Accelerated transformation of brushite to octacalcium phosphate in new biomineralization media between 36.5 °C and 80 °C

This study investigated the hydrothermal transformation of brushite (dicalcium phosphate dihydrate, DCPD, CaHPO₄·2H₂O) into octacalcium phosphate (OCP, Ca₈(HPO₄)₂(PO₄)₄·5H₂O) in seven different newly developed biomineralization media, all inspired from the commercial DMEM solutions, over the temperature range of 36.5 °C to 90 °C with aging times varying between 1 h and 6 days. DCPD powders used in this study were synthesized in our laboratory by using a wet-chemical technique. DCPD was found to transform into OCP in the Ca²⁺, Mg²⁺, Na⁺, K⁺, HCO₃^?, Cl^? and H₂PO₄^? containing aqueous biomineralization media in less than 72 h at 36.5 °C, without stirring. The same medium was able to convert DCPD into OCP in about 2 h at 75–80 °C, again without a need for stirring. Samples were characterized by using powder X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), and scanning electron microscopy (SEM).     

Behavior and failure of uniformly hydrided Zircaloy-4 fuel claddings between 25 °C and 480 °C under various stress states,including RIA loading conditions

The anisotropic plastic behavior and the fracture of as-received and hydrided Cold-Worked Stress Relieved Zircaloy-4 cladding tubes are investigated under thermal–mechanical loading conditions representative of Pellet–Clad Mechanical Interaction during Reactivity Initiated Accidents in Pressurized Water Reactors. In order to study the combined effects of temperature, hydrogen content, loading direction and stress state, Axial Tensile, Hoop Tensile, Expansion Due to Compression and hoop Plane Strain Tensile tests are performed at room temperature, 350 °C and 480 °C on the material containing various hydrogen contents up to 1200 wt. ppm (hydrides are circumferential and homogeneously distributed). These tests are combined with digital image correlation and metallographic and fractographic observations at different scales. The flow stress of the material decreases with increasing temperature. The material is either strengthened or softened by hydrogen depending on temperature and hydrogen content. Plastic anisotropy depends on temperature but not on hydrogen content. The ductility of the material decreases with increasing hydrogen content at room temperature due to damage nucleation by hydride cracking. The plastic strain that leads to hydride fracture at room temperature decreases with increasing hydrogen content. The influence of stress triaxiality on hydride cracking is negligible in the studied range. The influence of hydrogen on material ductility is negligible at 350 °C and 480 °C since hydrides do not crack at these temperatures. The ductility of the material increases with increasing temperature. The evolution of material ductility is associated with a change in both the macroscopic fracture mode of the specimens and the microscopic failure mechanisms.     

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.     

Crystal structure and thermal expansion of LaCr1−xMgxO3, 0 < x ≤ 0.25

Solid solution LaCr_1?xMg_xO₃, 0 < х ≤ 0.25 was prepared by heating stoichiometric amounts of appropriate oxides in air at 1400 °C, 48 h. At room temperature it crystallizes in orthorhombically distorted GdFeO₃-type structure (a ≈ √2 × a_per; b ≈ √2 × a_pe; c ≈ 2 × a_per, where a_per – perovskite subcell parameter). High-temperature X-ray powder diffraction (HT XRPD) and dilatometry revealed first order phase transition to rhombohedral perovskite phase (R-3c, a ≈ √2 × a_per, c ≈ 2√3 × a_per) at 260–311 °C (OR phase transition). Crystal structures of room-temperature orthorhombic and high-temperature rhombohedral phases for LaCr_0.75Mg_0.25O₃ were refined using HT XRPD data. Temperature of OR phase transition increases gradually with increasing of magnesium content. Low-temperature orthorhombic phase exhibits TEC lower in comparison with high-temperature rhombohedral one (e.g. for LaCr_0.85Mg_0.15O₃ TEC(O) = 8.8 ppm K^?1; TEC(R) = 11.6 ppm K^?1). TEC for rhombohedral phase increases with increasing magnesium content from 10.4 ppm K^?1 for LaCr_0.95Mg_0.05O₃ to 12.1 ppm K^?1 for LaCr_0.75Mg_0.25O₃.     

