MgAl2O4 Transparent Nano-Ceramics Prepared by Sintering under Ultrahigh Pressure

2007 ◽  
Vol 280-283 ◽  
pp. 549-552 ◽  
Author(s):  
Xiang Hui Chang ◽  
Tie Cheng Lu ◽  
Ying Zhang ◽  
Xiang Jie Luo ◽  
Qiang Liu ◽  
...  
Keyword(s):  
Grain Size ◽  
Low Temperature ◽  
Sintering Temperature ◽  
Ultrahigh Pressure ◽  
Transparent Ceramics ◽  
Grain Sizes ◽  
Average Grain Size ◽  
Temperature And Pressure ◽  
Sintering Characteristics ◽  
Sintering Condition

The first experimental work to produce transparent MgAl2O4 nano-ceramics was reported in this paper. The sintering characteristics of transparent nano-ceramics were investigated at relatively low temperature (800 ~ 1100°C) under ultrahigh pressure (2 ~ 5 GPa) using hydrostatic equipment. The morphologies and phases of ceramics were observed by means of SEM and XRD, respectively. The grain sizes of the ceramics are shown to be less than one hundred nanometers, far smaller than the sizes of common transparent ceramics. Furthermore, the higher the sintering temperature and pressure are, the greater the extent of densification is. At the same temperature, the higher the pressure is, the smaller the average grain size is. Under the same pressure, the higher the temperature is, the larger the average grain size is. The optimal sintering condition for preparing transparent nano-ceramics was also determined.

Preparation and Characterization of Transparent Nanocrystalline Ceramics

2008 ◽  
Vol 368-372 ◽  
pp. 402-406 ◽  
Author(s):  
Tie Cheng Lu ◽  
Xiang Hui Chang ◽  
Jie Zhang ◽  
Jian Qi Qi ◽  
Xiang Jie Luo
Keyword(s):  
Mechanical Properties ◽  
Grain Size ◽  
High Pressure ◽  
Low Cost ◽  
Nanocrystalline Ceramics ◽  
Grain Sizes ◽  
Average Grain Size ◽  
Sintering Characteristics ◽  
Sintering Condition

The transparent nanocrystalline MgAl2O4 spinel ceramics were synthesized at lowtemperature and high-pressure conditions with low-cost nano-sized MgAl2O4 powder. The sintering characteristics of transparent nano-ceramics were investigated at 500~700oC under 2 ~ 5 GPa. The optimal sintering condition for preparing transparent nano-ceramics was determined. The microstructure and phase composition of powder, as well as the microstructures, morphologies, optical properties, densities and mechanical properties of synthetic ceramics were investigated. The grain sizes of the synthetic ceramics are less than 100 nm, far smaller than those of usual transparent micron-ceramics, and the average grain size depends on the pressure and temperature. The transmittance at the saturation plateau can near 80%. The relative densities of all samples are less than 99%, however, they are highly transparent. The toughness, derived from energy dissipation, of the transparent nano-ceramics was investigated and was compared with that of transparent micron-ceramic.

Low temperature sintering of nano-SiC using a novel Al8B4C7 additive

2010 ◽  
Vol 25 (3) ◽  
pp. 471-475 ◽  
Author(s):  
Sea-Hoon Lee ◽  
Byung-Nam Kim ◽  
Hidehiko Tanaka
Keyword(s):  
Grain Size ◽  
Liquid Phase ◽  
Low Temperature ◽  
Sintering Temperature ◽  
Applied Pressure ◽  
Liquid Phase Sintering ◽  
Low Temperature Sintering ◽  
Densification Rate ◽  
Sintering Additive ◽  
Average Grain Size

Al8B4C7 was used as a sintering additive for the densification of nano-SiC powder. The average grain size was approximately 70 nm after sintering SiC-12.5wt% Al8B4C7 at 1550 °C. The densification rate strongly depended on the sintering temperature and the applied pressure. The rearrangement of SiC particles occurred at the initial shrinkage, while viscous flow and liquid phase sintering became important at the middle and final stage of densification.

