Effect of rate controlled sintering on microstructure and electrical properties of ZnO doped with bismuth and antimony oxides

1997 ◽  
Vol 12 (9) ◽  
pp. 2447-2454 ◽  
Author(s):  
Gaurav Agarwal ◽  
Robert F. Speyer
Keyword(s):  
Grain Size ◽  
Liquid Phase ◽  
Grain Growth ◽  
Elevated Temperatures ◽  
Antimony Oxide ◽  
Second Phase ◽  
Dopant Content ◽  
Average Grain Size ◽  
Rate Controlled ◽  
Grain Boundary Pinning

Various rate controlled sintering (RCS) schedules were used on isostatically pressed particulate compacts of ZnO with Bi2O3 and Sb2O3 additives. For low additive content, smaller average grain sizes with more rapid RCS schedules were attributable to thermal schedules which minimized the time at elevated temperatures where grain growth could occur. β–Bi2O3, Zn7Sb2O12, and Zn2Sb3Bi3O14 phases formed during/after sintering. Elevated heat-treatment temperatures favored the formation of Zn7Sb2O12 and additional β–Bi2O3, while Zn2Sb3Bi3O14 was dominant in sintered samples where the RCS schedule did not result in temperatures in excess of 1100 °C. Zn2Sb3Bi3O14 precipitated during sintering, functioning as grain boundary pinning sites which impeded ZnO grain growth. Bismuth and antimony oxide-based liquid facilitated sintering at lower temperatures, which in turn resulted in decreased average grain size. Rapid RCS schedules for samples with low dopant content resulted in lower sintering temperatures, since time was not allowed for Zn2Sb3Bi3O14 precipitation to deplete the liquid phase. For higher dopant contents, liquid phase was adequately plentiful, wherein longer RCS schedules resulted in lower sintering temperatures. Increasing concentration of second phase generally fostered decreased grain size and attenuated the effect of thermal schedule on the microstructure. Electrical resistance and breakdown voltage increased consistent with decreasing ZnO average grain size.

scholarly journals Kinetics of Austenite Grain Growth during a Continuous Heating of a Niobium Microalloyed Steel

2004 ◽  
Vol 467-470 ◽  
pp. 929-934 ◽  
Author(s):  
David San Martín ◽  
Francisca García Caballero ◽  
Carlos Capdevila ◽  
C. Carcía de Andrés
Keyword(s):  
Grain Size ◽  
Grain Boundaries ◽  
Heating Rate ◽  
Grain Growth ◽  
Continuous Heating ◽  
Second Phase ◽  
Austenite Grain Size ◽  
Austenite Grain ◽  
Average Grain Size ◽  
The Matrix

Grain growth is a thermally activated process in which the average grain size increases as temperature and time increases. The driving force for grain growth results from the decrease in the free energy associated with the reduction in total grain boundary energy. There are several known factors that influence the migration of grain boundaries such as second phase particles precipitated in the matrix and the solute elements segregated at grain boundaries. The austenite grain boundaries are revealed using the thermal etching method. Carbon extraction replicas were prepared to determine the composition and size of precipitates present in the matrix. In this work, the evolution of the average prior austenite grain size (PAGS) of a low carbon steel microalloyed with niobium is studied as a function of temperature and heating rate. Austenite grains show a two-stage growth. It has been found that as heating rate increases, the grain coarsening temperature (TGC) increases and the grain size at that temperature decreases. TGC temperature lies around 40-60°C below the temperature for complete dissolution of carbonitrides (TDISS).

scholarly journals Micro structural control of stabilized Zirconia ceramics (8YSZ) through modified conventional sintering methodologies

2010 ◽  
Vol 42 (1) ◽  
pp. 91-97 ◽  
Author(s):  
K. Rajeswari ◽  
Rajasekhar Reddy ◽  
U.S. Hareesh ◽  
B.P. Saha ◽  
R. Johnson
Keyword(s):  
Grain Size ◽  
Grain Growth ◽  
Structural Control ◽  
Grain Size Analysis ◽  
Size Analysis ◽  
Stabilized Zirconia ◽  
Average Grain Size ◽  
Conventional Sintering ◽  
Slip Cast ◽  
Rate Controlled

