Search

Zirconia‐corundum‐mullite composites were prepared from andalusite, ZrO2, and α‐Al2O3 and evaluated for application as solar thermal storage materials in this study. The effects of ZrO2 concentration (0–25 wt%) and sintering temperature(1500–1650°C) on the bending strength, phase composition, microstructure, dimensional stability, and thermal shock resistance of the samples were investigated. The results showed that sample C2 (containing 10 wt% ZrO2) sintered at 1600°C exhibited the best properties. A portion of Y2O3 existed in ZrO2, which excited a small amount of t‐ZrO2 in the sample after sintering, while the other portion of Y2O3 was separated from ZrO2 and participated in the formation of a high‐temperature liquid phase. The liquid phase reduced the dimensional stability of the sample. However, the liquid phase could also promote sintering, reducing the optimal sintering temperature, with lower sintering temperatures increasing the dimensional stability of the sample. Once again, the C2 sample exhibited the highest thermal shock resistance, with a strength loss of 2.76 MPa after 30 thermal shock tests. The thermal storage density(25–1100°C) of C2 was 1121 kJ/kg. In summary, sample C2 exhibits a high degree of dimensional stability and thermal shock resistance and can thus be used as a reliable solar thermal storage material. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Mullite ceramic materials have a number of excellent properties that make them an excellent choice for solar heat absorber materials in Concentrating Solar Power (CSP) systems. In this study, the effects of adding Co 2 O 3 and Fe 2 O 3 on the properties of mullite-based ceramics were studied, aiming to get excellent absorption rate and thermal shock resistance. The results show that the sample C2 (45.05 wt% 75 calcined bauxite, 45.05 wt% Suzhou clay, 9 wt% Fe 2 O 3 , 3 wt% Co 2 O 3) sintered at 1400 °C has the best comprehensive performance, with a bending strength of 143.28 MPa and a solar absorption rate of 92.2 % in the wavelength range of 0.3–2.5 μm. The bending strength increased by 31.36 % after thermal shock cycles for 30 times (1000 °C ∼ room temperature, air cooling). Generation of iron cobalt spinel and lattice distortion caused by Fe3+ and Co3+ into the mullite lattice combined to promote the absorption rate. In the meantime, the main crystalline phase columnar mullite showed a tight continuous interlaced network structure. The fracture mode was mainly transgranular fracture, which endowed C2 excellent thermal shock resistance. [ABSTRACT FROM AUTHOR]

ZrO 2 –Al 2 O 3 -A 3 S 2 (3Al 2 O 3 ·2SiO 2) composites are ideal Casting filter materials with excellent mechanical properties and thermal shock resistance. In this paper, 3Y–ZrO 2 (3 mol% Y 2 O 3 -stabilized ZrO 2) was added to kaolin and α-Al 2 O 3 to prepare ZrO 2 –Al 2 O 3 -A 3 S 2 composites by pressureless sintering. The results showed that when the addition amount of 3Y–ZrO 2 is 15 wt%, the bending strength and fracture toughness of the composites sintered at 1600 °C are 152.51 MPa and 3.52 MPa m1/2, respectively. The bending strength increased to 161.83 MPa after 30 thermal shocks (1100 °C to room temperature), with an increase rate of 6.11 %. The ZrO 2 crystals are evenly distributed between corundum and mullite crystals, effectively preventing abnormal growth of corundum and mullite crystals, and a small number of pores exist in the samples, which could act as a "buffer zone" to prevent the expansion of cracks in the thermal shock, resulting in high mechanical strength and excellent thermal shock resistance for composites. [ABSTRACT FROM AUTHOR]

In order to study the performance and feasibility of magnesia‐alumina spinel (MgAl2O4) ceramics for thermal storage in solar thermal power generation, MgAl2O4 was prepared by theoretical composition using α‐Al2O3 as aluminium source, fused magnesia, magnesite, and light burned magnesia as different magnesium sources and kaolin as additive. The effects of magnesium source and the additive on sintering properties, thermal shock resistance and thermal properties of MgAl2O4 ceramics were researched. The results shown sample A1 (with fused magnesia) sintered at 1670°C possessed the optimum comprehensive properties, the bending strength increased by 7.71% after 30 thermal shock times (room temperature‐1000°C, air cooling), the specific heat capacity was 1.05 J/ (g·K). Therefore, the MgAl2O4 ceramics exhibited great potential in high‐temperature thermal storage material. [ABSTRACT FROM AUTHOR]

