A study of the reduction of black cobalt oxide, using
hydrogen as the reductant, showed that the temperature
and time used for reduction exerted a profound influence
on the proportions of face centred cubic (a) and
hexagonal close packed (e) cobalt allotropes obtained
in the reduced metal powder. Reduction under certain
conditions yielded a faulted hexagonal cobalt powder
product which contained stacking faults.
The influence of oxygen and titanium on cobalt
materials showed that these impurities did not stabilise
the proportions of either the cubic or hexagonal phases
under the conditions, which were used.
The grinding of cobalt powders from different sources
showed different tendencies towards agglomeration, when
acetome was used as the milling fluid. It was found
that powders which contained an initially higher proportion
of the hexagonal phase -had a strong tendency towards
agglomeration during the initial stages of grinding.
The importance of the different phases of cobalt
present in the metal powders, and their different
agglomeration tendencies on grinding, on the milling
required for satisfactory densification of cobalt -
tungsten carbide compacts has been shown; it was
(iv)
found that hard metal alloys prepared using powders with
an initially higher proportion of the hexagonal phase
required less milling to achieve a given sintered density,
than did mixtures prepared with other cobalt powder*;.
A correlation analysis between the properties of the
milled hard metal powders and the properties of the sintered
compacts was carried out; it was found that the most
important correlation was between the specific surface
area of the milled hard metal powder and the coercivity
of the sintered product.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:wits/oai:wiredspace.wits.ac.za:10539/19194 |
| Date | January 2015 |
| Creators | Rees, G J |
| Source Sets | South African National ETD Portal |
| Language | English |
| Detected Language | English |
| Type | Thesis |
| Format | application/pdf, application/pdf, application/pdf |
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