Colloid chemical properties of hydrated tungsten trioxide hydrosols

Hydrosols of hydrated tungsten trioxide WO₃ ? nH₂O have been synthesized via peptization of a precipitate obtained by hydrolysis of potassium tungstate. It has been shown that the resulting sols are stable to aggregation in a pH range of 3.0–4.5. Hydrodynamic diameters and ζ potentials of WO₃ ? nH₂O particles have been determined as functions of dispersion medium pH. In addition, their density and degree of hydration have been found for the stable sols. The thickness of particle surface layers has been estimated.     

Synthesis and colloidochemical properties of yttrium oxohydroxyde hydrosols

Abstaract  It is shown that hydrosols of oxygen-containing compounds of yttrium may be prepared by the peptization and condensation methods. Basic characteristics of hydrosols, such as the size and shape of particles, their phase compositions, electrophoretic mobility, and the pH range of the dispersion medium where sols are stable with respect to aggregation, are determined. Coagulation thresholds of the sols are estimated in the presence of sodium nitrate and sulfate. It is found that the hydrosols coagulate reversibly. Concentration and aging of the sols give rise to the spontaneous formation of slightly structured thixotropic gels. The nature of the aggregation stability of hydrosols is suggested. Original Russian Text ? I.A. Belova, K.I. Kienskaya, A.S. Grodskii, V.V. Nazarov, 2008, published in Kolloidnyi Zhurnal, 2008, Vol. 70, No. 5, pp. 601–606.     

Synthesis and aggregation stability of europium oxohydroxide hydrosols

Europium oxohydroxide hydrosols that are resistant to aggregation have been obtained by the condensation method. The density of dispersed phase particles, phase composition and dispersity of the sols, electrokinetic potential of the particles, and its dependence on medium pH have been determined. The effect of dispersion medium pH on the mechanism and reversibility of particle aggregation has been studied. The nature of the aggregation stability of the synthesized europium oxohydroxide hydrosols has been discussed.     

Synthesis and Some Properties of Sols Prepared by Hydrolysis of Lanthanum Nitrate

The procedure for synthesis of hydrosols by hydrolysis of lanthanum nitrate was developed. The range of pH values was established corresponding to the maximum aggregation stability of sols. The photon-correlation spectroscopy was applied to determine the average hydrodynamic radius of sol particles, equal to 50 nm. The thresholds of fast coagulation of sol in the presence of sodium nitrate and sodium sulfate were determined.     

Aggregation Stability of SiO2, FeOOH, ZrO2, CeO2, and Natural Diamond Sols and Their Binary Mixtures: 2. The Photometric Study of Heterocoagulation of SiO2–FeOOH, SiO2–ZrO2, SiO2–CeO2, and CeO2–Natural Diamond Binary Systems in KCl Solutions

The aggregation stability of 1 : 1 and 3 : 1 (by volume) binary mixtures of two hydrophobic (SiO₂–FeOOH), one hydrophobic and one hydrophilic (SiO₂–ZrO₂, SiO₂–CeO₂), and two hydrophilic (CeO₂–natural diamond) sols was studied by photometry over a wide range of KCl concentrations at pH 6 and 3. The stability of the mixed binary sols was determined by the stability of the sol with a predominant particle number concentration. In the SiO₂–FeOOH system, the phenomenon of heteroadagulation stabilization was caused by the electrostatic factor of the stability of adsorbed SiO₂ particles and, in the SiO₂–ZrO₂ system, by the structural factor of the stability of adsorbed hydrophilic ZrO₂ particles. The stability of binary mixtures containing one or two hydrophobic components is qualitatively explained in terms of the Derjaguin theory of heterocoagulation of hydrophobic colloids. The stability of the binary system of two hydrophilic components (CeO₂–natural diamond) is determined by the structural component of the interaction energy of particles.     

