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Energy efficient buildings, propulsion components and thermal protection systems require materials with high thermal protective properties. Traditional polymer composites or ceramic materials have limited comprehensive applications because of their poor thermal protective properties or poor processability. Herein, a novel fire resistant and thermally insulating polymer/ceramic hybrid ceramifiable composite was developed based on low temperature sintering principle and foaming on fire strategy. Specifically, the influences of raw materials of low temperature ceramics, such as glass frit, phosphate, etc, on the properties of ceramifiable ethylene-vinyl acetate (EVA) composites were investigated. Its fire resistance and thermal insulation properties were evaluated by simulating different sintering environments. The results show that the ceramifiable composite exhibits the highest improvement in fire resistance because a crystalline phase was formed at high temperatures. Gas evolution from the thermal decomposition of ammonium polyphosphate (APP) and EVA contributes to the formation of the porous structure in ceramic residues. The optimal system can resist above 1000 °C flame for 30 min without disintegration, and the temperature of the unfired side was maintained around 200 °C. The reliability of the strategy was verified by the effective medium theory model. [Display omitted] [ABSTRACT FROM AUTHOR]

AlN is regarded as a promising ceramic material for high performance structural and high temperature applications due to its superior properties such as high thermal conductivity, excellent stability and wear resistance. However, challenges remain in fabricating AlN ceramics with high strength and high thermal shock resistance. In this work, AlN/YAlO 3 composites with different YAlO 3 contents (3–10 wt%) were prepared by a simple pressureless sintering method, and the impact of YAlO 3 content on mechanical properties and thermal shock resistance of AlN/YAlO 3 composites was investigated. Results show that the grain growth of AlN is inhibited and the densification is improved with the addition of 3 wt% and 5 wt% YAlO 3. Hence, the flexural strength and fracture toughness of AlN/YAlO 3 composites are improved due to the grain refinement and compactness enhancement, and the highest value, 369 MPa and 3.84 MPa m1/2, are reached by the AlN-5 wt% YAlO 3 composite. Moreover, the thermal shock resistance was assessed through theoretical forecast and cyclic thermal shock tests over a temperature range between 1000 °C and 1600 °C. Comparing with pure AlN, the thermal stress damage resistance parameters (R IV ) of AlN/YAlO 3 composites were increased, while their residual strengths and retention ratios after 10–50 cycles of thermal shock tests maintained a higher level as well. Microstructure analysis revealed that the thermal shock resistance of AlN/YAlO 3 composites was evidently improved attributing to various strengthening mechanisms such as crack deflection, crack branching and microcrack toughening. [ABSTRACT FROM AUTHOR]

Clays from Alhabia (Almería, Spain) have been investigated in this work using several analytical techniques: X-Ray Diffraction (XRD), X-Ray Fluorescence (XRF), thermal analysis (Thermogravimetry, TG, and its first derivative, DTG), Scanning Electron Microscopy (SEM) and Energy Dispersive X-Ray Spectroscopy (EDS). Texture characteristics (granulometry) and plasticity have been examined. The main ceramic properties (firing shrinkage, water absorption, bulk density, open porosity, flexural strength and thermal conductivity) have been determined using pressed and fired clay samples. Thus, the mineralogical, chemical, textural and ceramic features of these clays have been evidenced for the first time. The mineralogical analysis by XRD indicated that the clay samples are constituted by a mixture of chlorite and illite, as main clay minerals, being quartz and other minerals in lower relative proportion (calcite, gypsum and hematite). This finding is important because the investigations on chlorite-illite-calcitic clays are very scarce. The chemical analysis by XRF showed that silica and alumina are predominant, as expected by the mineralogy, with medium contents of calcium oxide, from calcite, and alkalis, from illite, being ∼8 and ∼5%, respectively, besides iron and titanium oxides (∼8%). The particle size analysis showed 71.76% of "clay fraction" (<2 μm) and 21.66% of silt fraction (2–50 μm). The plasticity index (Atterberg) was 14.3%, with acceptable moulding and extrusion properties. Thermal analysis by TG/DTG indicated a weight loss associated to dehydroxylation of structural water of the clay minerals and decarbonation of calcite by progressive heating. After the characterization of raw clays, the next step was the determination of ceramic properties of mixed and ground clays after firing using pressed bodies. For this purpose, two firing temperatures were selected (900 and 1100 °C) for 1 h. The examination of the resultant fired bodies indicated that porous ceramic materials (∼36% open porosity and ∼22% of water absorption capacity) can be obtained by firing at 900 ᵒC, with small variations in dimensions (<0.8% at 1100 °C). The porosity changed at relatively lower values by firing at 1100 °C (∼34–35%), being associated to the presence of decomposed calcite. Bulk density was found almost constant from 900 to 1100 °C, with a maximum value of ∼1.67 g/cm3 at 1100 °C. Flexural strength reached a maximum value of 34.47 MPa at 1100 °C for the ground sample. Finally, thermal conductivity after firing the clay bodies was found almost constant at 900 and 1100 °C (0.457 and 0.479 W/mK, respectively). Taking into account these results, the main applications of the Alhabia clays have been evaluated. These clays can be used for the fabrication of porous ceramic supports and tiles by firing at 900 °C. Firing the clays at higher temperature (1100 °C) is of great interest for the fabrication of ceramic tiles and ceramic bricks of higher flexural strength with variable porosity and practically constant in dimensions. It is economically important although at higher processing costs. Finally, it can be emphasized that this work is a contribution of a better scientific knowledge of chlorite-illite-calcitic clays as ceramic raw materials. [ABSTRACT FROM AUTHOR]

