Addition Of Strontium Research Articles

Enhancement of the photocatalytic response of Cu-doped TiO2 nanotubes induced by the addition of strontium

The influence of adding strontium to Cu-doped TiO2 nanotubes on the photocatalytic performance of the resulting materials was herein studied considering changes in structural, textural, optical and morphological properties. Addition of strontium was performed in a 0.2–1.0 wt% range while an optimized fixed Cu loading of 0.5 wt% was used. TiO2 nanotubes were obtained using alkaline hydrothermal treatment of P25 followed by a calcination treatment at 400 °C. The resulting TiNT material was then impregnated with copper using an incipient wetness impregnation followed by a new calcination at 400 °C (0.5Cu-TiNT). Strontium was then added under similar impregnation-calcination conditions. The effect of adding various amounts onto 0.5Cu-TiNT was therefore deeply characterized using X-ray diffraction, N2 adsorption–desorption measurements, scanning electron microscopy coupled with energy-dispersive X-ray analysis, Raman, UV–vis diffuse reflectance, X-ray photoelectron, and photoluminescence spectroscopies as well as determining dielectric properties.Results clearly emphasize that up to a Sr loading of 0.8 wt%, the addition of Sr results in in situ formation of Sr-O-Ti entities on the surface of 0.5Cu-TiNT. Above this threshold loading, excess Sr loading leads to the formation of segregated SrO species. Finally, a direct correlation was observed here between the optimized formation of surface Sr-O-Ti entities and an enhanced photocatalytic response due to improved stabilization of photogenerated charges on 0.5Cu-TiNT resulting from the ferroelectric interference of neighboring SrTiO3 entities.

Tailoring electrocaloric properties of Ba1-xSrxSnyTi1-yO3 ceramics by compositional modification

This paper presents compositional modifications on lead-free material system based on barium titanate to optimize its electrocaloric (EC) properties. By addition of strontium and tin we prepared solid solutions of Ba1-xSrxSnyTi1-yO3 (BSSnT-100∙x-100∙y) which allow for shifting of maximum EC effect to room temperature as well as broadening the temperature range of high EC temperature changes ΔTEC. Bulk ceramic samples of BSSnT were prepared by solid-state reaction route and the influence of Sn:Sr ratio on dielectric and ferroelectric properties was investigated. The EC temperature change was measured directly using resistance welded thermocouple wires. Most promising results could be achieved for BSSnT-18−6.5, which showed a maximum ΔTEC of 0.49 K around 30 °C with ΔTEC > 0.3 K in the temperature range from 10 °C to 50 °C under a comparatively low electric field change of 2 V μm−1.

Determination Of The Effect Of Cooling Rate And Strontium Amount On Eutectic Si Modification Performance Of A356 Alloy Via Casting Simulation

It is well-known that strontium addition into molten metal as a eutectic modifier increases the elongation and toughness values of the cast parts by refining the eutectic phases. However, when over-modification occurs, porosity increases due to some unwanted physical and chemical reactions that develop within the structure. On the other hand, it has been seen that high cooling rates tend to reduce the porosity of the alloy, decrease grain size and secondary dendrite arm spacing and refine eutectic silicon phase on Al-Si casting alloys. Within the scope of this project, it is aimed to investigate the effects of the cooling rate of cast part and the addition amount of strontium on the silicon modification behavior of Al A356 (AlSi7Mg) alloy parts using casting simulation environment. In order to examine the effect of strontium addition, 150, 250, 350 and 450 parts per million of strontium additions were chosen based on thermodynamic calculations. After the casting session of each Al A356 composition with different strontium amount by using special designed 5-spoke mold on casting simulation, thermal analysis was done by obtained thermocouple data from casting part’s each spoke. Obtained thermal analysis data was interpreted with the casting simulation outputs. Within all aspects, the 150 parts per million strontium addition on Al A356 alloy has been identified as the most useful simulation model in terms of casting performance.

