Rate of solidification

White cast iron is brittle and difficult to machine. It is made by controlling the composition and rate of solidification of the molten iron so that all the carbon is present in the combined form. Very abrasive- and wear-resistant, white cast iron is used as liners and for grinding balls, dies, and pump impellers. 

Apparently, the direct transition from vapor to solid is less common than the double transition vapor — liquid — solid, see, e.g., Refs.158-160). From the rate of solidification of metal droplets (average diameter near 0.005 cm) at temperatures 60° to 370° below their normal melting points, the 7sl was concluded158) to be, for instance, 24 for mercury, 54 for tin, and 177 erg/cm2 for copper. For this calculation it was necessary to assume that each crystal nucleus was a perfect sphere embedded in the melt droplet the improbability of this model was emphasized above. 

Provost A. and Bottinga Y. (1974). Rates of solidification of Apollo 11 basalts and hawaiian tholeiite. Earth. Planet. Scl Letters, 15 325-337. 

In this example, the equilibrium concentrations maintained at the interface are functions of the interface temperature, which in turn is a function of time. In addition, the velocity of the interface, v (i.e., rate of solidification), depends simultaneously upon the mass diffusion rates and the rates of heat conduction in the two phases, as may be seen by examining the two Stefan conditions that apply at the interface. For the mass flow the condition is... 

The second study (Ref 58), published in 1976, likewise noted a 10—11% shrinkage upon solidification, and studied the solubility of various gases in the melt, as well as the rate of solidification of the supercooled liq at various rates of heat removal and at various temps. The role of nucleating agents was discussed, and HNS was shown to be effective. The established physical principles of solidification were found fully applicable t TNT... 

As a eutectic front advances during solidification, the solutes must partition between the two phases, as suggested in Figure 10.19. With increased rates of solidification, there is less time for diffusion so the eutectic structures are finer. 

The formation and preservation of the uniform cell structure of either the solid polymer or frozen foam depend on the properties of the initial foam, i.e. on its expansion ratio and stability. On the one hand, the former two processes are determined mainly by the rates of drainage and internal foam collapse. On the other hand, however, they are affected by the rate of polymerisation and the increase in strength of the foam material. That is why optimisation of the processing properties of polymer foams can be achieved by decreasing both the rate of microsyneresis and drainage, and the rate of internal foam collapse. Along with that precise control of the rate of solidification, reduction of the water content and introduction of plastifiers are needed. 

The kinetics studies of solidification of urea-formaldehyde resins have shown [24] that at low solidifier (phosphoric acid) concentrations, in the range from 0.3 to 0.75%, a prolonged induction period of solidification is observed, lasting for ca. 30 min. The optimum rate of solidification is achieved at acid concentrations higher than 1-1.5%, but the process is strongly delayed at resin concentrations lower that 5-10%. 

As the case previously explained was comparable with fusion and solidification, and the velocity then discussed with the rate of solidification, so here the phenomena may be brought into delation with the physical phenomenon of evaporation, which, in analogy with the change of moving force just referred to, goes more slowly up to the occurrence of equilibrium, here reached when the vapour pressure has risen to a maximum. 

Figure 21 displays the data for temperature versus rate of solidification of a casting of a fan from an AL9 grade alloy the experiment reveals significantly slowed down solidification in an ultrasonic field. 

The mean growth rate of solidification is given by V KiG,/L, where G, is... 

Figure 11.10 is a semiquantitative approach to a rating of solidification products according to stability and technological simplicity [E2]. 

The shrinkage may vary from place to place depending on the rate of solidification. The simplest example is a solid block that solidifies rapidly on the outside the hard skin formed this way prevents further shrinkage of the inner part. This results in internal stresses which may lead to tearing and void formation. 

---