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Polymer-derived SiBCN ceramics with good high-temperature stability and temperature-sensitive properties can be used in real-time temperature monitoring in the aeronautical industry. However, previous investigations mostly focus on the temperature sensitivity of SiBCN ceramics but neglect the fast temperature conversion of the real operating environment and its effect on the temperature sensitivity, which hinders their further practical application. In this study, the response to rapid temperature changes of polymer-derived SiBCN was studied. SiBCN ceramics maintain excellent high-temperature semiconductor performance under rapid heating, and its direct-current (DC) conductivity increases with increasing temperature. The conductive mechanism conforms to the amorphous semiconductor formula, following three different transition mechanisms in different temperature regions. The resistance of SiBCN increases with the number of cycles during 100 cycles of 500–1200 °C, presenting excellent temperature-sensitivity and relatively good sensing stability. This work demonstrates that SiBCN ceramics can maintain excellent temperature-resistance under extreme environments with rapid heating and cooling, and it is hoped that this work could guide the development of temperature sensors for extreme environments in the future. [Display omitted] [ABSTRACT FROM AUTHOR]

M-YTaO 4 is one of the most promising candidates for the next-generation thermal barrier coatings. However, the CMAS-induced degradation of M-YTaO 4 is still in dispute. This work comprehensively investigates the CMAS corrosion of M-YTaO 4 at 1300 °C which provides new insights into the corrosion mechanism. CMAS attacks M-YTaO 4 forming a thick recession layer and the main corrosion product is accurately confirmed to be (Ca 2-x Y x)(Ta 2-y-z Mg y Al z)O 7 solid solution. The recession layer presented a small difference in Young's modulus with M-YTaO 4. No delamination cracking occurred during the thermal cycling process indicating good reliability. In addition, grain boundary infiltration of CMAS is first revealed in M-YTaO 4. The results have corrected the misjudgment of the corrosion mechanism and CMAS infiltration process in previous studies which provides guidelines for the design of M-YTaO 4 thermal barrier coatings. [ABSTRACT FROM AUTHOR]

As the flight speed of aircraft continues to increase, high-temperature wave-transparent materials for radomes or antenna windows face great challenges. The shortage of new high-performance wave-transparent materials is limiting the improvement of aircraft performance. In this work, dielectric and mechanical properties of RE 2 SiO 5 (RE = Ho, Er, Tm, Yb, and Lu) were investigated to explore their application as high-temperature wave-transparent materials. RE 2 SiO 5 (RE = Ho, Er, Tm, Yb, and Lu) ceramics possess relatively low dielectric constant and it is insensitive to the RE species. For the dielectric loss, they gradually decrease as the radius of rare earth ions decreases. In addition, RE 2 SiO 5 (RE = Ho, Er, Tm, Yb, and Lu) possesses good mechanical properties with high hardness and relatively low reduced modulus, and hardness is insensitive to the rare earth ion radii while the reduced modulus increases with the RE3+ ions radius decreases. They are larger than those of fused silica, the most used traditional high-temperature wave-transparent material. The results provide important material selection and optimization guidelines for RE 2 SiO 5 as the candidate for next-generation high-temperature wave-transparent materials. [ABSTRACT FROM AUTHOR]

Porous silica ceramics were prepared by a freeze-casting method using dual solvents as a template, and their microstructure can be regulated by different ratios of solvents. As the camphene content increases, the pore shape gradually changes from prismatic pores to spherical pores, and the pore size first decreases and then increases. A porous silica ceramic showed 76 % porosity and a uniform pore size of 6 µm. It presents excellent thermal insulation properties (thermal conductivity ∼0.17 W m−1 K−1), good compressive strength, and a stable dielectric constant (∼1.48). The results of this work shed light on the promising aerospace application of porous ceramics prepared by freeze-casting using dual solvents as a template. [ABSTRACT FROM AUTHOR]

