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.     

Differential Scanning Calorimetry at Hydrothermal Conditions of Amorphous Materials Prepared by Drying Sodium Silicate Solutions

Concentrated sodium silicate solutions with a molar SiO₂:Na₂O ratio of 3.3 and a SiO₂ content of 27 mass% were dried up to 63 d at temperatures between 40 and 100°C to residual water contents between 12 and 38 mass%. The dried solid materials were investigated by differential scanning calorimetry (DSC). Pressure tight autoclave crucibles were applied to suppress evaporation and boiling of the samples during heating. Two thermal events are discussed with respect to glass transition. This revised version was published online in August 2006 with corrections to the Cover Date.     

Untersuchungen an Reaktionsprodukten von Dinatriumdihydrogensilicathydraten – Na2H2SiO4 · xH2O – und Dinatriumsilicat – (Na2SiO3)x – mit Wasserstoffperoxid. III1. Über den Abbau von Dinatriumsilicat-3-Wasserstoffperoxid

Na₂SiO₃ · 3 H₂O₂ is an instable compound, delivering oxygen on storing at room temperature. The decomposition is of a radicalic nature. An intermediate resulting from this decomposition is Na₂SiO₃ · H₂O₂ · 2 H₂O; it slowly looses elemental oxygen yielding two hydrates: Na₂SiO₃ · 3 H₂O₂ und Na₂SiO₃ · H₂O, depending on the experimental conditions. Thermal decomposition of Na₂SiO₃ · 3 H₂O₂ leads to (Na₂SiO₃)_x or Na₂SiO₃ · H₂O. The latter is stable up to 480°C, above this temperature being converted to (Na₂SiO₃)_x by exothermic reaction. The existence of these compounds have been proved analytically and by X-ray powder diffraction.     

Studies on silicic acid and its salts: XV. 29Si NMR study of sodium silicate in solution

The ²⁹Si NMR study of aqueous solution of sodium silicate of mole ratio SiO₂ to Na₂O equals one shows that the degree of polymerization of sodium silicate decreases with the decrease of the concentration, but the concentration of monosilicate anion increases, and that the lower the salt concentration, the faster is the rate of increase of the anionic concentration. The effect of SiO₂/Na₂O mole ratio and the concentration of sodium silicate on chemical shifts and spin-lattice relaxation time, T₁, of Si species and the effect of salt on degree of polymerization of sodium silicate in solution were also investigated.     

Elastic and dynamical properties of alkali-silicate glasses from computer simulations techniques

This paper shows recent progresses in the field of computer simulations of inorganic glasses. Molecular dynamics simulations and energy minimization methods have been applied to calculate the elastic and transport properties of alkali silicate glasses of compositions xM₂O · (100 ? x)SiO₂ (with x = 0, 10, 15, 20, 25, 30 % mol for M = Li, Na and K) and of a soda-lime glass with composition 15Na₂O · 10CaO · 75SiO₂, which has been employed to ascertain the effect of the replacement of CaO for Na₂O. The excellent agreement of the computed results with the experimental data highlights the important predictive and interpretative role reached by computer simulations techniques.     

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.     

Zum Ionenaustausch einwertiger Kationen an synthetischen Natriumpolysilicaten mit Schichtstruktur

Ion Exchange of Monovalent Cations in Synthetic Sodium Polysilicates with Layer Structure Cation-exchange equilibria of synthetic sodium polysilicates Ilerit (Na₂O · 8.3SiO₂ 8.9 H₂O) and Magadiite (Na₂O · 13 SiO₂ · 6.8 H₂O) with H⁺, Li⁺ and K⁺ Ions were investigated with respect to their selectivity behaviour. The range of ion selectivity is: H⁺ > Na⁺ > Li⁺ > K⁺. Thermodynamic data ΔG, ΔH, and ΔS were determined by means of the integral thermodynamic equilibria constants K_th of the ion-exchange reactions.     

