Strontium Nitrate Solutions Research Articles

Exploring the Potential of Sr2+ for Improving the Post-Hardening Strength and Durability Characteristics of Cement Paste Composites

This study investigates the effects of strontium ions on enhancing the post-hardening strength and durability characteristics of hydrated cement composites, exploring their potential use as a rehabilitation method for aging concrete structures. A 30% strontium nitrate solution served as the source of strontium ions. Cement paste specimens with a water-to-cement ratio of 0.5, cured for 28 days, were submerged in the 30% strontium nitrate solution to facilitate strontium ion penetration. Compressive and flexural strength tests were conducted on the specimens and compared to those cured in deionized water. Moreover, the durability performance, including surface abrasion resistance, water sorptivity, and porosity, was examined. Scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), and X-ray diffractometry (XRD) analyses were also carried out to investigate the microscopic morphology and chemical characteristics of the specimens. Results indicated that the strontium-treated specimens exhibited notable enhancements in both compressive and flexural strengths, especially in flexural strength. The specimens also demonstrated improved surface abrasion resistance, decreased water absorption, and a marked reduction in porosity. SEM analysis revealed a densified microstructure in the strontium-treated cement paste specimens, and EDS and XRD analyses showed changes in their morphology and chemical compositions and structures, indicating the formation of new types of hydrates. Accordingly, this study suggests that the strontium ion treatment method has significant potential for the maintenance and restoration of aging cementitious materials.

Surface Treatment Using Strontium Nitrate Solution to Improve Strength of Hydrated Cement Composites

Surface Treatment Using Strontium Nitrate Solution to Improve Strength of Hydrated Cement Composites

Stable nitrogen and oxygen isotope fractionation during precipitation of nitrate salt from saturated solutions.

Nitrate is an oxyanion similar to CO3 - and thus should undergo stable N and O isotope fractionation during dissolution or precipitation. This process should dominate abiotic soil nitrate processes in hyperarid regions of Earth and possibly Mars. The N and O isotope fractionations during the precipitation of nitrate salt from saturated solutions at ~20°C were determined by two methods: rapid precipitation by antisolvent crystallization and slow uninhibited precipitation in a desiccator. In the antisolvent crystallization procedure, increasing volumes of acetone were added to samples of saturated sodium and strontium nitrate solutions to instantaneously precipitate nitrate salt. In the slow procedure (requiring weeks), slow evaporative water loss drove the process. There was little difference between the two procedures. Using a Rayleigh model, the calculated N fractionation (15 εproduct-residual ) ranged from 1.69‰ to 2.77‰, whereas for O, the 18 εproduct-residual values were between 1.27‰ and 4.61‰. The N isotope fractionation between NO3 - and the metal solid is similar to that between C in dissolved CO3 -2 and carbonates. We found that O versus N isotope plots of soil nitrate in a cold/dry Antarctic chronosequence had slopes similar to those from the experiments, revealing abiotic transport. In the Atacama Desert, where the soil nitrates are a mix of biological and tropospheric nitrate, there is an inverse relationship between soil N and O isotopes. These two relationships were compared with the isotope composition of nitrate from Martian meteorite EETA79001. While the N and O isotope composition of the Martian nitrate is remarkably similar to that of the present Atacama Desert, the interpretation of the slope of the O versus N isotopes remains ambiguous due to the limited number of samples. Additional NO3 samples from Martian meteorites are needed to address the question of abiotic versus biotic alteration of NO3 - on Mars.

