Particle Size Of Sol Research Articles

Tailoring the particle size of sol–gel derived silver nanoparticles in SiO 2

Metallic silver nanoparticles were prepared by the sol–gel method in amorphous SiO 2 matrix. The process includes complexation of an appropriate silicon alkoxide with AgNO 3, hydrolysis, polycondensation, and subsequent thermal treatment of the resulting powder. The thermal treatment conditions were optimized by differential thermal analysis (DTA) and differential thermal gravimetry (DTG) measurements. The size of the particles were determined by transmission electron microscopy (TEM) study. The metal particles were monodispersed in size and their mean diameters varied between 1 and 10 nm, depending upon the processing conditions. The particle size distributions were log-normal showing that the dominant particle growth mechanism is the coalescence. The effect of the oxidation temperature, the duration of oxidation, and the metal concentration on the particle size distribution was studied.

Functional Nanostructured Silica Powders Derived from Colloidal Suspensions by Sol Spraying

The preparation of silica powders derived from sols with a variety of primary particle sizes from 4 to 100 nm and the influences of preparation conditions such as drying temperature and initial concentration of precursor on the final powders morphology were investigated for the first time. The prepared silica powders have spherical morphology, and the final diameter (between 0.1 and 2 um) was controlled by changing the concentration of starting colloidal suspension. The preparation of silica based luminescent powders was investigated by adding europium ion as the dopant. The Eu-doped silica powders showed a visible-luminescence with wavelength of 613 nm, a red emission, under excitation of 394 nm light source. The effects of Eu-doping concentration, operation temperature and primary particle size of silica sols on the luminescence were also investigated.

Preparation of Stabilized Nanosized Tin Oxide Particles by Hydrothermal Treatment

Stable colloidal suspensions of tin oxide (content 0.9–6.1 wt%) were synthesized by subjecting conventionally prepared tin oxide gels to hydrothermal treatment with an ammonia solution (pH 10.5) at 200°C for 3 h in an autoclave. Based on X‐ray diffractometry analyses, the tin oxide crystallites after hydrothermal treatment were resistant to thermal growth at elevated temperatures, and this feature became more conspicuous as the tin oxide content of the colloidal suspension decreased. For the powder derived from a 1.8 wt% colloidal suspension, for example, the mean sizes of the tin oxide crystallites were 7.5 and 13 nm after calcination at 600° and 900°C, respectively, in comparison with corresponding values of 13.5 and 29 nm for the untreated gel‐derived powder. Thin film spin‐coated from the same suspension had good uniformity, packed with tin oxide grains (crystallites) of a mean size of 6 nm after calcination at 600°C. Optical determination of the tin oxide sol particle size, as well as gravimetric analysis of the dehydration from the powder samples, were conducted to determine effects of hydrothermal treatment.

Aqueous Sol−Gel Process in the Silica−Metasilicate System. A Microrheological Study

The electrochemical quartz crystal microbalance (EQCM) was used to investigate the sol−gel process from an aqueous sodium metasilicate solution at 25 °C and pH 3. From the EQCM data it was possible to obtain information on the changing rheological properties of the system during the whole process. Besides sensing changes in the rheological properties, the EQCM detected film formation on the sensor surface. This additional information was used to estimate, using a model for film formation kinetics, the sol particle size (the model prediction was confirmed by light scattering measurements). The particle size estimation was of importance in the analysis of the sol viscosity behavior during the earlier stages of the particle aggregation process. The analysis, based on a classical model for the viscosity of a dispersion of charged particles in an electrolyte, provided some insight into the initial aggregation phenomena and microgel formation. Determination of the gelling point was made by examining the evoluti...

The influence of the aging time of RuO 2 and TiO 2 sols on the electrochemical properties and behavior for the chlorine evolution reaction of activated titanium anodes obtained by the sol-gel procedure

The influence of the aging time of RuO 2 and TiO 2 sols used for the preparation of (40% RuO 2+60% TiO 2)/Ti anodes by the sol-gel procedure on the electrochemical properties and behavior for the chlorine evolution reaction of obtained anodes was studied. The electrochemical (active) surface area of the anode coatings was examined by cyclic voltammetry. The electrocatalytic activity and stability of obtained anodes for the chlorine evolution reaction were investigated by polarization measurements and accelerated stability test. The dependence of electrochemical properties of obtained activated titanium anodes on RuO 2 and TiO 2 sol particle size was established.

