Densification of Nanocrystalline Ceramics by Combustion Reaction and Quick Pressing

The technique of combustion reaction and quick pressing was adopted to prepare dense nanocrystalline ceramics. The densification process of magnesia compact with a particle size of 100 nm was investigated, under the applied pressure of up to 170 MPa, and the temperature of 1740–2080 K with ultra-high heating rate of above 1700 K/min. As a result, pure magnesia ceramics with a relative density of 98.8% and an average grain size of 120 nm was obtained at 1740 K and 170 MPa, while the ones with decreased relative density and increased grain size were produced under the increasing temperature and the identical pressure conditions. The results indicated that grain growth of the nanocrystalline magnesia was effectively restrained by the combined effect of the ultra-high heating rate and the high pressure. Moreover, under the particular sintering conditions, there existed an appropriate temperature range for the preparation of dense nanocrystalline magnesia, and the excessive temperature would not only exaggerate grain growth but also impede densification.

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Grain growth stagnation in the dense nanocrystalline yttria prepared by combustion reaction and quick pressing with an ultra-high heating rate

Journal of the European Ceramic Society ◽

10.1016/j.jeurceramsoc.2014.02.015 ◽

2014 ◽

Vol 34 (10) ◽

pp. 2475-2482 ◽

Cited By ~ 5

Author(s):

Jianghao Liu ◽

Zhengyi Fu ◽

Weimin Wang ◽

Jinyong Zhang ◽

Hao Wang ◽

...

Keyword(s):

Heating Rate ◽

Grain Growth ◽

Combustion Reaction ◽

High Heating Rate ◽

High Heating

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Nanostructure Evolution of ZnO in Ultra-fast Microwave Sintering

Materials Science Forum ◽

10.4028/www.scientific.net/msf.691.65 ◽

2011 ◽

Vol 691 ◽

pp. 65-71 ◽

Cited By ~ 2

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.

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

Materials Science Forum ◽

10.4028/www.scientific.net/msf.467-470.929 ◽

2004 ◽

Vol 467-470 ◽

pp. 929-934 ◽

Cited By ~ 2

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).

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Effect of the Heating Rate on the Spark-Plasma-Sintering (SPS) of Transparent Y2O3 Ceramics: Microstructural Evolution, Mechanical and Optical Properties

Ceramics ◽

10.3390/ceramics4010006 ◽

2021 ◽

Vol 4 (1) ◽

pp. 56-69

Author(s):

Lihong Liu ◽

Koji Morita ◽

Tohru S. Suzuki ◽

Byung-Nam Kim

Keyword(s):

Mechanical Properties ◽

Grain Size ◽

Heating Rate ◽

Spark Plasma Sintering ◽

Near Infrared ◽

Slow Heating ◽

High Heating Rate ◽

Plasma Sintering ◽

High Heating ◽

Spark Plasma

High strength transparent Y2O3 ceramics were fabricated from commercial powders using spark plasma sintering (SPS) technique by optimizing the heating rate. The heating rate significantly influenced the microstructures and the optical/mechanical properties of the Y2O3 ceramics. Grain growth was limited accordingly with increasing the heating rate. The ball milling process of the commercial Y2O3 powders is likely to further enhance the sinterability during the SPS processing. The dense Y2O3 ceramics, which were sintered by SPS with 100 °C/min, showed good transmittance range from visible to near infrared (IR). For a high heating rate of 100 °C/min, the in-line transmittance at a visible wavelength of 700 nm was 66%, whereas for a slow heating rate of 10 °C/min, it reduced to 46%. The hardness Hv tends to increase with increasing the heating rate and rigorously followed the Hall–Petch relationship; that is, it is enhanced with a reduction of the grain size. The toughness KIC, on the other hand, is less sensitive to both the heating rate and the grain size, and takes a similar value. This research highlighted that the high heating rate SPS processing can fabricate fully dense fine-grained Y2O3 ceramics with the excellent optical and mechanical properties.

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Effect of Annealing on Magnetic Properties and Domain Structures of FePt Thin Films by Rapid Thermal Annealing Technique

Advanced Materials Research ◽

10.4028/www.scientific.net/amr.79-82.911 ◽

2009 ◽

Vol 79-82 ◽

pp. 911-914

Author(s):

S.C. Chen ◽

T.H. Sun ◽

Po Cheng Kuo

Keyword(s):

