Polymerization Of Silicate Anions Research Articles

SUBSTANTIATION USE OF INORGANIC WATER SHUTOFF COMPOSITION FOR INCREASING OF DISPLACEMENT EFFICIENCY IN RESERVOIR OF FRACTURED-POROUS TYPE

The workis devoted to issuesof development of fractured-porousoil reservoirs. Discrete systems(caverns andfissures) have a significant impact onfiltering in them due to increased filtration characteristics in comparison with the matrix of the rock, so the process of displacing of oil by oil field or injected water is carried out faster. As a result, the water begins to enter the hole through fractures without performing useful work. In these conditions, technical and economic efficiency of development largely determines the timely and proper conduction of operations connected with the restriction of water flow to wells. For water suppression in fractured-porous reservoirs we have designed gell-forming water shut-off composition based on sodium silicate, as the initiator of gelation we used inorganic chromium salt (III). The mechanism of gelation of the composition is following: due to the process of polymerization of silicate anions through the reaction with cations of chromium a three-dimensional atomic chain are formed in the whole volume of the initial composition. The water shut-off composition has a wide range of adjustable time of gelling and strength (due to addition of different amount of cross-linking agent).There is dependences of the strength and time of gelling of water shut-off composition by the temperature that helps to quickly determine the optimal concentration of reagents for specific geological conditions. The effectiveness of the composition is confirmed by results of filtration experiments conducted on samples of natural core with modeling of thermobaric conditions. Proposedwater shut-off composition reduces the water cut of the displaced liquid by 24% and increase the rate of displacement of oil by water in fractured porous reservoir from 0.07 to 0.3.

Viscosities of CaO–SiO2–Al2O3–(R2O or RO) Melts

The effect of adding R2O (R=Li, Na and K) or RO (R=Ba, Mg) on the viscosities of CaO–SiO2–Al2O3 (CaO/SiO2=0.67, 1.00 or 1.22, Al2O3=20 mass%) melts has been measured by rotating crucible viscometer. In addition, structural characterizations of these quenched vitreous samples have been investigated by 27Al and 29Si MAS-NMR spectra.The viscosities of CaO–SiO2–Al2O3–R2O quaternary melts decreased with increasing the additive content of Li2O or Na2O. However, the viscosity of the melts increased with increasing the additive content of K2O. In the case of CaO–SiO2–Al2O3–RO quaternary melts, the viscosities of the melts with CaO/SiO2=0.67 decreased with increasing the additive content of BaO or MgO, however, the viscosities of the melts with CaO/SiO2=1.00 and 1.22 increased with increasing the additive content of BaO.In the case of CaO–SiO2–Al2O3–R2O, the analysis of 27Al MAS-NMR spectra and 29Si MAS-NMR spectra indicated that the degree of polymerization of silicate anions in the glasses decreased with the addition of Li2O or Na2O, and that the degree of polymerization of aluminosilicate anions in the glasses increased with the addition of K2O. It was estimated from the results that the increase in viscosities of CaO–SiO2–Al2O3–K2O melts was dependent on increase of aluminosilicate anions in the melts with the addition of K2O.In the case of CaO–SiO2–Al2O3–RO, the analysis of 27Al MAS-NMR spectra and 29Si MAS-NMR spectra indicated that the degree of polymerization of silicate and aluminosilicate anions in the glasses decreased with the addition of MgO. The degree of polymerization of aluminosilicate anions in the glasses increased with the addition BaO. It was estimated from the results that the increase in viscosities of CaO–SiO2–Al2O3–BaO melts was dependent on increase of aluminosilicate anions in the melts with the addition of BaO.

