Temperature is the most important parameter affecting densification. Higher sintering densities can be obtained much more rapidly by increasing the sintering temperature than by prolonging the sintering time. Below 1900℃ little densification occurs, unless very long sintering times are applied. For example, more than 50h are required to obtain 92% density for a tungsten powder of 4 µm particle size at 1800℃. At 2400℃, the time necessary to obtain high densities decreases to 1-2 hours and, at 3000℃, 20-30 minutes. The finer the starting tungsten powder, the more rapid the densification at a given temperature.
The influence of temperature and time on densification can be estimated by using so-called density diagrams, which are based on approximate sintering models. Nevertheless, empirical rate equations are used for industrial purposes to calculate e necessary sintering times at different temperatures.
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