Effect of thermo-mechanical treatment and strontium addition on workability and mechanical properties of Al Si Cu casting alloy

In this study, the potential application of Al-Si-Cu aluminum alloy (ALDC12), which is widely used in the high-pressure die-casting (HPDC) process, for fabricating a wrought product was evaluated. The effects of thermo-mechanical treatment and Sr addition on the microstructure, workability, and mechanical properties of the ALDC12 alloy were investigated in detail. The introduction of thermo-mechanical treatment significantly reduced the interconnectivity of the brittle eutectic Si phase formed during solidification and average grain size. Therefore, the uniformly distributed spherical Si particles and fine grain size considerably improved both the strength and ductility of the ALDC12 alloy. Furthermore, the addition of Sr effectively modified the eutectic Si phase in the casting process, which significantly reduced the occurrence of edge cracks in the subsequent rolling step and further improved the mechanical properties of the final sheets. Consequently, through microstructural control of the ALDC12 aluminum alloy by the thermo-mechanical treatment and Sr addition, it was possible to obtain suitable workability and significantly improved mechanical properties compared with those of cast products.

Characterization of properties of Vanadium, Boron and Strontium addition on HPDC of A360 alloy

The demand for lighter weight decreased thickness and higher strength has become the focal point in the automotive industry. In order to meet such requirements, the addition of several alloying elements has been started to be investigated. In this work, the additions of V, B, and Sr on feedability and tensile properties of A360 has been studied. A mold design that consisted of test bars has been produced. Initially, a simulation was carried out to optimize the runners, filling, and solidification parameters. Following the tests, it was found that V addition revealed the highest UTS but low elongation at fracture, while B addition exhibited visa verse. On the other hand, impact energy was higher with B additions.

Enhanced tensile properties of as-cast Mg-10Al magnesium alloy via strontium addition and hot working

The lightweight magnesium–aluminum alloys are extensively used in automotive and aerospace industries due to their high-specific strength and low alloying cost, Grain refining via alloying and hot deformation is known as a viable technique for the enhancement of mechanical properties of these alloys. Accordingly, in the present work, grain size refinement and improvement of tensile properties of Mg-10Al magnesium alloy ingot via strontium addition (up to 1 wt%) and hot working (extrusion process) were studied. It was revealed that the addition of Sr up to 0.05 wt% leads to grain refinement of Mg-Al-Sr alloys with the resulting best strength-ductility combination. The as-cast alloys were quite brittle with total elongations well below 5% and their ultimate tensile strength (UTS) values were below 200 MPa, which was attributed to the coarse as-cast structure with a high content of brittle intergranular β-Mg17Al12 phase. It was also found that the aspect ratio of the Al4Sr particles increases by increasing strontium content, which contributes to the deterioration of tensile properties at high strontium contents. Homogenization treatment at elevated temperatures led to the dissolution of the β phase, while the thermally stable Al4Sr particles remained undissolved. The extruded alloys showed remarkably higher strength and ductility compared to the as-cast ingots, which were related to the remarkable grain refinement induced by the recrystallization processes during the hot extrusion process, the disappearance of the deleterious network of the intergranular eutectic constituent, and providing high solute Al content. As a result, UTS of ~ 406 MPa and total elongation of ~ 24% were obtained for the extruded alloy with 0.05 wt% Sr.

Comparison of Silicon Phase in Al-20Si Alloys and Zn-27Al-3Si Alloys with Strontium Addition

The evolution of the silicon phase of hypereutectic Al-20Si alloys and Zn-27Al-3Si alloys with the addition of Sr (0, 0.06, 0.1, and 0.2 wt%) was investigated to understand the appearance of spherical primary silicon in Zn-Al–Si alloys but not in Al–Si alloys. With Sr content remaining unchanged (0.2%), dendritic primary silicon was observed to grow along the preferential direction in the Al-20Si alloy, while in the Zn-27Al-3Si alloy, faceted cells or smooth spherical patterns were observed on its surface. The cooling curves showed that a 0.2% Sr content helps reduce the precipitation temperature of primary silicon (approximately 10 °C in the Al-20Si alloy and 40 °C in the Zn-27Al-3Si alloy). From EPMA mappings, Sr was found mostly dissolved into the nodular primary silicon in the Zn-27Al-3Si alloy with a 0.2% Sr content, while there was no evidence that Sr atoms aggregate within dendritic primary silicon crystals in the Al-20Si alloy with 0.2% Sr content. Multiple twins were observed in the Sr-modified Zn-27Al-3Si alloy, which can be interpreted according to the IIT and TPRE growth mechanisms, while different parallel twins were observed in the Sr-modified Al-20Si alloy. Overall, it was determined that a higher undercooling rate and the preferential adsorption of Sr in primary silicon are advantageous to obtain spherical primary silicon.

