Preparation and performance study of cordierite/mullite composite ceramics for solar thermal energy storage

The employment of solar energy in recent years has reached a remarkable edge. It has become even more popular as the cost of fossil fuel continues to rise. Energy storage system improves an adjustability and marketability of solar thermal and allowing it to produce electricity in demand. This study attempted to prepare cordierite/mullite composite ceramics used as solar thermal storage material from calcined bauxite, talcum, soda feldspar, potassium feldspar, quartz, and mullite. The thermal physical performances were evaluated and characterized by XRD, SEM, EPMA, and EDS. It was found that the optimum sintering temperature was 1280°C for preparing, and the corresponding water adsorption was 11.25%, apparent porosity was 23.59%, bulk density was 2.10 mg·cm^?3, bending strength was 88.52 MPa. The residual bending strength of specimen sintered at 1280°C after thermal shock of 30 times decreased to be 57 MPa that was 36% lower than that before. The thermal conductivity of samples sintered at 1280°C was tested to be 2.20 W·(m·K)^?1 (26°C), and after wrapped a PCM (phase change materials) of K₂SO₄, the thermal storage density was 933 kJ·kg^?1 with the temperature difference (ΔT) ranged in 0‐800°C. The prepared cordierite/mullite composite ceramic was proved to be a promising material for solar thermal energy storage.     

纳米复合相变蓄热材料的制备与特性

相变蓄热材料（phase change materials,PCMs）是相变蓄热技术研究的基础。针对普通相变蓄热材料热导率低的缺点,采用纳米技术改善石蜡的相变传热性能,从而提高其热导率及热扩散系数。通过纳米颗粒-石蜡复合材料熔化过程测试和纳米颗粒沉降过程观察,确定铜纳米颗粒和Hitenol BC-10分别作为实验用纳米颗粒和分散剂,在制备稳定的纳米铜颗粒-石蜡复合相变材料的基础上,对其热物性进行了实验研究。结果表明纳米铜颗粒的添加使得石蜡热导率增幅最大,实验测得固态纳米铜-石蜡热导率提高7.9%,液态提高3.8%,而固、液态热扩散系数则分别提高了20.6%和16%。     

In situ synthesis and thermal shock resistance of a cordierite-mullite composite for solar thermal storage

Cordierite-mullite composite ceramic was synthesized in situ by semidry pressing and pressureless sintering from andalusite, kaolin, γ-Al₂O₃, talc, potassium feldspar, and albite in air. The effects of composition and sintering temperature on the density, bending strength, thermal shock stability, crystal phases, and microstructure of the specimens were studied. The results show that specimen B2 (the theoretical content of cordierite was 20 wt%) has excellent performance, that is, a bending strength of 104.59 MPa, 30 cycles of thermal shock resistance without cracking, and a loss rate of 13.12%. X-ray diffractometer (XRD) analysis and scanning electron microscope (SEM) micrographs showed that spherical cordierite crystals were grown on the surface of the mullite, therefore, the specimen possessed a superior bending strength and thermal shock resistance, where a great number of granules combined to restrain crack initiation as well as propagation over time during the thermal shock test. The thermal conductivity of specimen B2 was determined to be 3.83 W/(m·K) (36°C), and the sensible heat storage density was 1136 kJ/kg, with the temperature difference (ΔT) ranging from 0 to 800°C. Consequently, the cordierite-mullite composite is a potentially applicable material for solar thermal storage.     

Preparation and thermal shock resistance of anorthite solar thermal energy storage ceramics from magnesium slag

Anorthite solar thermal energy storage ceramics were fabricated from magnesium slag solid waste by pressureless sintering. The effects of CaO/SiO₂ ratio and sintering temperature on the physical, chemical, and thermophysical properties of ceramics were explored. X-ray diffraction results demonstrated that thermal shock process contributed to the formation of anorthite, and increasing CaO/SiO₂ ratio promoted the transformation of anorthite (CAS₂) into melilite (C₂AS). Some micro-cracks were found according to SEM analysis, forming by the mismatch of thermal expansion coefficients among phases. The combined effects of the low thermal expansion coefficient of anorthite and micro-crack toughing endowed the ceramic with good thermal shock resistance. Optimum comprehensive performances were observed in the sample with a CaO/SiO₂ ratio of 0.58 sintered at 1160°C, of which the specific thermal storage capacity was 0.63 J·g^-1·°C^-1(room temperature). The bending strength increased by 0.22% after 30 thermal shock times (room temperature-800°C, wind cooling). Therefore, the anorthite ceramics exhibited great potential for solar thermal energy storage.     

