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Precipitated hydrous zirconium oxide can be calcined to produce either a monoclinic or tetragonal product. It has been observed that the time taken to attain the final pH of the solution in contact with the precipitate plays a dominant role in determining the crystal structure of the zirconium oxide after calcination at 500 °C. The dependence of crystal structure on the rate of precipitation is observed only in the pH range 7–11. Rapid precipitation in this pH range yields predominately monoclinic zirconia, whereas slow (8 h) precipitation produces the tetragonal phase. At pH of approximately 13.0, only the tetragonal phase is formed from both slowly and rapidly precipitated hydrous oxide. The present results, together with earlier results, show that both the pH of the supernatant liquid and the time taken to attain this pH play dominant roles in determining the crystal structure of zirconia that is formed after calcination of the hydrous oxide. The factors that determine the crystal phase are therefore imparted in a mechanism of precipitation that depends upon the pH, and it is inferred that it is the hydroxyl concentration that is the dominant factor.

SummaryDelayed donor erythropoiesis and pure red‐cell aplasia (PRCA) complicate major‐ABO mismatched non‐myeloablative allogeneic stem‐cell transplantation. To characterize these events, we analysed red‐cell serology and chimaerism in lymphohaematopoietic lineages, including plasma cells and B cells, in 12 consecutive major‐ABO incompatible transplants following cyclophosphamide/fludarabine‐based conditioning. Donor erythropoiesis was delayed to more than 100 days in nine (75%) patients including six (50%) who developed PRCA. During PRCA, all patients had persistent anti‐donor isohaemagglutinins and recipient plasma cells (5–42%), while myeloid and T cells were completely donor in origin. In contrast, B‐cell chimaerism was frequently full‐donor when significant anti‐donor isohaemagglutinins persisted. Four patients with early mixed haematopoietic chimaerism and the prolonged presence of anti‐donor isohaemagglutinins and recipient plasma cells developed delayed‐onset (>100 days post‐transplant) red cell transfusion dependence and PRCA after myeloid chimaerism converted from mixed to full donor. These findings confirm that donor‐erythropoiesis is impacted by temporal disparities in donor immune‐mediated eradication of recipient lymphohaematopoietic cells during major‐ABO incompatibility and suggest that plasma cells are relatively resistant to graft‐versus‐host haematopoietic effects.