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Ceramic fibers are an important thermal insulation material that are not only widely used in extreme conditions, but also play an important role in energy conservation and energy efficiency for sustainable development. However, the practical application of conventional ceramic fibers has a high thermal conductivity in high-temperature environments, which hinders their widespread application. Here, a novel lamellar structured porous SiTiOC/C composite ceramic materials was designed and prepared with excellent thermal insulating properties. The unique microstructure endowed the porous SiTiOC/C composite ceramic materials with a high IR refractive index (93.81%) and an ultra-low thermal conductivity (0.0562 W·m−1 K−1 at 600 ℃). In addition, the porous SiTiOC/C composite ceramic materials not only exhibited excellent mechanical properties (4.46 MPa at 800 ℃), but also demonstrated impressive oxidation resistance and thermal stability. In summary, the proposed porous SiTiOC/C composite ceramic materials provide a reference for the development of high-temperature insulation with good mechanical properties. [ABSTRACT FROM AUTHOR]

High-entropy carbide ceramic materials exhibited excellent thermal and mechanical properties, making them highly sought after in high-temperature applications. However, the oxidation resistance of high-entropy carbide ceramic needed to be further improved. This work unraveled the oxidation behavior and mechanism of high-entropy carbide ceramic by introducing the Cr 3 C 2. The results indicated that the oxidation rate of (TiZrTaNbCr)C initially decreased with temperature up to 900 °C, followed by an increased with further temperature rise up to 1100 °C. At 800 and 900 °C, the parabolic oxidation rate constants were 0.70 and 0.17 mg2cm−4min−1, respectively. And the minimum thickness of oxidized layer was 60 µm at 900 °C for 120 min. This unusual phenomenon suggested the formation of different oxidation products. Specifically, the CrNbO 4 and Nb 2 Zr 6 O 17 oxide layer were formed at 900 °C, leading to an increased resistance to oxygen diffusion. Subsequently, loose oxidation products of Nb 2 O 5 were formed after 1000 °C, hindering the oxidation resistance. In the current study on oxidation resistance of high entropy carbides, this work showed a competitive performance. Overall, this study illustrated the oxidation mechanism and behavior of (TiZrTaNbCr)C and proposed a new avenue for the design of high-entropy ceramic components. [ABSTRACT FROM AUTHOR]

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]

The additive composition of an AlN ceramic substrate material was optimized to achieve high strength and thermal conductivity. MgO-CaO-Al 2 O 3 -SiO 2 (MCAS) glass and Y 2 O 3 were used as basic additives for improved sintering properties and thermal conductivity, thereby allowing for AlN to be sintered at a relatively low temperature of 1600 °C without pressurization. Yttria-stabilized zirconia (YSZ) was added (0–3 wt%) to further improve the strength of the AlN ceramic. YSZ and Y 2 O 3 reacted with AlN to produce ZrN, Y 4 Al 2 O 9 , and Y 3 Al 5 O 12 secondary phases. The formation of these yttrium aluminate phases improved the thermal conductivity by removing oxygen impurities, while ZrN formed at the AlN grain boundaries provided resistance to grain boundary fractures for improved strength. Overall, the AlN ceramic with 1 wt% MCAS, 3 wt% Y 2 O 3 , and 1 wt% YSZ exhibited excellent thermal and mechanical properties, including a thermal conductivity of 109 W/mK and flexural strength of 608 MPa. [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]

