Laurie S. McNeill

Fourier transform‐infrared studies of thin H2SO4/H2O films: Formation, water uptake, and solid‐liquid phase changes

Fourier transform-infrared (FTIR) spectroscopy was used to examine films representative of stratospheric sulfuric acid aerosols. Thin films of sulfuric acid were formed in situ by the condensed phase reaction of SO{sub 3} with H{sub 2}O. FTIR spectra show that the sulfuric acid films absorb water while cooling in the presence of water vapor. Using stratospheric water pressures, the most dilute solutions observed were >40 wt % before simultaneous ice formation and sulfuric acid freezing occurred. FTIR spectra also revealed that the sulfuric acid films crystallized mainly as sulfuric acid tetrahydrate (SAT). Crystallization occurred either when the composition was about 60 wt % H{sub 2}SO{sub 4} or after ice formed on the films at temperatures 1-4 K below the ice frost point. Finally, the authors determined that the melting point for SAT depended on the background water pressure and was 216-219 K in the presence of 4 x 10{sub {minus}4} Torr H{sub 2}O. Their results suggest that once frozen, sulfuric acid aerosols in the stratosphere are likely to melt at these temperatures, 30 K colder than previously thought. 30 refs., 10 figs.

The Importance of Temperature in Assessing Iron Pipe Corrosion in Water Distribution Systems

Temperature is expected to play a significant role in the corrosion of iron pipes in drinking water distribution systems. Temperature impacts many parameters that are critical to pipe corrosion including biological activity, physical properties of the solution, thermodynamic and physical properties of corrosion scale, and chemical rates. Moreover, variations in temperature and temperature gradients may give rise to new corrosion phenomena worthy of consideration by water treatment personnel.

Fourier transform infrared studies of the interaction of HCl with model polar stratospheric cloud films

Heterogeneous reactions involving hydrochloric acid adsorbed on the surfaces of polar stratospheric clouds (PSCs) are postulated to contribute to polar ozone loss. Using Fourier transform infrared (FTIR) spectroscopy to probe the condensed phase, we have examined the interaction of HCl with ice and nitric acid trihydrate (NAT) films representative of types II and I PSCs, respectively. For HCl pressures in the range of 10−7 to 10−5 Torr our FTIR studies show that a small amount of crystalline HCl·6H2O formed on or in ice at 155 K. However, for higher HCl pressures we observed that the entire film of ice rapidly converted into an amorphous 4:1 H2O:HCl mixture. From HCl-uptake experiments with PHCl = 8 × 10−7 Torr, we estimate roughly that the diffusion coefficient of HCl in ice is around 2 × 10−12 cm2/s at 158 K. For higher temperatures more closely approximating those found in the stratosphere, we were unable to detect bulk HCl uptake by ice. Our experiments also detected no bulk uptake of HCl by α-NAT or β-NAT under various temperature and pressure conditions. Indirect evidence suggests that HCl adsorption onto the surface of model PSC films inhibited the evaporation of both ice and NAT by 3–5 K.

Formation of model polar stratospheric cloud films

Fourier transform infrared spectroscopy was used to examine the competitve growth of films representative of polar stratospheric clouds. These experiments show that either crystalline nitric acid trihydrate ([beta]-NAT) or amorphous films with H[sub 2]O:HNO[sub 3] ratios close to 3:1 formed at temperatures 3-7 K warmer than the ice frost point under stratospheric pressure conditions. In addition, with higher HNO[sub 3] pressures the authors observed nitric acid dihydrate (NAD) formation at temperatures warmer than ice formation. However, their experiments also show that NAD surfaces converted to [beta]-NAT upon exposure to stratospheric water pressures. Finally, the authors determined that the net uptake coefficient for HNO[sub 3] on [beta]-NAT is close to unity, whereas the net uptake coefficient for H[sub 2]O is much less. 13 refs., 4 figs., 1 tab.

The sky is falling II: Impact of deposition produced during the static testing of solid rocket motors on corn and alfalfa

Tests of horizontally restrained rocket motors at the ATK facility in Promontory, Utah, USA result in the deposition of an estimated 1.5million kg of entrained soil and combustion products (mainly aluminum oxide, gaseous hydrogen chloride and water) on the surrounding area. The deposition is referred to as test fire soil (TFS). Farmers observing TFS deposited on their crops expressed concerns regarding the impact of this material. To address these concerns, we exposed corn and alfalfa to TFS collected during a September 2009 test. The impact was evaluated by comparing the growth and tissue composition of controls relative to the treatments. Exposure to TFS, containing elevated levels of chloride (1000 times) and aluminum (2 times) relative to native soils, affected the germination, growth and tissue concentrations of various elements, depending on the type and level of exposure. Germination was inhibited by high concentrations of TFS in soil, but the impact was reduced if the TFS was pre-leached with water. Biomass production was reduced in the TFS amended soils and corn grown in TFS amended soils did not develop kernels. Chloride concentrations in corn and alfalfa grown in TFS amended soils were two orders of magnitude greater than controls. TFS exposed plants contained higher concentrations of several cations, although the concentrations were well below livestock feed recommendations. Foliar applications of TFS had no impact on biomass, but some differences in the elemental composition of leaves relative to controls were observed. Washing the TFS off the leaves lessened the impact. Results indicate that the TFS deposition could have an effect, depending on the amount and growth stage of the crops, but the impact could be mitigated with rainfall or the application of additional irrigation water. The high level of chloride associated with the TFS is the main cause of the observed impacts.

The sky is falling: Chemical characterization and corrosion evaluation of deposition produced during the static testing of solid rocket motors

Static tests of horizontally restrained rocket motors at the ATK facility in Promontory UT, USA result in the deposition of entrained soil and fuel combustion products, referred to as Test Fire Soil (TFS), over areas as large as 30-50 mile (80-130 km) and at distances up to 10-12 miles (16-20 km) from the test site. Chloride is the main combustion product generated from the ammonium perchlorate-aluminum based composite propellant. Deposition sampling/characterization and a 6-month field corrosivity study using mild steel coupons were conducted in conjunction with the February 25th 2010 FSM-17 static test. The TFS deposition rates at the three study sites ranged from 1 to 5 g/min/m. TFS contained significantly more chloride than the surface soil collected from the test site. The TFS collected during two subsequent tests had similarly elevated chloride, suggesting that the results obtained in this study are applicable to other tests assuming that the rocket fuel composition remains similar. The field-deployed coupons exposed to the TFS had higher corrosion rates (3.6-5.0 mpy) than paired non-exposed coupons (1.6-1.8 mpy). Corrosion rates for all coupons decreased over time, but coupons exposed to the TFS always had a higher rate than the non-exposed. Differences in corrosion rates between the three study sites were also observed, with sites receiving more TFS deposition having higher corrosion rates.

Exploring student study behaviours in engineering: how undergraduates prepared textbook problems for online submission

ABSTRACT While textbooks serve as a primary source of content material and problem-solving practice for undergraduates in engineering, studies that investigate how engineering students prepare assignments based on textbook problems are limited. To examine how engineering students complete textbook-based assignments outside of class, this exploratory qualitative study retrospectively investigated the study behaviours of six undergraduates enrolled in a required, second-year undergraduate engineering course at a mid-size, public university in the western United States. Within the course, students solved textbook problems and electronically submitted problem answers for graded credit. Findings from in-depth, semi-structured interviews showed that students identified and used a variety of non-traditional and unsupported resources in personalised approaches to preparing assignments. Resource choice and use was affected by students’ preferences for timely support, convenience, and social connections. The online submission process seemed to influence students’ adoption of study behaviours and resources considered less effective for deep, conceptual learning.