How the grain-size composition of nickel carbonyl powders affects the structure of cermet bases of accumulator electrodes

Conclusions

• 1. The authors characterize the degree of dispersion and specific surface of light powders of Ni carbonyl with specific volumes of 1.1–2.06 cm³/g by sedimentation analysis, air filtration, and low-temperature adsorption of nitrogen. Comparison of the data with the corresponding characteristics of heavy powders (with specific volumes of 0.25 and 0.37 cm³/g) revealed marked differences in their dispersion character.

• 2. It has been found that the surface areas calculated by these three methods coincide only for powder with a specific volume of 0.25 cm³/g. Electron micrographs reveal that it consists of individual equiaxial particles, whereas light powders are agglomerates with a chain-like, fibrous structure.

• 3. For these light powders, none of the analytical methods revealed marked differences in their dispersion characters or specific surfaces; this is due to their inherent capacity to undergo aggregation during preparation from nickel carbonyl. These aggregates are very strong and could not be dispersed by the usual methods.

• 4. It has been established that sedimentation analysis (with use of a 1∶1 mixture of Vaseline oil and xylene as dispersion medium and processing of the experimental data by Tsyurupa's method) gives a correct picture of the dispersion character of the powders. In the case of light powders, the values of the mean hydrodynamic (or equivalent) radius, determined by this method, are not the dimensions of individual particles, but the diameter of the aggregate chain. It is postulated that it is just this value which determines the predominant pore radius of bases sintered from light powders. The differences between the specific volumes (bulk densities) of light powders are due to their packing, which depends on the length of the chains forming these aggregates.

• 5. The absence of marked differences in the dispersion character of this group of light powders is confirmed by a mercury-porometric investigation of the structure of cermet bases of accumulator electrodes obtained from them. These bases have virtually the same predominant pore radius (1–3 as compared to 7–10 mμ for bases sintered from heavy powders).

• 6. It has been found that accumulator plates made from Dzerzhinskii powder have superior specific characteristics and higher total pore volumes.