Coercivity enhancement of strontium hexaferrite nano-crystallites through morphology controlled annealing

In order to improve the performance of ferrite based permanent magnet materials, the evolution of magnetic properties with increasing particle size of anisotropic SrFe12O19 nano-platelets is investigated, allowing elucidation of the stable single domain (SSD) size. Phase-pure, ultra-thin platelet-shaped strontium hexaferrite (SrFe12O19) nano-crystallites have been successfully synthesized using a simple, green and scalable supercritical hydrothermal flow method. The flow reactor precursor is prepared from aqueous solutions of strontium nitrate, iron nitrate and sodium hydroxide. The samples were subsequently annealed at different temperatures (600–1100 °C) in intervals between 1 and 68 h in order to tune size and morphology. The nano-platelets grow anisotropically, with pronounced growth along the c-axis, which coincides with the magnetic easy axis. The annealing treatment gives rise to variations in platelet aspect ratio. Microstructural investigations by transmission electron microscopy (TEM) and Rietveld refinement of powder X-ray diffraction (PXRD) data, combined with vibrating sample magnetometry (VSM), reveal a significant correlation between size and morphology, on the macroscopic magnetic properties of the produced powders. The optimal single-domain crystallite dimensions are found from PXRD to be 62 nm thick and 76 nm wide, attaining a coercivity (Hc) of 459(10) kA/m (5.77 kOe), and a saturation magnetization (Ms) of 74.0(1) Am2/kg. A theoretical single domain critical size for SrFe12O19 particles is proposed, based on a disc-shaped ellipsoidal particle model in combination with the obtained experimental results. Particle shape is revealed to have an enormous influence on the SSD size, varying significantly for anisotropic particles compared to isotropic particles, and thus underlying the need for meticulous characterization in order to optimize the magnetic performance of specific systems.

Biodiesel production by soybean oil methanolysis over SrO/MgO catalysts: The relevance of the catalyst granulometry

The methanolysis of soybean oil was studied over magnesia supported SrO heterogeneous catalysts. The samples (0.05–0.35Sr/Mg atomic ratio) were prepared by contacting commercial MgO with aqueous solutions of strontium nitrate. Both Mg and Sr oxides were identified by XRD even for the lowest Sr content. The calcination temperature is a critical issue for the catalytic performances because carbonated and hydroxilated surface species are only removed for calcination temperatures higher than 575 °C. Carbonated species seems to be more soluble in methanol than oxide species thus increasing the rate of Sr leaching.In tested conditions (67 °C, methanol/Oil=9 and WCat/WOil=5%) prepared catalysts presented interesting initial methanolysis activities. Catalysts with atomic ratios Sr/Mg higher than 0.10, showed analogous catalytic behaviors giving FAME (biodiesel) contents higher than 94%.The catalysts deactivation can be ascribable to strontium loss detected by XRD and SEM–EDS. The residual strontium remains trapped in MgO pores and thus inaccessible to the reactants. This result emphasizes the relevance of the external surface area of the catalysts due to the size of the triglycerides molecules and of the oil micelles, which cannot diffuse into catalysts pores.No soap formation was observed in the tested conditions.

Physicochemical properties and cellular responses of strontium-doped gypsum biomaterials.

This paper describes some physical, structural, and biological properties of gypsum bioceramics doped with various amounts of strontium ions (0.19–2.23 wt%) and compares these properties with those of a pure gypsum as control. Strontium-doped gypsum (gypsum:Sr) was obtained by mixing calcium sulfate hemihydrate powder and solutions of strontium nitrate followed by washing the specimens with distilled water to remove residual salts. Gypsum was the only phase found in the composition of both pure and gypsum:Sr, meanwhile a shift into lower diffraction angles was observed in the X-ray diffraction patterns of doped specimens. Microstructure of all gypsum specimens consisted of many rod-like small crystals entangled to each other with more elongation and higher thickness in the case of gypsum:Sr. The Sr-doped sample exhibited higher compressive strength and lower solubility than pure gypsum. A continuous release of strontium ions was observed from the gypsum:Sr during soaking it in simulated body fluid for 14 days. Compared to pure gypsum, the osteoblasts cultured on strontium-doped samples showed better proliferation rate and higher alkaline phosphatase activity, depending on Sr concentration. These observations can predict better in vivo behavior of strontium-doped gypsum compared to pure one.

