scholarly journals Can Ultra-fast High Temperature Sintering (UHS) Boost Transparency of Alumina?

2021 ◽  
Author(s):  
Milad Kermani ◽  
Danyang Zhu ◽  
Jiang Li ◽  
Jinghua Wu ◽  
Yong Lin ◽  
...  
Keyword(s):  
Grain Size ◽  
High Temperature ◽  
Low Temperature ◽  
Green Density ◽  
Alumina Ceramics ◽  
Fine Grained ◽  
Reducing Atmosphere ◽  
Transparent Alumina ◽  
Rapid Sintering ◽  
First Time

Abstract Established routes for consolidation of transparent alumina ceramics by pressure-less sintering requires several hours of dwelling in a reducing atmosphere at a temperature exceeding 1600 ℃. Here, for the first time, we report on low temperature and ultrafast consolidation of translucent alumina ceramics. Transparency was promoted by the synergistic of high initial green density (62.7 %) and rapid sintering using Ultra-fast High Temperature Sintering (UHS) technique. The proposed approach, using a heating rate of 430 ℃/min and dwelling time of 15 minutes, resulted in ultra-fine-grained translucent alumina ceramics at 1359 ± 57 ℃ with a grain size of 0.39 µm, and an in-line transmittance of 28.7 % at a wavelength of 700 nm. For comparison, conventionally fired counterparts were opaque due to their incomplete densification, pore coalescence.

scholarly journals X-ray diffraction analysis of kaolin M1 and M2 via the Williamson–Hall and Warren–Averbach methods

2021 ◽  
pp. 174751982098472
Author(s):  
Lalmi Khier ◽  
Lakel Abdelghani ◽  
Belahssen Okba ◽  
Djamel Maouche ◽  
Lakel Said
Keyword(s):  
Grain Size ◽  
High Temperature ◽  
Low Temperature ◽  
Diffraction Analysis ◽  
Mechanical Resistance ◽  
X Ray Diffraction ◽  
Integral Breadth ◽  
X Ray ◽  
Mullite Phase

Kaolin M1 and M2 studied by X-ray diffraction focus on the mullite phase, which is the main phase present in both products. The Williamson–Hall and Warren–Averbach methods for determining the crystallite size and microstrains of integral breadth β are calculated by the FullProf program. The integral breadth ( β) is a mixture resulting from the microstrains and size effect, so this should be taken into account during the calculation. The Williamson–Hall chart determines whether the sample is affected by grain size or microstrain. It appears very clearly that the principal phase of the various sintered kaolins, mullite, is free from internal microstrains. It is the case of the mixtures fritted at low temperature (1200 °C) during 1 h and also the case of the mixtures of the type chamotte cooks with 1350 °C during very long times (several weeks). This result is very significant as it gives an element of explanation to a very significant quality of mullite: its mechanical resistance during uses at high temperature remains.

High-Ti magnetite in some fine-grained carbonatites and the magmatic implications

2002 ◽  
Vol 66 (3) ◽  
pp. 379-384 ◽  
Author(s):  
D. K. Bailey ◽  
S. Kearns
Keyword(s):  
High Temperature ◽  
Low Temperature ◽  
Composition Range ◽  
Volcanic Rocks ◽  
Coarse Grained ◽  
Slow Cooling ◽  
Fine Grained ◽  
Narrow Composition Range ◽  
Fast Quenching ◽  
Temperature Crystallization

AbstractMagnetite is present in most carbonatites, and in the most abundant and best-known form of carbonatite, coarse-grained intrusions, it typically falls in a narrow composition range close to Fe3O4. A fine-grained carbonatite from Zambia contains magnetites with an extraordinary array of compositions (from 18–1% TiO2, 10–2% Al2O3, and 16–4% MgO) outranging previously-reported examples. Zoning trends are from high TiO2 to high Al2O3 and MgO. No signs of exsolution are seen. Checks on similar rocks from Germany, Uganda and Tanzania reveal magnetites with comparable compositions, ranges, and zoning. Magnetites from alkaline and alkaline ultramafic silicate volcanic rocks cover only parts of this array. Magnetite analyses from some other fine-grained carbonatites, reported in the literature, fall in the same composition field, suggesting that this form of carbonatite may be distinctive. The chemistry and zoning would be consonant with rapid high-temperature crystallization in the carbonatite melts, with the lack of exsolution pointing to fast quenching: this contrasts with coarse-grained intrusive carbonatites, in which the magnetite compositions are attributed to slow cooling, with final equilibration at low temperature. In some complexes, both forms of carbonatite, with their different magnetite compositions, are represented.