h-BN is a two-dimensional ceramic material with a lamellar structure, known for its typical orientation characteristics on mechanical and thermal properties. By optimizing the size and arrangement of h-BN grains in the matrix, the anisotropic characteristics of h-BN ceramics can be fully utilized to obtain ceramic materials with high thermal conductivity or high strength. In order to study the effect of grain orientation distribution on the mechanical and thermal properties of materials, the index of orientation distribution (IOP) was used to quantitatively characterize the orientation degree of h-BN grains and analyzed the effect of h-BN grain size on material properties. The results show when the initial h-BN size is 13.50 μm, the ceramic has the highest orientation degree/-507, and the mechanical and thermal properties show obvious anisotropy. While the related properties of BN-YAG ceramics varies significantly with the decrease of initial h-BN grain size. [ABSTRACT FROM AUTHOR]

The high-entropy ceramic materials (Zr 0.25 Ce 0.25 Hf 0.25 Y 0.25)O 1.875 (H-0) and (Zr 0.2 Ce 0.2 Hf 0.2 Y 0.2 RE 0.2)O 1.8 (H-RE) (RE = La, Nd and Sm) with fluorite structure and homogeneous element distribution were prepared. With fluorite structure, fine grain size and high density, the H-0 and H-RE ceramics displayed low thermal conductivity, suitable thermal expansion coefficient, high hardness and fracture toughness. The effect of La, Nd and Sm on the mechanical, heat conductivity and heat expansion properties of high entropy ceramics were discussed. The single-phase high-entropy ceramic materials in this work are very suitable for application as thermal barrier materials. [ABSTRACT FROM AUTHOR]

Fabrication of ceramic materials containing high amount of porosity with controlled size and structure is a critical factor for various applications. In this study, porous alumina ceramics were prepared by addition of 5–30 vol% carbon black (CB) powders with different specific surface area (SSA) into the alumina matrix as a pore forming agent and application of partial sintering via spark plasma sintering (SPS) technique. After removal of CB particles from the ceramic structures, physical, mechanical, and thermal properties of the porous alumina ceramics were investigated. The open porosity level was detected between 38.48 and 59.81% depending on the type and amount of CB removed. The compressive strength of the sintered samples was measured as ∼150 MPa, which is ∼3 times higher than that of the conventionally sintered samples thanks to the strong neck formation between grains. The large pores formed by removal of CB agglomerates in case of using CB powders with SSA of 107 and 254 m2/g resulted in a change in thermal conduction mechanism from lattice vibration to thermal convection. [ABSTRACT FROM AUTHOR]