Slip cast Y2O3 stabilized Zirconia (8YSZ) ceramics was subjected to Conventional Ramp and Hold (CRH), Rate Controlled (RCS) and Two Stage Sintering (2SS) methodologies. Sintered samples were characterized for their densities and grain size analysis by Scanning Electron Microscopy. The slip cast samples sintered by CRH and 2SS have achieved 98 - 99 % of theoretical densities while RCS samples have exhibited a low density of 97 %. The samples exhibited an average grain size of 2.64 ?m by 2SS sintering in comparison to 8.83 ?m in case of CRH and 3.45 ?m in case of RCS. Controlled pore growth associated with RCS, when compared to CRH methodology is mainly responsible for the relatively smaller grain size observed with RCS. A four fold decrease in grain size i.e. 2.64 ?m observed with the two step sintering can be attributed to the fact that the first heating step to high temperature of 1550?C for a shorter duration closes the porosity without significant grain growth. The second step at 1375?C for a longer period of time imparts densification with limited grain growth.

Effect of Particle Size on the Zener Limit: A Monte Carlo Simulation Approach

2012 ◽  
Vol 560-561 ◽  
pp. 152-155 ◽  
Author(s):  
Kalale Raghavendra Rao Phaneesh ◽  
Anirudh Bhat ◽  
Gautam Mukherjee ◽  
Kishore T. Kashyap
Keyword(s):  
Monte Carlo Simulation ◽  
Particle Size ◽  
Grain Size ◽  
Monte Carlo ◽  
Grain Boundaries ◽  
Grain Growth ◽  
Second Phase ◽  
Particle Sizes ◽  
Second Phase Particles ◽  
Average Grain Size

2D Potts model Monte Carlo simulation was carried out on a square lattice to investigate the effects of varying the size of second phase particles on the Zener limit of grain growth, in two-phase polycrystals. Simulations were carried out on a 1000^2 size matrix with Q-state of 64, dispersed with second phase particles of various sizes and surface fractions, and run to stagnation. Different grain growth parameters such as mean grain size, largest grain size, fraction of second phase particles lying on grain boundaries, etc., were computed for the pinned microstructures. The pinned average grain size or the Zener limit increased with increase in particle size, as per the classic Smith-Zener equation. The Zener limit scaled inversely with the square root of the particle fraction for all particle sizes, while it scaled exponentially with the fraction of second phase particles lying on the grain boundaries (ϕ), for all particle sizes tested.

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 WO3 Doping on Microstructural and Electrical Properties of ZnO-Pr6O11 Based Varistor Materials

2013 ◽  
Vol 591 ◽  
pp. 54-60
Author(s):  
Xiu Li Fu ◽  
Yan Xu Zang ◽  
Zhi Jian Peng
Keyword(s):  
Grain Size ◽  
Electrical Properties ◽  
Grain Growth ◽  
Doping Level ◽  
Nonlinear Coefficient ◽  
Current Voltage ◽  
Average Grain Size ◽  
Current Voltage Characteristics ◽  
Voltage Performance

The effect of WO3doping on microstructural and electrical properties of ZnO-Pr6O11based varistor materials was investigated. The doped WO3plays a role of inhibitor in ZnO grain growth, resulting in decreased average grain size from 2.68 to 1.68 μm with increasing doping level of WO3from 0 to 0.5 mol%. When the doping level of WO3was lower than 0.05 mol%, the nonlinear current-voltage characteristics of the obtained varistors could be improved significantly with increasing amount of WO3doped. But when the doping level of WO3became higher, their nonlinear current-voltage performance would be dramatically deteriorated when more WO3was doped. The optimum nonlinear coefficient, varistor voltage, and leakage current of the samples were about 13.71, 710 V/mm and 13 μA/cm2, respectively, when the doping level of WO3was in the range from 0.03 to 0.05 mol%.

Effect of Warm Rolling on Microstructure and High Temperature Mechanical Behavior of a Nano-Structured Al-8Fe-2Mo-2V-1Zr Alloy

2005 ◽  
Vol 486-487 ◽  
pp. 411-414 ◽  
Author(s):  
Won Yong Kim ◽  
Jae Sung Park ◽  
Mok Soon Kim
Keyword(s):  
Particle Size ◽  
Grain Size ◽  
Elevated Temperatures ◽  
Hot Extrusion ◽  
Warm Rolling ◽  
Spray Forming ◽  
Grain Structure ◽  
Average Grain Size ◽  
Two Samples ◽  
Additional Process

Mechanical properties of a nano-structured Al-8Fe-2Mo-2V-1Zr alloy produced by spray forming and subsequent hot-extrusion at 420°C were investigated in terms of tensile test as a function of temperature. Warm rolling was adapted as an additional process to expect further refinement in microstructure. Well-defined equiaxed grain structure and finely distributed dispersoids with nano-scale in particle size were observed in the spray formed and hot extruded sample (as-received sample). The average grain size and particle size were measured to 500 nm and 50 nm, respectively. While it was found that warm rolling gives rise to precipitate fine dispersoids less than 10 nm without influencing the grain size of matrix phase, in the temperature range of RT∼150°C, distinguishable changes in ultimate tensile strength were not found between the as-received and warm-rolled samples. At elevated temperatures ranging from 350 to 550°C, warm-rolled sample showed a higher value of elongation than as-received one although similar values of elongation were observed between two samples at temperatures lower than 350°C.

