Amount Of Na Ions Research Articles

Durability of lightweight oil-well geopolymer system in sulfate environment

Sulfates when present in the formation water would attack and deteriorate the cementitious system. In the quest to investigate the possibility of using geopolymer systems in oil-well cementing, the durability of geopolymer in various corrosive environments has been simulated. Lightweight geopolymer systems exhibit different microstructural and macroscopic properties compared to the conventional geopolymer systems whose durability under sulfate attack has been widely investigated. It is therefore important to study the resistance of lightweight geopolymer to sulfate attack. A ternary geopolymer was formulated at 13 ppg (1.56 g/cm3) by admixing metakaolin, ground granulated blast furnace slag (GGBFS), and silica fume in an alkaline solution composed of sodium silicate and 10 M sodium hydroxide solution in a mass ratio 1:3. The geopolymer specimen was cured in a water bath at 163 °F for 72 h and subsequently submerged in a 50 g/L sodium sulfate solution for up to 2 days. The effect of the sulfate solution on the strength and the mechanism of the sulfate attack was analyzed using analytical techniques, pH, and ion exchange measurements. The compressive strength of the specimen at 72 h, having a value of 802 psi decreased by 19.8% and 26.2% after day 1 and day 2 in the sodium sulfate solution, respectively. Investigation of the mechanism indicated that the loss in strength was not a result of the formation of deleterious phases but rather the leaching of Na ions from the geopolymer indicated by the rise in the pH and amount of Na ions in the sodium sulfate solution after the geopolymer was submerged in a sulfate solution. Lightweight geopolymer has a relatively loose microstructure that reduces its tendency to inhibit the transport of alkalis during sulfate attack, making the effect of the sulfate environment more pronounced.

Elucidating cycling rate-dependent electrochemical strains in sodium iron phosphate cathodes for Na-ion batteries

Battery electrodes materials undergo significant mechanical instabilities which affect their longevity and exert rate-limitations during the cycling process. In this study, we investigate the rate-dependent mechanical response of sodium iron phosphate (NaFePO4, NFP) cathodes during Na intercalation via galvanostatic cycling at different rates by employing digital image correlation, electrochemical methods, and mathematical model. The mechanical behavior of the electrode shows strong dependance on the applied scan rate. At slower rates, electrode shows asymmetrical strain generation between anodic and cathodic cycles, which is attributed to the formation of cathode-electrolyte interface layers. The electrode undergoes smaller strain generation when cycled at slower rates when the same amount of Na ions is removed or inserted into the electrode. A mathematical model was developed to predict strain evolution in the composite electrode as well as the concentration profile of the Na ions in the electrode particles. Rate-dependent and time-dependent factors on the strain generation in the electrode are attributed to the capacity-dependent intercalation strains, rate-dependent mismatch strains, and time-dependent irreversible strains. The combination of in situ strain measurements with the analytical model provided new insight into the electrochemically induced mechanical deformations in Na-ion cathode electrodes.

Effect of Na-doped Mo layer as a controllable sodium reservoir and diffusion barrier for flexible Cu(In,Ga)Se2 solar cells

To overcome the absence of sodium (Na) and to prevent undesired impurity diffusion from stainless steel (STS) substrates, a bi-layer molybdenum (Mo) structure consisting of a 1-μm-thick Mo and Na-doped Mo (Mo:Na) with variable thickness was utilized as the back contact layer in copper–indium–gallium–selenide (CIGS) solar cells. Na ions were supplied to the CIGS absorber layer from the Mo:Na layer, and the amount of Na ions was controlled by changing the thickness of Mo:Na layer. The Na doping to the CIGS layer is verified by the X-ray photoelectron spectroscopy (XPS) and the dynamic secondary ion mass spectroscopy (D-SIMS). The recombination process in the bulk CIGS and the CdS/CIGS junction has been analyzed by temperature dependent current density–voltage (J–V–T) measurement. The D-SIMS showed that the amount of Na ions in the CIGS layer grown on Mo/Mo:Na/STS is comparable with that in the conventional CIGS film deposited on Mo coated soda-lime glass. Moreover, the bi-layer Mo also acts as a diffusion barrier layer against the Fe atoms, which deteriorate the quality of CIGS. The higher content of Na ions and the lower content of Fe ions in the CIGS layer lowered the recombination activation energy, series resistance and ideality factor, leading to improved junction quality. As a result, the short circuit current density and power conversion efficiency of the CIGS on the Mo and 600-nm-thick Mo:Na were improved by 8.1 and 69.4%, respectively, compared with those of CIGS solar cells fabricated without a Mo:Na layer.

