Effect Of Strontium Substitution Research Articles

Insights into the Reactivity of Gd2−xSrxFe2O7 (x = 0 ÷ 0.4) in CO Radical Hydrogenation

The effect of strontium substitution in the structure of the complex oxide Gd2SrFe2O7 on the production of light olefins by CO hydrogenation was investigated. Perovskite-type oxides Gd2−xSr1+xFe2O7 (x = 0; 0.1; 0.2; 0.3; 0.4) were synthesized by sol–gel technology and characterized by XRD, Mössbauer spectroscopy, BET specific area, acidity testing, and SEM. The experimental data revealed a correlation between the state of iron atoms, acidity, and catalytic performance. It was found that with an increase in the content of Sr2+ in the perovskite phase, the basicity of the surface and the oxygen diffusion rate increased. This contributed to the CO dissociative adsorption, formation of active carbon, and its further interaction with atomic hydrogen.

Effect of Strontium Substitution on the Tribocatalytic Performance of Barium Titanate.

This study investigates the impact of Sr doping on the tribocatalytic performance of BaTiO3 in degrading organic pollutants. Ba1-xSrxTiO3 (x = 0-0.3) nanopowders are synthesized and their tribocatalytic performance evaluated. By doping Sr into BaTiO3, the tribocatalytic performance was enhanced, resulting in an approximately 35% improvement in the degradation efficiency of Rhodamine B using Ba0.8Sr0.2TiO3. Factors such as the friction contact area, stirring speed, and materials of the friction pairs also influenced the dye degradation. Electrochemical impedance spectroscopy revealed that Sr doping improved BaTiO3's charge transfer efficiency, thereby boosting its tribocatalytic performance. These findings indicate potential applications for Ba1-xSrxTiO3 in dye degradation processes.

Effect of strontium substitution on functional activity of phosphate-based glass.

Phosphate-based glass (PBG) is a bioactive agent, composed of a glass network with phosphate as the primary component and can be substituted with various therapeutic ions for functional enhancement. Strontium (Sr) has been shown to stimulate osteogenic activity and inhibit pro-inflammatory responses. Despite this potential, there are limited studies that focus on the proportion of Sr substituted and its impact on the functional activity of resulting Sr-substituted PBG (PSr). In this study, focusing on the cellular biological response we synthesized and investigated the functional activity of PSr by characterizing its properties and comparing the effect of Sr substitution on cellular bioactivity. Moreover, we benchmarked the optimal composition against 45S5 bioactive glass (BG). Our results showed that PSr groups exhibited a glass structure and phosphate network like that of PBG. The release of Sr and P was most stable for PSr6, which showed favorable cell viability. Furthermore, PSr6 elicited excellent early osteogenic marker expression and inhibition of pro-inflammatory cytokine expression, which was significant compared to BG. In addition, compared to BG, PSr6 had markedly higher expression of osteopontin in immunocytochemistry, higher ALP expression in osteogenic media, and denser alizarin red staining in vitro. We also observed a comparable in vivo regenerative response in a 4-week rabbit calvaria defect model. Therefore, based on the results of this study, PSr6 could be identified as the functionally optimized composition with the potential to be applied as a valuable bioactive component of existing biomaterials used for bone regeneration.

Effect of strontium substitution in cobalt ferrite: Structural and optical studies

A set of strontium (Sr)-doped cobalt (Co) nanoferrites Co1-xSrxFe2O4 (x = 0.1 and 0.2) was synthesized using a sol-gel combustion method. The phase, nanocrystallinity, and optical properties of as-prepared and annealed samples were investigated. The average crystallite sizes obtained were 36, 40, and 30 nm for the nanoferrites with lattice parameters of 8.25, 8.30, and 8.30 Å, respectively. Raman spectroscopy confirmed the spinel structure of the ferrite crystals. The existence of cations at the octahedral and tetrahedral sites in the nanoparticles was also confirmed by X-ray photoelectron spectroscopy. Direct bandgap energy values of 1.29, 1.32, and 1.35 eV were determined and an applied temperature of 680 °C ensured the complete decomposition of precursors. The correlation between the Sr substitution in Co ferrite and the structural and optical changes is discussed.

