Effect of formulation of silica‐based solution on corrosion resistance of silicate coating on hot‐dip galvanized steel

Several silica‐based solutions with 50 g/l of SiO₂ were prepared from sodium silicate solutions and silica sol; the silicate conversion coatings were obtained by immersing hot‐dip galvanized steel sheets in these solutions. These solutions were characterized using high‐resolution transmission electron microscopy and ²⁹Si nuclear magnetic resonance; the morphology of the coatings was observed by SEM and atomic force microscopy while the corrosion resistance was evaluated by electrochemical measurements as well as neutral salt spray tests. The results show that the coatings obtained from the single silica sol solution had poor adhesion and the coating obtained from the sodium silicate solution with low SiO₂/Na₂O molar ratio was uneven. By adding the silica sol to the silicate solution with low molar ratio, uniform coatings with better protection property were obtained. According to the results of ²⁹Si nuclear magnetic resonance spectra, the effects of the distribution of silicate anions with various polymerization degrees in the silica‐based solutions on the microstructure and corrosion resistance of the silicate coatings are discussed. Copyright © 2016 John Wiley & Sons, Ltd.     

Vibrational and 29Si NMR spectroscopies of soluble silicate oligomers

Vibrational spectroscopy has been used to correlate the features of silicate solution spectra with ²⁹Si NMR spectra, as a function of SiO₂:Na₂O ratio and SiO₂ concentration. Assignments of infrared and Raman component bands have been made for different anion types and are consistent with results reported for crystalline silicates and silicate glasses. The extent of depolymerization of larger anions has been found to differ, depending on both the degree of dilution and alkalinity. The relative amounts of polymeric (Q⁴) silica and larger three dimensional (Q³_4R) anions are greater for the more siliceous solutions (3.3 and 2.95 ratio) at high concentrations. These large anions continue to be major contributors to the anion distribution even at 15 to 50 fold dilution. In the case of more alkaline solutions, especially below 2.5 ratio, the relative contribution of the large anions to the distribution drops rapidly, even with 2 or 3 fold dilution. At low concentrations, in very alkaline solutions, the anion distribution is mainly monomer, dimer and cyclic trimer. Vibrational spectroscopies show great promise for observing changes in anion distribution on a much shorter time scale than is possible with ²⁹Si NMR and can be useful for following reactions involving silicate solutions.     

Studies of the mechanism of formation of calcium silicate compounds by titration based on emission and atomic absorption spectroscopy

In this paper, the inhibition effect of silicate on emission or absorption of calcium was used for an investigation of the mechanism of formation of calcium silicate compounds. For that purpose, calcium chloride solutions were continuously titrated with a standard solution of sodium silicate (Na₂SiO₃), with simultaneous aspiration of the titrand into an air-hydrogen flame. During the titration, changes in the emission of the CaO-band at 622 nm and the CaOH-band at 554 nm were registered automatically on the recorder. Changes in the absorption of calcium were also registered at 422 nm. Thus curves of the same shape were obtained, with the same number of characteristic points, in which the SiO₂/Ca ratio is constant, when the concentration of silicate in the titrant varies. This fact suggests that calcium reacts with silicate to form compounds with a constant composition.Curves of the same shape were obtained by titration of a standard solution of sodium silicate, with a calcium chloride solution, while monitoring the changes in the absorption of calcium at 422 nm and changes in the emission of the CaO-band at 622 nm. In this case, the mole ratios SiO₂/Ca at the characteristic points of the curves were the same as in the case of the titration of calcium chloride solution with the silicate solution.On the basis of the mole ratios SiO₂/Ca at the characteristic points on the titration curves, which amount to 0.21, 0.33 and 0.50, the mechanism of formation of calcium silicate compounds was represented by chemical equations.It may be concluded that in the process of evaporation of spray droplets a chain of reactions take place, resulting in compounds that can be represented by the general formula xCaO·SiO₂.     