Stability of Aqueous Crystalline Quartz Dispersions in the Acidic pH Region: The Role of the Structural Component of the Particle Interaction Energy

On the basis of the data obtained by studying the sols of crystalline quartz in aqueous KCl solutions at pH 2.0, 3.0, and 6.2, the domains of the parameters of structural forces for SiO₂ particles are estimated using the method of flow ultramicroscopy and their dependence on the pH value of the dispersion medium is demonstrated.     

Production of Titanate Microspheres by Sol-Gel and Spray-Drying

Porous titanate precursor microspheres (20–60 m in diameter), with a high sorption capacity for radioactive wastes from nuclear reprocessing plants, have been produced on a 50 kg scale by spray-drying precursor sols. Well-dispersed, stable sols were produced by hydrolyzing acetic acid modified tetraisopropyltitanate and peptizing the titania hydrolysate with acidic zirconia sol. The resulting TiO2 /ZrO2 sols were routinely concentrated to 900 g dm–3 (oxide basis) and exhibited excellent stability. These sols were subsequently mixed with dispersible alumina powder and partially aggregated by adding calcium and barium nitrate salts. The resulting sols were spray-dried to produce microspheres with controlled porosity and morphology. The properties of the spray-dried powder were very dependent upon the chemical properties of the precursor sol. In particular, hollow spheres were produced from well-dispersed sols, whereas solid spheres could be produced from partially-aggregated sols.     

Steric stabilization of iron (III) hydroxide sols by various amino acids

The dispersion and coagulation phenomena of iron(III) hydroxide sols were investigated as a function of pH in the absence and presence of amino acids. The amino acids used were glycine,L--alanine,DL--amino-n-butyric acid,L-valine,L-leucine,L- isoleucine,L-glutamic acid andL-arginine. The turbidity measurements of the iron-(III) hydroxide sols, which were prepared by pouring an aqueous iron(III) chloride solution into boiling distilled water, were carried out using a spectrophotometer with an addermixer device and an automatic recording system. The zeta potentials of sol particles were obtained by ultra-microelectrophoresis. The change in turbidity of the sol, as a measure in stability of the sol, increased with increasing pH in the region of pH 2–8, and reached a maximum at the isoelectric point of the particles. The coagulation at the isoelectric point was prevented by adding amino acids, and the stabilization had an optimum point at concentrations which depended upon the kinds of amino acids. The remarkable dispersing effect of amino acids which occurred near the isoelectric point of the particles at the suitable concentration of the ammo acids may be due to the steric protection by amino acid adsorbed. The protective action was explained according to a modified DLVO theory, the modification for London-van der Waals force being applied in order to take the effect of the adsorption layer into account.     

A NMR Study on the Hydrolysis,Condensation and Epoxide Ring-Opening Reaction in Sols and Gels of the System Glycidoxypropyltrimethoxysilane-Water-Titaniumtetraethoxide

The examination of hydrolysis, homo- and hetero-condensation reactions, of the condensation degree and the extent of epoxide ring opening in the course of sol-gel process was carried out by means of liquid- and solid-state 29Si and 13C NMR in the system 3-glycidoxypropyltrimethoxysilane (GPTS)-titaniumtetraethoxide-water (molar ratio 1 : 1 : 1.5–14) which is frequently used for the synthesis of heterometal hybrid polymers. The monomeric silanol groups in the GPTS-prehydrolysate immediately co-condense with the Ti-tetraethoxide to Si–O–Ti bonds to an extent of about 50–60% which remain stable in sols and also in the corresponding gels at low amounts of free water (0.02 H2O/OR) in the sol. An increasing amount of free water in the sol (0.12 H2O/OR) leads to an increased hydrolytic cleavage of the heterometal bonds and to the formation of homo-condensed polysiloxanes. The condensation degree of RSiO1.5 units in the Ti-containing sols is with 30–60% relatively high in comparison to Ti-free GPTS sols (ca. 5%) whereas the condensation degree of GPTS derived gels (81%) was found to be similar to that of the Ti-containing gels (60–80%). Ti-tetraethoxide accelerates the ring opening reaction of the epoxide group in the sols in dependence on the water content. Up to 78% of the epoxide rings are opened after 24 h in the sol with the highest water content (2 H2O/OR). No epoxide rings can be detected in Ti-containing gels which derive from sols with an amount of free water of 0.12 H2O/OR. The results give a first insight into the different parallel reactions in this system and can contribute to more structure controlled syntheses of heterometal hybrid polymers.     

