Effect of precompression on pressure-transmitting efficiency of pyrophyllite gaskets

Pyrophyllite is widely used both as a gasket material and as a pressure-transmitting medium, especially for a large-volume press. Its pressure-transmitting efficiency mainly depends on the following factors: geometry of anvil and pyrophyllite block, chemical composition, density and strength. For a long time, most studies have been devoted to the first two factors, whereas the third one has been studied less. In this work, we report that the pressure-transmitting efficiency of pyrophyllite is improved by precompressing. The results show that pyrophyllite was fully densified when the pressure reached about 1 GPa. The press load for Ba I–II transition in the cubic large-volume pressure cell is reduced more than 8×10⁵ N by using the densified pyrophyllite, compared with the unprecompressed pyrophyllite. Namely, the press-load utilization efficiency was improved above 15% when the precompressed pyrophyllite is used as a pressure-transmitting medium.     

A hybrid pressure cell of pyrophyllite and magnesium oxide to extend the pressure range for large volume cubic presses

A hybrid pressure cell of pyrophyllite and magnesium oxide (HPCPM) used in large volume cubic presses is presented. In the HPCPM, a cubic frame which is made of pyrophyllite with face-centered square holes works as gaskets, and a heteromorphosis magnesium oxide works as the pressure-transmitting medium. Our experimental results indicated that the pressure-generation efficiency using the HPCPM was improved by about 40% than that using the traditional pyrophyllite pressure cell without decreasing the anvil truncation size (without sacrificing the sample volume). The HPCPM could pressurize samples of 1000 mm³ volume up to about 8 GPa, which is significantly higher than that available using the traditional pressure cell, which reports a highest pressure of about 6 GPa.     

Electron impact ionisation cross sections of cis- and trans-diamminedichloridoplatinum(II) and its hydrolysis products

ABSTRACT

We report total electron-impact ionisation cross sections (EICSs) of cisplatin, its hydrolysis products and transplatin in the energy range from threshold to 10?keV using the binary-encounter-Bethe (BEB) and its relativistic variant (RBEB), and the Deutsch-Märk (DM) methods. We find reasonable agreement between all three methods, and we also note that the RBEB and the BEB methods yield very similar (almost identical) results in the considered energy range. For cisplatin, the resulting EICSs yield cross section maxima of 22.09?×?10^?20?m² at 55.4?eV for the DM method and 18.67?×?10^?20?m² at 79.2?eV for the (R)BEB method(s). The EICSs of monoaquated cisplatin yield maxima of 12.54?×?10^?20?m² at 82.8?eV for the DM method and of 9.74?×?10^?20?m² at 106?eV for the (R)BEB method(s), diaquated cisplatin yields maxima of 7.56?×?10^?20?m² at 118.5?eV for the DM method and of 5.77?×?10^?20?m² at 136?eV for the (R)BEB method(s). Molecular geometry does not affect the resulting EICS significantly, which is also reflected in very similar EICSs of the cis- and trans-isomer. Limitations of the work as well as desirable future directions in the research area are discussed.     

Full-scale atomistic simulations of dislocations in Ni crystal by embedded-atom method

Full-scale atomistic simulations by the nudged elastic band method are performed to determine the energetics and core structures of dislocations in a Ni lattice using an embedded-atom method potential. We find that for an edge dislocation, the potential yields very weak coupling between the partials which move almost individually. For a screw dislocation, the coupling between the partials is somewhat stronger and the partials move with some dependence. As expected, the results indicate that stacking fault energy has a controlling influence on the coupling behaviour of the partials. The effective Peierls energies and stresses are 1.30?×?10^?6?eV/Å and 2.79?×?10^?6?μ for the edge dislocation, and 1.62?×?10^?4?eV/Å and 2.02?×?10^?4?μ for the screw dislocation.     

P–V–T equation of state of rhodium oxyhydroxide

A high pressure X-ray diffraction study of RhOOH was carried out up to 17.44?GPa to investigate the compression behavior of an oxyhydroxide with an InOOH-related structure. A fit to the third-order Birch–Murnaghan equation of state gave K₀?=?208?±?6?GPa, and K′?=?9.4?±?1.3. The temperature derivative of the bulk modulus was found to be ?K/?T?=??0.06?±?0.02?GPa K^?1. The refined parameters for volume thermal expansion were α₀?=?2.7?±?0.3?×?10^?5 K^?1; α₁?=?1.7?±?1.1?×?10^?8 K^?2 in the polynomial form (α(T)?=?α_0?+?α₁(T?300)). Our results show that RhOOH is very incompressible, and has a higher bulk modulus than other InOOH-structured oxyhydroxides (e.g. δ-AlOOH, ε-FeOOH, and γ-MnOOH).     