CeO 2 and Sc 2 O 3 co-stabilized ZrO 2 ceramics have attracted much attention as potential thermal barrier coatings (TBCs) materials for applications above 1300 °C. In this study, a series of Sc 0.04 Ce x Zr 0.96-x O 1.98 (SCZ, x = 0.08, 0.10, 0.12, 0.16) ceramic materials were synthesized with the solid-state method and their phase stability, microstructures and thermo-physical properties were systemically investigated by x-ray diffraction (XRD), Raman spectra, field emission scanning electron microscopy (SEM), thermal dilatometer, laser flash apparatus (LFA), and Vickers hardness tester. The results showed that Sc 0.04 Ce 0.12 Zr 0.84 O 1.98 (4S12CZ) and Sc 0.04 Ce 0.16 Zr 0.80 O 1.98 (4S16CZ) ceramic materials still maintained stable tetragonal phase structure after 100 h high temperature treatment at 1500 °C. SCZ had a high thermal expansion coefficient (TEC), low thermal conductivity, and high fracture toughness. The TEC of the ceramics increased with CeO 2 addition because lattice energy reduced with increasing substitution of Zr4+ by bigger Ce4+ while thermal conductivity decreased due to the increase of lattice distortion. Compared with 4S12CZ, 4S16CZ exhibited a higher fracture toughness of 6.48 ± 0.04 MPa m1/2 and showed the better anti-sintering property. Besides, the thermal conductivity, TEC and thermal cycling lifetime of 4S16CZ were optimal. The comprehensive performance of 4S16CZ suggested it could be explored as a promising TBC material for high-temperature application. [ABSTRACT FROM AUTHOR]

Thermal barrier coating (TBC) system is an essential technology in many fields associated to high temperatures. The main function of these TBCs is to protect the metallic parts against high temperatures over 1000 °C. However, degradation occurs both in thermal and mechanical performances during service. Thus, understanding the underlying degradation and failure mechanisms of TBCs is significant to assess and further enhance the durability and reliability of TBCs. Regarding the durability of TBCs, this paper reviews different failures mechanisms of TBCs caused by residual stresses, phase transformations, sintering, hot corrosion attack and oxidation. Subsequently, some methods are summarized to alleviate the undesirable effects of the causes, so as to extend the lifetime of TBCs. Regarding the thermal barrier performance of TBCs, the neoteric advances to resist degradation in thermal conductivity of TBCs are reviewed. In addition, some new ceramic materials with superior intrinsic properties are introduced for ultra-high temperature applications. In brief, this review correlates the microstructure and properties of TBCs for finer interpretation and degradation-resistant design on their thermal and mechanical properties, which would benefit the advanced TBCs in future engineering applications. [ABSTRACT FROM AUTHOR]

The use of ceramic cutting tools is limited due to their inherent brittleness. In this paper, metal phase Co is considered to strengthen Si 3 N 4 based ceramic tool materials. The effects of Co on room-temperature and high-temperature mechanical properties and thermal shock resistance of the material are studied. Compared with the composite without Co, the addition of Co can improve room-temperature fracture toughness of Si 3 N 4 based ceramic material at the cost of reducing its hardness. The flexural strength decreases a little in accordance with the reduced relative density. As the testing temperature increases, the fracture toughness first increases gradually and then decreases sharply while the flexural strength decreases gradually. Due to the oxidation inhibition effect, the Co-containing composite maintains higher flexural strength and fracture toughness than the Co-free composite at the specified test temperatures. The critical thermal shock temperature difference of the composite with Co is higher than that without Co, although before reaching the difference its residual bending strength is lower due to pores and thermal mismatch effect. The addition of Co can also inhibit the growth of thermal shock microcracks and improve the thermal fatigue resistance of Si 3 N 4 ceramic material. [ABSTRACT FROM AUTHOR]

Ba(Sr 1/3 Ta 2/3)O 3 (BST) ceramic was synthesized by a solid-state reaction method. The phase stability, microstructural evolution, and mechanical and thermal properties of the BST ceramic were investigated and characterized to evaluate the potential application of BST as a top coating material for thermal barrier coatings (TBCs). The results show that BST can maintain a stable hexagonal perovskite structure up to 1600 °C. Anisotropic growth of the grains above 1400 °C was observed. Its low elastic modulus and high fracture toughness suggest a high damage tolerance for the BST ceramic. In addition, the moderate coefficient of thermal expansion and superior heat insulation capability of the BST ceramic provide this ceramic the potential to serve as a top coating material of TBCs at higher temperature. [ABSTRACT FROM AUTHOR]

