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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

Bio-Functionalized Clay Nanoparticles for Wound Healing Applications

Vaiana, Christopher Anthony 11 July 2011 (has links)
No description available.
2

A route to enhanced intercalation in rubber silicate nanocomposites

Al-Yamani, Faisal M. 23 September 2005 (has links)
No description available.
3

Chain extension of polyamide-6 & polyamide-6/organoclay nanocomposites : control of thermal degradation of polyamide-6/organoclay nanocomposites during extrusion using a novel chain extender

Tuna, Basak January 2016 (has links)
Novel solutions to offset thermal degradation of polyamide-6 (PA-6) and organoclay (organically modified layered silicates) nanocomposites during melt compounding have been investigated. In this research, a novel chain extender (Joncryl ADR 3400) has been used to improve thermal stability of PA-6 and PA- 6/organoclay nanocomposites during melt compounding. The materials were compounded using a linear twin extruder and various laboratory scale mixers. The effects of organoclay and chain extender were studied using both processing methods. In order to replicate large scale production used in industry, a comprehensive plan of experimental work was carried out under different processing conditions (extrusion temperature and screw speed), organoclay and chain extender loading using a linear twin screw extruder. Rheology, mechanical and thermal properties were analysed and selected samples were also characterised by TEM and FTIR. Process induced degradation of PA-6 during the melt compounding was found to have significant influence on the rheological and mechanical properties. Rheological and mechanical characterisation clearly showed showed that incorporation of the chain extender minimised thermal degradation of PA-6 and nanocomposites during melt processing. Visual analysis of selected nanocomposites using TEM confirmed that chain extender increased the dispersion of nanoclays in the PA- 6 matrix. The crystallinity of the PA-6 was slightly affected by addition of organoclay and chain extender. The samples obtained by linear twin screw extrusion showed higher rheological properties than the samples from laboratory scale mixers suggesting better mixing and less thermal degradation during extrusion.
4

Síntese e pilarização de ácidos silícicos lamelares / Syntheses and pilarization of layered silicic acids

Pires, Cleo Thomas Gabriel Vilela Menegaz Teixeira 08 March 2010 (has links)
Orientador: Claudio Airoldi / Tese (doutorado) - Universidade Estadual de Campinas, Instituto de Química / Made available in DSpace on 2018-08-17T00:22:48Z (GMT). No. of bitstreams: 1 Pires_CleoThomasGabrielVilelaMenegazTeixeira_D.pdf: 3067472 bytes, checksum: c700c7da8e03afe86cb307d460e98b2c (MD5) Previous issue date: 2010 / Resumo: Nos últimos anos tem sido observado um crescente interesse na obtenção de materiais lamelares modificados, devido as suas propriedades únicas e consequentes aplicações científicas e tecnológicas possíveis. Ácidos silícicos como a magadeíta, a kaneíta e a ilerita são compostos extremamente versáteis, podendo-se variar os seus espaçamentos basais a partir de intercalações com grupos de cadeia carbônica longa ou troca iônica. Outras alterações possíveis são as substituições isomórficas do silício por átomos tri- ou tetravalentes como alumínio e titânio respectivamente, modificando as propriedades químicas da lamela. Neste trabalho os ácidos silícicos lamelares magadeíta, ilerita e kaneíta foram sintetizados pelo método hidrotérmico, contendo também átomos de Al e Ti inseridos na estrutura. Em todos os casos observou-se que conforme aumenta-se a quantidade de metal adicionado ou o tempo de tratamento hidrotérmico, ocorrem transições de fase que seguem a ordem: amorfa, fase lamelar de interesse, cristobalita e tridimita, bem como suas misturas em situações intermediárias. Diferentes métodos de pilarização com TiO2 foram exaustivamente testados, variando-se uma série de parâmetros. O método que se mostrou mais eficiente consistiu na utilização de CTAB e TBAOH como agentes espaçadores sob refluxo a 353 K, seguido de adição direta do alcoxido no material intercalado seco, então refluxados a 363 K sob fluxo de nitrogênio. Os materiais obtidos por este método possuem mesoporos com 4,8 nm de diâmetro em media, porem a área superficial obtida foi de apenas cerca de 270 m g. Nos materiais pilarizados foram imobilizados os fotocatalisadores pirílio (TPP) e tiapirílio (TPTP) de modo a provar a eficiência na degradação fotocatalítica do pesticida metidation. Os materiais híbridos apresentaram desempenho superior aos fotocatalisadores orgânicos puros, o que representa um ótimo ponto inicial para a otimização deste processo. Também o comportamento fotofísico dos corantes impregnados nos materiais pilarizados foram estudados / Abstract: Recently, the interest to obtain modified layered materials is increasing, due to their properties and possible scientific and technological applications. Silicic acids such as magadiite, kenyaite and ilerite are extremely versatile compounds, allowing to vary the basal spacing by intercalation with carbonic long chains groups or ionic exchange process. Other possible modifications are isomorphic substitution by aluminum, titanium or iron atoms, with changeing the lamella chemical properties. In this investigation layered silicic acids magadiite, ilerite and kenyaite, containing also Al and Ti atoms inserted into the lamellar structure, were synthesized by hydrothermal method. For all cases was observed that with the increase of metal amount added or the hydrothermal treatment time there are phase transitions, following the order: from amorphous, to layered phase to crystobalite and tridimite, as mixtures of them at intermediate situations. Different pilarization methods with TiO2 were exhaustedly tested by varying many parameters. The most efficient methods used CTAB and TBAOH as swelling agents under reflux at 353 K, followed by direct alcoxide addition on the dry material, then refluxed at 363 K with dry nitrogen atmosphere. These materials have mesopores with 4.8 nm average diameter, nevertheless just 270 m g surface area. Some pillared materials were used to immobilize the photocatalyst pyrylium (TPP) and thiopyrylium (TPTP) and then test in the photocatalytic degradation of methidathion pesticide. The hybrid materials showed a better activity than that of pure organic, what means a great initial point to optimize this process. The photophysic behavior of impregnated dyes on pillared materials was also studied / Doutorado / Quimica Inorganica / Doutor em Ciências
5

