SrO Powders Research Articles

Shape-stabilized phase change material for thermal energy storage: Sr+2 doped BaCO3 matrix incorporating polyethylene glycol

An Sr2+-doped BaCO3 matrix incorporating polyethylene glycol (PEG-6000) was developed using a simple impregnation process to build a shape-stabilized functional phase transition composite for application in thermal energy storage systems. A direct hydrothermal process was used to prepare a unique anhydrous rhombohedral BaCO3. The developed rhombohedral material, characterized following a hydrothermal reaction in the presence of 5 mol% Sr2+, was used to prepare extremely tiny porous particles (5 % SrBaCO3). The 5 % SrBaCO3 powder was hydrothermally produced and utilized to encapsulate PEG to create a phase change material (PCM) that prevents leakage of PEG during phase change. The shape-stabilized composite PCM (ss-PCM) that was prepared with nano- and micro-sized porous SrO powder and containing pure BaCO3 exhibited consistent and superior performance throughout a significant number of heat cycles. DSC results indicated that the melting temperature of the PEG/5BaCO3 is 60.17 °C, and the latent heat is 148.8 J/g. The R% (Impregnation ratio) and Eeff% (Efficient energy per unit mass of PEG) values of 5 % SrBaCO3 were more than those of 10 % SrBaCO3 and 15 % SrBaCO3, probably due to the presence of micro- and macro-pores and high pore volume. Additionally, it was clear from the XRF, EDX, and XPS data that Ba2+ segregation in 5 % SrBaCO3 was considerably less than that in 10 % SrBaCO3 and 15 % SrBaCO3. Compared to the long-established ss-PCMs, the developed composites exhibited much greater thermal enthalpy, higher thermal conductivity, and lesser super cooling. The presence of OH−1 on the surface of the PCM contributed to a reduction in the super cooling. Furthermore, the supporting materials improved the thermal conductivity of the PEG, overcoming the organic PCM's poor thermal conductivity. As pure PEG is infused in 5 % SrBaCO3, its super cooling effect is diminished by 15.5 %. Overall, the PCM with 5 % SrBaCO3/PEG preserves its capacity to store and release energy without a substantial modification its properties after multiple thermal heating and cooling cycles.

Tetrahedrally Coordinated sp3-Hybridized Carbon in Sr2CO4 Orthocarbonate at Ambient Conditions

We have synthesized the orthocarbonate Sr2CO4, in which carbon is tetrahedrally coordinated by four oxygen atoms, at moderately high pressures [20(1) GPa] and high temperatures (≈3500 K) in a diamond anvil cell by reacting a SrCO3 single crystal with SrO powder. We show by synchrotron powder X-ray diffraction, Raman spectroscopy, and density functional thoery calculations that this phase, and hence sp3-hybridized carbon in a CO44- group, can be recovered at ambient conditions. The C-O bond distances are all of similar lengths [≈1.41(1) Å], and the O-C-O angles deviate from the ideal tetrahedral angle by a few degrees only.

Metallothermic Production of Aluminum–Strontium Master Alloy for Modification of Silicon

Strontium master alloy is widely used in today’s aluminum foundries for modification of Al–Si alloys. In this study, Al–Sr master alloy was produced in molten Al alloy directly from strontium carbonate instead of using the pure strontium metal which is difficult to store in the air due to its high oxygen affinity. In a laboratory-scale induction furnace, SrCO3 and SrO powders were injected into the liquid metal via argon flow and subjected to reduction reaction. The oxygen-free medium required for the reduction was provided by the gas purged on both the surface and the inside of the liquid metal. Hence, the master alloy was produced directly by an economical process. Moreover, the addition of Mg to the reducing melt decreased the surface tension of the liquid aluminum; as a result, the reduction efficiency was increased. At the best of the results, the master alloy containing 5.15% Sr was obtained by reducing approximately half of the fed SrO by Al6Mg. This master alloy was used to modify A360 alloy, and the same modification effect as the commercial Al5Sr master alloy was observed.