Highlights • Nitrogen, sterilization and tallow origin impact leaf area, total biomass and SPAD. • Invasive tallow populations were higher in Y (II) than natives in sterilized soil. • Native tallow populations were higher in F v / F m than invasives in sterilized soil. • Leaf area of invasive tallow was higher with N and sterilization treatment. • Y (II) of both origins was lower with UV-B and soil sterilization treatment. Abstract Chinese tallow tree (Triadica sebifera) is native to China but is aggressively invading plant species in southeastern USA Growth of invasive T. sebifera has been shown to be promoted by N deposition and inhibited by UV-B radiation, and outperform that of the native origin, which indicate higher photosynthesis ability of the invasive origin. In T. sebifera 's native range, soil sterilization could increase its performance by suppression of soil pathogens. However, the interactive effects among these factors on photosynthetic characteristics of both native and invasive T. sebifera are still not understood. Here, we conducted a pot-experiment with both native and invasive populations of T. sebifera to test how N deposition, UV-B radiation and soil sterilization affect T. sebifera performance with respect to biomass and photosynthetic ability. Total biomass and the effective quantum yield of photosystem II (Y (II), correlates to plant CO 2 assimilation) of invasive populations were higher, but the maximum quantum yield of photosystem II (F v / F m , a stress indicator) was lower than that of the native populations in sterilized soil. Leaf biomass and leaf area of invasive populations were higher than that of the native populations. Leaf area of both native and invasive populations, total biomass of native populations and relative chlorophyll content of invasive populations were increased by N deposition. Leaf area of invasive populations was increased but that of the native populations was not affected by N deposition in sterilized soil. Y (II) was reduced by UV-B radiation and soil sterilization. These results suggest invasive T. sebifera populations were higher in CO 2 assimilation rate and lower in resistance to environmental stress. The stronger performance of T. sebifera from the invasive range could have been facilitated by N deposition via increased leaf area in sterilized soil even though no significant differences were observed by N deposition in active soil. The photosynthesis response of invasive plants to current global change factors should be considered in future studies determining differences in plant performance between the native and the invasive range and efficient management of invasive species. [ABSTRACT FROM AUTHOR]

RE 2 Si 2 O 7 disilicates are promising candidates for oxidation resistant interfacial phase in SiC fiber-reinforced SiC matrix composites due to their good damage tolerance, good phase stability and compatible thermal expansion coefficients with SiC. We herein investigate the capacity and mechanisms of plastic deformation in β-Lu 2 Si 2 O 7 by a combination of Hertzian indentation experiment and transmission electron microscopy observation. A large amount of (1 1 0) deformation twinning, dislocations and slip bands are observed. For the common twinning mode, fewer atomic shuffle types, small shear strain, and low shear modulus in the twinning direction help explain the prevalence of this mode. [ABSTRACT FROM AUTHOR]

Thermal conductivities of γ-Y 2 Si 2 O 7 , β-Y 2 Si 2 O 7 , β-Yb 2 Si 2 O 7 , and β-Lu 2 Si 2 O 7 were investigated by combined first-principles calculations and experimental evaluation. Theoretical calculation was used to predict the elastic properties, anisotropic minimum thermal conductivities, and temperature dependent lattice thermal conductivities. Experimentally, thermal conductivities of these disilicates were measured from room temperature to 1273 K. In addition, their experimental intrinsic lattice thermal conductivities were determined from the corrected thermal diffusivity data after removing the extrinsic contributions from phonon scattering by defects and thermal radiation. The experimental lattice thermal conductivities match well with the theoretical predictions. Furthermore, Raman spectra of the disilicates was measured and used to estimate the optical phonon relaxation time. The present results clearly disclose the specific material parameters that determine the low thermal conductivity of RE 2 Si 2 O 7 and may provide guidelines for the optimal thermal conductivity of rare earth disilicates. [ABSTRACT FROM AUTHOR]

