Activity Of Na2O Research Articles

Thermodynamic Equilibrium between Non-Stoichiometric Na-β-Alumina and α-Alumina

A solid-state electrochemical technique based on a potentiometric oxygen concentration cell has been used to characterize the thermodynamic stability of the phase mixture α-Al2O3 + Na-β-Al2O3 by determining its Na2O activity. In combination with phase analysis based on Rietveld refinement of X-ray diffraction patterns the magnitude and variability of the stoichiometric composition of the β-phase have been quantified. Upon variation of the Na2O content of the phase mixture, the Na2O activity resulting from the α/β-equilibrium has proved to be stable because both phases are readily inter-convertible. This behaviour guarantees that the material is eminently suitable as a stable sodium electrode, while simultaneously functioning as a sodium-ion conducting solid electrolyte. The temperature dependence of the logarithm of the Na2O activity has been found to be two-part. This is in line with the trend of the majority of critically assessed literature data thus demonstrating that former apprehension about the prevalence of a possible methodical flaw due to electronic conduction was unsubstantiated. As a conclusion, the knowledge about electronic conduction through Na-β-Al2O3 is advanced. The findings are the prerequisite for putting a straightforward solid-state CO2 sensor and sodium ion battery into practice.

Understanding the Competition Mechanism between Na2O and CaO for the Formation of the Initial Layer of Zhundong Coal Ash

The contents of alkali and alkaline earth metals are higher in Zhundong coal, and there are serious problems of slagging and fouling during the combustion process. Therefore, it is of great significance to reveal the mechanism of slagging and fouling in the boiler of Zhundong coal. In this paper, first-principle calculations based on density functional theory are used to study the competition mechanism of alkaline metal oxides during the combustion process in Zhundong coal by establishing the Na2O(110)/CaO(100)-SiO2(100) double-layer interface model. The results show that the bond lengths of the surface of Na2O(110) and CaO(100) with SiO2(100) after adsorption were generally lengthened and the value of bond population became smaller, which formed a stable binding energy during the reaction. The electron loss of Na is 0.05 e, the electron loss of Ca is 0.03 e, and the electron loss of Na2O is greater than that of CaO. The charge transfer on the surface of Na2O with SiO2 is obviously higher than that of CaO and the orbital hybridization on the surface of CaO with SiO2 is weaker than that on the surfaces of Na2O with SiO2. Na2O is easier to react with SiO2 than CaO. The adsorption energies on the surface of Na2O and CaO with SiO2 are −5.56 eV and −0.72 eV, respectively. The adsorption energy of Na2O is higher than that of CaO, indicating that Na2O is more prone to adsorption reactions and formation of Na-containing minerals and other minerals, resulting in more serious slagging. In addition, the XRD analyses at different temperatures showed that Na-containing compounds appeared before Ca-containing ones, and the reaction activity of Na2O is stronger than that of CaO in the reaction process. The experimental results have good agreement with the calculation results. This provides strong evidence to reveal the slagging and fouling of Zhundong coal.

Mineralogical and physicochemical constraints on the hydrothermalism of volcanic rocks in the Paraná Igneous Province, northwestern Paraná state, Brazil

Hydrothermally affected basaltic flows and volcaniclastic rocks in northwestern Paraná (Brazil) display textural features associated with secondary minerals, reflecting the temperature intensity and evolution of the hydrothermal process. Determination of the secondary mineralogy and the geochemical processes associated with their precipitation are addressed in this paper. The lithotypes that comprise the bulk of the Paraná Igneous Province have millimetric to centimetric vesicles filled by secondary minerals. Field data, petrographic descriptions, mineral characterization and mineral chemistry were used to analyze these secondary mineral phases. Matrix material in volcaniclastic rocks (e.g. shards, glass pisolites) precedes the precipitation of the secondary minerals. Coalescence and necking features are common in vesicles located on top of basaltic flows. Clay minerals identified as vesicle and/or fracture infillings include celadonite, illite/smectite (I/S) interestratifications, as well as montmorillonite and nontronite, with morphologies typical of authigenic volcanic processes such as cauliflower-like and honeycomb. The occurrence of different zeolites species is primarily controlled by CaO and Na2O activity in the hydrothermal fluid. Heulandite is the most pervasive zeolite, followed by stilbite and analcime. Calcite occurs in the center of vesicles, as the last crystallizing phase, or isolated in monomineralic vesicles. Vesicle formation occurred by magma degassing processes at temperatures of up to 1150 °C. However, infilling of these voids occurred later with the percolation of hydrothermal fluids external to the system. Although random from a geographical perspective, gradual decrease in temperature and fluid evolution were responsible for the systematic change in the mineral phases within individual vesicles. The hydrothermal fluid was marked by a Ca–Na signature, high cation/hydrogen ratio and low to intermediate temperatures, ranging between 50 and 200 °C. The controls for precipitation were mainly temperature and the chemical composition of the fluid, with high alkalinity and low H+ activity.