• A series (1-x)ZrO 2 - x TaO 2.5 ceramics are synthesized by solid state reaction. • The final product of 0.72ZrO 2 -0.28TaO 2.5 is mainly composed of TaZr 2.75 O 8. • TaZr 2.75 O 8 has good mechanical properties and excellent phase stability. • Thermal conductivity of the TaZr 2.75 O 8 bulk is lower than that of YSZ. • TaZr 2.75 O 8 has a moderate thermal expansion coefficient, around 9.14 × 10−6 K−1. A series of TaO 2.5 -doped ZrO 2 (1-x)ZrO 2 - x TaO 2.5 (x = 0.08, 0.15, 0.2 and 0.28) ceramics were synthesized by solid state reaction at 1600 °C for 20 h. XRD results reveal that no tetragonal ZrO 2 phase forms in the TaO 2.5 –ZrO 2 system. Instead, a mixture of monoclinic ZrO 2 (m -ZrO 2) and orthorhombic TaZr 2.75 O 8 can be detected for (1-x)ZrO 2 - x TaO 2.5 ceramic within compositions x ≤ 0.2. As the doping content increases, the content of m -ZrO 2 decreases and the final product in the composition of 0.72ZrO 2 -0.28TaO 2.5 is primarily composed of TaZr 2.75 O 8. Microstructure together with the thermophysical and mechanical properties of TaZr 2.75 O 8 ceramic were investigated for possible applications as thermal barrier coatings (TBCs). The thermal conductivity with a minimum value of 1.65 W/m·K at 800 °C for TaZr 2.75 O 8 ceramic is ∼30% lower than that of dense YSZ and the dense ceramic also has a moderate average thermal expansion coefficient (TEC), about 9.14 × 10−6 K−1 from room temperature (RT) to 1300 °C. Besides, TaZr 2.75 O 8 exhibits a high microhardness (11.85 ± 0.42 GPa) and fracture toughness (3.15 MPa·m1/2). These preliminary results indicate that TaZr 2.75 O 8 can be used as an alternative material for the ceramic layer in TBCs system with respect to its superior thermal and mechanical properties. [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]

Highlights • Thermal stability of PCM is enhanced by the porous nanoceramics. • The prepared FSPCM has a desirable latent heat and phase change temperature. • Thermal conductivity of FSPCM is about 7 times higher than that of pristine PCM. Abstract This work aims at preparing a novel form-stable composite phase change material (FSPCM), by loading stearic–capric acid (SA–CA) in porous nanoceramics which are employed as the supporting materials. The morphology and microstructure, chemical compatibility, thermal properties and thermal stability are analyzed. The results indicate that the prepared FSPCM freezes at 24.56 °C with latent heat capacity of 73.92 J/g and melts at 22.50 °C with latent heat capacity of 76.40 J/g. The as-prepared composite is demonstrated to reveal good physicochemistry stability and an acceptable absorption ratio. Moreover, the thermal conductivity of FSPCM is nearly 7 times higher than that of pristine PCM. [ABSTRACT FROM AUTHOR]

Abstract Two different SiC ceramics with a new additive composition (1.87 wt% Y 2 O 3 –Sc 2 O 3 –MgO) were developed as matrix materials for fully ceramic microencapsulated fuels. The mechanical and thermal properties of the newly developed SiC ceramics with the new additive system were investigated. Powder mixtures prepared from the additives were sintered at 1850 °C under an applied pressure of 30 MPa for 2 h in an argon or nitrogen atmosphere. We observed that both samples could be sintered to ≥99.9% of the theoretical density. The SiC ceramic sintered in argon exhibited higher toughness and thermal conductivity and lower flexural strength than the sample sintered in nitrogen. The flexural strength, fracture toughness, Vickers hardness, and thermal conductivity values of the SiC ceramics sintered in nitrogen were 1077 ± 46 MPa, 4.3 ± 0.3 MPa·m1/2, 25.4 ± 1.2 GPa, and 99 Wm−1 K−1 at room temperature, respectively. [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]

As polymers have the ability to be easily molded in to any shape, they have a wide range of applications in industry. Composites prepared by dispersing ceramics in to polymer matrix have higher thermal conductivity than the original polymer, and they still retain their high electrical resistance. In this work, polyvinyl butyral (PVB) is chosen as the polymer matrix. Ceramic nanoparticles like boron nitride (BN), zinc oxide (ZnO) and silicon carbide (SiC) are used as fillers. Polymer composites with different filler loading ratio (wt %) are prepared and their thermal and electrical properties are analyzed. FT–IR, XRD and TGA characterizations are also performed on the composites. The results indicated that PVB composite with hexagonal boron nitride (h–BN) showed the best improvement in thermal conductivity up to 0.5194 W m −1 .K −1 which is an increase of 131.87%, and volume resistivity of composites remained high, above the 10 10 Ω–cm level. [ABSTRACT FROM AUTHOR]