Grain Size ◽

Magnetic Properties ◽

Heating Rate ◽

Domain Structure ◽

Rapid Thermal Annealing ◽

Annealing Time ◽

Annealing Temperature ◽

High Heating Rate ◽

Fept Film ◽

High Heating

Single-layered FePt films of 30 nm thick were annealed at temperature between 300 and 800 °C for 1–180 sec by a rapid thermal annealing (RTA) with a high heating rate of 100 °C/sec. It is found that both the grain size and magnetic domain size of the FePt film increase with increasing annealing temperature and annealing time. The FePt films exhibited soft magnetic properties and without domain images were observed by magnetic force microscope (MFM) when the films were post-annealed at below 500 °C for 180 sec. The in-plane coercivity (Hc//) and perpendicular coercivity (Hc⊥) of FePt film increases significantly to 7.5 and 6.5 kOe respectively as annealing temperature increases to 600 °C. When the annealing temperature is increased to 700 °C, they are increased to 11.1 and 9.5 kOe, respectively, and the domain structure inclines to isolated domain. However, further increasing the annealing temperature to 800 °C, the Hc// and Hc⊥ values decrease to 9.8 and 8.9 kOe respectively due to largely increase the grain size of FePt and change the domain structure from isolation to continuity. On the other hand, in order to transform the FePt film from disordered γ phase to the ordered L10 phase, the annealing time of over 3 seconds is necessary when the film was post-annealed at 700 °C with a high heating rate of 100 °C/sec by RTA technique.

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Low-Temperature and Rapid Fabrication of Bulk Nano-TiO2 Ceramic

Materials Science Forum ◽

10.4028/www.scientific.net/msf.724.261 ◽

2012 ◽

Vol 724 ◽

pp. 261-264

Author(s):

Gui Wu Liu ◽

Wen Zheng Jian ◽

Hai Yun Jin ◽

Zhong Qi Shi ◽

Guan Jun Qiao

Keyword(s):

Grain Size ◽

Phase Transformation ◽

Relative Density ◽

Grain Growth ◽

Sintering Temperature ◽

Average Particle Size ◽

Applied Pressure ◽

Rutile Phase ◽

Uniaxial Pressure ◽

Average Particle

A self-made sectional die made of high-performance graphite, SiC ceramic and Ni-based superalloy was firstly designed and developed. The TiO2 ceramic, with original TiO2 powders of average particle size ~25 nm and 80 wt.% anatase + 20 wt.% rutile, was fabricated by plasma activated sintering (PAS) at 500600 °C for 3 min under applied uniaxial pressure of 2001000 MPa using the sectional die. The influences of sintering temperature and applied pressure on the density, phase transformation and grain growth of the TiO2 ceramic were investigated. The results showed that the sintering temperature and applied pressure played key roles in determining the relative density, phase composition and grain size of the TiO2 ceramic. The relative density and grain size increased and the anatase phase transformed into the rutile phase slowly or quickly as the sintering temperature or the applied pressure increased. In particular, the increase of sintering temperature was very advantageous to the phase transformation, and the increase of applied pressure was quite effective to inhabit the grain growth. All the averaged grain sizes of TiO2 ceramics were less than 100 nm in the present experimental conditions. Moreover, the relative density of the sintered ceramic were over 95% when the optimized sintering parameters were 600 °C × 500MPa or 500 °C × 1000MPa. The TiO2 ceramics were composed of only the rutile phase when the applied pressure and the sintering temperature were not less than 300 MPa and 550 °C, respectively.

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Microwave sintering of ZnO at ultra high heating rates

Journal of Materials Research ◽

10.1557/jmr.2001.0393 ◽

2001 ◽

Vol 16 (10) ◽

pp. 2850-2858 ◽

Cited By ~ 44

Author(s):

Geng-fu Xu ◽

Isabel K. Lloyd ◽

Yuval Carmel ◽

Tayo Olorunyolemi ◽

Otto C. Wilson

Keyword(s):

Grain Size ◽

Heating Rate ◽

Microwave Heating ◽

Grain Growth ◽

Rapid Heating ◽

Microwave Sintering ◽

Complete Suppression ◽

Heating Rates ◽

High Heating ◽

Size Uniformity

In this paper, a unique processing approach for producing a tailored, externally controlled microstructure in zinc oxide using very high heating rates (to 4900 °C/min) in a microwave environment is discussed. Detailed data on the densification, grain growth, and grain size uniformity as a function of heating rate are presented. With increasing heating rate, the grain size decreased while grain size uniformity increased. At extremely high heating rates, high density can be achieved with almost complete suppression of grain growth. Ultrarapid microwave heating of ZnO also enhanced densification rates by up to 4 orders of magnitude compared to slow microwave heating. The results indicate that the densification mechanisms are different for slow and rapid heating rates. Since the mechanical, thermal, dielectric, and optical properties of ceramics depend on microstructure, ultrarapid heating may lead to advanced ceramics with tailored microstructure and enhanced properties.

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