Organic-inorganic interaction and the growth mechanism of hydroxyapatite crystals in gelatin matrices between 37 and 80 °C

The crystal development of hydroxyapatite[HAp] phase in gelatin[GEL] matrices was investigated in the temperature range 37 to 80 °C by using X-ray diffraction, scanning electron microscopy(SEM), thermoanalytical measurement(DT/TGA), Fourier-Transformed Infra-Red(FT-IR) spectroscopy, and transmission electron microscopy(TEM) with electron diffraction(ED). It was found that during the coprecipitation of apatite phase in GEL matrices and the next aging process the crystallites were formed and developed through the two reaction mechanisms of organic-inorganic interaction between apatite phase and GEL molecules, and thermodynamic reaction for the crystal growing. The analytical evidences showed that there was a definite competition between these two mechanisms with the reaction temperature. Below 50 °C the crystal development of HAp was greatly suppressed by the existence of the GEL molecules, indicating the heterogeneous nucleation by the supposed number of carboxyl groups in GEL. Above 50 °C the effective organic components as a template for the heterogeneous nucleation of apatite crystallites were greatly degraded and so more amount of inorganic ions could be favorably accredited on the preexisting crystallites in virtue of the limited nucleation chance, finally resulting in the crystal growth. At higher temperature pretty big HAp crystals were developed with the depletion of the organics to be bound with crystallites in the slurry solution. Presumably it is believed that the poisoning of the functional groups in GEL molecules was vigorously occurred in the phosphoric acid environment above ∼ 50 °C.     

Electronic structure of Cu100−xZrx (x = 40, 50, 60) metallic glasses

The electronic structure of Cu_100−xZr_x (x = 40, 50, 60) metallic glasses was investigated by ultraviolet photoelectron spectroscopy and X-ray photoemission spectroscopy, the valence band spectra of these alloys were analyzed by a large shift of the Cu d-band peaks to higher binding energies upon increasing Cu content. Photoemission experiments and first-principles calculations prove that the values of density of states at Fermi level of Cu_100−xZr_x metallic glasses are mainly dominated by Zr rather than Cu. This work will enlighten further research on understanding the inheritance of metallic glasses and designing new metallic glasses with unique properties.     

Performance of R170 mixtures as refrigerants for refrigeration at −80 °C temperature range

The refrigeration performance parameters of two binary azeotropic mixtures of R170 + R23 and R170 + R116 and a ternary azeotropic mixture of R170 + R23 + R116 were measured systematically in the low-stage loop of a two-stage cascade system. In addition, the performance of the currently used R508B refrigerant was also measured at similar conditions for comparison. A two-stage cascade refrigeration testing apparatus was designed and assembled, in which an R404A system was used as the high-temperature refrigeration stage. Thermodynamic performance parameters of the low-stage loop such as the coefficient of performance (COP), cooling capacity, and the discharge temperature of these four mixtures were measured at various condensation and evaporating temperatures. The results show that the COP of the R170 + R116 binary mixture is up to 10% higher than that of R508B. These mixtures show good potential as low-temperature stage refrigerants for applications in the ?80 °C temperature range.     

The effects of superchilled storage at −2 °C on the microbiological and organoleptic properties of cold-smoked salmon before retail display

The aim of this study was to investigate the impact of superchilling (?2 °C) on the evolution of Listeria monocytogenes and organoleptic characteristics of cold-smoked salmon samples. An Hadamard matrix experimental design was carried out on artificially inoculated samples stored at +4 °C for 10 d and at +8 °C for 18 d to know the influence of four factors: salt content, strain, cold stiffening and superchilling time, on the level of L.monocytogenes in cold-smoked salmon. The growth of L. monocytogenes in naturally contaminated cold-smoked salmon and the organoleptic properties were investigated under superchilling conditions.Superchilling (?2 °C for 28 d) had a limited impact on some of the organoleptic properties but the level of L. monocytogenes at the end of the shelf-life (4 °C for 10 d and 8 °C for 18 d) could exceed the microbiological criterion set by the European legislation.     

Thermal stability of magnetron sputtered Si–B–C–N materials at temperatures up to 1700 °C

Thermal stability of deposited Si–B–C–N materials (film fragments or powders without a substrate) in inert gases (He and Ar) up to 1700 °C was investigated using differential scanning calorimetry, high-resolution thermogravimetry and X-ray diffraction measurements. Amorphous Si–B–C–N films were fabricated by dc magnetron co-sputtering of a single B₄C–Si target in two nitrogen–argon gas mixtures (50% N₂ + 50% Ar or 25% N₂ + 75% Ar). It was found that the deposited Si–B–C–N materials can be more stable at high temperatures in the inert atmosphere than the usually used substrates (e.g. SiC or BN). The materials with the compositions (in at.%) Si_32–33B₁₀C₂N_50–51, for which N/(Si + B + C) = 1.1–1.2, retained their amorphous structure up to 1600 °C without any structural transformations and detectable mass changes.     