Solar thermal absorbing materials are the key components of concentrating solar power. In this study, Fe 2 O 3 and TiO 2 co-doped corundum ceramics were prepared by pressureless sintering. The effects of different Fe 2 O 3 /TiO 2 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 Fe 2 O 3 /TiO 2 ratio, the appropriate amount of FeAlTiO 5 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% Fe 2 O 3 and 0.5% TiO 2) 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. [ABSTRACT FROM AUTHOR]

Anorthite solar thermal energy storage ceramics were fabricated from magnesium slag solid waste by pressureless sintering. The effects of CaO/SiO 2 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/SiO 2 ratio promoted the transformation of anorthite (CAS 2) into melilite (C 2 AS). 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/SiO 2 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. [ABSTRACT FROM AUTHOR]

Ho 2 O 3 was employed to improve the microstructural densification and performances of pressureless sintered corundum–mullite ceramic composites. This study investigated the influences of Ho 2 O 3 addition on the microstructure, physical properties and thermal shock resistances of the composites. The results indicated that sample AH5 (80 wt% Al 2 O 3 , 20 wt% coal series kaolin, and 5 wt% additional Ho 2 O 3), which was sintered at 1550 °C, showed the best comprehensive properties. In this Al 2 O 3 -rich and SiO 2 -poor system, a reaction between the Ho 2 O 3 and Al 2 O 3 –SiO 2 system produced an Ho 2 O 3 –Al 2 O 3 –SiO 2 liquid phase. This liquid phase increased the microstructural densification and resulted in a lower sintering temperature. The generation of mullite and holmium disilicate during thermal shocks improved the thermal shock resistance. The high bending strength and satisfactory thermal shock resistance of the as-prepared corundum–mullite ceramic composites showed their potential for use in heat transmission pipelines. [ABSTRACT FROM AUTHOR]

Summary: Compared with current research of simply improving the efficiency of thermal absorber or thermal storage, integrating two devices into one fundamentally avoids the heat transfer loss between the two devices. In‐situ self‐assembled SiCw(SiC whisker)/SiC composite ceramics for integrated thermal absorber and thermal storage were pressurelessly prepared from graded SiC, AlN, and Si powders by layered powder embedded sintering in a low temperature range from 1450°C to 1650°C. After sintered at 1550°C, sample A4 with 10.39 wt% Si not only exhibits optimal mechanical properties and excellent thermal shock resistance, but also has high thermal conductivity, thermal storage capacity, and solar absorptance as 6.74 W·(m K)−1, 984.75 kJ·kg−1, and 91.12%, respectively. Results indicate that the in‐situ self‐assembled SiC whiskers, formed by carburization reaction via VS mechanism in the stacking voids of SiC matrix, could greatly enhance the mechanical and thermal properties. We creatively proposed that the as‐prepared SiCw/SiC is promising to apply in integrated thermal absorber and storage system of solar thermal power generation. [ABSTRACT FROM AUTHOR]

TiO 2 is employed to improve the performance of pressureless sintered MgAl 2 O 4 –Si 3 N 4 ceramics in this study, aiming to make the ceramics more suitable for solar thermal absorbing materials in concentrating solar power. Effects of TiO 2 content on the microstructure and properties of the composites were the focus, especially the thermal shock and oxidation resistance. The results show that composite with 2 wt% TiO 2 sintered at 1620 °C has the highest bending strength exceed 320 MPa, which contributes to resist the thermal stress. Instead of being damaged after 30 thermal shock cycles (ΔT ≈ 1100 °C), the bending strength of the sample increases 12.03%. The weight gain rate is only 0.8964 mg/cm2 when finishing the oxidized process at 1300 °C for 100 h, and the oxidation kinetic obeys the parabolic low. Solar absorptance and thermal conductivity of the composite reach 93.5% and 13.27 W/(m·K) respectively. MgAl 2 O 4 –Si 3 N 4 composite can be presureless sintered at lower temperature, and it has better high temperature stability than Si 3 N 4 and SiC ceramics prepared via the same procedure, which makes it an ideal choice for solar thermal absorbing material. [ABSTRACT FROM AUTHOR]

