Acid- and amide-controlled sol–gel synthesis of SiO2-based polymer composites

Lithium aluminate (LiA102) has received much attention due to its promising use as a tritium breeding material in fusion reactors [1, 2], and as an electrolyte matrix for the molten carbonate fuel cell (MCFC) [3, 4]. LiA102 powder can be prepared by a solid-state reaction between 7-A1203 and a lithium compound such as carbonate and hydroxide, or a sol-gel method starting from metal alkoxides [11]. The sol-gel processing of LiA102 produces a powder with a better controlled ratio of lithium to aluminum due to the low processing temperature [5]. Various combinations of alkoxides of lithium and aluminum were tested to prepare LiA102 powder by Turner et al. [7]. They found that amorphous LiA102 was directly transformed to v-LiA102 at temperatures as low as 550 °C, when lithium methoxide and aluminium n-butoxide were hydrolyzed at 25 °C. Most of the research on the sol-gel route to LiA102 has involved preparation with powders; preparation methods using monolithic porous LiA102 were not seriously examined. In this letter, we propose a direct route to the preparation of pore-controlled monolithic LiA102 by a sol-gel method. Crack formation over the drying period has limited accessibility to this monolithic route [7, 8]. There have been several suggestions to avoid cracks during drying, such as DCCA (drying control chemical additive) addition [9], supercritical drying, and freeze drying [10]. The DCCA addition method has advantages over other methods. First, no costly additional equipment, such as high pressure equipment or freeze drier, is needed. Secondly, porosity can be controlled by varying the amount of DCCA or other additives such as carbon black or active carbon. Currently, fonnamide, dimethylformamide (DMF) [7, 8], glycerol, and oxalic acid [8] are widely used as a DCCA. Regarding the role of a DCCA, it is reported that the DCCA makes pore size larger and reduces capillary stress [7]. Specific roles of the DCCA, however, vary depending on the types of DCCA, and are not yet fully understood. The procedure for preparing monolithic gel is summarized in Fig. 1. Lithium isopropoxide (LiOC3H7) and aluminium isopropoxide (AI[OC3 H713), 0.05 moles of each, were mixed with 100 ml of isopropanol in a three-neck flask. This mixture was then stirred with a magnetic stirrer at 80 °C. After 2 h of stirring, yellowish brown precipitates were obtained at the bottom of the flask. These precipitates were mixed with 200 ml of ethanol, refluxing under nitrogen gas at 80 °C for 2 h. The 2012 I-'soUtrhp uomx'de ]

Influence of the synthesis process on the features of Y2O3-stabilized ZrO2 powders obtained by the sol–gel method

Effect of method of preparation and drying time on photophysical properties of coumarin 1 laser dye embedded in HCl catalysed sol–gel glasses

Sol–gel chemistry is an efficient tool to control the morphology and reactivity of solids. Drying is the crucial step due to the capillary forces exerted during the classic ambient drying process, which induces the collapse of the wet gel porosity. The use of N, N-dimethylformamide (DMF), a newly found DCCA were found to be effective in the sol–gel synthesis of crack-free silica gel monolith from tetraethoxysilane (TEOS) via acid catalyzed. We investigate the effect of N, N- dimethylformamide as DCCAs in simple inorganic silica obtained from tetraethoxysilane (TEOS) and the effects drying control chemical additives (DCCA) on gelatin time and physical properties of the dry gel were examined in an acidic silica sol-gel process.

Glass samples are prepared with different amount of glycerol as drying control chemical additive (DCCA) via acid catalysed sol–gel method. These samples are given solvent treatment namely rinse and dip with methanol while drying of the sample. In rinse treatment solid sample is rinsed with small amount of methanol while in dip treatment sample is dipped for 5 h in methanol. Comparative studies of these treated samples containing varied DCCA concentration are carried out by measuring optical transmission, mechanical strength and bulk density. Various instrumental techniques used for analysis are FTIR, DTA-TGA, XRD, SEM and TEM. The untreated samples take long time to dry up and to come out of the cuvette and show very less transmission in UV region which is much enhanced by solvent treatment. On the basis of this study, the solvent treated glass samples with DCCA amount 8 ml in the composition used are found to have the maximum UV transmission, good mechanical strength and may be useful as silica gel host matrices for solid state dye lasers and other applications. The UV transmission reported in the present studies is 90% in 337 nm region, which is the wavelength of N2 laser pumping.