Measuring spectral transmission and refractive index of AgCl1−xBrx (0 ⩽ x ⩽ 1) and Ag1−xTlxBr1−xIx (0 ⩽ x ⩽ 0.05) at the wavelength of 10.6 μm

We measured the complex refractive index at the wavelength of 10.6 μm with the help of Fourier transform infrared spectroscopy for polycrystalline plates of the following compositions AgCl_1−xBr_x (0 ⩽ x ⩽ 1) and Ag_1−xTl_xBr_1−xI_x, where x varied from 0 to 0.05. In order to do it we chose a segment of the spectrum, which was recorded with a high resolution (0.5 cm⁻¹) using the HgCdTe detector and which had a set of 10 identical peaks. It is shown that the real part of the refractive index rises along with increasing the substituting component fraction in the solid solution from 1.99 to 2.17 for AgCl_1−xBr_x and from 2.17 to 2.24 within the range of TlI mole fraction up to 0.05 for Ag_1−xTl_xBr_1−xI_x. We considered errors introduced by the spectrometer resolution and the accuracy rating of the micrometer, which was used to measure sample thickness. It is seen in the spectra, recorded for the second system with a lower resolution and using a deuterated and l-alanine doped triglycine sulfate detector, that increasing the thallium monoiodide fraction results in widening the transmission range towards bigger wavelengths. We also plan to use the obtained refractive index values for simulating mid-infrared optical fibers, the polycrystalline structure of which is close to the structure of the plates under investigation.     

Cold sintering of magnetic BaFe12O19 and other ferrites at 300 °C

Densifying ZnFe₂O₄ and BaFe₁₂O₁₉ at 300 °C to values greater than 90% of theoretical is demonstrated via hydroflux-assisted densification (HAD), a derivative of the cold sintering process employing non-aqueous, flux-based mass transport phases to facilitate particle consolidation. Previous attempts to cold sinter these materials with aqueous-based mass transport phases were not as successful with final densities?<?90%. Attempts to densify NiFe₂O₄ and (Ni_0.5Zn_0.5)Fe₂O₄ only achieved densities around 80%, indicating an alternative transport phase may be needed to achieve high densities in Ni-containing materials. Magnetic hysteresis measurements of the low-temperature densified BaFe₁₂O₁₉ samples produced magnetic saturation values as high as 93 emu/g and coercive fields as high as 1789 Oe, which are comparable to values reported in the literature for this material produced via other processing techniques. Additional techniques are suggested to further optimize the magnetic properties of BaFe₁₂O₁₉ densified following the HAD approach.

     

The isothermal section of the Al-Si-B ternary system at 700 °C and its applications

The isothermal section of the Al−Si−B ternary system at 700 °C has been calculated using FactSage software and experimentally determined using scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and x-ray powder diffraction(XRD). The calculated results show that there are six three-phase regions in the isothermal section: Liquid-Al+AlB₂+(Si), AlB₂+AlB₁₂+(Si), (Si)+AlB₁₂+SiB₃, AlB₁₂+SiB₃+SiB₆, AlB₁₂+SiB₆+SiB₁₄, AlB₁₂+SiB₁₄+(B). Four three-phase regions of Liquid-Al+AlB₂+(Si), AlB₂+AlB₁₂+(Si), (Si)+AlB₁₂+SiB₃ and AlB₁₂+SiB_n+(B) were confirmed experimentally, which are consistent with calculated results. The small AlB₂ particles in the Al-3B alloy have good refining effect on the primary α-Al phase in the Al-10Si alloy, which greatly refines the microstructure and improves the mechanical properties of the Al-10Si alloy.     

Compressive deformation of an Mg-Al-Si-RE alloy between 120 and 180 °C

The deformation behaviour of an Mg-Al-Si-RE (ASE210) alloy between 120 and 180 °C was investigated by means of uniaxial compression tests to identify possible differences in the deformation response compared with uniaxial tensile data. Early fracture was observed in the low-temperature/high strain rate regime, fracture occurring by crack propagation at 45° with respect to the compression axis. In the high-temperature/low strain rate regime, the flow curves exhibited the typical shape that is usually observed in materials where deformation is controlled by recovery of substructure. The peak flow stresses obtained in this regime of temperature and strain rate were compared with other data obtained by testing the same alloy in tension. The strength of the alloy was found to be slightly greater in compression than in tension, this difference gradually disappearing as strain rate decreased.     

