Hydroxide Sol Research Articles

Sorption of chromium hydroxide sol on silica studied by radiotracing

This study was undertaken to investigate the sorption behavior of chromium hydroxide sol on silica type adsorbent in aqueous solution. Radioisotopic tracer method was used to assess data. This technique allowed sensitive kinetic and equilibrium measurements in both direction: sorption and desorption, which are strongly dependent on solution conditions, such as pH, ionic strength or the presence of complexing species. Total removal of sol particles could not be achieved, even under the most favorable experimental conditions (acidification).

Structure and properties of sol-gel obtained SnO 2 and SnO 2-Pd films

Transparent fine-granular SnO 2 and SnO 2-Pd films (SnO 2 verage particle size 25–30 nm) have been obtained by annealing of tin hydroxide sols, stabilised with oleic acid. The structure of the films was investigated by TEM, ED and Mössbauer spectroscopy. In SnO 2-Pd films, annealed at 800 °C, palladium is present as homogeneously distributed thermally stable particles ( d = 5–8 nm). Observed isomeric shifts of 119Sn Mössbauer spectra suggests the presence of partially reduced tin ions, Sn 2+ and Sn 3+, in the films. Deeper reduction of SnO 2 and formation of SnO are observed in SnO 2-Pd films, annealed at 500 °C. Thin-film sensors based on sol-gel obtained SnO 2 and SnO 2-Pd are high-sensitive to different gases (H 2, CH 4, NO, CO). They enable detection of CO and CH 4, CO and NO selectively in mixtures by controlling of sensor's operating temperature.

Sol-gel synthesis of lanthanum chromite powder

Alkaline earth-doped LaCrO 3 is a satisfactorily conducting ceramic material for the interconnector of Solid Oxide Fuel Cells (SOFC). For the synthesis of highly sinterable LaCrO 3 powders spraydrying of adequate precursors like sols based on alkoxides has been used. Lanthanum chromium hydroxide sol was prepared by hydrolysis of synthesized methoxide complexes. The chemical reactions during hydrolysis and peptization of the precursors are described. The crystalline phase formation during heat treatment of spray-dried amorphous gel consisting of hydroxides and contaminant chloride ligands was characterized by thermal analysis methods (TG, DTG, DTA) and X-ray diffraction analysis. The progressive oxidation of Cr(III) by thermal dehydroxylation transforms the powder into fine crystallized La(III) Cr(V)hydroxo-oxychloride at 450 °C. A thermal treatment permits complete chlorine removal forming sinterable crystalline LaCrO 3 perovskite powder at temperatures above 720 °C. The same sol-gel process also can be applied to chlorine-free nitrate-containing alkoxide sols. The properties of sinterable lanthanum chromite powders obtained from these sols are compared with powders made by direct spray-drying of lanthanum-chromium nitrate solutions.

Hydrothermal deposition and characterization of ultrafine ZrO2 thin films

Abstract Ultrafine ZrO2 thin films (0.6 μm) have been prepared by a hydrothermal method on polycrystalline alumina substrates (α-Al2O3). The hydrothermal treatment of zirconium hydroxide sol in the temperature range of 100–240 °C for 6–72 h results in the formation of monoclinic single-phase films. The resulting films have a white appearance and are homogeneous, without visible pores and defects, and the average grain size in the film is 18 nm.

Preparation and Characterization of Fine‐Grain Yttrium‐Based Phosphors by Sol‐Gel Process

