NFs performance in the PV/T system regarding different significant parameters, e.g., thermal conductivity, volume fraction, mass flowrate, electrical, thermal and overall efficiency, etc. By conducting a comparative study among the metal oxide-based NFs, Al₂O₃/SiO₂-water NFs are mostly used to achieve maximum performance. The Al₂O₃-water NF has a prominent heat transfer feature with a maximum electrical efficiency of 17%, and a maximum temperature reduction of PV module of up to 36.9°C can be achieved by using the Al₂O₃-water NF as a coolant. Additionally, studies suggest that the PV cell’s efficiency of up to 30% can be enhanced by using a solar tracking system. Besides, TiO₂-water NFs have been proved to have the highest thermal efficiency of 86% in the PV/T system, but TiO₂ nanoparticles could be hazardous for human health. As a spectral filter, SiO₂-water NF at a size of 5 nm and a volume fraction of 2% seems to be very favorable for PV/T systems. Studies show that the combined use of NFs as coolants and spectral filters in the PV/T system could provide a higher overall efficiency at a cheaper rate. Finally, the opportunities and challenges of using NFs in PV/T systems are also discussed.     

Electrochemical performance of Nd0.6Sr0.4Co0.5Fe0.5O3−δ–Ag composite cathodes in intermediate temperature solid oxide fuel cells

The electrochemical performances of Nd_0.6Sr_0.4Co_0.5Fe_0.5O_3−δ–Ag composite cathodes have been investigated in intermediate temperature solid oxide fuel cells. The Nd_0.6Sr_0.4Co_0.5Fe_0.5O_3−δ–Ag cathodes prepared by ball milling followed by firing at 920 °C show the maximum performance (power density: 0.15 W cm⁻² at 800 °C) at 3 wt.% Ag. On the other hand, the Nd_0.6Sr_0.4Co_0.5Fe_0.5O_3−δ–Ag composite cathodes with 0.1 mg cm⁻² (0.5 wt.%) Ag that were prepared by an impregnation of Ag into Nd_0.6Sr_0.4Co_0.5Fe_0.5O_3−δ followed by firing at 700 °C (but the electrolyte–Nd_0.6Sr_0.4Co_0.5Fe_0.5O_3−δ assembly was prepared first by firing at 1100 °C) exhibit much better performance (power density: 0.27 W cm⁻² at 800 °C) than the composite cathodes prepared by ball milling, despite a much smaller amount of Ag due to a better dispersion and an enhanced adhesion. AC impedance analysis indicates that the Ag catalysts dispersed in the porous Nd_0.6Sr_0.4Co_0.5Fe_0.5O_3−δ cathode reduce the ohmic and the polarization resistances due to an increased electronic conductivity and enhanced electrocatalytic activity.     

Electrochemical thermal stability of the LiFePO4/LiNi0.8Co0.15Al0.05O2 blend cathode material for lithium ion batteries

为了改善LiNi_0.8Co_0.15Al_0.05O₂正极材料的电化学热稳定性能,加入LiFePO₄共混制成了LiFePO₄/LiNi_0.8Co_0.15Al_0.05O₂锂离子电池用混合正极材料。使用X射线衍射（XRD）和扫描电子显微镜（SEM）表征了结构和形貌,测试了电化学性能。结果显示,简单球磨的混合LiFePO₄/LiNi_0.8Co_0.15Al_0.05O₂正极材料中,纳米LiFePO₄粒子包覆在LiNi_0.8Co_0.15Al_0.05O₂粒子表面提高了混合正极材料在充放电过程中的电化学稳定性和结构稳定性。LiFePO₄/LiNi_0.8Co_0.15Al_0.05O₂混合正极材料在50 ℃下循环100周容量保持率为82.0%,明显地优于单一LiNi_0.8Co_0.15Al_0.05O₂材料的72.9%。