Water Structure at the Air−Aqueous Interface of Divalent Cation and Nitrate Solutions

The water surface structure of aqueous magnesium, calcium, and strontium nitrate solutions with six to seven water molecules on average solvating each ion was investigated using vibrational sum frequency generation (VSFG) spectroscopy. Raman (polarized) and infrared spectroscopies were used for understanding solvation effects. Infrared reflection spectra were analyzed to further understand the VSFG data. The VSFG spectral changes indicate that the divalent countercation species play a key role in the surface perturbation of the water. In addition, the data show that the solvated ions, and possibly their ion pairs, approach the aqueous surface. The identity of the divalent cation may cause a difference in the concentration gradient near the surface, thereby increasing the VSFG-active region, which then indicates an increase in the interfacial depth. The interface becomes thickened with Mg(2+) < Ca(2+) < Sr(2+). The free OH orientation measured from the surface normal from the salt solutions changes from 33 (from neat water) to approximately 60 degrees .

Preparation of cauliflower-like shaped Ba 0.6Sr 0.4TiO 3 powders by modified oxalate co-precipitation method

The quantitative barium–strontium titanyl oxalate (Ba 0.6Sr 0.4TiO(C 2O 4) 2·4H 2O, BSTO) precursor powders were prepared by the modified oxalate co-preparation method. It was based on the cation-exchange reaction between the stoichiometric solutions of oxalotitanic acid (H 2TiO(C 2O 4) 2, HTO) and barium + strontium nitrate solution containing stoichiometric quantities of Ba and Sr ions. The pyrolysis of BSTO at 800 °C/4 h in air produced the homogeneous cauliflower-like shaped barium–strontium titanate (Ba 0.6Sr 0.4TiO 3, BST) powders. The effect of polyethylene glycol (PEG) on morphology of BSTO and BST powders was also investigated. The characterization studies were carried on the as-dried BSTO and calcined BST powders by various physicochemical techniques, IR, X-ray diffraction (XRD), scanning electron microscopy (SEM), etc. The BSTO and BST powders obtained by aforementioned technique without PEG were homogeneous with spherical shape. The particles grew into spindle shape with the effect of PEG.

The characterization of Sr-doped nanocrystal grain microspheres and photodegradation of KN-R dye

Sr-doped nanostructured crystalline TiO2 microspheres were fabricated by sol–gel reaction using reversed suspension polymerization as a template, followed by soaking in strontium nitrate solution. The morphology, crystal structure and photoabsorption ability was characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD) and UV–vis spectrophotometer. The observation of SEM showed us that both the bare and Sr-doped microspheres presented the same honeycomb porous morphology. The XRD spectra affirmed that the incorporation of Sr was in the form of strontium titanate (SrTiO3) as eutectic structure with anatase TiO2. The photocatalytic efficiency of Sr-doped TiO2 microspheres was assessed by monitoring the photodecomposition of KN-R dye. The results revealed that Sr-doped microspheres provide higher efficiency than the unmodified, which is consistent with the analysis results of UV–vis absorption spectra. Obvious phenomenon of red-shift on UV–vis spectrum was seen comparison with the bare microspheres. Both the phenomena of red-shift and the photocatalytic activity improvement were attributed to the synergistic action between SrTiO3 and anatase TiO2. The degradation kinetics studies illuminated that the reaction was a representative zeroth order reaction.

X-ray diffraction and Raman spectroscopy investigations in concentrated aqueous solutions of yttrium and strontium nitrates

X-ray diffraction experiments on concentrated aqueous solutions of yttrium and strontium nitrates seem to demonstrate that a local order concerning the cations themselves exists. Molecular models built to interpret these experiments suggest that a disturbance of the quasi-close-packing of the cations is more marked for these nitrate solutions than for aqueous solutions of halide salts of the same cations. Raman spectra of both solutions show a multiple structure of some bands assigned to the internal vibrational motions of the nitrate anion in agreement with what was observed by Mathieu and Lounsbury for strontium nitrate solutions. A tentative interpretation of this result is proposed.

