Microwave Processing of Ceramics

2006 ◽  
Vol 45 ◽  
pp. 857-862 ◽  
Author(s):  
Isabel K. Lloyd ◽  
Yuval Carmel ◽  
Otto C. Wilson Jr. ◽  
Geng Fu Xu
Keyword(s):  
Thermal Conductivity ◽  
Grain Size ◽  
Heating Rate ◽  
Thermal Gradients ◽  
Heating Rates ◽  
Volumetric Heating ◽  
Wide Range ◽  
Conventional Sintering ◽  
Atmosphere Control ◽  
Very High

Microwave (MW) processing is advantageous for processing ceramics with tailored microstructures. Its combination of volumetric heating, a wide range of controlled heating rates, atmosphere control and the ability to reach very high temperatures allows processing of 'difficult' materials like high thermal conductivity AlN and AlN composites and microstructure control in more readily sintered ceramics such as ZnO. MW sintering promotes development of thermal conductivity in AlN (225 W/mK) and its composites (up to 150W/mK inAlN-TiB2 and up to 129 W/mK in AlN-SiC when solid solution is avoided). In ZnO, heating rate controls sintered grain size. Increasing the heating rate from 5°C/min. to 4900°C decreases grain size from ~10 μm (comparable to conventional sintering of the same powder) to nearly the starting particle size (~ 1μm). Microstructural uniformity increases with sintering rate since ultra-rapid MW sintering minimizes the development of thermal gradients due to heat loss.

Induction Hardening of a 0.40 % C Novel Microalloyed Steel: Effects of Heating Rate on the Prior Austenite Grain Size

2018 ◽  
Vol 941 ◽  
pp. 64-70
Author(s):  
Vahid Javaheri ◽  
Nasseh Khodaei ◽  
Tun Tun Nyo ◽  
David A. Porter
Keyword(s):  
Grain Size ◽  
Heating Rate ◽  
Prior Austenite ◽  
Induction Hardening ◽  
High Wear Resistance ◽  
Heating Rates ◽  
Austenite Grain Size ◽  
Austenite Grain ◽  
Prior Austenite Grain Size ◽  
Prior Austenite Grain

This work explores the effect of heating rate on the prior austenite grain size and hardness of a thermomechanically processed novel niobium-microalloyed 0.40 % carbon low-alloyed steel intended for use in induction hardened slurry pipelines. The aim was to identify the heating rates that lead to the maximum hardness, for high wear resistance, and minimum prior austenite grain size, for high toughness. For this purpose, a Gleeble 3800 machine has been employed to simulate the induction hardening process and provide dilatometric phase transformation data. The prior austenite grain structure has been reconstructed from the EBSD results using a MatlabR script supplemented with MTEX texture and crystallography analyses. Heating rates ranged from 1 to 50 °C/s and the cooling rate was 50 °C/s. The results show that the prior austenite grain size greatly depended on the heating rate: compared to the lower heating rates, the maximum heating rate of 50 C/s produces remarkably fine prior austenite grains and a fine final martensitic microstructure after quenching. In addition, a relation between the heating rate and the deviation from equilibrium temperature has been established.

Surface Dissolution of Hydroxyapatite Prepared by Microwave Sintering

2007 ◽  
Vol 330-332 ◽  
pp. 227-230
Author(s):  
Dong Seok Seo ◽  
Hwan Kim ◽  
Kyu Hong Hwang ◽  
Jong Kook Lee
Keyword(s):  
Grain Size ◽  
Grain Boundary ◽  
Heating Rate ◽  
Microwave Sintering ◽  
Starting Material ◽  
Dissolution Behavior ◽  
Distilled Water ◽  
Sintering Process ◽  
Conventional Sintering ◽  
Boundary Dissolution

The aim of this study was to prepare dense hydroxyapatite (HA) by microwave sintering and to evaluate the dissolution behavior in distilled water. Commercially-obtained HA powders having Ca/P ratio of 1.67 were used as a starting material. The as-received powder of granular type consists of nano-sized particles. Microwave sintering was operated at 1200°C for 5 min with a heating rate of 50°C/min. Microwave sintering process reduced grain size of HA, compared with the case of conventional sintering. During the immersion in distilled water for 3-14 days, grain boundary dissolution occurred and the dissolution extended into the bulk following this path. As a result, particles were separated from the structure leaving micron-scale defects.

