Papers by Keyword: High Pressure

Abstract: There is little datum related to microstructure and properties of Mg alloys squeeze-casted with pressure over 200 MPa. In this study, the microstructure and properties of Mg-6Zn-1.4Y (ZW61) alloy solidified under 100MPa to 800MPa were investigated. The results show that a remarkable microstructure refinement and porosity reduction can be reached through solidification under high pressure. The average grain size and the volume fraction of second phase, i.e. quasicrystal I-phase, decrease continuously with the increase of applied pressure. The tensile properties, especially elongation, are obvious enhanced because of the microstructure refinement and castings densification under high pressure. The ultimate tensile strength and elongation of ZW61 alloy in as-cast state are 243 MPa and 18.7% when the applied pressure is 800 MPa, which are increased by 35% and 118% respectively, compared with that of the gravity castings.

Abstract: The kinetic properties such as diffusivity and viscosity of the metal melt are the foundations to reveal the structure evolutions and the glass formation abilities during solidification of the investigated alloy, thus, to control the microstructures, defects and properties of materials. In this work, ab initio molecular dynamics simulations were utilized to investigate the kinetic and thermodynamic properties and the structural relaxations of Fe-X (X = 10-15 wt% Al, Cr, Mn and Ti, or 1-2wt% B and C) melts under various temperature and external pressure, which are in line with the interested concentration range of multi-component Fe-based alloys. The kinetics and structural relaxations are characterized by mean squared displacement, velocity autocorrelation function and self-intermediate scattering function. The thermodynamics properties including entropy and heat capacity are calculated by combining the vibrational and electronic contributions based on vibrational and electronic density of states. The predicted kinetics and thermodynamics properties under high temperature and pressure agree well with the experimental and theoretical results while the connection among structural relaxations and diffusion are revealed based on the Stokes-Einstein relation and the Hall-Wolynes (HW) relation. This work provides an insight into the structure-property relationships of metal melts, which are essential in the development of advanced multi-component Fe-based alloys.

Abstract: Ferroelectric ceramic solid solutions Li_xNa_1-xTa_yNb_1-yO₃ (х = 0.17; у = 0 – 0.5) with the perovskite structure have been obtained by the thermobaric synthesis method. Particularities of their microstructure, elastic properties, electrical conductivity and permittivity have been researched. It has been established that an increase in the thermobaric synthesis temperature leads to a decrease in the Young’s modulus value. Specific static conductivity values have been determined; charge carrier activation enthalpies Н_а have been calculated. The Curie temperature of the samples has been determined to decrease with an increase in tantalum content. A Ferroelectric ceramic solid solution Li_0.17Na_0.83Ta_0.1Nb_0.9O₃ was shown to undergo four structure phase transitions in the temperature range 300-820 К. A Li_0.17Na_0.83Ta_0.1Nb_0.9O₃ has been shown to be a high temperature superionic. Possible mechanisms of the detected phenomena are discussed.

Abstract: The most common residual viscosity correlation used in the petroleum models is JOSSI et al [1] where the residual viscosity is represented by a polynomial function of 4th degree involving the reduced density ρr ([(η-η*)ξ+10^-4]^1/4=Σ⁴₁₌₀(aiρrⁱ)). Based on this formula, it is possible to predict various uncertainties that can be accumulated and thus alter the performance of viscosity restitution which depends on several factors:The quality of the initial adjustment of the coefficients a_i;The precision on the density;The accuracy with which are known the characteristics of the constituents of bases;The validity of the rule of the mixtures selected for the determination of the pseudo-critical coordinates T_cm and P_cm and the equivalent molar mass of the mixture.As far as the results are concerned, we reveal that with the new set of coefficients it is possible to obtain a more preciserepresentation compared to that of JOSSI. The method of JOSSI seems to be especially interesting for the viscosities restitution of systems containing light and close paraffins. However, for some pure substances, the opposite situation could be true. Among the four equations-of-state used, it has been found that the cubic equation-of-stateof PENG and ROBINSON should not be used since we would like to generate the density. Finally, we are not expecting a perfect systematic representation. As demonstrated in our model, if for light alkanes one can expect an average deviation ofless than 10%, for certain pure substances the deviation exceeds 20%.

Abstract: Based on the density functional theory (DFT), the first-principles approach is used to study the electronic band structure of B-doped wuritzite ZnO with different pressure. The pressure effects on the lattice parameters, electronic band structures, and partial density of states (PDOS) of crystalline B-doped ZnO are calculated up to 8 GPa. Moreover, the evolution of the dielectric function, absorption coefficient (), reflectivity (), and the real part of the refractive index () at high pressure are also presented. Keywords: high pressure; density functional theory; B-doped ZnO.