Raman Spectral Studies of Aqueous Strontium Nitrate Solution Up to 450 °C and 40 MPa

Abstract We have studied the structure of aqueous strontium nitrate solution (2.8 M) at temperatures up to 450 °C and pressures of 22.6, 30.0, and 40.0 MPa using Raman spectroscopy technique. The strontium ion forms two species; one is the bound species in contact more strongly with the NO3− like the monovalent cation, and the other is the free species separated from the NO3−. The relative ratio of the bound species to the free ones remains unaltered with an increase in temperature up to 375 °C; above this temperature, however, the ratio significantly increases. The half-width at half peak height (hwhh) for the bound species is larger than that for the free species; it increases at 375 °C or above, suggesting that the bound species relaxes faster than does the free species. The relaxation for the bound species becomes significantly faster at the critical temperature. The number of water molecules of hydration around Sr2+, nH2O, is estimated by the comparison of Raman intensity and previous XAFS data. As the temperature increases, the nH2O gradually decreases. The value shows a remarkable decrease above 370 °C, indicating the displacement of water molecules from the solvation shell around Sr2+ and the concomitant entry of NO3− into the shell at higher temperatures.

Sorption of strontium by Mexican erionite

The apparent diffusion coefficient of Sr2+ in natural Mexican erionite from Sonora at different pH and concentrations were determined. Neutron activation was applied to measure the sorption of strontium. The apparent diffusion coefficient values showed that the mobility of Sr2+ through the cavities of the erionite depended on the concentration of strontium and the pH of the solution. As a consequence the sorption of this ion by the erionite was affected by these parameters and the maximum sorption of Sr2+ was at pH higher than 3 and 0.0094 mol·l−1 strontium nitrate solution.

Direct Modeling of EXAFS Spectra from Molecular Dynamics Simulations

A method for generating extended X-ray absorption fine-structure (EXAFS) spectra directly from molecular dynamics trajectories is described. Conventional molecular dynamics trajectories are run, and configurations from the trajectory are saved at periodic intervals. Clusters containing the EXAFS atom at the center are extracted from the configurations and used as input to the multiple scattering code FEFF6, which produces an EXAFS spectrum for each cluster. The separate spectra for the individual clusters are then averaged together to get a configurationally averaged EXAFS spectrum that can be compared directly with experiment. The method is tested on strontium chloride solutions and compared with recent experimental results on strontium nitrate solutions at both standard and supercritical conditions.

Imaging local mass-transfer rates within an impinging jet and studies of fast heterogeneous electron-transfer kinetics using the microjet electrode

The microjet electrode (MJE) is a recently introduced hydrodynamic electrode in which a jet of solution impinges on a disc ultramicroelectrode (UME) under conditions of well defined, variable and high mass-transfer rates. It is shown that these properties make MJE voltammetry a powerful technique for characterising rapid electron-transfer kinetics under steady-state conditions. The MJE approach is illustrated through studies of the hexacyanoferrate(II/III) couple in aqueous strontium nitrate solutions (0.2 mol dm–3). The standard rate constant is found to be 0.76 ± 0.11 cm s–1 and the transfer coefficient is in the range 0.35–0.55. Complementary mass-transfer imaging experiments, in which the transport-limited current at the UME is monitored as a function of the nozzle position, as a jet of solution is scanned over the electrode surface in a raster pattern, are shown to provide useful information on the positioning requirements of the MJE and a unique insight into the nature of mass transfer from an impinging jet. The spatial variation of local mass transfer deduced from these experiments is found to be in qualitative agreement with the theoretical predictions for the fluid velocity profile of the impinging jet under laminar flow conditions.