CaMnO 3 -based materials are very attractive among n-type thermoelectric oxides for high-temperature applications when they are appropriately doped. The main drawback of these materials is the cost associated to the necessary rare earth cations. This work aims decreasing the amount of these materials through a partial substitution of Ca 2+ by an equimolar mixture of K + and Yb 3+ , Ca 1-x (K 0.5 Yb 0.5 ) x MnO 3 , with x = 0.05, 0.10, 0.15, and 0.20. XRD studies have confirmed that the thermoelectric phase is the major one in all samples. Microstructure has shown the formation of large crystals, and an increasing porosity when the substitution is raised. This evolution has been confirmed through density measurements. Electrical resistivity has been drastically decreased for the 0.10 substituted samples, compared with the 0.05 ones, slightly increasing for higher substitution. On the other hand, absolute Seebeck coefficient and thermal conductivity are lower when the substitution is raised. The best ZT values have been achieved for the 0.10 substituted samples, which are around the typical reported in the literature for higher doping level. These results clearly point out to a decrease of the necessary rare earth dopant content to achieve similar performances in CaMnO 3 ceramics, which is of the main economic significance for their industrial production. [ABSTRACT FROM AUTHOR]

Са 3 (VO 4 ) 2 -based compositions are considered as promising multifunctional materials combining ferroelectric, optical nonlinear, and Ca 2+ -ion conductive properties. Their ferroelectric Curie points stretch from minimal for β -Ca 3 (PO 4 ) 2 -type compounds temperatures of about 800 K to very high. Investigated in this paper lead substitution for calcium is as a factor controlling ferroelectricity, ionic-conductivity and non-linear optical activity in Ca 3 (VO 4 ) 2 -based materials. Polar phase containing powders and ceramics in Ca 10.5- x Pb x (VO 4 ) 7 system are synthesized for 0 ≤ x ≤ 9.5 by the solid state method, and structurally characterized with X-ray powder diffraction and transmission electron microscopy. Dielectric properties, differential thermal analysis and second harmonic generation (SHG) evidence that Ca 10.5- x Pb x (VO 4 ) 7 solid solution (0 ≤ x ≤ 4.5) belongs to whitlockite-type ferroelectrics. SHG activity strongly increases with x up to its maximum at x = 4.5, where it has a record value among all studied before Ca 3 ( X O 4 ) 2 -related compounds ( X = P,V). Ferroelectric Curie temperatures of Ca 3 (VO 4 ) 2 drops from its known value T c = 1368 K ( x = 0) to 770 K ( x = 4.5). Crystal symmetry at T c changes from R 3 c to R 3 ¯ c . After this, one more phase transition to the symmetry R 3 ¯ m takes place, its temperature bringing down from 1387 K ( x = 0) to 804 K ( x = 4.5). Ferroelectric and non-ferroelectric phase transitions in the Са 10.5- x Pb x (VO 4 ) 7 are separated by a broad interval Δ T = 20–50 K and both classified as first-order transformations going in the sequence: R 3 c ↔ R 3 ¯ c ↔ R 3 ¯ m . Structures of Са 10.5- x Pb x (VO 4 ) 7 compositions with x = 0.5–4 were refined by the Rietveld method and peculiarities of the Pb 2+ cations distribution in the M 1 - M 3 and M 4 sites of β -Ca 3 (PO 4 ) 2 -type structure are discussed regarding the optical nonlinear, ferroelectric and ion-conductive properties. Manifold increased Ca 2+ - ion conductivity of Са 10.5- x Pb x (VO 4 ) 7 in vicinity of 1000 K at x = 4–4.5 in combination with their ferroelectric and optical nonlinear properties extends applicability of ion-exchange technologies to new promising materials. [ABSTRACT FROM AUTHOR]

Aerogel glazing units (AGUs) is a high-performance building glazing which can effectively reduce energy consumption due to its thermal and optical performance. In this paper, the effect on thermal and optical properties of AGUs with different particle sizes and filling thicknesses were investigated. The results indicated that visible light transmittance and solar direct transmittance of AGUs palpably increased as the particle size increased from 0.41mm to 0.93mm, while it lightly changed as the particle size continued to increase from 0.93mm. The heat transfer coefficient decreased by about 15% when the particle size was reduced from 2.7mm to 0.41mm. In conclusion, the increase of the thickness of aerogel can effectively decrease visible light transmittance, solar direct transmittance and heat transfer coefficient. Finally, color rendering index(CRI)the AGUs with different particle sizes and filling thicknesses were investigated and AGUs show good color performance. [ABSTRACT FROM AUTHOR]