X2-RE 2 SiO 5 orthosilicates are promising candidate environmental/thermal barrier coating (ETBC) materials for silicon-based ceramics because of their excellent durability in high-temperature environments and potential low thermal conductivities. We herein present the mechanical and thermal properties of X2-RE 2 SiO 5 orthosilicates based on theoretical explorations of their elastic stiffness and thermal conductivity, and experimental evaluations of the macroscopic performances of dense specimens from room to high temperatures. Mechanical and thermal properties may be grouped into two: those that are sensitive to the rare-earth (RE) species, including flexural strength, elastic modulus, and thermal shock resistance, and those that are less sensitive to the RE species, including thermal conductivity, thermal expansion coefficient, and brittle-to-ductile transition temperature (BDTT). The orthosilicates show excellent elastic stiffness at high temperatures, high BDTTs, very low experimental thermal conductivities, and compatible thermal expansion coefficients. The reported information provides important material selection and optimization guidelines for X2-RE 2 SiO 5 as ETBC candidates. [ABSTRACT FROM AUTHOR]

β-Lu 2 Si 2 O 7 is a promising candidate in the third generation of environmental barrier coating (EBC) materials for silicon-based ceramics due to its excellent high temperature environmental durability. However, the high temperature thermal and mechanical properties of β-Lu 2 Si 2 O 7 are seldom reported, which hinders the design and evaluation of its EBC applications. In this paper, pure and dense β-Lu 2 Si 2 O 7 sample was successfully fabricated and its mechanical properties, including Young's modulus, bulk modulus, shear modulus, Poisson's ratio, flexural strength, fracture toughness and hardness were investigated. The ball indentation test reveals that the main deformation mechanisms of β-Lu 2 Si 2 O 7 at room temperature are deformation twinning and dislocation glide, which indicate that β-Lu 2 Si 2 O 7 is a damage tolerant ceramic. In addition, the thermal expansion coefficient and thermal shock resistance were measured at high temperatures. β-Lu 2 Si 2 O 7 possesses excellent high temperature elastic stiffness up to 1470 °C, and the critical temperature difference for thermal shock resistance is 270 K. [ABSTRACT FROM AUTHOR]

Rare earth monosilicate (RE 2 SiO 5) is one of the most promising candidates as an environmental barrier coating (EBC) for SiC f /SiC ceramic matrix composites. But single-component RE 2 SiO 5 is hard to meet the multiple and harsh performance requirements of EBC which brings a significant challenge to their applications. Based on our previous research on single-component RE 2 SiO 5 ceramics, (Ho 0.4 Yb 0.3 Lu 0.3) 2 SiO 5 solid solution was designed and successfully fabricated in this work. Doping of multiple RE elements endows (Ho 0.4 Yb 0.3 Lu 0.3) 2 SiO 5 with excellent thermal insulation properties and matched thermal expansion coefficient with SiC f /SiC substrates. In addition, it exhibits lower elastic modulus and comparable hardness than that of single-component RE 2 SiO 5. (Ho 0.4 Yb 0.3 Lu 0.3) 2 SiO 5 also presents good resistance to calcium-magnesium alumino-silicates (CMAS) corrosion. Rational composition design allows (Ho 0.4 Yb 0.3 Lu 0.3) 2 SiO 5 to retain the merits of single-component RE 2 SiO 5 while taking advantage of the solid solution effect. The results of this work suggest (Ho 0.4 Yb 0.3 Lu 0.3) 2 SiO 5 as a promising EBC candidate. [ABSTRACT FROM AUTHOR]