Variable temperature 1H, 23Na,and 29Si MAS NMR studies on sodium silicate hydrates of composition Na2O · SiO2 · nH2O (n = 9, 6, 5): Local structure in crystals,melts, supercooled melts,and glasses

The local structure in crystals, melts, supercooled melts, and glasses of sodium silicate hydrates of composition Na₂O · SiO₂ · nH₂O (n = 9, 6, 5) is studied by variable temperature ¹H, ²³Na, and ²⁹Si MAS NMR spectroscopy. Detailed in situ investigations on the melting process of the crystalline materials reveal the importance of H₂O motion in the melting mechanism. Depending on the local coordination, crystallographically distinct Na sites show different behaviour during the melting process. Upon melting, the monomer silicate anions present in the crystalline hydrates undergo condensation reactions to oligomeric silicate anions. No recrystallization but glass formation occurs at low temperature if the melts were heated initially about 10 K above the melting point. In the glasses also oligomeric silicate anions are present with a preference for cyclotrimer species. In situ MAS NMR investigations and electric conductivity measurements of the melts, supercooled melts, and glasses suggest the distinction of three temperature ranges characterized by different local structure and dynamics of the sodium cations, water and silicate anions. These ranges comprise a glass and glass transition range A at low temperatures, an aggregation region B at intermediate temperatures, and a solution or electrolyte region C at high temperatures. In region B aggregation of sodium water complexes to hydrated polycation clusters is suggested, the dynamic behaviour of which is clearly different to that of the silicate anions, indicating that no long-lived contact ion pairs between sodium cations and silicate anions are formed.     

Pseudoheterogeneous polymerization of methyl methacrylate initiated by sodium bisulfite in presence of glassy powder of PbO?SiO2

The aqueous polymerization of methyl methacrylate with sodium bisulfite as initiator was catalyzed by PbO? SiO₂, PbO (70 mole %)? SiO₂ (30 mole %) with a particle size < 200 mesh had the highest catalytic effect. The average molecular weight obtained in the presence of amorphous PbO? SiO₂ glass was higher than that obtained in the presence of crystalline PbO—SiO₂ glass powder. In this system mild shaking increased the rate of polymerization. Silicon dioxide catalyzed the rate of polymerization to a higher extent than PbO, which had a slightly higher catalytic effect than lead silicate powder. The average molecular weight formed in the presence of PbO was higher than that formed in the presence of lead silicate, which in turn was higher than that formed in the presence of silicon dioxide. Increasing the initiator concentration decreased the average molecular weight. Mild shaking decreased the average molecular weight obtained when polymerization was carried out in air but increased it in a nitrogen atmosphere. Methanol decreased the conversion percentage of monomer to polymer and the average molecular weight due to its transfer reaction.     

Reaktionen von Natronwasserglas mit Kaolin unter hydrothermalen Bedingungen

Reactions of Sodium Silicate with Kaolin under Various Hydrothermal Conditions The reactions of sodium silicate (molar ratio SiO₂/Na₂O 3.8) with kaolin were investigated under various conditions of hydrothermal treatment in saturated water vapours in an autoclave. The products of reaction were identified by X-ray, electron-microscopic, and infrared methods. The results have shown that, under autoclave conditions, sodium silicate reacts with kaolin to alumosilicagel or to a crystallized zeolite mineral analcime Na₂O · Al₂O₃ · 4 SiO₂ · 2 H₂O. At the reaction kaolin dissolves and α-quartz simultaneously appears in the product of reaction.     

Untersuchungen im System SrO?SiO2?H2O

Investigation on the System SrO? SiO₂? H₂O On addition sodium silicate solutions to solutions of Sr(OH)₂, at room temperature strontium hydrogensilicates are precipitated which are always amorphous and contain silicate anions of various condensation degrees. At about 100°C at first also amorphous products are formed containing lower- and higher-molecular silicate anions. On standing of these precipitates at about 80°C under the mother liquor, however, cristallization occurs under complete degradation of the higher-molecular anions to monomeric resp. dimeric silicate anions. In dependence on the Na₂O: SiO₂ ratio of the sodium silicate solutions and on the Sr(OH)₂ concentrations the following crystalline compounds are formed: 1.25 SrO · 1 SiO₂ · 2 H₂O, 3 SrO · 2 SiO₂ · 3 H₂O and 3 SrO · 2 SiO₂ · 4 H₂O, with monomeric silicate anions; 2 SrO · 2 SiO₂ · 1.5 H₂O; 2 SrO · 2 SiO₂ · 2 H₂O, and 2 SrO · 2 SiO₂ · 3 H₂O, with dimeric anions.     

