Problems In Realistic Modelling Of Interfacial Reactions

1985 ◽  
Vol 54 ◽  
Author(s):  
Charles W. Allen ◽  
Gordon A Sargent
Keyword(s):  
Single Phase ◽  
Driving Forces ◽  
Thermodynamic Description ◽  
Nucleation Theory ◽  
Initial Reaction ◽  
Thermodynamic Prediction ◽  
Multiple Product ◽  
Solid Liquid ◽  
Reaction Processes ◽  
Reaction Problem

ABSTRACTFor modelling the reaction of chemically distinct materials in which intermediate alloy phases are formed a simple thermodynamic description is not adequate. Despite thermodynamic prediction of multiple product phases, a single phase generally forms first which is not necessarily that of greatest thermodynamic stability or of simplest structure. Such initial reaction processes may be modelled as metastable perltectoid (solid-solid) or perltectlc (solid-liquid) reactions, characterized by large thermodynamic driving forces with superimposed kinetic and morphological constraints. The interfacial reaction problem is reviewed in light of heterogeneous nucleation theory with emphasis on non-classical aspects.

Accurate thermodynamic description of vapor–liquid and solid–liquid equilibria of THF, water and gas hydrates with a unique set of parameters

2018 ◽  
Vol 117 ◽  
pp. 60-67 ◽  
Author(s):  
Ingrid Azevedo de Oliveira ◽  
Iuri Soter Viana Segtovich ◽  
Amaro Gomes Barreto Jr. ◽  
Frederico Wanderley Tavares
Keyword(s):  
Gas Hydrates ◽  
Thermodynamic Description ◽  
Solid Liquid ◽  
Vapor Liquid

scholarly journals Crystal Memory near Discontinuous Triacylglycerol Phase Transitions: Models, Metastable Regimes, and Critical Points

Molecules ◽  
2020 ◽  
Vol 25 (23) ◽  
pp. 5631
Author(s):  
David A. Pink ◽  
Marjorie Ladd-Parada ◽  
Alejandro G. Marangoni ◽  
Gianfranco Mazzanti
Keyword(s):  
Phase Transition ◽  
Critical Point ◽  
Single Phase ◽  
Hydrocarbon Chain ◽  
Temperature Data ◽  
Recent Time ◽  
Recent Experimental Data ◽  
Hydrocarbon Chain Length ◽  
Discontinuous Phase ◽  
Solid Liquid

It is proposed that “crystal memory”, observed in a discontinuous solid-liquid phase transition of saturated triacylglycerol (TAG) molecules, is due to the coexistence of solid TAG crystalline phases and a liquid TAG phase, in a superheated metastable regime. Such a coexistence has been detected. Solid crystals can act as heterogeneous nuclei onto which molecules can condense as the temperature is lowered. We outlined a mathematical model, with a single phase transition, that shows how the time-temperature observations can be explained, makes predictions, and relates them to recent experimental data. A modified Vogel-Fulcher-Tammann (VFT) equation is used to predict time-temperature relations for the observation of “crystal memory” and to show boundaries beyond which “crystal memory” is not observed. A plot of the lifetime of a metastable state versus temperature, using the modified VFT equation, agrees with recent time-temperature data. The model can be falsified through its predictions: the model possesses a critical point and we outline a procedure describing how it could be observed by changing the hydrocarbon chain length. We make predictions about how thermodynamic functions will change as the critical point is reached and as the system enters a crossover regime. The model predicts that the phenomenon of “crystal memory” will not be observed unless the system is cooled from a superheated metastable regime associated with a discontinuous phase transition.

Low-temperature synthesis and sintering of γ-Y2Si2O7

2006 ◽  
Vol 21 (6) ◽  
pp. 1443-1450 ◽  
Author(s):  
Ziqi Sun ◽  
Yanchun Zhou ◽  
Meishuan Li
Keyword(s):  
Single Phase ◽  
Synthesis Temperature ◽  
Densification Rate ◽  
Calcination Time ◽  
Low Temperature Synthesis ◽  
Temperature Synthesis ◽  
Liquid Reaction ◽  
The Stability ◽  
Yttrium Disilicate ◽  
Solid Liquid

In this article, a novel pressureless solid-liquid reaction method is presented for preparation of yttrium disilicate (γ-Y2Si2O7). Single-phase γ-Y2Si2O7 powder was synthesized by calcination of SiO2 and Y2O3 powders with the addition of LiYO2 at 1400 °C for 4 h. The addition of LiYO2 significantly decreased the synthesis temperature, shortened the calcination time, and enhanced the stability of γ-Y2Si2O7. The sintering of these powders in air and O2 was studied by means of thermal mechanical analyzer. It is shown that the γ-Y2Si2O7 sintered in oxygen had a faster densification rate and a higher density than that sintered in air. Furthermore, single-phase γ-Y2Si2O7 with a density of 4.0 g/cm3 (99% of the theoretical density) was obtained by pressureless sintering at 1400 °C for 2 h in oxygen. Microstructures of the sintered samples are studied by scanning electron microscope.