TiO2 was employed to develop cordierite glass–ceramics for thermal transmission pipeline binders by a melt‐quenching method. The effects of TiO2 on the phase composition, microstructure, and physical properties of glass–ceramics were studied. In addition, the thermal shock resistance of the glass–ceramics based binder was investigated. The results showed the formation of α cordierite could be increased by adding 1.0 wt% TiO2, thereby improving bending strength and decreasing the coefficient of thermal expansion. However, a 3‐5 wt% TiO2 additive resulted in massive generation of µ cordierite, which exhibited a negative effect on the above performances. After crystallization at 1000°C for 2 h, sample B1 (1 wt% TiO2 additional) displayed the best overall properties. It was demonstrated that cordierite glass–ceramics were satisfactory materials as heat transmission pipeline binders when the C2 binder (40 wt% frit, 60 wt% as‐prepared sample B1) was applied, which had a good thermal shock resistance. [ABSTRACT FROM AUTHOR]

Solar thermal power generation is an important direction of energy utilization, and thermal storage materials are the key to ensure the continuous use of energy. In this paper, forsterite - zirconia composite ceramics were prepared by adding different contents of 3Y–ZrO 2 and their physical properties, phase composition, microstructure thermal shock resistance and thermal physical properties were studied. The results showed that the water absorption, bulk density and bending strength of sample A3 sintered at 1600 °C (59.10 wt% fused magnesia, 40.90 wt% quartz and 30 wt% 3Y–ZrO 2) were 0.35 %, 3.27 g/cm3 and 83.66 MPa, respectively. The crystal phase of sample A3 was forsterite and c-ZrO 2. Mg2+ and Y3+ replace Zr4+, formed oxygen vacancy in the anion position, distort the coordination layer and release some interlayer stress to promote the stability of c-ZrO 2. In the sintering process, the zirconia solid solution existed in the form of second phase, which reduced the growth rate of periclase, facilitated the pore discharge in the sample and promotes sintering. The thermal conductivity of forsterite - zirconia composite ceramics at room temperature was 5.52 W/(m·K). At 1000 °C, the specific heat capacity and heat storage density were 1.09 J/(g·K) and 1062.36 kJ/kg, respectively. The forsterite - zirconia composite ceramic prepared in this study was suitable for high temperature environment, its heat storage capacity was excellent, and it was suitable for high temperature heat storage system. [ABSTRACT FROM AUTHOR]

Gd 2 O 3 was added to increase the properties of corundum–mullite ceramic composites by enhancing the microstructural densification using coal-series kaolin and α-Al 2 O 3. The effect of Gd 2 O 3 addition on the microstructure and properties of ceramic composites was explored. The results showed that the formation of Gd 2 O 3 –Al 2 O 3 –SiO 2 liquid phase could improve the bending strength, hardness, and acid resistance, since such liquid phase promoted microstructural densification via a reaction between Gd 2 O 3 and Al 2 O 3 –SiO 2 binary system in this Al 2 O 3 -rich and SiO 2 -poor system. The precipitation of mullite and gadolinium disilicate during thermal shocks resulted in enhanced bending strength. In particular, sample AG5 (80 wt% Al 2 O 3 , 20 wt% coal-series kaolin, and 5 wt% additional Gd 2 O 3) sintered at 1550 °C was considered as candidate for heat transmission pipeline for the optimum comprehensive performance. [ABSTRACT FROM AUTHOR]

Al 2 O 3 –CaAl 12 O 19 composites are ideal high-temperature structural ceramics, however, their poor thermal shock resistance limits their application under thermal shock conditions. In this work, ferrotitanium slag was used as the main raw material for composites preparation. Enhanced thermal shock resistance were obtained by adding 12.5 wt.% unstabilized monoclinic zirconia. A systematic analysis of the phase compositions and microstructural evolution with particular attention to crack propagation was performed. The improvement in thermal shock resistance is attributed to the enhanced crack propagation resistance. Furthermore, the enhanced crack propagation resistance is caused by multiple mechanisms, including the t -ZrO 2 -related stress-induced t → m phase transformation mechanism and the m -ZrO 2 -related microcracking mechanism. Coarsened ZrO 2 particles doped with TiO 2 from the ferrotitanium slag are beneficial to the occurrences of stress-induced transformation and microcracking. [ABSTRACT FROM AUTHOR]

