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Master's Dissertation
DOI
https://doi.org/10.11606/D.76.1994.tde-02042015-160721
Document
Author
Full name
Mauricio Simões de Lima
Institute/School/College
Knowledge Area
Date of Defense
Published
São Carlos, 1994
Supervisor
Committee
Aegerter, Michel Andre (President)
Eiras, José Antonio
Messaddeq, Younes
Title in Portuguese
Preparação e caracterização de mulita coloidal (3Al2O32SiO2) obtida pelo processo sol-gel
Keywords in Portuguese
Não disponível
Abstract in Portuguese
Neste trabalho, géis com composição de mulita estequiométrica (3Al2O3.2SiO2) contendo em peso 74% de Al2O3 e 26% de SiO2 foram preparados pelo processo sol- gel, a partir de uma dispersão coloidal de boemita (AlOOH) e uma solução de tetraetoxissilano [Si(OC2H5)4], variando as condições de pH e submetendo os produtos a vários tratamentos térmicos. O tamanho das partículas das dispersões coloidais de boemita foi determinado por espectroscopia de correlação de fótons e este e ∼ 70 nm. As fases cristalográficcas dos géis foram identificadas por difratometria de raio-X do pó, mostrando basicamente a presença de boemita e sílica amorfa a 60°C; sílica amorfa e alumina spinel a 500°C; sílica amorfa, uma fase spinel e as fases δ ,θ - alumina a 980°C; somente a fase mulita em 1250 e 1400°C para os géis preparados em pH 2.5 e as fases mulita e α - alumina nas mesmas temperaturas nos outros pH. A presença de mulita como fase única nos géis preparados em pH 2.5 leva a interpretação de maior homogeneidade neste valor de pH no processo de mistura dos precursore. Os resultados de análise de energia dispersiva de raio-X (EDX) e as analises térmicas diferencial (ATD) corroboram esta interpretação. A textura dos géis foi determinada por porosimetria gasosa de nitrogênio e mercúrio. Os materiais preparados em pH:s 1.5 e tratados a 60°C apresentam isotermas do tipo I e histereses do tipo H4 típicas de microporos (diâmetro < 2,5 nm). Os géis obtidos nos demais pH ,independente da temperatura, apresentam isotermas do tipo IV e histereses do tipo H2 típicas de mesoporos (diâmetro de poro entre 2.5 e 50 nm). A área superficial BET esta no intervalo de 40 a 300 m2/g. O tamanho médio de poro esta no intervalo de 2 a 14 nm. Os géis preparados em pH 1.5 e tratados a 500 e 980°C apresentam distribuições estreitas de tamanho de poro (∼ 4nm). A microestrutura dos géis foi determinada por microscopia eletrônica de varredura (MEV). Para os géis preparados em pH 2.5 e tratados a 1250 e 1400°C fez - se uma estimativa do tamanho médio de grãos pelo método planimétrico ou de Jeffries, obtendo-se 0.68 μm ± 0.04 μm e 0.84 μm ± 0.05 μm, respectivamente
Title in English
Not available
Keywords in English
Not available
Abstract in English
Gels with composition of the stoichiometric mullite (3Al2O3.2SiO2) containing 74% of Al2O3 and 26% of SiO2 in weight have been obtained by the sol - gel process. The sols have been prepared by mixing a colloidal dispersion of the boehmite (AlOOH) particles of 70 nm size and a tetraethoxysilane [Si(OC2H5)4] under pH of 0.5, 1.5, 2.0, 2.5 and 3.0. The gels have been submitted to various thermal treatments. Their crystallographic phases have been determined by powder X-ray diffraction. We have the presence of the boehmite and amorphous silica at 60°C; amorphous silica and spinnel alumina at 500 °C; amorphous silica, a spinnel phase and δ, θ - alumina at 980°C, mulite phase at 1250 and 1400°C for the gels prepared in pH 2.5 and mulite phase and α - alumina at the same temperatures in gels prepared at others pH. The presence of the mulite as unique phase in the gels prepared in pH 2.5 is due to a higher homogeneity of the precursors in the sols. The results of Energy Dispersive X-ray Analysis (EDX) and Differential Thermal Analysis (DTA) agree with this interpretation. The texture of the gels was determined by nitrogen and mercury porosimetry The materials prepared in pH ≤ 1.5 and heat treated at 60 °C show type I isotherms and type H4 hysteresis, typical of micro pores (diameter < 2.5 nm). The gels obtained at other pH, independently of the heat treatment temperature, show type IV isotherms and type H2 hysteresis, typically of mesopores (diameter 2.5-50 nm). The BET superficial area is around 40- 300 m2/g with an average size pore of approximately 2-14 nm. The gels prepared at pH 1.5 and heated at 500 and 980°C have a narrow distribution of pore size (∼ 4 nm) . The microstructure of the gels has been determined by Scanning Electron Microscope (SEM). The grain size has been estimated by the planimetric or Jeffries's method of the gels prepared at pH 2.5 and heat treated at 1250 and 1400°C; and found 0.68 μm ± 0.04 μm and 0.84 μm ± 0.05 μm, respectively
 
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2015-04-07
 
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