ＭｇＯ‐ＳｉＯ２系融体の液相線温度および粘度に及ぼすＲＥ２Ｏ３（ＲＥ＝Ｙ，Ｇｄ，Ｎｄ， ａｎｄ Ｌａ）添加の影響

The effect of adding RE2O3 (RE=Y, Gd, Nd and La) on the liquidus temperature of 45.2MgO-54.8SiO2 (mol%) system has been measured by the hot-thermocouple method. Moreover, The effect of adding RE2O3 (RE=Y, Gd, Nd and La) on the viscosity of 45.2MgO-54.8SiO2 (mol%) melt has been measured with a rotating crucible viscometer. In addition, structural characterization of the quench vitreous samples was investigated by using IR spectra. Liquidus temperature and viscosity decreased with increasing of RE2O3 content, depending on the ionic radius of adding rare-earth elements. A marked change was observed in the order of ionic radius from La to Y. These results indicate that RE2O3 behaves as a network modifier in RE2O3- (45.2MgO-54.8SiO2) melts. It is very likely that the RE2O3 with the larger ionic radius will modify the silicate networks more strongly. The IR spectra indicated that the degree of polymerization of silicate anions in RE2O3-(45.2MgO-54.8SiO2) melts decreased with increasing RE2O3 content.

Characteristics of Microhydrates Formed under Steam Conditions

This paper presents the physical properties and chemical composition of hydrates formed under steam conditions. The test specimens were made with cement as well as individual compounds. A comprehensive study on the characteristics of hardened hydrates in a microscopic scale was carried out. An improved polymerization of silicate anions resulting in an increased CaO/SiO2 ratio at an elevated temperature was verified by the nuclear magnetic resonance (NMR) spectroscopy analysis. Dense microstructures of hydrates and low content of Ca(OH)2 crystals were observed by the scanning electron microscope (SEM), energy dispersive spectrometer, environmental SEM, thermogravimetric analyzer (TGA), and x-ray diffractometer tests. Mercury intrusion porosimetry was used to examine the pore structures of hydrates. It revealed that the hardened paste made with the dry-mixture/steam-injection (DMSI) method developed microstructures with low porosity, small pore radius, and larger surface areas. These observations agree with the NMR/TGA test results. This paper also discusses the effects of sample fineness and compaction on the hydrates microstructures formed under steam environment. The test results verify the validity of the DMSI concept.

Disordered Molecular Sieve with Branched Mesoporous Channel Network

A disordered mesoporous silica material has been prepared using polymerization of silicate anions surrounding surfactant micelles in the presence of organic salts. The local structure of the material has been investigated using a transmission electron micrograph image of platinum wire grown inside the mesopores. This micrograph imaging technique, developed in the present work, clarifies that the pore structure is a three-dimensional, disordered network of short wormlike channels while the channel widths are uniform. The fully disordered channel branching similar to a three-dimensional fractal with truly uniform channel widths distinguishes the present material with respect to the recently found ordered mesoporous molecular sieve MCM-41. The branching channel structure has a remarkable advantage for adsorption and catalytic applications, compared with the MCM-41. The structure also exhibits outstanding hydrothermal stability. The recognition of the disordered, branching structure with uniform channel widths is expected to open a new class of noncrystalline molecular sieves, and the unique structures with good stability will provide new opportunities for rational design of heterogeneous catalysts, adsorbents, and other related materials.

Cement pastes of low water to solid ratio: An investigation of the polymerization of silicate anions in the presence of a superplasticizer and silica fume

Polymerization of silicate anions was investigated by the molybdate method in cement pastes with water to solid ratio of 0.28. Two series of samples - with and without superplasticizer admixture - were prepared using ordinary portland cement (OPC) in which 0, 5, 10, and 15 percent by weight was replaced by condensed silica fume (CSF). During the hydration ranging from 4 hours up to 50 days, the free lime content and insoluble residue were also determined. The 28 day compressive strengths of the hardened composites were between 79 and 108 MPa. The results from the molybdate complex confirm that the presence of CSF in hydrating blends and its pozzolanic activity influences the size dispersity of silica anions by increasing the proportion of polymers. It is also suggested that in the cement pastes of w/s ratio of 0.28, the conversion level of CSF by pozzolanic reaction decreased. Finally, a comparison is made between the polymerization characteristics of the 0.28 w/s-ratio pastes and pastes of w/s = 0.68 which have been hydrated for 6.3 years.