Effect of Low-Temperature Aging on Thermally-Induced Phase Transformation of NiTi Wire with a Wide Range of Grain Sizes

2021 ◽  
Vol 1042 ◽  
pp. 9-16
Author(s):  
Zhi Hao Zhao ◽  
Jian Ping Lin ◽  
Jun Ying Min ◽  
Yong Hou ◽  
Bo Sun
Keyword(s):  
Grain Size ◽  
Phase Transformation ◽  
Low Temperature ◽  
Thermally Induced ◽  
Grain Sizes ◽  
Average Grain Size ◽  
Wide Range ◽  
Low Temperature Aging ◽  
Niti Wires ◽  
Temperature Aging

Thermally-induced phase transformation (PT) is of significance and value to the application of NiTi alloy components. Low-temperature aging (LTA) treatment was used to alter PT characteristics of NiTi alloys avoiding undesirable grain growth. Effect of LTA on PT of NiTi wires with a wide range of grain sizes from 34 nm to 8021 nm was investigated in this study. As the average grain size varies from 34 to 217 nm, the temperature of the B2↔R transformation increase as a result of LTA, and the increasing effect is more obvious at a larger grain size. For NiTi alloys with average grain sizes ranging from 523 to 1106 nm, transformation sequence changes from B2↔B19' to B2↔R due to LTA. For the sample with an average grain size of 2190 nm, the B2↔B19' transformation is replaced by B2↔R←B19' after LTA. When the average grain size is larger than 2190 nm, transformation sequence changes from B2↔B19' to B2↔R↔B19' after LTA. Transmission emission microscope observations reveal that the above-mentioned PT behavior correlates with the coupled effect of grain size and precipitation. The precipitation of Ni4Ti3 in the grains with a size smaller than ~150 nm is inhibited after LTA, the temperature of B2→R of samples with average GS smaller than ~150 nm still is elevated due to the inhomogeneous grain size of NiTi wires.

The Effects of Sintering Temperature Variations on some Physical Properties of Al2O3-SiO2-PbO-MgO Laminated Tape System

2009 ◽  
Vol 421-422 ◽  
pp. 285-288
Author(s):  
Rosidah Alias ◽  
Ibrahim Azmi ◽  
Sabrina Mohd Shapee ◽  
Zulkifli Ambak ◽  
Zulfadli Mohamed Yusoff ◽  
...  
Keyword(s):  
Dielectric Constant ◽  
Grain Size ◽  
Dielectric Loss ◽  
Physical Properties ◽  
Sintering Temperature ◽  
Temperature Variations ◽  
Sem Micrographs ◽  
Grain Sizes ◽  
Average Grain Size ◽  
Tape System

An Al2O3-SiO2-PbO-MgO laminated tape system was prepared to investigate the dependence of some physical properties on various sintering temperatures, 840 °C, 880 °C, 920 °C and 960 °C. The results show that the effect of the increasing sintering temperatures was a fluctuating in the density value of the laminates. It was also observed that the dielectric constant and dielectric loss showed the lowest value for the sintering temperature of 880 °C. SEM micrographs of the laminate samples shows a mixture of grain sizes and the samples had a combination of small and large pores with the average grain size around 2.20-2.64 m.

Investigation of Isothermal Treatment on the Structural, Microstructure and Physical Properties of Li2O-Al2O3-SiO2 Glass-Ceramic

2020 ◽  
Author(s):  
Husniyah Aliyah Lutpi ◽  
Hasmaliza Mohamad ◽  
Tuti Katrina Abdullah
Keyword(s):  
Grain Size ◽  
Elevated Temperature ◽  
Physical Properties ◽  
Thermal Shock ◽  
Glass Ceramic ◽  
Crystalline Phase ◽  
Sintering Temperature ◽  
Isothermal Treatment ◽  
Crystalline Phases ◽  
Average Grain Size

