Effect Of Na2O Addition Research Articles

Effect of Na2O addition on crystallization behavior and properties of 25 wt%Al2O3–SiO2–CaO non-metallic inclusion-type oxides

The 25 wt%Al2O3–SiO2–CaO inclusion with high basicity has the characteristics of high melting point and strong crystallization tendency. The effect of Na2O addition on the crystallization behavior and properties of 25 wt%Al2O3–SiO2–CaO non-metallic inclusion-type oxides was systematically investigated in the current study. The time-temperature-transformation (TTT) diagrams and continuous-cooling-transformation (CCT) diagrams were constructed introducing the single hot thermocouple technology (SHTT). The crystallization temperature decreased from 1640.15 K to 1514.15 K with the Na2O content increased from 0 to 6.92 wt%, then rose to 1564.15 K when the content of Na2O was equal to 11.81 wt%. Above 1473.15 K, the incubation time was first prolonged and then shortened with the increase of Na2O content. The crystallization tendency was first inhibited and then promoted with increasing the Na2O addition. The XRD result showed that the precipitated crystals of the oxide system transformed from Ca2Al(AlSiO7) to NaCaAlSi2O7 when the content of Na2O exceeded 6.92 wt%. The FESEM micrograph showed that the morphology of crystals from all samples demonstrated spherical or rod-like. The calculated melting point decreased from 1840.81 to 1680.29 K then rose to 1755.56 K with the increase of Na2O content. The crystallization tendency or ability of the oxide system could be predicted by the initial crystallization potential, the viscosity at the melting point, the rate of change of viscosity with temperature as well as the activation energy of crystallization.

Study on the separation of silicon from refining slag of industrial silicon

During the process of production and refining of industrial silicon, the discharged slag usually contains more than 15 mass% of metallic silicon. However, the separation of silicon from slag is very difficult due to the close density of silicon and slag as well as the high viscosity of slag, which results in the waste of resources. In the present work, the effect of Na2O addition on the separation of silicon from slag is investigated in detail. It is found that the optimum separation condition of slag and silicon is 1723 K reacting for 60 min by adding 10 mass% Na2O to the slag. Viscosity and density are two important factors affecting the separation effect of silicon from slag. The addition of Na2O reduces the viscosity of slag and promotes the separation of silicon from slag. Even if the addition of Na2O will decrease the density of slag which is detrimental to the separation of silicon, the density variation is not the determining factor affecting the separation relative to viscosity. The separation and extraction of metallic silicon from silicon slag is of great significance for improving utilization of resources and reducing environmental pollution.

Effect of Na2O Addition on Phosphorus Dissolution from Steelmaking Slag with High P2O5 Content

Slag with high P2O5 content generated during the use of high-P iron ores is an important potential source of phosphate. Because the P-rich 2CaO·SiO2–3CaO·P2O5 solid solution in the slag was preferentially dissolved compared with other phases in aqueous solutions, selective leaching of P from slag with high P2O5 content was applied to recover soluble P in this study. To improve dissolution of the P-rich solid solution, the effects of Na2O addition on slag dissolution were investigated under different leaching conditions. The results show that a new 2CaO·SiO2–2CaO·Na2O·P2O5 solid solution was formed in the slag after Na2O was added, resulting in a higher dissolution ratio of P. However, at pH 7, further increase in Na2O content did not promote P dissolution because of phosphate precipitation. At pH 5, a better P dissolution was obtained and its dissolution ratio increased with an increase in Na2O content, indicating that Na2O addition promoted the dissolution of the solid solution from slag. In the citric acid solution, more than 90% of the solid solution was dissolved and the dissolution of the matrix phase was suppressed dramatically by Na2O addition, leading to a low dissolution ratio of Fe. An excellent selective leaching of P from slag was achieved.

Surface Active Effect of Na2O on the Rate of CO2 Dissociation on the Surface of Molten FeOx-Na2O and FeOx-SiO2-Na2O Systems

It is well known that P2O5 and Na2O have strong surface active effect in the molten oxide systems and affect the rate of oxidation or reduction of melts. In the previous work, the effect of P2O5 addition on the rate of CO2 dissociation on the surface of FeOx (FeO and Fe2O3)-based molten oxides was investigated by isotope exchange technique and it was confirmed that P2O5 strongly disturbs CO2 dissociation. In the present study, the effect of Na2O addition on the rate of CO2 dissociation on the surface of FeOx-Na2O and FeOx-SiO2-Na2O (mol%FeOx : mol%SiO2=65 : 35) melts was measured at 1773 K with PCO2/PCO=1 by isotope exchange technique. Reaction rate constant drastically increased with increasing Na2O content for the FeOx-Na2O system. On the other hand, rate constant gently increased for the FeOx-SiO2-Na2O system. The Fe3+/Fe2+ ratio of each system also slightly increased.To estimate the rate constant from the composition of melts, the relationship between the rate constant and the Fe3+/Fe2+ ratio for the FeOx-CaO-SiO2 system was also investigated. From the comparison of the estimated and observed rate constants, the strong promoting effect of Na2O for CO2 dissociation was confirmed in the FeOx-Na2O system.The surface active effect of Na2O was analyzed by “smoothed surface potential model”, and the nature of molten oxide was discussed. From the obtained values, the surface tension of the molten oxide was estimated as a function of Na2O concentration.

