Effect of sintering temperature on the elemental diffusion and electrical conductivity of SrTiO<Subscript>3</Subscript>/YSZ composite ceramic

The 50 vol% SrTiO₃/yttria-stabilized zirconia (YSZ) composite ceramic was prepared through powder sintering route in 1400～1500 °C. Only the cubic YSZ and SrTiO₃ phases are detected in all the sintered ceramics, and the typical XRD peak positions of both phases have varied dramatically. The grain sizes and relative densities of all specimens increase evidently with the sintering temperature. The width of the SrTiO₃/YSZ interfacial region increases from 100.4 to 468.8 nm as the sintering temperature rises from 1400 to 1500 °C. The total electrical conductivities of the sample sintered at 1500 °C are remarkably higher than those at 1400 and 1450 °C, while the ion transference numbers drop from 0.837 to 0.731 with sintering temperature from 1400 to 1500 °C. The variations in the electrical properties above can be interpreted based on the effects of sintering temperature on the elemental diffusions during the sintering process.     

Optimization of Paris–Edinburgh press cell assemblies for in situ monochromatic X-ray diffraction and X-ray absorption

We describe some important improvements allowed by the development of new cell assemblies coupled to opposed conical sintered diamond anvils in the Paris–Edinburgh press. We provide X-ray absorption and diffraction experiments carried out at pressures up to 16.5 GPa. The maximum temperature reached was 1800 K for P<10 GPa and 1300 K for higher pressures. The sintered diamond anvils are X-ray transparent and give access to a much larger X-ray window than the tungsten carbide anvils, even at the highest pressure. Therefore, X-ray measurements are performed using in situ cross-calibration simultaneously. We also describe a new heating setup used to reach high temperatures, despite the low conductivity of the sintered diamond core by deviating the electrical current using copper strips. These improvements are illustrated by recent data collected using angle dispersive in situ X-ray diffraction on liquid Fe-18%wt S and using EXAFS at the barium K-edge on Ba₈Si₄₆ silicon clathrates and at the iodine K-edge on iodine-intercalated nanotubes.     

Low-temperature sintering effects on NASICON-structured LiSn<Subscript>2</Subscript>P<Subscript>3</Subscript>O<Subscript>12</Subscript> solid electrolytes prepared via citric acid-assisted sol-gel method

LiSn₂P₃O₁₂ with sodium (Na) super ionic conductor (NASICON)-type rhombohedral structure was successfully obtained at low sintering temperature, 600 °C via citric acid-assisted sol-gel method. However, when the sintering temperature increased to 650 °C, triclinic structure coexisted with the rhombohedral structure as confirmed by X-ray diffraction analysis. Conductivity–temperature dependence of all samples were studied using impedance spectroscopy in the temperature range 30 to 500 °C, and bulk, grain boundary and total conductivity increased as the temperature increased. The highest bulk conductivity found was 3.64?×?10^?5 S/cm at 500 °C for LiSn₂P₃O₁₂ sample sintered at 650 °C, and the lowest bulk activation energy at low temperature was 0.008 eV, showing that sintering temperature affect the conductivity value. The voltage stability window for LiSn₂P₃O₁₂ sample sintered at 600 °C at ambient temperature was up to 4.4 V. These results indicated the suitability of the LiSn₂P₃O₁₂ to be exploiting further for potential applications as solid electrolytes in electrochemical devices.     

Semiconductor diamond heater in the Kawai multianvil apparatus: an innovation to generate the lower mantle geotherm

Semiconductor diamond is considered the best heater material to generate ultra-high temperatures in a Kawai cell. In two pioneering studies, a mixture of graphite and amorphous boron (or boron carbide, B₄C) was converted to semiconductor diamond in the diamond stability field and was confirmed to generate 2000°C and 3500°C, respectively. Following these works, we synthesized a homemade boron-doped graphite block with fine machinability. With this technical breakthrough, we developed a semiconductor diamond heater in a smaller Kawai-type cell assembly. Here, we report the procedure for making machinable boron-doped graphite, and the performance of the material as a heater in a Kawai cell at 15?GPa using tungsten carbide anvils and at ～50?GPa using sintered diamond anvils. Furthermore, we present a finite element simulation of the temperature distribution generated by a semiconductor diamond heater, which is much more homogeneous than that generated by a metal heater.     