Hydrothermal treatment of tin oxide sol solution for preparation of thin-film sensor with enhanced thermal stability and gas sensitivity

The effects of treating tin oxide gel hydrothermally in an ammonia solution at 200°C for 3 h were studied. The size of sol particles increased with increasing concentration of the resulting sol solution, i.e., 5, 8, 10 and 32 nm for 1.8, 3.2, 6.1 and 8.6 wt.% tin oxide sol as determined by an optical analyzer, whereas the crystallite size of tin oxide determined by X-ray diffraction analysis remained to be about 5–7 nm for all the solutions. The tin oxide powder collected was found to be resistant to grain growth on calcination, depending on the concentration of the sol solution. This tendency was maintained in the thin-films spin-coated on an alumina substrate from the sol solutions. The grain size of the film derived from 1.8 wt.% tin oxide sol was smaller than 10 nm in diameter after calcination at 600°C. This particular film exhibited an outstanding by high sensitivity to 800 ppm H 2 at 350°C, compared with conventional tin oxide elements of a sintered block type.

Film formation in the Bi2O3 — TiO2 — Fe2O3 ternary system

The processes of film formation in a ternary system are studied, beginning with the preparation of the working solution and up to coat firing. It is demonstrated that the properties and quality of a coating are determined at the stage of preparing a film-forming solution and depend on the size and shape of the sol particles, the film porosity, and the diffusion process at the glass-film interface.

Preparation and characterization of alumina membranes and alumina–titania composite membranes

Supported and unsupported γ-alumina membranes and alumina–titania composite membranes were prepared using the sol-gel method. In the course of preparation, effects of acid concentration, type of acid, alkoxide, and binder on the particle size of the sols and pore size of the membranes were investigated by thermogravimetry and differential thermal analysis, N2 physisorption, and light scattering. It was observed that the particle sizes of all the sols had only a small affect on the pore sizes of the membranes. Qualities of the membranes were improved by addition of polyvinyl alcohol as binder to the boehmite precursor. This resulted in less critical but more controllable drying and calcining procedures. Composite membranes with different pore sizes from 3.2 to 4.8 nm and surface areas retained above 100 m2/g could be regulated by different alumina-to-titania ratios.

Preparation of Silica and Alumina Single Oxides from Commercial Preformed Sols

High surface area silica and alumina powders were prepared from four commercially available colloidal silicas (Nyacol 830, 2040, 9950, and 2034DI) and three colloidal aluminas (Dispal 23N4−20, 18N4−20, and 11N7−12). Particle size distributions of the sols were obtained from dynamic light-scattering experiments and found to deviate significantly from the nominal sizes reported by the manufacturer. The sols were gelled via several methods, dried, and calcined at 773 K and above. A spherical particle packing model based on the measured sol particle size distributions was found to account for important textural properties such as surface area and pore volume of the calcined silica powders. For the calcined alumina powders, a better predictor for the textural properties was the crystallites whose aggregates form the precursor alumina sol. Nitrogen adsorption, diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy, and X-ray diffraction studies of the calcined silica and alumina powders were used t...

Effect of aging temperature on the structure of mullite precursor prepared from tetraethoxysilane and aluminum nitrate in ethanol solution

The effect of aging temperature on the structure of mullite precursor prepared by dissolving tetraethoxysilane (TEOS) and aluminum nitrate nonahydrate (ANN) in ethanol was investigated by liquid state 29Si and 27Al nuclear magnetic resonance (NMR) spectroscopy, small angle X-ray scattering (SAXS), powder X-ray diffraction (XRD) and solubility of ANN in ethanol. The aging temperatures examined were from 25 to 60 °C. With increasing aging temperature, polymerization of TEOS progressed, size of sol particles increased, and solubility of ANN largely increased but little change occurred in the coordination state of the Al ion. Mullite was obtained as the main crystalline phase only when the precursor solution aged at 60 °C was fired at 1000 °C, whereas the spinel phase was obtained as the main crystalline phase instead of mullite from the solutions aged at the other temperatures. It was therefore concluded that silica and alumina components in the precursor solution were in an intimately mixed state when the precursor solution was aged at 60 °C, but those aged under 60 °C were not as intimately mixed as the former. Intimate mixing of both components was achieved in the precursor solution aged at 60 °C by trapping of ANN solution in silica gel network.

