7 MPR March/April 20117 MPR March/April 2011 0026-0657/11 ©2011 Elsevier Ltd. All rights reserved.

In Business

Hot topic – the growth of high temperature microwave technologyHigh temperature microwave furnaces, while common in Asia, are only now beginning to be taken up by industry in the US and Europe. One company promoting this new technology is Spheric Technologies Inc. Chairman Joseph Hines spoke to Liz Nickels about the future of microwave in PM...

Microwave heating involves agitating polar molecules or ions, making them oscil-late in an electric or mag-

netic field. The motion of these particles is restricted by interaction between the particles and electric resistance, cre-ating molecular friction which heats the mass of the material (volumetric heating), with simultaneous heating of the outside and the inside of the material mass.

High-temperature microwave heating or processing technology for tempera-tures above 1,000°C can be used in the sintering and/or chemical synthesis of ceramic powders, powder metals and nano-powders.

Several high temperature furnaces are now in use in China and other parts of Asia, including Japan, Korea and India, for the chemical synthesis of phosphors for electronic lighting materials as well as sintering electronic components and other ceramic items. In China there is a development project using microwave technology to produce steel.

However, until recently, the primary market for high temperature microwave equipment outside Asia has been in the laboratories of universities and research centres. Continuous production-capable high-temperature microwave furnaces have not been available. In 2007, Spheric Technologies, based in Phoenix, Arizona,

USA, sold a MW-L0616V microwave sin-tering furnace to Halliburton, which is mainly used for research on advanced ceramic materials. In 2010 it installed the western hemisphere’s first high-temperature (1500+°C) AMPS continu-ous production microwave furnace at the NanoMaterials Innovation Centre (NMIC), Alfred University, New York, USA.

Now Spheric Technologies has signed an international co-operative marketing agreement with Victec Europe Limited. Both companies develop microwave technology and distribute microwave

furnaces built by Synotherm Corporation Ltd, China’s largest microwave furnace producer based in Changsha, China.

“Our respective companies are deter-mined to fully exploit the largely virgin industrial markets for high-tempera-ture, computerised microwave furnaces across all of Europe and the Western Hemisphere,” said Joe Hines. “Our companies are receiving inquiries from around the world.”

On offer are Synotherm’s labora-tory/pilot furnace HAMiLab-V System; the high vacuum HAMiLab-HV; and the

Figure 1. The difference between conventional and microwave heating. (Source: MPEC- Penn State.)

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AMPS System, which is a continuous horizontal furnace. Spheric’s batch system (HamiLab-V6) and continuous pusher type system (AMPS) offer compu-terized temperature programming in the 450-1600°C range, with adjustable tem-perature ramp-up rates and programma-ble hold stages and hold times.

The benefitsAccording to Hines, microwave technol-ogy is more energy efficient than con-ventional processing methods and up to 10 times faster. (In one example, energy cost per ton is US$120 compared to US$600 when processing Ni-Zn ferrites.) In a report by Penn State University and Japan’s National Institute for Fusion Science, it was suggested that micro-wave furnaces typically use up to 80% less energy than conventional furnaces. There is also no direct pollution. .

The end product produced with micro-wave is described as is finer-grained, with higher density. (fine microstruc-tures and near-theoretical densities). It has greater strength and durability than materials produced using conventional methods, can be more abrasion, ero-sion and corrosion-resistant, and has increased impact strength. Less post-sintering finishing is generally required and there is a lower shrinkage rate, and less raw material waste.

A new applicationWhile the furnaces are suitable for a number of duties, Spheric has researched using the AMPS microwave furnace for the solid state synthesis of lithium ferro phosphate (LiFePO4) used

as a cathode in lithium batteries, and has filed patents for the new method covering microwave techniques, mate-rial and technology. The company has also produced lithium ferro phosphate and lithium titanate(Li4Ti5O12) in larger advanced microwave systems.

According to Hines, his work has shown that microwave technology can process lithium battery materials cheap-er and faster than conventional methods. The Spheric system applies microwave in the drying and synthesis stages, yield-ing a phase pure product that requires little if any refinement. Production time is reduced from more than 10 hours (with conventional systems) to less than 30 minutes.

The commercial potential of this proc-ess could be significant, with lithium ferro phosphate demand at US$135 mil-lion in 2012, growing to US$330 mil-lion by 2017, according to The Freedonia Group. Current material prices range up

to $60 per kilogramme, with much of the material produced in Asia.

Scaling upKarl Cherian, director of applied research at Spheric, says that that while most microwave-assisted LFP synthesis has involved laboratory systems, the availability of advanced larger scale continuous high temper-ature microwave systems opens the door to full-scale commercial produc-tion. In a paper presented at the at the Materials Science & Technology confer-ence and exhibition, which took place in Houston, Texas, USA, in October 2010, he said that “resulting phase purity could be further improved by judicious time-temperature-microwave power profile programming and varia-tion of other parameters. The best time variable profile obtained in the batch system could be suitably adapted and

Figure 2. 92.5% Tungsten – 6.4% Nickel – 1.1% Iron, sintered at 1500°C. Left: using microwave technology; Right: conventional technique.

Figure 3. The continuous high temperature microwave furnace marketed by Spheric.

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transformed into a space variable profile in a recently com-missioned Advanced Microwave Pusher System for continu-ous processing, to achieve industrial production throughput levels.”

Other potential applications for high temperature micro-wave furnaces include microwave mineral processing, metal-ceramic cutting tool/moulds, advanced processing technologies for consolidated nanophase material, sin-tering of electronic, technical and transparent ceramics and microwave-assisted synthesis of high-tech ceramics and chemicals.

One significant application is that of sintering zirconia ceramics for dental bridges and crowns. The microwave sintering of zirconia is gaining market share and is a sig-nificant contributor to Spheric’s 2010 revenue. Microwave sintering of the material takes two hours versus eight hours for conventional furnaces. “We have a small microwave fur-nace sold to dental laboratories that can sinter dental parts in a tenth of the time conventional ovens generally take,” says Hines.

“Furnaces are also available that are suitable for the production of high-temperature coating and pigment materials.” he added. “We now have furnaces that will allow sintering of powder metals and other materials that require an artificial processing atmosphere, forming gas, freon, argon or a similar non-oxidizing atmosphere.”

“There are production applications for batch process-ing. As the use of microwave advances from the labora-tory to a production process, larger batch furnaces with the capability of maintaining vacuum required for sinter-ing titanium, for example, or other atmospheres required for other materials, are coming into industrial use.”

The equipment being used at Alfred University’s NMIC offers a way forward for scaling up the technology. “The equipment is an example of scale up to production-capable microwave technology, needing no further development for production applications,” Hines said. “It only needs to be adapted for an individual application. There are much larger versions of the continuous furnace available and in use for larger-scale production applications.”

The future“Until now, microwave has been used largely in academe and materials laboratories,” said Hines. “There are more and more industrial companies beginning to look at microwave technology. This is true for powder metal components and ceramic products alike.

“We believe that as experience and exposure to micro-wave processing gain momentum, and with commercially available production equipment, microwave technology will become an integral part of production processes that require high temperature. Just as the microwave oven has become a mainstay of the kitchen, high temperature industrial microwave furnaces will assume a similar posi-tion in powder metal and ceramic sintering – as well as the synthesis of high temperature processed nano-materials and chemicals.”

www.spherictechnologies.com