Novel ZrO 2 -fiber-reinforced porous Y 2 SiO 5 ceramic nanocomposites were fabricated by a simple pressureless sintering process. Y 2 SiO 5 nanoparticles were prepared by a sol-gel method, and the effects of sintering temperature and ZrO 2 fiber content on the microstructure, thermal properties, and mechanical properties of the porous Y 2 SiO 5 nanocomposites were studied. The mechanical properties and thermal conductivity of porous ZrO 2f /Y 2 SiO 5 nanocomposites were improved substantially with the introduction of ZrO 2 fibers. Compared with the specimens without added fibers, the composites with 10 vol% ZrO 2 fibers exhibited the optimum strengthening effects, including a high bending strength (i.e., 65.7 MPa), a low thermal conductivity (i.e., 0.55 W/(m·K)) and good machinability. The present work provides a simple procedure for improving the toughness and thermal insulation characteristics of porous ceramics. [ABSTRACT FROM AUTHOR]

A new lightweight and thermal insulating material was successfully prepared by impregnating Al 2 O 3 –SiO 2 aerogel into a porous mullite–zirconia fiber network with a quasi-layered microstructure. The microstructures, thermal and mechanical properties of the porous mullite–zirconia ceramics were investigated before and after the impregnating of Al 2 O 3 –SiO 2 aerogel. It was observed that the mullite and zirconia fibers combined well with aerogels. Compared with fibrous porous mullite-zirconia ceramics, the Al 2 O 3 –SiO 2 aerogel/porous mullite–zirconia composite exhibited higher compressive strength (i.e. 1.36 MPa in the z direction) and lower thermal conductivity (i.e. 0.052 W/(m·K)). The present work provides an efficient way to fabricate highly porous ceramics with high strength and ultra-low thermal conductivity, which find potential use in high-temperature thermal insulation materials. [ABSTRACT FROM AUTHOR]

A novel lightweight needled carbon fibre felt/phenolic resin (NCF-PR) aerogel composite was fabricated through vacuum impregnation using NCF as matrix and PR aerogels as filler. The PR aerogels was synthesized through polymerization-induced phase separation (PIPS), accompanied by solvent exchange and ambient pressure drying, from a resin mixture of PR with ethylene glycol (EG) as the porogen and hexamethylenetetramine (HMTA) as the catalyst. A homogeneous microstructure without macroscopic cracking and agglomeration was achieved in the composite, and the macropores between the fibres in the NCF were fully and uniformly filled by PR aerogels with high porosity and with large amounts of mesopores. The resulting NCF-PR aerogel composites exhibit low densities between 0.270 and 0.370 g/cm 3 , relatively high compressive strength, ranging from 0.83 to 11.02 MPa, and low thermal conductivities of 0.093–0.230 W/(mK) at room temperature. The thermal ablative properties of the aerogel composite were studied under arc jet conditions at a heat flux of 1.5 MW/m 2 for 33 s. The ablation results demonstrate that the NCF-PR aerogel composite could deliver good thermal ablative and insulative properties (linear ablation rates as low as 0.029 mm/s and internal temperature peaks below 90 °C at 38 mm in-depth position as the surface temperature exceeded 2000 °C). Therefore, this lightweight carbon/phenolic composite is an excellent heat-insulation and thermal-protection material with applications in the fields of energy-saving and aerospace. [ABSTRACT FROM AUTHOR]

In view of spacecraft re-entry applications into planetary atmospheres, hybrid thermal protection systems based on cork and ceramic matrix composites are investigated. Joints of NORCOAT LIÈGE cork with C/C SiC ceramic matrix composite were fabricated using a) high temperature commercial inorganic adhesives and b) in-situ polymerization of the cork on top of the CMC. Mechanical shear tests under ambient conditions and in liquid nitrogen are carried out. The ultimate shear strength of all the adhesive joints at room temperature varies between 0.52 and 0.78 MPa and is similar to that of the in-situ joints. At liquid nitrogen temperature the shear strength is enhanced by up to 80%, but the ultimate shear strain decreases up to 55%. The failure mode is discussed for the two types of the fabrication procedure. [ABSTRACT FROM AUTHOR]

