A nearly zero temperature gradient furnace system for high pressure multi-anvil experiments

A new furnace system with an almost zero temperature gradient throughout the sample area was designed for multi-anvil high pressure experiments. Test experiments of the new design were performed using 18/11 and 25/15 cell assemblies at 4?GPa, 1400°C and 1500°C, respectively. The temperature field within the sample capsules appeared to be very homogenous as indicated by Mg₂Si₂O₆–MgCaSi₂O₆ two-pyroxene thermometry, by direct temperature measurements using two thermocouples within the same assembly, and by distribution of solid and liquid phases in the sample capsule. The temperature gradient is estimated to be <2.4°C/mm over an area of 4?×?5?mm² within the furnace. It is significantly lower than standard multi-anvil experiments with straight or stepped furnace systems, which are at the levels of 20–200°C/mm.     

High pressure,high temperature them determination of triple point in CdSe

Abstract

Thermal investigation of melting in gas pressures (Nz) up to 17 kbar was used to determine p-T phase diagram of CdSe. The method, based on measurements of temperature gradient in the container wall during heating and cooling, allowed to obtain the temperature of fusion. The pressure dependence of the melting temperature was given for both low and high pressure phases. The triple point coordinates, equal to 10.90 kbar and 1221 °C confirm earlier measurements of Jayaraman et a1.     

Gasket temperature: an alternate technique for estimating sample temperature in a multi-anvil apparatus

It is common for sample temperatures to be estimated by the power input to the furnace in multi-anvil experiments in which a thermocouple cannot be used or the thermocouple failed during heating. Uncertainties using this technique are often on the order of ±85°C or larger. This paper describes a new method for estimating sample temperature using a second thermocouple outside all pressure media. Temperatures recorded at this external (gasket) thermocouple trend linearly with the internal (sample) thermocouple temperature. Because of thermal lag, it is necessary to determine the first gasket temperature (T₀) corresponding to the desired sample temperature. Accurate prediction of T₀ for the desired sample temperature can come from relatively few (5–6) gasket-temperature measurements made during the initial temperature ramp over a small temperature range (500–600°C). Using this method and manually ramping to T₀ allows for uncertainties in sample temperature estimation as small as ±20°C.     

Differential mobility analysis of nanoparticles generated by laser vaporization and controlled condensation (LVCC)

Silicon and iron aluminide (FeAl) nanoparticles were synthesized by a laser vaporization controlled condensation (LVCC) method. The particles generated by the laser ablation of solid targets were transported and deposited in the presence of well-defined thermal and electric field in a newly designed flow-type LVCC chamber. The deposition process of nanoparticles was controlled by the balance of the external forces; i.e., gas flow, thermophoretic and electrostatic forces. The size distributions of generated nanoparticles were analyzed using a low-pressure differential mobility analyzer (LP-DMA). The effect of synthesis condition on the size distribution was analyzed by changing the pressure of the carrier gas (20–200 Torr), the temperature gradient in the LVCC chamber (ΔT=0–190°C) and the electric field applied between the LVCC chamber plates (E=0–3000 V/m). It was found that electrostatic field was effective to selectively deposit small size nanoparticles (about 10 nm) with expelling large droplet-like particles.     

New processes in material production under high pressure

Abstract

To investigate processes of producing high-quality materials using high pressures of gas VNIIMETMASH has developed 3-400 MN hot isostatic presses (HIPes) with working pressure up to 200 MPa and temperature up to 2000°C. Ar and N2 are used as working gases. Frame and vessel units of such machines are of multi-element structure which eliminates the possibility of its fragmentation failure and instant release of compressed gas energy. HIPes are intended for healing defects in casting and compacting metallic, ceramic and composite materials.     

Diastereoselectivity and kinetics of hetero diels-alder reactions under high pressure

Abstract

The Hetero Diels-Alder reaction of enamino ketones and ethyl vinyl ether to give dihydropyrans is studied in different solutions under pressure up to 7 kbar. The kinetics is measured via on-line FT IR spectroscopy. The cycloaddition shows a remarkable pressure dependent increase in diastereo-selectivity. For the difference in activation volumes referring to the reaction to the two diastereomers, values up to 5.9 ± 0.5 cm³/mol are observed. The ratio of cis and trans diastereomers can be improved by almost one order of magnitude by changing pressure and temperature from 1 bar and 90 °C to 6 kbar and 0.5 °C.     