Single-crystal elasticity of the rhodochrosite at high pressure by Brillouin scattering spectroscopy

ABSTRACT

The sound velocity properties of single-crystal rhodochrosite (MnCO₃) were determined up to 9.7?GPa at ambient temperature by Brillouin scattering spectroscopy. Six elastic constants were calculated by a genetic algorithm method using the Christoffel's equations at each pressure. The elastic constants increased linearly as a function of pressure and its pressure derivatives ?Cij/?P for C₁₁, C₃₃, C₄₄, C₁₂, C₁₃, C₁₄ were 5.86 (±0.36), 3.82 (±0.44), 2.06 (±0.39), 5.07 (±0.27), 5.34 (±0.44), 1.52 (±0.24), respectively. Based on the derived elastic constants of rhodochrosite, the aggregate adiabatic bulk and shear moduli (K_s and G) were calculated using the Voigt-Reuss-Hill averages and the linear fitting coefficients (?K_s/?P)_T and (?G/?P)_T were 5.05(±0.26) and 0.73(±0.05), respectively. The aggregate V_p of rhodochrosite increased clearly as a function of pressure and its pressure derivative ?V_p/?P was 7.99(±0.53)?×?10^?2?km/(s?GPa), while the aggregate V_s increased slowly and ?V_s/?P was only 1.19(±0.12)?×?10^?2?km/(s?GPa). The anisotropy factor for As of rhodochrosite increased from ～40% at 0.8?GPa to ～48% at 9.7?GPa, while A_p decreased from ～19% to ～16% at the corresponding pressure.     

The effect of pressure on halothane binding to hydrated DMPC bilayers

Halothane binding to hydrated dimyristoylphosphatidylcholine (DMPC) bilayer membranes has been examined over a wide range of pressures from 10⁵ to 4?×?10⁸?Pa. We show that the solvation of halothane by the membrane and bulk water are both pressure dependent, with an increased pressure driving halothane into the membrane. Analysis of these results shows that this pressure dependence is not the cause of pressure reversal, the process whereby general anaesthetics lose their efficacy at pressures of about 8?×?10⁶ to about 2.5?×?10⁷?Pa.     

Effect of 100 MeV swift Si8+ ions on structural and thermoluminescence properties of Y2O3:Dy3+nanophosphor

Nanoparticles of Y₂O₃:Dy³⁺ were prepared by the solution combustion method. The X-ray diffraction pattern of the 900°C annealed sample shows a cubic structure and the average crystallite size was found to be 31.49?nm. The field emission scanning electron microscopy image of the 900°C annealed sample shows well-separated spherical shape particles and the average particle size is found to be in a range 40?nm. Pellets of Y₂O₃:Dy³⁺ were irradiated with 100?MeV swift Si⁸⁺ ions for the fluence range of 3?×?10^11_3?×?10¹³ ions cm^?2. Pristine Y₂O₃:Dy³⁺ shows seven Raman modes with peaks at 129, 160, 330, 376, 434, 467 and 590?cm^?1. The intensity of these modes decreases with an increase in ion fluence. A well-resolved thermoluminescence glow with peaks at ～414?K (T_m1) and ～614?K (T_m2) were observed in Si⁸⁺ ion-irradiated samples. It is found that glow peak intensity at 414?K increases with an increase in the dopant concentration up to 0.6?mol% and then decreases with an increase in dopant concentration. The high-temperature glow peak (614?K) intensity linearly increases with an increase in ion fluence. The broad TL glow curves were deconvoluted using the glow curve deconvoluted method and kinetic parameters were calculated using the general order kinetic equation.     

Direct measurement of magnetization isotherms of Fe64Ni36 Invar alloy in a diamond anvil cell

Magnetization isotherms of the Fe₆₄Ni₃₆ Invar alloy have been measured under pressure up to 5.3?GPa in magnetic field up to 5?T using a diamond anvil cell and SQUID magnetometer. The unambiguous change of the pressure parameter dlnM_S/dP (from ?9 to ?13×10^?2?GPa^?1) has been observed in a narrow pressure interval from 2.5 to 3.5?GPa at all temperatures in the range from 5 to 300?K. The pressure interval, where the sharp decrease in magnetization was observed, coincides with the critical pressures of the pressure-induced decrease in Fe-moment that were determined by the X-ray Magnetic Circular Dichroism and the X-ray Emission Spectra studies, recently. The pronounced decrease in the Curie temperature of the Fe₆₄Ni₃₆ alloy under pressure, dT_C/dP = ?44 ±2?K/GPa, has been confirmed.     