Influence of MCO3 (M=Ca, Sr, Ba)-doping on the non-ohmic properties of the ceramic varistor system SnO2–Co3O4–Cr2O3–Nb2O5

In this study, the influence of the addition of calcium, strontium and barium carbonates on the microstructure and the electrical properties of the SnO2–Co3O4–Cr2O3–Nb2O5 ceramic varistor system was investigated. The powder mixtures were previously studied by thermogravimetric analysis and differential scanning calorimetry showing the decomposition of carbonates into CaO, SrO, and BaO below 1000 °C. Then, green tablets were obtained and sintered at 1350 °C for 1 h under an ambient atmosphere. Later characterization by X-ray diffraction demonstrates a systematic increase on the lattice parameters as CaCO3 SrCO3, and BaCO3 were added. Scanning Electron Microscopy reveals a decreasing tendency for the average grain size. The electrical performance was evaluated in terms of electrical breakdown field (Eb) and non-linear coefficient (α). Although all the samples exhibited non-ohmic electrical behavior, the SrCO3-doped ceramic showed the highest non-linear coefficient (α = 10) compared to those doped with CaCO3 or BaCO3. A defect model is proposed to explain the way that Ca2+, Sr2+, or Ba2+ incorporates into SnO2 lattice.

4D X-ray tomography characterization of void nucleation and growth during deformation of strontium-added AZ31 alloys

We report the influence of strontium on the evolution of microstructural damage during tensile deformation of hot-rolled AZ31 alloys tested parallel to the rolling, transverse, and diagonal directions using a 4D (3D X-ray tomography plus time) technique. X-ray computed tomography images were collected at several strains during each tensile test, and again after the fracture had occurred, to quantify the nucleation, growth, and coalescence of voids. Adding strontium leads to the formation of Al4Sr particles in the microstructure. Cracking of these particles provides the primary micromechanism of damage nucleation. Increasing strontium content increases the size and number of Al4Sr particles, thereby increasing the number of potential sites for void nucleation. Despite this, the ductility of AZ31, as well as its strength, when tested in all three directions, is enhanced by adding Sr. Nanoindentation tests confirm that this is accomplished by reducing the matrix strength through a decreasing role of aluminum solid solution hardening, which is more than compensated by an increase in precipitation strengthening. Fracture occurs through the interactions of shear bands with second-phase particles. Shear fracture is dominant on the fracture surfaces of the strontium-free alloys, while void growth induced dimples are found in much greater number on the fracture surfaces of the strontium-added alloys. Void growth is accurately described by optimization of the Rice-Tracey model using regression analysis. This study explains why strontium additions to AZ31 can be used to improve both strength and ductility by controlling the evolution of damage during deformation.

Perovskite-type catalysts based on nickel applied in the Oxy-CO2 reforming of CH4: Effect of catalyst nature and operative conditions

Ni-based catalysts generated by in situ reduction of MNiOx (M: La, Sr and Ce) were investigated in the methane Oxy-CO2 reforming reaction. The precursors and catalysts were characterized by X-ray diffraction, Thermoprogrammed Reduction and Oxidation – TPR/TPO, Superficial Thermoprogrammed Reaction – TPSR, High-Resolution transmission electron microscopy and Raman spectroscopy. The addition of strontium gave rise to a less active catalyst, due to the formation of SrCO3, whose presence blocks the reactants access to the nickel active sites. It was found that the replacement of lanthanum with cerium led to an increase in the overall activity of the catalysts, favoring the breakdown of the C–H bond, and suggesting a mechanism of coke oxidation by the lattice oxygen.

