Spectroscopic study of the discoloration of transparent MgAl2O4 spinel fabricated by spark-plasma-sintering (SPS) processing

Morita, Koji; Kim, Byung-Nam; Yoshida, Hidehiro; Hiraga, Keijiro; Sakka, Yoshio

doi:10.1016/j.actamat.2014.10.030

Cited by 91 publications

(21 citation statements)

References 81 publications

(209 reference statements)

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“…However, when the onset of densification begins for the heat‐treated powder samples, it occurs at a much faster rate than the ethanol‐washed powder sample, and samples hot‐pressed with higher P i undergo more shrinkage (densification) during this stage due to the increased driving force for sintering from the applied P i . It is likely that by heat‐treating the powder prior to densification, impurities in the powder are removed, which may allow the powder to densify more readily. High‐temperature TGA of the different powder types showed that mass loss initiated around 825°C and 1200°C for the ethanol‐washed powders and heat‐treated powders, respectively.…”

Section: Resultsmentioning

confidence: 99%

“…Absorption in transparent ceramics is caused by secondary phases, and qualitatively manifests as a discoloration in a transparent sample. Several of the samples in this study have a distinct gray discoloration, which is a common defect observed in transparent spinel . In the case of spinel, the primary mechanisms for absorption were identified to be carbon contamination, oxygen vacancies, and impurities in the raw powder.…”

Section: Introductionmentioning

confidence: 82%

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Hot‐pressing platelet alumina to transparency

et al. 2019

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Alumina powder with a platelet morphology was hot-pressed to transparency with preload pressures of 0-8 MPa, maximum temperatures of 1750-1825°C, maximum pressures of 2.5-80 MPa, and isothermal hold times of 1-7 hours. Optical transmission (in-line and total), as well as optical losses (backward/forward scattering and absorption), of the hot-pressed samples were measured and related to the microstructure. Higher hot-pressing temperatures increase the in-line transmission. A gray discoloration of the samples (indicative of high absorption) was minimized by heat treating the powder in air prior to hot pressing and reducing the preload pressure. Maximum pressures above/below 10 MPa increased porosity, which decreased inline transmission and increased backward/forward scattering. Lower densities at higher pressures are attributed to a pore-swelling phenomenon. Increasing isothermal hold time decreased porosity, which increased in-line transmission and reduced backward/forward scattering. Best optical properties with an in-line transmission of 65.3% at 645 nm (0.8 mm thick) were achieved by hot-pressing heat-treated platelet alumina powder with a preload pressure of 0 MPa, maximum temperature of 1800°C, maximum pressure of 10 MPa, and an isothermal hold time of 7 hours. This high inline transmission, despite its large grain size (65 µm), is attributed to crystallographic orientation of the platelets during hot pressing.

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Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 82%

Hot‐pressing platelet alumina to transparency

et al. 2019

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“…Although highly transparent ceramics have been developed24 and successfully applied to some lasers and optical devices25, those with single-phase crystals in the nano-crystalline regime have never been produced by either sintering techniques3456724 or crystallization from glass or amorphous phases82627 under the ambient pressure and at relatively low pressures. On the other hand, the transparent nano-ceramics produced by these techniques have substantially low transparency relative to the single crystals in the visible light region1127 mainly due to the presence of a number of residual pores and/or defective regions along grain boundaries.…”

Section: Discussionmentioning

confidence: 99%

“…These transparent ceramics are made of crystals with grain sizes greater than a few hundred nanometres mainly due to grain growth at high temperature, while synthesis of such transparent ceramics with purely nano-crystals, having grain sizes <100 nm (ref. 2), at lower temperatures have not been realized345678 mainly because of the difficulty in removing inter-grain residual pores. However, it is predicted that the optical transparency will be significantly improved for the ceramics even with non-cubic crystals, if those made of nano-crystals are available910.…”

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confidence: 99%

Pressure-induced nano-crystallization of silicate garnets from glass

Irifune¹,

Kawakami²,

Arimoto³

et al. 2016

Nat Commun

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Transparent ceramics are important for scientific and industrial applications because of the superior optical and mechanical properties. It has been suggested that optical transparency and mechanical strength are substantially enhanced if transparent ceramics with nano-crystals are available. However, synthesis of the highly transparent nano-crystalline ceramics has been difficult using conventional sintering techniques at relatively low pressures. Here we show direct conversion from bulk glass starting material in mutianvil high-pressure apparatus leads to pore-free nano-polycrystalline silicate garnet at pressures above ∼10 GPa in a limited temperature range around 1,400 °C. The synthesized nano-polycrystalline garnet is optically as transparent as the single crystal for almost the entire visible light range and harder than the single crystal by ∼30%. The ultrahigh-pressure conversion technique should provide novel functional ceramics having various crystal structures, including those of high-pressure phases, as well as ideal specimens for some mineral physics applications.

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“…This contamination was confirmed by XPS (see supplementary information), and it is consistent with observations already made in the case of other systems, see for example Ref. [25,26]. In order to eliminate this contamination, a post‐annealing treatment had to be performed, by heating the pellets at 1100°C during 168 hours under flowing oxygen.…”

Section: Methodsmentioning

confidence: 99%

SPS‐assisted synthesis of InGaO₃(ZnO)_m ceramics, and influence of m on the band gap and the thermal conductivity

et al. 2020

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In this study, we report on the use of a two‐stage annealing treatment at 1100°C coupled to reactive Spark Plasma Sintering to reduce the synthesis temperature of InGaO3(ZnO)m (m = 1 to 9) dense polycrystalline pellets below 1200°C, in order to suppress the volatilization of ZnO and get a better control of the crystalline quality of the pellets. We show that using this treatment, dense single‐phase pellets can be prepared with randomly oriented grains. Besides, we evidence a monotonic evolution of the band gap in the series from 3.27 eV in InGaO3(ZnO) to 3.02 eV in InGaO3(ZnO)9, as well as a non‐monotonic evolution of the lattice thermal conductivity that reaches a minimum for InGaO3(ZnO)3, lower than 2 W m−1 K−1 above 350°C. Last, we propose a procedure for the high‐temperature measurement of the thermal diffusivity of oxides by the laser flash method to avoid possible reactions between the measured material and the graphite spray.

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Spectroscopic study of the discoloration of transparent MgAl2O4 spinel fabricated by spark-plasma-sintering (SPS) processing

Cited by 91 publications

References 81 publications

Hot‐pressing platelet alumina to transparency

Hot‐pressing platelet alumina to transparency

Pressure-induced nano-crystallization of silicate garnets from glass

SPS‐assisted synthesis of InGaO₃(ZnO)_m ceramics, and influence of m on the band gap and the thermal conductivity

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Spectroscopic study of the discoloration of transparent MgAl2O4 spinel fabricated by spark-plasma-sintering (SPS) processing

Cited by 91 publications

References 81 publications

Hot‐pressing platelet alumina to transparency

Hot‐pressing platelet alumina to transparency

Pressure-induced nano-crystallization of silicate garnets from glass

SPS‐assisted synthesis of InGaO3(ZnO)m ceramics, and influence of m on the band gap and the thermal conductivity

Contact Info

Product

Resources

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SPS‐assisted synthesis of InGaO₃(ZnO)_m ceramics, and influence of m on the band gap and the thermal conductivity