Estruturas 3D a partir de estruturas 2D : transformações hidrotérmica e topotática / 3D structures from 2D ones : hydrothermal and topoctatic transformation

Ramos, Francisca Solânea de Oliveira, 1985- 21 August 2018 (has links)
Orientador: Heloise de Oliveira Pastore / Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Química / Made available in DSpace on 2018-08-21T15:14:46Z (GMT). No. of bitstreams: 1 Ramos_FranciscaSolaneadeOliveira_M.pdf: 5550553 bytes, checksum: c97e45758df14cd712ea691a6174a574 (MD5) Previous issue date: 2012 / Resumo: A aplicação dos silicatos lamelares como catalisadores apresenta como limitações as baixas área superficial e acidez, porém, esses sólidos têm como principais propriedades a reatividade dos grupos Si-OH e Si-ONa da superfície de suas lamelas e sua capacidade de troca iônica. Em função disso, esses sólidos podem sofrer uma variedade de modificações em sua superfície e em seu espaço lamelar e até passar de uma estrutura 2D para uma estrutura 3D. As lamelas do silicato lamelar Na-RUB-18, além de serem recobertas por Si-OH e Si-O, são constituídas de cavidades de quatro anéis de cinco membros [5], presentes tanto no RUB-24 quanto na MOR, assim como em outros zeólitos, indicando que tal lamelar seja potencial precursor de estruturas zeolíticas. Por tais motivos, o presente trabalho teve como objetivo estudar e descrever como o Na-RUB-18 se transforma nas estruturas zeolíticas MOR e RUB-24, por processos hidrotérmico e topotático, respectivamente, e como essas estruturas 2D e 3D se relacionam. A gradual aproximação das lamelas do Na-RUB-18 e conseqüente condensação dos grupos Si-OH, ou seja, unidades Q ([O4Si]3Si-OH), ocasiona a formação de ligações Si-O-Si, unidades Q ([O4Si]4-Si), gerando a estrutura 3D. No caso do zeólito MOR, esse processo é induzido pela adição de uma fonte de alumínio, Al[OCH(CH3)2]3 ou Na2Al2O4. O presente trabalho também investiga a etapa de aproximação das lamelas do Na-RUB-18, ocasionando na sua condensação em RUB-24. A condensação das lamelas do precursor lamelar no RUB-24 via processo topotático é conduzida por um agente direcionador de estrutura, o íon trietilenotetramônio, comprovando que tal processo, como a transformação hidrotérmica, não acontece aleatoriamente / Abstract: The application of the layered silicates in heterogeneous catalysis has limitations such as low surface area and acidity. However, these solids also have ion exchange capacity and their surfaces can be covalently modified with silylation reagents. As a result, they can undergo a variety of surface changes yielding modifications in interlayer space and in the structure lamellar that may even cause collapse of a 2D structure to a 3D. The framework of layered silicate Na-RUB-18 is composed of four five-membered rings, [5] and its surface made of Si-OH and Si-ONa. The [5] cage is a building unit also found in zeolitic structures, as RUB-24 and MOR, indicating that the structure of Na-RUB-18 contains important elements of microporous materials structures and should be regarded as a potential precursor structure to the three-dimensional four-connected microporous framework silicates. This work aimed of studying and describing the transformations of the Na-RUB-18 into MOR and RUB-24 by hydrothermal and topotactic process, respectively. The gradual reduction of interlayer distance of the Na-RUB-18 led to the condensation of the Si-OH groups, Q units ([O4Si]3Si-OH), forming Si-O-Si bonds, Q units ([O4Si]4-Si), i.e., a 3D structure. In the preparation of MOR zeolite by hydrothermal transformation, the process is conducted through addition of a aluminum source, Al[OCH(CH3)2]3 or Na2Al2O4. This work also investigated the formation of RUB-24 through Na-RUB-18 collapsing. The topotactic reaction between Si-OH groups of the lamellar precursor was conducted by a structure-directing agent, triethylenetetrammonium ion, proving that this process, as the hydrothermal transformation, does not occur randomly / Mestrado / Quimica Inorganica / Mestra em Química
6