Densification behavior, mechanical and thermal properties of ZrC 1 − x ceramics with various C/Zr ratios of 0.6–1.0 have been investigated by two-step reactive hot pressing of ZrC and ZrH 2 powders at 30 MPa and 1500–2100 °C. The two-step reactive hot pressed ZrC 1 − x ceramic has a higher relative density (> 95.3%) than that (91.9%) of stoichiometric ZrC sintered at 2100 °C. A cubic Zr 2 C-type ordered phase forms in the ZrC 1 − x sample obtained at a ZrC/ZrH 2 molar ratio of 0.6 at a relatively low temperature of 1100 °C. The decrease in C/Zr ratio is beneficial to densification of ZrC 1 − x ceramic, however, excess grain growth occurs after sintering above densification temperature. The elastic modulus and Vickers hardness decrease with decreasing the C/Zr ratio. With decreasing the C/Zr ratio, both thermal conductivity and specific heat decrease due to the enhanced scattering of conducting phonons and electrons by carbon vacancies. [ABSTRACT FROM AUTHOR]

The aim of this study is to investigate a thermally robust green-yellow color converter for high-power solid state laser lighting applications. LuAG:Ce translucent ceramics (TCs) were synthesized via the spark plasma sintering (SPS) technique and LiF was used as additive. The as-prepared ceramics show remarkably superior thermal and luminescent properties: a high external quantum efficiency (77%), a low thermal quenching (4.1% drop at 200 °C), a good thermal conductivity (6.3 W m −1 K −1 ), and a high reliability (only a 1.9% drop after 1000 h, at 85 °C and 85% humidity). A prototype lamp using the TC (and a 450 nm laser diode), with the increasing driving power (up to 8.7 W), shows increasing luminous flux (238–472 lm) with stable luminous efficiency (54.3-56.6 lm/W). This indicates that the translucent ceramic can be used for high-power laser-lighting. [ABSTRACT FROM AUTHOR]

This paper presents the results of a combined experimental and theoretical study on a clay ceramic used for building applications. The thermal and mechanical properties of the clay ceramic were improved by addition of organic additives. The organic additives consisted of Olive Stone Flour (OSF), with round-shape particles of 55 µm, and Wheat Straw (WS), with 877 µm particles in the form of fibers. It was found that the combustion of OSF and WS resulted in a porosity formation during the firing process. The morphology of these pores corresponded to that of the organic additives. Therefore, the addition of small OSF particles decreased the median pore size of the clay ceramic. It improved the mechanical strength of the clay ceramic by 12% for an 8 wt% addition of OSF. On the other hand, the WS fibers increased the clay ceramic anisotropy. This resulted in a 41% improvement of the thermal conductivity using an 8 wt% addition of WS. Finally, a model was developed from these experimental results to predict the thermal conductivity and the mechanical strength of the clay ceramic with other organic additives. They were predicted from the parameters of the organic additives (i.e., true density, swelling degree, particle size distribution, particle shape factor). The predictions indicated that the thermal conductivity is improved by 50% with a 25% improvement of the mechanical strength using small organic fibers, which is a step forward in the development of fired clay bricks that can be used for both insulation and structure purposes in building applications. [ABSTRACT FROM AUTHOR]