Synthesis and thermal shock evaluation of porous SiC ceramic foams for solar thermal applications

Reticulated porous ceramics with structural features spanning across multiple length scales are emerging as the primary media in a variety of demanding mass and heat transfer applications, most notably solar-assisted synthetic fuel processing. In this study, we focus on engineering of the open pore silicon carbide (SiC)-based foams in such catalytic applications. We evaluate the mechanical integrity and thermal stability of these porous structures. X-ray tomography analyses of the 3D structures reveal the presence of dual pore size distribution different by up to an order of magnitude in length scale. We further study the effect of thermal shock—induced via water quenching—on the SiC structures and we conclude that the mechanical properties of the ceramic foams are significantly reduced after thermal stress. Comparison of SEM micrographs—before and after thermal shock—reveals that needle-like features appear inside the foam matrix. These elongated defects may be responsible for structural and mechanical weakening.     

Preparation and thermal shock resistance of solar thermal absorbing corundum ceramics for concentrated solar power

The absorptivity of solar thermal absorber materials affects the heliothermal conversion efficiency of concentrated solar power systems. The solar absorbing ceramics were prepared by the fixed mixture of bauxit, Fe₂O₃, and TiO₂ with adding CuO in different percentages. The absorptivity and thermal shock resistance with the effect of adding CuO in different percentages were studied. Fe₂O₃ and TiO₂ have excellent optical properties, and CuO decreases the material's band gap to boost the electronic transition and increase the material absorptivity. The results showed that the material is sintered at 1380°C with an excellent absorptivity of 94.00% in the spectrum range of 0.3–2.5 μm, and the bending strength is 132.94 MPa. The bending strength was increased by 21.07% after 30 thermal shock cycles (1000°C-room temperature, air cooling). The liquid phase facilitates the synthesis of hercynite with excellent high temperature properties. The hercynite improves the thermal shock resistance of the material.     

Research on high temperature thermal stability and safety of two types of composite inorganic phase change thermal storage materials

In this paper, nitrate (KNO₃, NaNO₃) and carbonate (Li₂CO₃, K₂CO₃, Na₂CO₃ and CaCO₃), which are composite inorganic phase change thermal storage materials suitable for industrial thermal storage, non-toxic and less corrosive, are used as phase change components, respectively. The thermal properties (melting point, latent heat) of 4 different ratios of nitrate phase change components and 6 different ratios of carbonate phase change components were studied, and a distribution ratio of molten salt phase change components was selected respectively. Using the principle of porous carrier adsorption, two types of composite molten salt thermal storage materials with the best ratio were prepared. The ease of decomposition of the thermal storage materials in different media atmospheres (Ar and air) was analyzed. TG-DSC-MS tested high temperature thermal decomposition products show that the composite nitrate thermal storage materials have stable physical and chemical properties and good safety when storing thermal at medium temperature (300℃), but they are easy to decompose NO and high temperature (500℃) or higher. NO₂ and air atmosphere are more likely to generate toxic gases, and composite carbonate thermal storage materials are more likely to generate CO in air than Ar, which affects the safety of the thermal storage process.     

两类复合无机相变储热材料高温热稳定性和安全性研究

以适合工业储热的复合无机相变储热材料硝酸盐（KNO₃、NaNO₃）和碳酸盐（Li₂CO₃、K₂CO₃、Na₂CO₃和CaCO₃）为相变组分,研究了4种不同配比硝酸盐相变组分和6种不同配比碳酸盐相变组分的热性能（熔点、潜热）差异,分别优选出一种熔融盐相变组分配比。利用多孔载体吸附原理,制备出两种最佳配比的复合熔融盐类储热材料,分析了储热材料在不同介质气氛中（Ar和air）分解难易程度,TG-DSC-MS联用测试的高温热分解产物表明,复合硝酸盐类储热材料在中温（300℃）储热时,物理化学性能稳定,安全性较好,但在高温（500℃以上）时易分解成NO和NO₂,且air气氛中更易生成有毒气体;而复合碳酸盐类储热材料在air中比在Ar中更易生成CO而影响储热过程中的安全性。     

