Metal parts made in the microwave oven

June 17, 1999

University Park, Pa. -- Anyone who uses a microwave knows that metals, such as aluminum foil, should not be placed in these ovens, but a team of Penn State material scientists is microwaving a wide range of powder metals and producing machine components with improved properties.

"Solid metals cause problems in microwaves because they reflect, rather than absorb, the microwave radiation," says Dr. Dinesh K. Agrawal, professor of materials, senior scientist and director of Penn State's Microwave Processing and Engineering Center. "Powder metals do absorb microwave radiation and can be heated and sintered, using microwaves."

Sintering is used to manufacture many parts made from ceramics, metals and combinations of materials. Green products composed of fine particles and a small amount of binder compressed and dried, are heated to a point where the binder disappears and, over time and higher temperatures, the material is fully sintered.

A solid, dense material forms after the microwave treatment. Microwave sintering allows complex shapes to be manufactured with savings in time and energy, but conventional sintering can take long periods of time and large amounts of energy.

"Our findings indicate that virtually any powder-metal green body can be sintered in 10 to 30 minutes in an appropriate microwave sintering apparatus," the researchers said in today's (June 17) issue of the journal Nature.

The Penn State research team, including Agrawal; Rustum Roy, the Evan Pugh Professor Emeritus of Solid State; Jiping Cheng, post-doctoral research associate; and Shalva Gedevanishvili, research associate, materials science, used commercial powder metal components of various compositions. Metals included iron, steel, copper, aluminum, nickel, molybdenum, cobalt, tungsten, tungsten carbide, and tin. The components included small gears, rings and tubes. They compared their microwaved products with products produced by conventional thermal sintering.

"We obtained essentially fully dense bodies with substantially improved mechanical properties compared to identical bodies sintered in the conventional manner," said Agrawal. The researchers found a homogeneous microstructure with very little porosity in the microwave sintered products.

The key to microwave sintering of powder metals is the specialized insulated sintering chambers. In conventional thermal sintering, the sintering oven is heated and this heat is transferred to the greenware, but microwaving does not heat the chamber, just the greenware. Without insulation, the heat generated in the greenware would be lost to the inside of the microwave cavity and it would take an enormous span of time to reach the required temperatures. The insulated chambers trap the heat and allow temperatures to rise rapidly.

The researchers can also alter the atmosphere of the chamber to include inert noble gases like argon or neon, hydrogen, nitrogen or forming gas -- 5 percent hydrogen and 95 percent nitrogen.

"Because microwave sintering takes less time and lower energy levels, it is cost effective," says Agrawal. "Commercialization of continuous processing equipment for microwave sintering is currently underway." Microwaving of powder metals, as opposed to solid metals, is possible because of the difference in surface area between fine powder particles and solid substances. While solid metals reflect microwaves, a surface effect on the particles allows them to absorb the microwave energy. The insulation material used in the microwave sintering process neither reflects nor absorbs microwaves, but is transparent to them at low temperatures.

Microwave sintering produces a finer grain size than conventional sintering and the shape of any porosities that do exist differs from the conventional product. The microwave produced porosities led to higher ductility and toughness.
-end-
EDITORS: Dr Agrawal is at 814-863-8034 or dxa4@psu.edu.

Penn State

Related Energy Articles from Brightsurf:

Energy System 2050: solutions for the energy transition
To contribute to global climate protection, Germany has to rapidly and comprehensively minimize the use of fossil energy sources and to transform the energy system accordingly.

Cellular energy audit reveals energy producers and consumers
Researchers at Gladstone Institutes have performed a massive and detailed cellular energy audit; they analyzed every gene in the human genome to identify those that drive energy production or energy consumption.

First measurement of electron energy distributions, could enable sustainable energy technologies
To answer a question crucial to technologies such as energy conversion, a team of researchers at the University of Michigan, Purdue University and the University of Liverpool in the UK have figured out a way to measure how many 'hot charge carriers' -- for example, electrons with extra energy -- are present in a metal nanostructure.

Mandatory building energy audits alone do not overcome barriers to energy efficiency
A pioneering law may be insufficient to incentivize significant energy use reductions in residential and office buildings, a new study finds.

Scientists: Estonia has the most energy efficient new nearly zero energy buildings
A recent study carried out by an international group of building scientists showed that Estonia is among the countries with the most energy efficient buildings in Europe.

Mapping the energy transport mechanism of chalcogenide perovskite for solar energy use
Researchers from Lehigh University have, for the first time, revealed first-hand knowledge about the fundamental energy carrier properties of chalcogenide perovskite CaZrSe3, important for potential solar energy use.

Harvesting energy from walking human body Lightweight smart materials-based energy harvester develop
A research team led by Professor Wei-Hsin Liao from the Department of Mechanical and Automation Engineering, The Chinese University of Hong Kong (CUHK) has developed a lightweight smart materials-based energy harvester for scavenging energy from human motion, generating inexhaustible and sustainable power supply just from walking.

How much energy do we really need?
Two fundamental goals of humanity are to eradicate poverty and reduce climate change, and it is critical that the world knows whether achieving these goals will involve trade-offs.

New discipline proposed: Macro-energy systems -- the science of the energy transition
In a perspective published in Joule on Aug. 14, a group of researchers led by Stanford University propose a new academic discipline, 'macro-energy systems,' as the science of the energy transition.

How much energy storage costs must fall to reach renewable energy's full potential
The cost of energy storage will be critical in determining how much renewable energy can contribute to the decarbonization of electricity.

Read More: Energy News and Energy Current Events
Brightsurf.com is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to Amazon.com.