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.

scholarly journals Temperature Dependence of the Thermal Conductivity of Materials for Microelectronic Packaging: Measuring and Modelling Effects of Microstructure and Impurities

1989 ◽  
Vol 167 ◽  
Author(s):  
Ralph B. Dinwiddie ◽  
David G. Onn
Keyword(s):  
Thermal Conductivity ◽  
Wide Temperature Range ◽  
High Purity ◽  
Impurity Concentration ◽  
Nonlinear Least Squares ◽  
Model Parameters ◽  
Microelectronic Packaging ◽  
Upper Limit ◽  
Wide Range ◽  
Very High

AbstractThe materials studied in this research, having a wide range of thermal conductivities, permit a study of the mechanisms which affect their behavior. Data on the thermal conductivity of several substrate materials, over a wide temperature range, were analyzed using the Klemens model. Parameters in this model, which include crystallite size and impurity concentration, are determined through a nonlinear least squares fitting routine and related, where possible, to values obtained by other techniques. This analysis predicts an achievable upper limit of 290 W/m.K for very high purity sintered AlN with 5 micron crystallites.

scholarly journals Microwave Sintering of Zirconia-Toughened Alumina Composites

1990 ◽  
Vol 189 ◽  
Author(s):  
H. D. Kimrey ◽  
J. O. Kiggans ◽  
M. A. Janney ◽  
R. L. Beatty
Keyword(s):  
Radiative Heat ◽  
Microwave Sintering ◽  
Temperature Gradients ◽  
Internal Stresses ◽  
Thermal Gradients ◽  
Volumetric Heating ◽  
Uniform Microstructure ◽  
Conventional Sintering ◽  
Alumina Composites ◽  
Zirconia Toughened Alumina

Microwave sintering possesses unique attributes and has the potential to be developed asa new technique for controlling microstructure to improve the properties of advanced ceramics. 1–6 Because microwave radiation penetrates most ceramics, uniform volumetric heating is possible. Thermal gradients, which are produced during conventional sintering because of conductive and radiative heat transfer to and within the part, can be minimized. By eliminating temperature gradients, it is possible to reduce internal stresses, which contribute to cracking of parts during sintering, and to create a more uniform microstructure, which may lead to improved mechanical properties and reliability. With uniform, volumetric temperatures, the generation of nonuniform particle/grain growth due to temperature gradients and associated sintering gradients can be regulated.

Bake Hardening Properties of Ultra-Rapid Annealed Ultra-Low Carbon Bake Hardening Steel

2014 ◽  
Vol 941-944 ◽  
pp. 127-131 ◽  
Author(s):  
De Chao Xu ◽  
Jun Li ◽  
Yan Dong Liu ◽  
Xiang Wei Kong
Keyword(s):  
Grain Size ◽  
Heating Rate ◽  
Rolling Reduction ◽  
Temper Rolling ◽  
Low Carbon ◽  
Heating Rates ◽  
Bake Hardening ◽  
Soaking Time ◽  
Rapid Annealing ◽  
Bake Hardening Steel

Ultra-rapid annealing (URA) experiments were carried out to study the effect of heating rate on the recrystallization kinetics, grain size and Bake-hardening (BH) properties of Ultra-low carbon Bake Hardening Steel annealing with different heating rates followed by gas cooling (about 100°C/s) with variation of soaking times. It was shown that the degree of grain refinement is controlled by the parameters of heating rates and soaking time of the Ultra-rapid annealing cycles. For the steels investigated, the final grain size decreases with increasing heating rate and increases with increasing soaking time. The effects of dislocation density, varied by means of non-temper rolling reduction and a temper rolling reduction of 1% on the Bake-hardening properties were investigated within an aging temperature of 170°C for 20 min.

Unconventional Methods of Sintering Inconel 718 MIM Samples

2016 ◽  
Vol 716 ◽  
pp. 830-839
Author(s):  
Olivier Dugauguez ◽  
Jose Manuel Torralba ◽  
Thierry Barrière ◽  
Jean Claude Gelin
Keyword(s):  
Mechanical Properties ◽  
Grain Size ◽  
Heating Rate ◽  
Inconel 718 ◽  
Fine Particle ◽  
Alloy Powder ◽  
Microwave Sintering ◽  
Conventional Sintering ◽  
Unconventional Methods ◽  
Super Alloy