Effects of strontium-substitution in sputter deposited calcium phosphate coatings on the rate of corrosion of magnesium alloys

Magnesium (Mg) alloys have significant potential for use as bioresorbable orthopaedic implant devices due to their controllable mechanical properties and an ability to promote new bone growth. However, difficulty lies with controlling the rate of corrosion in physiological conditions to ensure the load-bearing capability of the device is maintained for the required period of time, specifically until an adequate quantity of new bone tissue is formed. In this work, RF magnetron sputtering has been used to create calcium phosphate (CaP) and strontium-substituted calcium phosphate (SrCaP) thin film coatings on two Mg alloy systems (denoted WJK and ZEWX) that have been formulated for the fabrication of orthopaedic fracture fixation devices. A 14-day static-dynamic immersion study in simulated body fluid (SBF), shows that uncoated WJK substrates had a corrosion rate of 4.04 ± 0.15 millimetres per year (mmpy), which was reduced to 3.22 ± 0.17 mmpy with the application of a CaP coating, and to 2.92 ± 0.05 mmpy with a SrCaP coating. Uncoated ZEWX substrates had a corrosion rate of 3.36 ± 0.05 mmpy which was reduced to 2.98 ± 0.19 mmpy and 2.79 ± 0.03 mmpy, for CaP and SrCaP coatings, respectively. Whereas the sputter-deposited CaP and SrCaP coatings completely dissolve in SBF over the period of immersion, their presence at the outset significantly decreases the corrosion rate of both Mg alloys, as compared to the values for the uncoated substrates. Successful incorporation of Sr within the coating offers the potential for improved bioactivity with respect to directing the bone cell response to create new tissue.

Effect of strontium substitution on structural, sinterability, physicomechanical and biological properties of akermanite ceramic

Despite the excellent in vitro and in vivo performance of akermanite ceramic, its poor toughness and strength limit the biomedical application, particularly under load. Herein, the incorporation of strontium enhanced the physicomechanical properties of akermanite and this is ascribed to the decrease in grain size and better sinterability. To investigate the biological performance, the bone-cell interaction with sintered pellets was assessed by in vitro biocompatibility with human fetal osteoblast cell (hFOB). The cell viability using MTT assay revealed that the Ca1.9Sr0.1MgSi2O7 pellets with finer grain size provided better interaction between the cells compared to the unsubstituted counterpart with larger grain size. Our findings highlighted that the synergistic effect of controlled degradation rate and release of Sr2+ into the medium enhanced the in vitro biological properties of akermanite-based materials.

Effect of Strontium Substitution on the Physicochemical Properties and Bone Regeneration Potential of 3D Printed Calcium Silicate Scaffolds.

In this study, we synthesized strontium-contained calcium silicate (SrCS) powder and fabricated SrCS scaffolds with controlled precise structures using 3D printing techniques. SrCS scaffolds were shown to possess increased mechanical properties as compared to calcium silicate (CS) scaffolds. Our results showed that SrCS scaffolds had uniform interconnected macropores (~500 µm) with a compressive strength 2-times higher than that of CS scaffolds. The biological behaviors of SrCS scaffolds were assessed using the following characteristics: apatite-precipitating ability, cytocompatibility, proliferation, and osteogenic differentiation of human mesenchymal stem cells (MSCs). With CS scaffolds as controls, our results indicated that SrCS scaffolds demonstrated good apatite-forming bioactivity with sustained release of Si and Sr ions. The in vitro tests demonstrated that SrCS scaffolds possessed excellent biocompatibility which in turn stimulated adhesion, proliferation, and differentiation of MSCs. In addition, the SrCS scaffolds were able to enhance MSCs synthesis of osteoprotegerin (OPG) and suppress macrophage colony-stimulating factor (M-CSF) thus disrupting normal bone homeostasis which led to enhanced bone formation over bone resorption. Implanted SrCS scaffolds were able to promote new blood vessel growth and new bone regeneration within 4 weeks after implantation in critical-sized rabbit femur defects. Therefore, it was shown that 3D printed SrCS scaffolds with specific controllable structures can be fabricated and SrCS scaffolds had enhanced mechanical property and osteogenesis behavior which makes it a suitable potential candidate for bone regeneration.