Effect of Strontium Addition in Graphite Morphology and Nodularization of Hypoeutectic Cast Iron

Nodular graphite cast iron or known as spheroidal graphite cast iron structurally has a spherical graphite morphology with a matrix consisting of a ferrite-pearlite phase. In general, cast iron has a main alloy consisting of carbon and silicon where both elements have an influence on the potential of graphitization and castability. In this work, the influence of strontium (Sr) added to molten cast iron with a composition of 0, 0.04, 0.06 and 0.08 wt% to graphite morphology were studied. The sample obtained will be carried out a characterization process by observing macro and microstructures using optical microscope equipped with image data processing software that displays graphite fraction, size, form and nodularity. Analysis showed that Sr addition increase in nodularization of graphite from 19.6 % to 31.5% at 0.08 wt% Sr addition.

Revealing the effect of minor Ca and Sr additions on microstructure evolution and mechanical properties of Zn-0.6 Mg alloy during multi-pass equal channel angular pressing

In this study, the microstructure evolution and mechanical properties of Zn-0.6 (wt.%) Mg alloys with minor calcium (Ca) and strontium (Sr) additions (0.1 wt%) during multi-pass equal channel angular pressing (ECAP) were comparatively investigated. The obtained results illustrate that in addition to α-Zn matrix and network-shaped ternary α-Zn + Mg2Zn11 + MgZn2 eutectic structure, CaZn13 and SrZn13 particles are formed in as-cast Zn-Mg-Ca and Zn-Mg-Sr alloys, respectively. The CaZn13 particles exhibit cuboid shape, and their sizes are much larger than the ellipsoidal SrZn13 particles. After multi-passes ECAP, both α-Zn grains and eutectic structure are obviously refined owing to the dynamic recrystallization (DRX) process and mechanical crushing effect, while the CaZn13 and SrZn13 particles exhibit no obvious change. Moreover, the existence of cuboid CaZn13 particles with sharp corners are more effective to refine α-Zn matrix via the particle stimulated nucleation DRX mechanism, resulting in finer microstructure of Zn-Mg-Ca alloy. Since the CaZn13 particles could induce large stress concentration at their shape corners during deformation, which even causes crack of the particles in ECAP alloys, the ductility of Zn-Mg-Ca alloys is significantly deteriorated. Overall, the 12p ECAP Zn-Mg-Sr alloy exhibits optimal mechanical properties with ultimate tensile strength above 300 MPa and elongation higher than 20%. Nevertheless, the deformed Zn-Mg-Ca alloys possess poor ductility owing to the existence of CaZn13 particles, which should be avoided in future design of Zn-based biodegradable metals.

Strontium incorporation into biomimetic carbonated calcium-deficient hydroxyapatite coated carbon cloth: Biocompatibility with human primary osteoblasts.

It has already been shown that sono-electrodeposition can be used to coat activated carbon fiber cloth (ACC) with calcium phosphates (CaP) and we recently demonstrated that cathodic polarization at -1V/Hg/Hg2SO4 was the best parameter to obtain a carbonated calcium deficient hydroxyapatite (CDA) coating with optimal uniformity and homogeneity. In the present study, we investigated whether this technique was suitable to dope this carbonated CDA coating by partial substitution with another bivalent cation such as strontium. We show here that a strontium-substituted carbonated CDA coating can be produced and quantitatively controlled up to at least 10at.%. In this range we demonstrate that the presence of strontium does not modify either the textural or the structural properties of the carbonated CDA. Owing to the well-known effect of both carbonated CDA and strontium in bone formation, the biocompatibility of ACC coated or not with carbonated CDA or with strontium substituted carbonated CDA was tested using primary human osteoblasts. Our data revealed a positive and dose-dependent effect of strontium addition on osteoblast activity and proliferation. In conclusion, we show here that electrodeposition at -1V is a suitable and easy process to incorporate cations of biological interest into CaP coating.

Effects of Strontium-Doped β-Tricalcium Scaffold on Longitudinal Nuclear Factor-Kappa Beta and Vascular Endothelial Growth Factor Receptor-2 Promoter Activities during Healing in a Murine Critical-Size Bone Defect Model.

