Nontoxic Liquid Metal Alloy Could Substitute For Mercury
NewMerc, Ltd. (Blacksburg, VA), has begun producing a nontoxic, electrically-conductive, liquid metal alloy alternative to mercury. Although mercury is highly toxic, it is still used applications ranging from electrical switches and sensors to thermometers and dental fillings. The new alloy shares many of mercury's most desirable properties but is far more costly.
The alloy, called NewMerc, is based on gallium and indium alloyed with tin (which forms problematic organotins when released into the environment); copper and zinc; or bismuth. A key breakthrough in development of the alloy was the elimination of oxidation during processing. Gallium readily oxidizes to form gallium oxide, which wets out surfaces and keeps the metal from acting like a true liquid.
The best Newmerc alloys turn liquid at temperatures between -15 °C and -11 °C, compared to -39 °C for mercury. "We're working on pushing that lower, but not until get commercial interest in the alloys we've already developed," says James D. Rancourt, NewMerc president and the product's coinventor with Virginia Tech chemistry professor Larry T. Taylor.
"Besides, we're getting a lot of inquiries about high-temperature use in high-pressure boilers and possibly nuclear power plants," he continues. "Mercury's really reliable, but it begins to boil at 357 °C. This remains a liquid past 2,500 °C."
Rancourt sees several potential applications, starting with electrical float switches used to sense the level of sewerage and waste water, as well as on boat bilge pumps and home sump pumps. The switches are attached on one end to a fixed point. When the water level drops, the switch tilts downward and the liquid metal slides across its length. This creates a contact between two electrodes, completing a circuit and turning on a pump.
Float switches not based on mercury usually use a metal ball that rolls down the length of the switch to mechanically bridge the electrical contacts. This mechanical connection is less reliable than a liquid connection and has significantly higher contact resistance, says Rancourt.
The company spent the past 18 months developing applications while negotiating exclusive license agreements with several companies. "We had three offers that involved a sizable amount of money," says Rancourt, "but we realized that there would be no way to get the full environmental benefit of our product if we signed only one switch company and one thermometer company. We realized we would be business hypocrites if we took the short-term cash rather than pursued the long-term benefits."
Two months ago, the company terminated the negotiations and decided to offer NewMerc to any company that wanted to buy it. Instead of bundling technical support within a licensing agreement, it decided to provide support on a cost basis to companies that wanted it.
"We've spent four years building prototypes and testing switches for millions of cycles," says Rancourt. The key now, he says, is developing new designs that use less material.
"Most switch companies are not used to thinking about a material that costs $800/lb," he explains. "Yet NewMerc is half as dense as mercury, so we're really talking $400 on a volume basis. It's also 20 times more conductive than mercury. Instead of copying existing designs, we need to optimize our design to use it more effectively."
The initial research was funded and patented by Virginia's Center for Innovative Technology, and licensed to NewMerc Virginia Tech Intellectual Properties, Inc. (Blacksburg, VA), which handles licensing for Virginia Tech. Key patents include US 5,508,003 (Metallic material with low melting temperature); US 5,478,979 (Electrical switches and sensors which use a nontoxic liquid metal composition); and US 5,792,236 (Non-toxic liquid metal composition for use as a mercury substitute).
By Alan Brown
For more information: Dean Ash, Business Manager, NewMerc, Ltd. Blacksburg , VA. Tel: 540 951-2500, fax: 540/961-3602.