Search

ZrP2O7 ceramics exhibit poor mechanical properties after firing, as a major drawback. In this study, ZrP2O7 matrix composites reinforced with high silica fibers were prepared through pressureless sintering by varying the content and length‐to‐diameter ratio of the high silica fibers added to ZrP2O7 powder. After heat treatment at 1200‒1300°C, the room temperature flexural strength of the ZrP2O7 matrix composites with different amounts high silica fibers having different aspect ratios was 14.9‒45.2 MPa, the bulk density was 1.90‒3.03 g·cm−3, the apparent porosity was 2.37%‒39.39%, and the room temperature thermal conductivity was.47‒.95 W/(m·K). With an increase in the heat‐treatment temperature, driven by sintering and fiber crystallization, strength of the interfacial layer between the fibers and the matrix inside the ZrP2O7 matrix composites decreased and then increased. The transfer and blocking effects of the interface enabled effective transfer of the stress of the matrix to the fiber‐reinforced phase and prevented crack extension. The problem of inherent crystallization affecting high silica fibers at high temperatures was relieved by the ZrP2O7 ceramic matrix composites. [ABSTRACT FROM AUTHOR]

In this work, alumina foam ceramics (AFC) were prepared by foaming method, and AFC/salt composite phase change materials were prepared by melt infiltration method using AFC as skeleton materials. The results showed that AFC had good chemical compatibility with Na 2 SO 4 and NaCl. The salt contents of AFC/Na 2 SO 4 and AFC/NaCl were 37.8 wt% and 31.7 wt%, respectively, with compressive strength of 100.1 MPa and 72.8 MPa, thermal conductivity of 5.53 W/m·K and 6.40 W/m·K, and energy density of 1129 J/g and 1019 J/g, respectively. Due to the better wettability, AFC and Na 2 SO 4 form a chimeric structure, which has better binding and bonding strength, and is not prone to molten salt leakage. AFC/ Na 2 SO 4 is expected to be applied to industrial waste heat recovery and solar thermal power generation with periodic temperature changes. [ABSTRACT FROM AUTHOR]

In this study, La-doped BaZrO 3 -based composite ceramics Ba 1-x La x Zr 1-0.25x O 3 (x = 0–0.2) were successfully fabricated. The structure, phase composition, sintering behavior, and mechanical and thermal properties of the materials were investigated, and their thermodynamic stability was evaluated. The results revealed that the doping of La facilitated the formation of solid solution (Ba,La)ZrO 3 , and La 2 Zr 2 O 7 , leading to grain refinement and enhanced structural densification as well as grain boundary bonding of the samples. As La doping x ranging from 0 to 0.20, the average grain size of the specimens decreased from 6.14 μm to a minimum of 2.58 μm, the cold modulus of rupture increased significantly from 84.1 to 155.6 MPa. Moreover, the apparent porosity decreased from 11.2% to a minimum of 1.7% with a thermal conductivity gradually decreased from 5.501 W/mK to 2.802 W/mK. Additionally, thermodynamic calculations indicated the potential application of La-doped BaZrO 3 ceramics in the field of highly reactive alloy melting. [ABSTRACT FROM AUTHOR]

The sol-gel method is a technique used to create a controlled porous structure by building up colloidal particles during the gelation process. In this study, a sol-gel method was utilized to prepare fibrous/nano-Al2O3 insulation composites using glass fiber, nano-Al2O3, and silica sol as primary materials for performance characterization. The samples exhibited high porosities (78.35–81.30%) and low thermal conductivities (0.084–0.159 W m−1 k−1 at 200–600 °C). The introduction of nano-Al2O3 resulted in a well-distributed aperture hierarchy and promoted multidirectional heat transfer paths. The fibers were arranged in a three-dimensional structure, overlapping each other, while the nano-powders were dispersed in a liquid phase and cross-linked to form a spatial mesh structure. The findings of this research have potential applications in heat preservation and energy-saving. Highlights: The fibrous/nano-Al2O3 insulation composites had high porosities (78.35–81.30%) and low thermal conductivities (0.084–0.159 W m−1 k−1 at 200–600 °C). In addition, the inclusion of nano-Al2O3 resulted in a well-structured hierarchical pore distribution, which facilitated multidirectional heat transfer paths and ultimately led to a marked reduction in thermal conductivity of the samples. Moreover, the fibers were overlapped to create a three-dimensional structure, while the nano-powders were dispersed in the liquid phase and cross-linked to generate a spatial mesh structure. [ABSTRACT FROM AUTHOR]

In this contribution, Bi4B2O9 foam ceramics with porosity of 76.6%–85.8% and thermal conductivity of.062–.092(W/(m·K)) were successfully prepared for the first time by the foam casting method using bismuth oxide and boric acid as the main raw materials and gelatin as the gel forming agent. The effects of additive content and solid loading on the slurry, pore size, and distribution as well as mechanical and thermal properties of porous ceramics were investigated. The addition of gelatin led to the stable arrangement of the liquid‐gas interface, which eventually resulted in a foam with a stable pore structure. The sintered ceramics have a highly spherical morphology with typical micropores and cell window, which may also contribute to the low thermal conductivity of Bi4B2O9 foams. Bi4B2O9 foam with tailored properties and graded pore structure by adjusting the process parameters can be used as a high‐performance nuclear reactor insulation material. [ABSTRACT FROM AUTHOR]

Nano‐porous super thermal insulation composites are an important component in refractory and play a key role in energy‐saving. In this work, we adopt dry preparation technology and high‐temperature sintering and use nano‐Al2O3 and nano‐SiO2 as the main materials to prepare nano‐Al2O3/SiO2‐based composites for a range of performance characterization. According to this study, the as‐prepared nano‐Al2O3/SiO2‐based composites exhibited a high porosity (77.4%–89.6%) and a low thermal conductivity (.06–.134 W/(m k) at 200–800°C). The most striking finding of this study was the nanostructure that was successfully constructed in nano‐Al2O3/SiO2‐based composites and exhibited a well hierarchical aperture distribution. The as‐prepared nano‐Al2O3/SiO2‐based composites could be widely applied in energy‐saving and heat preservation applications. [ABSTRACT FROM AUTHOR]