Formation and crystallization of gels in the Na2O-SiO2-TiO2-ZrO2 system

5Na2O·95(SiO2 + TiO2 + ZrO2) gels together with Na2O-MO2 gels (MO2 = SiO2, TiO2, ZrO2) were synthesized and effect of Na2O addition to the gel formation and crystallization behavior were studied. From Si(OC2H5)4, Ti(iso-OC3H7)4, Zr(n-OC3H7)4 and NaOCH3 solutions in EtOH without H2O, transparent, opaque and heterogeneous gels were obtained. By SEM observation, it was found that the opague bulk gels, rich in TiO2 or ZrO2 component, contain agglomerated spherical particles of less than 10 μm diameter. Crystallization temperature (Tc) measured by DTA decreased sharply from 1258°C (SiO2) to 613°C (30Na2O·70SiO2) due to the increasing non-bridging oxygens in the Na2O-SiO2 system. But in the Na2O-TiO2 and Na2O-ZrO2 systems, Tc increased as Na2O content was increased up to 10 mol%. The thermal stability, defined by Tc/TL ratio, decreased from Tc/TL = 0.77 (SiO2) to 0.57 (5Na2O·95SiO2) or increased from Tc/TL = 0.30 (TiO2) to 0.67 (30Na2O·70TiO2) with Na2O addition. In the 5Na2O·95(SiO2 + TiO2 + ZrO2) system maximum Tc was 891°C at 5Na2O·76SiO2·19ZrO2 composition and decreased as TiO2 or ZrO2 contents increased. Compared with the SiO2-TiO2-ZrO2 gels, Tc of the 5 mol%Na2O containing gels (Na2O-SiO2-TiO2-ZrO2) was lower in SiO2 rich composition and higher in TiO2 or ZrO2 rich compositions. It is assumed that addition of Na2O changed the structure of amorphous TiO2 and ZrO2 someway to increase their thermal stability or amorphous forming ability. After DTA run up to 1000°C, cystalline phases precipitated in the 5Na2O·95(SiO2 + TiO2 + ZrO2) gels were determined by XRD analysis.

Effect of Na 2O addition on the properties and structure of germanate glass

The Li 2O (Na 2O)CaOAl 2O 3GeO 2 system, was prepared for infrared transmitting germanate glasses. The properties and structure of these glasses have been studied. The transition and crystallization temperatures are raised as Li 2O concentration is decreased and Na 2O concentration is increased. The refractive index and Abbe number are increased with increasing Na 2O content. The vibration modes observed in the high wave number regions of the FTIR spectra are from the symmetrical and antisymmetrical stretching and bending motions of GeO 4 tetrahedra.

Effect of Na2O Addition on the Optical Properties and Chemical Durability of Li2O–CaO–Al2O3–GeO2 Glass

By progressive weight percent substitution of Na2O for Li2O, at a constant ratio of concentration of CaO, Al2O3, and GeO2, the Li2O(–Na2O)–CaO–Al2O3–GeO2 system is prepared for infrared transmitting germanate glasses. The optical and chemical durability properties of these glasses have been studied. The infrared cutoff for these germanate glasses is about 7.2 µm longer than that of 5 µm for silicate glasses. The ultraviolet absorption edge for these glasses is near 306 nm, except for the glass which contained 6.44 wt% Na2O at 295 nm. The refractive indexes of these germanate glasses increase as Na2O content is increased. The Abbe number for all glass samples is about 62.03±4.07. The absorption coefficients for these germanate glasses at 2.5 µm and 500–700 nm are 0.023 mm-1 and 0.019 mm-1, respectively. The leaching results indicate that the glass with 3.22 wt% Na2O ( C3 glass) has the minimum weight loss in the chemical durability test.

The effect of Na2O addition on the magnetic properties of BaFe12O19 ferrites

The effect of Na2O addition on the magnetic properties of isotropic BaFe12O19 ferrites from hot-rolled mill scale was investigated. Na2O was added up to 0.2s%. The values of coercivity and energy product maximum are significantly increased, notably (BH)max from 0.8 to 0.9× 106 OeG, and those of intrinsic coercivity rise drastically from 2500 to 4000 0e when Na2O up to 0.15% is added after calcination. On the other hand, the magnetic properties of the ferrites gradually deteriorate and the values of intrinsic coercivity vary very little when Na2O up to 0.2% is added prior to calcination. The densification of ferrites is slightly decreased in the presence of the Na2O, regardless of the time at which it is added.