The chemical behaviour of chlorine in silicate melts

We have performed experiments at 0.5–2 GPa and 1200–1500 °C to investigate the dissolution behaviour of chlorine in silicate melts. The experiments were performed with chlorine fugacities controlled by mixtures of Ag, AgCl and AgI and oxygen fugacity buffered at C-CO-CO2 (CCO) and Re-ReO2. The results demonstrate that the initial chlorine dissolution mechanism involves the replacement of O2− in the silicate melt by two dissociated Cl− ions according to the reaction:Cl2 + [O2−]melt = 2[Cl−]melt + 0.5O2.The same dissolution mechanism applies to hydrous, fluid-saturated basalt at 100–200 MPa/1050 °C. Experiments using both an Fe-free haplobasaltic composition (An50Di28Fo22) and an Icelandic basalt followed the predicted dependence of Cl concentration on f(Cl2)0.5 and f(O2)0.25. This Henrian behaviour extends from 0 to at least 2.6 wt% Cl dissolved in the haplobasaltic composition, 1.6 wt% Cl in anhydrous basalt and ∼1.5 wt% Cl in fluid-saturated basalt. Deviations from Henry’s Law behaviour at higher concentrations are consistent with progressive association of Cl− ions. In the Henry’s Law region Cl concentration in the An50Di28Fo22 composition is given by (wt%):logClmelt=1.20632-94040PT-0.25logfO2+0.5logfCl2P is in GPa, T in kelvin, values in brackets are 1 standard error, and f(Cl2) and f(O2) refer to standard states of pure gas at 0.1 MPa and the temperature of interest. For the natural anhydrous basalt we obtain:logClmelt=0.98464-93070PT-0.25logfO2+0.5logfCl2By considering the P-T dependences of the Cl contents of melts we find that the concentrations observed in nature are extremely stable in basalt to very low pressures. Basalts containing the typical concentration range of 0.05–0.5 wt% Cl should, for example, only begin to degas their chlorine significantly, as HCl, at pressures in the range 0–5 MPa. Data on hydrous, fluid-saturated basalt at 100–200 MPa are, when corrected for dissolution of Ca, Na and K in the fluid, broadly consistent with our results for anhydrous basalt.Finally, we use recently evaluated thermodynamic data for sodalite (Na4Al3Si3O12Cl) to calculate the conditions under which this phase would stabilise in trachytes and phonolites. We find that the appearance of sodalite as a liquidus phase reflects a combination of low liquidus temperature and high Na2O activity rather than unusually high chlorine fugacity.

Electrochemical determination of activity of Na2O in Na2Ti6O13-TiO2 two phase system between 803–1000 K

Sodium oxide (Na2O) activity in NT6-TiO2 was measured using the EMF method with test electrode Pt,Na2Ti6O13+TiO2 (NT6-TiO2). NASICON (Na2Zr2Si2PO12) was used as the solid electrolyte in conjunction with a biphasic mixture of alpha alumina (α-Al2O3) and sodium beta alumina (Na2O.x Al2O3(8.5≤x<11)) as the reference electrode and measurements taken over the temperature range of 803≤T≤1000 K. Internal consistency of the cell was ensured by approaching the equilibration target temperature from both sides, during cooling and heating. EMF measurements showed linear dependency with temperature in the temperature range under study. The activity of Na2O in NT6-TiO2 in the temperature range under study was determined. This was found to be logaNa2O(NT6−TiO2)=1.20−13211T. This data is important in the determination of theoretical EMF for the calibration electrochemical sensors employing NT6-TiO2 electrode. Furthermore, it was found that, aNa2O(NT6−TiO2)>aNa2O(NASICON) indicating chemical stability when in contact with NASICON at higher temperatures.