Luminescence properties and cathodoluminescence degradation of Bi doped SrO powder

Bi3+ doped strontium oxide (SrO:Bi) phosphor powders were synthesized by the solgel combustion method using metal nitrates as precursors and citric acid as fuel. The optimum Bi3+ doping concentration was found to be 0.2 mol. %, and the optimum annealing temperature was found to be 1100 °C (2 h). The x-ray diffraction patterns corresponded with the known face-centered-cubic structure of SrO. Williamson–Hall plots showed that the crystallite size was in the range of ∼180 nm. Diffuse reflectance measurements of the pure host material showed that it was strongly reflecting (∼100%) down to a wavelength of about 230 nm, but when doped with Bi, an absorption band at 275 nm was observed that increased with Bi concentration. Scanning electron microscopy revealed a cubic morphology, and the grain size increased with annealing temperature. Photoluminescence measurements indicated that the phosphor exhibited efficient blue emission around 445 nm under UV excitation, which also occurred for electron irradiation, but slightly shifted about 5 nm to a longer wavelength. Auger electron spectroscopy (AES) was employed to analyze the surface chemical composition of the powder after pumping to a vacuum pressure of 2.6 × 10−8 Torr and back-filling the vacuum system with O2 to a pressure of 1.0 × 10−7 Torr. By simultaneous monitoring of the cathodoluminescence (CL) and AES peak-to-peak heights over time for 22 h, the CL degradation of the phosphor was investigated. SrO was found to be stable under electron irradiation. The phosphor may have potential applications in the fields of lighting and displays due to its broad blue emission.

BIOMIMETIC SYNTHESIS AND ANTIBACTERIAL PROPERTIES OF STRONTIUM OXIDE NANOPARTICLES USING OCIMUM SANCTUM LEAF EXTRACT

Objective: The investigation and synthesis of nanoparticles using green chemical methods is an emerging field due to ecologically derived materials. In the present study, the reaction under microwave irradiation technique is proposed for synthesizing the strontium oxide nanoparticles (SrO NPs) by reacting the strontium nitrate powder with Ocimum sanctum L. leaf extract followed by heat treatment at 500oC for 2 h.Methods: The crystalline nature, size, and morphological structure of the SrO powder sample were characterized by techniques such as powder X-ray diffraction (PXRD), scanning electron microscopy, ultraviolet (UV)-Vis spectroscopy, Fourier-transform infrared spectroscopy (FTIR) and photoluminescence (PL) spectral analysis. To investigate the antibacterial properties of SrO NPs, pathogens such as Escherichia coli, Staphylococcus aureus, Pseudomonas aeruginosa, Proteus vulgaris, Klebsiella pneumonia, and Morganella morganii was tested in Mueller–Hinton disc diffusion method.Results: The particle size of the SrO NPs is calculated to be 42 nm using Debye–Scherrer equation. The SrO NPs exhibited absorption peak in the range of 250–350 nm centered at 274 nm in UV region. In addition, it is demonstrated that band gap energy was calculated to be 5.39 eV from Tauc’s plot. The SrO NPs has shown the efficient antibacterial effect by inhibiting zone against Gram-negative bacteria.Conclusion: The main aim of the study is to synthesize cost-effective and eco-friendly green synthesis of SrO NPs from the OS (O. sanctum) leaf extract and their characterization. The mechanism for the formation of SrO NPs in the presence of eugenol as reducing agent is also discussed. The present green chemical approach using plant-based materials for the synthesis of nanoparticles enhances the eco-friendliness, compatibility, effectiveness, and reduces the toxicity.

Preparation of Al-Sr master alloys by the aluminothermic reduction of SrO using aluminum scrap at pilot plant scale

Al-Sr master alloys were prepared by aluminothermic reduction of SrO in molten aluminum processed from scrap. The trials were performed at 500 kg pilot plant scale, using a gas operated furnace with a silicon carbide crucible. The effect of temperature, initial magnesium concentration and agitation speed on the aluminothermic reduction rate of SrO powders was studied. Moreover, the microstructure of Al-Sr master alloys prepared has been analyzed by means of optical microscopy, X-ray diffraction (XRD), and scanning electron microscopy (MEB). In this sense, the morphology of secondary constituents and the structure of Al4 Sr phase were evaluated. The results showed that the aluminothermic reduction technique is useful for producing Al-Sr master alloys, observing the presence of the Al4 Sr intermetallic phase as the main secondary constituent.

