The experimental part of this thesis, Powder Processing of Bi-Pb-Sr-Ca-Cu-O Superconductors, contains of four main parts:​ a) Sample production techniques and their comparison (in terms of stoichiometry, phase composition, homogeneity, particle size, reactivity), characterisation of Bi-Pb-Sr-Ca-Cu-0 precursor powders;​ and the influence of the precursor powder properties, mainly in terms of particle size, on J_c of the Agsheathed tapes;​ b) methods of particle size reduction and particle size distribution measurements of the Bi-based superconducting precursor powder;​ c) investigation of the development of the high-temperature (Bi-2223) phase and its formation kinetics;​ d) effect of grain boundaries on electrical properties of the bulk Bi-Sr-Ca-Cu-0 system in terms of T_c and J_c values;​ and the effect of plastic deformation on grain boundaries and recrystallisation.

Three different chemical route sample production techniques, namely the freezedry, spray-dry and thermal co-decomposition methods, and the two-powder oxide route method were investigated experimentally. The most reactive chemical route utilised here was the freeze-drying method. The two-powder route was found to be intermediate in efficiency relative to the other techniques used here. The reactivity of the powders was related to the particle size and stoichiometric changes during heat treatment. It was found that the smaller the particle size, the higher the reactivity of the powder during sintering.

The final chemical stoichiometry of the 2223-phase and more particularly the state of particle agglomerates in the spray-dried powder are strongly dependent on the operating parameters of the spray-dry machine utilised, such as the inlet and outlet temperatures, rate of air drying, and the atomising air pressure. For this process, the optimum inlet and outlet temperatures were found to be 103 °C and 183 °C, respectively, and rate of air drying was 0.47 mm³/min, and the atomising pressure was 1.5 kg/cm\ respectively. Even after optimum temperatures, drying rate, and atomosing pressure were established, the precursor gave a lower yield of 2223 phase after a subsequent sintering than the precursors made by the other methods.

Various systems, consisting of agate and polypropylene grinding containers, agate and YSZ balls, and dry and wet milling, were used in planetary ball-milling, and YSZ balls and YSZ containers were used in wet and dry attrition milling. The differentlymilled powders were then evaluated by measurements of particle size, surface area, porosity, size distribution, and chemical analysis of Si, Zr and C contents. The results show that dry milling is much more efficient in planetary-milling than wet milling, whereas wet milling and dry milling gave quite similar results in attrition milling. Significant SiO₂ contamination was found in powder milled in an agate container with agate balls. Some C contamination from the polypropylene container was detected after milling, but negligible Zr from YSZ balls and C from the grinding carrier (hexane).

Effects of precursor particle size on J_c (77 K) values of the tapes produced by the powder in-tube (PIT) processes have been also investigated. Tapes were made from the milled powders made by spray drying and which had fine (1-2 pm), and coarse particle sizes (6-10 jam). They were packed by the powder-in-tube method (PIT) using the knocking method in which the silver tube was knocked against a metal block frequently during packing. The packed silver tubes were then mechanically worked into wires and tapes by square-rolling and flat-rolling. The resultant tapes were subjected to a heat treatment process consisting of three sintering steps with two intermediate pressings. Each sintering was conducted in air at 832 - 836 °C for 60 hours. Tape made from fine particles produced a higher J_c ( = 14,000 ± 4 A/cm² ) than that from coarse particles which produced J_c = 5,124 ± 4 A/cm² after heat treatment, clearly showing the effect of precursor particle size on J_c values.

After sintering for 40 hours at 850 °C in air (the heat-treatment affording maximum yield of 2223 phase) ball-milled oxide route powder has a larger grain size than equivalent powder which was not ball-milled, and higher J_c values (= 560 ± 5 A/cm²)-this is a good value compared to the similar materials made in other parts of the world. J_c value for unmilled powders was 520 ± 5 A/cm². Lower T_c (0) ( = 90K ) values are observed in larger Bi-2223 platelets as compared to T_c (0) = 94K for smaller grain size due to the weak-coupling at the grain boundaries as proposed in the Brick Wall Model. It also suggests that the majority Bi-2223 grains, grown as plates, have highangle [001] twist boundaries. Finally, it demonstrates that the recovery and the recrystallisation of the 2212 and 2223 grains, crushed upon ball-milling, occur in the sintering process.

For samples produced by a variety of methods and sintered for various times at 850 °C in air, the two-dimensional nucleation (random)-growth mechanism was found here to be attributable to the growth of the Bi-2223 grain in the a-b plane direction of the Bi-2212 matrix being much faster than in the c-direction, or that the plate-like precursor (2212) confines the 2223 product. It was shown here that the nucleation and the growth rate were very fast between 0 and 36 hours. At the final stage, between 36 and 60 h, because of the impingement of the growth fronts of different nuclei, the high formation rate of 2223 is suppressed.