X-ray study of SnO2 under high pressure and temperature generated with sintered diamond anvils

Abstract

In-situ X-ray diffraction technique using synchrotron radiation was applied for polymorphic transitions in SnO₂ under high pressure and temperature generated with 6–8 type double-stage multianvils made of sintered diamond. At 23.6 GPa, the mixed phases of rutile-type structure (R-SnO₂) and columbite-type (c-SnO₂) were heated: at 700°C peaks of fluorite-type structure (F-SnO₂) began to appear, and at 1000°C, C-SnO₂ and 5m later R-SnO₂ disappeared completely and a single phase of F-SnO₂ was recognized, indicating a direct transition from R-SnO₂ to F-SnO₂. The volume reduction of 5.3% was obtained for C-SnO₂→F-SnO₂ transition.     

A combination of a Drickamer anvil apparatus and monochromatic X‐rays for stress and strain measurements under high pressure

A modified Drickamer anvil apparatus has been developed to combine with monochromatic synchrotron radiation for high‐pressure X‐ray diffraction and radiography in the GSECARS bending‐magnet station, 13‐BM‐D, at the Advanced Photon Source, Argonne, USA. Using this experimental set‐up, deformation experiments can be carried out at pressures in excess of 30 GPa at high temperatures. Differential stresses and total axial strains of polycrystalline platinum and Mg₂SiO₄ ringwoodite have been measured up to 32 GPa at room temperature using tungsten carbide anvils. The total axial strain of the platinum increases with pressure and reaches about 55% at the highest pressure. A test run using a composite sintered diamond anvil system was performed. The use of X‐ray‐tranparent anvils enables the entire Debye rings to be observed up to 10° 2θ. With high‐energy photons (65–70 keV), this allows a coverage in Q (= 2π sinθ/λ) to about 3 Å^?1, thus making it possible to evaluate hydrostatic pressure and differential stress in crystalline minerals using diffraction. This, coupled with the ability to determine axial strain, allows deformation studies to be performed to pressures above 30 GPa.     

Effect of pH and high pressure at sub-zero temperature on the viability of some bacteria

The objective of this study was to investigate the viability of Escherichia coli and Staphylococcus aureus in apple juice after treatment with high pressure at sub-zero temperature and during subsequent storage at 5 and 20 °C. The viability of E. coli and S. aureus cells suspended in the apple juice with a pH of 3.8 did not decrease considerably after pressure treatment at 193 MPa and?20 °C. However, viability losses occurred during storage of samples after pressure treatment. Living cells of both strains were not detected in pressurized samples of apple juice stored for 10 days at 20°C. The lethal effect was lower when the samples after pressure treatment were incubated at refrigerated temperature; the number of E. coli and S. aureus decreased by 6 log cycles when the juice was stored for 10 days at 5 °C.     

Dielectric anomalous response of water at 60 °C

Recently, the paraelectric response of water was investigated in the range 0–100 °C. It showed an almost perfect Curie–Weiss behaviour up to 60 °C, but a slight change in slope of 1/ε_d versus T at 60 °C was overlooked. In this work, we report optical extinction measurements on metallic (gold and silver) nanoparticles dispersed in water, annealed at various temperatures in the range from 20 to 90 °C. An anomalous response at 60 °C is clearly detectable, which we associate to a subtle structural transformation in the water molecules at that temperature. This water anomaly is also manifested by means of a blue shift in the longitudinal surface plasmon resonance of the metallic nanoparticles for the solutions annealed at temperatures higher than about 60 °C. A reanalysis of 1/ε_d (T) for water in the whole temperature range leads us to conclude that the water molecule undergoes a subtle transformation from a low temperature (0–60 °C) configuration with a dipole moment μ₁ = 2.18 D (close to the molecular dipole moment of ice) to a high temperature (60–100 °C) configuration with μ₂ = 1.87 D (identical to the molecular dipole moment in water vapour).     

Moderate hydrostatic pressure–temperature combinations for inactivation of Bacillus subtilis spores

We report the effect of using moderate hydrostatic pressure, 40–140?MPa, at moderate temperature (38–58°C) to inactivate Bacillus subtilis spores in McIlvaine's citric phosphate buffer at pH 6. We have investigated several parameters: pressure applied, holding time, pressure cycling, and temperature. The kinetics of spore inactivation is reported. The results show that spore inactivation is exponentially proportional to the time the sample is exposed to pressure. Spore germination and inactivation occur at the hydrostatic pressures/temperature combinations we explored. Cycling the pressure while keeping the total time at high pressure constant does not significantly increase spore inactivation. We show that temperature increases spore inactivation at two different rates; a slow rate below 33°C, and at a more rapid rate at higher temperatures. Increasing pressure leads to an increase in spore inactivation below 95?MPa; however, further increases in pressure give a similar rate kill. The time dependence of the effect of pressure is consistent with the first-order model (R²?>?0.9). The thermal resistance values (Z_T) of B. subtilis spores are 30°C, 37°C, and 40°C at 60, 80, 100?MPa. The increase in Z_T value at higher pressures indicates lower temperature sensitivity. The pressure resistance values (Z_P) are 125, 125 and 143?MPa at 38°C, 48°C, and 58°C. These Z_P values are lower than those reported for B. subtilis spores in the literature, which indicates higher sensitivity at pressures less than about 140?MPa. We show that at temperatures <60°C, B. subtilis spores are inactivated at pressures below 100?MPa. This finding could have implications for the design of the sterilization equipment.     