Effects of strontium substitution on the structural distortion of hydroxyapatite by rietveld refinement and Raman Spectroscopy

The strontium (Sr) substitution plays critical roles in physical-chemical-biological properties of hydroxyapatite (HA) bioceramics due to the structural distortion induced by doping. Herein, the effects of Sr substitution on the structural distortion of HA were investigated systematically by Rietveld refinement and Raman spectroscopy. We compared the occupation possibility of Sr in the lattice and pointed out its preferred occupancy. The effects of doping on lattice parameters, bond length, bond angle and crystallite size were also studied. The evidence, that doping will give rise to the distorted structure, has been shown. In addition, the PO43−, Ca-PO4 and OH− vibrations were further studied to verify the structural evolution and distortion. This work may be helpful in further studying on the structure-property relationship of Sr substitution HA.

Effect of strontium substitution on the material properties and osteogenic potential of 3D powder printed magnesium phosphate scaffolds

3D powder printing is a versatile method for the fabrication of individual bone implants and was used for the processing of in vivo degradable ceramic scaffolds based on ammonium magnesium phosphate hexahydrate (struvite). In this study, synergetic effects could be achieved by the substitution of magnesium phosphate cements with strontium carbonate. This substitution resulted in 8.2 wt%, 16.4 wt%, and 24.6 wt% Sr2+ doped scaffolds, with a 1.9–3.1 times increased radiopacity compared to pure struvite. The maximal compressive strength of (16.1 ± 1.1) MPa found for strontium substituted magnesium phosphate was in the range of cancelleous bone, which makes these 3D printed structures suitable for medical application in low-load-bearing bone areas. In an ion release study over a course of 18 days, the release of strontium, magnesium, calcium, and phosphate ions from scaffolds was analyzed by means of inductively coupled plasma mass spectrometry. Independent of the scaffold composition the Mg2+ concentrations (83–499 mg/l) continuously increased in the cell media. The Sr2+ release varied between 4.3 μg/day and 15.1 μg/day per g scaffold, corresponding to a Sr2+ concentration in media between 1.14 mg/l and 7.24 mg/l. Moreover, decreasing calcium and phosphate concentrations indicated the precipitation of an amorphous calcium phosphate phase. The superior osteogenic properties of strontium substituted magnesium phosphate, e.g. the increase of osteoblast activity and cell number and the simultaneous suppression of osteoclast differentiation could be verified in vitro by means of WST-assay, TRAP-staining, and SEM imaging.

Effect of strontium substitution on microstructure and magnetic properties of electrospinning BaFe12O19 nanofibers

Barium ferrite micro/nano fibers were successfully prepared via the electrostatic spinning by using dimethyl formamide (DMF) as the solvent, and poly vinyl pyrrolidone (PVP) as the spinning auxiliaries. Effects of strontium substitution on the structure, morphology, and magnetic properties were investigated by scanning electron microscope (SEM), X-ray diffraction analysis (XRD), and vibration sample magnetometer (VSM). XRD patterns of the samples confirm that pure barium ferrite fibers form, and the Sr substitution makes the main peaks (110), (107), and (114) move to right slightly. Also, the FE-SEM images show that the Sr substituted fibers can keep complete fibrous morphology. Moreover, the VSM results demonstrate that the saturation magnetization can reach 56.7 emu/g when the fibers are calcined at 800°C.

