TEPIC - A New High Temperature Structural Foam

The formulation, processing characteristics, microstructure and mechanical properties of a new structural foam, suitable for use at service temperatures up to 200 C, are reported. In each of these respects, the foam is compared to an existing material, called APO-BMI that is currently in use. When these two foams are directly compared, the new foam, called TEPIC, is found to be superior in its mechanical performance. TEPIC is formulated from a non-carcinogenic isocyanate, a di-functional epoxide, and glass microballoons. The authors' approach was to combine chemistries known to form thermally stable products. The principal polymerization products are an oxizolidinone produced by the reaction of the isocyanate with the epoxide and isocyanurate rings formed by the trimerization of the isocyanate. Processing has been examined and large-scale production is discussed in detail. Compared to APO-BMI processing, TEPIC processing is facile and economical. The structure of the foam resembles a traditional rigid polyurethane foam rather than that of the APO-BMI. That is, the foam is comprised of a continuous resin phase rather than weakly bonded glass microballoons. At a density of 0.42 g/cm{sup 3} or greater, maximum pore size in TEPIC was less than 2 mm, as required for the application

The Influence of NGO Strategies on the Sustainability of Biosand Water Filters in Cambodia

This essay evaluates the effectiveness of NGO strategies to promote program sustainability using a case study of two NGOs that install biosand water filters in Cambodia. While the ownership-focused strategy of cost-sharing is the most commonly used and studied, there is evidence to suggest that certain more neglected strategies can have a greater impact. Drawing from nine months of fieldwork, 457 household surveys and five semi-structured interviews with NGO management personnel, the programmatic details of each program are presented along with other factors that relate to the continued use of biosand filters. Through a mixed methods approach this study finds that labor-sharing and monitoring contribute to a significant 15 percentage point difference in biosand filter continued use between the two NGOs. Meanwhile, the influence of cost-sharing remains elusive. This essay argues that the pervasive sentiment that cost-sharing can effectively promote sustainable outcomes allows NGOs using this policy to have a false sense of sustainability. Consequently, other strategies such as labor-sharing and monitoring that have been found to promote more sustainable outcomes are often neglected. Failure to use evidence-based sustainability strategies results in more program failures and prevents the achievement of desired poverty alleviation outcomes

Imaging indicator for ESD safety testing.

This report describes the development of a new detection method for electrostatic discharge (ESD) testing of explosives, using a single-lens reflex (SLR) digital camera and a 200-mm macro lens. This method has demonstrated several distinct advantages to other current ESD detection methods, including the creation of a permanent record, an enlarged image for real-time viewing as well as extended periods of review, and ability to combine with most other Go/No-Go sensors. This report includes details of the method, including camera settings and position, and results with wellcharacterized explosives PETN and RDX, and two ESD-sensitive aluminum powders

Characterization of the feedback between the instructor and student teams engaged in a virtual bioreactor laboratory project

This thesis characterizes the feedback between the instructor and student teams engaged in a Virtual Bioreactor (VBioR) Laboratory Project. The project allows senior-level chemical, biological, and environmental engineering students to apply their developing knowledge and skills in an industrially situated process optimization project. Feedback is an important tool for instructors to use to scaffold student learning, especially in the context of an ill-structured project. An ethnographic approach is taken for data collection; audio recordings and field notes are taken throughout the duration of the project. The characterization of feedback uses an episodes framework for discourse analysis to consider similarities and differences. Using this framework, thematic codes have been developed through a semi-emergent process to describe the content of Design Memo Meetings (DMMs) between an instructor and student teams. Student work products, post-DMM surveys, and post-project interviews are also considered as data sources for this research. The results of this research show that instructor feedback in this project is adaptable, conforming to the status of the student team at the beginning of the DMM. This adaptability is highlighted by differences in DMM themes that are supported by differences in the Design Strategy Memos that student teams bring to the meeting. Student perceptions of the DMM feedback are also presented

FLASHFOAM : a triboluminescent polymer foam for mechanical sensing.

The formulation and processing of a brittle polyurethane foam containing triboluminescent powder additives is described. Two powder additives, known to exhibit triboluminescence, were individually examined: triethylammonium tetrakis (dibenzoylmethanato) europate [NEt3H][Eu(DBM)4] and ordinary table sugar (sucrose, C12H22O11). In each instance, the powders were mixed into the polyol component of the foam. When combined with the isocyanate component, the resulting foams had these powders incorporated into their cellular structure so as to induce a triboluminescent response upon crushing during impact testing. The triboluminescent response of foam specimens containing each of these powder additives was characterized by measuring: the time rate of change in the optical output (measured as Watts), the peak optical output, the total integrated output (Watt-seconds), during the impact event. Foams containing the europate compound were found to yield several orders of magnitude higher output when compared to the sugar-containing foam. Strain rate and concentration of the powder (in the foam) were important variables with respect to optical output. Both the peak and total triboluminescent output increased with increasing powder concentration. Peak output was also found to increase with increasing strain rate. However, the total output was found to be roughly constant for a given concentration regardless of strain rate (over the strain rate range: 20 sec-1< e& < 150 sec-1). At very low strain rates, no triboluminescent response was measured

Protection of alodine coatings from thermal aging by removable polymer coatings.