Korea has developed an advanced reduced-activation alloy (ARAA) as a structural material for helium-cooled ceramic reflector test blanket module (HCCR-TBM) applications. The present paper describes the history of alloy development and the properties of ARAA, which has been produced at a 5 t scale using vacuum induction melting and electro-slag re-melting methods. ARAA is a 9Cr–1.2W based ferritic–martensitic steel with 0.01 wt.% Zr. The mechanical properties, thermal properties and physical and magnetic properties of ARAA show similar temperature dependencies to those observed for Eurofer 97. However, ARAA exhibits a much longer creep–rupture time than conventional RAFM steel, which suggests a positive effect on Zr addition. The enhanced creep strength of ARAA by the addition of Zr is attributed to the reduced temperature-dependence of the yield strength. [ABSTRACT FROM AUTHOR]

Dielectric properties of x (Na 0.5 K 0.5 )NbO 3 –(1− x )BaTiO 3 ( x =0.00 and 0.06) specimens were investigated in terms of changes in local atomic structure, according to the phase transition by elevating the overall temperature. A 0.06(Na 0.5 K 0.5 )NbO 3 –0.94BaTiO 3 (NKN–BT) specimen exhibited enhanced temperature stability along with an increased dielectric constant. The degree of reduction in tetragonality ( c / a ) at the Curie temperature was smaller in NKN–BT compared to that in pure BaTiO 3 , as calculated by Rietveld refinement. From a comparison of the pre-edge region in the Ti K -edge, it was determined that the off-center displacement of the Ti atom was also raised to 13.4% through NKN substitution, with a change in local orientation from the [001] to the [111] directions. The substitution by NKN, which has a different ionic radius and electrical charge compared with BaTiO 3 , causes structural distortion of the TiO 6 octahedra in the NKN–BT lattice, resulting in local polarization. These structural changes lead to the temperature stability of the dielectric constant and an overall improvement in the electrical properties of BaTiO 3 . [ABSTRACT FROM AUTHOR]

La 2 Ti 2 O 7 ceramic samples were prepared via conventional solid-state reaction route. The dielectric properties of La 2 Ti 2 O 7 were investigated as functions of temperature (113–1073 K) and frequency (100 Hz–1 MHz). Our results revealed that La 2 Ti 2 O 7 ceramics exhibit intrinsic dielectric response with a dielectric constant of ∼57 in the temperature range below 250 K. Three thermally activated dielectric relaxations were observed when the temperature higher than 250 K. The low-temperature relaxations R1 with the activation energy of 0.38 eV is found to be a polaron relaxation results from hopping holes. The high-temperature relaxations R2 and R3 are related to the conduction progress associated with the singly and doubly ionized oxygen vacancies, respectively. [ABSTRACT FROM AUTHOR]

Highlights: [•] SiC–W composites have been realized by SPS, starting with β-SiC nm and 20% weight W micro or nano grains dispersions. [•] Insertion of nano particles of W in the SiC matrix resulted in 300% increase of thermal conductivity at 1000°C as compared with the bare SiC sample. [•] A W foil can be joined to a SiC ceramic or composite using a thin powder buffer layer of V. Thermal diffusivity can be used to assess the joint quality. [ABSTRACT FROM AUTHOR]

Boride ceramics are materials of choice in extreme conditions. Among them, titanium borides have many applications due to their high hardnesses and melting points. The behavior of titanium borides may not be easily studied at very high pressures and temperatures by experimental means. Alternatively, molecular dynamics (MD) is a powerful computational tool to investigate the desired behavior of materials in certain conditions. In this study, we develop an interatomic potential for the Ti B system based on the second nearest-neighbor modified embedded atom method (2NN-MEAM) formulation. With the developed potential, MD simulations reproduce many physical, mechanical, and thermal properties of titanium borides with good accuracy. As an application of the developed potential, a series of nanoindentation simulations is also conducted to investigate the temperature dependence of the nanohardness of TiB 2 up to 1500 K. The results illustrate a linear dependence between nanohardness and temperature. [Display omitted] • We developed a 2NN-MEAM interatomic potential for the Ti B system. • The predicted properties of titanium borides agree with the experimental data. • Nanoindentation simulations of TiB 2 are performed at various temperatures. • Our simulations predict a linear decline of the nanohardness of TiB 2 in 0 K ∼ 1500 K. [ABSTRACT FROM AUTHOR]