Effect of the Mixing-Melt and Superheating on the Primary Si Phase of Hypereutectic Al-20%Si Alloy

2010 ◽  
Vol 146-147 ◽  
pp. 79-88
Author(s):  
Lian Deng Wang ◽  
Ding Yi Zhu ◽  
Zhe Liang Wei ◽  
Yong Lu Chen ◽  
Li Guang Huang ◽  
...  
Keyword(s):  
Grain Size ◽  
High Temperature ◽  
Low Temperature ◽  
Melt Mixing ◽  
Local Melting ◽  
Average Temperature ◽  
Present Alloy ◽  
Primary Si

The Al-20%Si alloy was prepared by mixing the high temperature melt of hypereutectic Al-30%Si alloy with the pre-crystallized low temperature hypoeutectic Al-10%Si alloy melt and then superheating the mixture, i.e., melts mixing and superheating (for short: MMS), combining with chemical metamorphism. The effect of pre-crystallized characteristic of the mixed melt on microstructure of Al-20%Si alloy was then investigated, The primary Si granules of the sample, poured by melt mixing with different composition and temperature, were well distributed with a grain size of less than 36μm. And after superheating, the primary Si phase of the mixed melt could be further refined and distributed more uniformly, which if adding the modificator into the mixed melt, the size of primary Si were been deceased and refined by less than 20μm. The analysis result shows that the decrease in the temperature of the mixed melt, from the average temperature of 740 °C for the mixture of Al-30%Si (900°C) and Al-10%Si (580°C) to 670°C for present alloy, leads to the increase in the degree of undercooling, and consequently to the refinement of primary Si. During the superheating, the growth, local melting, as well as the proliferation of primary Si occurred because of the unhomogeneous micro-distribution of the temperature and composition within the mixing melt, resulting in the further decrease in the grain size of primary Si. And adding the modificator could promote the effect of modification of primary Si of MMS process on the hypereutectic Al-Si alloy.

Densification kinetics of Alumina During Microwave Sintering

1992 ◽  
Vol 269 ◽  
Author(s):  
Jiping Cheng ◽  
Jinyu Qiu ◽  
Jian Zhou ◽  
Neng Ye
Keyword(s):  
High Temperature ◽  
Grain Growth ◽  
Microwave Field ◽  
Microwave Sintering ◽  
Alumina Ceramics ◽  
Kinetics Parameters ◽  
Fine Grained ◽  
Prolonged Time ◽  
Conventional Sintering ◽  
Kinetics Of

ABSTRACTSome kinetics parameters of alumina during microwave sintering were studied and compared with that during conventional sintering. The results demonstrated that the sintering rates for microwave processing were much greater than that for conventional processing, and the grain growth of alumina was rapid with prolonged time at high temperature in a microwave field. It was indicated that the microwave sintering at higher temperatures for a shorter time was favorable for preparing high density and fine-grained alumina ceramics.

scholarly journals Ultra-fast High Temperature Sintering (UHS) of ultra-fine-grained translucent alumina ceramics

Open Ceramics ◽  
2021 ◽  
pp. 100202
Author(s):  
Milad Kermani ◽  
Danyang Zhu ◽  
Jiang Li ◽  
Jinghua Wu ◽  
Yong Lin ◽  
...  
Keyword(s):  
High Temperature ◽  
Alumina Ceramics ◽  
Fine Grained

Synthesis of Sr4Al14O25:Eu2+, Dy3+ via Using Cyclodextrin as Chelating Agent by Sol-Gel Method

2014 ◽  
Vol 809-810 ◽  
pp. 702-706
Author(s):  
Wen Feng Xu ◽  
Cheng Li Liao ◽  
Fu Hang Xiong ◽  
Kui Li ◽  
Xiao Ling Liao
Keyword(s):  
Grain Size ◽  
Surface Morphology ◽  
Sol Gel ◽  
Chelating Agent ◽  
Gel Method ◽  
Sol Gel Method ◽  
Reducing Atmosphere ◽  
Average Grain Size ◽  
Pure Phase ◽  
First Time

Sr4Al14O25:Eu2+, Dy3+ luminescent phosphor was synthesized for the first time from using cyclodextrin as chelating agent by sol-gel method. The structural characterization, surface morphology and properties of the phosphor were studied. The results revealed that the target phosphor with relatively regular morphology, smaller grain size, pure phase and high crystallinity can be achieved at 1200°C for 4 h in a reducing atmosphere. The average grain size of the Sr4Al14O25:Eu2+, Dy3+ phosphor nanoparticles ranges from 50 to 100 nm . And the phosphorescence in blue-green (483 nm) by Eu2+.