Study of the formation of bimetallic aqueous Tl/Cu sols by gamma and electron irradiation

The spectral characteristics of the bimetallic sols produced by gamma and electron irradiation of mixed solutions of Tl⁺–Cu²⁺ ions in different ratios have been studied in aqueous medium. The intermediate transient species have also been characterized by the technique of pulse radiolysis. The rate constant for the reaction of Cu²⁺ion with the Tl⁺ ion reduction species was founded by 4×10⁹ dm³ mol⁻¹s⁻¹. Developmental absorption spectra in gamma radiolytic reduction of the mixed ions indicated reduction of Tl⁺ ion on the surface of small copper particles, resulting in bimetallic-sol with core of copper. The presence of a small concentration of Cu²⁺ ion was found to restrict the agglomeration process of thallium particles at near neutral pH conditions. The reducing capability of the bimetallic sols was found to be proportional to the thallium content in the sol. The observed UV–Vis spectra of the mixed Tl/Cu sols produced on electron irradiation showed much lower absorption in the higher wavelength region and were more close to that of the pure sol of the ion, present in higher concentration in the feed solution. Thus, the high dose rate-assisted stabilization of smaller thallium particles. Size of all these bimetallic sol particles was much less than 50 nm.     

Influence of Sol-Gel Synthesis Parameters on the Microstructure of Particulate Silica Xerogels

The influence of key sol-gel synthesis parameters on the pore structure of microporous silica xerogels was investigated. The silica xerogels were prepared using an acid-catalyzed aqueous sol-gel process, with tetraethoxysilane (TEOS) as the silicon-containing precursor. At high H2O : TEOS ratios, sols synthesized at pH 2–3 yielded minimum values of mean micropore diameter and micropore volume. Analysis of the resulting Type I nitrogen adsorption isotherms and the equilibrium adsorption of N(C4F9)3 indicated micropore diameters for these xerogels of less than approximately 10 Å.Xerogel micropore volumes corresponding to sols prepared at pH 3 and an H2O : TEOS ratio of r = 83 were consistent with nearly close packing of silica spheres in the xerogel. Xerogel microstructure was only weakly dependent upon H2O : TEOS ratio during sol synthesis for r > 10. Xerogel micropore volume increased rapidly with sol aging time during an initial induction period of particle formation. However, the xerogel microstructure changed only slowly with time after this initial period, suggesting potential processing advantages for the particulate sol-gel route to porous silica materials.Surface adsorption properties of the silica xerogels were investigated at ambient temperature using N2, SF6, and CO2. CO2 adsorbed most strongly, SF6 also showed measurable adsorption, and N2 adsorption was nearly zero. These results were consistent with the surface transport of CO2, and to a lesser extent SF6, observed in gas permeation studies performed through thin membrane films cast from similarly prepared silica sols.     

Physical Principles of the Photostimulated Aggregation of Metal Sols

Physical mechanisms of the reasons for dramatic (up to 10⁸ times) acceleration of the aggregation of sol metals under the action of light are proposed for the first time. These mechanisms were classified with allowance for the procedure of sol stabilization and type of dispersion medium; their comparative analysis was performed using the main types of silver sols as the most convenient model medium. Mechanisms proposed are based on the current notions of the theory of coagulation kinetics and stability of sols with account of interfacial processes, as well as of the theory of photoeffect corrected for the influence of dispersion medium and the amplification of local electromagnetic fields inherent in colloidal structures with fractal geometry.     