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.

Investigating the Relationships Between Structures and Properties of Al Alloys Incorporated With Ti and Mg Inclusions

2016 ◽  
Vol 138 (3) ◽  
Author(s):  
Halil Ibrahim Kurt ◽  
Ibrahim H. Guzelbey ◽  
Serdar Salman ◽  
Razamzan Asmatulu ◽  
Mustafa Dere
Keyword(s):  
Solid Solution ◽  
Grain Size ◽  
Elevated Temperatures ◽  
Solidification Process ◽  
Optical Microscope ◽  
Industrial Applications ◽  
Al Alloys ◽  
Average Grain Size ◽  
Solidification Processes ◽  
Grain Size And Shape

This study investigates the influence of titanium (Ti) and magnesium (Mg) additions on aluminum (Al) alloys in order to evaluate the relationship between the structure and properties of the new alloys. The alloys obtained at elevated temperatures mainly consist of Al–2Mg–1Ti, Al–2Mg–3Ti, Al–4Mg–2Ti, and Al–6Mg–2Ti alloys, as well as α and τ solid solution phases of intermetallic structures. Microstructural analyses were performed using X-ray diffraction (XRD), optical microscope, and energy dispersive spectrometry (EDS) techniques. Test results show that the average grain size of the alloys decreased with the addition of Ti inclusions during the casting and solidification processes, and the smallest grain size was found to be 90 μm for the Al–6Mg–3Ti alloy. In addition, tensile properties of the Al–Mg–Ti alloys were initially improved and then worsened after the addition of higher concentrations of Ti. The highest tensile and hardness values of the alloys were Al–4Mg–2Ti (205 MPa) and Al–6Mg–3Ti (80 BHN). The primary reasons for having higher mechanical properties may be attributed to strengthening of the solid solution and refinement of the grain size and shape during the solidification process. For this study, the optimum concentrations of Ti and Mg added to the Al alloys were 4 and 2 wt.%, respectively. This study may be useful for field researchers to develop new classes of Al alloys for various industrial applications.

The Study on TiAl Based Alloy Blade Casting Structure by Bottom Pouring Vacuum Suction Casting

2013 ◽  
Vol 442 ◽  
pp. 44-47
Author(s):  
Xi Cong Ye ◽  
Wei Guang Zhao
Keyword(s):  
Grain Size ◽  
Fine Structure ◽  
Grain Growth ◽  
Vacuum Suction ◽  
Suction Casting ◽  
Average Grain Size ◽  
B2 Phase ◽  
Blade Casting ◽  
Forced Cooling ◽  
Undercooling Degree

In this paper, the bottom pouring vacuum suction casting is used, and the TiAl-based alloy blade with good face quality was obtained. Bottom pouring vacuum suction casting obtained Ti-47Al-5Nb-0.5Si alloy fine structure, the average grain size is 20um or less. Metal permanent forced cooling effect increases the undercooling degree, and the formation of Ti5Si3 can hinder the grain growth and the formation of nucleation particles, and Nb elements are conducive to the formation of B2 phase, and these three reasons refined the grain size.

Ion Induced Grain Growth in Pd

1991 ◽  
Vol 235 ◽  
Author(s):  
D. A. Lilienfeld ◽  
P. Bøorgesen ◽  
P. Meyer
Keyword(s):  
Thin Films ◽  
Grain Size ◽  
Grain Growth ◽  
Low Temperatures ◽  
Nanocrystalline Materials ◽  
Ion Irradiation ◽  
Size Distributions ◽  
Careful Choice ◽  
Average Grain Size

ABSTRACTIon irradiation induced grain growth size distributions in Pd are examined at low temperatures. Two features are observed: 1) A majority of the grains saturate in size. 2) Some grains achieve sizes much larger than the average grain size and continue to grow with ion dose. However, by careful choice of ion mass and ion dose, it is possible to produce a sample possessing a monomodal grain size. This process will have applications in producing thin films of nanocrystalline materials.

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