Thermochemistry of MgAl2O4‐Al8/3O4 Defect Spinels

Navrotsky, Alexandra; Wechsler, B. A.; Geisinger, Karen L.; Seifert, F.

doi:10.1111/j.1151-2916.1986.tb04772.x

Cited by 102 publications

(63 citation statements)

References 19 publications

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“…This indicates that the solid solutions containing Mg 2ࢪ cations in the defect spinel lattice of g-alumina were formed between 0-10.0 massಚ MgO. Moreover, TAP-M050 transformed into a-alumina and a trace of magnesium aluminate spinel upon heating at 1200c C for 3 h. The formation of analogous spinel-type solid solutions between g-alumina and spinel 1ࢬxAl 83 O 4 ऄxMgAl 2 O 4 alternatively expressed as Mg x Al 8ࢬ2x3 O 4 was reported by Navrotsky et al 15 Thus, solid solutions with the nominal composition Mg x Al 8ࢬ2x3 O 4 , for x values ranging from 0 TAP-M0 to 0.0168 TAP-M050, could be formed in the present study.…”

Section: Methodsmentioning

confidence: 55%

Fabrication of Submicron Alumina Ceramics by Pulse Electric Current Sintering Using Mg2+-Doped Transition Alumina Powders

Hida¹,

Yajima²,

Yamaguchi³

et al. 2006

J. Ceram. Soc. Japan

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Mg2ࢪ -Έ၁ࢪǨᲡȪɳɧɒḠȡ᧸ǓǮəɳɁƑҽᠭệǺȗȚ ȽɞɧȷɵɻȪɳɧɒɃɱɧɋȷɁǽΰ⓯ ‫-‬ᨀଛগɿᮧᗱʶଉ ɿ୮‫ۑ‬ሳᘢɿᑴᨀ◯ʶɿ‫ل‬࡞ছЈఎগકకકȤᢼకકᲇࢫ380-8553 ϗʅ᭔ϗʅల⇙ʃ 4-17-1 ଉ ϗʅ᭔కᏡཪ⒈ἕ۰Ƀɻɇʀࢫ380-0928 ϗʅ᭔ϗʅల⇙ʃ 1-18-1Dense submicron-grained alumina ceramics were fabricated by pulse electric current sintering PECS using Mg 2ࢪ -doped transition alumina powders at 1200-1350c C under a uniaxial pressure of 40 or 80 MPa. The Mg 2ࢪ -doped transition alumina powders 0-0.50 massಚ MgO base were prepared through a new sol-gel route using high-purity polyhydroxoaluminum PHA and MgCl 2 solutions as starting materials. The composite gels obtained were calcined at 900c C and ground by planetary ball-milling. Upon heating, the composite gels transformed into a single-phase g-alumina or mixed phase of g-and x-aluminas, depending on the MgO content. The resultant transition alumina powders were solid solutions, in which Mg 2ࢪ cations were substituted into the crystal lattice. The powders were re-calcined to increase the content of a-alumina particles, which act as seeding for lowtemperature densification. Densification depended on the MgO content and loading pressure. The critical Mg 2ࢪ -doping for suppressing grain growth was found to be 0.10 massಚ MgO. Higher loading pressures led to full densification at lower temperatures, resulting in a more uniform and finer microstructure. Thus, dense alumina ceramics relative densityĽ99.6ಚ with a uniform microstructure composed of fine grains with an average size of 0.47 mm could be obtained by PECS at 1250c C under 80 MPa.

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Section: Methodsmentioning

confidence: 55%

Fabrication of Submicron Alumina Ceramics by Pulse Electric Current Sintering Using Mg2+-Doped Transition Alumina Powders

Hida¹,

Yajima²,

Yamaguchi³

et al. 2006

J. Ceram. Soc. Japan

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“…The crystal-chemical data for the ideal composition of MgAl 2 O 4 and with an excess of aluminum oxide are shown in Table 2 [12]. A higher unit cell parameter -a = 8.0878 Å -is reported in [15] for crystals of nonstoichiometric aluminomagnesium spinel of MgO × 3Al 2 O 3 composition grown by the Chochralski method.…”

mentioning

confidence: 99%

Synthesis of nonstoichiometric aluminomagnesium spinel with a tetragonal lattice (review)