Macro/mesopore SiOC ceramic monoliths of anisotropic structure were prepared by freeze casting, using methy phenyl polysiloxane (H44) or methy polysiloxane (MK) and (3-aminopropyl)triethoxysilane (APTES) as precursors. Influence of pyrolysis and testing temperature on compressive strength was investigated. Monoliths pyrolyzed at 700 °C had the highest compressive strength both at 77 K (14.0 ± 4.3 MPa) and 293 K (7.7 ± 1.8 MPa), regardless of precursors. Compressive strength of monolith in parallel direction is around twice as much as perpendicular direction. Compressive strength of both monoliths in liquid nitrogen (77 K) was around twice of that in air (293 K) probably due to low temperature and liquid resistance. Anisotropic expansion was observed, and the shrinkage in parallel direction was almost twice of that in perpendicular direction, which can be verified by the Schapery equation. Monolith made from H44 showed a much higher coefficient of thermal expansion at 77 K than monolith made from MK and APTES, probably due to difference in composition and measurement condition. Thermal conductivities and specific heat capacities displayed an upward trend from low to warmer temperature. The minimum and maximum values for thermal conductivity are 0.2 and 1.2 W m − 1 K − 1 . The maximum heat conductivities might be determined mainly by the macroporosity and the thermal conductivity of the hybrid material. [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]

The present GeTe 4 -AsTe 3 -AgI glasses extend the optical window to up to 25 μm and its glass-forming region has been explored for practical applications. Their structure, glass-forming ability, thermal stability, infrared transmitting properties were investigated. The results reveal that the GeTe 4 -AsTe 3 -AgI glasses exhibit a large glass-forming region situated around the GeTe 4 -rich domain. Raman analysis confirms the formed [GeTe 3 I] and [AsTe 2 I] units are mainly responsible for the improvement in glass-forming ability. The optimum 40GeTe 4 -30AsTe 3 -30AgI glasses exhibit a large optical window extending from 2 to 25 μm while being stable enough toward crystallization to permit the preparation of fibers and molded lenses. Under proper annealing at 150 °C, 40GeTe 4 -30AsTe 3 -30AgI glass-ceramics, with high mechanical and thermal properties while still keeping the IR transmittance unchanged, were obtained for the first time. [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]

This paper identifies gaps in the present state of knowledge and describes emerging research directions for ultra-high temperature ceramics. Borides, carbides, and nitrides of early transition metals such as Zr, Hf, Nb, and Ta have the highest melting points of any known compounds, making them suitable for use in extreme environments. Studies of synthesis, processing, densification, thermal properties, mechanical behavior, and oxidation of ultra-high temperature ceramics have generated a substantial base of knowledge, but left unanswered questions. Emerging research directions include testing/characterization in extreme environments, composites, computational studies, and new materials. [ABSTRACT FROM AUTHOR]

A single-phased anorthite porous ceramics was fabricated by foam-gelcasting technique using α-Al 2 O 3 , CaCO 3 and SiO 2 as starting material. Through adjusting foaming agent concentration and solid content in the slurry, tailored porosity (62–91%), pore size (7–350 μm), thermal conductivity (0.04–0.27 W/m·K) and compressive strength (0.27–13.39 MPa) were obtained. The experimental thermal conductivity was in good agreement with the universal model. The dependence of compressive strength on porosity can be described by the Gibson model. [ABSTRACT FROM AUTHOR]

The effects of SiC content (10–40 vol.%) on electrical, thermal and ablation properties of pressureless sintered ZrB 2 -SiC composites showing interfacial segregation of W-rich phases have been studied. The electrical resistivity was measured by four-probe method, whereas thermal diffusivity and coefficient of thermal expansion (CTE) were determined using laser-flash method and thermo-mechanical analyzer, respectively. Whereas thermal conductivities calculated from experimentally obtained thermal diffusivity values are found to be the highest for the ZrB 2 -20 SiC composite, both electrical conductivity and CTE decrease with increasing SiC content. The specimens were subjected to thermal shock by soaking at 800–1200 °C, followed by water-quenching. Further, some specimens were exposed to oxyacetylene flame (2200 °C) for 10 min. The damage was estimated from changes in mass, Young’s modulus, and hardness. The highest thermal shock and ablation resistance have been observed for the ZrB 2 -20 SiC composite, as thermal properties and formation of protective oxide scale play key role. [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]