Effect of strontium substitution on the structural and magnetic properties of La1.8Sr0.2MMnO6 (M = Ni, Co)-layered manganites

ABSTRACTSr-substituted perovskites, La1.8Sr0.2MMnO6 (M = Ni, Co), were synthesized using the solid-state reaction technique to present a systematic study on their morphological, structural and magnetic properties. The average grain size of the as-prepared La1.8Sr0.2NiMnO6 samples are in the range of 0.2–0.7 µm and those for La1.8Sr0.2CoMnO6 manganites are 0.1–2.8 μm, which is significantly less than that of unsubstituted La2NiMnO6 (LNMO) and La2CoMnO6 (LCMO) manganites. The XPS analysis enlightened about phase purity, binding energy and oxygen vacancy of La1.8Sr0.2MMnO6 manganites. The Sr-substituted LNMO has revealed a sharp ferromagnetic to paramagnetic phase transition at 160 ± 2 K, which is about 120 K less than that of parent LNMO. The Sr-substituted LCMO exhibited such a transition at 220 ± 2 K, which is 8 K less than that of parent LCMO. The temperature-dependent magnetization measurements suggest that the effect of Sr on the transition temperature in LNMO is more significant than that of LCMO.

Effect of Strontium Doping on the Structural, Morphological, and Dielectric Properties of PZT Ceramics

Strontium-modified lead zirconate titanate ceramics was prepared by the polymeric precursor method. The effect of Pb (II) substitution by Sr (II) in A site of the perovskite structure at molar percentages of 0.0, 0.2, 0.4 and 0.6 mol% was investigated through XRD and Rietveld method. The increasing of strontium amount displaces the morphotropic phase boundary toward to tetragonal phase and that results can be associated to the tetragonal lattice expansion besides the rhombohedral opposite phenomenon. The effect of strontium substitution on the dielectric properties for sintered ceramics is also investigated and showed the strontium substitution leads to reduction of weight loss and increasing of density for sintered ceramic. The Kc and Tc oscillates as function of ceramic morphology and is not possible to verify the existence of conductive intergrains defects by loss tangent curves. An intrinsic event can be occurring because considerable lattice distortion was verified in tetragonal and rhombohedral structures for powder samples.

Effects of strontium substitution on the phase transformation and crystal structure of calcium phosphate derived by chemical precipitation

This study focused on the effects of strontium substitution on the phase transformation and crystal structure of calcium phosphate. Chemical precipitation was used to prepare Sr-doped hydroxyapatite (HA) precursor powders. The phase transformation of the as-prepared samples during sintering was analyzed. The powders were characterized by X-ray diffraction, X-ray fluorescence spectroscopy, Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy. Quantitative analysis of the phase content and fine structure was performed by Rietveld refinement. Sr doping was found to facilitate the phase transformation from HA to beta-tricalcium phosphate (β-TCP) at 1000°C. The β-TCP content increased with increasing Sr content, causing a decline in the ratio of HA to β-TCP. With Sr contents of ≤5mol%, HA remained the major phase in the biphasic mixtures; in contrast, with Sr contents of ≥15mol%, the mass fraction of β-TCP exceeded 50%. The incorporation of Sr2+ into HA and β-TCP caused the lattice parameters of both phases to increase. Additionally, Sr incorporation slightly enhanced the binding energy of Ca. The study confirmed that Sr doping could be used to modulate the phase fractions of HA and β-TCP. The effective partial substitution of Sr in both HA and β-TCP makes these materials promising for bone repair.