To obtain composite ceramics with excellent thermal shock resistance and satisfactory high−temperature service performance for solar thermal transmission pipelines, SiC additive was incorporated into Al 2 O 3 −mullite−ZrO 2 composite ceramics through a pressureless sintering process. The effect of the SiC additive on thermal shock resistance was studied. Also, the variations in the microstructure and physical properties during thermal cycles at 1300 °C were discussed. The results showed that both thermal shock resistance and thermal cycling performance could be improved by adding 20 wt% SiC. In particular, the sample with 50 wt% Al 2 O 3 , 35 wt% Coal Series Kaolin (CSK), 15 wt% partially yttria−stabilized zirconia (PSZ), and 20 wt% SiC additional (denoted as sample A2) exhibited the best overall performance after firing at 1600 °C. Furthermore, the bending strength of sample A2 increased to 124.58 MPa, with an increasing rate of 13.63% after 30 thermal shock cycles. The increase in thermal conductivity and the formation of mullite were the factors behind the enhancement of thermal shock resistance. During the thermal cycles, the oxidation of SiC particles was favorable as it increased the microstructure densification and also facilitated the generation of mullite, which endowed the composite ceramics with a self−reinforcing performance. [ABSTRACT FROM AUTHOR]

In this paper, sialon/SiC composite ceramics were synthesized in situ from SiC, α-Si3N4, AlN, calcined bauxite, quartz, and Y2O3 via layered buried sintering at different temperatures (1540–1640 °C). The sialon/SiC composite ceramics designed in this study are expected to be used as thermal absorb materials in solar thermal power generation based on the good mechanical character and thermal shock resistance. The results showed that the β-sialon/SiC sample with 60 wt% silicon carbide sintered at 1600 °C exhibited the optimal performances with dense microstructure, high bending strength, and good thermal shock resistance. After 30 thermal shock cycles, the bending strength of β-sialon/SiC sample with 60 wt% silicon carbide was 66.68 MPa with a decrease of 4.79%. In thermal shock tests, SiC and Si3N4 in the sample were oxidized into amorphous SiO2, and small amount of sialon was decomposed into mullite, which resulted in good thermal shock resistance. It was believed that in situ sialon/SiC composite ceramics can be a promising candidate for solar absorber owing to good thermal shock resistance. [ABSTRACT FROM AUTHOR]

• Low-cost Al 2 O 3 -CaAl 12 O 19 can be prepared from ferrotitanium slag. • Ferrotitanium slag can significantly promote the sintering of alumina. • The dominant sintering mechanism is solid solution mechanism. • The sintering densification can improve the thermophysical properties. • The composites have the potential to be applied to thermal storage. Low-cost alumina/calcium-hexaluminate (Al 2 O 3 -CaAl 12 O 19) ceramic composites were prepared using ferrotitanium slag in this paper. By making use of the TiO 2 and MgO originally existing in ferrotitanium slag, the sintering densification of Al 2 O 3 -CaAl 12 O 19 composites was promoted. The results show that the optimum sintering temperature of the composites is 1500 ℃. The dominant sintering mechanism is the solid solution mechanism, i.e., Ti4+ and Mg2+ are dissolved in the CA 6 and Al 2 O 3 lattices and generate numerous defects, which ultimately enhance the lattice diffusion coefficient and matter transport. Sintering densification improves the specific heat capacity, thermal conductivity, and thermal shock resistance of Al 2 O 3 -CaAl 12 O 19 composites. Thermophysical properties analysis indicates that the composites can be potentially used for thermal storage and the slag-utilized ratio is about 60 wt.%. However, the layered cleavage of CA 6 limits further improvement of thermal shock resistance. [ABSTRACT FROM AUTHOR]

Solar high-temperature thermal power generation systems require thermal storage materials with excellent thermal shock resistance due to the large temperature difference during operation (in the range of 20–800 °C). In this study, mullite-based absorption and storage integrated ceramics were prepared using low-cost bauxite and kaolin as raw materials and Fe 2 O 3 as additive. The effect of Fe 2 O 3 on the thermal shock resistance of mullite-based ceramics was investigated. The results showed that the absorption and bending strength of sample BK4 (bauxite: 50 wt%, kaolin: 50 wt%, Fe 2 O 3 : additional 11 wt%) increased by 2.98% (89.8%) and 8.00% (147.10 MPa), with a storage thermal density of 1185.75 kJ kg−1 after 30 thermal shock cycles. The mechanism for the excellent thermal shock resistance of the ceramics is revealed from the aspect of the changes in phase and microstructure of the samples induced by the changes in the mass transfer rate during the thermal shock process. It was calculated that a unit volume of BK4 (with a raw material cost of about 154.22 USD) could generate 974.95 kW h of electricity (saving 119.92 kg of coal) when used in a solar thermal storage system. [ABSTRACT FROM AUTHOR]