The microstructures and properties of Fe2O3 and TiO2 co-doped corundum ceramics for solar thermal absorbing materials

Solar thermal absorbing materials are the key components of concentrating solar power. In this study, Fe₂O₃ and TiO₂ co-doped corundum ceramics were prepared by pressureless sintering. The effects of different Fe₂O₃/TiO₂ ratios on the phase composition, microstructure, thermal shock resistance and solar absorptance were investigated via XRD and EPMA testing. The results showed that, with the decrease of Fe₂O₃/TiO₂ ratio, the appropriate amount of FeAlTiO₅ would decompose into ferrite particles, which played a bridging role between the corundum grains making the samples have excellent thermal shock resistance. A6 (90% bauxite, 9.5% Fe₂O₃ and 0.5% TiO₂) sintered at 1460 °C had the optimum comprehensive properties, with a bending strength of 154.80 MPa and an absorptance of 89.20% in the spectral range from 0.3 to 2.5 μm. After 30 thermal shock cycles (1000 °C–25 °C, air-cooled), the bending strength of A6 was 222.05 MPa, and the absorptance was 90.40%, which were 43.44% and 1.35% higher than those before thermal shock, respectively. Therefore, it was suitable as an excellent solar thermal absorbing materials.     

空调用纳米有机复合相变蓄冷材料制备与热物性

针对目前空调用有机相变蓄冷材料热导率低的问题,将具有高导热性的纳米材料(MWNTs、Al₂O₃、Fe₂O₃)添加到所开发制备的二元复合有机蓄冷材料(质量比73.7:26.3的辛酸/肉豆蔻醇)中,从纳米材料的种类和浓度两方面,研究其对复合有机蓄冷材料热物性的影响。实验发现:对于MWNTs、Al₂O₃、Fe₂O₃ 3种纳米材料,当其质量分数分别小于0.3%、0.4%、0.8%时,对应纳米复合材料热导率随纳米材料浓度的增加幅度较为明显;与原二元复合有机相变蓄冷材料相比,添加0.3%的MWNTs,热导率提高26.3%;添加0.4%的Al₂O₃,热导率提高13.1%;添加0.8%的Fe₂O₃,热导率提高32.1%;当在一定纳米材料质量分数(如0.7%)下,加入纳米颗粒的复合材料导热性能效果依次为Fe₂O₃>MWNTs>Al₂O₃。不同纳米粒子的添加对原蓄冷材料的相变温度和相变潜热影响很小,相变温度变化波动最大为0.4℃,相变潜热变化波动范围最大为1.4%。     

Preparation and thermal shock resistance of cordierite-spodumene composite ceramics for solar heat transmission pipeline

Cordierite-spodumene composite ceramics with 5, 10, 15 wt% spodumene used for solar heat transmission pipeline were in-situ prepared via pressureless sintering from kaolin, talc, γ-Al₂O₃ and spodumene. Effects of spodumene on densification, mechanical properties, thermal shock resistance, phase composition and microstructure of the composite ceramics were investigated. The results showed that spodumene used as flux material decreased the sintering temperature greatly by 40–80 °C, and improved densification and mechanical properties of the composite ceramics. Especially, sample A3 with 10 wt% spodumene additive sintered at 1380 °C exhibited the best bending strength and thermal shock resistance. The bending strengths of A3 before and after 30 thermal shock cycles (wind cooling from 1100 °C to room temperature) were 102.88 MPa and 96.29 MPa, respectively. XRD analysis indicated that the main phases of the samples before 30 thermal shock cycles were α-cordierite, α-quartz and MgAl₂O₄, and plenty of β-spodumene appeared after thermal shock. SEM micrographs illustrated that the submicron β-spodumene grains generated at the grain boundaries after thermal shock improved the thermal shock resistance. It is believed that the cordierite-spodumene composite ceramics can be a promising candidate material for heat transmission pipeline in the solar thermal power generation.     

太阳盐/钢渣定型复合相变储热材料的制备与性能研究

全球范围内的能源短缺和环境污染问题迫使人们积极开发可再生新能源.储热技术是解决新能源不稳定性问题的关键技术.相变材料是重要的储热介质之一.熔盐相变材料因其储热密度高,可操作温度范围广的优势,成为储热材料领域研究的热点.为解决熔盐液相易泄漏、低导热和高成本的问题,选择钢渣为基体材料,制备了太阳盐/钢渣定型复合相变储热材料...     

