How does direct-resistance heating work during niobium sintering?

In the context of niobium processing, direct-resistance heating is a method used to sinter "green" niobium compacts in a vacuum at temperatures between 2,100 and 2,300 °C (3,800–4,150 °F).1

To perform this process, electrical contact is established using water-cooled copper clamps that feature brazed tungsten facings. The temperature is raised in a staged manner, which serves two critical purposes: it allows for the controlled evaporation of impurities and prevents the potentially damaging sudden release of gas from the material. This vacuum sintering process is essential for purifying the metal, ultimately resulting in improved mechanical properties.1