Manufacture of Corundum by Sintering

Sintered corundum is a family of grains produced from unfused alumina by sin­tering processes [JACK11, p. 29]. The aim of sintering is to form a solid ceramic body of a-Al2O3 with a regular, fine-crystalline structure [KLOC05a, p. 25]. This structure is supposed to have a good wear resistance in the abrasive grinding process [KLOC05a, p. 25]. Different manufacturing methods exist based on raw or purified bauxite.

2.1.3.1 Sintering of Bauxite

Sintering of bauxite is one process method (Fig. 2.7). Raw bauxite, water, binders, and pressing auxiliary agents are mixed and the resulting compound is extruded and cut into short cylinders [KLOC05a, p. 25, JACK11, p. 29]. The cylinders are then sintered in rotary kilns at temperatures of 1350-1500 °C [JACK11, p. 29]. The impurities in the bauxite act as auxiliary sintering agents [JACK11, p. 29]. This manufacturing procedure results in a homogeneous, fine-crystalline grit structure with increased toughness [ENGE02]. The extruded long corundum particles are also known as “Spaghetti corundum” [ENGE02, p. 6].