For increasing working stability of cordierite-spodumene composite ceramics for solar heat transmission pipeline, andalusite was utilized as modified additive to improve mechanical strength and thermal shock resistance of the composite ceramics. The effects of andalusite on densification, mechanical strength, thermal stability, phase composition and microstructure were studied. The experiment results showed that andalusite significantly influenced bending strength and thermal shock resistance of the composite ceramics. Especially, specimen B1 with 5 wt% andalusite sintered at 1400 °C achieved the best performances. The linear shrinkage, water absorption, apparent porosity, bulk density and bending strength were 5.62%, 0.02%, 0.06%, 2.19 g cm −3 and 104.94 MPa, respectively. After 30 thermal shock cycles (wind cooling from 1100 °C to room temperature), the residual strength of the specimen increased to 110.65 MPa, accompanying with −5.44% strength loss rate. The XRD and SEM analysis illustrated that mullite grains with short rod-like shape could prevent crack growth of inter-granular fracture to enhance bending strength of the specimens. Furthermore, the generation of β-spodumene grains with low thermal expansion coefficient after thermal shock improved thermal shock resistance of the composite ceramics. It is considered that the cordierite-spodumene composite ceramics with high densification, good mechanical strength and excellent thermal stability can be a potential material for high temperature thermal transmission pipeline in solar thermal power generation. [ABSTRACT FROM AUTHOR]

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-Al 2 O 3 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 MgAl 2 O 4 , 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. [ABSTRACT FROM AUTHOR]

MgAl 2 O 4 –Si 3 N 4 ceramics were fabricated via pressureless sintering by using α-Si 3 N 4 , α-Al 2 O 3 and MgO as starting materials. MgAl 2 O 4 was in-situ synthesized in the composite ceramics to improve the sintering process and high-temperature performance of Si 3 N 4 . Results show that the composite with approximately 30 wt% MgAl 2 O 4 sintered at 1620 °C exhibits the best physical properties, excellent thermal shock resistance, oxidation resistance and solar absorptance. No cracks were found after 30 thermal shock cycles (1100–25 °C, wind cooling). At the same time, the bending strength has experienced an improvement of 24.5%, which increases to 248 MPa. A dense oxide film is formed on the surface of the sample during oxidation at 1300 °C, which protects it from further oxidation. The oxidation kinetics of MgAl 2 O 4 –Si 3 N 4 ceramic transforms from passivation oxidation into activation oxidation with increasing MgAl 2 O 4 content. Only moderate amount of MgAl 2 O 4 (10–30 wt%) can provide the excellent oxidation resistance. These in-situ MgAl 2 O 4 –Si 3 N 4 composites could be a promising candidate for solar heat absorbing material. [ABSTRACT FROM AUTHOR]

Zirconia-alumina composite ceramics are the preferred materials for high temperature and thermal shock applications because of their excellent mechanical properties. In this paper, La 2 O 3 doped zirconia-alumina composite ceramics were prepared by using fused zirconia corundum and ZrO 2 as starting materials. The effects of La 2 O 3 on the phase composition, microstructure and properties of the composite ceramics were investigated by XRD and SEM. The results show that La 2 O 3 can reduce the sintering temperature and improve the bending strength of the samples. The bending strength and fracture toughness of the composite ceramics with 1.5 wt% La 2 O 3 sintered at 1480 °C are 299.17 MPa and 5.61 MPa m1/2, respectively. The strength loss rate of the sample after 30 thermal shocks (room temperature ∼ 1000 °C) is 2.67%, SEM shows that the grain sizes of alumina and zirconia in the sintered sample were about 5 μm and 2 μm, respectively. After 30 thermal shocks, the phase composition and microstructure of the sample have no significant change, indicating good thermal shock resistance of the composite ceramics. The excellent thermal shock resistance ensures porous medium combustion materials has a long service life. [ABSTRACT FROM AUTHOR]

Si3 N4- Si C composite ceramics used for volumetric receivers were fabricated by pressureless sintering of micrometer Si C, Si3 N4, andalusite, and other minor additions powders. Mechanical, thermal expansion, thermal conductivity, and thermal shock resistance properties were tested at different sintering temperatures. The best sintering temperature of optimum formula A2 is 1360°C, and the bending strength reaches 79.60 Mpa. And moreover, its thermal expansion coefficient is 6.401 × 10−6/°C, thermal conductivity is 7.83 W/(m K), and no crack occurs even subjected to 30 cycles thermal shock with a bending strength increase rate of 4.72%. X-ray diffraction results show that the phase constituents of the sintered products mainly consist of Si C, Si3 N4, mullite, and quartz. Microstructure that is most appropriate and exhibits maximal thermal shock resistance was detected using SEM. The porosity of Si3 N4- Si C ceramic foam prepared from formula A2 is 95%, which provides a rapid and steady action for the receiver. The evaluation of the present foam shows that Si3 N4- Si C ceramic composite is a good candidate for volumetric receivers. [ABSTRACT FROM AUTHOR]