Increasing contact ion pairing in the supercooled and glassy states of "dilute" aqueous magnesium, calcium, and strontium nitrate solution: implications for biomolecules

FTIR spectra of aqueous D 2 O solutions of magnesium (0.5 and 0.05 M), calcium (0.5, 0.2, 0.05, and 0.02 M) and strontium (0.5 M) nitrate in their glassy states at 78 K and of 0.5 M calcium nitrate in supercooled solution from 300 to 235 K are reported and compared with those recorded at 300 K. All four fundamental vibrational regions of the nitrate ion and a combination band could be evaluated by careful subtraction of the D 2 O solvent. Evidence for increasing contact-ion pairing in going from ambient temperature to the glassy state is based on (i) development of a new band in the v 4 band region at 727 cm -1 (Mg) and increasing intensity of the band at ≃740 cm -1 (Ca and Sr), (ii) doubling of bands in the v 1 and v 2 band regions, and (iii) fourth-derivative curves of the v 3 band region and its curve fitting (Ca)

Low temperature synthesis of ultrafine strontium titanate (SrTiO3) powders

Ultrafine (≍0.4 μm) strontium titanate powder was synthesized using strontium nitrate and potassium titanyl oxalate as precursors. An aqueous (0.1 M) potassium titanyl oxalate solution was added dropwise to a (0.1 M) strontium nitrate solution with continuous stirring at room temperature to precipitate strontium titanyl oxalate (STO). The precipitate, after careful washing with distilled water several times, was air-dried and calcined at 550 °C/6 h to obtain homogeneous, spherical, stoichiometric powder of SrTiO3 ≍0.4 μm in size. The calcined powder was characterized using different techniques such as XRD, DTA/TG/DTG, SEM, and IR.

Evidence for a new metastable crystalline phase of strontium nitrate

Abstract The undercooling of aqueous solutions of strontium nitrate a few mm3 in volume or microsized by dispersion within an emulsion is investigated. The experimental results are consistent with a succession of transformations in undercooled solutions of binaries. Following concentration, the undercoolings are from 14°C to 20°C for macrosamples or from 39°C to 60°C with emulsions. However it is observed that Sr(NO3)2 crystallizes into a metastable phase which can be preserved for a long time. The existence of this metastable crystalline phase has been evidenced by Differential Scanning Calorimetry and by an original evaporation method. The phase diagram, including the metastable phase, is presented.

Tracer studies of adsorption of Sr++ on copper

Adsorption of Sr++ ions on copper metal surfaces has been studied by the tracer technique. The strontium nitrate solutions of different concentrations were labelled with90Sr and the copper coupons of electrolytic quality were kept immersed in these solutions for different intervals of time. The activity of both the faces of the coupons were measured with a GM counter after washing and drying the coupons. Results have been obtained on the amount of adsorption as a function of time, concentration of strontium nitrate solution and temperature. The data have been found to be in accordance with the Freundlich adsorption isotherm equation. Interpretation of the data in the light of the findings of other authors in similar systems has been made.

A raman spectral study of ion pair formation in aqueous solutions of strontium nitrate

Raman spectra of aqueous solutions containing Sr2+ and NO 3 − exhibit lines characteristic of Sr(NO3)+ and Sr(NO3)2 in addition to those of the solvated nitrate ion. Intensities have been measured, and the quantities nobs, the average ligand number, andC F, the concentration of free nitrate ion have been evaluated. From these data two cumulative formation constants have been estimated for 25°C: β1=0.76±0.10 and β2=0.10±0.02. The dependence of the results on experimental limitations is discussed.

Tire Cord Dip Pick Up by Atomic Absorption Spectroscopy

Abstract Graphite furnace atomic absorption spectroscopy has been used to develop a quick and accurate test for tire cord dip pick up. Strontium nitrate solution is added to either predips or resorcinol-formaldehyde latex dips at predetermined levels of a few parts per million. Sufficient replicate analyses of one to three milligram samples of treated cord can be run to provide reliable data on both the absolute level of dip pick up and the short term uniformity of the dip. The technique offers substantial advantages in both turn-around time and total analysis time relative to wet gravimetric techniques in current use.