In this study, a manageable foam-casting technique for preparing novel magnesium borate foams (MBFs) with highly controllable performances is presented. MBFs were prepared using MgO and boric acid as the primary materials, with different amounts of foaming agents, thickening agents, and solid slurry contents. The results showed that the MBFs possess compressive strengths (0.74–11.32 MPa), low thermal conductivities (0.171–0.976 W/(m·K) at 200–800 °C), and high porosities (51.78–80.70%). Therefore, they can serve as novel architectural materials for heat preservation and partial load-bearing applications. [ABSTRACT FROM AUTHOR]

A two-step method, combined with cold isostatic pressing, was used to prepare CeO 2 -doped ZrP 2 O 7 ceramics, and their microstructure, mechanical properties, thermal conductivities, and dielectric properties were determined. It was found that CeO 2 doping could increase the Zr–P and P–O bond lengths, which in turn decreased the thermal conductivity of the ZrP 2 O 7 matrix. Doping with 12 wt% CeO 2 simultaneously reduced the sintering temperature and improved the mechanical properties of the ZrP 2 O 7 ceramics, while retaining its low thermal conductivity and good dielectric properties. The maximum cold modulus of rupture of a sample at 1250 °C was 75.91 MPa, which met most conditions for use at room temperature. A COMSOL model was used to predict the thermal conductivity, based on the microstructure, with a relatively high degree of accuracy. The thermal conductivity of the CeO 2 -doped samples was lower than 1.083 W/(m·K). The dielectric constant was in the range of 5.93–6.52 at 20–40 GHz, and the dielectric loss was less than 4 × 10−3. The ZrP 2 O 7 -doped ceramics have potential for application in millimetre wave technology, satellite communication, and vehicle radar fields, because they can meet the high thermal insulation requirements for these applications. • It is expected to be used as an integrated anti-heat insulation material for millimetre waves, satellite communications and vehicle radars. • Our work fills in the research on the mechanical and thermal insulation properties of CeO 2 doped ZrP 2 O 7 ceramic. • The effect of CeO 2 on the crystal structure of ZrP 2 O 7 was studied and the crystal structure after solid solution was drawn. • After CeO 2 is doped, it can strengthen the material through solid solution and particle reinforcement. • Established a 2D simulation model to better predict the thermal conductivity. [ABSTRACT FROM AUTHOR]

There is an urgent demand for multifunctional insulation materials with neutron shielding ability that can be particularly used in the nuclear energy system. GdBO3 ceramics are one of the candidates for such materials. In this study, GdBO3 ceramics were successfully synthesized using a simple solid‐phase method. The effect of boric acid content on the micro and macro properties of GdBO3 ceramics was explored. The experimental results indicate that the thermal conductivity of the resulting GdBO3 ceramics ranged from.12 to.68 W/(m⋅K), and lower thermal conductivity was achieved with smaller pore size and higher apparent porosity of the sintered product. Moreover, the mechanical properties of the samples in multiple temperature ranges can be improved by increasing boric acid content. Finally, neutron shielding permeability study, performed on the samples in different thicknesses, reveal that GdBO3 ceramics possessed excellent neutron shielding performance (NSP). The obtained results manifest that GdBO3 ceramics with outstanding heat insulation and NSP have a potential application in a nuclear reactor. [ABSTRACT FROM AUTHOR]

ZrP 2 O 7 -based fiber composites were prepared by in situ synthesis and their microstructure, thermal conductivity, mechanical and dielectric properties were determined. The chemical reaction with BPO 4 as the phosphorus source and nano-ZrO 2 as the zirconium source was initiated at 900°C, which promotes liquid-phase sintering and reduces the sintering densification temperature of the ZrP 2 O 7 -based fiber composites by generating small ZrP 2 O 7 grains and low-melting B 2 O 3. The lower sintering densification temperature and the appropriate amount of network formers effectively suppressed the high-temperature crystallization phenomenon of the high-silica-oxygen fibers, strengthened the interfacial bonding between the fibers and the matrix, and improved the interfacial debonding problem of the ZrP 2 O 7 -based fiber composites. It is found that the ZrP 2 O 7 -based fiber composites possess low dielectric constant, low dielectric loss, good thermal conductivity, and acceptable mechanical properties, which can meet the relevant application requirements of centimeter-wave technology. • After heat treatment at 1250°C, BZ4 possessed the best overall properties. • The interfacial bonding between fiber and matrix was improved by in-situ synthesis. • A small amount of B oxide was introduced in situ to improve the high temperature crystallization of the fibers. [ABSTRACT FROM AUTHOR]

Advanced nano-porous super thermal insulation materials are widely used in spacecraft, soler-thermal shielding, heat exchangers, photocatalytic carriers due to their low thermal conductivity. In this work, adopting dry preparation technology, nano-Al 2 O 3 , nano-SiO 2 , SiC and glass fibers as raw materials, novel nanometer alumina-silica insulation board (NAIB) were prepared. The preparation process was simple, safe, and reliable. In addition, the NAIB exhibited a high porosity (91.3–92.3%), small pore size (39.83–44.15 nm), low bulk density (0.22–0.26 g/cm3), better volumetric stability, and low thermal conductivity (0.031–0.050 W/(m·K) (200–800 °C)), respectively. The as-prepared NAIB could render them suitable for application as high-temperature thermal insulation materials. [ABSTRACT FROM AUTHOR]