et al. 2006

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The results of x-ray diffraction and IR-spectroscopic studies of samples of nonstoichiometric aluminomagnesium spinel Mg 1 -x Al 2 -y O 4 -z (OH) z formed after treating aluminomagnesium spinel synthesized by the sol-gel method at temperatures of 800 and 1100°C with concentrated acids, are reported. It was found that three phases of nonstoichiometric aluminomagnesium spinel Mg 1 -x Al 2 -y O 4 -z (OH) z with tetragonal lattices and a different type of superstructure are formed. The x-ray patterns of the two phases correspond to body-centered lattices with parameters a = 5.712 (3) Å, c = 8.092(3) Å, and a = 5.714(3) Å. The x-ray pattern of the third phase was indexed in a primitive tetragonal lattice: a = 5.718(3) Å, c = 24.261(27) Å.The noble spinel MgAl 2 O 4 -a mineral of high pressures and temperatures [1] -is encountered in the form of single, developed, octahedral crystals in metamorphic, highmagnesium rocks, has high hardness (7.5 -8.0 on the Moos scale), and despite the low atomic mass of magnesium and aluminum, high density (3.59 g/cm 3 ). Due to the possibility of substituting Mg 2+ and Al 3+ with transition metal ions (Mg 2+ ® Fe 2+ , Fe 3+ , Mn 2+ , Co 2+ ; Al 3+ ® Fe 3+ , Cr 3+ , V 3+ , Mn 3+ , Fe 2+ ), many varieties are found in nature [2]. The best known are ceylonite -a spinel of intermediate composition between MgAl 2 O 4 , and hercynite FeAl 2 O 4 ; chlorspinel -a bright green variety of intermediate composition between noble spinel and magnesioferrite MgFe 2 O 4 containing up to 7.2 wt.% Fe 2 O 3 ; chromspinel (composition intermediate between spinel and picrochromite MgCrO 4 ); gahnospinelwith a composition intermediate between spinel and gahnite ZnAl 2 O 4 . Aluminomagnesium spinels enriched with vanadium, nickel, cobalt, and manganese have been found. With respect to the variety of tints and shades of color, noble spinel is as good as multicolored corundum. Ruby spinelbright red, pink, and pinkish-red, purple-red, and orangered -is especially distinct among jewelry spinels. An alexandrite-like spinel whose color varies from violet in daylight to reddish-violet in artificial light, and "star spinel," whose asterism is due to microscopic rutile needle inclusions have been described. Pigments based on solid solutions of (Mg, Fe) [Al, Ti, Cr, Fe] 2 O 4 are widely used for decorating ceramic ware. The structure of noble spinel is of the type of structures incorporated in very close packing of atoms of the same size. The first studies of the structure of MgAl 2 O 4 (1915) showed that it is a derivative of cubic three-layer very close packing with filled tetrahedral and octahedral vacancies. There are eight formula units (Z = 8) -Mg 8 Al 16 O 32 -per unit cell. The structure of noble spinel is described by Fedorov symmetry group Fd3m. Structurally equivalent positions 8(a) A, 8(b) A * , 48(f) A ** correspond to 64 tetrahedral vacancies in it; 16(d) B, 16(c) B * correspond to 32 octahedral vacancies. Magnesium ions occupy octuple position 8(a) with point symmetry 43m; aluminum ions occupy centrosym...

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“…The Al 2 O 3 polymorph has a lattice parameter a o = 790.5 pm and is known to dissolve (in all proportions) in many spineltype aluminates [18,22]. No diffraction lines other than those corresponding to a single spinel-type phase were observed and provide strong evidence for spinel [22]. The main focus of this study is the development of homogeneously dispersed fine particles which is crucial for NO reduction under real application conditions.…”

Section: Characterization Of Catalystsmentioning

confidence: 94%

“…All the peaks matched well with the characteristic reflections of spinel (JCPDS card 780546). The Al 2 O 3 polymorph has a lattice parameter a o = 790.5 pm and is known to dissolve (in all proportions) in many spineltype aluminates [18,22]. No diffraction lines other than those corresponding to a single spinel-type phase were observed and provide strong evidence for spinel [22].…”

Section: Characterization Of Catalystsmentioning

confidence: 98%

Synthesis of Nickel and Zinc-Doped Aluminogallate Nanocomposite Spinels with the Hydrothermal Method and Wet Atomization for NO Reduction

Zahir

Mohamed

Suzuki

2016

Emiss. Control Sci. Technol.

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The levels of nitrogen oxides (NO x = NO + NO 2 ) released from both portable and standing combustion devices are on the increase, which contributes to serious environmental problems such as global warming and air pollution. The selective catalytic reduction (SCR) of NO x by hydrocarbons (HCs) is very effective, so there have been many studies of the performance of various catalysts for HC-SCR. In this study, Ga 2 O 3 -Al 2 O 3 -NiO-ZnO (GANZ) nanocomposite metal oxides were tested as catalysts for NO x reduction by C 2 H 4 . The spinel metal oxide powders were prepared with the hydrothermal reaction method. Aluminum, gadolinium, nickel, zinc nitrate, and ammonium carbonate salts are highly water soluble and were used in these syntheses. The hydrothermally synthesized powders were then processed with wet atomization to obtain highly dispersed fine particles. Finally, the spinel powders were tested in NO x reductions performed in the presence of high levels of oxygen and at a high space velocity, which are demanding conditions since most reported catalysts are not active in this environment. The synthesized product is an uncontaminated spinel phase of GANZ and was found to exhibit high catalytic activity even in the presence of 10 % H 2 O vapor and SO 2 at a high space velocity. GANZ catalysts were also synthesized with the co-precipitation and sol-gel methods for comparison.

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Thermochemistry of MgAl₂O₄‐Al_8/3O₄ Defect Spinels

Cited by 102 publications

References 19 publications

Fabrication of Submicron Alumina Ceramics by Pulse Electric Current Sintering Using Mg2+-Doped Transition Alumina Powders

Fabrication of Submicron Alumina Ceramics by Pulse Electric Current Sintering Using Mg2+-Doped Transition Alumina Powders

Synthesis of nonstoichiometric aluminomagnesium spinel with a tetragonal lattice (review)

Synthesis of Nickel and Zinc-Doped Aluminogallate Nanocomposite Spinels with the Hydrothermal Method and Wet Atomization for NO Reduction

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