Role Of Liquid Phase Research Articles

Role of liquid phase in the development of ice phase in monsoon clouds: Aircraft observations and numerical simulations

The effect of warm microphysical properties on ice processes is investigated in developing monsoon (MON) and premonsoon (PRE) cumulus clouds growing under different thermodynamic and aerosol conditions. We used airborne observations of cloud microphysical properties during the Cloud Aerosol Interaction and Precipitation Enhancement Experiment (CAIPEEX) and idealized large eddy simulation (LES) with the Weather Research & Forecasting (WRF) model coupled with the spectral-bin microphysics scheme. Airborne observations showed that ice microphysical properties including ice number concentration and ice water content (IWC) strongly depend on cloud base height, boundary layer water vapor mixing ratio, and cloud drop effective radius at the freezing level. The MON clouds in both high and low aerosol concentrations, characterized by a moister boundary layer and warmer cloud bases compared with PRE clouds, have broader drop size distributions (DSD) above the freezing level and produce more ice particles. Idealized WRF-LES simulations of MON and PRE clouds support the observed results with larger IWC in both polluted and clean MON clouds when compared to polluted PRE clouds, and the moisture differences play a more important role in altering the ice microphysical characteristics than aerosol number concentration. Cloud droplet and rain drop properties in both PRE and MON clouds greatly affect ice processes and change ice particle number concentration and types, through impacting drop freezing and riming. The larger IWC in the simulated MON clouds compared with PRE clouds is mainly due to enhanced deposition and riming as a result of the increased boundary layer moisture.

(Invited) Enhancing HER and OER Electrocatalysis

Fundamental understanding of the processes involved in that are behind the mechanism for electrochemical evolution of hydrogen and oxygen from water is considered critical in for further advancement of materials that could be implemented in electrolyzers,. Atomic scale insight at the electrified solid-liquid interfaces provides invaluable guidance to overcome limitations that cause a lower than desired operating efficiency of the devices. All of that highlights the need for development of more active, durable and cost effective oxygen evolution (OER) and hydrogen evolution (HER) reaction catalysts. While the majority of research is placed on the catalyst design and synthesis aiming to improve their efficiency, not too much less has been done to resolve and understand a the impact of the liquid phase of the interface at which reaction is taking place. In addition to surface structure, surface and subsurface composition and electronic properties, the role of liquid phase which is influencing the overall performance of an electrified interface is being investigated. Molecular species from the electrolyte and the nature of their interaction with the catalyst surface will be discussed. The knowledge acquired from two-dimensional surfaces has been employed to create real-world catalysts with superior properties.

The Role of Liquid Phase in SSM Processes

The present chapter reports a short history and a state-of-the art of semi-solid techniques, with particular emphasis to the role of the liquid-solid fraction, being the rheological behaviour of the semi-solid slurry crucial and fundamental. The general description, with the related theoretical fundaments, is based on the data available in the recent and the past literature and finally it is integrated with some experimental results of the research carried out by the authors.

Assessment of solid state and liquid phase sintering models by comparison of isothermal densification kinetics in W and W-Cu systems

The role of liquid phase and grain growth during the intermediate stage of sintering is investigated by comparing the isothermal densification rate of the tungsten skeleton in two systems: solid-state sintered W and liquid-phase sintered W-10wt%Cu. Densification curves at 1380 °C, i.e. well after completion of capillary rearrangement in W-Cu, are confronted to the predictions of a model that considers a single representative grain size with quasi-equilibrium interfaces and a monotonic increase in grain size and coordination with density. In both systems, the densification mechanism is taken to be governed by W diffusion along grain boundaries. For system W-Cu, a phenomenological law is proposed to allow accounting for the decrease in liquid surface curvature during funicular filling of the pores by the liquid-phase. The kinetics of grain growth is described via current literature model. Good agreement is demonstrated between experimental measurements and model predictions when relying on material parameter values given in literature. In system W-Cu, the detrimental effect of the decrease in dihedral angle is, at the beginning of the funicular stage, compensated by the contribution to sintering stress brought about by the concave curvature of liquid/vapour interface. The sensitivity of computational results to model hypotheses and material parameters is assessed. The most influential parameters are diffusivities along W grain boundaries and along W/vapour and W/Cu interfaces.

Role of Liquid Phase in Achieving a Fine Microstructure and Diffusive Phase Transition of MgO‐Doped BaTiO3

Two types of glass compositions, with MgO and CaO modifiers, respectively, were used to promote l`iquid‐phase sintering of 2 mol% MgO–BaTiO3 at 1280°C in reducing atmosphere (pO2=10−9 atm). By combining the observations of the grain size of about 1 μm for both specimens and the diffusive phase transition only when MgO modifier was used, it has been interpreted that an appropriate solubility of BaTiO3 is necessary to yield the fine and composite microstructures via a dissolution–reprecipitation process. Further, a reasonable dopant provision to BaTiO3 has been shown to be required to achieve the diffusive phase transitions.

Role of Liquid Phase in PTCR Characteristics of (Ba0.7Sr0.3)TiO3 Ceramics

The role of liquid phase in the enhancement of the PTCR (positive temperature coefficient of resistance) effect in (Ba 0.7 Sr 0.3 )TiO 3 (BST) with the addition of AST (4Al 2 O 3 . 9SiO 2 .3TiO 2 ) is investigated in this paper. The AST-BST samples were characterized with optical microscopy, transmission electron microscopy, energy-dispersive spectroscopy, and impedance spectroscopy. Microscopic observations showed that slower cooling might facilitate the precipitation of the (Ba,Sr)TiO 3 phase from the liquid phase on matrix grains since the amount of liquid phase was reduced with a decreasing cooling rate. Impedance spectroscopy indicated that this variation accompanied the change in the intrinsic properties of grain boundaries, which could not be explained by well-known oxidation effects. With the aid of a brick-layer model and high-resolution transmission electron microscopy (HRTEM), it appeared that the change in electrical characteristics of grain boundaries with decreasing cooling rate originated from the precipitation of (Ba,Sr)TiO 3 . Finally, the effect of precipitated (Ba,Sr)TiO 3 on the PTCR characteristics is discussed in terms of the acceptor-state density and the polarization state at grain boundaries.