Si 3 N 4 fiber-reinforced ceramic matrix composites are promising wave-transparent materials for antenna windows in hypersonic vehicles. The reinforcing fibers and fiber/matrix interface determine the performance and failure mode of the composite. BN are usually used as weakly bonded interphase due to its chemical inertness. Understanding the impact of the BN on Si 3 N 4 fibers at elevated temperatures is of crucial significance. In this work, a new phenomenon that BN coating significantly influences the crystallization behavior of the fibers was discovered. Notably, BN coating can raise the crystallization temperature of Si 3 N 4 fiber and prevent its crystallization even at 1600℃ in air. • BN coating hindered the crystallization process of Si 3 N 4 fiber that starts from the surface. • The crystallization of Si 3 N 4 fiber and oxidation is a competitive process. • The Si 3 N 4 fiber coated with BN does not crystallize under air atmosphere [ABSTRACT FROM AUTHOR]

• C. camphora litter removal increase nitrogen cycling functional gene abundance. • Nitrogen addition interacted with C. camphora litter impacting N 2 O emissions. • Nitrogen addition increased CO 2 emission rates only when litter was removed. • Litter removal consistently increased soil N 2 O emission in C. camphora plantations. Nitrous oxide (N 2 O) and carbon dioxide (CO 2) contribute substantially to global climate. Understanding N 2 O and CO 2 emission intensity from forest soil is important for greenhouse gas (GHG) budget and climate change mitigation. Litter decomposition and nitrogen (N) addition are two crucial factors impacting soil GHG production, but magnitude depends on litter characteristics. Cinnamomum camphora is used for leaf-harvesting for essential oil extractions, which may disturb litter input and hence soil GHG emissions. We conducted an in situ study over fourteen months in C. camphora plantations to compare litter removal to litter control, combined with N addition, quantify production of N 2 O and CO 2 in full-factorial complete-randomized design. Soil N 2 O emission rates were significantly influenced by litter and N treatment, while CO 2 emissions were only impacted by interactions between litter and N treatment. Specifically, soil N 2 O emission rates were increased by 681%, while copy number of five functional microbial genes associated with N 2 O productions were increased by 2.8 to 71.4 times following litter removal. C. camphora litter might have released chemicals associated with inhibition of related microbial activities. Soil CO 2 emission rates were 25% higher with litter removed and 34% lower with litter when N was added, further indicating inhibition effects of C. camphora litter on microbial activities. In future management of C. camphora plantations with intensive defoliation management and fertilization practice, litter regimes with more litter input should be considered in mitigation of soil GHG emissions, and hence global climate change. [ABSTRACT FROM AUTHOR]

Adding a certain amount of steel fibers can overcome the brittleness defects in geopolymer concrete and improve the mechanical properties, which has a broader application prospect. However, the research on the material properties of steel fiber-reinforced geopolymer concrete (SFGPC) after high temperature exposure is still very limited. Therefore, tests on 114 cubes and 57 prisms after exposure to high temperatures were conducted in this paper. The main variables were temperature (20 °C, 200 °C, 400 °C, 600 °C, and 800 °C), steel fiber volume content (0, 1 %, and 2 %), and concrete type (SFGPC and steel fiber-reinforced ordinary Portland cement concrete (SFOPC)). The results indicated that SFGPC with a steel fiber content of 1 % at 800 °C experienced a 53.6 % reduction in compressive strength, a 58 % reduction in splitting tensile strength, a 93.9 % reduction in elastic modulus, a 45.9 % reduction in toughness index, and a 274.5 % increase in peak strain, compared with room temperature. The 1 % fiber content enhanced the compressive strength by 10.3 %−36.5 %, the splitting tensile strength by more than 16 %, the peak strain by 9.6 %−32.7 %, and the toughness index by 24.4 %−64.6 % compared to the absence of fiber content. Based on the room temperature model, a constitutive model of SFGPC under uniaxial compression after high temperatures was developed. • Cubes and prisms of SFGPC after high temperature exposure were tested. • High temperature reduced the strength, elastic modulus, and toughness index. • Increasing fiber content enhanced the mechanical behavior of SFGPC. • A constitutive model under compression after high temperatures was developed. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • CAMS corrosion of RE 2 SiO 5 is linearly related to RE ionic radius. This stands for an efficient materials selection for its EBC applications. • Smaller RE leads to the decreased reactivity and this brings out shallower recession layer and better resistance to CMAS. • Optical basicity difference between RE 2 SiO 5 and CMAS can be used as an indicator for predicting their reactivity. Abstract Thermochemical reactions between rare earth (RE) monosilicates (RE 2 SiO 5) and molten calcium-magnesium-aluminosilicate (CMAS) at 1300 °C were investigated. Some RE 2 SiO 5 (RE = Tb, Dy, and Ho) dissolve readily into CMAS melts and thereby, crystalline Ca 2 RE 8 (SiO 4) 6 O 2 reprecipitate. Other RE 2 SiO 5 (RE = Tm, Yb, and Lu) resist CMAS attack, and a continuous layer of Ca 2 RE 8 (SiO 4) 6 O 2 establishes at the interface. The recession of RE 2 SiO 5 is related to RE ionic radius. RE 2 SiO 5 with small RE ionic radius exhibits good CMAS corrosion resistance due to its low reactivity with CMAS. This result is consistent with the same trend of difference in the optical basicity of RE 2 SiO 5 /CMAS. [ABSTRACT FROM AUTHOR]

