The density, strength and thermal conductivity of diatomite compacts were determined after heating the specimens in the temperature range between 200 and 1050 °C. The linear dimensional change of these specimens on heating was also measured. All properties changed during heating with the increase in firing temperatures and especially above 800 °C. The reduction of density, strength and thermal conductivity of diatomite compacts on firing at up to 600 °C can be attributed to the mass loss due to decomposition of the constituents such as hydrated silica, carbonates, etc. Heating these compacts above 600 °C resulted in shrinkage with a concomitant increase in bulk density, strength and thermal conductivity. Attempts were made to evaluate the fundamental factors which may be contributing to this change of properties during heat treatment. Analyses of data have been made using a sintering model, which assumes that after decomposition diatomite particles are composed of a large number of microspheres and that the change of properties (i.e., increase in density, strength and thermal conductivity) can be attributed to the growth of interparticle contact areas (similar to neck growth during sintering) . Equations for shrinkage, thermal conductivity and strength are all related to the bulk density and weight loss of the compacts, and are given by: For shrinkage, [formula omitted] For thermal conductivity, [formula omitted] For strength, [formula omitted] The validity of these equations has been tested with the experimental data of shrinkage, bulk density, weight loss, strength and thermal conductivity of pure diatomite compacts. The good agreement between the experimental results and the equations may be indicative that it is the increase in interparticle contact areas during the heat treatment which results in the increase in strength, bulk density and thermal conductivity. The general applicability of the equations, developed in order to explain the change in properties of pure diatomite compacts, was further tested with experimental data obtained from a commercial brand of diatomite insulating bricks. / Applied Science, Faculty of / Materials Engineering, Department of / Graduate

No description available.

Highly branched isoprenoid (HBI) alkenes are ubiquitous lipids which have been identified in numerous geochemical samples, ranging from recent sediments to ancient oils. At the outset of the current investigation, the diatomaceous algae Haslea ostrearia (C25 alkenes) and Rhizosolenia setigera (C25 or C30 alkenes) were the only reported biological sources of these compounds. However, there remained a poor correlation between isomers found in diatoms and those commonly reported in sediments and water column particles. In the present study, the structures of fourteen novel C25 HBI trienes, tetraenes and pentaenes, and four C30 HBI pentaenes and hexaenes have been rigorously characterised via gas chromatography-mass spectrometry (GC-MS) and nuclear magnetic resonance (NMR) spectroscopy following isolation from diatoms. The GC-MS characteristics of the four novel C30 HBIs and eight of the novel C25 HBIs characterised herein show an excellent correlation with those of the HBIs commonly reported in sediments and water column particles. In contrast to the HBIs characterised previously, which all possess a saturated branch point and fixed double bond stereochemistry, the common isomers (C25 and C30) possess an unsaturated branch point and exhibit E/Z isomerism about a trisubstituted double bond. Three diatoms belonging to the Pleurosigma genus have been identified as HBI producers. Of these, the benthic species P. intermedium and the planktonic species Pleurosigma sp. have been found to biosynthesise the common C25 HBI isomers. P. planktonicum has also been identified as a producer of C25 HBIs possessing a novel structural type. The HBI distributions in five distinct strains of R. setigera have been investigated, and these were found to be highly variable. Two strains isolated from the northwest Atlantic were found to produce a single, uncommon C25 HBI pentaene, which has also been reported in H. ostrearia. In contrast, R. setigera isolated from the Arabian Sea was found to produce C30 HBIs only, whilst two strains isolated from southern Brittany were found to co-produce the common C25 and C30 HBI isomers. Four diatom species belonging to the Haslea genus have also been newly identified as producers of C25 HBI alkenes. The HBI distributions in H. salstonica, H. crucigera, H. pseudostrearia and Haslea sp. were examined, and HBI production appears to be widespread within the Haslea genus. All of the HBIs identified in these Haslea spp. were of the structural type previously observed in H. ostrearia, and thus do not correspond to the HBI isomers most commonly reported in sediments and particles. Hydrocarbon extracts isolated from sediments and particulates from the Arabian Sea, Cariaco Trench, Peru upwelling region and the Black Sea were examined by GC-MS, and the HBI isomers in these samples were identified