The preparation, characterization, and luminescence of yttrium‐based phosphors such as europium activated yttrium oxide (red) and terbium activated yttrium aluminate (green) by sol‐gel processes is presented. The sols of yttrium hydroxide were synthesized by various routes. It was found that the sols obtained through an ion exchange column were pure and without any cross contamination. The aluminum hydroxide sols were prepared from aluminum chloride and ammonium hydroxide. A number of gel samples were synthesized by mixing stoichiometric amounts of and to obtain , and with trace amounts of rare earth, gels as activators. These gels were dried at 30 to 80°C. From the thermal analyses, all possible temperature transitions were identified. After calcination with different temperatures and durations, these phosphor powder samples were characterized for crystallization, spectral energy distribution, and morphology. The samples synthesized at lower temperatures (< 1000°C) were fully crystallized. The average particle size of these phosphors was in the range of 1 to 2 μm. From the luminescence spectral data, all possible transitions corresponding to in , and corresponding to in yttrium‐aluminum‐garnet (YAG) matrices were identified. The luminescent efficiencies of these phosphors were comparable with commercially available phosphors having larger particles (6 to 10 μm). The preparation of other yttrium‐based phosphors such as and (RE = Tm, Ce, Tb, and Eu) and the luminescence studies of these materials at low voltages for field emission display applications are in progress.

Flux Decline and Gel Resistance in Unstirred Ultrafiltration of Aluminium Hydrous Oxide Sols

The flux decline and the gel resistance during the unstirred ultrafiltration of colloidal dispersions of aluminium hydrous oxides were measured at a constant pressure difference of 50–300 kPa and a constant temperature of 293–313 K in a 200-cm3batch cell. The conventional cake filtration theory was employed to analyze the flux decline behavior. This simple theory predicts that theJm/Jratio rapidly approaches 2, as time approaches infinity. The time at which the gel resistance becomes equal to the membrane resistance ranged from 6 to 12 s under the conditions of our experiments and decreased with the bulk concentration. Thus, the deposited gel layer offered major resistance to permeate flow throughout the whole operation, except in the first few seconds. The specific gel resistance obtained by plotting (t − t1)/(V − V1) against (V − V1) and was compared for two different crystalline structures of aluminium hydrous oxides (boehmite and pseudoboehmite).

An experimental trial for the determination of the critical coagulation concentration using the sedimentation method

A method for determining the critical coagulation concentration (Cc) from the change in the transmittance of the sol with stand time after adding a coagulating agent is discussed. Potassium nitrate was used as the coagulating agent because the specific adsorption of electrolyte ions on the particle and the hydrolysis of electrolyte ions are negligible. Apparent critical coagulation concentrations,Cca, of iron (III) hydroxide and silver iodide sols were obtained from the transmittance vs. potassium nitrate concentration curves for various stand times. The values ofCca decreased with increasing stand time. TheCca value obtained for the shortest stand time was closer toCc obtained from the initial turbidity change of the sol by applying Rayleigh's law. The Hamaker constant for the particle in water was calculated from theCca value obtained at the shortest time and the experimentally determined outer Helmholtz plane potential. The calculated Hamaker constants were comparable to the theoretical values for iron (III) hydroxide and silver iodide.

Formation of fractal structures by aggregation of anisometric iron (III) hydroxide particles

Coagulation of anisometric iron (III) hydroxide sols has been studied by dynamic light scattering, TEM and ultra-small-angle X-ray scattering. The anisometry of rod-like individual colloidal particles can be characterised with a mean aspect ratio of 10. It was established for the first time, that the aggregates formed by coagulation of anisometric particles show definite fractal structure with a mass fractal dimension of 1.95 ± 0.05.

Colloidal stability of electrostatically stabilized sol particles.

The colloid stability of ferric hydroxide sol has been investigated at three different HCl concentrations. The total HCl concentration in the sols was A>B>C, the amount of HCl adsorbed was A=B>C. The parameters which characterize the stability (flocculation value, gelation concentration, repeptizability) are related to the amount of adsorbed HCl, because this property governs the hydrophility of the sols. In contrast, the peptizability of powders after drying the sols depends on the total concentration of HCl in the system. The hydrochloric acid impedes the condensation of surface groups to 〉Fe−O−Fe〈 bonds. From water vapor adsorption and heat of immersion data the hydration potential barrier is constructed which is comparable to the barrier according to the DLVO theory The differences and anomalies in the stability of sols are interpreted as differences in the hydrophility of samples.