Combustion synthesis process for the rapid preparation of high-purity SrO powders

Abstract A rapid, safe and simple technique for the production of high purity strontium oxide powders via a chemical combustion process is reported. The combustion reactions were performed to optimize the fuel to oxidizer ratios in the reaction mixtures required to obtain pure SrO powders by varying the molar ratio of chemical precursors and the temperature. The synthesized powders were characterized by X-ray diffraction, scanning electron microscopy, energy dispersive X-ray spectrometry, infrared spectroscopy, differential scanning calorimetry, thermogravimetric analysis, and N2-physisorption measurements. The results indicate that crystalline SrO was obtained using a 1:1 strontium nitrate: urea molar ratio at 1000 °C after 5 minutes. In addition, high-purity, homogeneous and crystalline SrO powders were easily produced in a short time via a chemical combustion process.

Synthesis and visible light photocatalytic activity of Ag spot-coated TiO2–60 wt% SrO composite powders

Nano-sized TiO2–60 wt% SrO composite powders were synthesized from titanium isopropoxide and Sr(OH)2·8H2O by use of a sol–gel method. Ag spot-coated TiO2–60 wt% SrO composite powders containing 3, 5, or 7 wt% Ag were synthesized by hydrothermal-assisted attachment, by use of Ag hydrosol in a high-pressure bomb at 250 °C and 450 psi. Nano-sized Ag particles approximately 5–25 nm in diameter adhered to the TiO2–60 wt% SrO2 composite powders. The photocatalytic activity of Ag spot-coated TiO2–SrO powders in the degradation of phenol showed that all were highly active when irradiated with UV light. TiO2–60 wt% SrO composite powder spot-coated with 5 wt% Ag was more photocatalytically active under visible light than TiO2–SrO composite powder.

Synthesis and luminescence properties of Eu 2+ -doped 8-coordinated SrO phosphors

Abstract Eu2+-doped SrO (SrO:Eu2+) phosphors were synthesized and their luminescence properties were investigated. Phosphors doped with different Eu2+ concentrations were synthesized by the thermal treatment of SrO and Eu powders on a single crystalline MgO substrate at 1500 °C in a reducing atmosphere of Ar and H2. X-ray diffraction measurements showed that the synthesized phosphors contained 8-coordinated SrO with an orthorhombic crystal system. The phosphors showed a strong blue emission at 456 nm, which was attributed to the Eu2+ concentration. In addition, a phosphor doped with 2 at% Eu2+ showed an internal quantum efficiency of 30%.

Preparation of LaGaO3 thin film for intermediate temperature SOFC by screen printing method (I)

La-doped ceria (Ce0.6La0.4O1.8 [LDC]) has been reported to be an effective buffer layer material for preventing the chemical reaction between Sr- and Mg-doped LaGaO3 (LSGM) electrolyte and Ni-based anode during sintering. However, it seems difficult to achieve a high power density on the cell using LDC buffer layer because of its low sintering and electrical conducting properties. In this study, effects of various sintering additives such as MgO, SrO, In2O3, Ga2O3, ZrO2, and LSGM oxide powders were studied for improving sintering density and electrical conductivity of LDC. Sintering property, phase formation, and electrical conductivity varied with the sintering agents. Addition of SrO, Ga2O3, or LSGM enhanced the sintering density of LDC while LSGM addition was effective to increase the electrical conductivity. LSGM sintering aid was inert with LDC accompanying no chemical reaction after sintering at 1,623 K. Therefore, it was considered that a small amount of LSGM addition as a sintering agent was desirable for improving sintering and electrical properties of LDC. Furthermore, a single cell using LSGM-added LDC buffer layer and LSGM electrolyte film was fabricated by a screen printing method after co-firing at 1,623 K. The obtained cell showed an almost theoretical open circuit voltage and a high maximum power density (0.725 W cm−2) at 973 K.

(Invited) Photoluminescence Properties of Alkaline-Earth Oxide Nanoparticles

Previous experiments have demonstrated that photoluminescence properties, both excitation and emission spectra, of powdered MgO depend strongly on the powder preparation and treatment. Similar dependencies have been found for CaO, SrO, and BaO powders. The observed broad photoemission bands have been attributed to the low-coordinated surface sites. Recent advances in nanoscale science and technology have made it possible to produce nearly monodispersed alkaline-earth oxide nanoparticles of very high surface area and investigate their optical properties in details. Here we present the results of our theoretical and experimental work in this area and present new results.

