Engineering topics

Upchurch, B. T.

Publications and source records attributed to Upchurch, B. T..

14 records

NASA NTRS1991

Recent advances in CO2 laser catalysts

This paper discusses several recent advances in CO2 laser catalysts including comparisons of the activity of Au/MnO2 to Pt/SnO2 catalysts with possible explanations for observed differences. The catalysts are compared for the effect of test gas composition, pretreatment temperature, isotopic integrity, long term activity, and gold loading effects on the Au/MnO2 catalyst activity. Tests conducted to date include both long-term tests of up to six months continuous operation and short-term tests of one week or more that include isotopic integrity testing.

Upchurch, B. T.↗

NASA NTRS1989

Recent advances in efficient long-life, eye-safe solid state and CO2 lasers for laser radar applications

The key problems in the development of eye-safe solid-state lasers are discussed, taking into account the energy transfer mechanisms between the complicated energy level manifolds of the Tm, Ho, Er ion dopants in hosts with decreasing crystal fields such as YAG or YLF. Optimization of energy transfer for efficient lasing through choice of dopant concentration, power density, crystal field and temperature is addressed. The tailoring of energy transfer times to provide efficient energy extraction for short pulses used in DIAL and Doppler lidar is considered. Recent advances in Pt/SnO2 oxide catalysts and other noble metal/metal oxide combinations for CO2 lasers are discussed. Emphasis is given to the dramatic effects of small quantities of H2O vapor for increasing the activity and lifetime of Pt/SnO2 catalysts and to increased lifetime operation with rare isotope (C-12)(O-18)2 lasing mixtures.

Hess, R. V.↗

NASA NTRS1987

Catalytic Oxidation of CO for Closed-Cycle CO2 Lasers

Stoichiometric mixture converted completely. High-energy pulsed CO2 lasers have potential for measuring many different features of atmosphere of Earth and particularly useful on airborne or space platforms. For this application, laser must be operated in closed cycle to conserve gas, especially if rare nonradioactive isotopes of carbon and oxygen used. However, laser discharge decomposes fraction of CO2 to CO and O2, causing rapid loss in power leading to erratic behavior. To maintain operation, CO and O2 must be recombined to form CO2.

Miller, I. M.↗

NASA NTRS1987

Characterization of Pt/SnO2 catalysts for CO oxidation

Results are presented of surface characterization of 2% and 1% (w/w) Pt on SnO2 catalysts which are being used in promoting the oxidation of CO in pulsed CO2 lasers. The N2 adsorption BET surface area for both catalysts is 6.9 sq m/g. The CO chemisorbed area at 313K is 0.17 sq m/g and 0.062 sq m/g for the 2% and 1% catalysts, respectively. Monitoring the reaction between CO and O2 by the same technique, at the same temperature yields a turn-over frequency (TOF) for the 2% catalyst of 2.7 x 100 molecules of CO2/site/s and for the 1% catalyst a value of 1.2 x 100. The ratio of the TOFs for the two catalysts is 2.2 which is approximately the ratio of the Pt loading.

Brown, K. G.↗

NASA NTRS1986

Catalytic recombination of dissociation products with Pt/SnO2 for rare and common isotope long-life, closed-cycle CO2 lasers

This paper reports results on recombination of pulsed CO2 laser dissociation products with Pt/SnO2 catalysts, and supporting studies in a surrogate laboratory catalyst reactor. The closed-cycle, pulsed CO2 laser has been continuously operated for one million pulses with an overall power degradation of less than 5 percent by flowing the laser gas mixture through a 2-percent Pt/SnO2 catalyst bed. In the surrogate laboratory reactor, experiments have been conducted to determine isotopic exchange with the catalyst when using rare-isotope gases. The effects of catalyst pretreatment, sample weight, composition, and temperature on catalyst efficiency have also been determined.

Brown, Kenneth G.↗

NASA NTRS1985

Optimization of the catalytic oxidation of CO for closed-cycle CO2 laser applications

This report develops a basis for the design of a catalyst bed for the recombination of CO and O2 in a closed-cycle CO2 laser system. The catalyst is 1% Pt on SnO2 having a BET surface area of 6.7 sq m/g and a specific void volume of 0.374 cu cm/g. The design conditions are: a catalyst bed temperature of 100 C and a circulating flow rate of 10 lambda/min. Under these conditions, the required quantity of catalyst for prolonged laser operation of 668g. The rat law for the reaction of a stoichiometric mixture of 1% CO + 1/2% O2 in helium was determined to be overall first order; however, additional experiments with non-stoichiometric gas mixtures of CO and O2 are needed to determine the order of the CO concentration and the order of the O2 concentration in the rate law.