The gas phase oxidation of HCOOH by Cl and NH2 radicals. Proton coupled electron transfer versus hydrogen atom transfer*

ABSTRACT

The reaction of formic acid (HCOOH) with chlorine atom and amidogen radical (NH₂) have been investigated using high level theoretical methods such BH&HLYP, MP2, QCISD, and CCSD(T) with the 6–311?+?G(2df,2p), aug-cc-pVTZ, aug-cc-pVQZ and extrapolation to CBS basis sets. The abstraction of the acidic and formyl hydrogen atoms of the acid by the two radicals has been considered, and the different reactions proceed either by a proton coupled electron transfer (pcet) and hydrogen atom transfer (hat) mechanisms. Our calculated rate constant at 298?K for the reaction with Cl is 1.14?×?10^?13?cm³?molecule^?1?s^?1 in good agreement with the experimental value 1.8?±?0.12/2.0?×?10^?13?cm³?molecule^?1?s^?1 and the reaction proceeds exclusively by abstraction of the formyl hydrogen atom, via hat mechanism, producing HOCO+ClH. The calculated rate constant, at 298?K, for the reaction with NH₂ is 1.71?×?10^?15?cm³?molecule^?1?s^?1, and the reaction goes through the abstraction of the acidic hydrogen atom, via a pcet mechanism, leading to the formation of HCOO+NH₃.     

六面顶压机立方压腔内压强的定量测量及受力分析

将六面顶压机立方压腔内置入电路,采用原位电阻测量确定Bi,Tl,Ba相变的方法,标定了压腔内不同位置的压力(强).通过标定立方压腔顶锤表面的压力并结合计算,分别得到了外部加载与压腔密封边受力以及合成腔体受力的对应关系.实验分析结果表明,随着外部加载的增加,当腔体压力达到5 GPa时,消耗在压腔密封边上的加载急剧上升,消耗在合成腔体的加载趋于不变,从而导致立方压腔压力达到上限.利用实验结果,分析了立方压腔在高压下的受力状态,解释了立方压腔的压力难以超过7 GPa的原因.结合立方压腔的几何结构,通过理论分析,提出了采用高体弹模量的物质作为传压介质,同时采用低体弹模量的物质作为密封边提高立方压腔压力上限的可行方案.通过定量标定叶腊石压腔轴向的压力梯度,给出了压腔内沿对称轴不同位置压力值的计算方法,此方法可为高压实验提供更精确的压力数据.     

ESR and optical study of Cu2+-doped bis-(5,5′-diethylbarbiturato)bis picoline Zn(II)

ESR studies were conducted on Cu²⁺-doped bis-(5,5′-diethylbarbiturato)bis picoline Zn(II). Two Cu²⁺ lattice sites, Cu²⁺(I) and Cu²⁺(II), were identified. These sites exhibit two sets of four hyperfine lines in all directions. The g factor and hyperfine splitting were calculated from ESR absorption spectra: g_x ?=?2.0201?±?0.002, g_y ?=?2.0900?±?0.002, g_z ?=?2.1634?±?0.002, A_x ?=?(30?±?2)?×?10^?4?cm^?1, A_y ?=?(40?±?2)?×?10^?4?cm^?1 and A_z ?=?(154?±?2)?×?10^?4?cm^?1. It was found that Cu²⁺ enters the lattice substitutionally. The ground-state wavefunction of the Cu²⁺ ion in this lattice was determined from the spin Hamiltonian constants obtained from the ESR studies. With the help of an optical absorption study, the nature of the bonding in the complex is also discussed.     

