Korean researchers have developed a heat treatment technology that can contribute to the expansion of low-E glass, which has been widely used in buildings due to its excellent heat insulation and energy saving effect.
A research team led by Dr. Kim Dae-ho at the Korea Electrotechnology Research Institute (KERI) Nano Hybrid Technology Research Center said that it has succeeded in developing a technology that can heat-treat metal nanofilms continuously and uniformly in a high speed using microwaves used in microwave ovens.
Using the technology, the team succeeded in uniform heat treatment of low-E glass, which flows at a speed of 100 mm per second, at a temperature higher than 500 degrees Celsius. The heat-treated low-E glasses had 30 percent increased conductivity due to the improved crystallinity of the coated silver nanofilms. As a result, the thermal infrared reflectance (adiabatic effect) of sunlight was improved by more than 5 percent, while the visible light transmittance (lighting effect) was improved by more than 2.5 percent. The team has established the basis for efficient heat treatment of large low-E glasses for commercialization by using microwave induction heating technology.
Microwave induction heating technology can instantaneously heat a thin film made of a conductive material, such as metal, using a microwave magnetic field of 2.45 GHz frequency used in microwave ovens.
Conventional induction heating technology could only be applied to millimeters (mm) thick materials, such as cooking induction devices, at frequencies of several tens of kHz. With the conventional technology, it was impossible to heat a nanofilm that is 1 micrometer or less in thickness.
The microwave Induction heating technology was developed based on a principle of generating induction currents by magnetic fields on the conductive surface to heat the nanofilms with resistance heat. Based on the high energy conversion efficiency of up to 70 percent conversion efficiency from electric energy to thermal energy, a thin conductive film that is a few nanometers thick can be rapidly heated to a temperature of 1,000 degrees Celsius or higher within one second. That is, only a conductive thin film requiring heat treatment is selectively and instantaneously heated at a high temperature.
In addition, the research team improved the technology to a level, where stable heat treatment is enabled, ensuring continuity and uniformity over a large area in addition to a small portion. The dielectric resonance, which is the core of microwave induction heating technology, enables the control of the heat distribution of nanofilm by modifying the magnetic field pattern. This enables stable heat treatment in large areas.