Pulse Electric Current Sintering and Strength of Sintered Alumina Using Transition Alumina Powders Prepared from Polyhydroxoaluminum Gel.

Yajima, Yoichi; Hida, Masahiro; Taruta, Seiichi; Kitajima, Kunio

doi:10.2109/jcersj.111.110

Cited by 10 publications

(26 citation statements)

References 26 publications

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“…This implies that the amount of -alumina abrasion powders generated by the wear of the pot and balls during milling [7] was very small. In the preliminary sintering study, the M 2+ -doped powders after planetary ball milling for 3 h could not attain full density by PECS at lower sintering temperatures because the seeding effect [7,22] was reduced due to the lower content of -alumina abrasion powders. Thus, the milled M 2+ -doped powders were re-calcined at 900°C for 3 h to enhance the seeding fine -alumina particles: the re-calcined powders, i.e., GA-M0 and GA-M0.1, were used for the PECS study.…”

Section: Methodsmentioning

confidence: 99%

“…The decrease in the transformation temperature by re-calcination can be explained in terms of the increased seeding effect due to the increase in the number of fine -alumina particles induced by ball milling and re-calcination. The decrease in -transformation temperature promotes low-temperature densification and the development of a fine-grained microstructure [7,22]. 3.2 Densification and microstructural evolution Figure 3 shows SEM micrographs of the polished and thermally etched surfaces of sintered GA-M0 and GA-M0.1 samples obtained by PECS at 1250°C under 80 MPa.…”

Section: Methodsmentioning

confidence: 99%

“…In these studies, transition aluminas were densified by hot-pressing [5] or sinter-forging [6], and alumina ceramics with an -alumina grain size of 200 nm or less were obtained. We have also focused on the use of transition alumina powders and attempted densification by pulse electric current sintering (PECS) using polyhydroxoaluminum (PHA) gel-derived γ-alumina powders [7][8][9]. As a result, we obtained fully densified alumina ceramics with a relatively high bending strength of ~860 MPa under optimized conditions [9].…”

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Fabrication of submicron alumina ceramics by pulse electric current sintering using M2+ (M=Mg, Ca, Ni)-doped alumina nanopowders

Odaka¹,

Yamaguchi²,

Hida³

et al. 2009

Ceramics International

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Dense submicron-grained alumina ceramics were fabricated by pulse electric current sintering (PECS) using M 2+ (M: Mg, Ca, Ni)-doped alumina nanopowders at 1250°C under a uniaxial pressure of 80 MPa. The M 2+ -doped alumina nanopowders (0-0.10 mass%) were prepared through a new sol-gel route using high-purity polyhydroxoaluminum (PHA) and MCl2 solutions as starting materials. The composite gels obtained were calcined at 900°C and ground by planetary ball-milling. The powders were re-calcined at 900°C to increase the content of α-alumina particles, which act as seeding for low-temperature densification. Densification and microstructural development depend on the M 2+ dopant species. Dense alumina ceramics (relative density ≥ 99.0%) thus obtained had a uniform microstructure composed of fine grains, where the average grain size developed for non-doped, Ni-doped, Mg-doped and Ca-doped samples was 0.67, 0.67, 0.47 and 0.30 m, respectively, showing that Ca-doping is the most promising method for tailoring of nanocrystalline alumina ceramics.Keywords: A. Sintering; A. Sol-gel processes; B. Grain size; D. Al2O3 3 IntroductionAs the grain size of fully dense alumina is reduced, significant benefits are observed in terms of improved mechanical properties [1,2], superior wear resistance [3] and optical transparency [4]. To obtain dense submicron-grained or nanocrystalline alumina ceramics (NCAs), studies on the densification of alumina have focused on the use of nanosized transition alumina powders as a starting powder [5,6]. In these studies, transition aluminas were densified by hot-pressing [5] or sinter-forging [6], and alumina ceramics with an -alumina grain size of 200 nm or less were obtained. We have also focused on the use of transition alumina powders and attempted densification by pulse electric current sintering (PECS) using polyhydroxoaluminum (PHA) gel-derived γ-alumina powders [7][8][9]. As a result, we obtained fully densified alumina ceramics with a relatively high bending strength of ~860 MPa under optimized conditions [9]. However, these alumina ceramics showed an inhomogeneous microstructure consisting of submicron-sized grains and a large number of elongated large grains due to the presence of impurities such as CaO and SiO2.It is well known that additives such as , CaO [14,15] and NiO [11] affect the sintering behavior of -alumina. MgO plays a particularly beneficial role in inhibiting grain growth of -alumina, which can be explained in terms of a solute drag (pinning) model [11,12]. While the effect of MO (M: Mg, Ca, Ni) addition to -alumina powders on grain growth inhibition has been studied extensively, there are few reports concerning the effects of M 2+ -doping on densification of γ-aluminas except for Mg 2+ -doping [16]. In particular, systematic studies on the densification behavior induced by PECS for various M 2+ -doped γ-alumina powders, in which M 2+ cations are substituted into the crystal lattice of γ-alumina, have been lacking.Thus, the present study extends the potentia...