Preparation of PEO ceramic coating on Ti alloy and its high temperature oxidation resistance

Ceramic coatings were prepared in Na₂SiO₃–Na₂CO₃–NaOH system by pulsed bi-polar plasma electrolytic oxidation on Ti–6Al–4V alloy. The phase composition, structure and the elemental distribution of the coatings were studied by XRD, SEM and energy dispersive spectroscopy, respectively. The thermal shock resistance of the coated samples at 850 °C was evaluated by the thermal shock tests. The high temperature oxidation resistance of the coating samples at 500 °C was investigated. The results showed that the coating was mainly composed of rutile- and anatase TiO₂, Increasing the concentration of Na₂SiO₃, TiO₂ content decreased gradually while the thickness of the coating increased. There were a large amount of micro pores and sintered particles on the surface of the coatings. Increasing concentration of Na₂SiO₃, the sintered particles on the surface turned large, and the Si content increased while the Ti content decreased gradually. When the concentration of Na₂SiO₃ was 15 g/L, the thermal shock resistance of the coatings was better than that of the coatings that prepared under other Na₂SiO₃ concentrations. The coating samples prepared under the optimized technique process based on the thermal shock tests improved the high temperature oxidation resistance at 500 °C greatly, whether considering the isothermal oxidation or the cyclic oxidation.     

Fracture toughness evaluation of WC–10 wt% Co hardmetal sintered under high pressure and high temperature

This work focused on fracture toughness studies of WC–10?wt% Co hardmetal fabricated through the high pressure/high-temperature technique. A powder mixture of WC–10?wt% Co was sintered at 1500–1900°C under a pressure of 7.7?GPa for 2 and 3?min. Vickers hardness test at two different loads of 15 and 30?kgf was done and fracture toughness of the sintered bodies was measured using the indentation method to obtain the effect of sintering parameters. Structural analyses were also performed via X-ray diffraction to investigate structure-related properties. Full density was achieved for high sintering temperature along with abnormal grain growth that reduced hardness. High hardness was observed ranging from 1200 to 1670?HV and fracture toughness increased with increasing sintering temperature up to the highest value of 17.85?MPa/m^1/2.     

High pressure studies on hesperitin production with hesperidinase free and immobilized in calcium alginate beads

The use of high pressure for the enzymatic synthesis of pharmacologically interesting molecules is a very important tool. Hesperidin and hesperitin exhibit anti-inflammatory, antimicrobial, antioxidant, and anticarcinogenic properties and prevent bone loss. However, hesperidin has a low bioavailability compared with hesperitin, due to the rutinoside moiety attached to the flavonoid. The aim of this work was the enzymatic production of hesperitin from hesperidin (soluble and insoluble) with hesperidinase free and immobilized in Ca-alginate beads, under high pressure conditions. The work was focused on the optimization of enzyme activity, studying the effects: pressure (50–150 MPa), temperature (35–75 °C), concentration of substrate (100–800 mg/L), and immobilization of hesperidinase. An 18-fold increase in hesperidinase residual activity was observed under high pressure conditions of 100 MPa compared to 0.1 MPa. A higher specificity of the hydrolytic reaction under high pressure (100 MPa) with a two-and three-fold increase in the ratio K _cat/K _M (specificity constant) at 55 °C and 75 °C was observed. A two-fold increase in the maximum activity at 100 MPa was observed with immobilized hesperinase compared to 0.1 MPa. In the second reutilization, almost a four-fold increase was obtained under high pressure conditions in comparison to atmospheric pressure.     