The use of methylene blue and acetic acid in magnifying endoscopic diagnosis of intestinal metaplasia in Barrett’s esophagus has been reported previously. Recently, the use of acetic acid or narrow-band imaging (NBI) has been described in magnifying endoscopic diagnosis of intramucosal adenocarcinomas arising from Barrett’s esophagus. Diagnosis by NBI is based on the examination of microvascular patterns. The characteristic microvascular patterns of intramucosal adenocarcinomas in Barrett’s esophagus are the mesh pattern and the loop pattern. The former appears on the lesion with dense round pits and the latter tend to appear on the lesion with elongated cancerous crypts. Acetic acid is used in the two methods of magnifying endoscopic diagnosis of adenocarcinoma: enhanced-magnification endoscopy and dynamic chemical magnifying endoscopy. In the former, the structure of the mucosal surface is observed after enhancement of the surface color with acetic acid to a clear white. In the latter, the difference between cancerous and noncancerous lesions is observed on the basis of the difference in duration of the whitening. These magnified views are very clear and facilitate the accurate diagnosis of cancerous lesions that are difficult to diagnose by conventional endoscopy. Because they help delineate the extent of cancerous lesions, these new methods of diagnosis support curative surgery of adenocarcinoma in Barrett’s esophagus by endoscopic submucosal dissection.

This paper deals with the preparation of TiO2–SiO2 ceramics by using formamide, glycerol, or oxalic acid as drying control chemical additives (DCCAs) in order to improve the physical properties of the products, control the rates of hydrolysis and polycondensation, as well as the particle size homogeneity and porosity distribution. It was found that when using DCCAs, the gelation time was longer than without any additives. In acidic solution, the hydrolysis reaction is rapid, and the gelation tends to be slow; in an alkaline medium, the polycondensation of Si–OH and Ti–OH groups takes place much faster. The higher rate of nucleophilic substitution associated with the DCCAs leads to larger particles of the bulk ceramics.

Chapter 14 - Greener synthesis and applications of hybrid sol–gel-processed materials

Abstract

Organically modified silicate thin films doped with colourimetric pH indicators methyl red and bromocresol green as pH responsive sol–gel hybrid materials

A new method to synthesize alumina aerogels was introduced in this article. Alumina aerogels were firstly prepared by sol-gel process, using Al(β) inorganic compound as a precursor, 1,2-epoxy propane as a gelation inducing agent (GIA) and methane amide as drying control chemical additive (DCCA), followed by ambient drying method (ADM). The bulk alumina aerogels were examined by TEM, SEM and BET method, which have similar qualities to those prepared by supercritical fluid drying method (SCFM). Propane oxide was introduced to accelerate the gelation rate of Al(β) ions and improve the homogeneity of pore distributions of aerogels, formamide as drying control chemical additive (DCCA) to improve the homogeneity of oxide particles in the gel texture. Alumina gels were aged and reinforced through a solvent exchanging of alcohol, the immersing of tetraethyl orthosilicate (TEOS)/alcohol and absolute alcohol at a certain temperature. The aged gels were dried at the ambient pressure and the bulk alumina aerogels with high surface areas and higher porosity were obtained. On the base of the relationship of the variation of alumina aerogels, structures with molar ratio of propylene oxide/Al, the structure of alumina aerogels can be controlled by adjusting molar ratio of propylene oxide/Al.

The role of N,N-dimethylformamide, a DCCA, in the formation of silica gel monoliths by sol-gel method

Preparation of sol–gel silica samples modified with drying control chemical additives

Influence of the type of solvent on the textural evolution of yttria stabilized zirconia powders obtained by the sol–gel method: Characterization and study of the fractal dimension

Alumina membranes without pinholes and cracks were prepared by the sol-gel process using ammonium aluminium sulphate as the starting material. The effects of different preparing conditions on morphology characteristics of the membrane were investigated by scanning electron microscopy and 3D rotational microscopy. The preparing conditions include the amounts of drying control chemical additives (DCCA), sintering procedure and sol-gel concentration. The results showed that PVA is a good crack-preventing reagent and the morphology of supported membranes was affected by many factors, including Al2O3 concentration, PVA/Al2O3 ratio, heating rate, membrane thickness and intrinsic defects of the substrate surface.