Formaldehyde vapour sensing property of electrospun NiO nanograins

Beads free polyvinyl alcohol (PVA)/NiO nanofibers with an average diameter of 400 nm were successfully prepared through the electrospinning method. NiO nanograins were formed along the axis of the nanofiber due to the calcination of as-spun fibers for 24 h at 450 °C and their presence was confirmed by FESEM. NiO nanograins were characterized by XRD, XPS and FTIR. The characterization results showed the presence of NiO in nanograins and its polycrystalline nature with ionic states. The sensing studies of NiO nanograins were performed towards the pulmonary disease breath markers and they showed better response towards formaldehyde vapour at 350 °C. Calcined NiO grains showed a good response towards the 11–1145 ppm of formaldehyde vapour at the operating temperature of 350 °C. NiO nanograins also showed quick response time (37 s) and recovery time (14 s) towards 46 ppm of formaldehyde. A sensing mechanism was proposed for the formaldehyde vapour interaction at 350 °C with NiO nanograins.     

Impact of Tuning Molar Ratio in the Starting Materials: <Emphasis Type="Italic">Magneto</Emphasis>-Transport Features of Hybrid YSr<Subscript>2</Subscript>Ru<Subscript>0.9</Subscript>Cu<Subscript>2.1</Subscript>O<Subscript>7.9</Subscript>

The impact of slightly tuning molar ratio in the starting materials on the physical properties of 1212-type rutheno-cuprate, YSr₂Ru_0.9Cu_2.1O_7.9 (nominal) samples prepared under four synthesis approaches are reported. Interestingly, all samples clearly show the differences in the physical properties of the samples prepared under different synthetic protocols. However, neither XRD nor EDX reveal any notable differences in the crystal structure or sample composition. All the samples exhibit magneto-superconducting properties (H _ext=5 Oe) which are slightly varied with synthetic approaches. The high field (H _ext=10 kOe) temperature dependence of magnetization data shows a sharp ferromagnetic transition around 150 K and all the samples obey Curie–Weiss linear behavior above 180 K. The experimental effective paramagnetic moment for the various samples is in the range of 2.5 and 2.7μ _B/Ru which are in line with the literature report. The magnetization, M(H) isotherm curves measured at 5 K and −10 kOe≤H≤10 kOe conditions reveal weak ferromagnetic-like hysteresis loops for all samples with returning moment (M _r) and coercive field (H _c), whereas the high field M(H) loops indicate soft ferromagnetic behaviors with magnetic saturation. The saturation moment of the samples is slightly varied with the synthesis approaches. None of the samples showed bulk superconductivity (T_c^{R = 0})T_{\mathrm{c}}^{R = 0}) down to 2 K, while all samples show onset transitions (T_c^onsetT_{\mathrm{c}}^{\mathrm{onset}}) except the sample prepared by approach-3. The latter approach sample shows semiconducting behavior down to 2 K. The T_c^onsetT_{\mathrm{c}}^{\mathrm{onset}} noticed at 34 K, 12 K, and 6 K for the sample prepared by approach-1, 2, and 4, respectively. The nearly linear dependence suggests that hopping conduction is dominant in certain temperature range for all samples. The magneto-transport features of these samples exhibit maximum magnetoresistance (MR) at low temperatures. Remarkably, the sample prepared by approach-1 shows largest −MR about 77% at low temperature 2 K and H=90 kOe which stimulates for further investigations. Among the four synthesis approaches employed in the present study, we can probably suggest that the approach-1 (0.5Y₂O₃+0.5SrO₂+1.5SrCuO₂+0.9RuO₂+0.6CuO) is the preferable method to achieve the best sample (in terms of magneto-transport features).     