Fast initializing solid state electrochemical carbon dioxide sensor fabricated by a tape casting technique using yttria stabilized zirconia and sodium beta alumina heterojunction

Solid-state bi-electrolyte carbon dioxide sensors with an yttira stabilized zirconia (YSZ) and sodium beta alumina (NBA) heterojunction were fabricated using the tape casting method to measure CO2 concentrations in the air. The enhanced interface between NBA, expressed by (1+x) Na2O·11 A12O3 and YSZ was made by the liquid phase sintering method while varying the ratio of Na2O/Al2O3 from x=0 to x=0.6. YSZ/Pt electrode was used as an air reference, maintaining a constant oxygen concentration of 21%, and Na2CO3 was used as a CO2 sensing electrode. The responses of the sensors to various concentrations of CO2 were evaluated at temperatures ranging from 550°C to 650°C. The electric potential difference of the sensors exhibited Nernstian behavior with sensitivity greater than 99% of the theoretical value at 650°C. The activity of Na2O at the bi-electrolyte junction remained constant, showing invariance with the CO2 concentrations tested. The time for the initial stabilization was as short as 66s.

Solubility of Metal Oxides in Na2o-B2O3 Melts Associated with Basicity

1. Introduction Molten salts have been used as slag, and as an oxidation inhibitor in the steel production process at high temperature. Steels and refractories are corroded by adherence of fused salts such as molten oxide to their surfaces at the solid-liquid interface. For example, casting nozzles made of refractory oxides are corroded by molten oxide used in continuous casting molds. Dissolution of oxides on the surface of materials in molten salts is thought to be the cause of hot corrosion1). So, it is necessary to understand the corrosion behavior to clarify the dissolution behavior of oxides in melts. The basicity of the fused salts, which is similar to pH in aqueous solution, is one of the dominant influencing factors in the dissolution behavior of metal oxides. In the range of basic of fused salts, metal oxides are dissolved via a basic dissolution reaction, and in the range of acidity, an acidic dissolution reaction dominates in melts1). Dissolution of metal oxides in molten Na2SO4 at 1173 K associated with basicity defined by Na2O activity is well known as an example of reaction of metal oxides with fused salts1). To clarify the dissolution behavior of protective oxide scales in a molten sulfate film under a corrosion environment of gas turbine blades and vanes, the dissolution behavior of metal oxides such as Fe2O3 and Cr2O3 in molten Na2SO4 was investigated. In the case of molten oxides, dissolution reactions of metal oxides in molten sodium silicate used in the steel process were investigated2). However, researches on the dissolution reaction of metal oxides in borate melt, which steel slag comprises, are not sufficient. In this study, the correlation between the basicity and the solubility of Fe2O3 and Cr2O3 in Na2O-B2O3 melt was investigated using the method applied to molten Na2SO4 3). 2. Experimental In order to measure the solubility of Fe2O3 and Cr2O3 powders in binary fused Na2B4O7-B2O3 melts at 1173 K and 1373 K in air, salts and oxide powders were placed in a platinum crucible and heated at 1173 K and 1373 K. The temperature of the platinum crucible was measured by an R-type thermocouple with a wire diameter of 0.2 mm. The basicity of the melt was measured by a basicity sensor using a solid electrolyte, and a coil of platinum wire was immersed and drawn out of the melt to quench the melt sample. To determine the quantity of soluble Fe or Cr in the melt, the quenched samples were analyzed by ICP-AES. To secure the chemical equilibrium of the melts, measurements were conducted after heating at 1173 K and 1373 K in air for more than 86.4 ks. 3. Results For the entire range of the tested basicity, the solubility of Fe2O3 was one order of magnitude higher than that of Cr2O3. The solubility of both Fe2O3 and Cr2O3 decreased as the basicity of the melt increased. From the oxides’ solubility dependence on the melt basicity, both Fe2O3 and Cr2O3 are suggested to dissolve by the basic dissolution reaction. Comparing the solubility of oxides with the same basicity at 1173 K and 1373 K suggests the possibility of organizing the solubility of oxides in Na2O-B2O3 melts in air by their basicity. References 1) R. A. Rapp et al.: JOM 1994. December 47-55 2) H. Khedim et al.: J. Non-Crysta. Solids. 356 (2010) 2734-2741 3) R. Toki et al.: Mater. Trans. 57 (2) (2016) 143-147

Role of volatiles (S, Cl, H2O) and silica activity on the crystallization of haüyne and nosean in phonolitic magmas (Eifel, Germany and Saghro, Morocco)