To further improve the properties of the porous alumina materials, which were prepared by using walnut shell as pore former with a multi-layer hierarchical structure, the multiple sol (zirconia sol, alumina sol, and silica sol)–impregnated walnut shell powder was utilized. The hygroscopicity and microstructure of walnut shell, and physical performances, thermal conductivity, and microstructure of porous alumina materials were characterized. The residual structure of walnut shells impregnated with multiple sols was left in the pores, which optimized the pore structure of materials. High-performance porous alumina materials were produced by successively impregnating with silica, alumina, and zirconia sols, which possesses low thermal conductivity of 0.166 W/(m·K) at 200 °C and ultra-high compressive strength of 84.4 MPa. The above excellent properties result in a great advantage for the existing materials. In addition, the feasibility of optimizing the structure and properties of the porous alumina materials, by using the residual structure of pore-forming agent, was further verified. [ABSTRACT FROM AUTHOR]

• A novel ZrP 2 O 7 ceramic foams were prepared by foaming method. • Our work fills the blank of above 60 % porosity of ZrP 2 O 7 ceramic. • The changes of microstructure and pore structure were demonstrated. • ZrP 2 O 7 ceramics foams has a ultra-low thermal conductivity. • We control the foam ceramic structure and performance by adjust the foaming agent, the solid content and the amount of CMC added. This study demonstrated the synthesis of novel zirconium pyrophosphate (ZrP 2 O 7) ceramic foams via a two-step method using a foam casting technique. The synthesised foams functioned as thermal insulators with a highly controllable performance. We investigated the effects of the addition of foaming and thickening agents as well as the solid content of the slurries on the slurry, mechanical properties, thermal conductivities, and microstructure of ZrP 2 O 7 ceramic foams. The ZrP 2 O 7 ceramic foams synthesised at 1473 K exhibited a porosity, compressive strength, and thermal conductivity of 75.2–89.1 %, 1.95–0.02 MPa, and 0.144–0.057 W/(m K) (298–573 K), respectively. The increase in the porosity to >60 % will facilitate applications based on the low thermal conductivities of the foams. [ABSTRACT FROM AUTHOR]

Sintering performance at high temperatures is a serious issue for tetravalent metal pyrophosphate MP 2 O 7 ceramics (M = Ti, Zr, Hf, Ge, Sn, etc.). Herein, we investigated the influence of high synthesis temperatures and amounts of ZrP 2 O 7 precursors on the properties of ZrP 2 O 7 ceramics. A ZrP 2 O 7 powder was first synthesised via a solid-state reaction; this powder was used in the fabrication of the ZrP 2 O 7 ceramic using a combination of two-step sintering and in situ bonding using MgO as the sintering aid. The phase composition and microstructure of the ZrP 2 O 7 powder as well as the ZrP 2 O 7 ceramic were studied by X-ray diffraction and scanning electron microscopy. The physical properties and room-temperature thermal conductivity of the ZrP 2 O 7 ceramic were investigated. The ceramic exhibited high thermal stability at 1350 °C. This study indicates that the mechanical properties of the ZrP 2 O 7 ceramic can be enhanced while maintaining their low thermal conductivity by sintering it at 1300 °C with the addition of an appropriate amount of the ZrP 2 O 7 precursors to the ZrP 2 O 7 powder. • A novel two-step sintering and in situ bonding method. • The potential of ZrP 2 O 7 ceramics as thermal insulation materials was demonstrated. • We investigated the influence of high synthesis temperatures and amounts of ZrP 2 O 7 precursors on the properties of ZrP 2 O 7 ceramics. [ABSTRACT FROM AUTHOR]

Fiberboard (FB) is extensively utilized in heat‐insulating refractory materials owing to its lightweight nature and excellent resistance to high temperatures. Nevertheless, the inadequate mechanical properties and limited dimensional stability of FB hinder its further application. The vacuum filtration was utilized in this study to manufacture inorganically modified insulation FB, incorporating plus fiber/1260 fiber and silica sol as the primary constituents and sepiolite powder (HS) as the modifier. The experimental results show that the fabricated samples exhibited extremely high porosity (75.3%–90.2%) and low thermal conductivity (.063–.15 W m−1 K−1, 200–800°C). The fibers were arranged in a three‐dimensional structure, overlapping with each other, and the silica sol adhered to the fibers, forming a spatial mesh structure through cross‐linking. Importantly, the incorporation of HS was effective in controlling the agglomeration of the silica sol, leading to a more uniform distribution within the fibers. Additionally, the study found that the mechanical properties (high hardness (64–72 HA)) and high‐temperature durability of the FBs were enhanced due to the flocculant modification. This study highlights promising prospects for industrial applications and offers a cost‐effective admixture for modifying and preparing high‐performance FBs, which is expected to see broad adoption in thermal insulation and energy conservation applications. [ABSTRACT FROM AUTHOR]

The efficient optimisation of radiation shielding materials (RSMs), which protect people from potential radiant threats, is highly desirable; however, it remains challenging. This study addresses the low-cost fabrication of the ceramic-based RSMs, aluminium borate-based ceramics using Bi 2 O 3 as a novel simultaneous shielding agent and sintering promoter. The phase compositions, microstructures, sintering kinetics, and performances of the as-prepared Bi 2 O 3 doped aluminium borate ceramics (BDABCs) are systematically researched. Finally, co-shielding tests for neutron and gamma radiation are performed. The results demonstrate that Bi 2 O 3 can positively influence the sintering densification process of BDABCs via the evident reduction in the sintering activation energy. The migration of the Bi 2 O 3 –B 2 O 3 liquid phase affects the pore structure, crystal morphology, and thermal conductivity of the samples. The obtained BDABCs exhibited highly reliable mechanical properties with a maximum elastic modulus and modulus of rupture of 124.3 GPa and 54.9 MPa, respectively; controllable thermal conductivity from 1.32 to 6.16 W m−1 K−1; and 12 wt% Bi 2 O 3 -doped sample (1400 °C × 3 h, 1.5 cm) shows the best radiation shielding performance, including 58.6% neutron and 26.6% γ rays. The obtained results manifest the enormous potential of BDABCs as structural materials and functional RSMs. [ABSTRACT FROM AUTHOR]