Preparation of goat milk powder with Lactobacillus casei L61 and antioxidant peptides: optimization of the composite thermal protectants and evaluation of storage stability

Abstract

The Lactobacillus casei L61 has great ability for producing antioxidant peptides. For reducing the mortality of L. casei L61 in spray drying process, the Box-Behnken design (BBD) was adopted to optimize the composite thermal protective agent formula. The results exhibited that the composite thermal protective agent formula of L. casei L61 contained glucose at 6.03% (w/v), skim milk at 18.98?g/L, and glycerol at 12.50?mL/L. Under the optimal conditions, the average survival of L. casei L61 in the fermented goat milk reached 14.58?±?0.72% after heat treatment at 75?°C for 10?min, which was higher than the control (13.14%). The average hydroxyl free radical scavenging activity of L. casei L61 reached 85.09?±?0.98%, which was not significantly different from the predicted value (86.83%). Therefore, the BBD is feasible for optimizing the composite thermal protective agent formula of L. casei L61. Under the optimal conditions with the inlet air temperature of 130?°C and feed rate of 4.5?mL/min, the maximum viable counts and survival rate of L. casei L61 were 7.46?×?10⁸ cfu/g and 23.41?±?1.28%, respectively. More importantly, the storage stability of antioxidative probiotic goat milk powder was predicted by temperature acceleration test. The shelf life of antioxidative probiotic goat milk powder was estimated to be 352?days at 4?°C and 117?days at 25?°C, embodying the great long-term stability. This study provides a technical reference for industrialized production of probiotic goat milk powder.     

Preparation and properties of novel ceramic composites based on microencapsulated phase change materials (MEPCMs) with high thermal stability

Ceramic composites are widely used in medium/high temperature thermal energy storage (TES) and catalysis. Due to the high latent heat of phase change materials (PCMs), it is an effective method to improve the TES capacity by combining PCMs with ceramic materials. However, PCMs are easy to leak after being heated, so they need to be microencapsulated. Furthermore, for porous ceramic catalytic composites, the leakage of PCMs will block the pores, which seriously hinders their application. In this paper, a novel microencapsulated phase change material (MEPCM) with thermal expansion void was prepared using “double-layer coating, sacrificing inner layer” method. Based on that, two kinds of ceramic composites have been prepared. One is a TES material which composed of alumina, glass frit (GF) and MEPCMs. Thermal analysis results showed that the composite can still maintain stable heat storage performance after 200 melting-solidification cycles with little latent heat loss. Another is a multifunctional porous composite phase change material (CPCM) by loading Ce and Mn as catalyst via solution combustion synthesis (SCS) method, which can be used in low temperature SCR catalysis and other catalytic fields (100–300 °C). Based on MEPCMs with thermal expansion void, the two ceramic composites show great potential in energy storage and catalysis.     

添加碳素复(混)合相变储热材料的研究及应用进展

相变储热材料因具有储热密度大、相变温度变化小且过程易控制等优点而在许多领域具有重要应用。但传统的相变储热材料存在导热系数低及固-液相变过程中液态泄漏问题,阻碍了其实际应用。碳材料如石墨、碳纤维、碳泡沫和膨胀石墨,他们都具有高导热系数、低密度和良好的化学稳定性。将碳材料添加到相变储热材料中或与相变储热材料进行复合,从而构成碳素复(混)合相变储热材料,储热材料的导热系数及其性能可明显提高。本文综述了碳素复(混)合相变储热材料的研究进展。利用膨胀石墨的多孔特性吸附有机物制备膨胀石墨基复合相变储热材料,其储热密度大、导热系数高、性能稳定、成本低且在固-液相变过程中没有液态的流动性问题,是未来研究和应用最重要的碳素复合相变储热材料。     

