Spongy-like deposits

The electrode surface roughness at low level of coarseness can be increased in some different ways other than dendrites (spongy-like deposit,33 honeycomb-like structure,76,77 pyramid-like deposit,83 etc.) on the microscale. The properties of electrodeposits on nanoscale should be also taken into consideration.84,85 Further investigation will show which one of them is the best for this purpose. This chapter is written in order to initiate it. 

Anhydrous fibrous silicas formed in connection with high temperature metallurgical operations were noted as long ago as 1852 by Schnabel and 1859 by Rose. Soft, silky fibers of more than 98% SiO, were classed as aphanitic (invisible) silica, and also known as lussatite. Around 1910. in the mouths of electric furnaces making silicon carbide, a soft spongy gray deposit called elephant s ear" was identified as microfibrous amorphous silica (67). It is likely that all of these were silica W. 

In the Co-Ni alloy powder deposit with the highest percentage of Co (85 at.%), Fig. 5.13, different types of agglomerates could be detected (1) spongy-like agglomerates of the size of about 5(X) pm... 

The electrolytic deposit should be salmon-pink in colour, silky in texture, and adherent. If it is dark, the presence of foreign elements and/or oxidation is indicated. Spongy or coarsely crystalline deposits are likely to yield high results they arise from the use of too high current densities or improper acidity and absence of nitrate ion. 

The nucleus of spongy deposit, i.e., hedgehog-like particle, appears when amplification of surface coarseness on the nucleus in spherical diffusion control growing starts. It was shown earlier [118] that this amplification is very fast so the induction time when growing nucleus enters mixed control can be taken also as induction time of spongy formation. It follows from Eqs. (2.139) and (2.140) that and decrease with increasing overpotential. 

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