Solar absorption and thermal storage integrated ceramics (SATS ceramics) are new thermal storage materials that directly absorb sunlight, which improve the solar-to-thermal conversion efficiency. In this paper, SATS ceramics were developed by using calcium and iron-rich steel slag as the starting material. On the basis of composition characteristics of steel slag and performance requirements of SATS ceramics, the target phases of magnesioferrite spinel (MgFe 2 O 4) and monticellite (CaMgSiO 4) were designed and successfully synthesized in the SATS ceramics by the addition of magnesite and quartz. Phase composition, microstructure, physical properties, thermal shock resistance, solar absorptance and thermal storage performance were investigated. The results show that SATS ceramics with the addition of magnesite and quartz possess better properties than the ceramics prepared from 100 wt% steel slag. Particularly, the solar absorptance and thermal storage density of the SATS ceramics with the target phase of MgFe 2 O 4 are 84.7% and 1057.57 kJ kg−1 (25–800 °C), which increased by 3.04% and 21.87% compared to reference sample, respectively. In addition, it still presents higher strength of 64.83 MPa after 30 thermal shock cycles (25–800 °C) than the other samples, indicating good thermal shock resistance. Surprisingly, the utilization rate of steel slag reaches up to 97.89 wt%. This work not only develops a low-cost SATS ceramics, but also provides a new high-value utilization approach to steel slag. [ABSTRACT FROM AUTHOR]

Al 2 O 3 ceramics were prepared by introducing Fe 2 O 3 –TiO 2 -Sm 2 O 3 composite additive, in which the content and ratios of Fe 2 O 3 and TiO 2 remained constant, but Sm 2 O 3 was variable. The phase transformation, micromorphology, physical properties and thermal properties were investigated. The results showed that Fe 2 O 3 and TiO 2 made the grains high sintering activity through a solid solution mechanism, which promoted grain growth, but Sm 2 O 3 preferred to form SmFe 4 Al 8 O 19 at the grain boundaries, which slowed grain growth and refined the grains. With the increase in Sm 2 O 3 , the grain refinement of SmFe 4 Al 8 O 19 became outstanding, and the grain diameter gradually decreased, which is favorable for denser sintering. However, only a proper amount of Sm 2 O 3 in the Fe 2 O 3 –TiO 2 -Sm 2 O 3 composite additive resulted in better thermal shock resistance. The Al 2 O 3 ceramics with 9 wt% Fe 2 O 3 -1 wt% TiO 2 -5 wt% Sm 2 O 3 sintered at 1520 °C exhibited the optimum properties, yielding an increase in the bending strength by 6.60% after 30 thermal shocks, a thermal conductivity of 13.33–5.64 W/(m·K) (25–800 °C) and a specific heat capacity of 0.94–1.25 J/(g·K) (25–800 °C), all of which demonstrate the potential for thermal storage. [ABSTRACT FROM AUTHOR]

High-temperature thermal storage materials have received urgent attention for efficient thermal transfer in solar thermal power generation. Corundum ceramics doped with Fe 2 O 3 and TiO 2 were prepared via a pressureless sintering. A Fe 2 O 3 –TiO 2 system with different Fe 2 O 3 /TiO 2 ratios was applied to corundum ceramics. Phase composition, microstructural evolution, sintering properties, high temperature resistance and thermophysical properties were evaluated. The results indicated that Fe 2 O 3 and TiO 2 rendered the grains highly active and enhanced the bonding between grains due to existing stably in the lattice of corundum. In addition, decrease in the Fe 2 O 3 /TiO 2 ratio led to a new phase of FeAlTiO 5 , which refined the grains. These effects gave the samples good sintering properties and thermal shock resistance, but the thermal expansion coefficient mismatch between FeAlTiO 5 and corundum deteriorated the high-temperature (1300 °C) stability. Formula C1 (Fe 2 O 3 /TiO 2 ratio of 9:1) sintered at 1600 °C had the optimum comprehensive properties, possessing a bending strength loss rate of 1.54% after 30 cycles of thermal shock (1100 °C-room temperature, air cooling) and a constant strength retention rate of approximately 71.34% after 90 h high-temperature cycle. The corresponding thermal conductivity and specific heat capacity were 18.81 W/(m·K) and 1.02 J/(g·K) at 25 °C, which was suitable as a high-temperature thermal storage material. [ABSTRACT FROM AUTHOR]