To constrain the crystallization of alkaline and volatile-rich lavas present in intraplate settings, we studied the petrological features and the geochemical composition of major, trace, and volatile elements of mineral and bulk-rock of two sodalite-bearing phonolites: (1) hauyne-plagioclase-bearing Si-K-rich phonolite from Laacher See (Germany) and (2) nosean-nepheline-bearing Si-poor phonolite from Saghro (Morocco). In hauyne-bearing phonolites (55–59 wt% SiO2, K > Na, Na+K/Al = 0.96–1.08), we found that the low silica and low sodium activity promoted the early crystallization of S-rich hauyne (13.7–13.9 wt% SO3, 0.4 wt% Cl) + S-rich apatite (0.7–0.9 wt% SO3), titanite, and rare pyrrhotite followed by clinopyroxene-plagioclase-sanidine at relatively low pressure and temperature (P = 250 MPa and T = 850 °C) and oxidized condition (ΔNNO-NNO+1, where NNO is nickel-nickel oxide buffer). The crystallization of hauyne occurred at fluid-undersaturated conditions from a silicate melt with 6 wt% H2O, 0.17–0.23 wt% Cl, 0.11–0.4 wt% S, and 0.07–0.14 wt% F. Nosean-bearing phonolites from Saghro are silica-poor and peralkaline (52–54 wt% SiO2, Na > K, Na+K/Al = 1.2) and crystallized at higher P and T (300 MPa and 950 °C) and more reduced conditions (NNO) compared to hauyne-bearing phonolites. The incongruent reaction to form nosean requires high silica and Na2O activity. The mineral assemblage and composition suggest early crystallization of nepheline followed by nosean (7.8–8.8 wt% SO3; 1–1.1 wt% Cl). The sequence of crystallization is: clinopyroxene + nepheline + S-poor apatite (<0.04 wt% SO3) + pyrrhotite followed by nosean and titanite. Nosean-bearing magmas are fluid-undersaturated with relatively low volatile content (4 wt% H2O, <0.25 wt% Cl, <0.056 wt% S, 0.08–0.1 wt% F), although Cl may have exsolved during ascent and formed a fluid phase (NaCl-bearing). Both hauyne- and nosean-bearing phonolites are last equilibrated at relatively low pressure and high temperature. Hauyne and nosean crystallized at oxidized and volatile-rich pre-eruptive conditions. They record the volatile concentrations at depth and may be used as oxybarometer. The incongruent reactions involved to form hauyne and nosean suggest that phonolitic magmas became more oxidized during crystallization. The initial volatile concentrations in basanite/nephelinite magmas, from partial melting of volatile-bearing K2O-rich mantle rock, should have been one important factor influencing the crystallization of hauyne-bearing Si-K-rich phonolite and nosean-bearing Si-poor phonolite in intracontinental setting.

Hot Corrosion of SiC/BN/SiC Composites

SiC fiber-reinforced SiC matrix composites with a BN interphase (SiC/BN/SiC) are proposed for hot-section turbine engine applications. NaCl ingested into the engine in marine environments can react with sulfur impurities present in fuel forming molten sodium sulfate deposits resulting in hot corrosion. Hot corrosion of bulk SiC has been investigated, however, the effects of BN on SiC corrosion, as well as an understanding of hot corrosion resistance of SiC fibers and SiC matrix materials produced by different processing routes has not been elucidated. In this study, Na2SO4-induced hot corrosion of model materials (i.e. bulk CVD or Hexoloy SiC with thin BN surface films) and SiC/BN/SiC composites was characterized in furnace studies at temperatures between 900 and 1150°C, for times up to 96 hours, and in O2 with 2.5 or 1000 ppm SO2. Na2SO4 was applied to the surface of coupons prior to furnace exposure. After exposure, the amount of corrosion was determined from weight change measurements. Corrosion products were characterized by Scanning Electron Microscopy, Energy Dispersive Spectroscopy, and dissolution followed by Inductively Coupled Plasma Optical Emission Spectroscopy. Thin film BN appeared to increase the hot corrosion attack of the model materials. The composites exhibited more severe hot corrosion than the model materials, especially in matrix areas with initial porosity. Sylramic fibers underwent more attack than Hi-Nicalon-S fibers. Ceramic matrix composites were also exposed in a Mach 0.3 Burner Rig at 950°C for times of 24 and 45 hours. Simulated seawater (NaCl in deionized H2O) was injected into the burner rig, reacted with sulfur in the fuel to form Na2SO4 (8ppm) to induce hot corrosion. Severe hot corrosion was observed under these conditions. Microstructural and compositional characterization of the corrosion products is underway. Finally, solubility of relevant oxides in sodium sulfate will be determined as a function of Na2O activity at 900°C to elucidate the SO2 and SO3 partial pressure dependence of hot corrosion of silica- and boria- forming materials.