• The CaO-MgO-SiO 2 -Al 2 O 3 -CaF 2 (CMSAC) glass was first used as a sintering aids for Al 2 O 3 to enhance the flexural strength of composites. • The CMSAC glass/Al 2 O 3 ceramic can be densified when sintered at 910 °C and has good dielectric and mechanical properties. • The CMSAC glass/Al 2 O 3 ceramic has a high flexural strength of 310±14 MPa, which is higher than most LTCC materials reported previously. • The excellent mechanical properties are mainly attributed to three aspects: grain refinement, improved fracture energy, and the synergistic effect of the relative contents of Al 2 O 3 and the CMSAC glass. A high flexural strength low temperature co-fired ceramic material was obtained by mixing the CaO-MgO-SiO 2 -Al 2 O 3 -CaF 2 glass and Al 2 O 3 by the weight percentage of x Al 2 O 3 +(1- x)CaO-MgO-SiO 2 -Al 2 O 3 -CaF 2 (x = 30, 35, 40 and 45 wt.%). The sintering behavior, crystalline component, mechanical, electrical and thermal properties were investigated in depth. The X-ray diffraction data demonstrated that Al 2 O 3 , CaMgSi 2 O 6 , and Mg 2 SiO 4 were formed during the sintering process. The glass/ceramic composites with 35 wt.% Al 2 O 3 sintered at 910 °C for 2 h exhibited excellent mechanical properties, with a flexural strength of 310±14 MPa. The excellent mechanical properties are mainly attributed to the following three aspects: grain refinement, improved fracture energy, and the synergistic effect of the relative contents of Al 2 O 3 and the CaO-MgO-SiO 2 -Al 2 O 3 -CaF 2 glass. The results suggest that the CaO-MgO-SiO 2 -Al 2 O 3 -CaF 2 glass/Al 2 O 3 composites can be regarded as promising candidates for low temperature co-fired ceramic substrate applications. [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]

• NdHfO composites materials and NdHfO "stuffed" pyrochlore solid solutions. • Thermal conductivity, luminescence, and oxygen ion conductivity were studied. • (Nd 2- x Hf x)Hf 2 O 7+ x /2 (x = 0.2) composite shows the lowest thermal conductivity. • (Nd 2- x Hf x)Hf 2 O 7+ x /2 (x = 0.2, 0.32) composites show the highest conductivity. • Narrow-band luminescence of the NdHfO composites has been observed. The phase composition, microstructure, electrical and thermal conductivity of Nd 2± x Hf 2± x O 7±δ ceramic materials have been studied. (Nd 2- x Hf x)Hf 2 O 7+ x /2 (x = 0.2, 0.32, 0.39) composites, containing 4–16 wt% HfO 2 , have the highest conductivity and the brightest narrow-band luminescence among materials under study. The (Nd 2- x Hf x)Hf 2 O 7+ x /2 (x = 0.2) composite, containing ∼ 4 wt% HfO 2 , is shown to have the lowest thermal conductivity: 1.52 W m–1 K–1 at 300 K. XRD and Raman spectroscopy results show that (Nd 2- x Hf x)Hf 2 O 7+ x /2 (x = 0.2, 0.32, 0.39, 1.14) are composites consisting of a mixture of pyrochlore solid solutions with Hf on the Nd site and two HfO 2 polymorphs (m - HfO 2 and γ 2 - HfO 2 nanodomains). The properties of the (Nd 2- x Hf x)Hf 2 O 7+ x /2 (x = 0.2, 0.32, 0.39, 1.14) composites are compared to that of the Nd 2 (Hf 2- x Nd x)O 7- x /2 (x = 0, 0.1) pyrochlores, and the best properties were shown by the (Nd 2- x Hf x)Hf 2 O 7+ x /2 (x = 0.2, 0.32) composites. [Display omitted] [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]

