Comment on “A New Alumina Hydrate, “Tohdite,” by G. Yamaguchi, H. Yanagida and S. Ono”

Phase equilibria investigations and thermodynamic modeling of the PbO–Al2O3 system

“…Therefore, that valuew as considered for modeling in our work, with an estimated deviationof±10 8 C. Forthe compound (1 :1), bothGeller &Bunting [4] and Kuxmann and Fischer [6]a gree about the decomposition temperatureo f 1000 8 Cw hich was measured directly by differential thermal analysis (DTA), and which is close to that found by Shim and Jacob [19]. We therefore used that value for modeling, also withadeviation of ±10 8 C. Considering the peritectic decomposition temperatureo ft he compound (1 :6), there is al ack of consistency in the experimental values since it has not been determined clearly and presents great differences that can be over1 00 8 C [ 2,5,12]. However, for all suggested modelings of the system PbO-Al 2 O 3 [3,21,23], the calculated temperatures are distributed around 1511 8 C [21].…”

“…The intermediate compound PbAl 2 O 4 (1 :1)w as evidenced, and two invariant transformationsw ere measured, corresponding to the decomposition of (1 :1)and to aeutectic transformation. Later, Torkar et al [5] suggested adetailed phase diagram with full composition range between 600 8 Ca nd 1100 8 C ( Fig. 2).T hey evidenced three intermediate compounds, i) PbAl 12 O 19 (1 :6)s howing ah exagonals ymmetry D 4 6h and as mall solubilityr ange; ii) PbAl 2 O 4 (1 :1)w hich was found to be monoclinic with two possible groups C 2 2 P2 1 or C 2 2h P2 1 = m; and iii) the compound Pb 2 Al 2 O 5 (2 :1)w ith acubicstructure.…”

“…Optical, XRD and DTA1 000 865 87.7 ±2 [5] XRD and DTA 970 -1000 800* 1100 830 90 - [12] X-ray spectroscopyand XRD -->1 000 --- [6] DTA9 55 1000 -8 58 96.5 - [2] Knudsen effusion cell, XRD, and EDS lyte [19]. Their results allowed them to calculate the peritectic temperatures of (2 :1)a nd (1 :1).…”

Phase equilibria in the PbO--Al/sub 2/O/sub 3/ system

“…The liquidus position was approximated by a straight line ~!6 = -5 X 10-4 T + L 456 (9) w•here the temperature is in degrees Kelvin. The natural logarithm of the aetivity coefficient in the range of applicability of equations (8) and (9) is shown as the diagonal set of numbers in Table 2.…”

Synthese und Kristallstruktur von Pb2LnAl3O8 (Ln = Eu, Gd) / Synthesis and Crystal Structure of Pb2LnAl3O8 (Ln = Eu, Gd)

“…B ekannt sind PbA l20 4 [1,2,3] und P b 2A l20 5 [1] welches sich später als P b 9A l80 21 [4] h e ra u s stellte. Kürzlich w urde ausgeführt, daß die P a ra m eter von PbA l20 4 auch in eine höhersym m etrische R aum gruppe transform iert w erden können [5].…”