Modification of Al–Si alloys by metallothermic reduction using submerged SrO powders injection

Aluminum–silicon (Al–Si) casting alloys are the most frequently used alloys in the automotive industry. The modification of its microstructure is an important practice for refining the large needles of the eutectic silicon into fine fibrous or lamellar particles. In this study, the chemical and microstructural analyses of the samples taken during the submerged SrO powders injection tests in magnesium (Mg)-containing molten Al–Si alloys demonstrated the feasibility of Sr uptake in the bath, as SrO is reduced through metallothermic reactions in the molten alloys, producing a suitable silicon eutectic modification effect. The parameters that were evaluated during the experiments included temperature of the molten bath, size of SrO powders, initial Mg concentration in the molten alloy, and injection time. Based on the characterization of the reaction products of partially reacted SrO particles using the scanning electron microscope (SEM) as well as the X-ray diffraction (XRD) analysis of the samples of dross obtained during the injection tests, the sequence of the reaction was proposed. It was observed that the initial Mg content is a key parameter in accelerating the reaction rate through chemical reactions that produce MgAl 2O 4 as the main reaction product.

Synthesis and Characterization of Single-Crystal Strontium Hexaboride Nanowires

Catalyst-assisted growth of single-crystal strontium hexaboride (SrB6) nanowires was achieved by pyrolysis of diborane (B2H6) over SrO powders at 760-800 degrees C and 400 mTorr in a quartz tube furnace. Raman spectra demonstrate that the nanowires are SrB6, and transmission electron microscopy along with selected area diffraction indicate that the nanowires consist of single crystals with a preferred [001] growth direction. Electron energy loss data combined with the TEM images indicate that the nanowires consist of crystalline SrB 6 cores with a thin (1 to 2 nm) amorphous oxide shell. The nanowires have diameters of 10-50 nm and lengths of 1-10 microm.

A kinetic study of the strontium extraction by metallothermic reduction using submerged SrO powders injection

This work reports the results of laboratory experiments conduced to follow the kinetics of strontium recovery into the Al–Mg alloy by metallothermic reduction of SrO. The reagent was incorporated to molten alloy by the use of submerged powders injection technique. The variables analyzed were the injection time, the melt temperature and the initial magnesium content. Magnesium is added to the melt to increase the reactivity and reduce the surface tension of the molten aluminum. It was possible to increase the strontium content from 0 to 5 wt.% after 60 min of treatment. The results were fitted to a general kinetic equation, which allowed it to obtain the kinetic parameters, i.e. order of reaction and activation energy of the process. As the main mechanism of the strontium recovery process is of diffusive type, the global process rate increases as the temperature and initial amount of the magnesium increased.

X-ray photoelectron spectroscopic studies of vanadium-strontium-borate [(V 2O 5) x(SrO) 0.2(B 2O 3) 0.8− x] oxide glasses

Vanadium-strontium-borate glasses with the chemical composition [(V 2O 5) x (SrO) 0.2(B 2O 3) 0.8− x ], where 0.4≤ x≤0.8, have been investigated by X-ray photoelectron spectroscopy (XPS). The core-level binding energies of V 2p, Sr 3p, B 1s and O 1s have been measured. The doublet peaks attributed to Sr 3p 3/2 and Sr 3p 1/2 in the Sr 3p spectra have essentially the same binding energies for all glass samples, regardless of the composition, but shifted by about 0.6 eV towards higher binding energies than those of the SrO powder. The B 1s peaks, with essentially the same full-width at half-maximum (FWHM), have the same binding energy, which is lower than those of the B 2O 3 powder by ∼0.7 eV. The O 1s core level spectra exhibit significant composition-dependent changes and were deconvoluted into two peaks. The variation in the ratio of the peak areas is discussed in terms of the local structure. The quantitative ratio (V 4+/V total), for each glass sample, has been determined from the analysis of the V 2p core level spectra. The ratio remains practically constant independent of vanadium concentration within experimental uncertainties.