Pendent drop measurements of the polypropylene/polystyrene interfacial tension between 220°C and 270°C

The interfacial tensions of molten polypropylene/polystyrene have been measured using the pendent drop method between 220°C and 270°C. The obtained tension values are comparable with those of most of the molten polymer pairs, though their linear decrease as a function of temperature is steeper. The interaction parameter of Good and Girifalco lies within the range of values for all other polymer pairs.     

The effects of sintering atmosphere on the chemical compatibility of hydroxyapatite and particulate additives at 1200°C

According to Le Chatelier's principle, dehydration and the associated decomposition of hydroxyapatite (HAP) to biodegradable unhydrated calcium phosphates during sintering may be suppressed under a moist sintering atmosphere (thermodynamic effect), or possibly under a pressurized sintering atmosphere (physical effect), by opposing the release of water. The present study explored this possibility. High-purity powdered additives were used to minimize impurity and morphological effects. Al₂O₃, C, SiC, SiO₂, ZrO₂, and 316L stainless steel were all trialled at an addition level of 20 vol%. Heat treatment was at 1200°C for 1 h under two experimental atmospheres and two corresponding control atmospheres: flowing H₂O/O₂ mix—ambient air as a control; pressurized (1 MPa) argon—ambient argon (0.1 MPa) as a control. Specimens were analysed for decomposition by X-ray diffraction (XRD), for densification by porosity measurement, and for microstructural uniformity by energy dispersive spectroscopy (EDS) and image analysis. Significant decomposition occurred under all atmospheres with the exception of flowing H₂O/O₂ which eliminated decomposition in the HAP-Al₂O₃, HAP-ZrO₂, and HAP-316L systems, and reduced the decomposition levels from near completion to 50% in the HAP-SiC and HAP-SiO₂ systems. Moistureless pressurization had little effect. Microstructural uniformity was confirmed. No generalized atmosphere-densification interrelationships were observed.     

Fatigue-creep interaction performance of Incoloy 825 nickel-based superalloy at 650 °C

The fatigue-creep interaction performance of Incoloy 825 nickel-based superalloy at 650 °C was investigated through introducing the tensile, compressive, and tensile-compressive strain hold time at the controlled total strain amplitude Δϵ_t = 0.3 %∼0.7 %. The results show that the Incoloy 825 nickel-based superalloy exhibits the cyclic hardening behavior, the cyclic hardening behavior followed by cyclic softening behavior and the cyclic hardening behavior followed by cyclic stability during the cyclic deformation with tensile strain hold time, while the alloy exhibits the cyclic hardening behavior and the cyclic hardening behavior followed by the cyclic stability during the cyclic deformation with compressive and tensile-compressive strain hold time. The relationship between both plastic and elastic strain amplitudes with reversals to failure for the alloy shows a single slope linear behavior, which can be described by the Coffin-Manson and Basquin equations, respectively. The deformation mechanism of the alloy under three loading condition of fatigue-creep interaction is mainly the planar slip. In addition, under three loading condition of fatigue-creep interaction, the cracks initiate and propagate in the transgranular mode.     

Oxidation kinetics of zirconium in water vapour between 750 and 1250°C

The zirconium oxidation has been followed in H₂/H₂0 gas mixtures by microgravimetry and morphological observations between 750 and 1250°C. The reaction rate is governed by a mixed regime of oxygen diffusion through multiplex oxide layers of zirconia and an oxygen solid solution. After the metal core has disappeared the reaction proceeds by direct oxidation of the solid solution. Different kinetic behaviours have been shown according to the phase couples present.     

Extensometer probe indentation during low-cycle fatigue of plain and circumferentially notched cylindrical bars at 550 °C

Cyclic stress–strain tests were undertaken at 550 °C on (i) plain and (ii) notched specimens of different acuities in several low- and highly-alloyed ferritic steels (1CrMoV, NF616, TB12M and HCM12A). Axial strains were measured between the minimum sections of the (semi-circular) notches using a longitudinal extensometer, while surface hoop strains were measured by means of a diametral extensometer with probes located at the notch root. Over a period of 100 cycles, softening occurred in both specimen types. Cycle-by-cycle embedding was observed for the (diametral) probe tips and was entirely due to testpiece working in the cyclic state, the sprung-load extensometer force being far lower than that encountered in conventional indentation experiments. An interpretation of the effect is offered (a) in terms of the internal stress state produced during cycling and (b) by an energy argument to explain the ‘ranking order’ of resistance to penetration. The effects of cyclically-induced oxidation, possible mechanisms for the embedding effect and likely reduction in endurance are considered.