Thermo-mechanical properties of Penly reactor envelope at temperatures up to 200°C

This paper reports on an experimental investigation conducted to study the effects of high temperatures of up to 200°C on the phase composition, pore structure development and physico-mechanical properties of concrete at the PENLY nuclear power plant (France). The concrete specimens were manufactured under laboratory conditions from identical materials used at the construction site in PENLY, and then stored at 20°C/100% R.H. for 28 days and exposed to temperatures of 40°C, 60°C, 100°C, 200°C, and 20°C/60%R.H., respectively. Test results revealed that an intense structural integrity degradation of PENLY concrete occurs between 100°C and 200°C due both to a loss of water bound in hydrated cement minerals and to subsequent air void formation. This phenomenon is related to an increase in the median pore radius and total porosity values, as well as to a decrease in the dynamic and static moduli of PENLY concrete. The reduction in volume of the hydrate phase is believed to be the reason behind the rapid expansion, over a short time interval, due to a time-limited moistening of the specimen by released water with a sudden rise in temperature, followed by a stabilised period of shrinkage and creep.     

Ti3SiC2-formation during Ti–C–Si multilayer deposition by magnetron sputtering at 650 °C

Titanium Silicon Carbide films were deposited from three separate magnetrons with elemental targets onto Si wafer substrates. The substrate was moved in a circular motion such that the substrate faces each magnetron in turn and only one atomic species (Ti, Si or C) is deposited at a time. This allows layer-by-layer film deposition. Material average composition was determined to Ti_0.47Si_0.14C_0.39 by energy-dispersive X-ray spectroscopy. High-resolution transmission electron microscopy and Raman spectroscopy were used to gain insights into thin film atomic structure arrangements. Using this new deposition technique formation of Ti₃SiC₂ MAX phase was obtained at a deposition temperature of 650 °C, while at lower temperatures only silicides and carbides are formed. Significant sharpening of Raman E_2g and A_g peaks associated with Ti₃SiC₂ formation was observed.     

Thermal stability of mixtures of the extractant and nitric acid at temperatures from 90 to 120°С

The thermal stability of mixtures of tri-n-butyl phosphate (TBP) with HNO₃ was studied in the temperature range from 90 to 125°C. In mixtures with the irradiated extractant at 110°C, intense exothermic processes initiated by oxidation of extractant radiolysis products are possible, whereas at 90°C oxidation of the irradiated extractant is accompanied by weak heat and gas evolution. In the temperature range from 110 to 120°C, exothermic oxidation processes in nonirradiated mixtures start after long induction period (hours), develop gradually, and do not have an avalanche character. Below 110°C, heating of mixtures of the extractant with HNO₃ at the HNO₃ concentration from 8 to 15.7 M is accompanied by gas evolution without exothermic effects. On the whole, oxidation processes in extraction mixtures at temperatures below the “start” parameters of thermal explosion are not dangerous from the viewpoint of the probability of thermal explosion, even at prolonged heating.     

Tests on impact behaviour of micro-concrete-filled steel tubes at elevated temperatures up to 400°C

Concrete-filled tubular (CFT) columns are being more and more utilized in construction of tall buildings and bridges. The CFT column system, which has been proved to have excellent load carrying capacity and ductility, by static and simulated seismic loading tests, also has good dynamic impact behaviour. The impact resistance of small-size micro-concrete-filled steel tubes under axial impact load at elevated temperatures up to 400°C was experimentally studied by using a spilt Hopkinson pressure bar. The stress and strain time history curves of the tested specimens were recorded to analyze the impact behaviour of CFT at elevated temperatures. The failure patterns and the influence of temperature on the impact resistance of CFT are discussed. The test results show that CFT has an excellent impact resistant capacity at elevated temperatures and the dynamic behaviour of core concrete under high temperatures was discovered. A simplified calculation method to determine the impact resistant capacity of CFT at elevated temperatures is presented, which is validated by the tested results.     

Thermal expansion of hydroxyapatite between − 100 °C and 50 °C

Hydroxy apatite (HAp) ceramic was synthesized using traditional sintering. Dilatometric and lattice thermal expansion properties of a HAp ceramic were evaluated at temperatures of ? 100–50 °C. In that temperature range, the dilatometric thermal expansion coefficient and the lattice thermal expansion coefficient of the HAp ceramic were, respectively, 10.6 × 10^? 6/°C and 9.9 × 10^? 6/°C. Furthermore, thermal expansion properties of a human tooth were measured. The thermal expansion coefficient of the horizontal direction perpendicular to the growing direction of a tooth was 15.5 × 10^? 6/°C; that of the vertical direction along with the direction of tooth growth was 18.9 × 10^? 6/°C at the temperature range described above.     