On the liquidus curve for GaN

Abstract

A Quasi-Chemical Equilibrium approach was used to discuss the experimental results of three phase (Ga-GaN-N₂) equilibrium conditions for the temperature range 1200-1580°C and pressure 0. 1-1. 45 GPa. The best fitting was obtained for the melting temperature of 2531 K which is in reasopable agreement with the value of 2791 K calculated by Van Vechten¹.     

Investigations of texture formation in geomaterials by neutron diffraction with high pressure chambers

Abstract

This paper suggests a classification of texture in quartzitic rocks. Possible mechanisms of texture formation and their relation to tectonic processes are discussed.

A scheme for the experimental varification of some models describing the evolution of deformation structures in geological materials in dependence on various erxternal conditions (high pressures, temperatures, various loadings, etc.) acting on a sample is proposed.

To investigate “in situ” the mechanisms of texture formation in rocks, high pressure devices are under construction. They will be built of a special T_i ? Z_r alloy, which has zero coherent scattering lenght and therefore is well suited for neutron diffraction investigations. Two different devices are proposed. The first one allows neutron diffraction measurements of sample volumes up to 4 cm³, a hydrostatic pressure of 1, 5 GPa, a temperature of 300° C, and uniaxial compression up to 50 kN. Pressure temperature and axial load are measured inside the chamber. Besides during the experiment, diagrams of load, elastic wave velocities and acoustic emission will be recorded. The second chamber is designed to investigate the mechanisms of texture formation in polycrystal samples (rocks or their imitations) at temperatures up to 800° C and axial compression with a force of up to 150 kN.     

Optimization of magnetron deposition process for formation of high-quality oriented ZnO films

The thickness distribution and structure of ZnO films deposited by DC-magnetron sputtering of a zinc target in argon-oxygen gaseous medium at substrate temperature of 27°C and gas pressure in the chamber within 5×10^?3 ? 5×10^?2 mm Hg was investigated. It was revealed that the use of a target with a certain depression in the sputtering zone allows depositing high quality c-oriented films at lower gas pressure than with a flat target. The dependence of film quality on geometric factors is interpreted on the basis of theoretical computations with the assumption that the film structure is improved when the flux of deposited Zn particles decreases while their energy increases.     

Synthesis of nano-polycrystalline diamond from glassy carbon at pressures up to 25 GPa

ABSTRACT

Nano-polycrystalline diamond (NPD) with various grain sizes has been synthesized from glassy carbon at pressures 15–25?GPa and temperatures 1700–2300°C using multianvil apparatus. The minimum temperature for the synthesis of pure NPD, below which a small amount of compressed graphite was formed, significantly increased with pressure from ～1700°C at 15?GPa to ～1900°C at 25?GPa. The NPD having grain sizes less than ～50?nm was synthesized at temperatures below ～2000°C at 15?GPa and ～2300°C at 25?GPa, above which significant grain growth was observed. The grain size of NPD decreases with increasing pressure and decreasing temperature, and the pure NPD with grain sizes less than 10?nm is obtained in a limited temperature range around 1800–2000°C, depending on pressure. The pure NPD from glassy carbon is highly transparent and exhibits a granular nano-texture, whose grain size is tunable by selecting adequate pressure and temperature conditions.     

A planetary environment and analysis chamber (PEACh) for coordinated Raman–LIBS–IR measurements under planetary surface environmental conditions

A planetary environment and analysis chamber (PEACh) has been developed at Washington University in St. Louis, in order to perform in situ multiple spectroscopic measurements on geological samples under relevant planetary environmental conditions and to support future planetary missions, with particular interest on Mars. The pressure in the chamber can range from ambient to 3 × 10⁻² mbar. The simulated atmospheric composition and pressure are regulated via a combination of needle and ball valves connecting the chamber with containers filled with premixed gas. The temperature of the samples can be controlled in a range from ambient to − 100 °C. The in situ analytical techniques implemented (and to be implemented) are laser Raman spectroscopy, laser‐induced breakdown spectroscopy (LIBS), near‐IR reflectance spectroscopy, mid‐IR attenuated total reflectance spectroscopy, and microscopic imaging. The coordinated spectroscopic sensing on the same geological sample under well‐controlled atmospheric conditions in the PEACh establishes a way to link the results from the laboratory experiments to the spectral data obtained by landed and orbital planetary exploration missions, which will facilitate understanding the surface processes by which mineral phases occur and their association with atmospheric changes. Copyright © 2011 John Wiley & Sons, Ltd.     

