Effect of preparation method on sinterability and properties of nanocrystalline MgAl₂O₄and ZrO₂-MgAl₂O₄materials

Abstract

toughened alumina.18 Zirconia is also known to exhibit excellent mechanical properties and superior fracture tough-Nanocrystalline MgAl 2 O 4 and ZrO 2 -MgAl 2 O 4 ness because of its unique phase transformations occurring powders were synthesised by combustion and convenover stress or temperature.19 According to Fujita et al., an tional solid state reaction routes. T he synthesised addition of 20 wt-%ZrO 2 to MgAl 2 O 4 followed by hot powders were processed, dry pressed, and sintered for pressing may increase fracture toughness and bend strength 3 h at temperatures ranging f rom 1550 to 1625°C. T he to 6•3 MPa m1/2 and 400 MPa respectively.10-12 In general, sintered pellets were then characterised in terms of ZrO 2 -MgAl 2 O 4 composite material exhibits better thermal phase (XRD), microstructure (SEM), relative density, shock resistance and chemical inertness than pure MgAl 2 O 4 , apparent porosity, water absorption, hardness, three and in the form of a honeycomb structure this composite point bend strength, and f racture toughness. T he XRD material nds application for molten metal ltration of studies revealed that ZrO 2 was present in tetragonal superalloys and cast steels.20 form in the case of combustion synthesised powders The most common method used for preparation of (CSP), whereas in powders obtained by solid state ceramic powders involves the solid state reaction of comreaction (SSP) it was present in the monoclinic ponent oxides at elevated temperatures. This method suVers form. T his study also revealed that the addition of from several limitations and may not produce a material ZrO 2 improved the mechanical properties of sintered with compositional homogeneity.21-28 It is also known that MgAl 2 O 4 samples: 20 wt-%ZrO 2 -MgAl 2 O 4 composites powders with particle size å 200 nm can be sintered to prepared f rom CSPs and conventional SSPs and sinproduce materials with ne grained microstructure and tered at 1625°C for 3 h had f racture toughness of 5•96 desirable properties. In order to produce ZrO 2 -MgAl 2 O 4 and 4•33 MPa m 1 / 2 and three point bend strength of 269 and 98 MPa respectively. Higher sintered density, composites with good compositional homogeneity, they the presence of tetragonal zirconia as a major phase, have also been prepared by methods including coprecipiand the ner microstructure are probably responsible tation,21 vapour phase oxidation,22 spray pyrolysis,23 freeze for the superior mechanical properties exhibited by drying,24 and sol-gel processing.25 Recently, Hwang and sintered CSP materials as compared with the sintered Kim have adopted the reaction sintering method for the SSPs. BCT /577 preparation of 10 wt-% cubic stabilised zirconia/spinel composites with relative density of around 98%, fracture tough-T he authors are in the Ceramic Materials Division, ness of 12 MPa m1/2, and strength of 240 MPa from a International Advanced Research Centre for Powder pressed compact mixture of monoclinic zirconia (baddeley-Metallurgy and New Materials, Balapur PO, ite) and Mg-Al metal...

Aqueous slip casting of MgAl2O4 spinel powder

“…Nevertheless, both samples have similar microstructures with equi-axed grains which are tightly packed. These results are well comparable with those reported for the MAS materials in the literature (Ganesh et al 2003).…”

“…In our earlier studies, a single-phase MAS was identified when a stoichiometric mixture of α-Al 2 O 3 and calcined caustic MgO was compacted by die-pressing (200 MPa) or by extrusion and calcined at 1350 • C for 1 h (Ganesh et al 2001(Ganesh et al , 2002b(Ganesh et al , 2003(Ganesh et al , 2004(Ganesh et al , 2005). In the present study, the mixture of raw materials was consolidated by TIG (Bergström 1994) from organicbased suspensions containing 40 vol.%.…”

“…The gelation mechanism involved in this process was mainly based on the cooling up of dissolved dispersant molecules, inducing in situ gelation (i.e., TIG) and the formation of a rigid network bridging the suspended particles (Bergström 1994). The dried mass was calcined in an electrically heated open-air muffle furnace for 1 h at 1000-1400 • C to obtain a stoichiometric MAS powder (Ganesh et al 2001(Ganesh et al , 2002b(Ganesh et al , 2003(Ganesh et al , 2004. The MAS powder was then crushed, ground in an hammer mill (Retsch GmbH, model SK1, Haan, Germany) and planetary ball milled (Retsch GmbH, PM400, Haan, Germany) at 200 rpm for 3 h in an absolute ethanol.…”

“…Bulk density (BD), apparent porosity (AP), and water absorption (WA) capacity of sintered samples were measured according to Archimedes principle (ASTM C372) using Mettler balance (AG 245, Mettler Toledo, Heuwinkelstrasse, Switzerland). On an average, three density measurements were performed for each sample in this study (±0·01 error) (Ganesh et al 2001(Ganesh et al , 2002b(Ganesh et al , 2003(Ganesh et al , 2004. XRD patterns were recorded on a Bruker (Karlsruhe, Germany) D8 advanced system using diffracted beam monochromated Cu K α (0·15406 nm) radiation source.…”

New synthesis methods of MgAl2O4 spinel

“…1,2,17 In the previous papers, [18][19][20][21] we have evidenced certain advantages of the organic precursors method based on the thermal decomposition of the heteropolynuclear complex combination resulted from the oxidation reaction of 1,2-ethanediol by the metallic nitrates by comparison with other unconventional methods. The aim of this work consists in the synthesis of MgAl 2 O 4 , using this method and the accomplishment of a comparative study relative to sol-gel route and combustion method taking into consideration the advantages and disadvantages of that.…”