Abstract The present work aims to investigate the effects of isothermal treatment on the structural, microstructure and physical properties of Li2O-Al2O3-SiO2 glass-ceramic. Sintering temperature plays a major role in producing the desired lithium aluminosilicate (LAS) glass-ceramic crystalline phases. This work also aims to achieve a low thermal expansion coefficient β-spodumene (LiAlSi2O6) crystalline phase with improved density and lower porosity, which can be useful for the applications with thermal shock properties. The LAS glass-ceramic was fabricated by the melt-quenching technique at 1550 °C for 5 h before being isothermally sintered at an elevated temperature of 900 to 1200 °C for 30 min. The evolution of LAS glass-ceramic crystalline phases was identified using differential thermal analysis and the β-spodumene exothermic peak appeared at 999 °C. Based on the X-ray diffraction results, the complete transformation of β-spodumene from high-quartz solid solution (β-quartz) occurred at 1000 °C. However, the sintering temperature did not change the crystalline phase when sintered above 1000 °C, but the lattice parameter of the crystal structure was slightly altered. Moreover, it was observed that the LAS glass-ceramic grain size increased with temperature, whereby the smallest average grain size recorded (0.61 µm) for LAS glass-ceramic sintered at 1100 °C. Meanwhile, the fully densified LAS glass-ceramic at 1100 ° C was measured at 2.47 g/cm3 with 0.52% porosity. The isothermal treatment at elevated temperature indicated that sintering at 1100 °C provided a denser, less porous, and small average grain size which is preferred for thermal shock resistance applications.

Effect of Annealing on Nanocrystalline Structure of Nb3Sn Diffusion Layers in Composites with Internal Tin Sources

2010 ◽  
Vol 297-301 ◽  
pp. 126-131 ◽  
Author(s):  
E.N. Popova ◽  
Vladimir V. Popov ◽  
E.P. Romanov ◽  
S.V. Sudareva ◽  
L.V. Elohina ◽  
...  
Keyword(s):  
Grain Size ◽  
Carrying Capacity ◽  
Nanocrystalline Structure ◽  
Diffusion Annealing ◽  
External Diameter ◽  
High Temperature Annealing ◽  
Grain Sizes ◽  
Diffusion Layers ◽  
Average Grain Size ◽  
Complete Transformation

Multifilamentary Nb3Sn-based superconducting composites manufactured by an internal-tin method have been studied by transmission (TEM) and scanning (SEM) electron microscopy. The main goal of this study is to reveal the effect of diffusion annealing regimes as well as the external diameter of the wires on the structure of nanocrystalline Nb3Sn layers (average grain size, grain size distribution, layer thickness, amount of Sn, etc.). It is demonstrated that multistep diffusion annealing results in quite a complete transformation of Nb filaments into Nb3Sn though some amount of the residual Nb remains in the filaments center. With an external diameter decrease the superconducting layers structure has been found to refine and get somewhat more uniform. An additional high-temperature annealing results in marked growth of Nb3Sn grain sizes and their scattering in sizes, which may negatively affect the current-carrying capacity of a wire.

Characterization of Defect Nucleation and Propagation in Fe2O3+FCC-Al Nanocomposites During Uniaxial Tensile and Compressive Deformations

2006 ◽  
Author(s):  
Vikas Tomar ◽  
Min Zhou
Keyword(s):  
Molecular Dynamics ◽  
Grain Size ◽  
Defect Formation ◽  
Voronoi Tessellation ◽  
Orientation Distribution ◽  
Uniaxial Tensile ◽  
Grain Sizes ◽  
Classical Molecular Dynamics ◽  
Average Grain Size ◽  
Nanocrystalline Structures

The objective of this research is to analyze uniaxial tensile and compressive mechanical deformations of α-Fe2O3 + fcc Al nanoceramic-metal composites using classical molecular dynamics (MD). Specifically, variations in the nucleation and the propagation of defects (such as dislocations and stacking faults etc.) with variation in the nanocomposite phase morphology and their effect on observed tensile and compressive strengths of the nanocomposites are analyzed. For this purpose, a classical molecular dynamics (MD) potential that includes an embedded atom method (EAM) cluster functional, a Morse type pair function, and a second order electrostatic interaction function is developed, see Tomar and Zhou (2004) and Tomar and Zhou (2006b). The nanocrystalline structures (nanocrystalline Al, nanocrystalline Fe2O3 and the nanocomposites with 40% and 60% Al by volume) with average grain sizes of 3.9 nm, 4.7 nm, and 7.2 nm are generated using a combination of the well established Voronoi tessellation method with the Inverse Monte-Carlo method to conform to prescribed log-normal grain size distributions. For comparison purposes, nanocrystalline structures with a specific average grain size have the same grain morphologies and the same grain orientation distribution. MD simulations are performed at the room temperature (300 K). Calculations show that the deformation mechanism is affected by a combination of factors including the fraction of grain boundary (GB) atoms and the electrostatic forces between atoms. The significance of each factor is dependent on the volume fractions of the Al and Fe2O3 phases. Depending on the relative orientations of the two phases at an interface, the contribution of the interface to the defect formation varies. The interfaces have stronger effect in structures with smaller average grain sizes than in structures with larger average grain sizes.