Polymerization of Hydrolysis Products of Methyltriethoxysilane in Aqueous Solutions

The structure and distribution of chemical species of hydrolysis and polycondensation products of methyltriethoxysilane in aqueous solutions containing sodium ions have been studied with the trimethylsilylation technique and by 29 Si n.m.r. spectroscopy. 11 trimethylsilylated derivatives of the products were obtained from the solutions. The recovery of methyltrisilanol (CH 3 Si(OH) 3 was much higher than that of the monosilicic acid in an aqueous sodium silicate solution at the same Si concentration and the same sodium ion-to-silicon molar ratio, suggesting that the polymerization of silicate anions is easier than that of hydrolysis products of methyltriethoxysilane in aqueous solutions. On the basis of the distribution, assignment of 29 Si n.m.r. peaks corresponding to low-molecular weight species formed from methyltriethoxysilane has been discussed

X-ray diffraction analysis on the structure of the glasses in the system PbOSiO 2

The structures of PbO·SiO 2 and 2PbO·SiO 2 glasses have been analyzed by use of X-ray diffraction data and pair function method. For PbO·SiO 2 glass, a model consisting of chains of PbO 3 pyramids and silicate chains showed good agreement with the observed RDF. For 2PbO·SiO 2 glass, the present authors reported previously a model in which chains of PbO 3 pyramids are connected with SiO 4 tetrahedra, while the chromatographic analyses of silicate anions by Götz et al. and Smart et al. showed that silicate anions are distributed from monomer to polymer in the glass. We reexamined the structure of this glass referring to these results. Three representative models containing isolated SiO 4, Si 4O 12 rings and (SiO 3) n chains respectively as well as PbO 3 chains were constructed and the RDFs were calculated with changing structure parameters. These three models showed satisfactory agreement with the observed data, showing that silicate anions are distributed from monomer to polymer in 2PbO·SiO 2 glass and an increase of SiO 2 content leads to polymerization of silicate anions to longer chains up to PbO·SiO 2 composition, while the chains of PbO 3 pyramids remain unchanged.

Polymerization of silicate anions in solutions at low concentrations

Adsorption of tetrahedral-forming ions, such as silicates and phosphates, is considered to be the main cause of retention of these anions on the surfaces of hydrated Al- and Fe-oxides. The importance of this retention in natural and man-caused phenomena has been the subject of many investigations. When adsorption studies are conducted, the role of the surface and the charges developed on it by the potentially determining ions tend to be emphasized, while the nature of the sorbate is rarely considered or investigated. Nevertheless, the excluded or equilibrium solution is the seminal source of information in the formulation of adsorption mechanisms or models. The ionic species present in the equilibrium solution are practically always taken for granted, that is, from data previously published. They are thought to be a simple function of solution pH, without further analysis of ionic speciation changes that occur during the sorption process. Here, we provide direct experimental evidence, using an advanced and sensitive spectroscopic technique, laser Raman spectroscopy (LRS), that aqueous equilibrium silicate solutions at low concentrations contain polymeric and/or other anionic complexes and not just monomeric species. These low concentrations are similar to those used in most previous sorption experiments on Fe- and Al-sesquioxides and on tropical acidic soils. Our findings clearly indicate that any mechanisms and models that are proposed to describe anion sorption on sesquioxides should consider that silicates, and probably some other tetrahedral-forming anions, are not present in solution solely as monomeric ionic species as most investigators have assumed1–11. Irregularities in fitting experimental data to models previously reported prompted this research2–4,6,12.

Effects of water on the glass transformation temperature of rhyolitic rock melt.