Synthesis and structural chemical examination of faujasite type zeolite and its new structural modification

On the basis of the aluminate solution of alumina production and sodium silicate a faujasite-type zeolite was synthesized as well as its new structural modification. Thermostability nature and temperature of dehydration of this zeolite were found. It is shown that the ratio of the starting components SiO₂/Al₂O₃ and Na₂O/Al₂O₃ greatly affects the direction of the crystallization of zeolites.     

Effect of sodium silicate on the nature of crystallization products in calcium phosphate systems

Solid phases have been prepared in Ca(NO₃)₂–(NH₄)₂HPO₄–Na₂SiO₃–NH₄ОН–H₂O (c _Са/c _P = 1.70) systems with widely varying amounts of the sodium silicate dopant (у = c _Si/c _P = 0–5). The product formed under the test conditions is highly disperse and poorly crystallized apatite, in which up to 1.4 mol of phosphates (per mole of the salt) is substituted by carbonate and silicate ions. The excessive SiO ₄ ^4? anions in the system are hydrolyzed to yield amorphous SiO₂. When the silicon agent is in a considerable excess over the phosphate agent (у ≥ 2), minor calcium hydrosilicate is identified in the solid phase. The coprecipitation of the aforementioned compounds results in microcomposites with developed surface areas exceeding 100 m²/g.     

The Viscosity Properties of Sodium Silicate Solutions

Using a NDJ-1 rotational viscometer and an AR500 rheometer, both static and dynamic viscosities of sodium silicate solutions were measured with changes of concentration, temperature, modulus (molar ratio of SiO₂ to Na₂O), shear rate and chemical additives. Static results show that viscosity increases monotonously with concentration varying from 15 to 55%, decreases with temperature rising from 15 to 70 °C, and has a minimum value at a modulus of about 1.8. Measured data can be fitted quantitatively either by the Krieger-Dougherty expression or the Arrhenius equation with good agreement. This fact suggests that the sodium silicate solutions exhibit the properties of a suspension, in which the silicate anions, mainly constructed of Q ¹ and Q ² groups, act as a binder; the colloidal particles mainly constructed of Q ³ and Q ⁴ groups and small cations, act as effective rigid particles. Dynamic results show a shear thickening property in the high shear-rate regime, and a Newtonian property in the low shear-rate regime.     

Über den Einfluß von Temperatur und Fremdionen auf Eigenschaften und Bau der Natriumwasserglaslösungen

The Influence of Temperature and Impurities Addition on the Properties and the Constitution of Sodium Water Glass Solutions Sodium water glass (NaWG-)solutions of constant composition (SiO₂/Na₂O = 3,3; C_SiO2 = 6,2 M) and different concentration of impurities (Fe, Al, Ti, Cu, chloride, sulfate) were investigated in dependence on temperature by means of the dye absorption method, ¹H- and ²³Na-NMR spectroscopy. It is shown, that the differences in the dye absorption spectra of normalized technical NaWG-solutions, mainly depend on the Fe-concentration in the solutions and their thermal history. From the results follow a crosslinking of polymeric silicate species by Fe? O? Si bonds and/or hydrogen bridges and a fully or partially degradation of these bonds at higher temperatures (150°C).     