One of the main challenges for commercialising calcium looping (CaL) as a CO 2 capture technology is maintaining a high level of sorbent reactivity during long-term cycling. In order to mitigate the decay in carrying capacity, research has moved towards producing enhanced sorbents. However, this creates potential problems related to ease of scaling up production techniques and production costs, and raises the question as to whether such approaches can be used at large scale. On the other hand, a key advantage of CaL over other carbon capture technologies is synergy with the cement industry, i.e., use of spent sorbent as a feedstock for clinker production. In this work two enhanced materials: (i) limestone doped with HBr through a particle surface impregnation technique; and (ii) pellets prepared from limestone and calcium aluminate cement, were tested in a 25 kW th dual fluidised bed pilot-scale reactor in order to investigate their capture performance and mechanical stability under realistic CaL conditions. Moreover, the spent sorbent was then used as a raw material to make cement, which was characterised for phase and chemical composition as well as compressive strength. The HBr-doped limestone showed better performance in terms of both mechanical strength and stability of the CO 2 uptake when compared to that of pellets. Furthermore, it was shown that the cement produced has similar characteristics and performance as those of commercial CEM 1 cement. This indicates the advantages of using the spent sorbent as feedstock for cement manufacture and shows the benefits of synthetic sorbents in CaL and suitability of end-use of spent sorbents for the cement industry, validating their synergy at pilot scale. Finally, this study demonstrates the possibility of using several practical techniques to improve the performance of CaL at the pilot scale, and more importantly demonstrates that commercial-grade cement can be made from the lime product from this technology. [ABSTRACT FROM AUTHOR]

Rare earth (RE) silicates are promising candidates for environmental and thermal barrier coating (ETBC) materials. Low thermal conductivity is one of the main concerned thermal properties in ETBC design. We herein adopted multiple phonon scattering mechanisms to lower thermal conductivity of (Y x Yb 1-x ) 2 SiO 5 solid solutions. Bulk samples were prepared by hot pressing method and RE atomic occupations, Raman spectra, thermal conductivities were measured as well as Debye temperature was obtained from temperature dependent Young's modulus. It is interesting to note that huge mass and size misfits between Yb and Y ions dominate the decrement of thermal conductivity. Furthermore, Yb 2+ increases the concentration of oxygen vacancy, and it further decreases heat conduction. This work highlights the possible defect engineering in RE silicates for their advances in ETBC applications. [ABSTRACT FROM AUTHOR]