Gel-derived SiO2–CaO–P2O5 bioactive glasses and glass-ceramics modified by SrO addition

The effect of SrO substitution for CaO in two sol–gel glasses with different chemical compositions (mol%) A2Sr: (54−x)CaO–xSrO–6P2O5–40SiO2 and S2Sr: (16−x)CaO–xSrO–4P2O5–80SiO2 (x=0, 1, 3 and 5) stabilized at 700°C on their structure (XRD, FTIR) and bioactive properties (SBF test) was investigated. Preliminary in vitro tests using human articular chondrocytes of selected A2Sr glass were also conducted. Moreover, the subject of this study was to detect the changes on material properties after heat treatment at 1300°C. The results show that the effect of strontium substitution on structure, bioactivity and crystallization after treatment at both the above temperatures strongly depends on CaO/SiO2 molar ratio. The presence of 3–5mol% of strontium ions creates more expanded glass structure but does not markedly affect crystallization ability after low temperature treatment. Sintering at 1300°C of A2 type glasses results in crystallization of pseudowollastonite, hydroxyapatite and also Sr-substituted hydroxyapatite for 3–5mol% of SrO substitution. The increase of strontium concentration in silica-rich materials after sintering leads to appearance of calcium strontium phosphate instead of calcium phosphate. Bioactivity evaluation indicates that substitution of Sr for Ca delays calcium phosphate formation on the materials surface only in the case of silica-rich glasses treated at 700°C. Calcium-rich glasses, after both temperature treatments, reveals high bioactivity, while crystal size of hydroxyapatite decreases with increasing Sr content. High temperature treatment of high-silica glasses inhibits their bioactivity. Preliminary in vitro tests shows Sr addition to have a positive effects on human articular chondrocytes proliferation and to inhibit cell matrix biomineralization.

Dielectric characteristics of Sr substitution on Ca0.4Sm0.4TiO3 ceramics at microwave frequency

Effect of strontium substitution on microwave dielectric behavior and sintering conditions of Ca0.4Sm0.4TiO3 (0.01≤x≤0.1) ceramics were investigated. The sintering temperature was significantly lowered from 1450°C for pure Ca0.4Sm0.4TiO3 to 1370°C for x>0.03. Notably the dielectric constant of (Ca0.4−xSrx)Sm0.4TiO3 ceramics also improved with increasing x content and the Qf value also remained over 10,000GHz with 0.01≤x≤0.1. The resultant dielectric properties have made Ca0.4Sm0.4TiO3 ceramics as very interesting materials for microwave communication and passive component applications.

Glass ionomer cements: Effect of strontium substitution on esthetics, radiopacity and fluoride release

ObjectiveSrO and SrF2 are widely used to replace CaO and CaF2 in ionomer glasses to produce radiopaque glass ionomer cements (GIC). The purpose of this study was to evaluate the effects of this substitution on release of ions from GIC as well as its effect on esthetics (translucency) and radiopacity. Materials and methodsCements were produced from ionomer glasses with varying content of Sr, Ca and F. The cements were stored in dilute acetic acid (pH 4.0) for up to 7 days at 37°C. Thereafter, the cements were removed and the solution was tested for F−, Sr2+, Ca2+, and Al3+ release. Radiopacity and translucency were measured according to BS EN ISO 9917-1:2003. ResultsIon release was linear to t1/2 suggesting that this is a diffusion controlled mechanism rather than dissolution. The fluoride release from the cements is enhanced where some or all calcium is replaced by strontium. Radiopacity shows a strong linear correlation with Sr content. All cements were more opaque than the C0.70 0.55 standard but less opaque than the C0.70 0.90 standard which is the limit for the ISO requirement for acceptance. SignificanceThis study shows that the replacement of calcium by strontium in a glass ionomer glass produces the expected increase in radiopacity of the cement without adverse effects on visual properties of the cement. The fluoride release from the cements is enhanced where some or all calcium is replaced by strontium.

