Ambient Laboratory Air Research Articles

Double resonance multiphoton ionization determination of mercury vapor

A laser-based method for the photoionization of Hg is reported which uses two single-photon resonances and thus avoids the high-power densities required for the efficient excitation of multiquantum transitions. The method was used to measure Hg concentrations in the ambient laboratory air. The 100-mL air samples were found to contain from 40 to 70 pg of Hg (0.4-0.7 ng/L). While this is approximately 10 times the level found in what are considered unpolluted environments (12), it is still more than a factor of 100 below maximum acceptable levels (13). Ultimate detection limits may be estimated. The integrated signal for the smallest standard used (1 ..mu..L of air, 15.4 pg of Hg) is 3.98 (arbitrary units), while the standard deviation for integration of a series of blank cycles is +/-0.029. At a signal-to-background noise ratio of 2 the calculated detection limit is 220 fg of Hg.

Comparisons of Volatile Organic Compound Monitors Equipped with Cryogenic Preconcentrators

The performances of two nominally identical automated monitors for quantifying volatile organic compounds were compared on identical ambient laboratory air samples. The monitors incorporate cryogenic preconcentration subunits specially designed for controlled release of liquid nitrogen to establish a −150°C trap temperature. Measured trends in concentration for perchloroethylene, toluene, chloroform, Freon 113, methyl chloroform, and benzene showed good agreement even at sub-ppbv levels during automated overnight runs, although some effects of adsorption were evident. In a second set of runs, concentration results for one system were plotted versus those for the other. The plots were linear and, precise, but slightly biased. Qualitative comparisons using diluted automobile exhaust are also shown.

Urea, Calcium, Potassium and Sulfur Impregnation of Whole Corn—Development and In Vitro Evaluation

A method of impregnating whole corn grain to meet the nitrogen and mineral requirements of growing-finishing lambs was developed. Several compounds were compared as calcium (Ca), potassium (K) and sulfur (S) sources based on solubility in a urea solution. A laboratory study was used to evaluate two urea-mineral solutions containing urea, calcium chloride, potassium acetate and sodium thiosulfate. The ratio of these compounds to whole corn was based on a final product containing 12% crude protein, .37% Ca, .50% K and a 10:1 N (from urea) to S ratio (dry matter basis). Dry stored corn and high moisture corn were mixed on a horizontal rolling device with either 11 or 6.5 ml solution/100 g corn dry matter. Both solutions provided the same quantity of salts; only water addition varied. The impregnated corn was then dried by either ambient laboratory air for 24 h or heat (95 C) for 1 h to 88% or higher dry matter content. A washing procedure was used to determine the relative amounts of added nutrients absorbed by, or adhered to, corn kernels. Neither corn source, stored or high moisture, nor drying method had any affect on N, Ca or K retention with the exception of more (P<.01) retained Ca in stored corn. The reduced volume of added water resulted in increased (P<.01) Ca retention as well. Although washing reduced (P<.01) the amounts of N, Ca and K in impregnated corn, 79, 70 and 59% of the added N, Ca and K, respectively, remained associated with the kernels. In an in vitro ammonia-N release study, ammonia-N concentration in the incubation medium was lowered (P<.05) during several of the first 6 h of a 24-h incubation when impregnated corn was compared with liquid urea-supplemented corn.

Utilization by sheep of whole shelled corn impregnated with urea, calcium, potassium and sulfur.

Twenty-eight growing wether lambs (33.9 kg), adapted to urea for 40 d, were used in a metabolism study to determine if urea impregnation of corn could improve urea utilization. The following diets were compared: 1) whole shelled corn alone, 2) whole shelled corn impregnated with urea, calcium (Ca) as CaCl2, potassium (K) as KC2H3O2, and sulfur (S) as Na2S2O3 X 5H2O, 3) whole shelled corn fed with a dry supplement containing urea, Ca, K and S and 4) whole shelled corn fed with a dry supplement containing soybean meal, Ca and K. Additions were made to provide diets containing 12% crude protein, .37% Ca and .50% K. A 10:1 N (from urea) to S ratio, dry basis was used in urea-containing diets. Corn (90% dry matter) in diet 2 was impregnated by spraying 1.1 liters of an aqueous solution containing the above salts per 10 kg of corn dry matter. After mixing for 10 min in a horizontal mixer, the corn was dried in a laboratory grain drying bin with ambient laboratory air for 48 h. Lambs were fed 350 g of the respective diets plus 35 g orchardgrass hay twice daily during a 20-d metabolism trial. On the last day of the trial, ruminal fluid samples were collected at 0, 1, 2, 3, 4, 5 and 6 h postfeeding and jugular blood was obtained at 0 and 6 h postfeeding. Nitrogen-supplemented diets resulted in increased (P less than .01) absorption and retention of N. Digestibility of dry matter, organic matter and NFE tended to be greater in lambs fed impregnated corn than in lambs fed the other diets.(ABSTRACT TRUNCATED AT 250 WORDS)

Mechanical-contact-induced transformation from the amorphous to the partially crystalline state in metallic glass

Sliding friction and wear experiments and electron microscopy and diffraction studies were conducted to examine the metallurgical microstructure of a metallic glass surface strained in sliding contact. Friction and wear experiments were conducted with aluminium oxide spheres 3.2 and 6.4 mm in diameter sliding, in reciprocating motion, on a metallic foil with a composition of Fe 67Co 18B 14Si 1 at a sliding velocity of 1.5 mm s -1 (frictional heating is negligible) with a load of 2.5 N at room temperature and in a laboratory air atmosphere. The results of the investigation indicate that the amorphous alloy (metallic glass) can be crystallized during mechanical contact. Crystallites with a size range of 10–150 nm are produced on the wear surface of the amorphous alloy. A diffused honeycomb-shaped structure formed by dark gray bands is also produced during sliding. Considerable plastic flow occurs on an amorphous alloy surface with sliding and the flow film of the alloy transfers to the aluminium oxide pin surface. Multiple slip bands due to shear deformation are observed on the side of the wear track. Two distinct types of wear debris were observed as a result of sliding: an alloy wear debris and/or powdery and whiskery oxide debris. The wear rate of Fe 67Co 18B 14Si 1 was 5 × 10 -9 mm 3 N -1.