Effect of temperature and water as additive on the MW and thermal properties of copoly(p-phenylene/biphenylene sulfide)s

Copoly(p-phenylene/biphenylene sulfide)s, PPBS were prepared from sodium sulfide trihydate(Na₂S·3H₂O), p-dichlorobenzene (DCB), and 4,4′-dibromobiphenyl (DBB) comonomers in N-methyl-2-pyrrolidinone (NMP) solvent using an autoclave. The molecular weights of PPBS copolymers were determined by high temperature (210°C) GPC in 1-chloronaphthalene solvent. The reaction temperature had little effect on the molecular weights of PPBS copolymers with water as additive at the level of 3 mol H₂O per 1 mol Na₂S. PPBS copolymer, however, showed maximum molecular weight of M_w = 24.1 × 10³ with the total water content of 9 mol H₂O per 1 mol Na₂S at an optimum polymerization temperature of 270°C. The resulting PPBS copolymer sample showed higher T_g (by 30°C) and lower T_m (by 10°C) than PPS homopolymer prepared under similar conditions. © 1996 John Wiley & Sons, Inc.     

Thermal properties of sodium metasilicate hydrates

The heats of fusion and heat capacities at 298.2 K of Na₂SiO₃·5H₂O, Na₂SiO₃·6H₂O and Na₂SiO₃·9H₂O have been measured by DSC. The enthalpies and entropies of fusion increase with the water content of the hydrate and the entropy of fusion per mole of water is almost constant. The application of DSC/DTA to the analysis of metasilicate hydrate mixtures is discussed.     

Cesium and strontium exchange by the framework potassium titanium silicate K3HTi4O4(SiO4)3·4H2O

Potassium titanium silicate with a semicrystalline framework of the formula K₃HTi₄O₄(SiO₄)₃·4H₂O has been prepared under mild hydrothermal conditions and its protonic form, H₄Ti₄O₄(SiO₄)₃·8H₂O, was obtained by acid treatment of the potassium compound. A comparative ion exchange testing of the H₄Ti₄O₄(SiO₄)₃·8H₂O towards alkali and alkaline earth metals in a broad pH and concentration range was carried out. It was found that potassium titanium silicate is a moderately weak cation exchanger, possessing high ion exchange capacity (up to 4–5 meq/g) and showing preference for heavy alkali and alkaline earth metals uptake. The selectivity of K₃HTi₄O₄(SiO₄)₃·4H₂O towards Cs⁺ and Sr²⁺ ions in alkaline and acid media in the presence of competitive inorganic ions and certain organic compounds was also studied. The data obtained suggest that despite the existence of well defined tunnel structure with parameters fitting for cesium ion in the K₃HTi₄O₄(SiO₄)₃·4H₂O, potassium titanium silicate could remove cesium (and strontium) efficiently only under some specific conditions, namely, at pH close to neutral and in the absence of competitive ions and especially of organic complexing agents.     

The mechanism of self-diffusion of ions in silicate systems

The special features of diffusion processes in noncrystalline models of SiO₂, CaO · SiO₂, and 2CaO · SiO₂ with small admixtures of sodium oxide were studied by the method of molecular dynamics at 2000 and 3000 K. A purely ionic model with Born-Mayer potentials and parameters taken from the literature was used. In addition to the usual analysis of the mean-square displacements of particles, the maximum square displacements in each separate run 10000 time steps long were analyzed. Fairly long tunnels in the structure of silica were detected in the SiO₂-Na₂O system containing two sodium atoms only. Sodium ions can traverse these tunnels and execute a reciprocating motion in them at an approximately thermal velocity. The addition of calcium oxide gradually makes the silicate structure more compact, and long tunnels cease to exist in calcium meta-and orthosilicate models.     