ChemInform Abstract: Synthesis of Calcium Titanate from Titanium Hydroxide Sol and Calcium Hydroxide or Carbonate.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Stabilized Aluminum Oxide Prepared by Heat Treatment of Aluminum Hydroxide Sols in a Carbon Matrix

Transition aluminum oxides with increased thermal stability were obtained by placing dispersed aluminum hydroxides in a carbon matrix, their particles being respectively quasispheroidal and fibrous, and holding at a temperature of 2000 K in an argon atmosphere for 30 min; afterwards, the carbon phase was burned in air at 1073 K. Subsequent calcination in air showed that the specimens of Al 2O 3 still consisted of the fibrous and quasi-spheroidal particles and that their increased specific surface was conserved. Simultaneously, a delay in the phase transitions to corundum and stabilization of the δ-Al 2O 3 phase at 1473 K was observed.

Dynamic moduli change of aluminum hydroxide sol during sol-gel transition

Aluminum hydroxide sol was prepared by the sol-gel method. Dynamic moduli such as storage and loss moduli were measured to investigate the relative dominance of elastic and viscous contributions to the viscoelastic response of aluminum hydroxide sol during sol-gel transition. The loss modulus, a measure of viscous response. is larger than the storage modulus, a measure of elastic response, for the sols of low particle concentrations. But at a high particle concentration above 15.3 wt%, the storage modulus is found to be larger than the loss modulus. This inversion from a viscous to an elastic response with the increase of particle concentration is attributable to the formation of gel structures by the aggregation of dispersed particles

Some Comments on the Production of Medium Sized Spherical Particles by Anion and Water Extraction Variant of Sol-Gel Process

AbstractMedium sized spherical particles (with diameters below 100 μm) of ceramic materials (Al203 and Al203 +8%TiO2) were produced in the following steps: (1) preparation of concentrated hydroxide sols of cations by extraction of anions using Primene JMT, (2) formation of sol emulsion in 2-ethylhexanol-1 containing various amounts of surfactants (EH), (3) gelation of emulsion drops by extraction of water with partially dehydrated EH, (4) non-destructive thermal treatment. Principal properties of the sol depend on the temperature of the extraction process. For preparation of lowanionic sols a two step extraction process, separated by digestion of the aqueous phase at boiling point, was necessary. It was found that the parameters of emulsion formation as well as the properties of the sols significantly influence the particle size distribution. It was concluded that lowering of the sol- EH interracial tension by the surfactant does not influence the process. On the contrary the “anti-clustering” effect of surfactants is essential for preparation of perfect spherical powders. The thermal decomposition of gels to oxides is determinant for densities, specific surface area and carbon content. Medium sized spherical powders are free flowing. The compactibility and sinterability of those powders are poor. However drastic reduction of particle size by milling (connected with their transformation to irregular shape) significantly improves the sinterability.

Synthesis of pillared smectites from hydrous metal oxide sol-smectite mixtures under reflux conditions

A novel method for the synthesis of pillared smectites (cross linked intercalated smectites) by refluxing a mixture of bentonite (2 wt%) and nano hydroxy aluminium oxide (boehmite, AlOOH) sol in aqueous medium is reported. Mixed sol containing boehmite and hydrous cerium oxide has resulted in mixed oxide pillared smectites. The various conditions of the intercalation are reported and the characteristics of the intercalated smectites have been evaluated using XRD, surface area analysis and thermogravimetric techniques. The presnet method is shown to be effective in reducing the time of pillaring. High order of intercalation 20 Å and specific surface area of 260 m 2 g −1 are achieved by this method. Further, the possibility of handling a higher concentration of the smectite, which has been a limiting factor in the usual methods, is highlighted. The dielectric constants of the dried smectites after intercalation by reflux are compared with those prepared by usual methods. The present technique of refluxing a mixture of mono ion exchanged smectite and hydrous metal oxide sols is novel due to its capability to intercalate smectites having high surface area, increased interlayer spacing and also enhanced thermal stability.