Abstract: LaMgAl11O19–Yb3Al5O12 ceramic composites were prepared by pressureless sintering process at 1700°C for 10h in air. The microstructure and thermophysical properties of the composites were characterized by X-ray diffraction, scanning electron microscopy, high-temperature dilatometer and laser flash diffusivity measurements. LaMgAl11O19–Yb3Al5O12 ceramic composites are composed of magnetoplumbite and garnet structures. LaMgAl11O19–Yb3Al5O12 ceramic composites exhibit typical linear increase in thermal expansion with the increase of temperature. The measured thermal diffusivity gradually decreases with increasing temperature. Thermal conductivity of LaMgAl11O19–Yb3Al5O12 ceramic composites is in the range of 2.6–3.9 W·m−1·K−1 from room temperature to 1200°C. [Copyright &y& Elsevier]

Abstract: LaCo1−x Ni x O3 (0≤ x ≤0.2) ceramics were prepared by solid state reaction and their thermoelectric properties were investigated from room temperature (RT) to 400°C. In the range from RT to 180°C, LaCoO3 showed a large negative Seebeck coefficient, but it changed to a positive value above 180°C. However, the Seebeck coefficient became positive in the whole investigated temperature span due to Ni substitution for Co even for a tiny amount, but its absolute value decreased significantly with increasing Ni content. The LaCo0.9Ni0.1O3 composition showed an enhanced power factor with a maximum value of 1.41×10−4 Wm−1 K−2 at room temperature, which is about 3.5 times higher than that of un-doped LaCoO3. Because the power factor decreased and the thermal conductivity increased apparently with temperature, the ZT values were not increased at elevated temperatures, in spite of a relatively large ZT value of 0.031 at a low temperature (50°C) obtained in the composition LaCo0.9Ni0.1O3. [ABSTRACT FROM AUTHOR]

Abstract: The knowledge of thermal properties of technical components or internals in chemical reactors is often a key characteristic for planning and designing chemical engineering processes. As an alternative to packed beds or packings, sponges turned out to be used in new application fields in chemical and process engineering. Therefore an experimental study was performed to investigate the two-phase thermal conductivity of solid ceramic sponges made of alumina, mullite and oxidic-bonded silicon carbide (OBSiC) at moderate temperatures. A two-dimensional model is used for analysing the measured temperature profiles and for calculating the thermal conductivity. It can be observed, that the thermal conductivity increases with decreasing porosity and is nearly constant when the pore size (ppi number) is varied. The thermal conductivity data are modelled by an approach similar to the well known Krischer model. Compared to a packed bed of spherical particles, the values of the thermal conductivity of sponges turn out to be about five times higher. [Copyright &y& Elsevier]

Abstract: To study the thermal stability of polymer derived SiBNC ceramics, a polyborosilazane was pyrolyzed in N2 and NH3/N2 atmosphere, respectively. The as-pyrolyzed products were annealed in N2 atmosphere at 1200–1850°C for 2h. The chemical composition and phase structure of the as-pyrolyzed and annealed ceramics were investigated by element analysis, XRD and FT-IR. The results show that all the ceramics exhibit excellent high temperature stability. They are fully amorphous to 1700°C, and only partial crystallization, giving a mixture of Si3N4, BN and SiC phases, is observed upon heating at 1850°C. The N2 pyrolyzed products show better stability than the NH3/N2 pyrolyzed products and have less tendency to crystalline at higher temperatures. Better retention of nitrogen at high temperatures is also observed for the N2 pyrolyzed products. [Copyright &y& Elsevier]

Abstract: This work mainly involved the preparation and characterization of form-stable paraffin/porous silica ceramic composite. The paraffin acts as thermal absorb material and porous silica serves as the supporting material, which provides structural strength and prevents the leakage of melted paraffin. Results indicate that the composite remained solid above the melting temperature of paraffin while the mass fraction of paraffin reached to 75%. Moreover, scanning electronic microscope (SEM) observed the paraffin dispersed into porous network of silica ceramics. Fourier transformation infrared spectroscope (FTIR) indicated that the composite formation of porous silica and paraffin were physical. Differential scanning calorimeter (DSC) determined the melting temperature and heat storage capacity of the composite to be 56.3°C and 165.16kJ/kg, respectively. [Copyright &y& Elsevier]