Preparation of Thermostable Highly Dispersed Titanium Dioxide from Stable Hydrosols

A large set of stable nanodispersed TiO₂ hydrosols differing in particle structure and dispersion medium composition was synthesized. For highly dispersed TiO₂ samples obtained by calcination of dried sols at 500°C phase compositions, sizes of primary crystallites, and specific surface areas were found. The factors affecting thermal stability of TiO₂ nanoparticles were analyzed. The sol containing the most thermostable nanoparticles was used to produce a highly efficient catalyst for cyclohexanone ammoximation.     

Stability of Suspensions of Bioactive Particles Using Hybrid Organic–Inorganic Solutions as Dispersing Media

Functional coatings incorporating different types of particles developed by the sol–gel method have been proposed in the last few years for diverse applications. This work focuses on the preparation of homogeneous coatings prepared from stable suspensions with 10 wt% of glass and glass ceramic particles in a hybrid organic–inorganic solution as dispersing media. For this purpose, the pH was shifted up to 6–7 by adding tetrapropylammonium hydroxide (TPAH) which behaves as a cationic surfactant being probably adsorbed on the particles surface, while the sol maintains stable. Rheological measurements were performed to study the stability of the suspensions prepared at different conditions such as the kind and concentration of dispersant and the pH conditions. After sintering at 450^∘C/30 min, coatings around 2 μ m in thickness were obtained.     

Preparation of TiO2 Sol Using TiCl4 as a Precursor

A titanium dioxide sol with narrow particle size distribution was synthesized using TiCl₄ as the starting material. The sol was prepared by a process where HCl was added to a gel of hydrated titanium oxide to dissolve it. The resulting aqueous titanic acid solution was heated to form titanium dioxide sol. The effects of preparation parameters were investigated. TiCl₄ was slowly added to distilled water at 5°C. Aqueous solution of sodium hydroxide was added to adjust the pH of the system to 8–12. After aging for a period of time, the peptized sol was filtered and sufficiently washed. The filtered cake was repulped in water. Hydrochloric acid was slowly added to the solution with stirring. After condensation reaction and crystallization, a transparent sol with suspended TiO₂ was formed. XRD results show that the crystalline phase was anatase. The suspended TiO₂ particles were rhombus primary particles with the major axis ca. 20 nm and the minor axis ca. 5 nm. The TiO₂ particles prepared at pH 8 had the largest surface area of 141 cm³/g and it was microporous. The compositions of the solution which yielded the smallest suspended TiO₂ particles were TiO₂:HCl (35% HCl) = 1:1 (molar ratio), concentration of TiO₂ = 10%. Hydroxypropyl cellulose with viscosity of 150–400 cps was added as a dispersant. The sol was excellent in dispersibility and long-term stability. Transparent thin films could be obtained through dip-coating glass substrate in the sol. The dip-coating on glass can be less than three times to have one monolayer TiO₂. The transparent TiO₂ thin film had strong hydrophilicity after being illuminated by UV light.     

Preparation and stability of silica sol/TPGDA dispersions and its application in the UV-curable hybrid coatings for fire protection

A series of silica sols modified by γ-methacryloxypropyltrimethoxysilane (MPS) were synthesized by the acid-catalyzed sol–gel method, and then the solvent in these sols were extracted under several vacuum distillation conditions. The stability of the sol after the distillation can be improved by means of increasing the dosage of MPS and incorporating reactive diluent TPGDA into the sol as new dispersion medium. Optimized samples have maintained stable for over 180 days. The sol dispersions and UV-curable organic compounds were mixed to form the hybrid coatings for fire protection. Effects of the distillation treatment and the cosolvent anhydrous ethanol added into the reaction solution on thermal and combustion performances and physical properties of the hybrid coatings were studied by thermogravimetric analysis, microscale combustion calorimeter, limit oxygen index test and UL-94 horizontal test, etc. The results showed that the distillation treatment for the sol was necessary to improve thermal performance and physical properties of the hybrid coatings. In addition, in the flammability experiment, hybrid coatings showed a quick and efficient protection of the substrate.     