A novel silica aerogel/porous Y 2 SiO 5 composite was prepared by freeze casting and sol-gel impregnation. Porous Y 2 SiO 5 ceramics with different solids contents were prepared at 1400 °C. The pore structure, porosity and mechanical properties of the porous Y 2 SiO 5 ceramics before and after impregnating of silica aerogel were investigated. The results show that the room-temperature thermal conductivity decreases and the compressive strength increases remarkably while impregnating porous Y 2 SiO 5 with silica aerogel. The silica aerogel/porous Y 2 SiO 5 composite exhibits a high compressive strength (i.e. 9.3 MPa) and a low thermal conductivity (i.e. 0.260 W/(mK)). This work reports an optimal processing method of silica aerogel/porous Y 2 SiO 5 composite with the potential application as a high-temperature thermal insulation material. [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]

High density reduced graphene oxide (rGO) reinforced aluminum nitride (AlN) composites were successfully fabricated by the one-step spark plasma sintering (SPS) method. Raman spectra showed that the raw material of GO was thermal reduced to rGO during the SPS process, and the reduction of GO can be strongly affected by the carbonaceous atmosphere. With the rGO content increasing (0–2 wt %), the dispersion of rGO and relative density of the composites decreased, decreasing the elastic modulus and hardness accordingly. However the flexural strength had a slight increase when rGO content was ≤1 wt%, and the fracture toughness increased from 3.5 to 5.2 MPa m 1/2 with the rGO due to the crack bridging and pulling out of rGO. The thermal conductivity of the composites was low and sharply decreased from 92.5 to 37.4 W m −1 K −1 with the addition of rGO, which are attributed to the low crystalline quality and high vacancy defects in rGO and the increase of interfacial thermal resistance. [ABSTRACT FROM AUTHOR]

Low-lead content (1 − x )BT– x PMN ( x = 0, 0.025, 0.05, 0.075, 0.10 and 0.15) ceramics were prepared by a two-step conventional mixed-oxide method. The crystal structure, phase transitions behavior, thermal, Raman and electrical properties of these ceramics were investigated for the first time. The compositions show formation of perovskite-type solid solutions and undergo a sequence of phase transitions characteristic of pure BT (except for samples with x = 0.075 and x = 0.10 in which a direct tetragonal–rhombohedral phase transition, and x = 0.15 in which only cubic–rhombohedral phase transition, was observed). Dielectric studies revealed that, with a rise of PMN content, the dielectric behaviors of the obtained ceramics changed from that of normal ferroelectrics to relaxor-like ones. The transition temperatures and the maximum electric permittivity decrease with increasing PMN content in the system. In general, the transition temperatures observed by means of dielectric studies are in good agreement with those obtained from XRD and DSC measurements. The possible origin of the observed effects was discussed. We suggest that the presented materials can be a good starting point for the development of new low-lead electronic ceramics. [ABSTRACT FROM AUTHOR]

Thermal diffusivity of mullite fused ceramics was determined from room temperature up to 500 °C at intervals of 100 °C. The ceramic material was formed by combining kaolinite as the matrix and silicon nitride as the filler powder. The ceramics were sintered at 1000 °C, 1100 °C, and 1200 °C to study the structural differences. Thermal diffusivity data showed that the addition of silicon nitride affects the composites heat flow and this behavior is noticeable at 1100 °C and 1200 °C samples. The thermal diffusivity data was plotted on 1000/T graph to demonstrate a linear relation for filler effects of silicon nitride on the mullite matrix. Additions of 25% and 30% silicon nitride sintered at 1200 °C exhibited thermal diffusivity values lower than pure mullite crystal at 0.55–0.45 mm 2 /s. These values suggest that heat conduction across the system was interrupted by silicon nitride nanoparticle additions via micropore formations. These samples have potential applications for high temperature thermal insulation. [ABSTRACT FROM AUTHOR]