Effects of deposition temperature and hydrogen flow rate on the properties of the Al-doped ZnO thin films and amorphous silicon thin-film solar cells

A compound of 98 mol% ZnO and 1 mol% Al₂O₃ (AZO, Al:Zn = 98:2) was sintered at 1350 °C as a target and the AZO thin films were deposited on glass using a radio frequency magnetron sputtering system. The effects of deposition temperature (from room temperature to ～300 °C) on the optical transmission spectrum of the AZO thin films were studied. The Burstein–Moss shift was observed and used to prove that defects in the AZO thin films decreased with increasing deposition temperature. The variations in the optical band gap (E _g) values of the AZO thin films were evaluated from plots of (αhv)²=c(hν?E _g), revealing that the measured E _g values increased with increasing deposition temperature. The effects of the H₂ flow rate during deposition (0 %～11.76 %, deposition temperature of 200 °C) on the crystallization, morphology, resistivity, carrier concentration, carrier mobility, and optical transmission spectrum of the AZO thin films were measured. The chemical structures of the Ar-deposited and 2 % H₂-flow rate-deposited AZO thin films (both were deposited at 200 °C) were investigated by XPS to clarify the mechanism of improvement in resistivity. The prepared AZO thin films were also used as transparent electrodes to fabricate amorphous silicon thin-film solar cells, and their properties were also measured.     

Synthesis and characterization of in situ nanocrystalline intermetallic phase reinforced AlTiSi amorphous matrix composite

Composites with partially amorphous matrix were synthesized by mechanical alloying of an Al₅₀Ti₄₀Si₁₀ elemental powder blend in a high energy planetary ball-mill, followed by high pressure (8 GPa) low temperature (350–450°C) sintering. Microstructural studies and compositional micro-analysis were carried out using scanning and transmission electron microscopy, and energy dispersive spectroscopy, respectively. Phase evolution as a function of milling time and isothermal temperature and their thermal stability was determined by X-ray diffraction at room or elevated temperature and differential scanning calorimetry, respectively. The microstructure of composites sintered between room temperature and 450°C showed nano-size (≈50 nm) crystalline precipitates of Al₃Ti dispersed in an amorphous matrix. The composites sintered at 400°C with 8 GPa pressure exhibited the highest density (3.58 Mg/m³), nanoindentation hardness (8.8 GPa), Young's modulus (158 GPa) and compressive strength (1940 MPa). A lower hardness and modulus on sintering at 450°C is attributed to additional amorphous to nanocrystalline phase transformation and partial coarsening of Al₃Ti.     

Nano-polycrystalline diamond synthesized through the decomposition of stearic acid

ABSTRACT

Here we report a novel route for synthesizing nano-polycrystalline diamond (NPD) using stearic acid (C₁₈H₃₆O₂) as a starting material under high pressure and high temperature. The obtained NPD shows a transparent dark-yellowish color similar to the standard NPD synthesized from graphite and consists of extremely fine diamond grains (～10?nm). The temperature required for the present synthesis of pure transparent NPD is as low as 1000°C at 13 and 17?GPa, which is surprisingly lower than that for conventional NPD synthesis (1800–2000°C). The amorphous-like, extremely poorly crystalline graphite produced by the thermal decomposition of stearic acid likely provides preferential nucleation sites for diamond and significantly lower the activation energy. The removal of volatile components such as H₂O generated through the decomposition from the system is a key to obtain pore-free transparent NPD. Magnesite, MgCO₃ and periclase, MgO can be used as an efficient H₂O remover through the hydration reaction.     

Calibration of berlinite (AlPO4) as Raman spectroscopic pressure sensor for diamond‐anvil cell experiments at elevated temperatures

Changes in the band position of the 462 and the 1111 cm^–1 A₁ modes of berlinite (AlPO₄) with temperature and pressure were determined in situ to 500°C and to 10 GPa using Raman spectroscopy and diamond‐anvil cells. These bands shift in opposite directions with pressure and, likewise, with temperature. At a known temperature, the relative difference of both band positions (Δν)_P,T can therefore be used as a pressure gauge that does not require calibration of the spectrometer. At ambient pressure, the observed temperature dependence of this relative difference of the line positions is very close to linear and can be described by (Δν)_{T, 0.1 MPa} (cm^–1) = 0.0181 T – 0.46 where 23 ≤ T (°C) ≤ 500. Along the 23°C isotherm to 10 GPa, pressure and relative wavenumber difference (Δν)_{P, 23°C} are related by the equation P (GPa) = 0.00083 [(Δν)_{P, 23°C}]² – 0.062 (Δν)_{P, 23°C}. Both equations can be combined to determine pressures at higher temperatures under the assumption that the change in (Δν)_P,T with pressure is insensitive to temperature. Copyright © 2011 John Wiley & Sons, Ltd.     