In this work, calcium hexaaluminate was used as a skeleton material to develop a composite phase change material with sodium sulfate for high temperature thermal energy storage applications. The results showed that a good chemically compatibility existed between calcium hexaaluminate and sodium sulfate, and the optimal sodium sulfate content of the composite phase change materials was 50 wt%, which have a latent heat of phase change of 85.27 J/g, an energy density of 1861 J/g, a compressive strength of 88.77 MPa and a thermal conductivity at room temperature (25 °C) of 1.13 W/m·K. On the other hand, the addition of alumina enhances the thermal conductivity of the composite phase change materials. The composite phase change materials are expected to be used in industrial waste heat recovery and solar thermal power generation. • The calcium hexaaluminate was used as a novel skeleton material to develop shape-stabilized sodium sulfate. • The composites have an energy density of 1861 J/g and a thermal conductivity of 1.128 W/m k−1. • The thermal conductivity of the composites added with 20 wt% Al 2 O 3 reached 1.36 W/m k−1, which increased by21.3%. • With an operating temperature of 870-900 ℃, the composite PCMs can be used as a high-temperature thermal energy storage material. [ABSTRACT FROM AUTHOR]

Carbon fibers (CFs) can be introduced to castables, due to the relative higher thermal conductivity and stronger damping properties. In this research, microstructural evolution of carbon fibers (CFs) in the presence of mixture of silicon and silica powders under the protection of carbon black was studied in the temperature range of 1000–1300 °C by means of X-ray diffraction (XRD) and scanning electron microscopy (SEM). The results show that some small amorphous SiO x globules were formed on the surface of CFs at the temperature below 1200 °C. With the increase of the treated temperature, the size of globules became bigger and reached maximum at 1200 °C. The growth of SiO x globules can be controlled by vapor-solid mechanism. In addition, the effects of these CFs on properties and microstructure of mullite-corundum castables were studied. The results showed that the CFs with SiO x globules (CFs/SiO X) could significantly improve the mechanical properties of the castables because the interfacial bonding strength between CFs/SiO x and matrix is much stronger than the untreated CFs. [ABSTRACT FROM AUTHOR]

Generally, a multilayer structure is present inside a walnut shell, and the residual structure of the walnut shell is retained after impregnation and firing. When the walnut shell is used as a pore‐forming agent, this structure helps in improving the mechanical and thermal insulation properties of the lightweight porous materials. In this study, porous mullite materials (PMMs) with plant morphological structure pores were prepared using a‐Al2O3 and silica powder as the raw materials with addition of sol‐impregnated walnut shell powder (WSP). The influence of sol type and firing temperature on the pore structure of the PMMs was analyzed, which affected the compressive strength and thermal conductivity. The plant morphological porous structure was observed in the samples after sol impregnation. After firing at different temperatures, the porous structure gradually contracted and supported the pores, improving the mechanical properties, while the complex porous structure increased the heat conduction path, thereby improving the insulation performance. Using WSP impregnated with silica‐sol and zirconia‐sol as pore‐forming agents, PMMs with higher compressive strength and relatively low thermal conductivity (TC) were prepared. [ABSTRACT FROM AUTHOR]

To improve the mechanical and thermal insulation properties of lightweight alumina, which was prepared by using pore‐forming agent from biological sources, the silica sol‐infiltrated corn stalk was utilized. Spring back and hygroscopicity of corn stalk powder as well as cold compressive strength, thermal conductivity, microstructure, and pore size distribution of lightweight alumina were characterized. The results indicate that impregnation of silica sol leads to different degrees of decrease in spring back height due to achieving better mesh by silica gel between the corn stalk powders, and then improves the formability, although at the same time the large number of hydrophilic groups results in an increase in hygroscopicity. Furthermore, sol impregnated pore‐forming agent optimizes the microstructure of the lightweight alumina pores. Lightweight alumina with a cold compressive strength up to 48.64 MPa was produced, and with the silica sol concentration of 3 wt%, lower thermal conductivity values at all test temperatures were obtained. Hence, the use of corn stalk impregnated with the appropriate concentration of silica sol as pore‐forming agent could enhance the mechanical and thermal insulation properties of lightweight alumina for the spheroidization of pore shape, randomization of pore distribution as well as miniaturization of pore size. [ABSTRACT FROM AUTHOR]

In this contribution, a manageable foam-casting technique for the preparation of novel aluminum borate foams (ABFs) as thermal insulators with highly controllable performances is presented. ABFs were fabricated from α-Al 2 O 3 and 2Al 2 O 3 ·B 2 O 3 with the addition of various amounts of foaming agents, thickening agents, and slurry solid contents. The dispersions and rheological properties of the slurries were then examined, followed by exploration of microstructural evolution and testing of mechanical/thermal properties. It should be noted that the generated micro-pores generated and interlocking rod-like 9Al 2 O 3 ·2B 2 O 3 crystals may lead to superior mechanical tolerances and lower thermal conductivities for the ABFs. In general, the as-prepared ABFs with porosities ranging from 73.8 to 96.3 vol%, compressive strengths of 8.20–0.15 MPa, and thermal conductivities of 0.228–0.046 W/(mK) (200–800 °C) could render them suitable for application as high-temperature thermal insulating materials. [ABSTRACT FROM AUTHOR]

Chamotte is one of the most commonly used raw materials for aluminosilicate refractories. The present work concerns the high‐temperature performance of the chamotte‐zircon composite. The crystalline phase, mechanical property, and thermal conductivity were evaluated. In addition, the finite element method was applied to analyze stress distribution. Zircon accelerated the melting of cristobalite in chamotte during sintering. After adding zircon, a drastic elastic modulus change at about 230°C was avoided, and the infrared shielding effect of zircon reduced the thermal conductivity when the temperature was greater than 500°C. At last, based on the results of finite element method, increasing zircon content reduced stress concentration. [ABSTRACT FROM AUTHOR]