Crystal growth and characterization of MgB2: the relation between structural and superconducting properties

We discuss the important aspects of synthesis and crystal growth of MgB2 under high pressure (P) and temperature (T) in the Mg–B–N system, including the optimization of P–T conditions for reproducible crystal growth, the role of liquid phases in this process, the temperature dependence of crystal size and the effect of growing instabilities on single-crystal morphology. Extensive experiments have been carried out on single crystals with slightly different lattice constants and defect concentrations, which have revealed the possible effects of Mg deficiency and lattice strain on the superconducting properties of MgB2 (Tc, Jc, residual resistivity ratio, anisotropy, etc).

Catalytic Effects of Metals on Direct Nitridation of Silicon

Catalytic effects were investigated on the direct nitridation of silicon granules, impregnated with 0.125–2.0% by mass of calcium, yttrium, iron, copper, silver, chromium, or tungsten, in a stream of nitrogen with 10% hydrogen, using a tubular flow reactor operated at temperatures ranging from 1200° to 1390°C. Calcium and yttrium suppressed the formation of β‐silicon nitride while iron enhanced the formation of β‐silicon nitride over the temperature range investigated. An addition of 0.125% calcium resulted in about 99% overall conversion with 100%α‐phase and a 2.0% yttrium addition yielded an overall conversion over 98% with an α‐phase content above 97%. Copper promoted not only the nitridation but the formation of α‐silicon nitride at 1200°C, but enhanced the β‐phase formation at higher temperatures. The role of liquid phases on the formation of α‐/β‐silicon nitride was also discussed based on the nitridation of silicon impregnated with copper, calcium, silver, chromium, and tungsten.

Superplastic Deformation of Aluminum Systems at 500-650 °C with or without Presence of Liquid Phase

Three aluminum base materials were studied over the high temperature range of 500-650 °C, in an attempt to examine the role of liquid phase on controlling deformation mechanisms based the observed m- and Q-values. For the two near-pure At systems, the 1050 At and AO, no solute-induced incipient partial melting was expected, and the solidus and liquidus temperatures should merge to near 655±5 °C. The m-values of these materials were consistently scattered with 0.1-0.25 up to the extrahigh temperature of 650 °C. The high activation energy in the A0 material at T>600 °C is postulated to be related to the load transfer effect or bubble-induced stress reduction, but not the liquid phase role in explaining the deformation mechanism. In the 6061A1, an appreciable amount of liquid should have been present at 590 and 610 °C. The low activation energy of 20 kJ/mole over the temperature range of 570-610 °C might reflect the transition of deformation mechanisms, though no pronounced increase in m-values was observed even at 610 °C. This result was controversial and needs future studies.

Grain Boundary Migration in Ceramics

During ceramic fabrication, densification processes compete with coarsening processes to determine the path of microstructural evolution. Grain growth is a key coarsening process. This paper examines grain boundary migration in ceramics, and discusses the effects of solutes, pores, and liquid phases on grain boundary migration rates. An effort is made to highlight work in the past decade that has contributed to and advanced our understanding of solute drag effects, pore-boundary interactions, and the role of liquid phases in grain growth and microstructural evolution. Anisotropy of the grain boundary mobility, and its role in the development of anisotropic (anisometric) microstructures is discussed as it is a central issue in recent efforts to produce ceramic materials with new combinations of properties and functionality.

The Role of Liquid Phase on Superplastictiy in Metals and Ceramics

The Role of Liquid Phase on Superplastictiy in Metals and Ceramics

Effect of manganese on sintering processes in the Ti-Fe system. III. High-temperature x-ray diffraction investigation of the sintering process

The temperatures of accelerated formation of intermetallic compounds in the Ti-Fe-Mn system correspond to the temperatures of sharp changes in the direction and rate of the sintering process and also of the appearance of heat evolution peaks. The rate of heating of compacts to sintering temperatures affects the mechanism of formation of intermetallic compounds: At lower rates of heating intermetallic compounds are formed by solid-phase reaction, while at higher rates the role of liquid phase grows. A relation has been established between the composition of the intermetallic compounds forming during sintering and the behavior of specimens during this process at various heating rates. At higher rates of heating of Ti-Fe-Mn compacts Ti-Fe intermetallic compounds are formed containing no Mn; the behavior of these specimens during sintering is similar to that of Ti-Fe compacts (the specimens grow). At lower heating rates intermetallic compounds alloyed with Mn are formed, and growth of specimens is followed by their shrinkage.

Hot-Pressed Iron Alloys in the Presence of Liquid Phase (2nd Report)

The role of liquid phase and pressure on the densification mechanism of hot pressing of iron-carbon alloys in the presence of liquid phase was clarified and also a strengthening of the alloys was investigated. With an increase of the sintering temperature, both sintering of iron powder and diffusion of carbon into iron powder occurred simultaneously and then densification proceeded by an easy movement of solid phase under a constant pressure of 10 kg/cm2 in the presence of liquid phase above the solidus line.After cooling, the bending strength of Fe-2%C alloy was decreased by the presence of cementite network. The alloys were strengthened by annealing at 1100°C for 3 hrs in a vacuum or by addition of 3%Cu or Ni. An Fe-3%Ni-1.7%C alloy made by this process provided a bending strength of 280 kg/mm2.