High Temperature Microwave Heating in Refractory Materials

Berteaud, A. J.; Badot, Jean-Claude

doi:10.1080/00222739.1976.11689007

Cited by 79 publications

(23 citation statements)

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“…A typical example is alumina with very slight dielectric losses at room temperature (close to 10 À3 ) and can reach fusion temperatures in several minutes in a microwave cavity [75]. This effect is a consequence of a strong increase of conduction losses associated with thermal activation of the electrons which pass from the oxygen 2p valence band to the 3s3p conduction band.…”

Section: Thermal Dependency Of Dielectric Permittivitymentioning

confidence: 99%

“…For solid reagents or materials, microwave heating can rapidly lead to fusion, depending on the thermal dependence of dielectric properties and, especially, on increase of conductivity with temperature (Section 1.1.2.4 and Ref. [75]). Consequently, most local thermal fluctuations can be amplified and temperatures close to 1000 C can easily be reached in a few seconds.…”

Section: Hot Spots and Heterogeneous Kineticsmentioning

confidence: 99%

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Microwave‐Material Interactions and Dielectric Properties, Key Ingredients for Mastery of Chemical Microwave Processes

Stuerga¹

2006

Microwaves in Organic Synthesis

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The main focus of the revised edition of this first chapter is essentially the same as the original -to explain in a chemically intelligible fashion the physical origin of microwave-matter interactions and, especially, the theory of dielectric relaxation of polar molecules. This revised version contains approximately 60% new material to scan a large range of reaction media able to be heated by microwave heating. The accounts presented are intended to be illustrative rather than exhaustive. They are planned to serve as introductions to the different aspects of interest in comprehensive microwave heating. In this sense the treatment is selective and to some extent arbitrary. Hence the bibliography contains historical papers and valuable reviews to which the reader anxious to pursue particular aspects should certainly turn.It is the author's conviction, confirmed over many years of teaching experience, that it is much safer -at least for those who rate not trained physicists -to deal intelligently with an oversimplified model than to use sophisticated methods which require experience before becoming productive. Because of comments about the first edition, however, the author has included more technical material to enable better understanding of the concepts and ideas. These paragraphs could be omitted, depending on the level of comprehension of the reader. They are preceded by two different symbols -k for TOOLS and j for CONCEPTS.After consideration of the history and position of microwaves in the electromagnetic spectrum, notions of polarization and dielectric loss will be examined. The orienting effects of electric fields and the physical origin of dielectric loss will be analyzed, as also will transfers between rotational states and vibrational states within condensed phases.Dielectric relaxation and dielectric losses of pure liquids, ionic solutions, solids, polymers and colloids will be discussed. Effect of electrolytes, relaxation of defects within crystals lattices, adsorbed phases, interfacial relaxation, space charge polarization, and the Maxwell-Wagner effect will be analyzed. Next, a brief overview of 1 thermal conversion properties, thermodynamic aspects, and athermal effects will be given.

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Section: Thermal Dependency Of Dielectric Permittivitymentioning

confidence: 99%

Section: Hot Spots and Heterogeneous Kineticsmentioning

confidence: 99%

Microwave‐Material Interactions and Dielectric Properties, Key Ingredients for Mastery of Chemical Microwave Processes

Stuerga¹

2006

Microwaves in Organic Synthesis

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“…In this context however, the thermodynamic challenges associated with equation 3 (ΔH ≥ 2000 kJ mol -1 47 ) are compounded by the poor dielectric properties of alumina. With a dielectric constant, ε′ and dielectric loss, ε″ of 9.1 and 0.004 respectively, 48 although the penetration depth of alumina is far superior to aluminium (10 m vs. 1.7 μm), 35 the loss tangent is orders of magnitude lower. Hence, it is only at elevated temperature that Al2O3 begins to heat effectively in a microwave field.…”

Section: -41mentioning

confidence: 99%

Rapid, energy-efficient synthesis of the layered carbide, Al₄C₃

2015

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The phase-pure binary aluminium carbide, Al4C3 can be synthesised in vacuo from the elements in 30 minutes via microwave heating in a multimode cavity reactor. The success of the reaction is dependent on the use of finely divided aluminium and graphite starting materials, both of which couple effectively to the microwave field. The yellow-brown powder product was characterised by powder X-ray diffraction, scanning electron microscopy / energy dispersive X-ray spectroscopy thermogravimetric-differential thermal analysis and Raman spectroscopy. Powders were composed of hexagonal single crystallites tens of microns in diameter (Rhombohedral space group R3 ̅ m; Z = 3; a = 3.33813(5) Å, c = 25.0021(4) Å) and were stable to 1000 °C in air, argon and nitrogen. Equivalent microwave reactions of the elements in air led to the formation of the oxycarbide phases Al2OC and Al4O4C.

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“…Initially the work focused on drying [1], however in the mid-1970's the first attempts were made to utilise microwaves in ceramic sintering [2]. Research over the next ten years showed that substantial heating effects could be generated and materials densified, however the work was too uncoordinated for substantial progress to be made.…”

Section: Introductionmentioning

confidence: 99%

When Should Microwaves Be Used to Process Technical Ceramics?

Binner

Vaidhyanathan

2008

MSF

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This paper attempts to shed light on why the stand alone microwave processing of technical ceramics, despite being one of the most popular field with respect to volume of research performed, is still struggling to achieve priority status with respect to commercialisation. To obtain some answers to this enigma and determine when microwaves should be used to process technical ceramics, three case studies are explored. The conclusion is that microwaves should be used to process technical ceramics when specific advantage can be taken of the intrinsic nature of microwave energy and not simply as an alternative energy source. In addition, it is concluded that from a commercialisation view point hybrid processing is often a better approach than the use of pure microwaves.

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High Temperature Microwave Heating in Refractory Materials

Cited by 79 publications

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Microwave‐Material Interactions and Dielectric Properties, Key Ingredients for Mastery of Chemical Microwave Processes

Microwave‐Material Interactions and Dielectric Properties, Key Ingredients for Mastery of Chemical Microwave Processes

Rapid, energy-efficient synthesis of the layered carbide, Al₄C₃

When Should Microwaves Be Used to Process Technical Ceramics?

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High Temperature Microwave Heating in Refractory Materials

Cited by 79 publications

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Microwave‐Material Interactions and Dielectric Properties, Key Ingredients for Mastery of Chemical Microwave Processes

Microwave‐Material Interactions and Dielectric Properties, Key Ingredients for Mastery of Chemical Microwave Processes

Rapid, energy-efficient synthesis of the layered carbide, Al4C3

When Should Microwaves Be Used to Process Technical Ceramics?

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Product

Resources

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Rapid, energy-efficient synthesis of the layered carbide, Al₄C₃