Abstract: First-principles calculations are performed to study the electronic structures and optical properties of the As-doped ZnO under pressure up to 8 GPa. After doped, the electron density difference demonstrates the considerable electron charge density redistribution, which induces the effect of As-doped ZnO to increase the charge overlap between atoms. Moreover, as the pressure increases, the conduction and valence band shift to lower and higher energies, respectively. The shifts of the conduction and valence band result in a decreasing band gap. Additionally, the calculated optical constants of As-doped ZnO under pressure are also presented. Keywords: high pressure; As-doped ZnO; optical properties, Density functional theory.

Abstract: The influence of high pressure and manganese on Fe-rich phases (FRPs) and mechanical properties of Al-14Si-2Fe alloy with rheo-squeeze casting (RSC) were investigated. The semi-solid alloy melt was prepared using ultrasonic vibration (UV), then formed by squeeze casting (SC). Results shows that the FRPs in as-cast Al-14Si-2Fe-(0.4,0.8)Mn alloys with SC are composed of coarse plate-shaped δ-Al₄(Fe,Mn)Si₂, long needle-shaped β-Al₅(Fe,Mn)Si and bone-shaped α-Al₁₅(Fe,Mn)₃Si₂ phases when the pressure is 0 MPa. During the solidification of the alloys with RSC, the FRPs are first refined by UV, then furtherly refined as the pressure increases. With RSC, the FRPs in Al-14Si-2Fe-0.8Mn alloy are finer and rounder than that of the Al-14Si-2Fe-0.4Mn alloy under the same pressure. The FRPs in RSC Al-14Si-2Fe-0.8Mn alloy are mainly granular particles with an average diameter of about 12 μm under 300 MPa. For the alloy with the same composition, the ultimate tensile strength (UTS) of RSC sample is higher than that of the SC sample. Under the same forming process, the UTS of Al-14Si-2Fe-0.8Mn alloy is higher than that of the Al-14Si-2Fe-0.4Mn alloy.

Abstract: The adhesion performance of Cold Sprayed coatings depends on the quality of the substrate [1,2,4,8]. Before deposition, the surface of substrate must be prepared to a specific required quality, which promotes the anchoring of sprayed coating. Grit Blasting (Samson et al.) [1] is known as the conventional surface preparation before Cold Spraying. But such method causes issues: a) shallow roughness, which does not strengthen bonds between layer and substrate; b) embedment of particles in the substrate, which creates discontinuity of the material at the interface and causes cracks that degrade the layer. Recently, Laser [2] and Pulsed Water Jet (PWJ) [1] have been tested as substrate preparation methods. These methods have shown their ability to generate improved roughness without particle embedment. PWJ has particularly shown interest in Al substrate to generate crevices, which are anchors for the Cold Sprayed coatings. Nevertheless, Laser affects thermally the substrate and induces constraints that may disadvantage the coating quality. PWJ generates liquid effluents. Besides some substrates such as ferrous metals can react with oxygen of water leading to corrosion and coating adhesion weakness.

Abstract: We present high-quality optical data and density functional theory calculations for the structural and vibrational properties of solid naphthalene (C₁₀H₈) under pressure up to 21.5 GPa. Our results demonstrate that almost all the modes shift toward higher frequencies and some peaks are broadened with increasing pressure. Comparing the pressure effect on the shortest intermolecular distances and on the bond lengths we confirm the expected result that the intramolecular interaction are less sensitive to pressure than the intermolecular interactions. These findings are shown to be in agreement with experimental results and hint towards the evolution of intermolecular interaction with pressure. Moreover, within our data the lattice modes exhibit more drastic changes than intramolecular modes, which are due to there being greater intermolecular distortions than intramolecular under applied pressure. In combination with theoretical and experimental studies, these results permit detailed characterization of the structural and vibrational changes of naphthalene as a function of pressure.

Abstract: A composed mixed acidophilic, iron-oxidizing culture (FIGB) and a thermo-acidophilic enrichment culture (TK65) were used to evaluate microbial iron(III) reduction coupled to oxidation of reduced inorganic sulfur compounds (RISCs) under high pressure. Experiments were done in batch culture in high pressure vessels at 1 and 100 bar. Microbial abundance and activity were determined by measuring iron(II) concentration, direct cell counting, T-RFLP and quantitative real-time PCR. The data indicate that both cultures are able to reduce soluble iron(III) by oxidation of sulfur compounds under anaerobic conditions. At high pressure (100 bar) these acidophiles were capable of growing and microbial ferric iron reduction was only partially inhibited. These results indicate that acidophiles can be barotolerant and their activities are contributing to sulfur and iron cycling in anaerobic environments including deep ore deposits which is highly relevant for in situ leaching operations.