NO interaction with thermally activated CaO and SrO surfaces

By using temperature-programmed desorption gas analysis, thermal desorption (TD) of N 16O with a small amount of N 18O was observed in the temperature range 400–1000 K after N 18O adsorption on both CaO and SrO powders at room temperature. TD's of N 2 and N 2 16O with a small amount of N 2 18O were also observed in the temperature range 400–600 K. Based on IR measurements, NO, (NO) 2 and tentative NO 2 (or NO 3) species were found after N 16O adsorption on CaO powders. This suggests that oxygen exchange of N 18O with CaO and SrO may occur through NO 2 − or NO 3 − type intermediates during migrating on the surfaces involving of a lattice oxygen. N 2O desorption may be due to the decomposition of (NO) 2, while exchange process is not clear.

Phosphorescence and Thermoluminescence of UV-Irradiated SrO Powders at Temperatures from 120 K to 350 K

Long-lived phosphorescence and thermoluminescence (TL) from UV-irradiated SrO powders under high vacuum are observed at low temperature. Phosphorescence decays following a t-1 law below 160 K in the time range 10-103 s. The emission spectra of phosphorescence and TL have a peak at 2.7 eV. The luminescence is quenched by O2 gas exposure at low temperatures. On the basis of the phosphorescence decay and TL glow curves, plausible emission mechanisms are discussed in terms of a thermally assisted tunneling recombination model between distant electron and hole traps and a first-order decay model with an energy distribution of trap depth. The observations are well described by the recombination model.

A study of the reactions between ZrC and some metal oxides

High temperature chemical reactions of ZrC powder or ZrC coating on alumina spheres with CeO 2, UO 2 and SrO were studied. CeO 2 reacts with ZrC at 1473–2073 K to give Ce 2O 3 and Ce 2Zr 2O 7. Virtually no reactions were observed in UO 2-ZrC mixtures at 1673–1973 K. SrO reacts with ZrC above 1273 K to form SrZrO 3, Sr vapor and, presumably, CO. The SrZrO 3 formation on ZrC coated spheres contained in a bed of SrO powder was rapid at 1673 K. All particles suffered serious damages on the ZrC coatings by the reaction with SrO. Though the Sr concentration in the ZrC was below the detection limit, Sr was found to be distributed within the alumina kernel.

Luminescence and other spectroscopic studies of the reaction of pyridine and oxygen with thermally activated SrO

The reaction of pyridine and O2 on SrO powder has been studied using several different spectroscopic techniques to characterise the intermediate and the final products. Reflectance spectroscopy has been used to demonstrate the formation of the 4,4′-bipyridyl negative ion when pyridine is adsorbed on SrO. Subsequent adsorption of oxygen leads to the formation of the O–2 ion by a one-to-one electron transfer process from the organic ion and photoluminescence studies confirm that the 4,4′-bipyridyl molecule is also formed on the surface when the electron transfer occurs.

Reflectance spectra of surface states in strontium oxide and barium oxide

Reflectance spectra of SrO and BaO powders outgassed at temperatures up to 1073 K have been measured over the range from text-decoration:overlineν= 20 000 cm–1 to text-decoration:overlineν= 52 000 cm–1. Spectral features attributable to exciton states are described, and the effects of O2, N2O, CO2 and H2O on the spectra are reported. Fluorescence occurs when spectra are measured in vacuo. SrO-coated MgO and BaO-coated MgO have also been studied. The spectra show two regions separated by an absorption edge which is centred at 44 000 cm–1 for SrO and 31 500 cm–1 for BaO. On the low text-decoration:overlineν side of the edge the spectra are sensitive to the adsorption of the gases, but exposure to gases causes little or no change in the spectra on the high text-decoration:overlineν side (except for H2O vapour which reacts in depth). The absorption bands at low text-decoration:overlineν are ascribed to excitons bound at surface ions and those at high text-decoration:overlineν to excitons bound at ions in the bulk.The chemical interaction of the gases with the surface states increases in intensity in the order O2 < N2O < CO2 < H2O for SrO and N2O < O2 < CO2 < H2O for BaO. The results are correlated with those for MgO and CaO reported previously.