Pulsed Electric Current Sintering of Transparent Alumina Ceramics

Dao

et al. 2019

Acta Metall Slovaca

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Transparent MgAl2O4 ceramic could be found in a wide range of applications for both military and civil sector due to its high melting point, good mechanical properties, small refractive index (1.71) and its ability to allow light in range from UV to mid-IR to pass through. In the present work, transparent MgAl2O4 was fabricated from metal nitrates via two steps. Firstly, the MgAl2O4 nanopowder was synthesized via solution combustion synthesis from the metal nitrates. Secondly, the powder was then consolidated by Pulsed Electric Current Sintering (PECS) technique to fabricate transparent ceramic. XRD patterns of the obtained powder showed the peaks of only MgAl2O4 phase. Besides, the atomic compositions of magnesium, aluminium and oxygen determined by EDX analysis were approximately corresponded to 1:2:4 of the molecular formula of MgAl2O4. After deagglomerating for 48 hours using soft ball-milling, the powder had the average particle of 27 nm. Transparent MgAl2O4 samples, which were sintered with two-step sintering mode of 1050oC/60 minutes-1400oC/20 minutes, permitted the transmission of visible and infrared light with the transmittance up to 80%, Vickers hardness of 14.2 GPa, and fracture toughness of 1.1 MPa.m1/2. The results are a critical step toward fabrication of high-quality transparent ceramics from metal nitrates.

Section: Introductionmentioning

confidence: 98%

FABRICATION OF TRANSPARENT MgAl2O4 SPINEL CERAMICS BY PECS PROCESSING OF COMBUSTION - SYTHESIZED NANOPOWDERS

Dao

et al. 2019

Acta Metall Slovaca

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“…Transparent polycrystalline Al 2 O 3 ceramics have a high potential to replace the single crystal sapphire in many industrial applications. Besides its good mechanical properties as well as good optical transparency, the main advantage of polycrystalline Al 2 O 3 is the simpler production method along with the lower cost by various sintering techniques such as pulsed electric current sintering (PECS) or hot isostatic pressing (HIP) [1][2][3][4][5]. Moreover, with the sintering techniques, the polycrystalline Al 2 O 3 samples can be shaped much more easily while the single crystal sapphire normally requires machining for shaping after the production of a large bulk.…”

Section: Introductionmentioning

confidence: 99%

“…Using that special punch-die setup has limitation in the sample size. Our group has studied PECS with two-step temperature profile, referred as two-step PECS (TS-PECS) to fabricate transparent polycrystalline Al 2 O 3 [2,3,5]. The meaning of the first step at lower temperature is for additional densification with limited grain growth.…”

Section: Introductionmentioning

confidence: 99%

Influences of TiO₂ or Y₂O₃ doping on the homogeneity of polycrystalline Al₂O₃ produced by pulsed electric current sintering

Journal of Asian Ceramic Societies

Shirai

Xin

et al. 2021

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Influences of TiO 2 or Y 2 O 3 dopants on pressure-assisted sintering of polycrystalline Al 2 O 3 were investigated to control the microstructure of sintered Al 2 O 3 as well as to improve the homogeneity of transparent Al 2 O 3 samples. The transparent polycrystalline Al 2 O 3 samples with and without the dopants were fabricated by two-step pulsed electric current sintering (TS-PECS). By the grain boundary segregation by the dopants, both TiO 2 and Y 2 O 3 depressed the densification and grain growth processes during the sintering of polycrystalline Al 2 O 3 . The principle originalities of this work include the relationship between the homogeneities of microstructure and of optical transmittance of large-size polycrystalline Al 2 O 3 and the consequent doping strategy for controlling of homogeneity of transparent polycrystalline Al 2 O 3 prepared by twostep PECS. Doping of Y 2 O 3 dramatically reduced the grain size of polycrystalline Al 2 O 3 and improved its optical transparency. The homogeneity of the microstructure and the optical transparency of the large-sized polycrystalline Al 2 O 3 with 0.1 mol% Y 2 O 3 was improved. The addition of TiO 2 also slightly retarded densification and reduced the grain size of the sintered Al 2 O 3 samples. However, TiO 2 dopant is not good for applications of transparent Al 2 O 3 because it caused a dark color in transparent polycrystalline Al 2 O 3 samples by uncertain reasons.

Reduction of black dots in transparent polycrystalline alumina produced by pulsed electric current sintering with various chemical powder treatments

Nanko

Dang

2016

J. Ceram. Soc. Japan

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Micrometer-sized porosity, which cannot be recognized by typical density measurement method, was observed inside transparent polycrystalline alumina prepared by pulsed electric current sintering (PECS). The pores derive from hard agglomerates in starting powder and appear as black dots inside transparent bulk samples. In this study, porosity coming from the agglomeration was studied to degrade by chemical and mechanical treatments. Starting alumina powder was mixed with some surfactants as aqueous solutions. The slurries were ball-milled in 1 d, followed by drying and heat treatment to obtain treated alumina powders. Sintering of those alumina powders was carried out by two-step PECS technique. Transparent alumina specimens were evaluated by the density of black dots and the apparent transmittance. In summary, their treatments of alumina powder can break agglomerates and dramatically reduce the total density of black dots within transparent polycrystalline alumina. Consequently, the transmittance of polycrystalline alumina increased, from 68% for untreated sample to 7274% for treated samples.