纳米材料/十四酸混合相变蓄热材料的制备与特性

选用纳米金属Cu和碳素材料石墨烯纳米片（GnPs）为改性剂分别添加至十四酸（MA）中,制备出Cu质量分数为1%、2%、3%和4%的Cu/MA混合相变蓄热材料及GnPs质量分数为1%、2%和3%的GnPs/MA混合相变蓄热材料,并对混合相变材料性能进行表征。结果表明：Cu/MA固态和液态热导率随Cu质量分数增加呈线性提高,1%（质量）GnPs/MA固态热导率较纯MA显著提高101.51%,随GnPs质量分数增加,热导率增幅减缓;FT-IR谱图表明Cu与MA及GnPs与MA间的混合均为物理作用;DSC结果显示添加Cu或GnPs可降低MA的过冷度和相变潜热,且随质量分数增加,相变潜热逐渐降低;4%（质量）Cu/MA和3%（质量）GnPs/MA放热时间相比于纯MA分别减少了23.4%和38.7%;4%（质量）Cu/MA和3%（质量）GnPs/MA在经历300次快速热循环试验后,晶体结构和相变温度基本保持不变,相变潜热分别降至168 J·g^-1和181 J·g^-1左右,仍满足蓄放热要求,两种材料均具有良好的热循环稳定性。     

硬脂酸/二氧化硅复合相变储热材料制备及性能研究

采用“溶胶-凝胶”工艺制备出具有不同硬脂酸质量分数的硬脂酸/二氧化硅复合相变储热材料,运用SEM、XRD和DSC等手段对复合相变储热材料的结构与性能进行了表征和测试。复合相变储热材料是硬脂酸嵌入到二氧化硅三维纳米网孔中形成的,其相变温度和相变潜热均随硬脂酸质量分数的增加而增大,且相变温度低于纯硬脂酸,相变潜热与对应质量分数下的硬脂酸相当。实验结果表明,硬脂酸/二氧化硅复合相变储热材料具有储热密度大、性能稳定以及导热系数较高等优点。     

Highly filled multilayer thermoplastic/graphene conducting composite structures with high strength and thermal stability for electromagnetic interference shielding applications

Polyvinyl chloride (PVC)/graphene and poly(methyl methacrylate) (PMMA)/graphene nanocomposites were made by solution casting technique with graphene weight fractions of 1, 5, 10, 15, and 20%. Multilayer structures of the composites were made by hot compression technique to study their electromagnetic interference shielding effectiveness (EMI SE). Tensile strength, hardness, and storage modulus of the nanocomposites were studied in relation with graphene weight fraction. There has been a substantial increase in the electrical conductivity and EMI SE of the composites with 15–20% filler loading. Differential thermal analysis of the composites shows improved thermal stability with an increase in graphene loading. PMMA/graphene composites have better thermal stability, whereas PVC/graphene composites have superior mechanical properties. About 2 mm thick multilayer structures of PMMA/graphene and PVC/graphene composites show a maximum EMI SE of 21 dB and 31 dB, respectively, in the X band at 20 wt % graphene loading. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47792.     

Effect of nano aluminum nitride filler on mechanical,thermal, and dielectric properties of the glass/mullite composites for low-temperature co-fired ceramic applications

Mullite/glass/nano aluminum nitride (AlN) filler (1–10 wt% AlN) composites were successfully fabricated for the low-temperature co-fired ceramics applications that require densification temperatures lower than 950°C, high thermal conductivity to dissipate heat and thermal expansion coefficient matched to Si for reliability, and low dielectric constant for high signal transmission speed. Densification temperatures were ≤825°C for all composites due to the viscous sintering of the glass matrix. X-ray diffraction proved that AlN neither chemically reacted with other phases nor decomposed with temperature. The number of closed pores increased with the AlN content, which limited the property improvement expected. A dense mullite/glass/AlN (10 wt%) composite had a thermal expansion coefficient of 4.44 ppm/°C between 25 and 300°C, thermal conductivity of 1.76 W/m.K at 25°C, dielectric constant (loss) of 6.42 (0.0017) at 5 MHz, flexural strength of 88 MPa and elastic modulus of 82 GPa, that are comparable to the commercial low temperature co-fired ceramics products.     

氢气刻蚀法制备Pt/CNTs复合材料及其热稳定性

采用碳化硅高温热分解法制备整齐排列的直立碳纳米管阵列,并对其进行Pt金属粒子修饰,通过氢气刻蚀法可以将闭口碳纳米管阵列开口,并将Pt纳米粒子嵌入到碳纳米管中。这种新型Pt/CNTs复合材料具有独特的电子限域效应,有助于抑制金属催化剂的烧结,对提高其后续催化活性和应用性能有着重要意义。