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

Yajima, Yoichi; Yamaguchi, Tomohiro; Taruta, Seiichi; Kitajima, Kunio

doi:10.2109/jcersj.111.786

Cited by 8 publications

(6 citation statements)

References 12 publications

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“…The powders consisted of mixtures of nanoparticles of ~80 nm α-alumina and γ-alumina, whose α-and γ-alumina content varied depending on the calcination conditions of the gels. The use of PHA-derived γ-alumina powders, 3,[14][15][16] which are inherently agglomerated, limits the homogeneity of the seed distribution attainable when a dry process is employed for seeding.…”

Section: Introductionmentioning

confidence: 99%

Densification of Ca-doped alumina nanopowders prepared by a new sol–gel route with seeding

Odaka

Yamaguchi

Fujita³

et al. 2008

Journal of the European Ceramic Society

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This paper demonstrates that the Ca-doped alumina nanopowders prepared by a new sol-gel route using polyhydoxoaluminum (PHA) and CaCl 2 solutions under α-alumina seeding represent a viable option for producing fine-grained ceramics. Appropriate conditions for producing Ca-doped alumina nanopowders suitable for low-temperature finer-grained densification were 0.10 mol% Ca-doping, 5 mass% α-alumina seeding and a calcination temperature of 900˚C. These conditions led to the formation of new nano-sized alumina powders, which consisted of ~80 nm α-alumina particles and γ-alumina nanoparticles. Using these Ca-doped nanopowders, fully densified alumina ceramics with a uniform microstructure composed of fine grains with an average grain size of 0.66 μm could be obtained at 1375˚C.Clearly, the Ca-doped nanopowders obtained here through the proposed sol-gel route are very suitable for fabricating dense, fine-grained alumina ceramics because an undoped sample with 5 mass% seeds led to a microstructure with an average grain size of 1.39 μm at 1375˚C.

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Section: Introductionmentioning

confidence: 99%

Densification of Ca-doped alumina nanopowders prepared by a new sol–gel route with seeding

Odaka

Yamaguchi

Fujita³

et al. 2008

Journal of the European Ceramic Society

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“…Thus, we also focused on the fabrication of alumina ceramics using transition alumina powders and attempted densification by pulse electric current sintering PECS using polyhydroxoaluminum PHA gel-derived transition alumina a powder of mixed phase g-and x-alumina or single-phase g-alumina powders. [3][4][5] Consequently, fully densified alumina ceramics having a relatively high bending strength of ࣽ860 MPa were obtained by PECS under optimized conditions. 5 However, the alumina ceramics consisted not only of submicron-sized grains but also a large number of elongated large grains due to the presence of impurities such as CaO and SiO 2 .…”

Section: Introductionmentioning

confidence: 99%

“…[3][4][5] Consequently, fully densified alumina ceramics having a relatively high bending strength of ࣽ860 MPa were obtained by PECS under optimized conditions. 5 However, the alumina ceramics consisted not only of submicron-sized grains but also a large number of elongated large grains due to the presence of impurities such as CaO and SiO 2 .…”

Section: Introductionmentioning

confidence: 99%

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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“…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].…”

Section: Introductionmentioning

confidence: 99%

“…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.…”

Section: Introductionmentioning

confidence: 99%

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

Cited by 8 publications

References 12 publications

Densification of Ca-doped alumina nanopowders prepared by a new sol–gel route with seeding

Densification of Ca-doped alumina nanopowders prepared by a new sol–gel route with seeding

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 M2+ (M=Mg, Ca, Ni)-doped alumina nanopowders

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