Vaporization and caloric studies on sodium niobate

Thermodynamic studies of a polycrystalline sodium niobate (NaNbO3) under equilibrium conditions by the method of Knudsen effusion mass spectrometry (KEMS) were conducted in the temperature range 1250–1485K. The vaporization of pure Na2O(c) was investigated at temperatures of 900–1165K. Thermodynamic quantities of sublimation enthalpy, activity, and entropy were derived from the partial pressures of gaseous Na, Na2O, and O2 over the sodium niobate and pure sodium oxide reference samples. The sublimation enthalpy of Na from NaNbO3(c) at T=1370K was ΔsubH1370K0(Na)=465±9kJmol−1. Heat capacity measurements under constant pressure (Cp(T)0) by Dynamic Scanning Calorimetry (DSC) in the temperature range 298–1450K resulted in six polynomial equations for each branch of the five transitions. Below the first phase transition at 639K the Cp(T)0 values increased from 97 to 123Jmol−1K−1. Beyond this transition and up to the third one at 792K, Cp(T)0 gently inclined from about 120 to a maximum value of 123Jmol−1K−1. Finally, beyond the fifth transition at 907K it approximated to an almost constant value of 115Jmol−1K−1. The enthalpy and the entropy values were calculated from the Cp(T)0 polynomials and from the vaporization studies. The enthalpy of the five transitions in sodium niobate, ΔtrsH2980(NaNbO3(c)) were measured by drop calorimetry. Deduced from empirical and experimental approaches, the heat of reaction for oxides was ΔrH2980(NaNbO3(c))=−94.3±7kJmol−1 and the heat of formation was ΔfH2980(NaNbO3(c))=−1250.8±7kJmol−1. The thermodynamic activity of Na2O in sodium niobate was temperature dependent, and its values varied from 2.6×10−3 to 8.3×10−4 in the range 1100–1250K. NaNbO3(c) has a long-term stability in the temperature range including the transition to cubic phase at 907K.

Na2O activity and thermodynamic mixing properties of SiO2–Na2O–CaO melt

Electro-motive force (EMF) measurement using concentration cell with direct contact between sample and reference melts has been carried out to determine the Na2O activity of silicate melt. Thermodynamic mixing properties of silicate melts have been examined based on the temperature and compositional dependences of the Na2O activity. The Na2O activities for soda silicate melt and soda aluminosilicate melt measured by the method of this study are in agreement with previously reported values. The Na2O activities for (100−x−y)SiO2–xNa2O–yCaO (x=12–30; y=5–22, mol%) melts have been measured between 1273K and 1573K. The Na2O activity increases with increasing Na2O and CaO content when the melt is a depolymerized composition. The effect of Na2O and CaO contents on the Na2O activity decreases with increasing SiO2 content. They can be interpreted in terms of Gibbs energy of mixing as a concave function of composition. The comparison of partial molar entropy of mixing for soda-lime silicate and sodium silicate melts suggests the existence of local maximum of the entropy of mixing in depolymerized composition of SiO2–Na2O–CaO system. The effect of CaO on redox reaction of iron in silicate melt calculated from the Na2O activity is quantitatively consistent with that measured by voltammetry and wet-chemical analysis.

Thermodynamic mixing properties of liquids in the system Na 2O-SiO 2

Enthalpies of fusion have been measured by differential scanning calorimetry for a Na 2O-SiO 2 system at 50, 66.6, and 74.4 mol% SiO 2. Enthalpies of mixing of liquids obtained from different calorimetry techniques are critically evaluated. The data on calorimetric enthalpy, activity of Na 2O, cristobalite liquidus, and immiscibility gap are used to determine the enthalpy and entropy of mixing of sodium–silicate liquids are determined as a function of composition by the least squares method. The derived mixing properties are based only on the experimental data and are independent of any assumption about the structure and chemical species in liquids. The enthalpy of mixing has a minimum value of −120 kJ/mol at 35–40 mol% SiO 2 and is convex upward around 80–90 mol% SiO 2. The entropy of mixing have a maximum value of + 6 J/K-mol at 75 mol% SiO 2, and it decreases with the SiO 2 content to −5 J/K-mol at 40 mol% SiO 2. This decrease in entropy can be accounted for by ideal mixing of Q 4, Q 3, and Q 0 + 1 + 2 (= Q 0 + Q 1 + Q 2) species in the liquids and is responsible for the negative temperature dependence of the partial molar Gibbs energy of mixing of Na 2O, observed in activity measurements. Comparison of the present results with previous values suggests that a quasi-chemical model and the Adam–Gibbs model overestimate the configurational entropy of mixing of liquids.