Surface characteristics of AZ91D alloy anodized with various conditions

Anodic oxidation of an AZ91D magnesium alloy was carried out in an attempt to increase the corrosion resistance. The alloy was placed in an electrolyte containing 0.1 M sodium silicate (Na₂SiO₃), 2.0 M sodium hydroxide (NaOH) and 0.1 M sodium phosphate (Na₃PO₄), and treated with a current density of 100–400 mA/cm² for 1 to 4 min. After the anodic oxidation treatment, the surface characteristics were analyzed by SEM, X‐ray diffraction (XRD) and a surface roughness tester. The corrosion resistance was determined by measuring the corrosion potential and corrosion current density using potentiodynamic polarization in a 3.5 wt% NaCl electrolyte solution. Although the anodic oxidation treatment with the base electrolyte resulted in an arrival voltage ranging from 60 to 70 V, the addition of silicate tended to reduce this arrival voltage by approximately 10–20 V and decrease the critical voltage required for the formation of a porous oxide film. The pore size and film thickness increased with increasing applied current and treatment time. The addition of silicate to the electrolyte resulted in films with a homogeneous pore size and a film thickness increasing with the increasing applied current and treatment time. XRD showed the formation of a new MgO and Mg₂SiO₄ phase. The formation of Mg₂SiO₄ was attributed to the presence of SiO₄^4? in the film. After the addition of silicate, the corrosion potential increased and corrosion current decreased, resulting in improved corrosion resistance. Copyright © 2008 John Wiley & Sons, Ltd.     

Study on the Salting-out Effect using Silica Species by FAB-MS

The salting-out effect has been characterized on the basis of the relative peak intensity of silica species, observed by FAB-MS (fast atom-bombardment mass spectrometry) in solutions of sodium chloride, sodium nitrate, sodium sulfate, calcium chloride, lithium chloride and magnesium chloride. A critical change in the peak intensity ratios of the linear and cyclic tetramers of silica against the sodium ion (Na⁺) concentrations was observed at Na⁺ concentration between 0.1 and 1 mol⋅dm⁻³. The degrees of the changes of these peak intensity ratios increased in the order NaNO₃ < Na₂SO₄ < NaCl. In CaCl₂ solutions, these peak intensity ratios changed significantly at Ca²⁺ concentrations between 0.05 and 0.5 mol⋅dm⁻³. The salting-out effect observed is the total change in the concentration of silica brought about by complex factors, such as the changing solubility of silicate complexes, the increases in the concentrations of different kinds of soluble silicate complexes induced by changes in the hydrophobicity and hydrophilicity of the solution, and the contribution of hydrolysis.     

Local structure and chemical durability of FeOOH-fixed sodium silicate glass prepared from water glass

A 12M HCl solution of iron oxyhydroxide (a-FeOOH: goethite) was mixed with water glass (18Na₂O^.36SiO₂ ^.46H₂O) at room temperature. The mixture (sol) changed into a dry gel when dried at 25 °C for 120 hours in air. Glass-ceramic and glass samples were prepared when the dry gel was heated for 1-3 hours in an electric furnace at 800 and 900 °C, respectively. The ⁵⁷Fe Mössbauer spectrum of the dry gel is composed of a magnetic hyperfine structure owing to the formation of g-FeOOH (lepidocrocite). By contrast, the ⁵⁷Fe Mössbauer spectrum of glass-ceramic and glasses is composed of paramagnetic Fe(III) with distorted tetrahedral symmetry. This proves that Fe(III) atoms occupy network-forming Si(IV) sites in the FeOOH-fixed sodium silicate glass. A leaching test of the silicate glass in the acid rain simulant composed of HNO₃ (pH 3.5) and H₂SO₄ (pH 3.5) revealed high chemical durability, indicating that Fe(III) is firmly fixed in the glass matrix.     

The formation of aqueous magnesium silicate in the interaction of solutions of magnesium chloride and sodium metasilicate

Conclusions When solutions of magnesium chloride and sodium metasilicate, taken in the ratio 6MgCl₂8Na₂SiO₃, are poured together, chiefly a hydrated magnesium silicate with an admixture of amorphous silica SiO₂·nH₂O is formed.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 10, pp. 2178–2181, October, 1970.     

