Corundum (a-Al2O3) and water (H2O) can result in gibbsite (Al(OH)3, Eq. 2.1) or diaspore (AlO(OH), Eq. 2.2) [LUDE94, p. 77]. The reaction to the relatively soft gibbsite in Eq. 2.1 is likely at temperatures from 0 to 300 °C and pressures up to 1000 bar [LUDE94, p. 79].
Al2O3 + 3H2O! 2 Al(OH)3(gibbsite, Knoop hardness 2 GPa) (2-1)
Al2O3 + H2O! 2 AIO(OH)(diaspore, Knoop hardness 7 GPa) (2-2)
Kumagai and Kamei found heavy attrition wear at the corundum grits when grinding titanium and titanium alloys [KUMA84]. A possible reaction for machining of titanium and titanium alloys with corundum is shown in Eq. 2.3 [KUMA84].
2Al2O3 + Ti! 3TiO2 + 4Al
In the grinding contact between corundum and steel, an iron spinel FeO Al2O3 can form [KLOC09, KIRK74]. This happens according to the reaction 2.4, after the chip surface has oxidized to FeO [LAUE79, p. 59]. Iron spinels can form an interim
layer between corundum grits and chip adhesions, which are more likely to adhere onto the spinel than onto bare corundum [LAUE79, p. 68 f.].
FeO + Al2O3 ! FeAl2O4 (2.4)