Corundum-based ceramics were prepared by two methods. The first used Fe 2 O 3 and TiO 2 as additives to react with α-Al 2 O 3. The second made full use of Al 2 O 3 , SiO 2 and TiO 2 in calcined bauxite, and Fe 2 O 3 was used as an additive. The SiO 2 -TiO 2 -Fe 2 O 3 system was designed to influence corundum. The effects of Fe 2 O 3 , TiO 2 and SiO 2 on physical properties, phase transformation, microstructure, thermophysical properties and thermal shock resistance were investigated. Results showed that Fe 2 O 3 and TiO 2 realized densification sintering through entering in the lattice of corundum, and the solubility of Fe 2 O 3 was higher than that of TiO 2. In addition, the excess TiO 2 tend to synthesize iron aluminum titanate in the grain boundaries, which could refine the grains and improve the mechanical properties. The SiO 2 -TiO 2 -Fe 2 O 3 system reduced significantly the sintering temperature, but the imperfect microstructure impaired the properties. Corundum-based ceramics prepared by Fe 2 O 3 , TiO 2 and α-Al 2 O 3 had the optimal properties. The thermal conductivity and thermal storage density were 14.81 W/(m·K) (25 °C), 837 kJ/kg (25–800 °C), respectively. No cracks were formed after 30 thermal shock cycles (1100 °C-room, air cooling), and the bending strength increased by 2.59%. This study supports the application of corundum-based ceramics as a promising thermal storage candidate. [ABSTRACT FROM AUTHOR]

To guarantee the efficiency of solar thermal power generation, the solar thermal storage material is required to have excellent thermal shock resistance to withstand the process of long-term thermal cycles. In this study, solar thermal storage ceramics were prepared using high calcium and high iron steel slag as the main raw material, adding cordierite and using the pressureless sintering method. The effects of cordierite addition on the physical properties, phase composition, microstructure, thermal storage and thermal shock resistance of the samples were investigated by XRD, SEM and so on. The results show that the addition of cordierite promotes densification and improves thermal shock resistance. The optimal level of addition is 10 %. When the temperature is 1240 °C, the bulk density and bending strength of the B5 (10 wt% cordierite) are 3.03 g cm−3 and 92.52 MPa, respectively. The bending strength of B5 after 30 thermal shock cycles is 97.06 MPa, which is 4.91 % higher than that before 30 thermal shock cycles. The thermal storage density is 867.95 kJ kg−1. This work not only analyzes the feasibility of this material for high-temperature service but also provides a new way for high-value utilization of high calcium and high iron steel slag. [ABSTRACT FROM AUTHOR]

Mullite whisker reinforced porous SiC membrane supports were fabricated by an in situ reaction bonding technique using SiC particles as skeleton materials, fine kaolin and α-Al 2 O 3 powder as bonding agents, activated carbon as pore-forming agent and MoO 3 as additive, and pressureless firing at 1350–1520 °C for 2 h in air. The effects of firing temperature and MoO 3 addition amount on the properties of membrane support, such as open porosity, bending strength, microstructure and phase composition, thermal shock resistance and air permeability were investigated. The results showed that the morphology of the mullite whiskers and properties of porous SiC membrane supports were greatly influenced by the firing temperature and MoO 3 addition amount. The membrane support with 8 wt % MoO 3 , fired at 1450 °C for 2 h, exhibited outstanding properties, including a bending strength of 24.69 ± 0.86 MPa, an open porosity of 43.30 ± 0.58%, a corresponding strength retention rate of 95.22% after 30 times cyclic thermal shock and Darcian permeability coefficient k 1 and non-Darcian permeability coefficients k 2 of 6.18 × 10−9 m2 and 1.50 × 10−3 m, respectively. [ABSTRACT FROM AUTHOR]