Aqueous polymerization of acrylamide initiated by acidic potassium permanganate–ascorbic acid redox system

The polymerization of acrylamide initiated by the acidic permanganate–ascorbic acid redox pair has been studied in aqueous media at 30 ± 0.2°C in nitrogen atmosphere. The initial rate of polymerization has been found to be proportional to nearly the first power of the catalyst KMnO₄ concentration within the range 6.0 × 10^?3–14.0 × 10^?3 mole/l. The rate is proportional to the first power of the monomer concentration within the range 4.00 × 10^?2–12.0 × 10^?2 mole/l. However, the rate of polymerization is independent of ascorbic acid concentration within the range 3.0 × 10^?3–6.0 × 10^?3 mole/l., but the further increase of the concentration depresses the rate of polymerization as well as maximum conversion. The initial rate increases but the maximum conversion decreases as the temperature is increased within the range 20–35°C. The overall energy of activation has been found to be 9.8 kcal/mole. The optimum amount of sulfuric acid is essential to initiate the polymerization but its presence in excess produces no effect either on the rate of reaction or the maximum conversion. Water-miscible organic solvents and salts, e.g., CH₃OH, C₂H₅OH, (CH₃)₂CHOH, KCl, and Na₂SO₄, depress the rate. Slight amounts of MnSO₄ · H₂O and a complexing agent NaF increase the rate of polymerization. Cationic and anionic detergents have been found to decrease and increase the rate, respectively, while nonionic surfactants have no effect on the rate of polymerization.     

Synthesis of Zeolite ZSM-2 Using Zeolite NaX as Seeds

Introduction Oxygen and nitrogen have been produced tradition-ally by cryogenic distillation of air. Methods for the non-cryogenic separation based on selective adsorption have been developed and commercialized since the 1970s and have led to a cost-effective process for this important separation.1 Low-silica zeolites are important materials for producing oxygen by selective adsorption of nitrogen. In 19891990, a new generation of lith-ium-based adsorbents was developed.2,3 Highly lithium exc…     

Preparation of Forsterite by the Geopolymer Technique—Gel Compositions as a Function of pH and Crystalline Phases

Mg-bearing silicate precursor gels have been prepared by mixing 0.74 mol/L sodium metasilicate and 1.48 mol/L magnesium nitrate solutions. Caustic soda solution of 1.0 mol/L concentration was introduced to regulate pH. The magnesium nitrate solution was added dropwise to the sodium silicate solution in equi-volume at various pH values. Raw and heat-treated gels were characterized by XRF, TG-DTA, XRD and FE-SEM. As a result, gel compositions were dependent on pH values of mixing solutions. The pH value yielding stoichiometric forsterite composition, MgO/SiO₂ = 2 was reached at pH 9.3. In addition, this value was pH 8.4 for stoichiometric enstatite composition, MgO/SiO₂ = 1. With decreasing pH from 9.3, the ratio became less than 2 and forsterite and enstatite precipitated by heating the gels. With increasing pH from 9.3, the ratio became more than 2 and forsterite and periclase precipitated by heating the gels. DTA curves showed a characteristic exothermic peak centered at 700–900^∘C, indicating relatively low temperature formation of crystalline phases due to the presence of polycondensed frame works of silicates in the precursor gels.     

29Si- und 23Na-Festkörper-MAS-NMR-Untersuchungen an Modifikationen des Na2Si2O5

²⁹Si and ²³Na Solid State MAS NMR Investigations of Modifications of the Sodium Phyllosilicate Na₂Si₂O₅ . The results of ²⁹Si- and ²³Na-MAS NMR investigations on four modifications of the synthetic Na₂Si₂O₅ demonstrate that the α-, β- and δ-modifications are characterized unequivocally by the parameters of the corresponding NMR spectra. The studies on γ-Na₂Si₂O₅ show that this sample contains a large amount of secondary compounds. For α- und β-Na₂Si₂O₅ the the structural details of the silicate sheets are reflected by the ²⁹Si MAS NMR spectra while from the ²³Na MAS NMR spectra conclusions about the coordination number of the sodium atoms can be derived. The ²⁹Si MAS NMR investigations on δ-Na₂Si₂O₅ indicate that the silicate sheet of this modification consist of identical SiO₄-tetrahydra the parameter of which differ from those of α- and β-Na₂Si₂O₅. The ²³Na MAS NMR studies show that in the interlayer space of δ-Na₂Si₂O₅ two nonidentical sodium atoms exists. The NMR results give rise to the suggestion that one of the sodium is surrounded by five and the other one by six oxygen atoms.