Sol-gel synthesis of transparent alumina gel and pure gamma alumina by urea hydrolysis of aluminum nitrate

gamma-Alumina was synthesized by a sol-gel method with the aluminum ion hydrolysis control performed by urea. The initial saturated Al3+/urea solution presented urea coordinated with the aluminum ion, as shown in the C-13 NMR and Al-27 NMR spectra and longitudinal relaxation times, T-1, from the latter. The substitution of water molecules in the Al3+ coordination shell by urea controlled the hydrolysis process and provided an extensive nucleation during the initial steps of the aluminum hydroxide formation due to urea thermolysis at 90degreesC. The resulting sol, composed of Al(OH)(3) nanoparticles, coalesced and became a transparent gel permeated by a solution of urea and the polycation ion [Al13O4(OH)(24)(H2O)(12)](7+). The freshly prepared gel was transformed, under heating at 300degreesC, directly to gamma-alumina, characterized by FTIR, Al-27-MAS-NMR and S-BET techniques, without delta- or theta-phases, as a consequence of the high degree of homogeneity of the gamma-alumina precursor.30313514

Kinetics of the gamma ->alpha-alumina phase transformation by quantitative X-ray diffraction

This work reports the kinetics of alpha-alumina transformation from gamma-alumina, prepared by the sol-gel method from a solution of saturated aluminum nitrate and urea. The gamma-alumina phase transformed directly into alpha-alumina at 750, 800, 850 and 900 degrees C, without any intermediate phases, such as theta- or delta-alumina. The kinetics of gamma -> alpha-alumina phase transformation was monitored by determination of alpha-alumina fraction formed through quantitative X-ray diffraction (XRD), with calcium fluoride added as an internal standard. The crystallised fractions of alpha-alumina increased sigmoidally with time, indicating that the gamma -> alpha-alumina phase transformation had a nucleation and growth mechanism. The kinetic parameters for this transformation were determined through the Kolmogorov-Johnson-Mehl-Avrami (KJMA) model and the Arrhenius' law. The apparent activation energy, the Avrami exponent, n, and the t(0.75)/t(0.25) ratio determined for the transformation were, respectively, of (201 +/- 4) kJ mol(-1) (2.1 +/- 0.2) and (2.1 +/- 0.1). The apparent activation energy is lower than the values previously reported for the gamma -> alpha-alumina transformation, as a consequence of the high surface area (425 m(2)/g) of gamma-alumina. The t(0.75)/t(0.25) ratio of (2.1 +/- 0.1) suggested that the alpha-alumina growth was plate-like, which was confirmed by the SEM micrograph of alpha-alumina.4282830283

Experimental and Monte Carlo simulation: the role of urea in mullite synthesis

Mullite was synthesized by a sol-gel process employing aqueous solution of silicic acid, aluminum nitrate and urea in high concentration (9 mol/l), t-Mullite crystallizes at temperatures around 1050 degreesC, the fraction of the spinel phase formed was small and the apparent activation energy obtained by fitting the XRD results with the JMAK model was (770 +/-4) kJ mol(-1). Monte Carlo simulations were performed to investigate the site-site correlation function for ion (I)-urea (Ou) and ion (I)-water (Ow) interactions, g(r(Iou)) and g(r(IOw),), respectively. The integration of these two correlation functions indicated the presence of four water and two urea molecules in the first Al3+ coordination shell. The Al-27 nuclear magnetic resonance (NMR) results also indicate the presence of species like [Al(H2O)(4)(urea)(2)](3+). (C) 2001 Elsevier Science Ltd. All rights reserved.21675976

Cuidados com a pele adotados por gestantes assistidas em serviços públicos de saúde Cuidados con la piel adoptados por gestantes atendidas en servicios públicos de salud Skin Care adopted by pregnant women seen by public health services

OBJETIVOS: Descrever os cuidados com a pele adotados por mulheres no período gestacional e identificar a adequação das práticas utilizadas. MÉTODOS: Estudo descritivo exploratório com participação de 124 gestantes atendidas em quatro unidades básicas de saúde da região Leste do Município de São Paulo. RESULTADOS: A maioria das gestantes afirmou cuidar da pele (74,2%), entretanto, constatou-se inadequação de várias práticas que podem contribuir no desencadeamento de alterações cutâneas; mais da metade das mulheres (56,5%) afirmou não ter recebido orientações acerca dos cuidados com a pele. CONCLUSÕES: Os resultados evidenciaram a importância da inclusão da abordagem sobre os cuidados da pele nos programas de educação em saúde desenvolvidos em serviços que proporcionam atendimento à gestante.<br>OBJETIVOS: Describir los cuidados con la piel adoptados por mujeres en el período gestacional e identificar la adecuación de las prácticas utilizadas. MÉTODOS: Estudio descriptivo exploratorio realizado con la participación de 124 gestantes atendidas en cuatro unidades básicas de salud de la región Este del Municipio de Sao Paulo. RESULTADOS: La mayoría de las gestantes afirmó cuidar la piel (74,2%), no obstante, se constató inadecuación de varias prácticas que pueden contribuir en la aparición de alteraciones cutáneas; más de la mitad de las mujeres (56,5%) afirmó no haber recibido orientaciones acerca de los cuidados con la piel. CONCLUSIONES: Los resultados evidenciaron la importancia de la inclusión de temas relativos al cuidado de la piel en los programas de educación en salud desarrollados en los servicios que proporcionan atención a la gestante.<br>OBJECTIVES: To describe skin care practices used by women during pregnancy and to determine if these practices are adequate. METHODS: A descriptive exploratory study with 124 pregnant women enrolled in four basic health units in the eastern region of São Paulo. RESULTS: Most of the women affirmed that they practiced skin care regimens (74.2%), however, several practices were found to be inadequate and could contribute to the onset of skin changes. More than half of these women (56.5%) noted that they had received guidance about skin care. CONCLUSIONS: The results showed the importance of including information related to skin care when developing health education services for pregnant women