Abstract: In order to investigate the relationship between pore structure and thermal conductivity as well as mechanical strength, porous alumina ceramics (PAC) with various pore structures were fabricated, using starch as the pore‐forming agent. Fractal theory was employed to characterize the pore size distribution more accurately than ever used parameters. The results show that the increase in starch content in PAC leads to an enhanced porosity, a higher mean pore size, and reduced fracture dimension, thermal conductivity and strength. The fractal analysis indicated that the fractal dimension decreases gradually and reaches its minimum value with increasing the starch content up to 25 wt%, but the further incorporation results in an opposite trend. It is suggested from micro‐pore fractographic analysis that the optimization of both thermal insulation performance and mechanical strength are positively correlated with the increase in the mean pore size and proportion of 2‐14 μm pores but negatively corrected with the porosity. These results provide a new perspective and a deeper understanding for fabrication of PAC with both excellent thermal insulation and mechanical performance. [ABSTRACT FROM AUTHOR]

Injecting lance is a key equipment for hot metal pretreatment. In this work, the lance castables with high mechanical properties and thermal shock resistance were obtained by adding alumina bubbles, due to its spherical shape and hollow structure. It is found that the addition of alumina bubble improves the flow values of castables. The bulk density values of samples with the addition of 4 wt% alumina bubbles (AB4) were the best of all the experimental castables. Alumina bubble addition is effective in heightening the thermal expansion, thermal conductivity of mullite castables and can resist the sharp decrease in thermal expansion above 1300 °C. The addition of alumina bubble can improve the mechanical strength of mullite castables. After heating at 1400 °C, a strong chemical bond forms between the bubbles and the binding phases. Due to the appropriate bonding at the alumina bubble/matrix interface, AB4 castable exhibits a relatively better thermal shock resistance. [ABSTRACT FROM AUTHOR]

In this study, we designed four groups of A-substituted medium-entropy perovskites, synthesized (Ba 0.4 Sr 0.4 Ca 0.1 La 0.1)ZrO 3 , a non-equimolar medium-entropy perovskite, and studied its microstructural uniformity. The medium entropy of these perovskites imparts unique mechanical and thermal properties. Compared to pure BaZrO 3 , the cold moduli of rupture of the four samples improved by 164.29%, 121.22%, 91.49%, and 81.87%, respectively, and the relative density increased from 69.47% to over 90%. The thermal conductivities of these materials were lower than those of conventional low-thermal-conductivity perovskite materials, with a minimum value of 1.513 W/(m·K). The high strengths and low thermal conductivities of these novel perovskite materials could provide vast opportunities for various future applications. [ABSTRACT FROM AUTHOR]

Used calcined clay, waste foundry sand (WFS), was adopted to prepare aggregates with the addition of clay, alumina powder, and bran. Bulk density, porosity, cold crushing strength, phase compositions, microstructure, and thermal conductivity were investigated. Thermal calculation was adopted to assess the generation of the liquid phase during sintering. In the specimens composed of WFS and clay, the increase in clay concentration led to a decrease in cold crushing strength even if the variation in bulk density was not obvious. When WFS, clay, alumina powder, and bran were adopted in manufacturing aggregates, the addition of bran influenced the phase composition of the samples because of the formation of pores. With an increased WFS content, the cold crushing strength improved due to an increase in the amount of liquid phase during the sintering process. The thermal conductivities obtained from the samples by mechanical pressing were ideal and showed the influence of heat shielding effect from zircon. [ABSTRACT FROM AUTHOR]

The paper reports the effects of fly ash particle size on the properties of the lightweight insulation materials. The microstructure and mechanical properties of lightweight insulation materials are separately investigated by SEM (scanning electron micrograph) and tabulate thermal conductivity apparatus methods. In addition, the effects of particle size distribution of fly ash on the properties of lightweight insulation materials is studied by grey incidence analysis. The results show that when the ball milling time increases, the particle size of fly ash decreases and the distribution becomes narrow. At the same time, the polymerization state of fly ash would be depolymerize from high poly structure to low polymeric structure. Moreover, the linear shrinkage, bulk density, compressive strength, acid resistance and thermal conductivity of lightweight insulation materials have also increased, but the apparent porosity decreases. And the studies highlight that when the content of fine fly ash particles increases, the nucleation and growth of mullite is accelerated and the sintering driving force is improved at high temperature, which have a positive effect on improving the physicochemical properties of materials. The particles ranging from 20 to 30 μm has a great influence on the linear shrinkage, bulk density, compressive strength, acid resistance rate and thermal conductivity of lightweight insulation materials. [ABSTRACT FROM AUTHOR]

In the present work, carbon black (CB) works as a pore-forming agent in the preparation of alumina porous ceramics. The pore structures ( i.e. mean pore size, pore size distribution and various pores size proportions) were characterized by means of Micro-image Analysis and Process System (MIAPS) software and mercury intrusion porosimetry. Then their correlation and thermal conductivity as well as strength were determined using grey relation theory. The results showed that the porosity and mean pore size increased against the amount of CB, whereas the thermal conductivity, cold crushing strength and cold modulus of rupture reduced. The <2 μm pores were helpful for enhancing the strength and decreasing the thermal conductivity whereas the >14 μm pores had the opposite effects. [ABSTRACT FROM AUTHOR]