Experimental evaluation of effective atomic number of composite materials using back-scattering of gamma photons

A method has been presented for calculation of effective atomic number (Z_eff) of composite materials, by using back-scattering of 662?keV gamma photons obtained from a ¹³⁷Cs mono-energetic radioactive source. The present technique is a non-destructive approach, and is employed to evaluate Z_eff of different composite materials, by interacting gamma photons with semi-infinite material in a back-scattering geometry, using a 3^″?×?3^″ NaI(Tl) scintillation detector. The present work is undertaken to study the effect of target thickness on intensity distribution of gamma photons which are multiply back-scattered from targets (pure elements) and composites (mixtures of different elements). The intensity of multiply back-scattered events increases with increasing target thickness and finally saturates. The saturation thickness for multiply back-scattered events is used to assign a number (Z_eff) for multi-element materials. Response function of the 3^″?×?3^″ NaI(Tl) scintillation detector is applied on observed pulse-height distribution to include the contribution of partially absorbed photons. The reduced value of signal-to-noise ratio interprets the increase in multiply back-scattered data of a response corrected spectrum. Data obtained from Monte Carlo simulations and literature also support the present experimental results.     

Benzoylferrocene-modified carbon nanotubes paste electrode as a voltammetric sensor for determination of hydrochlorothiazide in pharmaceutical and biological samples

The electrooxidation of hydrochlorothiazide (HCT) at the surface of a benzoylferrocene modified multi-walled carbon nanotube paste electrode was studied using electrochemical approaches. Under the optimized conditions (pH 7.0), the square wave voltammetric peak current of HCT increased linearly with HCT concentration in the ranges of 6.0?×?10^?7 to 3.0?×?10^?4 M. The detection limit was 9.0?×?10^?8 M HCT. The diffusion coefficient (D?=?1.75?×?10^?5 cm²/s) and electron transfer coefficient (α?=?0.45) for HCT oxidation were also determined. The proposed sensor was successfully applied for the determination of HCT in human urine and tablet samples.     

Effects of the AlN nucleation layer thickness on the crystal structures of an AlN epilayer grown on the 6H-SiC substrate

The influence of the LT-AlN(NL) growth times on the mosaic structure parameters of the AlN layer grown on the LT-AlN(NL)/6H-SiC structures as well as the dislocation densities and the strain behaviours in the AlN epilayers has been investigated using XRD measurements. The growth times of the LT-AlN(NL) were changed to 0, 60, 120, 180, and 240?s. We observed that the mosaic structure parameters of the AlN epilayers were slightly affected by the LT-AlN(NL) growth times. However, the dislocation densities in the AlN layer are affected by the growth times of the LT-AlN(NL) layer. The highest edge dislocation density (5.48?×?10¹⁰?±?2.3?×?10⁹?cm^?2) was measured for the sample in which 120?s grown LT-AlN(NL) was used. On the other hand, highest screw type dislocation density (1.21?×?10¹⁰?±?1.7?×?10⁹?cm^?2) measured in the sample E that contains 240?s growth LT-AlN(NL). The strain calculation results show that the samples without LT-AlN(NL) suffered maximum compressive in-plane strain (?10.9?×?10^?3?±?1.8?×?10^?4), which can be suppressed by increasing the LT-AlN(NL) growth times. The out-of-plane strain also has a compressive character and its values increase with LT-AlN(NL) growth times between 60 and 180?s. Same out-of-plane strain values were measured for the LT-AlN(NL) growth times of 180 and 240?s. Furthermore, the form of the biaxial stress in the AlN epilayer changed from compressive to tensile when the LT-AlN(NL) growth times were greater than 120?s.     

Studies on the synthesis and characterization of Zn1− x Cd x S and Zn1− x Cd x S:Mn2+ semiconductor quantum dots

Quantum dots (3–4?nm) of Zn_{1? x} Cd _x S (both free of Mn²⁺ and with Mn²⁺ incorporated) were synthesized through a novel solvothermal-microwave irradiation technique. Detailed structural analysis of the Zn_{1? x} Cd _x S and Zn_{1? x} Cd _x S:Mn²⁺ (x?=?0, 0.25, 0.5, 0.75 and 1) materials was carried out using powder X-ray diffraction technique. For all the compositions, the crystallite size was controlled to less than 1.5?nm. The optical energy gap for Zn_{1? x} Cd _x S was found to vary from 3.878 to 2.519?eV and for Zn_1?x Cd _x S:Mn²⁺ it varies from 3.830 to 2.442?eV when x is increased from 0 to 1. Overall, the optical energy gap could be tuned from a minimum of 2.442?eV to a maximum of 3.878?eV. DC conductivity analysis (from 40°C to 150°C) and electrical energy gap analysis for all the compositions were also performed. The dc conductivity for Zn_{1? x} Cd _x S solid solutions varies from 0.3840?×?10^?10 to 8.7782?×?10^?10?mho/m at 150°C and for Zn_{1? x} Cd _x S:Mn²⁺ it varies from 0.5751?×?10^?10 to 9.8078?×?10^?10 mho /m at 150°C (for x?=?0 to x?=?1). The method of synthesis and the results observed in this investigation may assist in the fabrication of optical devices when the required operational performance falls under the range observed in the study.     