Abstract: The limited scheelite type Cd1−3x □ x Gd2x MoO4 solid solution, where 0< x ≤0.25 and □ are cationic vacancies have been successfully synthesized by high-temperature annealing of CdMoO4/Gd2(MoO4)3 mixtures composed of 50.00mol.% and less of Gd2(MoO4)3. The obtained materials as well as CdMoO4 and Gd2(MoO4)3 were characterized by powder XRD, DTA–TG, DSC, and SEM techniques. A phase diagram of the pseudobinary CdMoO4–Gd2(MoO4)3 system was constructed. The eutectic point corresponds to 1350±5K and ∼70.00mol.% of Gd2(MoO4)3 in an initial CdMoO4/Gd2(MoO4)3 mixture. With decreasing of Gd3+ amount in the crystal lattice of CdMoO4, a melting point of the Cd1−3x □ x Gd2x MoO4 solid solution increases from 1351 (x =0.25) to 1408K (x =0). EPR method was used to identify the paramagnetic Gd3+centers in Cd1−3x □ x Gd2x MoO4 for different values of x parameter as well as to select biphasic samples containing both Cd0.2500□0.2500Gd0.5000MoO4 and Gd2(MoO4)3. [Copyright &y& Elsevier]

Abstract: This study introduces a novel surface treatment (thermal silicatization) for bonding to zirconia ceramics. The method is based on the application of a solution containing silane, distilled water, and absolute ethanol, followed by heat treatment at 150°C for 1h and 600°C for 2h for deposition of a reactive siloxane network on the zirconia surface. The thermal silicatization was compared with traditional coupling agents for ceramic bonding (silane, zirconia primer, and/or adhesive), evaluating the shear bond strength of a dual-cured resin luting agent to yttria-stabilized zirconia. For the thermal silicatization method, two groups were tested: one group with silane applied to the ceramic (Sit) and another group with the application of silane and adhesive (SitA). Data were analyzed by ANOVA on ranks and Dunn's test (5%). The zirconia primer yielded higher bond strength compared with silane and/or adhesive. The combination of zirconia primer and adhesive generated higher bond strength than the primer alone. The group Sit showed higher bond strength than most of the groups while the bond strength of SitA had higher bond strength than all other groups. Deposition of a silicate layer on the zirconia surface was confirmed by x-ray energy dispersive spectroscopy. In conclusion, the proposed thermal silicatization method might promote the bonding of resin luting agents to dental zirconia ceramics. The proposed method is simpler and more cost-effective compared to other methods described in the literature as it could applied to the internal surface of zirconia frameworks using the same sintering protocol of the veneering ceramic. [Copyright &y& Elsevier]

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]

The objective of this work was to examine linear thermal expansion of virgin and poled 0.57Pb(Sc1/2Nb1/2)O3–0.43PbTiO3 ceramics between 30°C and 600°C by contact dilatometry. The thermal expansion dL/Lo of the virgin ceramic increases with increasing temperature until approximately 260°C. The physical and technical thermal expansion coefficients were determined. At 260°C the physical thermal coefficient is 2.08×10−6 K−1. Between 260.0°C and 280.0°C an anomaly in the thermal expansion vs. temperature and an endothermic peak in the differential scanning calorimetry curves correspond to the phase transition region from tetragonal to cubic phase. At temperatures from 280°C to 600°C the thermal expansion dL/Lo increases again. In the derivative of the dL/Lo heating curves of the poled ceramics, additionally to the anomaly at 270°C, also the anomaly at 160°C is observed, which is associated with the depolarization of the material during heating. [ABSTRACT FROM AUTHOR]

