The present invention provides a method and an apparatus for measuring the amount of unburned carbon in a sample of fly ash using infrared photoacoustic absorption. One preferred method according to the present invention involves directing modulated infrared radiation at a sample of fly ash and measuring the acoustic signal produced when the unburned carbon in the sample absorbs the radiation producing a thermal wave which propagates through the sample to generate a minute acoustic wave at interfaces between the carbon particles and gas surrounding the particles. One preferred apparatus includes a source of modulated infrared radiation, a chamber for containing the sample, a microphone to detect the acoustic signals, lock-in amplifier to separate the desired photoacoustic signal from noise at other frequencies, and a PC computer to provide output from the amplifier. This apparatus identifies the acoustic signal for determination of the amount of unburned carbon in the sample.
ISURF Reference Number
Iowa State University Research Foundation, Inc.,
Waller, David and Brown, Robert C., "Photoacoustic measurement of unburned carbon in fly-ash" (1997). Iowa State University Patents. 145.