Protective Al-rich mullite coatings on Si- based ceramics against hot corrosion at 1200 °C

The hot-corrosion behavior of uncoated SiC, bulk mullite and CVD grown mullite coatings in contact with Na 2SO 4 were investigated at 1200 °C. The range of thermodynamic activity of Na 2O (10 − 4 to 10 − 6 ) simulated in this study makes the oxide very basic leading to high reaction rates with SiO 2. Uncoated SiC corroded severely, forming various Na 2O·SiO 2 compounds with a significant weight gain. Even though the thermodynamic activity of silica is reduced in mullite, several compounds in Na 2O·SiO 2·Al 2O 3 system were formed in case of bulk mullite. CVD based mullite coatings with high alumina content at the top surface of the coating, and therefore reduced SiO 2 activity, offered protection to the underlying SiC in corrosive environments. As predicted correctly by thermodynamic calculations, the trend in weight gain with the coated SiC samples followed the theoretically calculated SiO 2 activity in Al-rich mullite.

CO2 sensing performances of potentiometric sensor based on Na1+xZr2Si2PO12 (0 &lt; x &lt; 3)

Potentiometric CO2 sensors based on NASICON (Na1+xZr2Si2PO12) were fabricated by combining with a Li2CO3-BaCO3 (1:2 in molar ratio) auxiliary phase. The CO2 sensing properties of NASICON (x = 0, 1, 2, 2.75) sensors were investigated under dry condition at 450°C. The electromotive force (EMF) values of NASICON sensors were proportional to the logarithm of CO2 concentrations in the range of 250 to 2500 ppm. When exposed to dry air containing 250 ppm CO2, the EMF values of each sensor continuously changed toward a negative potential. From a X-Ray Diffraction (XRD) measurement, it was confirmed that new crystal phases such as Li2ZrO3, ZrO2, Na2Zr(PO4)2 and Na5Zr(PO4)3 were formed at the interface between sensing electrode and solid-state electrolyte, because of reaction between Li2CO3 and NASICON. The result of XRD measurement suggested that the base-EMF change closely related with the decrease of Li+ activity in auxiliary phase and Na2O activity in NASICON.

Determination of Na 2O activities in silicate melts by EMF measurements

An EMF cell using a Na-β″-alumina electrolyte has been designed for the quantification of the thermodynamic activity of Na 2O ( aNa 2O) in a series of sodium-bearing silicate liquids at high temperature. Initial experiments have been performed using Na 2O–0.663WO 3 and Na 2O–0.555MoO 3 as reference liquids. Values of aNa 2O derived for Na 2O–2SiO 2 binary melt are found to be in excellent agreement with data from the literature, confirming the validity of the method. To extend use of this experimental set-up to higher temperature, the aNa 2O of industrial C-glass has been calibrated as a reference liquid at temperatures up to 1263 °C. The influence of additions of CaO, Al 2O 3 and B 2O 3 on the Na 2O activity of binary sodium-silicates has been quantified. For each glass composition, measured values of aNa 2O are a function of temperature, log( aNa 2O) varying as a function of inverse absolute temperature. Activation energies derived from these data are all generally similar with the exception of industrial E-glass, which is rich in Al and poor in Na. At constant temperature, additions of network forming Al 2O 3 and B 2O 3 to a Na 2O–SiO 2 binary melt yield a decrease of the activity of Na 2O, while addition of network modifying CaO results in an increase in ( aNa 2O). These changes are qualitatively consistent with predictions based upon expected modifications of melt structure. However, measured values of log( aNa 2O) do not correlate perfectly with theoretical models of glass basicity, suggesting that either sodium activity is decoupled from melt basicity, or that current models are insufficient to calculate that parameter, in particular for the case of liquids poor in Na and rich in Al.