The baddeleyite-type high pressure phase of Ca(OH)2

Abstract

A phase transition from Ca(OH)₂ I (portlandite) to Ca(OH)₂ II at high pressure and temperature has been confirmed, using in situ x-ray diffraction in a multianvil high pressure device (DIA). The structure was determined at 9.5 GPa and room temperature from data collected after heating the sample at 300°C at 7.2 GPa in a diamond anvil cell. Both the Le Bail fit and preliminary Rietveld refinement suggest that the new phase, which reverts to Ca(OH), I during pressure release, has a structure related to that of baddeleyite (ZrO₁); it is monoclinic (P2₁/c) with a= 4.887(2), b= 5.834(2), c = 5.587(2), β = 99.74(2)°. The coordination number of Ca increases from six to seven (5 + 2) across the transition. At 500°C, the phase boundary is bracketed at 5.7 ± 0.4 GPa by reversal experiments performed in the DIA.     

Autoadhesion of High‐Molecular‐Weight Monodisperse Glassy Polystyrene at Unexpectedly Low Temperatures

Abstract

Healing of symmetric interfaces of amorphous anionically polymerized high‐ and ultrahigh‐molecular weight (HMW and UHMW, respectively) polystyrene (PS) in a range of the weight‐average molecular weight M _w from 102.5 (M _w/M _n = 1.05) to 1110 kg/mol (M _w/M _n = 1.15) was followed at a constant healing temperature, T _h, well below the glass transition temperature of the polymer bulk [T _g‐bulk = 105–106°C as measured by differential scanning calorimeter (DSC)]. The bonded interfaces were shear fractured in tension on an Instron tester at ambient temperature. Autoadhesion at symmetric HMW PS–HMW PS and UHMW PS–UHMW PS interfaces was detected mechanically after healing at T _h = 38°C for 107 hr, and even at 24°C (for longer healing times). The occurrence of autoadhesion between the surfaces of the UHMW PS with M _w = 1110 kg/mol at 24°C implies that the glass transition temperature at the interface, T _{g‐interface}, of this polymer was a least lower: by 82°C than its DSC T _g‐bulk, by 30–40°C than the Vogel temperature, T _∞—the lowest theoretical value of a kinetic T _g‐bulk at infinite long time—and by 20°C than T ₂ (a “true” thermodynamic T _g‐bulk corresponding to a second‐order phase transition temperature). To our knowledge, this is the first observation of such nature, which gives further evidence of the lowering of the T _g at polymeric surfaces and the persistence of this effect at early stages of healing of polymer–polymer interfaces.     

Raman study of datolite CaBSiO4(OH) at simultaneously high pressure and high temperature

Using an in situ method of Raman spectroscopy and resistance‐heated diamond anvil cell, the system datolite CaBSiO₄(OH) – water has been investigated at simultaneously high pressure and temperature (up to Р ~5 GPa and Т ~250 °С). Two polymorphic transitions have been observed: (1) pressure‐induced phase transition or the feature in pressure dependence of Raman band wavenumbers at P = 2 GPа and constant T = 22 °С and (2) heating‐induced phase transition at T ~90 °С and P ~5 GPа. The number of Raman bands is retained at the first transition but changed at the second transition. The first transition is mainly distinguished by the changes in the slopes of pressure dependence of Raman peaks at 2 GPa. The second transition is characterized by several strong changes: the wavenumber jumps of major bands, the merging of strong doublets at 378 and 391 cm⁻¹ (values for ambient conditions), the splitting of the intermediate‐intensity band at 292 cm⁻¹, and the transformation of some low‐wavenumber bands at 160–190 cm⁻¹. No spectral and visual signs of overhydration and amorphization have been observed. No noticeable dissolution of datolite in the water medium occurred at 5 GPa and 250 °С after 3 h, which corresponds to typical conditions of the ‘cold’ zones of slab subduction. Copyright © 2014 John Wiley & Sons, Ltd.     

The room-temperature ferromagnetism of defect-rich ZnMgO semiconductor thin films

The positive temperature coefficient of resistance (PTCR) characteristics of Na₂Ti₆O₁₃ (NT)-doped 0.94BaTiO₃–0.06(Bi_0.5Na_0.5)TiO₃ (BBNT) ceramics were investigated in order to evaluate the effect of NT as a new additive for lead-free PTCR thermistor application. The BBNT ceramic sintered at 1325°C exhibited a relatively high Curie temperature (T _C ) of 158°C while its PTCR characteristic was not satisfactory for thermistor application. However, doping with NT significantly influenced the PTCR behavior of BBNT ceramic. It is considered that NT was responsible for grain growth of the BBNT by forming a liquid phase during sintering due to its low melting temperature of 1300°C. The grain growth resulted in the enhanced PTCR characteristics of BBNT ceramic. In particular, 0.1 mol% NT doped BBNT ceramic exhibited excellent PTCR performance of low resistivity at room temperature (1.6×10² Ω cm), resistivity increase near T _C (1.28×10⁴) and high T _C of 158°C, suitable for lead-free PTCR thermistor application.