Abstract
When powders are compressed statically by the piston compression the porosity decreases. The typical example of the process of po-wder compression indicates the various forms according to the nature of powder as shown in Fig. 1. In the previous reports the author already confirmed that the relationship between ratio of compressed volume C=(V O-V)/V O and pressure P is represented in the following equation :
C=(V O-V)/V O=ab P/(1+b P),
where V O= initial volume of powder, V O= volume of powder under static load P, a and b are the characteristic constants of powder.
"a" corresponds to the limiting value of ratio of compressed volume C ∞, that is the initial porosity. "b" corresponds to the coefficient of compression and has the meaning related to the rheological behavior of powders. In the case of ordinary powders "a" indicates the value 30 to 800 (Table 1).
From the above equation we get
P/C=1/ab+1/aP.
The plot of P/C against P from this equation will give a straight line of positive slope 1/a, with an intercept 1/ab. It is as shown in Fig. 2. The applicability of this equation is of a wide range of compression process. This equation comprises the Athy's equation and also the applicability is better than the equations of Balshin and Nutting as shown in Fig. 4. When compressed powders became free from load, the volume expansion took place as shown in Table 1.
Concerning the relation between the porosity and the shape of particles of powders the author examined the difference of spherical and non-spherical powders as shown in Table 2.
In the case of tapping compression, if we take the tapping number instead of P, the good applicability of its process was observed as shown in Fig. 5.
Besides these, in relation to the anomaly in the infrared spectra, the author observed that the double decomposition reaction between oxalic acid or some oxalates and alkali halide took place by the powder compression (Table 4, Fig. 6, 7, 8.). In this case it was confirmed that the presence of water vapor played an important part in these reactions.