Thermal stability of retained austenite in Cr–Ni weld metals at low temperatures

Abstract

As environmental temperature decreases, the amount of retained austenite is more likely to greatly reduce due to the thermal austenite–martensite transformation caused by the decreased thermal stability of retained austenite, probably making its amount lower than the required content. In the present study, the thermal stability of retained austenite in Cr–Ni weld metals was investigated to see whether sufficient retained austenite can be maintained at low temperatures. The specific experimental procedure is as follows: briefly, the samples were cooled in turn from room temperature to 0, ?20, ?40, ?60, ?80, ?100 and ?196°C; the amount of retained austenite at the above temperatures was measured using X-ray diffraction. Through investigating the dependence of the content of retained austenite on temperature, it was revealed that when the content of retained austenite is <20%, retained austenite can be maintained until ?196°C.     

Thermal stability up to 800?°C of a Ni–4?wt% Al nanocomposite

Abstract  

The thermal stability up to 800 °C of a nanocrystalline (NC) Ni (mean grain size ~25 nm) with ~4 wt% Al dispersed in the form of ~160-nm-sized particles, which was fabricated by co-electrodeposition from a nickel sulfate bath, has been investigated using differential scanning calorimetry (DSC), transmission electron microscopy (TEM) and X-ray diffraction (XRD). The results showed that microstructural evolution of the composite is temperature dependent, i.e., normal grain growth of the NC Ni, ~0.6 wt% Al solution into the Ni matrix and direct reaction between Al and Ni to form Ni₃Al precipitates occurred at ~290, ~325 and ~575 °C, respectively. The distribution of Al in Ni matrix with temperature is fully discussed.     

Mechanical properties of ultra-lightweight cement composite at low temperatures of 0 to −60 °C

This paper presents an experimental study on mechanical properties of an innovative ultra-lightweight cement composite (ULCC) at low temperatures down to −60 °C in comparison with those at ambient temperature. Those properties include stress-strain curve, ultimate strength, elastic modulus, Poisson ratio, and flexural tensile behavior. Effect of curing condition is also evaluated. In addition, the performance of the ULCC is compared with that of a normal weight concrete (NWC) and a lightweight concrete (LWC) with similar 28-day compressive strength. The cylindrical compressive strength of the NWC and LWC was increased generally with the reduction in temperature. However, the same phenomenon was not observed for the ULCC. The elastic modulus of the ULCC did not change much, whereas the elastic modulus of the NWC increased significantly with the reduction of temperature from 30 °C to −60 °C. Strain of the ULCC at the peak load was generally much higher than that of the NWC and LWC, and was generally not affected by the temperature. The flexural strength of the three concretes was increased with the reduction in temperature. Duration of the moist curing did not affect the performance of the ULCC under compression significantly, but influenced its flexural strength significantly.     

Measurement of linear thermal expansion coefficient of alkali-activated aluminosilicate composites up to 1000 °C

The effect of high temperatures up to 1000 °C on the length changes of two alkali-activated aluminosilicate composites, one of them with quartz sand aggregates, the second with electrical porcelain, is analyzed in the paper. The thermal strain vs. temperature functions of both materials are found to increase monotonically in the whole temperature range studied so that the thermal expansion mismatch (the gel undergoes thermal shrinkage, the aggregates expand with increasing temperature) results in positive values of the apparent linear thermal expansion coefficient. The composite material with electrical porcelain aggregates exhibits a more desired thermomechanical behavior which is a consequence of the better high-temperature thermal stability of electrical porcelain as compared to quartz. In a comparison with Portland-cement based composites, the linear thermal expansion coefficient of both studied aluminosilicates is substantially lower in the whole temperature range of 20–1000 °C.     

(AlCrTaTiZr)N/(AlCrTaTiZr)N0.7 bilayer structure of high resistance to the interdiffusion of Cu and Si at 900 °C

In this study, a multi-component (AlCrTaTiZr)N/(AlCrTaTiZr)N_0.7 bilayer structure of about 15 nm thick was developed as a diffusion barrier material for Cu interconnects. The as-deposited (AlCrTaTiZr)N_0.7 layer was characterized to be an amorphous structure, and the (AlCrTaTiZr)N layer was a nanocomposite structure. After annealing at a high temperature of 900 °C, the Si/(AlCrTaTiZr)N/(AlCrTaTiZr)N_0.7/Cu film stack structure with the bilayer diffusion barrier remained stable. Only a slight amount of Cu penetrated into the top (AlCrTaTiZr)N_0.7 layer. However, neither interdiffusion of Cu and Si through the (AlCrTaTiZr)N layer occurred, nor did any silicides form, indicating the excellent diffusion resistance of the bilayer structure.     