A diffusion-controlled procedure to close pores in ceramic membranes

A diffusion-controlled caulking treatment using aqueous colloidal silica to plug large pores in ceramic membranes is described. Unlike the conventional slip-casting process, this more controllable process can, in principle, be tailored by proper silica particle size selection to allow minimal deposition in the small desirable pores while enabling the elimination of large, less selective pores. The 2000 Å Anodisc® membrane has been chosen as a model for the development of the procedure. Via the diffusion-controlled process, a majority of the 2000 Å pores were closed using 100 to 200 Å silica with negligible deposition on external membrane surfaces. The technique, therefore, is promising for selective closure of large undesirable pores without surface fouling or closure of desirable 100 Å or smaller pores. The efficiency of the procedure has been characterized by a number of independent methods. The gas and water permeability of the caulked membranes decreased one and two orders of magnitude, respectively. Pore size analyses by a variation of the bubble point test and by rejection measurements of polyethylene glycol (MW 1500 to 12000) have found the average pore size of the dried silica-treated membranes to be approximately equal to the precursor silica sol particle size used in the treatment. While this suggests less than close packing in the large pores, the low permeability of the silica-treated membrane demonstrates that the treatment is highly effective. Indeed, given the selective caulking capability of this approach, it appears to be an attractive means of healing defects in microporous ceramic membranes.

Time dependence of particle size and particle number of silica sols under reflux conditions

In this paper some results of work on the kinetics of aggregation of silica particles obtained by the sol-gel method are reported. The silica gel was prepared by mixing tetraethyl orthosilicate, ethanol, water, and a cobalt salt (cobalt (II) acetylacetonate). The chemical reaction was carried out under reflux conditions ( T = 75°C). The aggregation was followed using dynamic light scattering from the onset of the chemical reaction. A systematic and reproducible behavior of the growth of the silica sols was obtained. The system begins with sols of relatively small sizes (around 100 nm), but within a short time the particle size increases to around 1 μm. After this increase, damped oscillations in size are observed until the radius remains constant. The particle size in this regime is similar to the initial values of the sols. The oscillations in the particle size profile can be explained as being a non-linear effect in the chemical process because one stage of the reaction is autocatalytic.

Small angle neutron scatteirng investigations of water sorption in porous silica and ceria gels

The processes of adsorption and capillary condensation of water in silica and ceria gels having different pore sizes have been investigated by small angle neutron scattering (SANS). These gels have been prepared by a sol—gel method and are composed of monosized spherical particles packed with a defined short-range order. Mean pore sizes, r p, were controlled by the sol particle size and were ∼ 2.9 and ∼ 2.0 nm for silica gels and < 2.0 nm for the ceria gel. SANS measurements have been made at progressive stages of equilibrium water uptake by exposing the gels to increasing vapor pressures. By selecting the water composition ( H 2 O D 2O ratio) to give a contrast match with the oxide adsorbent, it has been made possible to analyze changes in the SANS behavior in terms of the development of an adsorbed film and growth of a capillary-condensed meniscus at the points of particle contact. Such an analysis is satisfactory for the two mesoporous silica gels but does not accord with the behavior of the microporous ceria gel. Here there is evidence that a volume filling process occurs, where the density of the sorbate is appreciably less than that in the bulk. This lower density is tentatively ascribed to a difference in the ordering of water molecules when they are confirmed in the micropores compared to that imposed by H bonding in the bulk liquid.

Thermodynamic considerations on the contribution of the dissociation of silanol groups to the stability of silica sols

A new relationship for the free energy of silanol-group dissociation on silica sol particles is derived, including both an electrical and a chemical part. Using an equation for the calculation of the dissociation equilibrium based on the simple Gouy-Chapman model of the electrochemical double layer, we discuss the contribution of this term to stabilization of silica sol in a weak alkaline aqueous dispersion. We find minima of the Helmholtz free energy in dependence on dispersion composition. They are identified as stable states in a thermodynamic sense. Relation results between sol composition and particle size of thermodynamic stable states.

Titania and alumina ceramic membranes

This paper discusses the physical-chemical properties of γ-Al 2O 3 and TiO 2 ceramic membranes which have been prepared by sol-gel techniques from alkoxide starting materials. Mean pore size and pore size distributions are examined using N 2 sorption analysis. Particle size of sols as measured by in situ quasi-elastic light scattering is compared with SEM analysis of sintered membranes. Crack-free unsupported monoliths with thicknesses up to 120 μm have been prepared of γ-Al 2O 3. Supported TiO 2 membranes have been fabricated with thicknesses up to 0.5 μm. The γAl 2O 3 membranes are obtained from “particulate” sols, while for TiO 2 both “particulate” and “polymeric” sols have been used to produce membranes.