Miller, I. M.↗

NASA NTRS1984

Non-catalytic surfaces for metallic heat shields

The magnitude of the atom recombination coefficients needed for metal heat shield surfaces on Shuttle-type vehicles is analyzed and discussed. Prior work which identifies surfaces having low catalytic activity is reviewed. Arc tunnel tests to evaluate catalytic activity are described and the difficulties of such tests are discussed. Results are presented which show major differences between atom recombination and atom exchange from molecules. Results of surface analysis show that bulk and surface composition of a coating are different.

Swann, R. T.↗

NASA NTRS1984

Iterative and function-continuation Fourier deconvolution methods for enhancing mass spectrometer resolution

Mass spectrometer data in the form of ion current versus mass-to-charge ratio often include overlapping mass peaks, especially in low- and medium-resolution instruments. Numerical deconvolution of such data effectively enhances the resolution by decreasing the overlap of mass peaks. In this paper two approaches to deconvolution are presented: a function-domain iterative technique and a Fourier transform method which uses transform-domain function-continuation. Both techniques include data smoothing to reduce the sensitivity of the deconvolution to noise. The efficacy of these methods is demonstrated through application to representative mass spectrometer data and the deconvolved results are discussed and compared to data obtained from a spectrometer with sufficient resolution to achieve separation of the mass peaks studied. A case for which the deconvolution is seriously affected by Gibbs oscillations is analyzed.

Ioup, J. W.↗

NASA NTRS1983

Developing mass spectrometric techniques for boundary layer measurement in hypersonic high enthalpy test facilities

Thermodynamic flow properties of gases in the boundary layer or the flowfield have been mainly deduced from pressures and temperatures measured on a model. However, further progress with respect to an understanding of these properties requires a more complete characterization of the layer including determination of the gas composition and chemistry. Most attempts to measure boundary layer chemistry involve the employment of a mass spectrometer and an associated gas sampling system. The three major limiting factors which must be addressed for species measurement in aerothermodynamic investigations on models at reentry stream velocities, are gas sampling effects, instrument limitations, and problems with data acquisition. The present investigation is concerned with a concentrated effort to quantitatively identify and correct for instrument and sampling system effects, and to develop a miniaturized high performance mass spectrometer for on-model real-time analysis of the boundary layer and its associated atmosphere.

Wood, G. M., Jr.↗

NASA NTRS1983

Evaluation of catalyst for closed cycle operation of high energy pulsed CO2 lasers

Several catalyst materials have been tested for efficiency of converting CO and O2 to CO2 for use in a high energy CO2 laser. The composition of the gas mixtures was monitored by mass spectrometry and gas chromatography. A copper/copper oxide catalyst and a platinum/tin oxide catalyst were used for closed cycle operation of a CO2 laser (0.7 joules/pulse), operating at 10 pulses/sec.

Rogowski, R. S.↗

NASA NTRS1981

Data enhancement and analysis through mathematical deconvolution of signals from scientific measuring instruments

Mathematical deconvolution of digitized analog signals from scientific measuring instruments is shown to be a means of extracting important information which is otherwise hidden due to time-constant and other broadening or distortion effects caused by the experiment. Three different approaches to deconvolution and their subsequent application to recorded data from three analytical instruments are considered. To demonstrate the efficacy of deconvolution, the use of these approaches to solve the convolution integral for the gas chromatograph, magnetic mass spectrometer, and the time-of-flight mass spectrometer are described. Other possible applications of these types of numerical treatment of data to yield superior results from analog signals of the physical parameters normally measured in aerospace simulation facilities are suggested and briefly discussed.

Wood, G. M.↗

NASA NTRS1975

On-line mass spectrometric monitoring of the polymerization of a phenolic-resin-based material

Polymerization of phenolic-resin-based materials requires elevated temperatures. The low thermal conductivity of these materials has led to the use of dielectric heating techniques in lieu of standard convection oven heating to obtain a satisfactory cure. The curing rate and therefore the quality of the cured material depends on the heating rate and maximum temperature attained, parameters which are extremely difficult to measure in dielectric heating units. The dielectric curing of these materials was monitored by using a mass spectrometer to measure the partial pressure of phenol in the gas evolved during polymerization. The resulting plots of phenol partial pressure as a function of time have a characteristic shape, and these may be used to indicate the attainment of complete curing. The validity of the mass spectrometric technique was confirmed by chemical analysis of the polymerized samples.

Aikens, D. A.↗

NASA NTRS1975

Determination of water content using mass spectrometry

Mass spectrometer is used to measure small quantities of water present in different materials. System has been applied in measuring water and gases desorbed from microcircuitry insulation, can also be used with foods, polymeric materials, and organic solvents.

Wood, G. M.↗

NASA NTRS1975

Dynamic delta method for trace gas analysis

Method has been developed in which measurements are made only over viscous flow range, eliminating fractionation before the molecular leak and problems due to surface elution.

Wood, G. M.↗