Removable polymer coatings were evaluated as a means to suppress dehydration of Alodine chromate conversion coatings during thermal aging and thereby retain the corrosion protection afforded by Alodine. Two types of polymer coatings were applied to Alodine-treated panels of aluminum alloys 7075-T73 and 6061-T6 that were subsequently aged for 15 to 50 hours at temperatures between 135 F to 200 F. The corrosion resistance of the thermally aged panels was evaluated, after stripping the polymer coatings, by exposure to a standard salt-fog corrosion test and the extent of pitting of the polymer-coated and untreated panels compared. Removable polymer coatings mitigated the loss of corrosion resistance due to thermal aging experienced by the untreated alloys. An epoxide coating was more effective than a fluorosilicone coating as a dehydration barrier

Evaluation of microporous carbon filters as catalysts for ozone decomposition

Ozone is produced in small quantities in photocopiers and laser printers in the workplace and large quantities in industrial waste water treatment facilities. Carbon filters are commonly used to decompose this unwanted ozone. The three most important factors in producing a filter for this purpose are flow properties, efficiency, and cost. Most ozone decomposition applications require very low back-pressure at modest flow rates. The tradeoff between the number of pores and the size of the pores will be discussed. Typical unfiltered emissions in the workplace are approximately 1 ppm. The maximum permissible exposure limit, PEL, for worker exposure to ozone is 0.1 ppm over 8 hours. Several methods have been examined to increase the efficiency of ozone decomposition. Carbon surfaces were modified with catalysts, the surface activated, and the surface area was increased, in attempts to decompose ozone more effectively. Methods to reduce both the processing and raw material costs were investigated. Several sources of microporous carbon were investigated as ozone decomposition catalysts. Cheaper processing routes including macropore templating, faster drying and extracting methods were also studied

Synthesis, characterization and reactivity of some permethyltantalocene alkylidenes and unusually stable metallaoxetanes

Several tantalaoxetanes have been prepared and the X-ray crystal structure of O-exo-Cp_2*Ta(OCHPhCH_2)CH_3 is reported (Cp* = η^5-C_5Me_5). The kinetic products of the reactions of Cp_2*Ta(=CH_2)CH_3 with paraformaldehyde or benzaldehyde are O-endo-Cp_2*Ta(CH_2CH_20)CH_3 and O-endo-Cp_2*Ta(CH_2CHPhO)CH_3, respectively. These tantalaoxetanes undergo an acid and base-catalyzed isomerization to O-exo-Cp_2*Ta(OCH_2CH_2)CH_3 and O-exo-CP_2*Ta(OCHPhCH_2)CH_3 followed by thermal decomposition to Cp_2*Ta(=O)CH_3 and the appropriate olefin. Cp_2*Ta(=CH_2)H deoxygenates epoxides to form Cp_2*Ta(=O)CH_3 and olefin. No intermediates are observed in this deoxygenation under conditions where the appropriate tantalaoxetanes are stable and would have been spectroscopically observed. Stereolabeled epoxides were deoxygenated to probe the mechanism for the possible intermediacy of a 1,4-biradical. Retention of stereochemistry of the resulting olefin was observed and is indicative of a concerted mechanism. These results and their implications for the mechanism of olefin epoxidation are discussed. Treatment of Cp*_2 TaCI_2 with a variety of substituted benzyl potassium reagents affords an equilibrium mixture of CP*_2 Ta(=CHC_6H_5)H, 1, and Cp*_2 Ta(o-CH_2C_6H_4)H, 2, which interconvert presumably via the unstable 16 electron intermediate [Cp*_2Ta(CH_2C_6H_5)]. Several derivatives substituted at the phenyl ring have been prepared to explore the effect of both sterics and electronics on the a-hydrogen migration equilibrium. Trapping of the benzyl intermediate by methylenetrialkylphosphoranes results in methylene transfer to give Cp*_2 Ta(=CH_2)CH_2C_6H_5. The substituted benzyl derivatives have provided a system to determine the influence of phenyl sUbstituents on migratory aptitude of the benzyl group

Expancel Foams: Fabrication and Characterization of a New Reduced Density Cellular Material for Structural Applications

This study was initiated to produce a low-density centering medium for use in experiments investigating the response of materials to shock-loading. While the main drivers for material selection were homogeneity, dimensional stability, performance and cost, other secondary requirements included fine cell size, the ability to manufacture 5--10 cm-sized parts and an extremely compressed development time. The authors chose a non-traditional methodology using a hollow, expandable, polymeric microballoon material system called Expancel{reg_sign}. These microballoons are made from a copolymer of polyacrylonitrile (PAN) and polymethacrylonitrile (PMAN) and use iso-pentane as the blowing agent. The average diameter (by volume) of the unexpanded powder is approximately 13 {micro}m, while the average of the expanded powder is 35--55 {micro}m, with a few large microballoons approaching 150--200 p.m. A processing method was developed that established a pre-mixed combination of unexpanded and expanded Expancel at a ratio such that the tap (or vibration) density of the mixed powders was the same as that desired of the final part. Upon heating above the tack temperature of the polymer, this zero-rise approach allowed only expansion of the unexpanded powder to fill the interstices between the pre-expanded balloons. The mechanical action of the expanding powder combined with the elevated processing temperature yielded flee-standing and mechanically robust parts. Although mechanical properties of these foams were not a key performance requirement, the data allowed for the determination of the best temperature to heat the samples. Processing the foam at higher temperatures enhanced both modulus and strength. The maximum allowable temperature was limited by dimensional stability and shrinkback considerations. Tomographic analysis of foam billets revealed very flat density profiles. Parts of any density between the low density expanded powder (approximately 0.013 g/cm{sup 3}) and the higher density unexpanded powder (approximately 0.5 g/cm{sup 3}) can be produced using this technique. The extremely wide range of accessible densities, ease of processing, relatively inexpensive materials, uniformity of the density, scaleable nature of the process should make this technology highly competitive for a variety of Defense Programs and commercial applications