Vanadium contamination on the stability of zeolite USY and efficient passivation by La2O3 for cracking of residue oil

It is of great significance to identify the destructive role of high deposited vanadium on the USY-based cracking catalysts and find a facile approach to vanadium passivation for processing residue oil. Herein, the destruction degree of the steam-treated vanadium-contaminated USY zeolites, which also contained a certain amount of Na ions, was investigated by N2 physical adsorption, NH3-TPD, HRTEM, 27Al MAS NMR and catalytic cracking evaluation. The results reveal that high deposited vanadium causes severe damage to the structure of USY, resulting in a sharp deterioration in cracking performance. Furthermore, CeO2 and La2O3 were studied as vanadium passivating agents. The introduction of La2O3 using physical mixing could preserve the zeolite structure to a large extent without altering the properties of USY. The superior passivation performance might be mainly attributed to the fact that La2O3 introduced by simple physical mixing prefers to interact with vanadium species, rather than migrate into the channels and cavities of zeolites USY.

Rate capability for Na-doped Li1.167Ni0.18Mn0.548Co0.105O2 cathode material and characterization of Li-ion diffusion using galvanostatic intermittent titration technique

Spherical Li1.167−xNaxNi0.18Mn0.548Co0.105O2 (0⩽x⩽0.1) particles were prepared by spray pyrolysis, and subjected to electrochemical characterization for lithium battery applications. It was confirmed that Na doping enhances the charge/discharge rate capability. The structure of prepared samples was characterized by XRD: the c-axis lattice parameter increases with increase in the amount of Na ions (parameterized by x, above). The Na-doped sample with x=0.05 shows capacities of 208 and 184mAhg−1 at high current densities of 1.0C and 2.0C, respectively. These values are enhanced, compared to values of 189 and 167mAhg−1 for the bare sample. The ratio of the capacity at 1.0C to that at 0.1C is enhanced from 77% for the bare sample to 84% for the Na-doped sample with x=0.05. The Li diffusion coefficients obtained from the galvanostatic intermittent titration technique (GITT) are higher for Na-doped samples than for the bare sample. In particular, the Na-doped sample (x=0.05), in the potential range around 4V, has a higher DLi+ value of 3.34×10−9cm2s−1, compared with 1.35×10−9cm2s−1 for the bare sample. The Na-doped samples (0<x<0.075) show high capacity retention: the Na-doped sample (x=0.05) shows a capacity retention of 92% compared to 83% for the bare sample.

Physicomechanical Properties of Ceramic Materials Prepared with Chemical Dispersion of Aluminum Alloy Grade AK12

An aluminum hydroxide residue forms during chemical dispersion of aluminum alloy grade AK12, containing a considerable amount of Na ions. These ions affect the structure and phase composition of ceramic specimens, since as a result of sintering they form a second phase, i.e., nepheline, which is uniformly distributed over Al2O3 grain boundaries. The effect of degree of washing of original Al2O3 powder on physicomechanical properties of ceramics from these powders, such as ultimate strength in bending, impact strength, density, porosity, and crack resistance, is studied.

The effect of ppm-level Na impurity on the structure of SiO2-supported Mo catalysts prepared in a clean room

To investigate the effect of alkali impurity in Mo/SiO2 on the MoO x structure on SiO2 surfaces SiO2-supported Mo oxides were prepared with various amounts of Na ions in a class-1 clean bench with a laminar flow in a class-1000 clean room. The Na concentrations were varied in the range 0-5000 ppm, while the Mo loading on SiO2 was maintained at 0.7 wt%. The Mo-Na/SiO2 samples obtained were characterized by diffuse reflectance UV-visible and Raman spectroscopy. Three types of Mo species were identified: octahedral monooxo Mo monomer species, Na2Mo2O7 and MoO3. At less than 100 ppm Na both octahedral Mo monomers and MoO3 species were formed on SiO2. The MoO3 species was transformed to Na2Mo2O7 at 2000 ppm Na, where the Na ions interact directly with the Mo species on the surface. The octahedral monooxo Mo monomer species seems not to be influenced significantly by Na impurity.

Molecular recognition by Na-loaded alumina pillared clay

Varying amounts of Na ions have been loaded to alumina pillared montmorillonite by dispersing it into an NaNO 3 solution, followed by titration with NaOH. The amount of Na ions loaded increased with the pH of the dispersion. As the amount of Na increased, nitrogen adsorption capacity decreased, but the total amount of water adsorption increased. Xylene uptake by the pillared clay decreased in a different manner for the p- and m-isomers as the amount of Na increased, and the uptake ratio of the p- to m-isomers (p/m) had a maximum of ca. 2 for the sample with 0.066 mmol of Na g −1 . This finding suggested that the molecular recognition properties of the interlayer micropores of the pillared clay can be finely tuned by controlling the amount of Na ions.