The glass transformation temperature (Tg) of rhyolitic rock melt was considerably influenced by the content of water in the melt. Tg determined by means of the differential thermal analysis-thermogravimetric analysis under various experimental conditions ranged from 490° to 760°, and decreased linearly with increasing water content in the melt at Tg. The experimental equation for the relation was Tg=778-223WH2O. The decrease of Tg with the increase of water may be explained by a decrease of the degree of polymerization of silicate anions in the rock melt as was analogized from the case of organic polymer solution. In the experiments under the same conditions (sample grain size, heating rate), a strong correlation was observed between Tg and water released between Tg and 950°C. On the other hand, it was difficult to find a certain relationship between Tg and water released at above 950°C. These results can be explained in terms of the difference of the force constant of OH bonding of water. The water which had a smaller force constant dissociated from the melt structure at lower temperature, moved freely among the melt structure and destroyed Si-O-Si bonds by the collision with the bonds. Thus the water had a direct effect upon Tg.

Silicate groupings in glassy and crystalline 2PbO·SiO 2

The type and the amount of silicate groupings existing in glassy and crystalline 2PbO·SiO 2 have been determined by direct chemical methods: paper chromatography, trimethylsilylation combined with gas-liquid partition chromatography and by the molybdate method. The results obtained by these three different methods are in good agreement and demonstrate, that glassy 2PbO·SiO 2 and each of the three main crystalline polymorphs are characterized by its own specific silicate anion distribution: the distribution in vitreous 2PbO·SiO 2 is of a polyanionic nature; in TPb 2SiO 4 dimetic groups [Si 2O 7] 6− prevail; M 1Pb 2SiO 4 contains predominantly [Si 4O 12] 8− rings and HPb 2SiO 4 is a typical polysilicate with chain anions [SiO 3 2−] n . The results fit a structural model according to which glass is a random array of discrete polyatomic groupings; the gradual transition from the glassy state to the stablest crystalline structure is connected with degradation and polymerization of silicate anions.

PbO-SiO 2 melts: structure and thermodynamics of mixing

Thermodynamic properties of PbO-SiO 2 melts, obtained from published data and calculated from freezing point depressions, reflect the gradual polymerization of silicate anions in the melt as the SiO 2 PbO ratio is increased. The free energy of mixing curve at 1000°C has a minimum at 40 mole % SiO 2 and is convex-upward between 72 and 98 mole % SiO 2. The latter is an indication of metastable liquid immiscibility. The free energy minimum is correlated with the maximum in the distribution of nonbridging oxygens in the melt. In SiO 2-poor melts, the activities of PbO and SiO 2 (pure liquid standard states) show sharp negative deviations from ideality. The PbO activity reflects the paucity of free oxygen species in the melt whereas the SiO 2 activity reflects the depolymerized state of the silicate anions. In more SiO 2-rich melts, the activity of SiO 2 shows a positive deviation from ideality which is qualitatively correlated to a polymerization parameter. The heat of mixing term has a minimum of −2000 cal at 35 mole % SiO 2 and a maximum of +200 cal at 90 mole % SiO 2. The minimum is associated with the exothermic heat effect obtained during the reaction ( O 0) + ( O 2−) = 2( O −), whereas the maximum corresponds to the endothermic heat effect obtained when coordination polyhedra of oxygens form around the Pb cation. The entropy of mixing curve has the same form but is systematically smaller than a theoretical curve calculated on the assumption of random mixing of oxygen species. The discrepancy is due to the entropy loss obtained by the clustering of oxygen species to form complex silicate species.

Density and structures of ternary silicate melts

Using the maximum bubble pressure method the (density, composition) relationships occurring as the result of replacement of Fe2+ ions in an iron silicate by Ca2+, Mn2+, Co2+ and Ni2+ ions along the composition line containing 29 mole % silica in the respective ternary silicate systems have been determined at 1410°C. The calculated (oxygen density, composition) relationships indicate that a change in the anionic configuration of ternary silicate melts occurs along iso-silica mole fraction lines in the system and this conclusion agrees with polymerization models of basic silicates. Correlation is obtained between the composition dependence of the activities of constituent metal oxides in ternary silicate melts and the composition dependence of the anionic configuration. The anionic configuration, or degree of polymerization of silicate anions occurring in a basic silicate melt, is discussed in terms of the relative energetics of possible ionic associations.