Effect of Ni(II) substitution on phase stabilization electrical properties of BICo(III)VOX.20 oxide-ion conductor

The BICO_0.20–xNI_xVOX solid electrolyte was synthesized by the standard solid-state reaction. The effect of Ni(II) substitution for Co(III) on phase stabilization and oxide-ion performance has been investigated in the compositional range 0?≤?x?≤?0.20 using X-ray powder diffraction, differential thermal analysis and AC impedance spectroscopy. The highly conductive γ′-phase was effectively stabilized at room temperature for compositions with x?≥?0.13 whose thermal stability increases with Ni content. The complex plane plots of impedance were typically represented at temperatures below 380?°C, suggesting a major contribution of polycrystalline grains to the overall electrical conductivity. The dielectric permittivity measurements revealed the fact that suppression of the ferroelectric transition is compositionally dependent. Interestingly, the maximum ionic conductivity at lower temperatures (~2.56?×?10^?4?S^?cm^?1 at 300?°C) was observed for the composition with x?=?0.13. The variation of low-temperature conductivity with Ni content was accompanied with a general drop in the corresponding values of ΔE_LT. However, the local minimum high-temperature conductivity, σ₆₀₀?°C?~?2.26?×?10^?2?S^?cm^?1 for x?=?0.10, coupled with a local maximum value of ΔE_HT?~?0.48?eV was attributed to an increased defect trapping effect correlated with the V(V)?→?V(IV) reduction at elevated temperatures.     

Equation of state and thermal expansivity of LiF and NaF

The high-pressure and high-temperature behaviors of LiF and NaF have been studied up to 37 GPa and 1000 K. No phase transformations have been observed for LiF up to the maximum pressure reached. The B1 to B2 transition of NaF at room temperature was observed at ～28 GPa, this transition pressure decreases with temperature. Unit-cell volumes of LiF and NaF B1 phase measured at various pressures and temperatures were fitted using a P–V–T Birch–Murnaghan equation of state. For LiF, the determined parameters are: α₀ = 1.05 (3)×10^?4 K^?1, dK/dT = ?0.025 (2) GPa/K, V ₀ = 65.7 (1) Å³, K ₀ = 73 (2) GPa, and K′ = 3.9 (2). For NaF, α₀ = 1.34 (4)×10^?4 K^?1, dK/dT = ?0.020 (1) GPa/K, V ₀ = 100.2 (2) Å³, K ₀ = 46 (1) GPa, and K′ = 4.5 (1).     

Microstructural evolution and changes in mechanical property of irradiated Fe–0.6Cu alloy under uniaxial tension stress in reactor

Structural materials for commercial reactor are usually used under conditions of stress. However, the evaluation of the microstructural evolution and the changes in the mechanical property induced by the neutron irradiation in structural materials does not typically consider the effect of stress since it is difficult to carry out neutron irradiation testing under conditions of stress. In this study, a model alloy (Fe–0.6Cu) of reactor pressure vessels was irradiated by neutrons at 573?K with a dose of about 3.2?×?10²¹?neutrons/m² (E?>?0.1?MeV), corresponding to 5.2?×?10^?4?dpa (displacement per atom), with and without tension stress. The tension stress caused elastic deformation in the specimens. The size of microvoids in the irradiated sample with tension stress was larger than that in the sample without tension stress. However, the effects of stress on the formation of Cu precipitates and the changes in the mechanical property were not clear.     

Mechanistic and kinetics study of the gas phase reactions of methyltrifluoroacetate with OH radical and Cl atom

Theoretical investigations are carried out on the title reactions by means of ab initio and DFT methods. The optimized geometries, frequencies and minimum energy path are obtained at MPWB1K/6-31+G(d,p) level. Single point energy calculations are performed at MP2 and QCISD(T) levels of theory. Energetics were further refined by calculating the energy of the species with a high level G2(MP2) method. The rate constant of the two reactions are calculated at 298?K and 1?atm using Canonical Transition State Theory (CTST) utilizing the ab initio data obtained during the present study. The rate constant values are found to be 5.5?×?10^?14 and 5.9?×?10^?14?cm³ molecule^?1 s^?1, respectively which are in good agreement with the experimental data.