Physico-Chemical Properties of Supported and Unsupported γ-Al2-O3 and TiO2 Ceramic Membranes

Abstract Supported and unsupported γ-Al2O3 and TiO2 ceramic membranes have been prepared by sol-gel techniques from alkoxide precursors. Several physico-chemical properties of these materials have been determined. N2 sorption analysis has been used to determine pore size distributions and mean pore sizes. Particle sizes of sols as measured by “in situ” quasi-elastic light scattering are discussed in the light of SEM analyses of the sintered membranes prepared from these sols. Crack-free unsupported monoliths of Al2O3 with thicknesses up to 100 μm have been prepared. Similarly, supported Al2O3 and TiO2 membranes with thicknesses of 0.5 μm have been produced. Preliminary measurements of the permselectiyities of supported membranes have also been made.

Preparation of Pb (Ti, Zr) O&lt;sub&gt;3&lt;/sub&gt; Precursor Sols from Metal Alkoxides

Clear PZT sols have been prepared by controlled hydrolysis of Pb, Ti and Zr mixed alkoxide solutions in methoxy-ethanol. The water/methoxy-ethanol ratio which gives clear sol decreases with increasing alkoxide concentration at a constant alkoxide composition, and decrease as Zr alkoxide in Pb and Zr mixed alkoxide is substituted by Ti alkoxide. Sols dried at 70°C were analyzed by XRD, TEM and EDX. The particle size of sols was 10-40nm by TEM, which depends on the composition. The XRD result showed that dried powders are amorphous, which crystallize at above 600°C. EDX analysis of particles showed that PbTiO3 and PbZrO3 powders are chemically homogeneous at a particle level. On the other hand, PZT powder was less homogeneous.

Surface-enhanced raman spectroscopy using nonaqueous colloidal silver

Silver colloids have been prepared by the direct borohydride reduction of silver nitrate in a variety of nonaqueous solvents: acrylonitrile, tetrahydrofuran, dimethyl sulfoxide, acetonitrile, and N,N′dimethylformamide (DMF). The dispersions were stable without the addition of ionic or polymeric stabilizing agents. Colloidal silver is formed spontaneously in DMF upon the addition of AgNO 3. UV—visible absorption spectrophotometry has been used to characterize sol particle size and sol stability. Colloids prepared in DMF and CH 3CN are suitable for use in surface-enhanced Raman spectroscopy (SERS). The first SERS spectrum of a neutral species adsorbed at a nonaqueous-metal interface has been obtained: that of tert-butylamine in an acetonitrile silver sol. This is also the first SER spectrum obtained from an anhydrous colloidal dispersion. The adsorbate-surface interactions and adsorbate orientation are discussed.

Surface‐Enhanced Raman scattering spectra of aqueous silver borohydride sols of pyridine and deuterium‐containing pyridines

AbstractSurface‐enhanced Raman scattering spectra of aqueous silver horohydride sols of pyridine, pyridine‐4‐d, pyridine‐2,6‐d2 and pyridine‐3,5‐d2 are reported. Depolarization ratios are given as a function of pyridine concentration for a number of pyridine bands over a substantial range of concentrations. Evidence is presented of multiple site adsorption and a new interpretation of these Raman spectra is proposed. The evidence indicates that the surface enhancement derives essentially from the presence of long linear segments of chains of silver spheres in the aggregating sols. The concentration dependence of the depolarization ratios and of the average silver sol particle size show that the depolarization ratio characterizes the extent of dendritic growth of sol aggregates and is thus the same for every Raman band in a given preparation at the same time in the history of its evolution, independent of the rotational characteristics of the sol particles or of the adsorbed pyridine molecules.

Estimation of Specific Surface of developed Silver by Thiosulphate Adsorption*

AbstractBy tracer methods it was demonstrated that thiosulphate is most tenaciously adsorbed to developed silver or silver foil. A limiting amount was held by any surface: one thiosulphate ion being estimated for every three silver atoms in the surface. On bleaching developed silver with acid dichromate, no decrease in radioactivity occurred, demonstrating quantitative formation of silver sulphide from adsorbed thiosulphate. On the basis of these observations, the silver sulphide content of bleached photographic images can be used to estimate the specific surface of the silver. Reasonable estimates were obtained of the particle size of a Carey-Lea silver sol. In agreement with earlier X-ray determinations, the mean filament diameters of developed silver from a series of emulsions did not increase much with increased undeveloped grain size.