05/01736 Gaseous emissions from burning diesel, crudeand prime bleachable summer yellow cottonseed oil in a burner for drying seedcotton

Liquid phase sintering permits lower temperatures to be used to produce SiC with a consequent saving in terms of cost, while maintaining mechanical properties. For application at elevated temperatures, corrosion resistance must also be maintained. Oxidation in air at 1000 and 1300°C of a SiC sintered with additions of Al2O3+Y2O3 resulted in protective oxidation kinetics with rates approximately an order of magnitude greater than generally available low-additive SiC. The contaminants present in combustion atmospheres, particularly S and Na, have a marked influence on the rate of material degradation depending on the partial pressure of SO3 and thus the sulphur content of the fuel. Burner rig tests at 1000°C resulted in high rates of attack due to the formation of a low viscosity Na-silicate surface layer in a low sulphur fuel combustion gas (Jet A1 kerosene). With a low-sulphur fuel (1% S marine diesel) the high SO3 partial pressure resulted in a low Na2O activity and limited acid (SiO2) base (Na2O) reaction. At 1300°C, similar rates of material degradation were observed. Details of the oxidation kinetics and oxidation product morphologies are given.

Experimental Studies of the Alkali Behaviour in Blast Furnace Type Slags

In a preceding paper, existing data on the chemical behaviour of alkali compounds and their influence on physical properties of BF slags as well as on materials circulation in the BF operations were critically reviewed. In the present work, new investigations based on fundamental experiments and thermochemical modelling are introduced. They have been focused on the determination of both chemical activity of Na2O and kinetics of Na2O and K2O evaporation from BF-type slags. The results for the activities aNa2O agree fairly well with data obtained from calculation based on the slag model of H. Gaye which seems generally suitable to predict chemical activities in molten slags. Kinetics of alkali evaporation from BF-type slags follow a first-order reaction. The rate constants for K2O are remarkably higher than those for Na2O. Alkali evaporation is enhanced with decreased %(CaO)/%(SiO2) ratio and lower Al2O3 content and is increased with temperature. It is further favoured under reducing conditions in the absence of iron oxide in the slag.

Long-term stability of potentiometric CO2 sensors based on Nasicon as a solid electrolyte

Five solid-state potentiometric CO2 sensors of the type: CO2, O2, Ag, M2CO3–BaCO3 |Nasicon| X, Pt, O2 (where M=Li or Na, X—Na2O activity buffer) were investigated. The effects of electrode composition and operating temperature on long-term performance of sensors were determined. It was found that the sensors with Na2Ti6O13/Na2Ti3O7 reference electrode show stable signal during 1000 h. No effect of the sensing electrode composition was observed. The optimal operating temperature of the studied sensors was 748 K. The formation of liquid phase at this temperature at the sensing electrode/solid electrolyte interface is suspected to be responsible for improvement of the sensors performance. The reactivity between sensing electrode and solid electrolyte materials at higher temperatures leads to sensors instability.

Long-term stability of potentiometric CO2 sensors based on Nasicon as a solid electrolyte

Five solid-state potentiometric CO2 sensors of the type: CO2, O2, Ag, M2CO3–BaCO3 |Nasicon| X, Pt, O2 (where M=Li or Na, X—Na2O activity buffer) were investigated. The effects of electrode composition and operating temperature on long-term performance of sensors were determined. It was found that the sensors with Na2Ti6O13/Na2Ti3O7 reference electrode show stable signal during 1000h. No effect of the sensing electrode composition was observed. The optimal operating temperature of the studied sensors was 748K. The formation of liquid phase at this temperature at the sensing electrode/solid electrolyte interface is suspected to be responsible for improvement of the sensors performance. The reactivity between sensing electrode and solid electrolyte materials at higher temperatures leads to sensors instability.

The activity of sodium oxide in molten float glass by EMF measurements

The Na 2O activity in the molten float glass composed of 13.2 m/o Na 2O, 70.2 m/o SiO 2, 10.0 m/o CaO, 5.9 m/o MgO, etc. was determined in the temperature range from 1260 to 1380 K by means of galvanic cells using Na–β″-alumina as solid electrolyte. The Na 2O activity, a Na 2O , accompanying the reaction Na 2O (dissolved in Na 2O–WO 3 melt)=Na 2O (dissolved in molten glass) was found to be given by log a Na 2 O =−5.88−6.32×10 3 T −1 as a function of temperature, and the relative partial molar enthalpy of Na 2O was calculated to be Δ H Na 2 O =−121.0 kJ/ mol .