Mannesmann gets high density by carbon-free sintering

A study was made of the solid state equilibrium relations in the Ho2O3, SiO2 system within the temperature range 1100–1600 C. Four silicates were identified: (1) Ho2)O3·SiO2, stable throughout the temperature range considered, with an elementary monoclinic cell with lattice constants a = 10.35 Å, b = 6.710 Å, c = 12.35 Å and β = 102.5; (2) 2Ho2O3·3SiO2, stable above 1300°C, with an elementary hexagonal cell with lattice constants a = 9.340 Å and c = 6.722 Å; (3) Ho2O3·3SiO2, with two crystalline modifications, one of which is stable between 1150 and 1250C with an elementary monoclinic cell with lattice constants a = 6.843 Å, b = 8.916 Å, c = 4.703 Å and β = 102.12°, whilst the other, also monoclinic, is stable above 1250°C with lattice constants a = 5.580 Å, b = 10.830 Å, c = 4.690 Å and β = 96.15; (4) Ho2O3· 6SiO2, stable only up to 1150°C.