Molecular Simulation of Dipsersion and Mechanical Stability of Organically Modified Layered Silicates in Polymer Matrices

Fu, Yao-Tsung 19 April 2011 (has links)
No description available.
7

Chain Extension of Polyamide-6 & Polyamide-6/Organoclay Nanocomposites. Control of thermal degradation of polyamide-6/organoclay nanocomposites during extrusion using a novel chain extender

Tuna, Basak January 2016 (has links)
Novel solutions to offset thermal degradation of polyamide-6 (PA-6) and organoclay (organically modified layered silicates) nanocomposites during melt compounding have been investigated. In this research, a novel chain extender (Joncryl ADR 3400) has been used to improve thermal stability of PA-6 and PA- 6/organoclay nanocomposites during melt compounding. The materials were compounded using a linear twin extruder and various laboratory scale mixers. The effects of organoclay and chain extender were studied using both processing methods. In order to replicate large scale production used in industry, a comprehensive plan of experimental work was carried out under different processing conditions (extrusion temperature and screw speed), organoclay and chain extender loading using a linear twin screw extruder. Rheology, mechanical and thermal properties were analysed and selected samples were also characterised by TEM and FTIR. Process induced degradation of PA-6 during the melt compounding was found to have significant influence on the rheological and mechanical properties. Rheological and mechanical characterisation clearly showed showed that incorporation of the chain extender minimised thermal degradation of PA-6 and nanocomposites during melt processing. Visual analysis of selected nanocomposites using TEM confirmed that chain extender increased the dispersion of nanoclays in the PA- 6 matrix. The crystallinity of the PA-6 was slightly affected by addition of organoclay and chain extender. The samples obtained by linear twin screw extrusion showed higher rheological properties than the samples from laboratory scale mixers suggesting better mixing and less thermal degradation during extrusion. / Republic of Turkey, Ministry of National Education. / The full text was made available at the end of the embargo, 31st Dec 2019.
8

Online Impedance Spectroscopy of Thermoset Nanocomposites for Materials In Situ Process Control

Jacobs, John David 28 July 2009 (has links)
No description available.
9

The Chemistry of Dimethacrylate-Styrene Networks and Development of Flame Retardant, Halogen-Free Fiber Reinforced Vinyl Ester Composites