It was hypothesized that strontium (Sr)-doped β-tricalcium phosphate (TCP)-based scaffolds have a positive effect on the regeneration of large bone defects (LBD). Readouts in our mice models were nuclear factor-kappa beta (NF-κB) activity and vascular endothelial growth factor receptor-2 (VEGFR-2) promoter activity during the healing process. A 2-mm critical-size femoral fracture was performed in transgenic NF-κB- and VEGFR-2-luciferase reporter mice. The fracture was filled with a 3D-printed β-TCP scaffold with or without Sr. A bioluminescence in-vivo imaging system was used to sequentially investigate NF-κB and VEGFR-2 expression for two months. After sacrifice, soft and osseous tissue formation in the fracture sites was histologically examined. NF-κB activity increased in the β-TCP + Sr group in the latter stage (day 40–60). VEGFR-2 activity increased in the + Sr group from days 0–15 but decreased and showed significantly less activity than the β-TCP and non-scaffold groups from days 40–60. The new bone formation and soft tissue formation in the + Sr group were significantly higher than in the β-TCP group, whereas the percentage of osseous tissue formation in the β-TCP group was significantly higher than in the β-TCP + Sr group. We analyzed longitudinal VEGFR-2 promoter activity and NF-κB activity profiles, as respective agents of angiogenesis and inflammation, during LBD healing. The extended inflammation phase and eventually more rapid resorption of scaffold caused by the addition of strontium accelerates temporary bridging of the fracture gaps. This finding has the potential to inform an improved treatment strategy for patients who suffer from osteoporosis.

Mesoporous Strontium-Doped Phosphate-Based Sol-Gel Glasses for Biomedical Applications.

Mesoporous phosphate-based glasses have great potential as biomedical materials being able to simultaneously induce tissue regeneration and controlled release of therapeutic molecules. In the present study, a series of mesoporous phosphate-based glasses in the P2O5-CaO-Na2O system, doped with 1, 3, and 5 mol% of Sr2+, were prepared using the sol-gel method combined with supramolecular templating. A sample without strontium addition was prepared for comparison. The non-ionic triblock copolymer EO20PO70EO20 (P123) was used as a templating agent. Scanning electron microscopy (SEM) images revealed that all synthesized glasses have an extended porous structure. This was confirmed by N2 adsorption-desorption analysis at 77 K that shows a porosity typical of mesoporous materials. 31P magic angle spinning nuclear magnetic resonance (31P MAS-NMR) and Fourier transform infrared (FTIR) spectroscopies have shown that the glasses are mainly formed by Q1 and Q2 phosphate groups. Degradation of the glasses in deionized water assessed over a 7-day period shows that phosphate, Ca2+, Na+, and Sr2+ ions can be released in a controlled manner over time. In particular, a direct correlation between strontium content and degradation rate was observed. This study shows that Sr-doped mesoporous phosphate-based glasses have great potential in bone tissue regeneration as materials for controlled delivery of therapeutic ions.

Structural, morphological and magnetic properties of strontium substituted lanthanum nickelate La2−xSrxNiO4 (0 ≤ x ≤ 0.5)

Employing the standard reaction method, partially strontium substituted lanthanum nickelate Bulk La2−xSrxNiO4 (x = 0, 0.1, 0.2, 0.3, 0.4, and 0.5) materials have been prepared by solid-state reaction method. The gross structure and phase purity of La2−xSrxNiO4 materials were examined by powder X-ray diffraction (XRD) technique. The X-ray diffraction patterns indicate that the structure phase of La2−xSrxNiO4 does not change by the addition of strontium up to x = 0.5. The XRD results show the formation of single tetragonal phase. The average crystallite/grain sizes of the La2−xSrxNiO4 samples were calculated by using Debye-Scherer formula. The magnetic measurement was observed by (M−H) curve, the surface morphology/topography of as-synthesized materials (pellets) was determined by Atomic Force Microscope (AFM) Field Emission Scanning Electron Microscope (FESEM) and Transmission Electron Microscopic analysis (TEM). The AFM and FESEM micrographs show many porous which closely packed themselves. These micrographs also reveal that the increase the strontium concentration in the materials, the grain size of La2−xSrxNiO4 also increases.

Radiopacity of computer-aided design/computer-aided manufacturing composite resin blocks.

