Paper 6.6

REDOX EQUILIBRIA BETWEEN PHOSPHATES AND PHOSPHIDES IN PHASE DIAGRAMS  M / P / O (M = Cr, Mn, Co, Ni, Cu)

 

Blum Matthias1, Gerk Michael 2, Glaum Robert1, Özalp Durzun2, and Schmidt Anette2

 

1 Inst. f. Anorg. Chemie; Gerhard-Domagk-Str. 1, D-53121 Bonn (Germany)

2 Inst. f. Anorg. u. Analyt. Chemie; Heinrich-Buff-Ring 58, D-35392 Gießen (Germany)

 

Redox equilibria between transition metal phosphates and corresponding phosphides are of great importance to many technical applications like heterogenous catalysis and anti-corrosive coatings. Detailed information on such phase relations is also the prerequi-site to the systematic selection of experimen-tal conditions for crystal growth of phosphi-des and phosphates, especially by chemical vapour transport. 1 However, prior to our own work, only the phasediagram Fe/P/O 2 was well established. In the meantime we have determined the equilibrium relations for several more systems M/P/O (M: transition metal). 3 - 7

Experiments to determine the phase equilibria in the systems M/P/O (M = Cr, Mn, Co, Ni, Cu) (Fig. 1 – 3) were carried out in sealed evacuated silica tubes using iodine as mineralizer. Generally, the metals, phospho-rus, phosphides accessible by chemical vapor transport, and phosphates deposited from aqueous solution were used as starting materials. In exceptional cases only, P4O10 was used.

Oxygen equilibrium pressures have been measured for Co/P/O and Ni/P/O. 8

 

Fig. 1  Phase diagram Cr / P / O at 1000°C. 7 A: Cr 2P2O7, B: Cr3(PO4)2, C: Cr7(PO4)6, D: CrPO4, E: Cr3(P2O7)2, F: Cr4(P2O7)3, G: Cr2P4O13, H: CrP3O9. 

 

Fig. 2  Phase diagram Co / P / O at 800°C. 5 A: Co 3(PO4)2, B: Co2P2O7, C: Co2P4O12, D: CoP4O11, E: P4O10.

 

 

 

 

 

 

 

 

 

 

 

Fig. 3  Phase diagram Cu / P / O at 600°C. 3 A: Cu 5O2(PO4)2, B: Cu4O(PO4)2, C: Cu3(PO4)2, D: Cu2P2O7, E: Cu2P4O12, F: CuP4O11, G: Cu2PO4. References

1 C. Gleitzer, Eur. J. Solid State Inorg. Chem. 1991, 28, 77. 2 R. Gruehn, R. Glaum, Angew. Chem. 2000, 112, 706. D. 3 Özalp, Ph.D. Thesis, Univ. of Gießen (1993). 4 M. Gerk, Ph.D. Thesis, Univ. of Gießen (1996). 5 A. Schmidt, Ph.D. Thesis, Univ. of Gießen (2002). 6 M. Blum, planned Ph.D. Thesis, Univ. of Bonn. 7 R. Glaum, Habilitation Thesis, Univ. of Gießen (1999), this thesis is available via internet: http://bibd.uni-giessen.de/ghtm/1999/uni/h990001.htm.
8 M. Blum, K. Teske, R. Glaum, Z. anorg. allg. Chem. 2003, 629,