The mechanism of natural precipitation processes has been studied using as a model system the one-dimensional double diffusion of the precipitating components in a gel. It was found, theoretically and experimentally, that precipitation under conditions of double diffusion occurs when the equivalent concentrations of both precipitating components are equal to a " critical " concentration. Under the experimental conditions used here the conventional solubility law does not apply. A general relation is deduced which enables the estimation of the relative error in the determination of the critical concentration for precipitation. Theoretical treatments of other authors are discussed.Precipitation processes occurring in nature are mostly controlled by diffusion of the precipitating components to the place where precipitation starts.In our previous paper we described the precipitation in gels of components which diffused towards the place of precipitation. Whatever the nature of the precipitating components and initial conditions are, it seems that under condition of double diffusion precipitation starts at a place and at a time defined by a critical concentration for precipitation.In this paper we attempt to explain the stoichiometry of the formation of precipitates under conditions of double diffusion. The formation of lead chromate precipitate in agar gel under conditions of one-dimensional double diffusion of the precipitating components, lead nitrate and potassium chromate, was chosen as a model system.
THEORYOne-dimensional diffusion of two precipitating components A and B, through a gel can be described by Fick's second law of diffusion :
The results of thermodynamic analysis and the characterization of alloys in the ternary system Au-In-Sb are presented in this study. Thermodynamic analysis was carried out by applying the Toop and Muggianu predicting methods in sections from the Au, In and Sb corner, respectively, with the following ratios 1:3 and 3:1. in the temperature interval from 873 to 1673 K. Characterization of the alloys in section Au-In-Sb was performed using optical microscopy, SEM/EDX analysis and by hardness measurements of the investigated alloys
The results of the determination of the thermodynamic properties for ternary
systems Cr.Co.Me (Me = Mo, Al) using a new general solution model for the
predictions are presented in this work. For five sections (with mole ratio
Co :Me = 2:8, 4:6, 5:5, 6:4, 8:2) investigated in each ternary system at
temperature of 2000 K, integral molar excess Gibbs energies and partial
molar thermodynamic properties of chromium were calculated.
Lead-free soldering has become very popular in the world recently, especially in electronics, because of high ecological demands in industry. Some of lead-free solder alloys are already used in electronic industry, but despite that investigations are still going in order to find suitable replacement for Pb-Sn standard solder. In this paper phase equilibria and characterization of Sn-In-Ag alloys in section In:Ag = 7:3 are investigated. The results of phase diagram calculation are obtained by ThermoCalc software, and characteristic temperatures by DSC method. The results of XRD analysis, optical microscopy, microhardness and electrical conductivity are also presented. These results are given in order to contribute the knowledge about lead-free solders, especially Sn-In-Ag solder alloys, which are potential candidates for replacement standard lead solders
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