This study aimed to clarify the degree of difference in radiopacity between sixteen CAD/CAM composite resin blocks, one ceramic block, and teeth of the same thickness on radiographs. The radiographic density of CAD/CAM composite resin blocks was measured and the results were compared with the corresponding values for enamel and dentin. Additionally, the study analyzed the constituent elements of each type of CAD/CAM composite resin block and conducted an examination to identify those elements exerting an influence on radiopacity. Compared to the enamel, there were five blocks with significantly higher radiopacity, two blocks with the same level in radiopacity, and ten blocks with notably lower radiopacity. Compared to the dentin, there were ten blocks with significantly higher radiopacity, one block with the same level in radiopacity, and six blocks with notably lower radiopacity. All of the CAD/CAM composite resin blocks for molars contained barium and strontium.This result suggests that the addition of heavy metals, for example, barium, strontium, and zirconium, would be effective in providing CAD/CAM composite resin blocks with radiopacity.

Mechanical Properties and Conductivity of Low-Pressure Die-Cast 319 Aluminum Prepared with Hot Isostatic Pressing, Thermal Treatment, or Chemical Treatment

Low-pressure die-cast (LPDC) 319 Al alloy is commonly processed with hot isostatic pressing (HIP), heat treatment, and chemical eutectic silicon modification for advanced automotive applications. Yet, the microstructure can be similarly influenced by each of these processes, which may obscure their isolated benefits. Hence, this study aimed to differentiate their effects by processing step blocks of LPDC 319 alloy with either a HIP or ambient-pressure heat treatment, each for 2 h at 500 °C, or with strontium additions up to 150 ppm. Both chemical and thermal modifications of eutectic silicon were found to effectively improve alloy conductivity. However, the potential benefits of strontium to alloy strength and hardness were offset by the decreases in density associated with the addition. In contrast, the as-cast, unmodified samples featured relatively high densities, although this limited the ability of the HIP treatment to reduce porosity. With identical temperatures and heating times, both the HIP and heat treatment promoted comparable Al2Cu dissolution and silicon spheroidization. Accordingly, both treatments generally improved hardness and strength, and increased thermal and electrical conductivities by up to 12.5%. Thus, these processing parameters can each contribute to the development of enhanced engineering components individually, thereby reducing the need for their combined application.

Nickel Supported on Alkaline Earth Metal–Doped γ-Al2O3–La2O3 as Catalysts for Dry Reforming of Methane

Nickel catalysts supported on γ–Al2O3 doped with La2O3 and alkaline earth oxides (MgO, CaO, and SrO) were investigated in the dry reforming of methane. The samples were prepared with wet impregnation method and characterized by BET surface area, X–ray diffraction (XRD), and scanning electron microscopy (SEM) techniques. The results showed that addition of these dopants decrease the specific surface area (SBET) of oxides and/or catalysts. XRD results revealed the presence of different phases of Al2O3, as well as La(OH)3, La2O2CO3, MgO, CaCO3 and SrCO3. The addition of alkaline earth promoters (MgO, CaO, and SrO) increased the catalytic activity and stability of the catalysts. The Ni/SrLaAl catalyst presented the best activity and stability, which is explained by the strong basicity of strontium. SEM analysis after reaction indicates formation of carbon over the spent catalyst and that addition of strontium stabilized the surface of the catalyst by homogeneous dispersion of the particles.

Interactions Between Strontium and Sodium Fluorosilicate in the Combined Treatment of A319 Al Alloy

The mechanical properties of cast aluminum–silicon alloys are typically improved by eutectic silicon modification and melt degassing. First, trace strontium additions can modify the silicon phase and relieve stress concentrations at the naturally coarse, acicular particles. Second, chemical degasser additions, such as sodium fluorosilicate, can remove dissolved hydrogen gas from the aluminum melt to prevent the formation of deleterious gas porosity. However, combining both treatments is difficult, due to the tendency of the two chemicals to react and reduce their effectiveness. Nonetheless, there is limited research outlining specific procedures to enable their maximum potency, with both additions. In this work, the effects of strontium and sodium fluorosilicate on the eutectic silicon morphology and casting porosity in A319 aluminum alloy were investigated. This included a comprehensive study of the fading of their individual additions as well as the influence of separating the two chemical additions by various time intervals. The results of the melt treatments were characterized using optical microscopy, density measurements, and analysis of strontium contents using optical emission spectrometry. It was found that the maximum potency of both treatments was achieved by degassing prior to strontium additions, featuring both satisfactory silicon modification and porosity reductions.