On the Types of Bond Developing between the Aluminium and Iron (III) Hydroxides and Organic Substances

During the coagulation-flocculation processes involved in the treatment of surface waters, dissolved organics are also incorporated into the aluminium and iron (III) hydroxide flocs. A part of the dissolved organics can thus be removed by simple solid-liquid phase separation techniques, like sedimentation, flotation, sand filtration. According to laboratory evidence, durable bonds between the coagulant, or the metal hydroxides thereof, develop only over the extremely short (a few seconds) period which elapses from the formation of the metal hydroxides to the intense aggregation of the metal hydroxide sols. The bonds between these latter and the organic substances are mainly of the hydrogen bridge type, but other secondary chemical bonds and adsorption are also involved. Owing to the chemical structure and relatively low concentration levels of the organic substances, direct valence chemical bonds between the coagulants or the metal hydroxides thereof and the organic substances develop to a slight extent only.

Paper Whiteners: I. Titania Coated Silica

A well defined white pigment (whitener) was prepared by coating monodispersed silica particles with titania. The hiding power of this powder was evaluated as a function of the particle diameter, the thickness of the titania shell, and the calcination temperature. The calculations of Mie scattering coefficients were used to optimize the optical properties of such whiteners, which showed a close agreement with the measured quantities. In addition, colloidal dispersions of uniform particles of titanium hydrous oxide sols were prepared by precipitation from a homogeneous solution of titanyl sulfate at 90°C.

Relationship between the microstructure of boehmite gels and their transformation to alpha-alumina

The gelation of aluminium hydroxide sols from aluminium propoxide and aluminium sec-butoxide has been studied at high temperature and high molar ratio of water under acidic conditions, up to 1.1 molar ratio of nitric acid per aluminium alkoxide. The resultant boehmite-type gel structure can vary to a broad extent as a function of the precursor type and the acid amount. On heating, these different boehmite gel structures transform, through transition forms of alumina to alpha-alumina, at 1100 °C. The rate of transformation of the gels to alpha-alumina depends on the boehmite microstructure. Short boehmite platelets (ordered) transform to alpha-alumina faster than larger ones, but for full densification, at a temperature as low as 1100 °C, it is necessary that the boehmite should be at least 70% of its theoretical density.

Sedimentation and gelation of flocculated iron(III) hydroxide sols

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTSedimentation and gelation of flocculated iron(III) hydroxide solsMiklos Zrinyi, Marta Kabai-Faix, Ferenc Horkay, and Szilveszter FuhosCite this: Langmuir 1993, 9, 1, 71–76Publication Date (Print):January 1, 1993Publication History Published online1 May 2002Published inissue 1 January 1993https://doi.org/10.1021/la00025a018RIGHTS & PERMISSIONSArticle Views121Altmetric-Citations8LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (3 MB) Get e-Alerts Get e-Alerts

Colloidal stability of electrostatically stabilized sol particles. Part I: The role of hydration in coagulation and repeptization of ferric hydroxide sol

FeO(OH)·0.5 H2O powders were prepared by drying portions of a FeO(OH)·0.5 H2O sol at different relative vapor pressures, and the adsorption of water on the powders was determined. The magnitude of electrostatic potential barrier for the sol is of about 9 mJ·m−2. The reduction in the immersion enthalpy and in the surface free-energy in a range of the relative vapor pressures of 0.0–0.9 is as high as 140 mJ·m−2 and 130 mJ·m−2, respectively.

On the elastic and swelling behaviour of swollen poly(vinyl alcohol) networks filled with anisometric colloidal iron(III) hydroxide sol particles

AbstractA new method of preparing filled networks has been developed. Well‐characterized, colloidal iron(III) hydroxide particles are incorporated into chemically cross‐linked poly(vinyl alcohol) gels. Evidence for the random distribution of individual particles is provided by transmission electron microscopy. A filler‐induced gel collapse was observed when the strength of repulsion forces between filler particles is decreased by the screening of Coulombic interactions with electrolytes.