Molecular fluorophores and semiconductor quantum dots (QDs) have been used as cellular imaging agents for biomedical research, but each class has challenges associated with their use, including poor photostability or toxicity. Silicon is a semiconductor material that is inexpensive and relatively environmental benign in comparison to heavy metal-containing quantum dots. Thus, red-emitting silicon nanoparticles (Si NPs) are desirable to prepare for cellular imaging application to be used in place of more toxic QDs. However, Si NPs currently suffer poorly understood photoinstability, and furthermore, the origin of the PL remains under debate. This dissertation first describes the use of diatomaceous earth as a new precursor for the synthesis of photoluminescent Si NPs. Second, the stabilization of red PL from Si NPs in aqueous solution via micellar encapsulation is reported. Thirdly, red to blue PL conversion of decane-terminated Si NPs in alcohol dispersions is described and the origins (i.e., color centers) of the emission events were studied with a comprehensive characterization suite including FT-IR, UV-vis, photoluminescence excitation, and time-resolved photoluminescence spectroscopies in order to determine size or chemical changes underlying the PL color change. In this study, the red and blue PL was determined to result from intrinsic and surface states, respectively. Lastly, we determined that the blue emission band assigned to a surface state can be introduced by base addition in originally red-emitting silicon nanoparticles, and that red PL can be restored by subsequent acid addition. This experimentally demonstrates blue PL is surface state related and can overcome the intrinsic state related excitonic recombination pathway in red PL event. Based on all the data collected and analyzed, we present a simple energy level diagram detailing the multiple origins of Si NP PL, which are related to both size and surface chemistry.

Abstract Production of pulp and paper from raw wood involves the washing of substantial quantities of highly coloured material from the wood pulp. Although most of this colour is trapped within the mill and the mills wastewater treatment system, discharge of coloured wastewater remains a problem of public concern. Lake Rotorua, New Zealand is filled with sediment consisting almost exclusively of diatoms. The most abundant species, Aulacoseira, has been shown to have very small pores, less than 200 nm, that could be very useful for the capture and holding of large organic molecules. Lake Rotorua is situated close to the two largest pulp and paper mills in New Zealand and may have to be dredged to solve a problem of eutrophication. Wastewaters generated at the Kinleith (Tokoroa) and Tasman (Kawerau) mills in the North island of New Zealand have been used to assess the characteristics of colour removal by Lake Rotorua diatoms. Vacuum filtration through the diatoms succeeded in removing colour but proved to be impractically slow as an industrial process. Addition of diatoms to wastewater streams in stirred experiments showed that significant adsorption took place. The majority of the colour was removed within 30 seconds of mixing. The efficiency of colour removal was found to vary between wastewater streams within the mills. The pH dependency of this removal was tested and found to be most effective in a pH range of 3.6 to 5. Attempts to reuse the diatoms showed that chemical backwash regimes were more effective than calcination. This study concluded that surface silanols were likely to be the principle agent in forming coagulants with the colour material and were subsequently trapped on the diatom surfaces, but more importantly within the pores.

No description available.

In the United States, we have been battling the bed bug (Cimex lectularius L.) resurgence for over ten years. Current treatment methods are labor intensive, time consuming, and very expensive. Many studies have evaluated the efficacy of treatment methods, but few have focused on bed bug suppression in multi-unit housing. Low income, multi-unit housing residents lack basic bed bug knowledge and are particulary vulnerable to bed bug infestations because they are unable to afford conventional treatment. In this study, diatomaceous earth (D.E.), an inexpensive desiccant dust labeled for bed bug control, was evaluated for its efficacy in killing bed bugs, and determined to be successful. A proactive bed bug suppression program that included D.E. was implemented in a low-income housing facility in Harrisonburg, VA. The program consisted of inexpensive, low toxicity, integrated bed bug management methods, including a novel strategy for applying a perimeter barrier of D.E. in apartment units (n = 121). Over the course of one year, both the number of initial infestations and the costs associated with bed bug treatments were reduced. Low-income, multi-unit housing residents (n = 479) from three cities (Harrisonburg and Richmond, VA; New Orleans, LA) were surveyed before and after an educational seminar to assess their bed bug. After attending the seminar, residents (n = 112) significantly improved (P < 0.0001) their bed bug knowledge, and were able to correctly answer more bed bug-related questions than they had before the educational seminar. / Master of Science in Life Sciences