Ammonia gas sensor based on SnO2 nanostructure with the enhanced sensing capability at low temperatures

ABSTRACT

We investigated the gas-sensing performance of tin oxide nanowires for ammonia gas at low temperature (～ 50°C). Tin oxide nanostructures were deposited at 1000°C and 1100°C on gold-coated silicon substrates using the physical vapor deposition method. Gas-sensing measurements were made for ammonia gas at various strengths (i.e. 50, 100 and 200?ppm) and the sensing performance was compared at low temperature for both the samples e.g. nanostructures deposited at 1000°C and 1100°C. Due to the highly oriented structure, the sample deposited at 1000°C shows high sensing capability at low temperature as compared to the regular tetragonal phase observed at 1100°C. The morphological and structural properties of nanowires were systematically examined using the scanning electron microscopy and X-ray diffraction.     

Oriented growth of CoPt nanoparticles by pulsed laser deposition

The magnetic nanoparticles of Fe/FeCo/FePt, in the past, in a PLD system were grown by us using argon ambient gas pressure of about 0.1–75.0 mbar, as the ambient gas pressure can be used to tune the energy of the incident plasma plume species, the expansion volume, the growth duration, etc. which can control the particle size. In present paper, we report the direct synthesis of small-sized nanoparticles even when no ambient gas was used, with the experiments being done in higher vacuum of about 10^?5 mbar in PLD chamber. The deposition rate under vacuum condition is significantly higher than the deposition rate at high ambient pressure. The study of inplane and outplane magnetic properties, along with XRD results, confirmed that the as-deposited CoPt nanoparticles thin film has oriented growth. The as-deposited CoPt nanoparticles are in magnetically soft fcc phase and a post deposition annealing at 600°C resulted in phase transition to magnetically hard fct phase.     

Comparison of the Raman pressure shift and the Raman temperature shift of benzene and diamond with the ruby soale

Abstract

In order to serve as substitute for the pressure ruby scale at high temperature, the breathing mode of bemsens (990 cm^?1) and the first order Raman mode of diamond (1333 cm^?1) have been studied as a function of pressure and temperature in the range of 0–15 GPa and 25–400°C. The diamond and bensene Raman frequency shifts are shoft to be of valuable use as a pressure scale at high temperature. A further advantage of bensene is to remain a suitable pressure transmitting medium up to 350°C and 15 GP.     

Effect of the Initial Temperature on the Characteristics of the Shot with a Block Charge

The effect of the initial temperature on the characteristics of the shot is studied for high-density block charges prepared by pressing powder grains coated with a polymer film. The experiments were carried out on laboratory barrel setups of caliber 7.62 and 14.5 mm with recording the muzzle velocity and pressure. Two shot schemes are considered: a classical scheme with the block charge placed in the chamber, and a hybrid scheme, with the block charge attached to the projectile, burning as it travels along the barrel. The effect observed at various initial temperatures of the block charge is compared with similar data for a standard poured-powder charge, for which the temperature gradient within ±50°C is 2.1?2.5% per 10°C. The experiments showed that, at positive temperatures, the temperature gradient for block propellant charges is appreciably smaller, 0.9?1.2% for the traditional shot scheme and 0.8% for the hybrid scheme. At negative temperatures of the block propellant charges, the characteristics of the shot decline significantly, which, however, can be restored to the temperature gradient typical of the standard shot by boosting the igniter.     

Pressure and Temperature Probe for Studies of Biological Materials

In our previous paper [1] a high pressure technique for monitoring pressure up to 700 MPa and temperature from m 40 °C to +100 °C in several pressure vessels simultaneously was reported. This technique, applied in Unipress High Pressure Multivessel Apparatus for studies of biological materials, revealed some limitations. In this paper we propose a new solution which allows to overcome them. In this solution two different pressure media are used, separated from each other: one suitable for biological studies and the other proper for electric sensors. A new integrated pressure/temperature probe is presented in which manganin pressure gauge is confined in a metal bellows separating the two pressure transmitting media. The bellows can be easily assembled or disassembled, allowing promptly to refill pressure medium or to replace the pressure gauge. Temperature is measured by constantan/copper thermocouple. The probe is linked to data acquisition system. Taking into account temperature dependence of the manganin pressure gauge, simultaneous measurements of the resistance of pressure gauge and thermocouple voltage allow to compute pressure at any temperature. The new probe is integrated with the bottom closure of the pressure vessel which also incorporates capillary inlet. Such a design leaves free access from the top of the vessel, allowing easy mounting the studied samples as well as other additional probes.     