Synthesis, characterization and ion exchange properties of the framework sodium titanium germanate Na3H(TiO)3(GeO)(GeO4)3·7H2O

Sodium titanium germanate with a semicrystalline framework (STG) of the formula Na₃H(TiO)₃(GeO)(GeO₄)₃·7H₂O was synthesized under mild hydrothermal conditions and its proton form, H₄(TiO)₃(GeO)(GeO₄)₃·8H₂O (STG-H), was prepared by acid treatment of the sodium compound. The STG was characterized by elemental analysis, TGA, FT-IR, and X-ray powder diffraction. A comparative ion exchange examination of the STG-H towards alkali and alkaline earth metals in a broad pH and concentration range was carried out. It was found that the STG is a moderately weak cation exchanger, possessing high ion exchange capacity (up to 4.0 meq/g) and showing preference for heavy alkali and alkaline earth metals. The STG selectivity towards Cs⁺ and Sr²⁺ ions in the presence of competitive metal ions and certain organic compounds was also studied. The data obtained suggest that the sodium titanium germanate is a more selective exchanger for Sr²⁺ ion than its titanium silicate analogue, K₃H(TiO)₄(SiO₄)₃·4H₂O.     

KHSO4 · H2O/SiO2‐Catalyzed,One‐Pot,Solvent‐Free Synthesis of Pyrazolines,Tetrahydrocarbozoles and Indoles using Microwave Irradiation

A new high‐yielding, operationally simple, solvent‐free, and mild method for preparation of pyrazolines, tetrahydrocarbazoles, and indoles has been developed using KHSO₄ · H₂O impregnated on SiO₂. The reactions have been probed under microwave irradiation (MWI), and ultrasonic and thermal conditions, employing different solid supports. The data revealed that KHSO₄ · H₂O impregnated on SiO₂ under MWI provides the best yields in a shorter time under solvent‐free reaction conditions.     

Thermal studies on sodium silicate hydrates. IV. Thermal stability of sodium silicate hydrates Na2[SiO2(OH)2]·nH2O(n = 4, 5, 7, 8). Phase relations and decomposition characteristics under open-system conditions

Thermoanalytic studies carried out on hydrate phases Na₂[SiO₂(OH)₂]·nH₂O (n = 4, 5, 7, 8) reveal two phase transitions at elevated temperatures under open-system and non-isothermal conditions

Congruent melting at temperatures T_mp is followed by condensation at temperatures T_c > 380 K with subsequent formation of solid Na₂[SiO₃]. Foamingof the melts upon condensation is observed through heating stage microscopy. In situ ²⁹Si NMR experiments proved oligomeric or endless chain-type anions, [Si_1+nO_2+3n(OH)₂]^(2+2n)?, to be formed in the melts under open-system conditions. From DTA double peak configurations at temperatures T_c the thermal decomposition of the melts is shown to occur in a two-step reaction, uniformly with all four hydrate phases.Isothermal studies below melting temperatures show distinct decomposition of crystalline Na₂[SiO₂(OH)₂]·8H₂O to crystalline Na₂[SiO₂(OH)₂]·4H₂O whereas all the other crystallinephases within this hydrate series dehydrate to amorphous waterglass-type materials under identical experimental conditions in long-term annealing experiments. This exceptional phase relation between the octa- and the tetrahydrate has also been proved by X-ray powder diffraction heating experiments.     

Über die Konstitution der Silicatanionen im Kobaltäthylendiaminsilicat

On the Constitution of Silicate Anions in Cobalt Ethylenediamine Silicate A crystalline and acid-soluble silicate of the composition 1 Co₂O₃ · 6 en · 7.2 SiO₂. 26 H₂O was obtained by the reaction of cobalt ethylenediaminehydroxide solution with tetramethoxysilane. Chemical, kinetic, chromatographic, and x-ray investigations showed that this silicate is an acid double four-ring silicate of the formular [Co(en)₃]₂[H₃Si₈O₂₀] · 16–28 H₂O. The preparation of a cobalt propylenediamine (l,2 and 1,3)-silicate is described.     