Microstructure and deposition kinetics of Nb prepared by chemical vapor deposition

2018 ◽  
Vol 32 (22) ◽  
pp. 1850257 ◽  
Author(s):  
Yan Wei ◽  
Da Wei Zhang ◽  
Jun Wang ◽  
Hong Zhong Cai ◽  
Xu Xiang Zhang ◽  
...  
Keyword(s):  
Grain Size ◽  
Chemical Vapor Deposition ◽  
High Temperature ◽  
Low Temperature ◽  
Deposition Rate ◽  
Vapor Deposition ◽  
Deposition Temperature ◽  
Chemical Vapor ◽  
Deposition Kinetics ◽  
Hydrogen Flow

The deposition kinetics and microstructure of chemical vapor deposition (CVD) of Nb on the Mo substrate at different deposition variables is investigated. The morphology of CVD Nb is columnar, it exhibits a strong preferred orientation and its growth direction is perpendicular to the substrate surface, the deposition rate and grain size increased with the increase of deposition temperature. The deposition rate conforms to the Arrhenius formula, the activation energy [Formula: see text] at high temperature and low temperature is 0.85 kJ/mol and 7.2 kJ/mol, respectively. The rate-limiting step for CVD Nb at high temperature is chemical reaction step, whereas that is the mass transport step at low temperature. Chlorination temperature has a weak influence on deposition rate and grain structure, the deposition rate and grain size of CVD Nb increased with the increase of the chlorine flow and hydrogen flow, the maximum deposition rate is [Formula: see text], thus, the optimum deposition temperature is 1200[Formula: see text]C, chlorination temperature is 350[Formula: see text]C, hydrogen flow is 400 ml, chlorine flow is 200 ml.

Transparent nanocrystalline MgO by rapid and low-temperature spark plasma sintering

2004 ◽  
Vol 19 (9) ◽  
pp. 2527-2531 ◽  
Author(s):  
Rachman Chaim ◽  
Zhijian Shen ◽  
Mats Nygren
Keyword(s):  
Grain Size ◽  
Low Temperature ◽  
Oxygen Vacancy ◽  
Spark Plasma Sintering ◽  
Color Centers ◽  
Reducing Atmosphere ◽  
Plasma Sintering ◽  
Average Grain Size ◽  
Spark Plasma ◽  
Nanocrystalline Mgo

We investigated superfast densification of nanocrystalline MgO powders by spark plasma sintering (SPS) between 700 °C and 825 °C under applied pressures of 100and 150 MPa. Fully-dense transparent nanocrystalline MgO with a 52-nm average grain size was fabricated at 800 °C and 150 MPa for 5 min. In-line transmissionsof 40% and 60% were measured compared to MgO single crystal, for the yellowand red wavelengths, respectively. Densification occurs by particles sliding over each other; the nanometric grain size and pores lead to the optical transparency. The light brownish color of the nanocrystalline MgO is due to the oxygen vacancy color centers, originating from the reducing atmosphere of the SPS process.

Effects of grain size on high temperature creep of fine grained, solution and dispersion hardened V–1.6Y–8W–0.8TiC

2011 ◽  
Vol 417 (1-3) ◽  
pp. 299-302 ◽  
Author(s):  
T. Furuno ◽  
H. Kurishita ◽  
T. Nagasaka ◽  
A. Nishimura ◽  
T. Muroga ◽  
...  
Keyword(s):  
Grain Size ◽  
High Temperature ◽  
High Temperature Creep ◽  
Fine Grained ◽  
Temperature Creep

High Temperature Tensile Properties of Equal Channel Angular Pressed Al-Zn-Mg-Cu Alloy

2012 ◽  
Vol 31 (6) ◽  
pp. 675-678 ◽  
Author(s):  
Süleyman Tekeli ◽  
Ahmet Güral
Keyword(s):  
Grain Size ◽  
High Temperature ◽  
Tensile Tests ◽  
Fine Grained ◽  
Angular Pressing ◽  
Cu Alloy ◽  
Elongation To Failure ◽  
Electron Microscopes ◽  
High Temperature Tensile ◽  
Scanning Electron Microscopes

AbstractIn this study, ultra fine-grained microstructure was produced in Al–Zn–Mg–Cu alloy by equal channel angular pressing (ECAP) at 200 °C and a pressing speed of 2 mm s−1 using route C. The microstructure of the specimens was characterized by transmission and scanning electron microscopes. The results showed that the mean grain size of the specimens effectively decreased with increasing pass number. That is, while the grain size of unECAPed specimen was 10 µm, this value decreased to 300 nm after 14 passes. High temperature tensile tests were carried out at a strain rate of 1 × 10− 2 and temperature of 250 °C in the specimens with different pass number. It was seen that the flow stress decreased and the elongation to failure significantly increased with increasing pass number. The highest elongation to failure value of 90% was obtained in the specimen after 14 passes.

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