Rosario, Astrid Christa 12 December 2002 (has links)
One of the major classes of polymer matrix resins under consideration for structural composite applications in the infrastructure and construction industries is vinyl ester resin. Vinyl ester resin is comprised of low molecular weight poly(hydroxyether) oligomers with methacrylate endgroups diluted with styrene monomer. The methacrylate endgroups cure with styrene via free radical copolymerization to yield thermoset networks. The copolymerization behavior of these networks was monitored by Fourier Transform Infrared Spectroscopy (FTIR) at various cure conditions. Reactions of the carbon-carbon double bonds of the methacrylate (943 cm-1) and styrene (910 cm-1) were followed independently. Oligomers possessing number average molecular weights of 700 g/mole were studied with systematically increasing levels of styrene. The Mortimer-Tidwell reactivity ratios indicated that at low conversion more styrene was incorporated into the network at lower cure temperatures. The experimental vinyl ester-styrene network compositions deviated significantly from those predicted by the Meyer-Lowry integrated copolymer equation at higher conversion, implying that the reactivity ratios for these networks may change with conversion. The kinetic data were used to provide additional insight into the physical and mechanical properties of these materials. In addition to establishing the copolymerization kinetics of these materials, the development of halogen free fiber reinforced vinyl ester composites exhibiting good flame properties was of interest. Flame retardant vinyl ester resins are used by many industries for applications requiring good thermal resistance. The current flame-retardant technology is dependent on brominated vinyl esters, which generate high levels of smoke and carbon monoxide. A series of halogen free binder systems has been developed and dispersed in the vinyl ester to improve flame retardance. The binder approach enables the vinyl ester resin to maintain its low temperature viscosity so that fabrication of composites via Vacuum Assisted Resin Transfer Molding (VARTM) is possible. The first binder system investigated was a polycaprolactone layered silicate nanocomposite, which was prepared via intercalative polymerization. Transmission Electron Microscopy (TEM) and X-ray Diffraction (XRD) data indicated a mixed morphology of exfoliated and intercalated structures. The mechanical properties and the normalized peak heat release rates were comparable to the neat vinyl ester resin. Alternative binder systems possessing inherent flame retardance were also investigated. A series of binders comprised of novolac, bisphenol A diphosphate, and montmorillonite clay were developed and dispersed into the vinyl ester matrix. Cone calorimetry showed reductions in the peak heat release rate comparable to the brominated resin. / Ph. D.
10

Electrodeposition of Nickel and Nickel Alloy Coatings with Layered Silicates for Enhanced Corrosion Resistance and Mechanical Properties

Tientong, Jeerapan 08 1900 (has links)
The new nickel/layered silicate nanocomposites were electrodeposited from different pHs to study the influence on the metal ions/layered silicate plating solution and on the properties of the deposited films. Nickel/layered silicate nanocomposites were fabricated from citrate bath atacidic pHs (1.6−3.0), from Watts’ type solution (pH ~4-5), and from citrate bath at basic pH (~9). Additionally, the new nickel/molybdenum/layered silicate nanocomposites were electrodeposited from citrate bath at pH 9.5. The silicate, montmorillonite (MMT), was exfoliated by stirring in aqueous solution over 24 hours. The plating solutions were analyzed for zeta potential, particle size, viscosity, and conductivity to investigate the effects of the composition at various pHs. The preferred crystalline orientation and the crystalline size of nickel, nickel/layered silicate, nickel/molybdenum, and nickel/molybdenum/layered silicate films were examined by X-ray diffraction. The microstructure of the coatings and the surface roughness was investigated by scanning electron microscopy and atomic force microscopy. Nickel/molybdenum/layered silicate nanocomposites containing low content of layered silicate (1.0 g/L) had increase 32 % hardness and 22 % Young’s modulus values over the pure nickel/molybdenum alloy films. The potentiodynamic polarization and electrochemical impedance measurements showed that the nickel/molybdenum/layered silicate nanocomposite layers have higher corrosion resistance in 3.5% NaCl compared to the pure alloy films. The corrosion current density of the nickel/molybdenum/layered silicate nanocomposite composed of 0.5 g/L MMT is 0.63 µA·cm-2 as compare to a nickel/molybdenum alloy which is 2.00 µA·cm-2.

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