Final Report: Low-Cost, Mercury-Free Electrical Switches and RelaysEPA Contract Number: EPD06044
Title: Low-Cost, Mercury-Free Electrical Switches and Relays
Investigators: Kovar, Robert F.
Small Business: Infoscitex Corporation
EPA Contact: Manager, SBIR Program
Project Period: March 1, 2006 through August 31, 2006
Project Amount: $69,966
RFA: Small Business Innovation Research (SBIR) - Phase I (2006) RFA Text | Recipients Lists
Research Category: SBIR - Pollution Prevention , Small Business Innovation Research (SBIR) , Pollution Prevention/Sustainable Development
In Phase I, low-cost, non-toxic, non-volatile, electrically conductive liquids were examined that were found to be suitable for use in switches and relays as replacements for mercury metal. Computational analysis was first used to identify the most promising ionic liquid (IL) candidates for synthesis, characterization, and testing. The IL component was designed to exhibit properties that would make it ideal for use in an electrical switch; namely, remaining a non-viscous liquid between -40ºC and +350ºC, being thermal-oxidatively and electrochemically stable, and exhibiting resistance to fire. Selected IL candidates were tested for electrical conductivity, negative surface meniscus formation, and environmental safety. Feasibility was demonstrated by constructing and testing a simple IL electrical switching device.
Computational analysis yielded two potential ILs to examine during this Phase I—candidates “A” and “B.” Viscosity was used as a determining factor for conductivity, because it has been shown to be related in previous experiments by our partner, University of Notre Dame. Vapor pressures in these ILs are so small, they are nearly immeasurable, estimated at approximately 1E-10 bar at 300 K, making them much less volatile than mercury. During initial testing, candidate A exhibited better overall ionic conductivity than candidate B, but both were less conductive than mercury metal, which is an electronic conductor. A tilt switch was designed to accommodate that unique property of ILs, operating at low voltage (12 volts) and extremely low current to activate an LED device when contact is made. This design can prevent accidental discharge of a car battery in case the switch may be left in the “on” position. Karl Fisher titration was performed to determine water content of the liquids, and the amount of water was nearly immeasurable. Both liquids were determined to be thermally stable across a typical operating range, based on differential scanning calorimetry and thermogravimetric analysis. Contact angle testing on glass revealed that the two liquids had very similar contact angles (25.5% and 28%). Furthermore, ionically conductive additives were introduced to the liquids to increase conductivity. The final configuration of 10 percent of one ionically conductive additive in candidate A had a stable conductivity across all frequencies and was tested in the switch device. It was demonstrated that the Infoscitex switch was able to light the LED when turned in the “on” position and turn off the LED when tilted to the “off” position. An additional switch configuration of 10 percent of another ionically conductive additive in candidate A was measured to have the highest single conductivity, and it also was capable of operating the switch.
ILs are low-cost, non-toxic, non-volatile, electrically conductive liquids that are suitable for use in electrical switches and relays as replacements for mercury metal, which is known to be toxic and volatile. Tests proved that, although IL switches conducted by an ionic mechanism were less electrically conductive than mercury, they offered a viable alternative material for electrical switches and relays when used in the novel Infoscitex switch design with a low-voltage, low-current LED device. Current mercury switches are toxic and heavy; unreliable ball bearing switches are heavy, with limited capability. Infoscitex IL switches can be used as a direct, drop in replacement for these current switches, and will be non-toxic, lightweight, simple in design, more reliable and efficient, and lower in cost than ball bearing switches when produced in quantity. Ionically conductive additives were successfully applied to increase the base IL’s conductivity. The Phase I results clearly indicate that feasibility was successfully demonstrated and that further refinement, scale-up, and commercialization of the IL Mercury-Free Electrical Switch should continue into Phase II.