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Section: Methodsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

mentioning

confidence: 99%

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Fabrication of submicron alumina ceramics by pulse electric current sintering using M2+ (M=Mg, Ca, Ni)-doped alumina nanopowders

Odaka¹,

Yamaguchi²,

Hida³

et al. 2009

Ceramics International

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“…We have shown that the use of M 2+ -doped -aluminas [3,7,8] synthesized through a polyhydroxoaluminum (PHA) sol-gel process [9][10][11] yields a fine grain size upon sintering due to the intimate mixing of dopants at an atomic level. Among the divalent cation dopants reported in our previous study, Ca 2+ is by far the best dopant for suppressing the grain growth of -alumina upon heating [7].…”

Section: Introductionmentioning

confidence: 99%

Densification of rare-earth (Lu, Gd, Nd)-doped alumina nanopowders obtained by a sol–gel route under seeding

Odaka

Yamaguchi

Fujita³

et al. 2009

Powder Technology

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Rare-earth (RE: Lu, Gd, Nd, 0.10 mol%)-doped alumina nanopowders were prepared by a new sol-gel route using polyhydroxoaluminum (PHA) and RECl3 solutions under -alumina (~75 nm) seeding. Among the rare-earth dopants studied, Lu yields the most suitable nanopowders for low-temperature densification. The 0.10 mol% Lu-doped nanopowders, which were obtained at a calcination temperature of 900°C under 5 mass% -alumina seeding, consisted of ~80-nm -alumina particles and -alumina nanoparticles. Using these Lu-doped alumina nanopowders, fully densified alumina ceramics with a uniform microstructure composed of fine grains with an average size of 0.61 μm could be obtained at 1400°C by pressureless sintering. Clearly, the Lu-doped nanopowders obtained here represent a viable option for fabricating dense, finer-grained alumina ceramics because an undoped sample with 5 mass% seeds gave a microstructure with an average grain size of 1.78 μm at 1400°C.

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“…3),4) Alumina ceramics having a relative density of 99÷ or more were obtained by PECS after the transition alumina powder was ground using a planetary ball mill. A relatively high bending strength of 740 MPa was realized when a mixed powder of galumina and xalumina was used 3) and a bending strength of 850 MPa was attained when single phase galumina powder was used. 4) The transition alumina powders prepared in the previous study 3),4) were ground using a planetary ball mill consisting of a 93÷pure alumina pot and 99.9÷pure alumina balls; the powder obtained is hereafter referred to as LP.…”

Section: Introductionmentioning

confidence: 99%

Effect of Milling Media Purity on Pulse Electric Current Sintering and Strength of Alumina Ceramics Prepared from Transition Alumina Powder

Yajima

Yamaguchi

Taruta

et al. 2003

J. Ceram. Soc. Japan

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Alumina ceramics were densied at sintering temperatures of 12501550 C by pulse electric current sintering (PECS) using transition alumina powder of mixed phases of g and xalumina prepared from polyhydroxoaluminum (PHA) gel. The starting highpurity powder (HP) was obtained by grinding the alumina powder with a planetary ball mill using a highpurity alumina (purity: 99.9÷) pot and balls to prevent contamination derived from the abrasion powder worn during the milling. The HP thus obtained realized full densication at sintering temperatures 50100 C lower than those of the corresponding lower purity powder (LP), which was obtained by grinding with a planetary ball mill using a 93÷pure alumina pot and 99.9÷pure alumina balls. The HP could also provide alumina ceramics with higher bending strengths (approximately 860 MPa) than those obtained using LP.

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Pulse Electric Current Sintering and Strength of Sintered Alumina Using Transition Alumina Powders Prepared from Polyhydroxoaluminum Gel.

Cited by 10 publications

References 26 publications

Fabrication of submicron alumina ceramics by pulse electric current sintering using M2+ (M=Mg, Ca, Ni)-doped alumina nanopowders

Fabrication of submicron alumina ceramics by pulse electric current sintering using M2+ (M=Mg, Ca, Ni)-doped alumina nanopowders

Densification of rare-earth (Lu, Gd, Nd)-doped alumina nanopowders obtained by a sol–gel route under seeding

Effect of Milling Media Purity on Pulse Electric Current Sintering and Strength of Alumina Ceramics Prepared from Transition Alumina Powder

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