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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

Impregnação de Pinus Caribaea Hondurensis com álcool furfurílico e tetra-etil-ortosilicato / Pinus Caribaea Hondurensis infused with furfuryl alcohol and tetra ethyl orthosilicate

Magalhães, Washington Luiz Esteves 08 September 1998 (has links)
Pinus caribeae hondurensis foi impregnado pelo processo vácuo/pressão, com tetra etil ortosilicato (TEOS) e álcool furfurílico (FFA). Os reagentes foram introduzidos com seus respectivos catalisadores ácidos, e após aquecimento promoveu-se a polimerização no interior da madeira. Os métodos de caracterização utilizados foram a difração de raios-X, a microscopia eletrônica, a espectroscopia de infravermelho e a ressonância nuclear magnética de sólido. O tratamento com TEOS trouxe pequenas melhorias na resistência mecânica e na estabilidade dimensional da madeira. Houve formação do gel de TEOS entre as cadeias de celulose com diminuição de sua cristalinidade. Foram analisadas as causas da perda de resistência mecânica e aumento da estabilidade dimensional da madeira tratada com FFA. A madeira impregnada com FFA apresentou aumento da cristalinidade da celulose e comportamento frágil na fratura. A resina de FFA não preenche o lúmem das células da madeira, mas reage com os sítios OH e deposita-se na superficie das paredes celulares. O duplo tratamento, primeiramente com TEOS e depois com FFA, melhora a estabilidade dimensional sem diminuir a resistência mecânica da madeira / Pinus caribeae hondurensis was infused with tetra ethyl orthosilicate (TEOS) and furfuryl alcohol (FFA) using the vacuum/pressure processing. The reagents were instilled together with theirs acidic catalysts. After heat processing, the reaction was started within the wood. The characterization was carried out using of x-ray diffraction, scanning electron microscopy, infrared spectroscopy and solid state nuclear magnetic resonance. Infusing wood with TEOS leads to slight enhancements of the mechanical resistance and dimensional stability. Gel from TEOS reactions was formed between the cellulose chains with decrease of cristalinity. The causes of mechanical resistance lowering and dimensional stability increase were analyzed in wood treated with FFA. FFA instilled wood showed increased cellulose cristalline ordering and also fragile fracture behavior. FFA resin did not soak into the wood cell lumen, but reacted with OH sites and covered the cell wall surfaces. Double treated wood, first with TEOS and later with FFA, had the dimensional stability improved without decrease in mechanical resistance
2

Impregnação de Pinus Caribaea Hondurensis com álcool furfurílico e tetra-etil-ortosilicato / Pinus Caribaea Hondurensis infused with furfuryl alcohol and tetra ethyl orthosilicate

Washington Luiz Esteves Magalhães 08 September 1998 (has links)
Pinus caribeae hondurensis foi impregnado pelo processo vácuo/pressão, com tetra etil ortosilicato (TEOS) e álcool furfurílico (FFA). Os reagentes foram introduzidos com seus respectivos catalisadores ácidos, e após aquecimento promoveu-se a polimerização no interior da madeira. Os métodos de caracterização utilizados foram a difração de raios-X, a microscopia eletrônica, a espectroscopia de infravermelho e a ressonância nuclear magnética de sólido. O tratamento com TEOS trouxe pequenas melhorias na resistência mecânica e na estabilidade dimensional da madeira. Houve formação do gel de TEOS entre as cadeias de celulose com diminuição de sua cristalinidade. Foram analisadas as causas da perda de resistência mecânica e aumento da estabilidade dimensional da madeira tratada com FFA. A madeira impregnada com FFA apresentou aumento da cristalinidade da celulose e comportamento frágil na fratura. A resina de FFA não preenche o lúmem das células da madeira, mas reage com os sítios OH e deposita-se na superficie das paredes celulares. O duplo tratamento, primeiramente com TEOS e depois com FFA, melhora a estabilidade dimensional sem diminuir a resistência mecânica da madeira / Pinus caribeae hondurensis was infused with tetra ethyl orthosilicate (TEOS) and furfuryl alcohol (FFA) using the vacuum/pressure processing. The reagents were instilled together with theirs acidic catalysts. After heat processing, the reaction was started within the wood. The characterization was carried out using of x-ray diffraction, scanning electron microscopy, infrared spectroscopy and solid state nuclear magnetic resonance. Infusing wood with TEOS leads to slight enhancements of the mechanical resistance and dimensional stability. Gel from TEOS reactions was formed between the cellulose chains with decrease of cristalinity. The causes of mechanical resistance lowering and dimensional stability increase were analyzed in wood treated with FFA. FFA instilled wood showed increased cellulose cristalline ordering and also fragile fracture behavior. FFA resin did not soak into the wood cell lumen, but reacted with OH sites and covered the cell wall surfaces. Double treated wood, first with TEOS and later with FFA, had the dimensional stability improved without decrease in mechanical resistance
3

Chemical Changes in Groundwater of Northern Utah Valley, Utah

Fairbanks, Paul E. 01 May 1982 (has links)
Northern Utah Valley is one of the fastest growing areas of Utah and has increasing needs for domestic, industrial, and agricultural water. To meet these needs, groundwater and surface water systems must be understood to maximize their use. Chemical studies of the sediment mineralogy and related water-chemistry give insight to the movement of the water. There are three major aquifers present in the valley: shallow Pleistocene; deep Pleistocene; and Tertiary. They are composed of sands and gravels and are separated by confining layers (aquitards) composed mostly of clay. Along the flanks of the bordering mountains there are undifferentiated aquifers which act as conduits supplying water for aquifers in the valley. Sediment samples from aquifers and confining layers were obtained by rotary and cable-tool drilling. X-ray diffraction analyses showed that the aquifers are mainly composed of quartz, calcite, and dolomite, whereas the con fining layers contain illite and montmorillonite with some kaolinite, quart z and calcite. One hundred nine water samples were collected in this study from s ur face water, spring water, undifferentiated aquifer water, shallow Pleistocene aquifer water, deep Pleistocene aquifer water and Tertiary aquifer water. Results show that the ground water system has several geochemical cells in each aquifer, due to diverse areas of recharge. Three major water types can be identified in different areas of the shallow Pleistocene aquifer, three in different areas of the Tertiary aquifer, and four in different areas of the deep Pleistocene aquifer. The differences in these water types are related to the composition of the mountain recharge areas and positions of faults within the valleys. The aquifer composition exerts relatively little influence on the chemistry of the ground water. Mountains of predominantly carbonate rocks produce recharge waters rich in calcium and bicarbonate. Mountains of predominantly granitic rocks produce recharge water low in mineral content. Valley sediments near major faults produce highly mineralized waters.
4

What is a Chemical? Fourth-Grade Children's Categorization of Everyday Objects and Substances

Emenike, Mary Elizabeth 02 September 2010 (has links)
No description available.

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