Nanostructure Evolution of ZnO in Ultra-fast Microwave Sintering

2011 ◽  
Vol 691 ◽  
pp. 65-71 ◽  
Author(s):  
Rodolfo F. K. Gunnewiek ◽  
Ruth Herta Goldsmith Aliaga Kiminami
Keyword(s):  
Grain Size ◽  
Zinc Oxide ◽  
Grain Growth ◽  
Microwave Sintering ◽  
High Heating Rate ◽  
Heating Rates ◽  
Grain Sizes ◽  
Average Grain Size ◽  
Conventional Sintering ◽  
Holding Temperature

Grain growth is inevitable in the sintering of pure nanopowder zinc oxide. Sintering depend on diffusion kinetics, thus this growth could be controlled by ultra-fast sintering techniques, as microwave sintering. The purpose of this work was to investigate the nanostructural evolution of zinc oxide nanopowder compacts (average grain size of 80 nm) subjected to ultra-rapid microwave sintering at a constant holding temperature of 900°C, applying different heating rates and temperature holding times. Fine dense microstructures were obtained, with controlled grain growth (grain size from 200 to 450nm at high heating rate) when compared to those obtained by conventional sintering (grain size around 1.13µm), which leads to excessively large average final grain sizes.

Dielectric Properties of Nanograined BaTiO3 Ceramics Fabricated by Aerosol Deposition Method

2011 ◽  
Vol 485 ◽  
pp. 183-186 ◽  
Author(s):  
Tsutomu Furuta ◽  
Saki Hatta ◽  
Yoichi Kigoshi ◽  
Takuya Hoshina ◽  
Hiroaki Takeda ◽  
...  
Keyword(s):  
Grain Size ◽  
Room Temperature ◽  
Annealing Treatment ◽  
Aerosol Deposition ◽  
Dielectric Measurement ◽  
Deposition Method ◽  
Grain Sizes ◽  
Average Grain Size ◽  
Aerosol Deposition Method ◽  
Polarization Electric Field

Freestanding BaTiO3 ceramics films were fabricated using the aerosol deposition (AD) method and the size effect of nanograined BaTiO3 ceramics was demonstrated. Dense BaTiO3 thick film fabricated by the AD method was crystallized and detached from substrate by an annealing treatment at 600 °C, and then the grain size was controlled by a reannealing treatment at various temperatures. As a result, freestanding BaTiO3 thick films with various grain sizes from 24 to 170 nm were successfully obtained. Polarization–electric field (P–E) measurement revealed that BaTiO3 ceramics with grain sizes of more than 58 nm showed ferroelectricity, whereas BaTiO3 ceramics with an average grain size of 24 nm showed paraelectricity at room temperature. Dielectric measurement indicated that the permittivity decreased with decreasing grain size in the range of 170 to 24 nm.

Synthesis of Nanocrystalline 0.94Bi0.5Na0.5TiO3-0.06BaTiO3 Powder by a Citrate Method

2008 ◽  
Vol 368-372 ◽  
pp. 103-105
Author(s):  
Zhi Bin Tian ◽  
Xiao Hui Wang ◽  
Ji Li ◽  
Wei Zhao ◽  
Long Tu Li
Keyword(s):  
Grain Size ◽  
Electrical Properties ◽  
Traditional Method ◽  
Sintering Temperature ◽  
Ph Value ◽  
Precursor Solution ◽  
Milling Process ◽  
Citrate Method ◽  
Nano Powder ◽  
Average Grain Size

A citrate method to synthesize 0.94Bi0.5Na0.5TiO3-0.06BaTiO3 nano-powder was studied. The stable gel was obtained by the control of the pH value and temperature of the precursor solution. The BNBT nano-powder was produced after calcining the xerogel at 600°C~800°C. The average grain size of the powder calcined at 700°C for 3 h is 50 nm, and the grain size of the ceramic sintered at 1080°C is 0.7 μm. The sintering temperature used is 100°C lower than the BNBT ceramic prepared by traditional method, but the electrical properties were comparable. In addition, it was found that the ball-milling process has important effect on the morphology of the ceramics and the orientation crystals were eliminated due to the disintegration of agglomerates during milling.

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