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.
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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