scholarly journals Self-Consolidation Mechanism of Nanostructured Ti5Si3Compact Induced by Electrical Discharge

2015 ◽  
Vol 2015 ◽  
pp. 1-8 ◽  
Author(s):  
W. H. Lee ◽  
Y. W. Cheon ◽  
Y. H. Jo ◽  
J. G. Seong ◽  
Y. J. Jo ◽  
...  
Keyword(s):  
Electrical Discharge ◽  
Single Phase ◽  
External Pressure ◽  
Surface Oxide ◽  
Complete Conversion ◽  
Rapid Cooling ◽  
Pinch Force ◽  
Powder Particles ◽  
Solid Bulk ◽  
Solid Liquid

Electrical discharge using a capacitance of 450 μF at 7.0 and 8.0 kJ input energies was applied to mechanical alloyed Ti5Si3powder without applying any external pressure. A solid bulk of nanostructured Ti5Si3with no compositional deviation was obtained in times as short as 159 μsec by the discharge. During an electrical discharge, the heat generated is the required parameter possibly to melt the Ti5Si3particles and the pinch force can pressurize the melted powder without allowing the formation of pores. Followed rapid cooling preserved the nanostructure of consolidated Ti5Si3compact. Three stepped processes during an electrical discharge for the formation of nanostructured Ti5Si3compact are proposed: (a) a physical breakdown of the surface oxide of Ti5Si3powder particles, (b) melting and condensation of Ti5Si3powder by the heat and pinch pressure, respectively, and (c) rapid cooling for the preservation of nanostructure. Complete conversion yielding a single phase Ti5Si3is primarily dominated by the solid-liquid mechanism.

Thermoelectric Performance of Half-Heusler TiNiSn Alloys Fabricated by Solid-Liquid Reaction Sintering

2010 ◽  
Vol 654-656 ◽  
pp. 2795-2798 ◽  
Author(s):  
Yoshisato Kimura ◽  
Chihiro Asami ◽  
Yaw Wang Chai ◽  
Yoshinao Mishima
Keyword(s):  
Figure Of Merit ◽  
Single Phase ◽  
Electrical Power ◽  
Reaction Sintering ◽  
Sintering Process ◽  
Liquid Reaction ◽  
Dimensionless Figure Of Merit ◽  
Maximum Value ◽  
Gas Atmosphere ◽  
Solid Liquid

A new fabrication process was proposed for half-Heusler type TiNiSn thermoelectric alloys. Based on the result that the TiNiSn phase can be formed easily at the Sn(Liquid)/TiNi(Solid) interface, the liquid-solid reaction-sintering process was developed using TiNi and Sn powders. The TiNi compound powders were prepared by the atomization method using argon gas atmosphere. We have fabrictaed nearly single-phase TiNiSn alloys and evaluated their thermoelectrical properties; the presnt TiNiSn alloys have large electrical power factor of about 3.5 mWm-1K-2, and the maximum value of dimensionless figure of merit, ZT = 0.67, can be achieved at around 700 K even without tuning of the carrier concentration through alloying elements.

scholarly journals Influence of Blade Type on the Flow Structure of a Vortex Pump for Solid-Liquid Two-Phase Flow

Machines ◽  
2021 ◽  
Vol 9 (12) ◽  
pp. 353
Author(s):  
Hui Quan ◽  
Yanan Li ◽  
Lei Kang ◽  
Xinyang Yu ◽  
Kai Song ◽  
...  
Keyword(s):  
Flow Structure ◽  
Liquid Flow ◽  
Single Phase ◽  
Solid Phase ◽  
Internal Flow ◽  
Phase Flow ◽  
Centrifugal Pumps ◽  
Two Phase ◽  
Vortex Pump ◽  
Solid Liquid

Vortex pumps have good non-clogging performance owing to their impellers being retracted into retraction cavities, but they are much less efficient than ordinary centrifugal pumps. In this paper, numerical simulations were performed on a model of the 150WX200-20 vortex pump for four different blade types, and the influence of blade structure on pump performance was determined. The simulations revealed the existence of axial vortices in the flow passage between the blades in the impeller region. The geometric characteristics of these axial vortices were more regular in two-phase solid-liquid flow than single-phase liquid flow. The presence of the solid phase reduced the vortex strength compared with the single-phase flow and suppressed the increase in size of the secondary circulation vortex. It was found, however, that the blade shape had a greater influence on the circulating flow than the presence of the solid phase. The flow state of the medium flowing out of the impeller domain had a direct effect on the circulating flow with this effect being related to the law governing the flow of the medium in the flow channel between the blades. It was found that the performance of a front-bent blade was the best and that of a curved blade the worst. This influence of blade type on the internal flow structure was used to further explain the relationship between the internal flow structure and the external characteristics of the vortex pump, the understanding of which is crucial for blade selection and hydraulic optimization.

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