Measurements of the complex shear modulus of polymers under hydrostatic pressure usina the quartz resonator method

Abstract

The quartz resonator method measures the complex shear modulus or compliance of viscoelastic materials in the frequency range from 50 kHz to 140 MHz at temperatures between ?150°C and 300°C and pressures up to 1 GPa. This method can be applied to viscous fluids or polymer melts -even in their glassy or seminystalline regime.

The phase diagram of poly(diethylsiloxane) PDES (a mesophase polymer) was determined for two samples with different molecular weight at pressures up to 400 MPa and temperatures between 20°C and 100°C. Phase transitions are indicated by a sharp bend in the shear compliance although the volume effect of the mesophase-isotropic transition vanishes around 80 MPa.

The pressure dependence of the glass relaxation process (in PVAc), was studied by measuring the change of the complex shear modulus with pressure at constant temperatures between 95°C and 145°C and pressures up to 600 MPa. Additionally to the relaxation process, also the pressure dependence of the real part of the shear modulus in the glassy region can be determined for testing the dislocation concept in the meandermodell by W. Pechhold.     

An in vitro thermal analysis during different light-activated hydrogen peroxide bleaching

This study measured the critical temperature reaching time and also the variation of temperature in the surface of the cervical region and within the pulp chamber of human teeth submitted to dental bleaching using 35% hydrogen peroxide gel activated by three different light sources. The samples were randomly divided into 3 groups (n = 15), according to the catalyst light source: Halogen Light (HL), High Intensity Diode Laser (DL), and Light Emmited Diode (LED). The results of temperature variation were submitted to the analysis of variance and Tukey test with p < 0.05. The temperature increase (mean value and standard deviation) inside the pulp chamber for the HL group was 6.8 ± 2.8°C; for the DL group was 15.3 ± 8.8°C; and for the LED group was 1.9 ± 1.0°C for. The temperature variation (mean value and standard deviation) on the tooth surface, for the group irradiated with HL was 9.1 ± 2.2°C; for the group irradiated with DL were 25.7 ± 18.9°C; and for the group irradiated with LED were 2.6 ± 1.4°C. The mean temperature increase values were significantly higher for the group irradiated with DL when compared with groups irradiated with HL and LED (p < 0.05). When applying the inferior limits of the interval of confidence of 95%, an application time of 38.7 s was found for HL group, and 4.4 s for DL group. The LED group did not achieve the critical temperatures for pulp or the periodontal, even when irradiated for 360 s. The HL and DL light sources may be used for dental bleaching for a short period of time. The LED source did not heat the target tissues significantly within the parameters used in this study.     

Effects of hydrostatic pressure and temperature on catalytic activity of Horse Liver Alcohol Dehydrogenase (HLADH)

Abstract

We have studied the effects of hydrostatic pressure and/or temperature on the catalytic activity of Horse Liver Alcohol Dehydrogenase (HLADH). The Vmax, Km and thermo-dynamical activation volume were determined versus pressure in the range of 0.1 to 225 MPa at ambient temperature (29°C) and at the optimal temperature of HLADH (53°C).     

Behavior of thermocouples under high pressure in a multi-anvil apparatus

We have conducted experiments to study the behavior of W5%Re–W26%Re (type C) and Pt10%Rh–Pt (type S) thermocouples under high pressure in a multi-anvil apparatus. The electromotive force (emf) between four different or three identical thermocouple wires was measured up to 15?GPa and 2100?°C. Mechanical and chemical stability of the thermocouples was examined during and after the experiments. Due to the effect of pressure on the emf/temperature relation, the temperature reading of the type C minus that of the type S thermocouple rises to +5?°C then falls to ?15?°C between room temperature and 1500?°C at 5?GPa, and to +25?°C and then ?35?°C between room temperature and 1800?°C at 15?GPa. In addition, we observed variations in the emf/temperature relation caused by uncertainties in the position and geometry of hot junctions in a steep temperature gradient, and by variable distribution of pressure gradient and non-hydrostatic stress on the thermocouple wires. These errors are estimated at 1.6% for the type S thermocouple up to 1700?°C, and 0.8% for the type C thermocouple up to 2100?°C. Self-diffusion and chemical contamination of the thermocouples by high-purity insulating ceramics appear negligible for the type S thermocouple at 1700?°C for one hour, and for the type C thermocouple at 2100?°C for half an hour. In contrast, large-scale displacement of the hot junction due to dislocation of the type C thermocouple wires and plastic deformation of the type S thermocouple wires may lead to large errors in temperature measurement (±200?°C).