Increasing use of engineered nanomaterials presents concerns as some nanoparticles appear to be harmful to both human health and the environment. Effective treatment methods are required to remove problematic nanoparticles from (waste)water streams. Porous media filtration, commonly used for the removal of particulate matter, shows promise for nanoparticle treatment. The goal of this work is to investigate the potential of porous media filtration for the abatement of nanoparticles from aqueous waste streams. To this end, an automated method was developed that allows real-time and in-situ monitoring of nanoparticle transport and retention in porous media using online measurement of UV-visible absorbance or fluorescence. Development of fluorescent-core nano-silica (n-SiO₂) in controllable sizes provided an excellent tracer for nanoparticle transport in porous media. Measurement of n-SiO₂ by destructive techniques is complicated by high natural Si background levels. Fluorescence monitoring enables real-time measurement, facilitating rapid evaluation of n-SiO₂ transport. Synthesized n-SiO₂ remain in their primary sizes making an evaluation of the behavioral change of particles due to transition into the "nano" range possible. A comparison of the role of particle size on transport in porous media displayed the importance of particle number concentration as the dominance of site-specific adsorption may be obscured by simple mass concentration evaluation.T he effectiveness of different bed materials, namely, sand, activated carbon (AC), and diatomaceous earth (DE), for the removal of TiO₂ nanoparticles (n-TiO₂) from aqueous streams was investigated. DE proved promising for n-TiO₂ capture shown by its high bed capacity (33.8 mg TiO₂ g⁻¹(medium)) compared to AC (0.23 mg TiO₂ g⁻¹(medium)) or sand (0.004 mg TiO₂ g⁻¹(medium)). The presence of organic and synthetic contaminants produced varying effects on n-TiO₂ retention, mostly due to either enhanced electrostatic or steric interactions. Application of a process simulator combining physical straining with site-specific interactions, delineating physisorption from chemisorption and diffusion limited interactions, enabled the accurate fit of n-TiO₂ transport in sand, AC and DE. The fitting process revealed the advantage of DE due to increased physisorption and physical straining of n-TiO₂. Modeling of this system afforded the elucidation of controlling retention mechanisms and provides a basis for future scaling and system design.

Shape-preserving silica magnesiothermic reduction is a gas-solid reaction used to convert complex, 3-dimensional SiO₂ structures into replicas composed of a two-phase product of MgO and Si. The MgO/Si components of this reaction are found to form an interwoven aggregate product structure, which is suitably robust that the MgO phase can be selectively dissolved to yield porous Si. Here, the kinetics and mechanisms of growth of this robust product structure have been studied. The aggregate product structure was deduced to result because stacked layers of MgO/Si product phases with planar interfaces are geometrically unstable, owing to the growth kinetics of the products. The interwoven nature of the aggregate may be explained by the presence of an amorphous magnesium silicate phase ahead of the MgO/Si product during reaction. Complex composition gradients in the magnesium silicate can lead to tortuous and branching growth of MgO and Si phases as the magnesium silicate is consumed by reaction. In addition, a large residual stress (> 5 GPa) was measured in the MgO/Si product layer formed during reaction of planar quartz. Despite the presence of such a large stress, no distortion or cracking of reacted structures was found to occur after reaction in the temperature range 650-900 °C. XRD-based residual stress measurements and morphological observations of product films on reacted quartz substrates were used to evaluate possible mechanisms of stress relief in the structure. It was found that the migration of MgO to the external surface of the product layer could be correlated to the rate of stress relaxation that occurred in annealed product films. Finally, applications of silica magnesiothermic reduction and derivative processes were studied in the fields of chemical catalysis and optical chemical sensing.

