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Tantalum capacitors play an important part in modem electronics. They are used in the most demanding of circuit applications, because of their outstanding characteristics, such as: compatibility with Surface Mounted Technology, small size, ability to operate over relatively wide temperature spectrum, and high reliability. Whereas the production of capacitors more than tripled over the last eight years, the amount of powders needed for this increase grew by no more than 10%. One of the main reasons for this development has been the achievement of powder producers to increase the capacitance/g of Tantalum powder. Today there are powders available with a CV/g value of 40-50 K and higher. The development of high CV powders was a complicated process made possible by using finer powders, the introduction of sophisticated agglomeration techniques and deoxidization. High capacitance powders have to be sintered at lower temperatures or shorter sinter times to preserve the high surface area. The lowering of sintering temperature results in decreasing the purification of the powder during sintering. Therefore, high capacitance powders have to be purer before the sintering than low capacitance powders of the past.

The variation of the photocurrent with temperature is found to obey the relation i = i0e−E/RT in naphthalene, stilbene, diphenyl, terphenyl, β-methylanthracene, anthracene, azulene, and pyrene. The activation energies have been measured and are found to increase in the above order. These activation energies show no apparent correlation with the corresponding activation energy of semiconduction, and it is suggested they are associated with the charge carrier transport process.

The spectral response, voltage dependence, and intensity dependence of the surface photocurrent in naphthalene, terphenyl, pyrene, stilbene, and azulene have been measured. Pyrene and naphthalene have a high sensitivity for photoconduction at the long-wavelength edge of the optical absorption spectrum. In the spectral response of pyrene three peaks appear at 4475 Å, 4275 Å, and 4100 Å. It is suggested that these peaks are due to weak optical absorptions to energy levels which are highly efficient in promoting conduction. It is possible that a similar effect occurs in naphthalene, where maximum photoconductivity coincides with a weak absorption reported by McClure and Schnepp. Azulene only shows photoconductivity at wavelengths corresponding to absorption to the second singlet state.

The variation of the photocurrent and dark current on melting naphthalene and biphenyl was studied. A large increase in the value of the photocurrent was observed. This change is very similar to that of the dark current. It is concluded that the increased mobilities of the charge carriers in the melt are mainly responsible for the change in both cases. The existence of photoconduction in the non-crystalline state is discussed.

In order to investigate further the nature of the proton resonance shifts accompanying hydrogen bonding, and their relation to the properties of the hydrogen bond, the resonance shift of the acceptor molecule chloroform, interacting in turn with a variety of donor molecules, was measured. The donor liquids chosen were (Et)3N, (Et)2O, PrF, (Me)CO, and EtCN. These are all virtually non-associated in the pure state and may be expected to form simple 1:1 hydrogen-bonded complexes with chloroform, whose existence was confirmed by measuring the binary freezing-point phase diagrams. The difference between the proton shift of chloroform at infinite dilution in each of the donor solvents and at infinite dilution in inert hydrocarbon solvents was taken as the "association" shift representing the difference between chloroform in the hydrogen bonded complex and unassociated chloroform. These shifts correlate well with the expected hydrogen bond strengths in each system and the relative donor strength of the individual solvent molecules. The proton resonance technique appears as a promising method for measuring these properties.

The effects of various complexing agents on the homogeneous reduction of mercuric salts by molecular hydrogen in aqueous solution were determined. In all cases the kinetics suggest that the rate-determining step is a bimolecular reaction between a mercuric ion or complex and a hydrogen molecule, probably leading to the formation of an intermediate mercury atom. The reactivity of various mercuric complexes was found to decrease in the following order: HgSO4 > Hg++ > HgAc2, HgPr2 > HgCl2 > HgBr2 > Hg(EDA)2++. Addition of anions such as OH−, CO3=, Ac−, Pr−, and Cl−, in excess of the amounts required to form stable mercuric complexes, was found to increase the rate. An interpretation of these effects is given.