Ac susceptibility measurements have been used to monitor the changes in the superconductive properties of sintered and uniaxially pressed samples of Pb-stabilized 2223-phase bismuth cuprate ceramic as the structural damage was annealed in air in a sequence of steps in temperature between 500 and 850 °C. It is concluded that below 600 °C a relaxation of residual stresses is responsible for a 2% shrinkage in sample volume and a small improvement in bulk superconductive transition temperature, Tc. Above 700 °C, a recovery of the original properties occurs through grain regrowth governed by an activation energy of ∼200 kJ/mol. However, in the region between 600 and 700 °C, a decrease in Tc of ∼40 K appears to be the result of plastic flow and amorphization associated with local decomposition of 2223 which reduces the effective grain size and weakens the intergranular superconductive coupling.

Superconducting composite samples were prepared by sintering a mixture of metallic silver and Bi(Pb)–Sr–Ca–Cu–O powder in air. For Ag contents between 0 and ∼15 vol. %, the bulk critical temperature was depressed as much as 40 K, and the relative proportion of the 2223 phase with respect to the 2212 phase was decreased, compared to the pure sample. However, as the Ag content was increased to between 19 and 70 vol. %, critical temperatures above 100 K were measured by transport and ac susceptibility techniques, and the relative proportions of the phases were restored to that of the pure sample. The limit of bulk superconductivity was reached at 73 vol. % Ag where the bulk critical temperature was ∼85 K. For higher Ag contents bulk superconductivity was not observed. Our results also show that sintering in air of silver-clad tapes containing Bi(Pb)–Sr–Ca–Cu–O powder, either by itself or with silver powder, need not be detrimental to the final superconductive properties.

During cementing operations, the hydrostatic pressure of the cement slurry column is utilized to control the reservoir pressure. However, when the well extends through weak formations, it is often necessary to lighten the hydrostatic pressure of the slurry by lowering the density to avoid hydraulically fracturing the reservoir rock. Densities of cement slurries can be lowered by adding pozzolanic lightweight additives such as fly ash. Fly ashes have found utility in numerous oil and gas well cementing applications, namely: 1) fly ash can be dry-blended with regular Portland cements or hydrated lime for use in primary cementing; 2) lightweight cement compositions can be formulated by adding lime and finely ground quartz to fly ash/cement mixtures; and 3) an ultralight-weight pozzolanic microsphere cement, with densities as low as 0.96–1.64 g/cm3, can be formulated by blending Portland cements with hollow microspheres isolated from fly ash. This paper discusses the physical and chemical properties of each of these cement slurries, along with their relative advantages and disadvantages. Areas of future research are also discussed.