In this investigation, three different ways of sintering Inconel 718 MIM samples are compared. The conventional way of sintering in a furnace will be compared to FAHP and microwave sintering. The difficulty of these two methods is to be able to control the shrinkage of the sample and so its shape. These methods have yet not been investigated with a super alloy powder and so, the effects of a high sintering rate on a MIM sample. By accelerating the sintering kinetics, the thermal behavior may be modified. Hence, the behavior of the Inconel 718 sintered by field assisted and microwave sintering has been investigated. The sintered samples were all injected from a feedstock composed of a fine particle Inconel powder and a binder principally composed of CAB and PEG. They were debinded into water for 24h and put in a furnace at 500°C during 2 hours. The heating rate of the furnace was set to 5°C/min until 1290°C during 2 hours. The heating rate of the FAHP was set to 50°C/min until 1250°C during 15 minutes. The microwave samples were sintered around 1300°C during 1 hour, the temperature was increased progressively by steps of 100°C. The effects of the different process on the microstructure and the mechanical properties are then compared. There was no difference in distribution of pores between the conventional sintering and the FAHP sintering but a finer grain size showed better hardness. The microwave sintering of a MIM sample is more complex and the best properties were not obtained.

THE EFFECTS OF OVERPRESSURE, LITHOLOGY, CHEMISTRY AND HEATING RATE ON VITRINITE REFLECTANCE EVOLUTION, AND ITS RELATIONSHIP WITH OIL GENERATION

1994 ◽  
Vol 34 (1) ◽  
pp. 418 ◽  
Author(s):  
Ganjavar Khavari Khorasani ◽  
Johan K Michelsen
Keyword(s):  
Organic Matter ◽  
Heating Rate ◽  
Vitrinite Reflectance ◽  
Intrinsic Property ◽  
Confining Pressure ◽  
Rate Dependency ◽  
Heating Rates ◽  
Transformation Ratio ◽  
Oil Generation ◽  
Wide Range

Overpressure has been regarded by several authors to retard vitrinite reflectance evolution. The previously presented data regarding overpressure, however, are inconclusive because the covariation between burial rate, fluid pressures and heating rate has been overlooked. The present results show that the thermal effect of overpressure in shales has no important influence on the observed relationship between temperature and reflectance. The pressure acting on vitrinite and other solid organic matter is mainly lithostatic, and the influence of overpressure on the confining pressure of vitrinite is negligible. The apparent relationship between vitrinite reflectance and lithology is closely linked with important differences in the chemistry of vitrinites. Systematic differences in the reflectance of vitrinites in coals and interbedded shales are associated with variations in the concentration of lignin-derived products in the source organic matter, and their state of biochemical/chemical modifications governed by the depositional conditions. Vitrinite reflectance is related to both the transformation ratio and the molecular structural organisation of the vitrinite. In immature vitrinites subjected to intermediate to high heating rates, the ultrafine textural heterogeneity is enhanced, retarding the reflectance increase, compared to those heated at low rates, for the same change in transformation ratio. There exists a small but systematic difference between the heating-rate dependency of vitrinite reflectance versus heating-rate dependency of oil generation.To reflect the slow evolution of reflectance through the zone of extensive oil generation, kinetic models for predicting reflectance employ wide activation energy distributions. Due to this intrinsic property, it is simple to calibrate or predict reflectance, but the use of reflectance for predicting oil generation or calibration of thermal models has a low precision, with a wide range of solutions with equally good fits.

Study on Thermal Conductivity of SPS-Sintered Si3N4 Ceramics after Heat-Treatment

2005 ◽  
Vol 475-479 ◽  
pp. 1279-1282 ◽  
Author(s):  
Xin Lu ◽  
Xiao Shan Ning ◽  
Wei Xu ◽  
He Ping Zhou ◽  
Ke Xin Chen
Keyword(s):  
Thermal Conductivity ◽  
Heat Treatment ◽  
Heating Rate ◽  
Great Influence ◽  
Heating Rates ◽  
Plasma Sintering ◽  
Heat Treated ◽  
Different Temperatures ◽  
Spark Plasma ◽  
Si3n4 Ceramics

α-Si3N4 ceramics were sintered at a low temperature of 1773K by using a spark-plasma-sintering (SPS) method with different heating rates, and then they were further heat-treated at different temperatures from 1773K to 2273K, to study the effect of the heating rate of SPS on the microstructure and the thermal conductivity of Si3N4 ceramics after the heat-treatment. Results show that the heating rate of SPS has great influence on the phase transformation and the microstructure of the β-Si3N4, but it has little influence on the thermal conductivity of the ceramics. This proves that the thermal conductivity of the ceramics does not have an obvious relationship with the ratio and the size of the columnar β-Si3N4 grain.

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