First, walnut shell powder (WSP) was impregnated with different impregnating reagents:5% ZrO2 sol, 7% Al2O3 sol, and 3% SiO2 sol. Then, porous Al2O3 materials were prepared using a-Al2O3 micropowder as the main starting material and the treated WSP as the pore forming agent. The effects of the sol impregnated WSP on the pore structure, the thermal conductivity and the mechanical properties of the porous Al2O3 materials were investigated. The results show that the morphological changes of WSP are clearly observed in the pores of the porous Al2O3 materials, which is an important factor in optimizing the pore structure of ceramics. Porous Al2O3 ceramics of low thermal conductivity (0.297 W · m-1 · K-1 at 200 °C) and high compressive strength (43.5 MPa) can be obtained adopting the WSP impregnated with 3% SiO2 sol. Furthermore, mullite cross network structure is also found in the pores of the material. [ABSTRACT FROM AUTHOR]

Traditional carbon blocks for blast furnaces are mainly produced with electrically calcined anthracite owing to its good hot metal corrosion resistance. However, this kind of material shows low thermal conductivity and does not meet the demands for cooling of the hearth and the bottom of blast furnaces. In this article, a new kind of a high-performance carbon block has been prepared via ceramic-bonded carbon (CBC) technology in a coke bed at 1673 K (1400 °C) using artificial graphite aggregate, alumina, metallic aluminum, and silicon powders as starting materials. The results showed that artificial graphite aggregates were strongly bonded by the three-dimensional network of ceramic phases in carbon blocks. In this case, the good resistance of the CBC blocks against erosion/corrosion by the hot metal is provided by the ceramic matrix and the high thermal conductivity by the graphite aggregates. The microstructure of this carbon block resembles that of CBC composites with a mean pore size of less than 0.1 μm, and up to 90 pct of the porosity shows a pore size <1 μm. Its thermal conductivity is higher than 30 W · m · K [293 K (20 °C)]. Meanwhile, its hot metal corrosion resistance is better than that of traditional carbon blocks. [ABSTRACT FROM AUTHOR]

This study introduces BaZrO 3 with a perovskite structure as a second phase combined with MgO to prepare composites and apply these magnesium matrix composites in high-temperature fields. The prepared composites have good dimensional stability (linear change rate <1%) and better cold compression strength (50–110 MPa) compared to fused magnesite. Sintered samples containing 5 wt % BaZrO 3 possessed a better elastic modulus and flexural strength at 1600 °C compared to fused magnesite. BaZrO 3 formed a glass phase with CaO and SiO 2 in the fused magnesite sand at high temperatures, which was distributed between the particles of MgO. The BaZrO 3 inhibited grain growth, promoted the exclusion of pores, and significantly reduced the thermal conductivity of the sintered samples. Scanning electron microscopy images indicated that compared to single-phase MgO, the composite sample produced a glass phase after a thermal shock, filling its pores, resulting in enhanced retention of the sample mechanical properties and better thermal shock stability. This study demonstrates that magnesium matrix composites with BaZrO 3 have promising applications in high-temperature materials. [ABSTRACT FROM AUTHOR]

This study introduces a feasible approach for preparing Al2O3‐based ceramics with highly controllable performance via binder jetting. The Al2O3‐based ceramics were prepared using Al2O3 and H3BO3 as raw materials. The results showed that the samples prepared with 0.24 mol H3BO3 exhibited high apparent porosity (64%–66.67%), well‐bending strength (3.46–8.53 MPa), and low thermal conductivity (0.113–0.329 W·m−1·k−1 at 200–800°C). It was observed by an electron microscope that the increase of boric acid content led to the in‐situ formation of more aluminum borate grains in the sample. Meanwhile, the remaining Al2O3 reacts with silicon oxide in the impregnation solution to form mullite whiskers. The whiskers ensured that the sample had superior mechanical properties and lower thermal conductivities. Based on the above properties, the possibility of Al2O3‐based ceramics application in the aerospace field can be speculated. [ABSTRACT FROM AUTHOR]

Basalt cotton (BC) has a cotton-like structure due to the three-dimensional skeleton built by basalt fiber overlapping, which exhibit high flexibility. To explore the application of BC, hollow silica spheres (HSSs) were planted on the three-dimensional skeleton of BC by combining a sol–gel method and a sacrificial template method, to obtain HSS/BC composites. Scanning electron microscopy revealed that HSSs were successfully adhered to the three-dimensional skeleton of BC and retained 69% adhesion ratio under magnetic vibration at a certain frequency. HSS/BC composites with a thermal conductivity of 0.042 W/m·K were a promising choice for flexible thermal insulation. [ABSTRACT FROM AUTHOR]

To replace the existing diatomite brick used in the field of medium and low temperature (below 1000 °C) thermal insulation and realize the comprehensive utilization of waste resources, a novel foamed insulation material was prepared with waste granite via a direct foaming method. In particular, the proportion of waste granite reached 88 wt%. The optimum parameter for the specimens were obtained at 1050 °C with 8 wt% foam and milling time of waste granite was 7 h. Meanwhile, the experimental results showed that the bulk density was 0.7 g/cm3, the linear shrinkage was 3.71%, the total porosity was 73.59%, the compressive strength was 8.0 MPa, the linear shrinkage of resintering at 900 °C for 8 h was 0.2%, and the thermal conductivity was 0.108 W/(m·K) at 300 °C. The effects of particle size of waste granite, content of foam on the macro and micro properties were systematically investigated, then the MIAPS software was used to obtain the pore structure parameters. Finally, the relationship between the pore structure and properties of specimens under different variables was analyzed based on image method and fractal geometry. The results show the potential use of waste granite as the main raw material to replace the use of natural diatomite brick. [ABSTRACT FROM AUTHOR]