Neue Verbindungen im System CaO/SiO2/CaCl2/H2O

New Compounds in the System CaO/SiO₂/CaCl₂/H₂O The hydrothermal formation of novel calcium silicate hydrates of compositions 5 CaO · 2 SiO₂ · CaCl₂ · 4 H₂O, 5 CaO · 2 SiO₂ · CaCl₂ · 2 H₂O and 4 CaO · 2 SiO₂ · CaCl₂ · H₂O from Ca₃SiO₅ and mixtures of CaO and SiO₂, respectively, in presence of calciumchloride at 200°–350 °C is described. From molybdate-reaction, ²⁹Si MAS NMR, DTA and TG measurements it is concluded that these compounds are based on disilicate anions and are to be interpreted as calcium hydroxide disilicate chlorides.     

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.     

Structure and ion exchange properties of tunnel type titanium silicates

A large number of titanium silicates are known to exist in the mineral realm and recently a considerable literature has developed concerned with the synthesis and properties of these and related compounds. This paper describes two such families that have tunnel structures filled with cations that may easily be exchanged. A sodium titanosilicate of ideal formula, Na₂Ti₂O₃(SiO₄)₂·2H₂O, is tetragonal and built up of Ti₄O₄ cubane-like structures linked together by silicate groups in the a and b directions in the form of a square. In the c-axis direction, the cubane groups are linked by oxo-groups to form a framework enclosing tunnels parallel to the c-axis direction. The several ion exchange sites were identified based upon X-ray diffraction studies and the reason for the great affinity of this compound for Cs⁺ elucidated. The second family of compounds have the general composition M₃H(TiO)₄(SiO₄)₃·4H₂O (M=alkali metal cation) and have the pharmacosiderite structure. The sodium or potassium phases are selective for Sr²⁺ and Cs⁺. These compounds are cubic and have similar Ti₄O₄ cubane-like groups. In this case, the connectivity via silicate groups extends along all three crystallographic axes equally. This change in crystal system has a profound effect upon the ion exchange behavior. This effect, as well as the effect of germanate substitutions for silicate, will be described.     

手性纳米磷酸锌钠的热化学研究

Chirai sodium zincophosphate nanocrystalline has been prepared and characterized. The standard molar enthaipy of the following reaction 12Na3PO4·12H2O（s）＋ 12ZnSO4·7H2O（s）= Na12（Zn12P12O48）·12H2O（s）＋ 12Na2SO4（s）＋216H2O（1） was determined by solution reaction calorimetric at 298.15 K, and calculated to be 33.666±0.195 kl/mol. From the results and other auxiliary quantities, the standard enthalpy of formation for sodium zincophosphate nanocrystalline was derived to be △fHm^⊙ [Na12（Zn12P12O48）·12H2O（s）, 298.15 K] =- 24268.494 ± 0.815 kJ/mol.     

Osmotic coefficient data for Na2SiO3 and Na2SiO3–NaOH by an isopiestic method and modeling using Pitzer's model

Osmotic coefficient and water activity data for Na₂SiO₃ and mixed Na₂SiO₃–NaOH aqueous solutions were obtained at 25°C by employing the isopiestic method. The binary Pitzer's parameters, β⁽⁰⁾, β⁽¹⁾, and C^φ, for Na₂SiO₃ and the mixing parameters, θ_{OH⁻SiO²⁻3 and} Ψ_{Na⁺OH⁻SiO²⁻3} were estimated using the osmotic coefficient data. The experimental osmotic coefficient data were correlated well with Pitzer's model. Mean activity coefficients of Na₂SiO₃ and NaOH for the solutions were predicted by Pitzer's model with the parameters obtained. Finally, the presence of metasilicic species, when sodium metasilicate (Na₂SiO₃·9H₂O) is dissolved in aqueous alkaline solution, was established by titration with hydrochloric acid.