Lu 2 SiO 5 is a promising candidate of environmental barrier coatings (EBC) for silicon based ceramics due to its excellent high temperature stability. However, little information is available for the mechanical and thermal properties of Lu 2 SiO 5 , which frustrated evaluation of its performances for EBC applications. In this paper, dense Lu 2 SiO 5 ceramic is successfully fabricated from Lu 2 O 3 and SiO 2 powders by in situ hot pressing/reaction sintering at 1500 °C. Mechanical properties, including Young's modulus, bulk modulus, shear modulus, Poisson's ratio, fracture toughness, Vickers hardness, and bending strength are reported for the first time. Lu 2 SiO 5 possesses excellent high temperature mechanical properties up to at least 1300 °C. Thermal stress for the case of Lu 2 SiO 5 or Y 2 SiO 5 coating on silicon bond coat and thermal stress resistance parameter are also estimated based on the experimental mechanical and thermal properties. The present results suggest that Lu 2 SiO 5 has better reliability than Y 2 SiO 5 in harsh thermal environment. [ABSTRACT FROM AUTHOR]

Reasonable structural design is significant to enable the performance in advanced energy storage devices. Herein, a 3D honeycomb-like CoMn 2 O 4 nanoarchitecture (CMO) on nitrogen-doped graphene (NG) coating Ni foam (denoted as Ni/NG/CMO) flexible battery-type electrode was prepared by a facile two-step hydrothermal strategy. The honeycomb-like CoMn 2 O 4 arrays not only provide abundant active sites but can also be closely combined with the Ni foam/NG substrate, which enables high reversible capacity and good cycle stability during the long cycles. Benefiting from the compositional features and 3D honeycomb-like nanoarchitecture, the Ni/NG/CMO composite electrode displays improved electrochemical performance with remarkable specific capacity of 527.0C g−1 at a current density of 1 A g−1, outstanding rate capability (338.6C g−1 even at 20 A g−1). In addition, a flexible binder-free supercapattery device has been assembled with Ni/NG/CMO as positive electrode and 3D Ni/NG as negative electrode. Such a supercapattery delivers a high energy density of 44.1 Wh·kg−1 at 992.6 W kg−1, 20.3 Wh·kg−1 at 12430.0 W kg−1 as well as excellent cycling durability. The 3D honeycomb-like Ni/NG/CMO could be considered as an advanced flexible battery-type material for high capacity and energy density fields. • 3D honeycomb-like Ni foam/nitrogen-doped graphene/CoMn 2 O 4 has been synthesized. • The Ni/NG/CMO electrode exhibits remarkable specific capacity of 527.0C g−1 at 1 A g−1. • The Ni/NG/CMO//Ni/NG supercapattery is successfully designed. • The device has achieved a satisfied energy density of 44.1 Wh·kg−1. [ABSTRACT FROM AUTHOR]

With the increased demand for high operating temperature of gas turbine engines, corrosion by molten calcium-magnesium-alumino-silicate (CMAS) exhibits a significant challenge to the development of durable environmental barrier coatings (EBCs). EBC candidates, γ-Y 2 Si 2 O 7 , β-Yb 2 Si 2 O 7 , and β-Lu 2 Si 2 O 7 were explored on their corrosion resistance to CMAS melts at 1300 °C and 1500 °C for 50 h. Interaction and degradation mechanisms were investigated and the corrosion behaviors showed different trends at high temperatures. At 1300 °C, RE 2 Si 2 O 7 dissolves into CMAS melts and apatite phases reprecipitate forming a thick recession layer. However, when the temperature increases to 1500 °C, CMAS melts vigorously penetrate through the grain boundary of RE 2 Si 2 O 7 and 'blister' cracks form throughout the samples. The reduced grain boundary stability at 1500 °C promotes the penetration of CMAS melts in RE 2 Si 2 O 7. Grain boundary engineering is critically demanded to optimize CMAS corrosion at high temperatures. [ABSTRACT FROM AUTHOR]

