David Duane Waller

US Patent:

55961460, Jan 21, 1997

Filed:

Jun 6, 1994

Appl. No.:

8/254153

Inventors:

David Waller - Ankeny IA
Robert C. Brown - Ames IA

Assignee:

Iowa State University Research Foundation, Inc. - Ames IA

International Classification:

G01N 2900

US Classification:

73590

Abstract:

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.