Reaction Sintering of AlMg–MgO for the Production of MgAl₂O₄‐Spinel‐Based Composite Ceramics

Abstract

Reaction sintering is presented as a new process to produce AlMg spinel-based ceramics. High oxidation yields of the metallic precursor and full homogenization to single-phase MgAl 2 O 4 -ceramics are achieved. Five process stages are distinguished and characterized with particular emphasis on the wetting stage of molten alloy on MgO. If the onset of wetting is efficiently controlled extremely high oxidation rates and full oxidation yields near 100% are reached at moderate temperatures up to 10001C. The resulting microstructure is generated without any ongoing shrinkage and it can be characterized by its closed porosity, which suggests the production of gastight porous fittings and components. 553J ournal

Thermodynamics and Kinetics of the Formation of Al2O3/ MgAl2O4/MgO in Al-Silica Metal Matrix Composite

“…are recognized as simpler and cheaper ceramic oxides amenable for the in-situ generation of Al 2 O 3 , MgAl 2 O 4 , and MgO in Al alloy. [23][24][25][26][27][28][29][30][31][32] The different important displacement reactions possible during the reduction of SiO 2 in Al-Mg alloy are given subsequently: [33] SiO 2 s ð Þ þ 2Mg ðlÞ ! 2MgO ðsÞ þ Si ðlÞ DG 1023K ¼ À268: 22 (Table I).…”

MgAl2O4‐Spinel Synthesized by High‐Energy Ball Milling and Reaction Sintering

“…This has to be interpreted by the fact that the molten phase was retained as original metallic particles and no wetting and spreading out of the liquid phase occured below 700°C. Oxidic shells of the metallic particles are generally supporting this microstructural stability 15 . This effect has obviously also to be claimed for the milled powder particles when their initial shape and scaling was distorted during milling and their newly formed surfaces and interfaces were subjects of highly activated in statu nascendi reactions .…”

“…However, the reactions were in this case time‐delayed, less pronounced, and needed clearly more time and higher temperatures. The single stages of the reaction sequence of unmilled powders have been previously described by Kuntz et al 15 and are discussed here with respect to additional features by the milling treatment.…”

“…4). The extremely high reaction rate was enabled by improved wetting of MgO by the liquid phase which was possible at these elevated temperatures 15 leading to a fast and dramatic increase of the AlMg/MgO‐interfacial area with the effect of spontaneous formation of the spinel phase. The fracture of the oxide layers and the wetting process started around 200 K beyond the melting temperature.…”

“…Kuntz et al 15 described the reaction bonded spinel (RBS) method to produce spinel‐parts with negligible shrinkage during sintering and high gas‐tightness in spite of significant residual porosity. In contrast to conventional fabrication routes RBS used aluminum and magnesia as precursor components.…”