INVESTIGATION OF THE NIOBIUM-OXYGEN SYSTEM. II. SOLUTION OF OXYGEN IN NIOBIUM AND PRECIPITATION OF OXIDE FROM SUPERSATURATED MIXED CRYSTALS

Journal Article · Fri Nov 01 04:00:00 EST 1963 · Z. Metallk.

OSTI ID:4128117

Gebhardt, E; Rothenbacher, R

The solubility limit of oxygen in niobium between 500 and 1900 deg C was determined by measurement of electrical conductivity, microhardness, and lattice parameter. The results showed, that the concentration of saturation is temperature dependent. It increases from 1.1 at.% O at 750 deg C to 5.5 at.% 0 at 1540 deg C. In this temperature range it can be described by the equation ln c/ sub max/= 3.829-7700/RT (c/sub max/in at.% O). There were considerable deviations from this relation above 1540 and below 750 deg C. It can be assumed, that the deviations above 1540 deg C are partially caused by degassing of the niobium samples and partially by instability of the highly supersaturated alpha - solid solution during quenching. The deviations, which were found between 750 and 500 deg C were due to the effect, that no complete equilibrium between oxide and alpha -solid solution was reached. In the range of the temperature dependent solubility of alpha -solid solutions experiments were conducted on precipitation of oxides from homogeneous supersaturated niobium --oxygen solid solutions, which were obtained by quenching. Quenching temperature was 1460 deg C, the aging temperatures were between 1000 and 500 deg C. Metallographic and x- ray investigations showed that the nature of the oxide precipitation depends on the aging temperature. At aging temperatures between 1000 and 800 deg C precipitation of NbO occurred only on grain boundaries. Between 700 and 500 deg C particles were found in addition in the interior of the grains. Some of these particles showed a crystallographic habit. Below 550 deg C plate shaped particles of NbO/sub z/ were found. This phase has a crystallographic habit and can be distinguished by polarized light. The simultaneous formation of several oxide phases indicates, that there is no equilibrium at lower aging temperatures and that some of the observed oxides are metastable phases. (auth)

• Research Organization: Max-Planck-Institut fur Metallforschung, Stuttgart
• NSA Number: NSA-18-005805
• OSTI ID: 4128117
• Journal Information: Z. Metallk., Journal Name: Z. Metallk. Vol. Vol: 54
• Country of Publication: Country unknown/Code not available
• Language: German

Related Subjects

ALLOTROPY
CONFIGURATION
DEGASSING
DISTRIBUTION
ELECTRIC CONDUCTIVITY
EQUATIONS
GRAIN BOUNDARIES
HARDNESS
HEAT TREATMENTS
HIGH TEMPERATURE
LATTICES
LIGHT
METALLOGRAPHY
METALS, CERAMICS, AND OTHER MATERIALS
NIOBIUM
NIOBIUM OXIDES
OXYGEN
PARTICLES
PLATES
POLARIZATION
PRECIPITATION
QUENCHING
SOLID SOLUTIONS
SOLUBILITY
SOLUTIONS
STABILITY
TEMPERATURE
X RADIATION