Graduate Thesis Or Dissertation

 

Optical diffraction study of ultrasonic sound velocity in nitrous oxide and ammonia gases Public Deposited

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  • The velocity of sound in gases was measured, using an ultrasonic wave train as a diffraction grating. The fundamental problems involved in the optical technique are discussed. An apparatus utilizing an objective lens of focal length 1.5 m and aperture f/20 was constructed and used at an ultrasonic frequency close to one Mc sec⁻¹ to photograph the diffraction of the Hg 5461 A line in argon, nitrogen, nitrous oxide, and ammonia at pressures from 0.23 to 10 atm, with exposures between 0.02 and 1100 seconds. In later work, optics based on the Lyot coronagraph were added to the apparatus, causing a reduction in background light. The intensity of the first-order diffraction image was found to be proportional to the square of pressure. By superimposing the diffraction image produced by a non-dispersive gas used as a standard on the image produced in the unknown gas, it was possible to measure V² with an error of ± 0.2 percent. Sources of this error are discussed. A well-defined dispersion curve was found for nitrous oxide, from which a relaxation time at one atm and 300° K of T = 0.99 x 10⁻⁶ sec was obtained, in excellent agreement with the results of workers using ultrasonic absorption or interferometry. Sound velocity measurements in ammonia at pressures up to six atm yielded V₀² = 19.122 x 10⁴m²sec⁻², in excellent agreement with the theoretical value. A correction for the non-ideality of ammonia, V²[subscript exp] = V[subscript i]² (1 - 13.9 x 10⁻³p), was determined. No dispersion was observed in ammonia at f/p values up to 2.15 Mc sec⁻¹atm⁻¹. When the results of other workers are critically evaluated, applying the correction formula determined here, all but one previously reported dispersions in ammonia disappear. The dispersion reported by Petralia for rotational relaxation is found to fit the V² limits predicted for vibrational relaxation and gives a relaxation time of about 0.6 x 10⁻⁸sec. The factors contributing to the width of the diffracted lines are discussed, and a method for using the line width to determine the maximum in the absorption curve is suggested.
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  • description.provenance : Made available in DSpace on 2014-04-30T22:02:59Z (GMT). No. of bitstreams: 1 StrauchJosephG1966_Redacted.pdf: 1200731 bytes, checksum: 7a786f7e71810aa6f2481bfa4f3608d6 (MD5) Previous issue date: 1965-07-15
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