Abstract Rare earth (RE) silicates X1-RE 2 SiO 5 (RE = La, Nd, Sm, Eu, and Gd) are comprehensively investigated as promising thermal barrier coating candidates. The mechanical, thermal, and corrosion resistance properties are evaluated by theoretical exploration and experimental measurement. Mechanical properties and corrosion resistance to calcium-magnesium alumino-silicates (CMAS) melts of X1-RE 2 SiO 5 are linearly correlated with ionic radius of RE elements. Elastic moduli increase with the decrease of ionic radius of RE3+. X1-RE 2 SiO 5 with larger RE3+ exhibits better resistance to molten melts corrosion. For thermal properties, they are not obviously sensitive to RE species. All X1-RE 2 SiO 5 demonstrate low thermal conductivities and their magnitudes are significantly modified by concentration of defects. Thermal expansion coefficients of X1-RE 2 SiO 5 are more or less close and are compatible with the value of superalloy. The results highlight X1-RE 2 SiO 5 as potential thermal barrier coating candidates with overall properties. [ABSTRACT FROM AUTHOR]

Global warming and nitrogen (N) deposition are important factors impacting soil carbon (C) and N cycling. Termites are important ecosystem engineers that can also strongly affect C and N cycling, potentially in interaction with warming and N deposition. In addition, non-additive effects that magnify or reduce their impacts on soil element cycles may occur when termite nests and adjacent soils are mixed due to their divergent properties but this has not been investigated. Here, we collected termite nests and trails built in wood (“termite nest soils”) and adjacent control soils in forests at Lu Mountain (Jiangxi, China) to investigate effects of termites, warming, and N deposition on C and N processes. We measured CO 2 emissions, N 2 O emissions, net N mineralization, and net nitrification when soils were incubated at different temperatures (15 °C, 25 °C, or 35 °C) and levels of N deposition (control vs. 4 g N m − 2 ). Termite nest soils were characterized by higher dissolved organic C and CO 2 emissions. CO 2 emissions decreased with N addition and increased with temperature. N 2 O emissions increased with N deposition and increased with temperature, especially in termite nest soils and mixed soils. Net N mineralization rates increased with temperature but increases were smaller and more gradual in control and mixed soils than in termite soils. Mixing termite nest soils and control soils imposed synergistic (N mineralization: up to 57% higher than expected; nitrification: up to 170% higher; N 2 O emissions without N addition: 18% higher) and antagonistic (CO 2 emissions: 7% lower; N 2 O emissions with N addition: 28% lower) mixing effects, indicating termite impacts on soil C and N cycling might be under- and over-estimated, respectively, based on each soil alone. In light of the remarkable abundance of termites, the effects of mixing termite nest soils and the control soils on soil C and N cycling should be considered in the context of global change. [ABSTRACT FROM AUTHOR]

Polycrystalline YAl 3 C 3 ceramic was fabricated by an in situ hot-pressing process using YH 2 , Al, and C powders as starting materials. The crystal structure of YAl 3 C 3 was determined by X-ray diffraction and ab initio calculations to be a hexagonal space group P6 3 /mmc. The lattice parameters are a = b = 3.424 Å, c = 17.291 Å, and the atomic positions are Y at 2a (0, 0, 0), Al1 at 2d (1/3, 2/3, 3/4), Al2 at 4f (1/3, 2/3, 0.138), C1 at 2c (1/3, 2/3, 1/4), and C2 at 4f (1/3, 2/3, 0.6045). The reaction synthesis path for YAl 3 C 3 was presented. Microstructure observations revealed that YAl 3 C 3 ceramic had plate-like grain morphology. The elastic, mechanical and thermal properties of YAl 3 C 3 were investigated. Most significantly of all, the Young’s modulus of YAl 3 C 3 could retain 276 GPa (85% of that at room temperature) at 1500 °C, suggesting that YAl 3 C 3 is a promising lightweight high temperature structural material. [ABSTRACT FROM AUTHOR]