Mercouri Kanatzidis envisions a refrigerator that not only would keep the Maytag repairman pining by a silent phone, but could put him out of business altogether. Gone would be the noisy compressors, the environmentally dubious coolants, and the dust bunnies under the cooling coils. Instead, says the chemistry professor at Michigan State University, the unit would rely on electricity flowing through specially designed semiconductors to keep the inside of the icebox chilled. Those same semiconductors also could be used to convert wasted heat in auto exhaust pipes, power-plant smokestacks, or other sources into valuable electricity.