Structural, dielectric, magnetic, and nuclear magnetic resonance studies of multiferroic Y-type hexaferrites

The effect of strontium substitution on structural, magnetic, and dielectric properties of a multiferroic Y-type hexaferrite (chemical formula Ba2−xSrxMg2Fe12O22 with 0 ≤ x ≤ 2) was investigated. Y-type hexaferrite phase formation was not affected by strontium substitution for barium, in the range 0 ≤ x ≤ 1.5, confirmed by x-ray diffraction and Raman spectroscopy measured at room temperature. Two intermediate magnetic spin phase transitions (at tempertures TI and TII) and a ferrimagnetic-paramagnetic transition (at Curie temperature TC) were identified from the temperature dependence of the magnetic susceptibility. Magnetic transition temperatures (TI, TII, and TC) increased with increasing strontium content. Magnetic hysteresis measurements indicated that by increasing strontium concentration, the coercivity increases, while the saturation magnetization decreases. The 57Fe NMR spectrum of the Y-type hexaferrite measured at 5 K and in zero magnetic field showed remarkable differences compared to that of other hexaferrites due to their different number of tetrahedral and octahedral iron sites. The temperature and frequency dependence of the dielectric permittivity evidenced broad peaks with frequency dispersion in correspondence of the Curie temperature.

Structural, Magnetic and Dielectric Studies on Strontium Substituted Nd2CuO4 System

The substitution of Strontium on T'–structured Nd2CuO4 system has been carried out through solid state reaction tech-nique. From the Powder XRD patterns, it is found that the compounds are formed in single phase and crystallizes in orthorhombic structure. The variation in lattice parameters with decreasing nature of volume of the prepared com-pounds confirms the incorporation of lower atomic radii Strontium in Neodymium site. Surface morphology and ele-mental composition studies are also carried out to know the nature of the compounds and effect of Strontium substitu-tion in Nd2CuO4 system. The paramagnetic nature of all the prepared compounds has been identified through magnetization studies and the results are correlated with the electron spin resonance studies by the way of variation in resonance field and broad peak width. Increasing order of dielectric constant on higher doping concentration of Strontium and the least value of dielectric loss at higher frequencies confirms the improved surface transport properties of the prepared compounds.

Chemical and electronic characterization of cobalt in a lanthanum perovskite. Effects of strontium substitution

Two different cobaltites, LaCoO 3 and La 0.5Sr 0.5CoO 3− δ , have been prepared and characterized by means of high energy Co K-edge and low energy O K-edge X-ray absorption spectroscopy (XAS). Even though half of the La(III) is substituted by Sr(II), little or no changes can be detected in the formal oxidation state of cobalt atoms. The presence of strontium cations induces two main effects in the chemical and electronic state of the perovskite. The charge balance with Sr(II) species is reached by the formation of oxygen vacancies throughout the network, which explains the well-known increase in the reactivity of this substituted perovskite. O K-edge XAS experiments show that the Sr(II) species induce the transitions of d electrons of cobalt cations from low to high spin configuration. We propose that this change in spin multiplicity is induced by two cooperative effects: the oxygen vacancies, creating five coordinated cobalt atoms, and the bigger size of Sr(II) cations, aligning the Co–O–Co atoms, and favoring the overlapping of π-symmetry cobalt and oxygen orbitals, reducing the splitting energy of e g and t 2g levels.

Effect of strontium substitution on the composition and microstructure of sol–gel derived calcium phosphates

Sr-doped calcium phosphates have been prepared by sol–gel chemistry. All samples exhibit two phases: hydroxyapatite (HAp) and tricalcium phosphate (β-TCP). With respect to undoped sample, the Sr-doped samples exhibit higher proportion of β-TCP phase but the quantity appears to be quite independent of the doping level. To explain the mismatch with the nominal stoichiometry, the presence of amorphous CaO and SrO compounds have been postulated and their proportions evaluated. The insertion of Sr2+ ions in the two crystalline phases HAp and β-TCP is almost total for low doping levels but quite incomplete for the highest doping level. The majority of the inserted Sr2+ ions are in the β-TCP phase. Considering the acknowledged beneficial effect of Sr2+ on the bone regeneration process, the effective partial substitution of Sr in biphasic calcium phosphate makes these materials very interesting for clinical applications.