BaZrO 3 with the ABO 3 perovskite structure can be doped at the A or B sites to obtain the corresponding properties. In this study, BaZrO 3 was doped with Ca2+, Sr2+, Ti4+, and Ce4+. The structure, phase composition, and mechanical and thermal properties of the composites were investigated. The sintered Ba 1-x Ca x ZrO 3 samples with x = 0.2 and 0.4 exhibited relatively superior comprehensive behaviours; the cold modulus of rupture was increased by 127.36% and 134.59%, while that for BaZr 0 · 8 Ti 0 · 2 O 3 and BaZr 0 · 8 Ce 0 · 2 O 3 was increased by 99.30% and 112.37%, respectively. Further increases in strength and density were obtained in the Ba 0 · 8 Ca 0 · 2 Zr 0 · 8 Ti 0 · 2 O 3 and Ba 0 · 6 Ca 0 · 4 Zr 0 · 8 Ti 0 · 2 O 3 co-doped samples, and the corresponding apparent porosities were greatly decreased from 30.6% to below 1.0%. The thermal conductivities of the doped samples were generally low, achieving a minimum of 0.361 W/(m·K). The combination of high strength and low thermal conductivity demonstrate the significant application potential of BaZrO 3 -based composite materials. [ABSTRACT FROM AUTHOR]

In this study, three-B-site perovskite Ba(Zr 1–2x Ti x Ce x)O 3 (x=0–0.2) materials with the co-substitution of Ti4+ and Ce4+ at the Zr-site of barium zirconate (BaZrO 3) were successfully prepared. The analyses of XRD & Rietveld method, SEM, and TEM indicated that the substituted ions Ti4+ and Ce4+ entered the BaZrO 3 lattice to form a single-phase solid solution, showing a conventional primitive cubic perovskite structure (Pm-3 m space group), and its lattice parameters gradually increased from 0.4192 nm to 0.4206 nm with x value. The sample with x=0.1 exhibited relatively optimal structural uniformity and densification, as well as comprehensive physical properties. The sample Ba(Zr 0.8 Ti 0.1 Ce 0.1)O 3 showed a minimum mean grain size of 1.50 μm. And due to the combined effect of solid solution formation and grain refinement, it displayed an apparent porosity of 1.42 % with a cold modulus of rupture (CMOR) of 123.8 MPa, and a thermal conductivity at ambient temperature of 2.197 W/mK. Furthermore, this three-B-site perovskite Ba(Zr 1–2x Ti x Ce x)O 3 exhibits excellent high-temperature stability. This study demonstrates the promising application of the dense, high-strength, and low-thermal conductivity Ba(Zr 0.8 Ti 0.1 Ce 0.1)O 3 perovskite material in the field of advanced refractory ceramics. • A three-B-site perovskite Ba(Zr 1–2x Ti x Ce x)O 3 (x=0–0.2) were prepared via high-temperature solid-state method. • The analyses indicated the formation of a solid solution, showing a conventional primitive cubic perovskite structure. • Sample Ba(Zr 0.8 Ti 0.1 Ce 0.1)O 3 displayed an apparent porosity of 1.42 % with a cold modulus of rupture of 123.8 MPa, and a thermal conductivity at ambient temperature of 2.197 W/mK. [ABSTRACT FROM AUTHOR]

In this study, a two-step method combining the direct foaming process with the control of solid content and heat treatment temperature was employed to prepare ZrP 2 O 7 -CePO 4 composite porous materials with varying porosities. The results indicate that an increase in solid content and heat treatment temperature leads to a reduction in porosity and average pore size while simultaneously improving the mechanical properties. The porosities, compressive strengths, thermal conductivities, ε and Tanδ ranged from 63.2 to 85.3 vol%, 19.43 to 0.99 MPa, 0.089 to 0.088 W/(m·K), 1.64 to 2.72, and 0.88 × 10−3 to 1.99 × 10−3, respectively. Electromagnetic simulations have validated that ZrP 2 O 7 -CePO 4 composite porous ceramics, when used as the core layer material for A-sandwich antenna radomes, exhibit excellent transmittance properties. This suggests the potential application of these materials for supersonic aircraft antenna radomes. • A novel ZrP 2 O 7 -CePO4 porous ceramic were prepared by foaming method combining a two-step method. • Our work greatly improved the compressive strength of high-porosity ZrP 2 O 7 with low thermal conductivity. • The dielectric properties of ZrP 2 O 7 ceramics with high porosity were studied for the first time in this study. • The feasibility of ZrP 2 O 7 -CePO 4 ceramics for supersonic aircraft is verified by electromagnetic simulation. [ABSTRACT FROM AUTHOR]

Abstract To improve the properties of porous alumina ceramics, which were typically prepared by adding pore-forming agents, rice husk (RH) as pore-forming agent was pretreated with zirconia sol. The effects of sol-treatment on the thermal conductivity and compressive strength of the resultant ceramics were characterized. Furthermore, the pore size distribution, pore shape, microstructure, and phase evolution also were studied. The results showed that the RH pretreatment optimizes the microstructure of the ceramic pores. Moreover, complete morph-genetic RH is clearly observed in the pores, which is established as a key factor in improving the properties of the resultant ceramic. The thermal insulation properties are determined to significantly improve, although the thermal conductivity increases slightly with the increment of zirconia sol concentration from 5 to 10 wt%. Meanwhile, after sintering at 1550 °C, the compressive strength is significantly greater for the specimen prepared with 10 wt% zirconia sol-treated RH (65.56 MPa) than that with untreated RH (43.37 MPa). Hence, it was demonstrated that the use of zirconia sol-pretreated RH as a pore-forming agent could enhance the mechanical and thermal insulation properties of porous alumina ceramics. [ABSTRACT FROM AUTHOR]

In this study, municipal solid waste incineration fly ash (MSWI FA) was used as a new raw material for the ceramics industry and a novel ultra-low thermal conductivity calcium silicate-based foams (CSFs) was prepared by the direct foaming method. The effects of the addition of foam and borax on the sintering behavior and microstructural evolution of the CSFs were investigated. With the optimal amount of foam, the CSFs had an apparent porosity of 63.43%–67.49%, bulk density of 0.75–0.84 g/cm3, compressive strength of 1.83–3.21 MPa, and room-temperature thermal conductivity of 0.213–0.235 W/(m·K). Notably, the whisker morphology, pore structure, and sintering behavior of the samples can be controlled by changing the amount of borax. The prepared ceramic foams can be applied in the fields of thermal insulation, filtration, and catalyst carriers. [ABSTRACT FROM AUTHOR]