Solvothermal synthesis of graphene sheets at 300 °C

Graphene nanosheets (GS) had been solvothermally synthesized through reducing hexachloro-1,3-butadiene (C₄Cl₆) by metallic sodium (Na) in polyethylene glycol-600 (PEG-600) at 300 °C. Atomic force microscopy (AFM) and high-resolution transmission electron microscopy (HRTEM) investigations indicated that 1–3 graphite layers could be observed. The Raman spectrum showed that the peak of 2D band at 2693 cm^? 1 of GS had a smaller wave number and stronger intensity compared to the 2717 cm^? 1 of commercial graphitic flakes. Meanwhile, the I_D/I_G value of GS was 0.40 indicating a lower density of defects of GS. The possible reaction process was that C₄Cl₆ was dechlorinated by Na in the presence of PEG-600 to produce carbon framework, then these newly produced carbon framework would connect to each other to form the hexagonal network of graphene.     

Microstructural characterization of nitrided beta Ti–Mo alloys at 1400 °C

In this work, the two Ti₉₂Mo₈ and Ti₈₄Mo₁₆ alloy compositions were gas nitrided at 1400 °C. The microstructure and the chemical composition of the gas nitrided surfaces were investigated by scanning electron microscopy and by electron probe microanalysis. Two internal needle-like nitride precipitates, α-(Ti,N) and δ-TiN_0.3, were observed. Their crystallographic orientation relationships in the β matrix were determined by electron backscattering diffraction.     

Thermal diffusivity of zirconium–niobium alloys at high temperatures

Experimental results are presented on the temperature-concentration dependences of thermal diffusivity, specific electrical resistivity, and thermal conductivity of zirconium-niobium alloys at high temperatures.     

Thermal stability of Si–MCM-41 in gaseous atmosphere

The thermal stability of Si–MCM-41 in different atmosphere (air, O₂, NH₃, N₂, and Ar) has been investigated in the present work; as-synthesized Si–MCM-41 was heat-treated at 800–1030 °C for 6–12 h in the selected atmosphere. Based on absorption–desorption isotherms and low-angle XRD measurement of the treated samples, it was found that the thermal stability varied greatly in different atmosphere. As-synthesized Si–MCM-41 retained mesoporous structure up to 1010 °C in NH₃, N₂, and Ar environment, but in air and O₂ environment, the highest thermal stable temperature of mesoporous structure in Si–MCM-41 was no more than 900 °C.     

Virial coefficients of neon,argon, and krypton at temperatures up to 3000°k

The second and third virial coefficients are calculated for a (12–7, ) pair model potential. With their help the fourth virial coefficient is determined from the experimental p, , and T data. The limits of applicability of the equation of state obtained is indicated.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 52, No. 6, pp. 974–977, June, 1987.     

Density of copper-aluminum alloys at temperatures up to 1400°c determined by the gamma-ray technique

The absolute method of penetrating gamma radiation has been used to measure temperature dependence of density for the Cu-Al alloys, which contain 0 to 100 at % of one of the components, in the temperature range between room temperature and 1300–1400°C. Based on the experimental values of density, the parameters of the linear approximation of its temperature dependence have been calculated. These parameters have been used then to calculate values of density at certain values of temperature and to plot density isotherms. Density jumps at melting for the specimens have also been determined.     

Virial coefficients of methane,ethane, and propane at temperatures up to 1500°K

The second and third virial coefficients are calculated for the (12-7, ) model pair potential. With their help the fourth virial coefficient is determined from the experimental data for P, V, and T. The limit of applicability of the equation of state obtained is indicated.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 53, No. 4, pp. 589–593, October, 1987.     

Ultralow density carbon aerogels with low thermal conductivity up to 2000 °C

Ultralow density (0.052 g cm^?3) carbon aerogels (CAs) were prepared for ultrahigh temperature thermal insulation, and their thermal conductivities were determined by laser flash method. The CAs have a total thermal conductivity as low as 0.601 W m^?1 K^?1, which is only one third of the value for closed-pore carbon foam (CF) with a density of 0.054 g cm^?3, at 2000 °C under 0.15 MPa argon. The solid, gaseous, and radiative conductivities of the CA are all much lower than those of the CF, because of the special nanoporous and pearl-necklace nanoparticle structures of the CA. The ultralow density CA clearly demonstrates its great potentials as thermal insulations for extreme applications.     

Thermal diffusivity of Y–Ho system solid solutions at high temperatures

The experimental results on the thermal diffusivity of solid phase Y–Ho alloys at high temperatures are presented. The mechanisms of the energy career dispersion in these substances are considered.