Visible light irradiated photocatalytic and magnetic properties of Fe-doped SnS<Subscript>2</Subscript> nanopowders

Fe-doped SnS₂ (SnS₂:Fe) nanopowders were synthesized by cost effective chemical method and characterized by thermo gravimetric-differential thermal analysis, X-ray diffraction, scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy and vibrating sample magnetometer techniques. The photocatalytic activity was evaluated for the degradation of congo red dye under visible light irradiation. XRD studies indicate that both the undoped and doped SnS₂ nanopowders exhibit hexagonal crystal structure with a strong (1 0 1) preferential growth. Nanosized grains are evinced from the TEM images. XPS spectra confirmed the presence of Fe in the doped samples. Photodegradation efficiency increased with increase in Fe doping concentration and the SnS₂:Fe nanopowder with 10 wt% Fe doping concentration exhibits a maximum efficiency of 93.94% after 180 min light irradiation. Ferromagnetic ordering of pure SnS₂ improved with Fe doping. The outcome of the results indicated that Fe-doped SnS₂ nanopowders are well suited as diluted magnetic semiconductor and also can be used as an efficient photocatalyst.     

Evaluation of Microstructural, Mechanical Properties and Corrosion Behavior of AISI Type 316LN Stainless Steel and Modified 9Cr-1Mo Steel Exposed in a Dynamic Bimetallic Sodium Loop at 798 K (525?°C) for 16,000 Hours

Changes occurring in the chemical composition, microstructure, mechanical properties, and carburization behavior of type 316LN stainless steel and modified 9Cr-1Mo steel on exposure to flowing sodium at 798?K (525?°C) for 16,000?hours in a bimetallic loop are discussed in this article. Type 316LN stainless steel revealed a degraded layer of approximately 5???m depth. No significant microstructural changes were observed in the case of modified 9Cr-1Mo steel exposed to sodium. The carburization depth in type 316LN stainless steel was approximately 100???m and the surface carbon concentration was 0.374?wt?pct. In the case of modified 9Cr-1Mo steel, the carbon concentration at the surface was approximately 3.50?wt?pct and the depth of carburization was nearly 75???m. The concentration of nickel and chromium decreased from the bulk to the surface of type 316LN stainless steel, leading to the formation of a ferrite layer. The concentration of these two elements reached the original matrix concentration at around 30???m. Sodium-exposed material indicated an increase in yield strength by 10?pct and reduction in ductility by 34?pct vis-à-vis annealed material. No such changes in strength and ductility were observed in the case of modified 9Cr-1Mo steel. A decrease in impact energy was noticed for sodium-exposed type 316LN stainless steel and modified 9Cr-1Mo steel vis-à-vis as-received material.     

Impact of High Pressure and High Temperature on Annealed Oxygen-deficient CoSrO<Subscript>3−<Emphasis Type="Italic">δ</Emphasis></Subscript> Perovskites: Structural and Magnetization Studies

In this brief article, structural, magnetization studies of oxygen deficient perovskite cobalt oxides CoSrO_3?δ synthesized in two different ways are reported. The structural refinements (JANA2006) of X-ray powder diffraction data indicate that the sample prepared under ambient pressure (stage-1) shows a hexagonal structure with P6₃/mmc (194) as a possible space group. The stage-1 sample subsequently sintered at 1450?°C for 1–2 h under high-pressure 6 GPa conditions (stage-2) crystallizes in tetragonal symmetry with I4/mcm (140) space group having a=5.444(7) Å and c=7.68(2) Å. While the stage-1 sample exhibits a paramagnetic nature in the magnetic susceptibility, M(T), measurements, interestingly the sample annealed under high-pressure conditions shows ferromagnetism in the magnetic susceptibility, M(T) and field dependence magnetization, M(H) measurements. The high-pressure annealed sample shows hysteresis opening with a quite large coercive field of 7.3 kOe at 1.8 K. The temperature dependence of the inverse molar susceptibility curves exhibits linear behavior in the high-temperature regime and could be fitted to the Curie–Weiss expression, χ(T)=C/(T?θ _W). The experimental values of θ _W and p _eff obtained from the linear region of the inverse molar magnetic susceptibility curves are found to be: ?210.7(5) K and 2.38(2) μ _B/Co for stage-1 and 260.2(7) K and 1.87(3) μ _B/Co for stage-2 samples, respectively. A negative sign of θ _W indicates rather strong antiferromagnetic correlations in the stage-1 sample. Apart from these results, the structural parameters reported by various groups for the strontium-based perovskite cobalt oxides are also presented in the form of literature collections.     