Corundum-mullite composite ceramics have high hardness, small plastic deformation and other excellent performances at high temperature. Corundum-mullite composite ceramics were fabricated from andalusite and α-Al 2 O 3 by in-situ synthesis technology. Effects of mullite/corundum ratio and sintering temperatures on the water absorption, apparent porosity, bulk density, bending strength, thermal shock resistance, phase composition and microstructure of the sample were investigated. Results indicated that the in-situ synthesized mullite from andalusite combined with corundum satisfactorily, which significantly improved the thermal shock resistance as no crack formed after 30 cycles of thermal shock (1100 °C-room temperature, air cooling). Formula A4 (andalusite: 37.31 wt %, α-Al 2 O 3 : 62.69 wt %, TiO 2 in addition: 1 wt %, mullite: corundum=6:4 in wt %) achieved the optimum properties when sintering at 1650 °C, which were listed as follows: water absorption of 0.15%, apparent porosity of 0.42%, and bulk density of 3.21 g⋅cm −3 , bending strength of 117.32 MPa. The phase composition of the sintered samples before and after thermal shock tests were mullite and corundum constantly. The fracture modes of the crystals were transgranular and intergranular fractures, which could endow the samples with high thermal shock resistance. [ABSTRACT FROM AUTHOR]

Cordierite-based glass–ceramic adhesives for bonding solar heat transmission ceramic pipelines were fabricated successfully using Suzhou kaolin, talc and commercial alumina as the main raw materials, TiO 2 as nucleation agent, waste glass powder and frit 242 as high-temperature fluxes. Bonding behavior, phase transformation, microstructure, thermal shock resistance and thermal cycling properties of the adhesives were investigated, and bonding mechanism was studied. The results indicated that adhesives B4 (composed of 60 wt% cordierite glass–ceramic and 40 wt% frit 242) after heat treatment (nucleated at 800 °C for 2 h and then crystallized at 950 °C for 2 h) exhibited the optimal performances with a shear strength of 10.26 MPa, which exceeded the industrial standard (JC/T 547-2005) of 1 MPa. The analysis of bonding mechanism showed that the glass of adhesive that filled up the pores in matrix surface and penetrated inside contributed to the high shear strength. Adhesives B4 had good thermal shock resistance and thermal cycling properties, as the shear strength of samples after 30 thermal shock cycles (1100 °C-room temperature, air cooling) was 8.51 MPa, which increased to 26.93 MPa with an increase rate of 162.48% after 100 thermal cycles (200–1100 °C). During thermal shocks or thermal cycles, cordierite particles crystallized at the interfaces to form a pinning-in effect, contributing to a higher shear strength. [ABSTRACT FROM AUTHOR]

Cordierite-mullite-corundum composite ceramics for solar heat transmission pipeline were fabricated via pressureless sintering at a low sintering temperature with added Sm 2 O 3 . The effects of Sm 2 O 3 on sintering behaviors, mechanical property, phase transformation, microstructure, thermal shock resistance and thermal conductivity of the composite ceramics were investigated. TEM analysis results demonstrated that Sm 3+ located in glass and grain boundaries to facilitate the densification via the liquid-phase sintering mechanism and improve bending strength by grain refinement, respectively. Proper addition (3 wt%) of Sm 2 O 3 could promote the crystallization of cordierite, and improve thermal shock resistance of the composite ceramics with an increasing rate of 16.70% for bending strength after 30 thermal shock cycles (air cooling from 1100 °C to RT). The composite ceramics possessed a superior thermal shock resistance, where a large amount of particles were formed to suppress crack initiation and propagation during thermal shock. Cordierite-mullite-corundum composite ceramics with proper Sm 2 O 3 addition (3 wt%) had a lower thermal conductivity than that of composite ceramics without Sm 2 O 3 addition by strengthening the scattering of phonon, which could reduce the heat loss during solar heat transmission process. [ABSTRACT FROM AUTHOR]

Cordierite/silicon carbide (SiC) composite ceramics with 10, 20 and 30 wt% cordierite were in-situ prepared via pressureless firing technique using silicon carbide, alumina, Kaolin and talc as starting materials. The results show that the synthesized composites all exhibited the good physical and mechanical properties. Among those, A2 composite with 20 wt% in-situ cordierite fired at 1280 °C exhibited the better bending strength and thermal shock resistance. The improvement of thermal shock resistance could be attributed to the proper cordierite wrapped around SiC, the homogeneous distribution of pores, the well-grown grains, as well as the formation of some glass phase. During the thermal shock test, a small amount of glass phases generated from the oxidation of SiC could react with Al 2 O 3 and MgO, and then more cordierite was formed due to the incorporation of nucleating agent TiO 2 . With in-situ cordierite content rising, both absorptance and emittance of composite reduced, but A2 composite had the better absorbing ability for the solar energy. It is believed that these in-situ cordierite/SiC composites should be a promising candidate to apply in the field of solar absorber coating owing to the better thermal shock resistance and absorptance of solar energy. [ABSTRACT FROM AUTHOR]