Submitted by Mario BC (mario@bc.ufrpe.br) on 2017-02-22T14:21:22Z No. of bitstreams: 1 Izanielle Batista dos Santos.pdf: 695252 bytes, checksum: 87a9486b9be20199fbb71b6da8e965e5 (MD5) / Made available in DSpace on 2017-02-22T14:21:22Z (GMT). No. of bitstreams: 1 Izanielle Batista dos Santos.pdf: 695252 bytes, checksum: 87a9486b9be20199fbb71b6da8e965e5 (MD5) Previous issue date: 2016-07-29 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES / Brazil is a country with enormous potential for the production of grain. However, the country faces serious problems in the control of stored grain pests. The Sitophilus zeamais Motsch. (Coleoptera, Curculionidae) is one of the most destructive pests of corn, whose control is done by insecticides, however, their indiscriminate use has led to the development of resistant populations. In this context, Diatomaceous Earth stands in the control of stored grain pests. In view of this, the objective of this study was to investigate whether there are differences among Brazilian populations of S. zeamais in its Diatomaceous Earth resistance capacity associated with some behavioral characteristics of locomotion and of S. zeamais control efficiency. We used four populations of S. zeamais from the states of the Federal District (DF), Minas Gerais (MG) and Pernambuco (PE). The bioassay control efficiency was structured in a factorial (3 doses of Diatomaceous Earth x 3 exposure times) with four replications. Each repetition was constituted by ten adult insects, placed in Petri dishes containing corn treated with diatomaceous earth. The number of live insects by repetition after 24, 48 and 72 hours of exposure to Diatomaceous Earth. The behavioral bioassay was structured in a factorial (4 people x 3 doses of Diatomaceous Earth), where each repetition consisted of a single insect housed in the Petri dish. The movement of the insects was recorded and their locomotor behavior was observed for ten minutes. The tested variables were distance (cm) traversal velocity (cm. S-1), moving time (s) and number of stops. The results demonstrate an increased mortality of insects S. zeamais with increasing doses. There was also different responses among populations of S. zeamais in their behavioral resilience associated with decrease in distance traveled, the number of stops of insects with increasing doses. Confirming the existence of behavioral resistance in populations of S. zeamais studied. In view of this, the elucidation of possible behavioral changes in populations of S. zeamais exposed to Diatomaceous Earth can provide new ways to increase the effectiveness in the management of this pest. / O Brasil é um país com enorme potencial para a produção de grãos. No entanto, o país enfrenta sérios problemas no controle de pragas de grãos armazenados. O Sitophilus zeamais Motsch. (Coleoptera, Curculionidae) é uma das pragas mais destrutivas do milho, cujo controle é feito por inseticidas, entretanto, seu uso indiscriminado tem ocasionado o desenvolvimento de populações resistentes. Neste contexto, a Terra Diatomácea destaca-se no controle de pragas de grãos armazenados. Em vista disto, o objetivo deste trabalho foi investigar se há diferença entre as populações brasileiras de S. zeamais na sua capacidade de resistência à Terra Diatomácea associada a alguma característica comportamental de locomoção e a eficiência de controle de S. zeamais. Foram utilizadas quatro populações de S. zeamais provenientes dos estados do Distrito Federal (DF), Minas Gerais (MG) e Pernambuco (PE). O bioensaio eficiência de controle foi estruturado em um fatorial (3 doses de Terra Diatomácea x 3 tempos de exposição) com quatro repetições. Cada repetição foi constituída por dez insetos adultos, colocados em placas de Petri contendo milho tratado com Terra Diatomácea. Foi contabilizado o número de insetos vivos por repetição após 24, 48 e 72 horas de exposição a Terra Diatomácea. O bioensaio comportamental foi estruturado em um fatorial (4 populações x 3 doses de Terra Diatomácea), onde cada repetição foi constituída por um único inseto alojado em placa de Petri. O movimento dos insetos foi gravado e seu comportamento locomotor foi observado durante dez minutos. As variáveis testadas foram distância percorrida (cm), velocidade de caminhamento (cm. s-1), tempo em movimento (s), e número de paradas. Os resultados demonstram uma mortalidade crescente de insetos de S. zeamais com o incremento das doses. Observou-se também, respostas diferentes entre as populações de S. zeamais em sua capacidade de resistência comportamental associada a diminuição da distância percorrida e do número de paradas dos insetos com o incremento das doses. Confirmando a existência de resistência comportamental nas populações de S. zeamais estudadas. À vista disso, a elucidação de possíveis modificações comportamentais de populações de S. zeamais expostas à Terra Diatomácea pode proporcionar novos caminhos para aumentar a efetividade no manejo dessa praga.