Kinetics of corrosion fatigue crack growth in high strength low-alloy steels in 3.5%NaCl aqueous solution.

Corrosion fatique crack growth rates as a function of the stress intensity factor range were investigated in the 3.5% NaCl aqueous solution of various temperatures between 278K and 333K under a constant applied electrochemical potential of -1050mV vs. Ag/AgCl reference electrode. Generally speaking, crack growth is enhanced as solution temperature rises. The corrosion fatique crack growth rate-stress intensity factor range curve can be divided into three distinct stages independent of testing temperature; at low ΔK levels or Range I, corrosion fatigue crack growth rate is strongly dependent on ΔK and slightly on testing temperature. In the range of moderate ΔK or Range II, the extent of which depends on testing temperature, the ΔK dependence of the crack growth rate curves disappears and crack growth rate reaches a limiting value. The apparent activation energy for the rate limit region of Range II was found to be approximately 40.0kJ/mole, which can be compared well with that for apparent hydrogen diffusion in steel. At higher ΔK levels or in Range III, corrosion fatigue crack growth rates coincide with those obtained in ambient laboratory air, indicating that the corrosion fatigue crack growth in this range is not affected essentially by the aqueous environment.

A versatile sample isolation, chemical modification and introduction system designed for a physical electronics model 548 electron spectrometer

X-ray photoelectron spectroscopy (XPS or ESCA) has been extensively used in recent years to investigate the chemical composition of various surfaces. In our laboratory XPS has been used primarily to monitor elemental atomic ratios and binding energy shifts produced by surface modifications of glassy carbon samples. A major method of modification has been by radio frequency plasma treatments to improve surface electrochemical properties. To maintain surface integrity for XPS analysis by avoiding exposure of the treated sample surface to oxygen, water vapor or other contaminants in the ambient laboratory air, a versatile sample treatment and transfer system has been built and attached to the analysis chamber of a Physical Electronics Industries Model 548 Electron Spectrometer. The resulting system has proven to be more suited to meet our needs than any previously reported or commercially available system. The system consists of two sample transfer side-arms, each with a magnetically coupled transfer rod compatible with our custom sample carriers. The sample isolation side-arm is used exclusively to enter samples into the analyzer chamber without contamination. The general purpose side-arm has two appendage ports which support a radio frequency plasma chamber, a sample introduction lock and a combination chemical treatment/electrochemical cell chamber. Each of the appendage ports and the two transfer housings can be isolated using UHV gate valves. The sample transfer and transport mechanisms and the system performance are discussed. Examples of the effects of exposure of RF plasma treated glassy carbon surfaces to air and water vapor are use to demonstrate the capabilities of the sample handling system.

50-Fold Difference in Region-II Fatigue Crack Propagation Resistance of Titanium Alloys: A Grain-Size Effect

Fatigue crack growth rates (da/dN) in ambient laboratory air have been determined for a wide variety of materials from four basic α + β titanium alloy systems. Each material was cyclically loaded with a haversine waveform and a load ratio, R = 0.10. The results indicate that, at a constant value of stress-intensity range (ΔK), the width of the da/dN data band exceeds an order of magnitude. For example, at ΔK = 21 MPa·m1/2, a 50-fold difference in fatigue crack propagation rates is observed. Analysis of the crack growth rate data at this point indicates a systematic dependence on grain size (l), viz. that da/dN decreases with increasing l. An interpretation of this effect is offered in terms of reversed (cyclic) plastic zone size considerations.

Carbon Dioxide and Ethylene Control of Spore Germination in Onoclea sensibilis L

Regulation of spore germination in the fern Onoclea sensibilis L. was investigated by applying CO(2) alone and in combination with ethylene. Sterile spores were sown aseptically on Knops solution in loosely capped culture tubes, enclosed individually in 2-liter chambers, and grown under continuous white light. When maintained in enclosed containers with the ethylene-absorbent mercuric perchlorate and with atmospheres enriched up to 2% CO(2) (v/v), spores germinated without any inhibition. Higher levels of applied CO(2) were progressively inhibitory. Inhibition by CO(2) was reversible. When CO(2) was permitted to escape and spores were exposed subsequently to ambient laboratory air, recovery from inhibition occurred within 48 hours. Also, inhibition by CO(2) was specific, since the same degree of inhibition resulted regardless of whether spores were treated with exogenous CO(2) for 48, 72, or 96 hours. The effect on germination of 1 mul/l added ethylene depended upon the amount of applied CO(2). When containers of KOH were enclosed and ambient CO(2) was absorbed, inhibition of germination by 1 mul/l exogenous ethylene was 90%. When CO(2) was applied in concentrations from 0.25 to 1.0% (v/v), CO(2) increasingly antagonized the inhibitory action of 1 mul/l added ethylene. Thus, photoinduced germination of spores was regulated by competitively interacting levels of CO(2) and ethylene.