Diffusion-Controlled Processes in Microwave-Fired Oxide Ceramics

Janney, Mark A.; Kimrey, H.D.

doi:10.1557/proc-189-215

Cited by 119 publications

(63 citation statements)

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“…Until now, sintering behaviors of alumina have been most extensively investigated [18][19][20][21][22] and, in some cases, alumina/zirconia composites have also been investigated for the purpose of examining the effect due to the difference in absorptivity for millimeter-wave. 23) According to previous results, the decrease of densification temperature ranges from 100 to 400°C in millimeter-wave sintering of alumina.…”

Section: Millimeter-wave Sintering Of Alumina and Alu-mentioning

confidence: 99%

“…According to the tracer experiment by Janney et al, 21) it was found that the activation energy of 18 O in sapphire is reduced to 60 % of its value in conventionally-heated sapphire. Enhancement in mass transfer has also indicated in the behavior of radial constriction of nano pore in alumina membrane under millimeter-wave radiation.…”

Section: Millimeter-wave Sintering Of Alumina and Alu-mentioning

confidence: 99%

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Characteristics of Millimeter-wave Heating and Smart Materials Synthesis

Makino

2007

ISIJ Int.

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Characteristics and advantages of heating processing based on millimeter-wave are described from the standpoint of the interaction between electromagnetic energy and solid materials. High capabilities of the electromagnetic processing are indicated by exemplifying several successful results such as sintering of alumina and AlN and post-annealing of aerosol-deposited PZT films. In these examples, it is shown that well-characterized properties such as high thermal conductivity and high bending strength are obtained by the inherent effect in the millimeter-wave processing. In the millimeter-wave processing, high thermal conductive AlN with over 210 W/(m · K) can be synthesized by rapid sintering at lower temperature, compared with the conventional method. Suppression of the interfacial reaction between PZT film and substrate steel can also be attained using the millimeter-wave processing. It is explained that the high capabilities of applying millimeter-wave processing to smart materials synthesis originates from the non-thermal effects due to high frequency field of millimeter-wave.KEY WORDS: millimeter-wave; microwave effect; ponderomotive force; multi-phonon; enhanced mass transfer; rapid densification; selective heating. ISIJ International, Vol. 47 (2007), No. 4, pp. 539-544 Review(ii) easier injection of high powder, (iii) easier designing of compact applicator, (xi) suppression of local overheating (thermal runaway) due to the less temperature dependence of dielectric loss. Further, stable heating can be attained in the composite materials even if selective heating arises from the difference of dielectric losses in constitutional materials.In the heating of materials by microwave, dielectric loss, eЉ(w), is the important factor and can be divided into three factors due to ionic conduction, electric dipole and phonon in the following;where e c Љ(w), e d Љ(w) and e Љ ph (w) are the dielectric loss contributed by ionic conduction, electric dipole and phonon. In an ionic crystal having cation and anion vacancies eЉ(w) can be expressed by the following equation 2,11) ;....... (2) where where e(0), e(∞) and t i are the dielectric losses at zero and infinite frequencies and relaxation time, respectively.The term of eЉ ph (w) is generated from multi-phonon process, which is one of the non-thermal effects, and becomes important in the millimeter-wave and far-infrared regions. In an ionic crystal with low concentration of vacancies, however, the multi-phonon process is also the important mechanism for the absorption of microwave energy in the range from 2 to 20 GHz. According to Sparks et al., (4) where w f and G are the resonant frequency of fundamental reststrahrent transverse phonon mode and relaxation velocity coefficient, respectively.Influence of vacancy concentration on the dielectric loss eЉ(w) has been indicated by examining the dependence of eЉ(w) on the microwave frequency in NaCl single crystals with different vacancy concentration.11) In the temperature range below about 500 K, the difference in the v...

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Section: Millimeter-wave Sintering Of Alumina and Alu-mentioning

confidence: 99%

Section: Millimeter-wave Sintering Of Alumina and Alu-mentioning

confidence: 99%

Characteristics of Millimeter-wave Heating and Smart Materials Synthesis

Makino

2007

ISIJ Int.

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“…[9][10][11] The difference in heating behavior between the two ovens is considered to be due to the difference in the electric field distributions in the oven. In the single-mode applicator, the electric field is more concentrated 12) in a certain area of the wave guide, which caused effective heating in the localized area and resulted in the thermal runaway, although its power was lower power than the multimode case.…”

Section: Single Mode Ovenmentioning

confidence: 99%

“…There are number of reports on the TRW by theoretical analysis 9) and by experimental work. 10) One of the causes for TRW is the heat spot 20) generated in a specimen, because of the permittivity difference in the existing phases or because of the selective heating. 21) Usually the permittivity of oxides increases as temperature, 22) so it is considered that the heating occurs selectively at high permittivity phases and the temperature increase is accelerated.…”

Section: Occurrence Of Thermal Runawaymentioning

confidence: 99%

Microwave Heating Behavior of Blast Furnace Slag Bearing High Titanium

2005

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“…1 Specific examples include microwave sintering of ceramics, [2][3][4][5] microwave-driven radioactive tracer ion diffusion, 6 microwave-driven ion-exchange reactions in glasses, 7 microwave joining of ceramics, 8 microwave ͑spin-odal͒ decomposition of solid solutions, 9 synthesis of metalcarbide powders, 10 and promotion of organic imidization reactions. 11 Understanding and explaining these observations has been complicated by difficulties in accurately characterizing the internal thermal state of a microwave-heated specimen.…”

Section: Introductionmentioning

confidence: 99%

Microwave ponderomotive forces in solid-state ionic plasmas

et al. 1998

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Numerous observations have been reported in the literature of enhanced mass transport and solid-state reaction rates during microwave heating of a variety of ceramic, glass, and polymer materials. An explanation for these controversial observations has eluded researchers for over a decade. This paper describes a series of recent experimental and theoretical investigations that provide an explanation for these intriguing observations in terms of ponderomotive forces acting on mobile ionic species. The ponderomotive phenomenon, like its conventional-plasma analog, can be described in the continuum model limit by combining the continuity, Poisson's, and transport equations. However, the solid-state plasma version typically manifests as a result of gradients in mobile charge mobility ͑e.g., near physical surfaces or interfaces͒, whereas the conventional plasma ponderomotive transport is typically a consequence of gradients in the radiation field intensity. Both cases can be captured in a single, general, mathematical articulation developed in terms of the mobile particle fluxes.

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Diffusion-Controlled Processes in Microwave-Fired Oxide Ceramics

Abstract: Processing oxide-based ceramics using microwave ,leating leads to a number of unexpected results, which can only be interpreted in terms of enhanced diffusion.

Cited by 119 publications

References 10 publications

Characteristics of Millimeter-wave Heating and Smart Materials Synthesis

Characteristics of Millimeter-wave Heating and Smart Materials Synthesis

Microwave Heating Behavior of Blast Furnace Slag Bearing High Titanium

Microwave ponderomotive forces in solid-state ionic plasmas

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