Precipitation-redispersion of cerium oxide nanoparticles with poly(acrylic acid): toward stable dispersions

We exploit a precipitation-redispersion mechanism for complexation of short chain polyelectrolytes with cerium oxide nanoparticles to extend their stability ranges. As synthesized, cerium oxide sols at pH 1.4 consist of monodisperse cationic nanocrystalline particles having a hydrodynamic diameter of 10 nm and a molecular weight of 400 000 g mol(-1). We show that short chain uncharged poly(acrylic acid) at low pH when added to a cerium oxide sols leads to macroscopic precipitation. As the pH is increased, the solution spontaneously redisperses into a clear solution of single particles with an anionic poly(acrylic acid) corona. The structure and dynamics of cerium oxide nanosols and their hybrid polymer-inorganic complexes in solution are investigated by static and dynamic light scattering, X-ray scattering, and chemical analysis. Quantitative analysis of the redispersed sol gives rise to an estimate of 40-50 polymer chains per particle for stable suspension. This amount represents 20% of the mass of the polymer-nanoparticle complexes. This complexation adds utility to the otherwise unstable cerium oxide dispersions by extending the range of stability of the sols in terms of pH, ionic strength, and concentration.     

Study of the Lead Environment in Liquid and As-Dried Precursors of PZ, PT and PZT Thin Films

The environment of lead and zirconium atoms in liquid and as-dried precursors for PbZrO3 (PZ), PbTiO3 (PT) and Pb1.1Zr0.53Ti0.47O3 (PZT) thin film deposition were analyzed by EXAFS. The sols were prepared by 2-methoxyethanol route with lead acetate and lead oxide as lead sources. Pb—O—M (M = Zr and/or Ti, depending on the sol composition) linkages were determined in all sols. The choice of lead source weakly influences the lead environment, and strongly influences that of zirconium in both PZ and PZT sols. By drying lead oxide based sols the Pb–M correlation is moderately reduced in PZ, PT and is strongly reduced in PZT.     

Effect of the polymerization parameters on the morphology and spherical particle size of poly(styrene-<Emphasis Type="Italic">co</Emphasis>-divinylbenzene) prepared by precipitation polymerization

Poly(styrene-co-divinylbenzene) microspheres having a diameter range of 3.0–4.5 µm were synthesized by precipitation polymerization under various conditions, then the effects of the polymerization parameters such as monomer and initiator concentration, and used cosolvents on the characteristics of the final particles were compared with those in dispersion polymerization. It was found that precipitation polymerization is more sensitive to polymerization conditions than dispersion polymerization, and that precise control of polymerization parameters is therefore essential for individually stable spherical particles. Monomer and initiator concentration, and the use of cosolvents significantly vary the morphology and the size of the final particles. However, the uniformity of the microspheres is not greatly affected by the polymerization parameters.     

Large Size Recyclable Colored Glass Plates Prepared from Organic Colorant Dispersed Silica Sols by the Dipping Method

We have prepared the recyclable colored glass plates of blue, green, or red by coating organic colorant dispersed silica sols. Phthalocyanine-type or diketopyrrolopyrrole-type compounds were used as colorants for colored coating and the sol coated glass plates were heat-treated at 300–400°C. The coating was done by using a dipping-withdrawing equipment designed originally for coating large sized glass plates with 2 m in length and 1 m in width. The colored coating films were uniform and transparent with low haze values less than 1.0% and with thickness of 120–540 nm. The visible light transmittance of the colored glass plates was controlled in the relatively wide range of 50–90% by changing the film thickness or the colorant concentration in the coating sols. The practical durabilities of the blue colored glass plate against abrasion, scratch, chemicals and UV-light were acceptable to the specification required for interior glass products.