In this study, a new mullite-foamed ceramic, reinforced with in-situ SiC whiskers (MCS) and applied as the insulating lining of thermal equipment used in cement production, was investigated. Compared with a conventional mullite-foamed ceramic (MC), the MCS phase composition, microstructure, compressive strength, thermal conductivity and alkali corrosion resistance were investigated by using X-ray diffraction, scanning electron microscopy, energy dispersive X-ray spectroscopy, and Factsage® software. The results showed that after being fired in granular coke, the SiC whiskers formed into MCS struts and were distributed in the pores between the interconnected needle-like mullite. Although the formation of SiC with higher conduction slightly increased MCS thermal conductivity, it significantly enhanced the compressive strength and alkali corrosion resistance of the foamed ceramic. Compared with the MC, although the MCS had higher bulk density (3.9%), and higher thermal conductivity (9.5% at 800 °C), it was more important that greatly improved compressive strength (by 60%) and better alkali corrosion resistance was achieved. [ABSTRACT FROM AUTHOR]

Mullite-corundum foamed ceramics were prepared by direct-foaming method using white clay and industrial alumina as raw materials, and calcium aluminate cement (CAC) as the binder. Effects of the calcium aluminate cement content on the phase compositions, microstructures and properties of the foamed ceramics were investigated through X-ray diffractometer (XRD), scanning electron microscopy (SEM) and energy dispersive spectrometer (EDS), etc. The results showed that with increasing the calcium aluminate cement content from 0 wt% to 8 wt%, the viscosities of the initial slurries decreased, the porosities of the samples improved, the thermal conductivities decreased, and the compressive strengths increased first and then decreased. The optimized sample with 4.0 wt% CAC content had a high porosity of 80.8%, a low bulk density of 0.56 g/cm3 and a low thermal conductivity of 0.232 W/(m·K) (800 °C). On the foundation of research results, the Gong equation (GE model) and a modified GE model were used to predict the thermal conductivity at 200 °C and 800 °C of the mullite-corundum foamed ceramics with different pore characteristics and phase compositions, respectively. [ABSTRACT FROM AUTHOR]

Abstract Mullite-corundum foamed ceramics were prepared by direct-foaming method using white clay and industrial alumina as raw materials, and micro-pore-foaming agent (MPFA, the main composition was sodium dodecyl benzene sulfonate) as foaming agent. Effect of the MPFA addition on the phase compositions, microstructures and physical properties of the foamed ceramics were investigated by X-ray diffractometer (XRD), scanning electron microscopy (SEM) and energy dispersive spectrometer (EDS), etc. The results showed that the specimens fired at 1500 °C mainly consisted of needle-like mullite, corundum, and a small amount of glass phase. The MPFA decreased the viscosities and then increased the volume expansion of foamed slurries. Meanwhile, the adding of the MPFA caused the increases of apparent porosities and average pore sizes, and the decrease of strengths of the fired specimens. The optimized product was a specimen with 1.0 wt% MPFA fired at 1500 °C which had a high porosity of 73.7%, a proper compressive strength of 3.05 MPa, a low thermal conductivity of 0.287 W/(mK) (1000 °C) and a positive reheating linear change. Based on the experimental dates, an emendatory GE model was presented, which could predict accurately the effective thermal conductivity at 1000 °C of the mullite-corundum foamed ceramics with different pore characteristics. Highlights • The mullite-corundum foam ceramics with low conductivity and sufficient strength were prepared. • The optimized product was a specimen with 1.0 wt% MPFA fired at 1500 °C. • A modified GE model, taking the conduction and radiation into account, was presented. [ABSTRACT FROM AUTHOR]

Abstract In this study, four mullite foam ceramics with porous struts and low thermal conductivities, were prepared by direct-foaming method from white clay and industrial alumina with the addition of sodium carboxymethyl cellulose (CMC) as foam stabilising agent. The effect of the CMC addition on the phase composition, pore characteristics, and strength was analysed through XRD, SEM and EDS, etc. The great part of struts for the foam ceramics was the needle-like mullite, the rest was the minor corundum and quartz. The addition of CMC decreased the apparent porosity of foam ceramics and pore area fractions of their struts, while the phase composition was nearly unaffected. Furthermore, the compressive strengths and the thermal conductivities of the foams ceramics increased. The optimized product contained 0.15 wt% CMC, which combined a high porosity of 81.3%, shown a low thermal conductivity of 0.095 W/(mK) (at 350 °C) and a minor positive reheating linear change. [ABSTRACT FROM AUTHOR]

Foamed mullite-SiC ceramics were prepared by using white clay, industrial alumina and silicon powder as raw materials. The effects of the clay content on the phase composition, microstructure and thermal properties of foamed ceramics were investigated by X-ray diffractometer (XRD), scanning electron microscopy (SEM) and energy dispersive spectrometer (EDS). The fired foamed mullite-SiC ceramics contained mullite, corundum and β-SiC. With an increase of clay content, the apparent porosity decreased, while the compressive strength and thermal conductivity increased. The optimized composition had a clay content of 44 wt% clay, which yield a high porosity of 72.9%, an excellent compressive strength of 5.6 MPa and a low thermal conductivity of only 0.267 W/(m·K). An adjusted GE thermal conductivity model assuming an appropriate emissivity of 0.35 was highly capable to predict the effective thermal conductivities of the foamed mullite-SiC ceramics with different pore characteristics at 800 °C. • The mullite-SiC foamed ceramics with low conductivity were prepared. • Microstructure and properties were optimized by changing clay content. • The optimized product was a specimen with 44 wt% clay content. • A revised model was presented to predict effective thermal conductivities. • Code-Aster was used to analyse heat-insulating performances of foamed ceramics. [ABSTRACT FROM AUTHOR]