Zirconium carbide (ZrC) is a refractory ceramic presenting interesting properties such as a high melting point, a very high hardness and a good thermal stability. For these reasons, this material is considered as a candidate for fuel coating for fourth-generation reactors in particular for the Gas cooled Fast Reactors (GFR). The ceramic temperature could reach 1200°C in normal reactor operation and reach 1700°C in accidental conditions. It is therefore important to assess the ZrC thermal retention capacity regarding abundant and/or volatile fission products. This paper deals with the behavior of Xenon which is the major gaseous fission product created during fission. Previous studies have shown that Xenon remained motionless in an “Oxygen-poor” matrix such as ZrC0.95O0.05, up to temperatures of 1800°C. However, Zirconium oxycarbides are known to be very sensitive to oxidation. This study aims therefore at studying the behavior of Xenon in Zirconium oxycarbide samples with different Oxygen contents. Xenon is introduced by ion implantation and the samples are annealed in secondary vacuum in the temperature range 1400°C–1800°C. The Oxygen profiles are determined by using the 16O(4He, 4He)16O nuclear reaction at 7.5MeV and the concentration profiles of Xenon are measured by Rutherford Backscattering Spectrometry at each step of the treatment. The results show that the behavior of the material during annealing with respect to oxidation is strongly related to its initial Oxygen content. More generally, the higher the initial Oxygen content, the more important is the oxidation. Consequently, the Xenon migration is enhanced in Oxygen rich Zirconium carbides. [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: Sih name="sbnd" />C ceramics were prepared from a methyl silicone preceramic polymer and rice bran by a simple method. Dried rice bran powder was blended with a molten preceramic polymer (Silres 610) at various ratios by a Brabender-type static mixer. Composites were made from them by crosslinking at 250°C in a hot press and porous ceramics were made by pyrolysing them at 900°C. The produced porous ceramics were characterised by measuring their density, ceramic yield, volume shrinkage, hygroscopic expansion, and compressive strength. Additionally, the fabricated ceramics were examined by SEM, and FTIR. Ceramics made from Silres 610/rice bran 50/50 ratio showed the highest compressive strength (2.7MPa) along with the highest ceramic yield (47.8%), but the lowest hygroscopic expansion, and volume shrinkage. On the other hand, the 20/80 ratio showed the lowest ceramic yield and compressive strength but the volume shrinkage higher than the 50/50 ratio. All ceramics showed negligible hygroscopic expansion. [Copyright &y& Elsevier]

Abstract: In this research report, a sintering process of porous ceramic materials based on Al2O3 was employed using a method where a cation precursor solution is embedded in an organic fibrous cotton matrix. For porous green bodies, the precursor solution and cotton were annealed at temperatures in the range of 100–1600°C using scanning electron microscopy (SEM) and thermogravimetric (TG) analysis to obtain a porous body formation and disposal process containing organic fibers and precursor solution. In a structure consisting of open pores and interconnected nanometric grains, despite the low porosity of around 40% (calculated geometrically), nitrogen physisorption determined a specific surface area of 14m2/g, which shows much sintering of porous bodies. Energy dispersive X-ray (EDX) and X-ray diffraction (XRD) analytical methods revealed a predominant amount of α-Al2O3 in the sintered samples. Thermal properties of the sintered Al2O3 fibers were obtained by using the Laser Flash which resulted in the lower thermal conductivity obtained by α-Al2O3 and therefore improved its potential use as an insulating material. [Copyright &y& Elsevier]

Abstract: The effect of heat treatment on the optical activity of ormocers (aminopropyl-modified silica) is studied using photoluminescence and ultraviolet diffuse reflectance spectroscopy techniques. The thermal stability of the modified silica is also investigated by X-ray diffraction and thermogravimetric analyses. Great withstanding of aminopropyl group located inside the silica network is found at high temperature. Distinct blue and green bands are observed in the modified silica nanoparticles after heat treatment using different temperatures, whereas some optical activities in the area of near-ultraviolet and infrared relating to the OH-related and carbon-related species and non-bridging oxygen hole center, respectively, diminished. The decrease in the band intensity besides band shift was evidences for changing the structural defect owing to releasing and decomposing of aminopropyl group from the nanoparticle surface. Some ultraviolet bands were detected because of the existence of oxygen-related defect. [Copyright &y& Elsevier]