Abstract: Lanthanum zirconate (La2Zr2O7, LZ) and CeO2 doped La2Zr2O7 (LCZ) ceramic were synthesized by the coprecipitation–calcination method. The chemical compositions, phase compositions, thermophysical properties of these materials were investigated. Inductively coupled plasma-atomic emission spectrometry (ICP-AES) and XRD results revealed that the compositions of all prepared ceramic materials were in the range of the synthesis of single La2Zr2O7 with pyrochlore structure. After the prepared ceramic powders were mechanically ball-milled, vacuum dried, molded by cold pressure and densified by sinter at 1650°C for 10h, the bulk density of the sample was measured by the Archimedes method with an immersion medium of deionized water, a high-temperature dilatometer, DSC and laser thermal diffusivity method were used to analyze its thermal expansion coefficient, specific heat and thermal diffusivity. The results showed that, with the temperature increasing, the thermal expansion coefficient (TEC) of these ceramics increased, while the thermal conductivity decreased. The thermal expansion coefficient of La2Zr2O7 was enhanced clearly by adding CeO2, and its thermal diffusivity and specific heat were all changed slightly. The thermophysical results also indicated that TEC of LCZ was slightly higher than that of conventional Y2O3–8wt.% ZrO2 (8YSZ), but its thermal conductivity was lower than that of 8YSZ. The lower thermal conductivity of LCZ was mainly attributed to more oxygen vacancies and larger atomic weight of substitutional atom (La, Ce). These results imply that LCZ can be explored as the candidate material for the ceramic layer in TBCs system. [Copyright &y& Elsevier]

Rare earth zirconates are considered as one class of the ideal candidate high-temperature structural materials. In this paper, a series of Y 3 Al 5 O 12 doped Sm 2 Zr 2 O 7 [(1- x)Sm 2 Zr 2 O 7 - x Y 3 Al 5 O 12 , x = 0, 0.05, 0.1, 0.2, 0.3, mol.%] composite ceramics were prepared at 1600 °C. The influence of Y 3 Al 5 O 12 doping on microstructure, mechanical properties and thermal conductivity of Y 3 Al 5 O 12 doped Sm 2 Zr 2 O 7 were investigated. The results showed that the composite ceramics were mainly composed of Sm 2 Zr 2 O 7 , Y 3 Al 5 O 12 and a small amount of SmAlO 3 phases. The grain size of Sm 2 Zr 2 O 7 in composite ceramics obviously decreased with the increase of Y 3 Al 5 O 12 doping concentration. The fracture toughness of 0.8Sm 2 Zr 2 O 7 -0.2Y 3 Al 5 O 12 composite ceramic was (2.50 ± 0.14) MPa·m1/2, which was the highest among the investigated ceramic materials, and was about twice as high as that of pure Sm 2 Zr 2 O 7 ceramic. The thermal conductivity of composite ceramics increased with the rise of Y 3 Al 5 O 12 doping concentration at above 600 °C. 0.8Sm 2 Zr 2 O 7 -0.2Y 3 Al 5 O 12 composite ceramic had almost no change in grain size and phase composition before and after sintering at 1400 °C for 100 h, suggesting that 0.8Sm 2 Zr 2 O 7 -0.2Y 3 Al 5 O 12 composite ceramic had good sintering resistance at 1400 °C. A series of (1- x)Sm 2 Zr 2 O 7 - x Y 3 Al 5 O 12 composite ceramics were prepared at 1600 °C. The composite ceramics were mainly composed of Sm 2 Zr 2 O 7 , Y 3 Al 5 O 12 and a small amount of SmAlO 3 phases. With the increase of Y 3 Al 5 O 12 concentration, the grain size of Sm 2 Zr 2 O 7 obviously decreased. The fracture toughness of 0.8Sm 2 Zr 2 O 7 -0.2Y 3 Al 5 O 12 composite ceramic was (2.50 ± 0.14) MPa·m1/2, which was the highest among the investigated ceramic materials, and was about twice as high as that of pure Sm 2 Zr 2 O 7 ceramic. The grain size of 0.8Sm 2 Zr 2 O 7 -0.2Y 3 Al 5 O 12 ceramic sintered for 100 h did not significantly grow at 1400 °C. Image 1 • A series of Y 3 Al 5 O 12 doped Sm 2 Zr 2 O 7 ceramics were successfully prepared at 1600 °C. • The grain size of Sm 2 Zr 2 O 7 obviously decreased with Y 3 Al 5 O 12 concentration rising. • 0.8Sm 2 Zr 2 O 7 -0.2Y 3 Al 5 O 12 had the highest fracture toughness among the specimens. • 0.8Sm 2 Zr 2 O 7 -0.2Y 3 Al 5 O 12 ceramic had good sintering resistance at 1400 °C. [ABSTRACT FROM AUTHOR]