Annealing Effects in (Hg,Cr)Sr2CuO4+δ: Transport and X-Ray Absorption Studies

Superconducting (Hg_1–x Cr _x )Sr₂CuO₄₊, x 0.36, samples of 1201-type, synthesized in partial vacuum, show T _c ^onset of 58 K, T _c (R = 0) 52 K. It is found that T _c is not affected by the subsequent Ar or O₂ annealing treatment. Remarkably, the annealed samples show significant improvement in the diamagnetic signal. Hg L₃-edge measurements on 1201 samples show divalent state of mercury. The Cu K-edge spectra for the samples, after taking due account of the impurity phases, show noticeable modifications in the split main peak features on Ar or O₂ annealing, suggesting changes in the crystal field asymmetry. In the superconducting (SC) samples, a weak but distinct signature of Cu¹⁺ is seen. The Cu¹⁺ feature is absent in all the non-SC 1201 samples as well as in the impurity phase SrCuO₂ and Sr₂CuO₃ samples. An attempt is made to explain the observed Cu¹⁺ feature in SC (Hg,Cr)-1201 in the light of the available reports.     

Superconductivity and Magnetism in R 2CaBa2Cu5O z (R=La, Pr, Nd and Eu)

A series of compounds R ₂CaBa₂Cu₅O _z (R=La, Pr, Nd and Eu) have been synthesized by conventional solid state reaction and characterized for their structural, superconducting and magnetic properties. All compounds crystallize with the tetragonal LaBa₂Cu₃O _z type structure, space group P4/mmm. Among the four compounds studied here, R=La, Nd and Eu are superconductors with superconducting transition temperatures (T _c ^R=0) of 72, 40 and 55 K, respectively. On the other hand, neither superconductivity nor magnetic ordering is seen for R=Pr down to 3 K. The effect of the magnetic field on the susceptibility and (magneto) resistance for the superconducting samples has been investigated. The superconductivity of compounds with magnetic rare-earth ions Nd and Eu exhibit a profound influence of the magnetic field, whereas the application of the magnetic field has a limited effect on the La compound. The Pr compound is paramagnetic and does not exhibit magnetic ordering either.     

An experimental study of mass transfer in pulse reversal plating

An experimental study has been made of the limiting pulse current density for a periodic pulse reversal plating of copper on a rotating disc electrode from an acidic copper sulfate bath containing 0.05m CuSO₄ and 0.5M H₂SO₄. The measurements were made over a range of the electrode rotational speeds of 400–2500 r.p.m., pulse periods of 1–100 ms, cathodic duty cycles of 0.25–0.9, and dimension-less anodic pulse reversal current densities of 0 to 50. The experimental limiting pulse current data were compared to the theoretical prediction of Chin's mass transfer model. A satisfactory agreement was obtained over the range of a dimensionless pulse period ofDT/ ²=0.001–1; the root mean square deviation between the theory and 128 experimental data points was ±8.5%.Notation C _b bulk concentration of the diffusing ion (mol cm^–3) - C _s surface concentration of the diffusing ion (mol cm^–3) - D diffusivity of the diffusing ion (cm² s^–1) - F Faraday's constant (96 500C equiv^–1) - i current density (A cm^–2) - i ₁ cathodic pulse current density (A cm^–2) - i ₃ anodic pulse reversal current density (A cm^–2) - i ₃ ^* dimensionless anodic pulse reversal density defined asi ₃/i _lim - i _lim cathodic d.c. limiting current density (A cm^–2) - i _{lim, a} anodic d.c. limiting current density (A cm^–2) - i _PL cathodic limiting pulse current density (A cm^–2) - i _PL ^* dimensionless limiting pulse current density defined asi _PL/i _lim - m dummy index in Equation 1 - n number of electrons transferred in the electrode reaction (equiv/mol) - l time (s) - t ₁ cathodic pulse time (s) - i ₃ anodic pulse reversal time (s) - T pulse period equal tot ₁+t ₃ (s) - T ^* pulse period defined asDT/ ² (dimensionless) Greek letters thickness of the steady-state Nernst diffusion layer (cm) - electrode potential (V) - _de time-averaged electrode potential (V) - _m eigenvalues given by Equation 2 (dimensionless) - ₁ cathodic duty cycle (dimensionless) - ₃ anodic duty cycle in pulse reversal plating (dimensionless) - kinematic viscosity (cm² s^–1) - electrode rotational speed (rad s^–1)