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.

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.

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.

Doctor of Philosophy / Department of Horticulture, Forestry, and Recreation Resources / Kimberly A. Williams / The use of calcined clays contributes properties of nutrient and water retention to soilless root media, which varies greatly depending on the parent clay and calcining treatment. This research characterized phosphate (PO[subscript]4) sorption of various calcined clay products, including low volatile and regular volatile material (LVM and RVM) 2:1 Attasorb clays (Engelhard Corp.), 2:1 Terra Green LVM clays (Oil-Dri Co.), and Turface (Profile Products LLC) at various particle sizes; 1:1 kaolin clays (Thiele Kaolin Co.) in powder form, and diatomaceous earth (Diatomite, Eagle Picher Minerals, Inc.). Three of the calcined materials, Terra Green montmorillonite and Attasorb attapulgite (which had high PO[subscript]4-sorption based on isotherms), and diatomaceous earth (which had negligible PO[subscript]4-sorption) were evaluated as components of soilless root media in two separate greenhouse experiments. The effect of the calcined materials, rate of incorporation (0%, 5%, 10% and 20% by volume in a mix with peat and perlite), and PO[subscript]4-P application rate (0, 5, 15, 45 mg.L[superscript]-1 PO[subscript]4-P) on plant growth, effluent P content and water use were determined during production and post-production of Impatiens wallerana Hook f. 'Tempo Rose'. The calcined materials varied in their ability to adsorb PO[subscript]4-P and generally yielded L-type isotherms. Laboratory results indicated potential for substantive P retention by several of the calcined materials when used in container production. For most materials, PO[subscript]4-P sorption did not show pronounced pH dependence. During production and post-production, the test materials not only improved PO[subscript]4-P retention but also water retention and water use efficiency while still maintaining optimal physical properties at incorporation rates of 5 to 10%. Diatomaceous earth resulted in PO[subscript]4-P retention not significantly different from the calcined clays.

The subject of this thesis is selected parameters cement mortars with partial replacement of Portland cement diatomaceous earth. This work provides information on the basic properties of diatomaceous earth and its deposits with a focus on deposit in Borovany. From the properties is very important pozzolanic activity due to the high content of amorphous silica of this soil. The main use of diatomaceous earth is in the area filtration and is used widely as a nutritional supplement. In the building industry, diatomite can be applied as an admixture to mortar and concrete, where it can, with its abilities, improve some physical mechanical properties. In the experimental part was diatomaceous earth, in its raw and calcined form, tested as admixture for cement pastes and mortars. The main criterion for evaluating these composites was bulk density, flexural and compressive strength. It was also investigated mineralogical composition, microstructure, freeze–thaw resistance and sulfate resistance.