Grain growth definition

With the definition of the pore mobility, it is possible to analyze the influence of the interactions between the pores and the grain boundaries on the kinetics of grain growth. There are two cases that can be considered (i) the pore becomes separated from the boundary and (ii) the pore remains attached to the boundary. 

As proven by many authors, the dependence of the type (a) definitely implies a parabolic law for the mean size, as in the case of normal grain growth. The basic... 

Discussion. The turbidity of a dilute barium sulphate suspension is difficult to reproduce it is therefore essential to adhere rigidly to the experimental procedure detailed below. The velocity of the precipitation, as well as the concentration of the reactants, must be controlled by adding (after all the other components are present) pure solid barium chloride of definite grain size. The rate of solution of the barium chloride controls the velocity of the reaction. Sodium chloride and hydrochloric acid are added before the precipitation in order to inhibit the growth of microcrystals of barium sulphate the optimum pH is maintained and minimises the effect of variable amounts of other electrolytes present in the sample upon the size of the suspended barium sulphate particles. A glycerol-ethanol solution helps to stabilise the turbidity. The reaction vessel is shaken gently in order to obtain a uniform particle size each vessel should be shaken at the same rate and the same number of times. The unknown must be treated exactly like the standard solution. The interval between the time of precipitation and measurement must be kept constant. 

Fig. 13.11. Simplified cross-section diagram showing the structure of heartwood (duramen). Definition of grain (G = Lc (mm)) and texture (T = Bf/Lc) Lc, width of an annual growth ring Bi, early or spring wood Bf, late or summer wood (Vivas, 1997)...

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