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

Abstract

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.

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

“…The sources of divalent cations were MCl2•nH2O (M=Mg, Ca, and Ni, Wako Pure Chemical Industries). Each chloride was dissolved in distilled water and added to the PHA solution to form 0.10 mass% MO against the mass of Al2O3 obtained from the PHA solution, as in the case of Mg 2+ doping [16]. The mixed solutions were stirred thoroughly at room temperature and then held at 60°C for 2 days or more for gelation.…”

“…PECS was performed at 1250°C for a holding time of 5 min under a uniaxial pressure of 80 MPa [16]. A heating rate of 200°C/min was employed with care to prevent overshoot at the sintering temperatures.…”

“…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.…”

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

“…Thus, the refinement of alumina powder processing techniques is key to obtaining a fine-grained microstructure. Recently, nanopowders such as transition alumina [1,2], Mg 2+ -doped -alumina [3] and nano-grained -alumina [4][5][6] powders have attracted much attention as starting raw powders for fabricating dense, finer-grained alumina ceramics, because they have intrinsic nanocrystalline nature. Doping of alumina ceramics has become an effective method of tailoring grain size and shape and grain boundary structure.…”

“…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].…”