Formation and sintering of spinels (MgAl2O4) in reducing atmospheres

The influence of in situ spinel formation on microstructure and phase evolution of MgO–C refractories

“…20 The thermochemical studies on oxide/nonoxide refractory showed the reducing atmosphere caused the reduction and volatilization of oxide components at higher temperatures. 21 It was also reported that the reduction could be sever due to the presence of car- bon as a component of carbon containing refractories. 22,23 In addition, Sainz et al 22 found that the spinel structure and its thermochemical stability could be influenced by atmosphere and oxygen partial pressure.…”

A thermodynamic approach to obtaining transparent spinel (MgAl2O4) by hot pressing

“…The bimodal grain growth of LiF-free samples has already been observed during MgAl 2 O 4 spinel sintering without any sintering aids and in reducing atmospheres, as encountered in hot pressing with graphite tooling. 34,35 When no liquid phase is formed, the end result is generally a fine-grained, poorlysintered material. On the other hand, to explain the exaggerated grain growth, Meir [34] suggested that, alongside the Mg(g) evolution (e.g.…”

“…The formation of free MgO during spinel sintering has been documented experimentally by processing the material under either CO/CO 2 reducing atmosphere with oxygen partial pressure P O 2 ∼10 −10 Pa or simply in air (P O 2 ∼2 × 10 4 Pa). 35 Large grains grow at the expense of smaller ones, which eventually form regions where pores tend to segregate and remain trapped. Pore closure is inhibited when the pores are trapped amongst grains no larger than the pores themselves, leading to the apparent bimodal grain distribution.…”

Discovery of Al2O3 particles incorporation mechanism in plasma electrolytic oxidation of AM60B magnesium alloy

“…Therefore, the change of intensity of various phases indicates the phase change during the coating deposition process under the given experimental conditions [14,15]. The relative quantity of the two phases in the 900 s coatings formed in solution with and without Al 2 O 3 suspension was compared as an example using Jade 6.5 software by taking the area ratio of main peaks of (4 0 0) for MgAl 2 O 4 and (2 0 0) for MgO [4,16]. The relative ratios are 2.2 and 0.5 for the PEO coatings formed in solutions with and without Al 2 O 3 suspension, respectively, clearly demonstrating an increase of the MgAl 2 O 4 /MgO ratio in the coating with Al 2 O 3 addition.…”