Nanocomposite protective coatings based on Ti–N–Cr/Ni–Cr–B–Si–Fe,their structure and properties

The first results of manufacturing and investigations of a new type of nanocomposite protective coatings are presented. They were manufactured using a combination of two technologies: plasma-detonation coating deposition with the help of plasma jets and thin coating vacuum-arc deposition. We investigated structure, morphology, physical and mechanical properties of the coatings of 80–90 μm thickness, as well as defined the hardness, elastic Young modulus and their corrosion resistance in different media. Grain dimensions of the nanocomposite coatings on Ti–N–Cr base varied from 2.8 to 4 nm. The following phases and compounds formed as a result of plasma interaction with the thick coating surface were found in the coatings: Ti–N–Cr (200), (220), γ-Ni₃–Fe, a hexagonal Cr₂–Ti, Fe₃–Ni, (Fe, Ni)N and the following Ti–Ni compounds: Ti₂Ni, Ni₃Ti, Ni₄Ti, etc. We also found that the nanocomposite coating microhardness increased to H = 31.6 ± 1.1 GPa. The Young elastic modulus was determined to be E = 319 ± 27 GPa – it was derived from the loading–unloading curves. The protective coating demonstrated the increased corrosion resistance in acidic and alkaline media in comparison with that of the stainless steel substrate.     

Magnetic and electrical behaviour of La0.67Ba0.33Mn1 − xFexO3 perovskites

(La_0.67Ba_0.33)Mn_1 ? xFe_xO₃ manganites compounds have been prepared by doping up to 20% of Fe at the Mn site. As previously reported in the literature paramagnetic (PM) to ferromagnetic (FM) phase transition has been observed in materials with low Fe doping (≤ 10%). In our x = 0 and x = 0.05 compounds the Curie temperature (T_C) is close to room temperature. Above 10% Fe amount, specimens exhibit a glass magnetic behaviour with a spin- or cluster-like freezing process that can be related to a loss of ferromagnetic double exchange interaction. Below 10% of Fe³⁺ doping electrical-resistivity measurement shows metal – semiconductor transition with a maximum peak of resistivity (ρ_max) at a temperature T_P close to T_C. Above 10% of Fe³⁺ doping amount the materials exhibit only semiconductor behaviour. Both T_C and T_P decrease with doping rates with an increasing difference in temperature (T_P being lower than T_C). Results are consistent with a reduction of the number of available hopping sites for the Mn e_g(↑) electron due to substitution of Mn³⁺ by Fe³⁺ that suppress the double exchange (DE) interactions.     

Structural and optical properties of BaTi2O5 thin films prepared by pulsed laser deposition at different substrate temperatures

BaTi₂O₅ thin films were prepared on MgO (1 0 0) substrates by pulsed laser deposition. The effect of substrate temperature (T_sub) on the structural and optical properties of the films, such as crystal phase, preferred orientation, crystallinity, surface morphology, optical transmittance and bandgap energy, was investigated. The preferred orientation of the films changed form (7 1 0) to (0 2 0) depending on T_sub, and the b-axis oriented BaTi₂O₅ thin film could be obtained at T_sub = 973–1023 K. The surface morphology of the films was different with changing T_sub, which showed a dense surface with an elongated granular texture at T_sub = 973–1023 K. The crystallinity and surface roughness increased at the elevated substrate temperatures. The as-deposited BaTi₂O₅ thin films were highly transparent with an optical transmittance of ～70%. The bandgap energy was found to decrease with increasing substrate temperature, from 3.76 eV for T_sub = 923 K to 3.56 eV for T_sub = 1023 K.     

Enteric coating process of diclofenac sodium pellets in a fluid bed coater with a wurster insert: Influence of process variables on coating performance and release profile

The objective of this work was to study the coating process of diclofenac sodium pellets, with the commercial aqueous coating suspension for enteric release – Acryl-Eze® MP, in a fluid bed coater with a Wurster insert. Coating experiments were performed following a 2² factorial design to determine the influence of process variables on coating performance, measured by the two response variables: efficiency (η_%) and agglomeration index (m_agg%). Both response variables were found to be affected by inlet temperature and suspension flow rate with a 95% confidence level. This work also studied the release of diclofenac sodium coated and uncoated pellets in HCl 0.1 N and pH 6.8 phosphate buffer media. Results showed that the release of diclofenac sodium during the buffer stage was affected by the prior exposure to the HCl 0.1 N medium and a polymer weight gain above 9.7% (2.7 mg/cm²), was needed to modify the release in such a way that it remained below 10% for the first 120 min in HCl 0.1 N and above 75% in pH 6.8 for the next 45 min. Neither the drug content nor the release profiles were significantly affected by storage at 40 °C and 75% relative humidity.     

Synthesis of RuSr2GdCu2O8 − δ superconductors by the sol–gel route

The RuSr₂GdCu₂O_8 − δ (Ru-1212) superconductors have been prepared through the sol–gel route. We found that 1030 °C is the optimum annealing temperature for the formation of the Ru-1212 superconductors synthesized by the sol–gel route. X-ray powder diffraction analysis indicates that nearly all the peaks from the samples can be indexed to a single phase of Ru-1212, tetragonal symmetry with lattice parameters a = b = 3.382 Å, c = 11.478 Å and space group I4/mmm. The RuSr₂GdCu₂O_8 − δ superconductors prepared by the sol–gel method exhibit onset transition temperature T_c-onset near 55 K and zero resistance temperature T_c-zero at 45 K.     

High-temperature electrical resistivity and heat capacity studies on nano-crystalline geikielite

We report here for the first time the temperature dependence of the electrical resistivity and heat capacity of nano-crystalline MgTiO₃ geikielite of up to 1000 K. The temperature dependence of heat capacity of nano-crystalline geikielite expressed as C_p = 46.44(5) + 0.0502(2)T − 4.56 × 10⁶T² + 1.423 × 10³T^− 0.5 − 8.672 × 10^− 6T^− 2, where C_p = is specific heat expressed in J/mol. K and T is the temperature in K. Both the electrical resistivity and heat capacity behaviour show that the geikielite (both the natural and synthetic nano-crystalline samples) are stable and remains electrically insulating up to 1000 K.     

Preparation and characterization of LiFe1/2Ni1/2VO4

A layered ceramic oxide, LiFe_1/2Ni_1/2VO₄ has been prepared using solid-state reaction technique. The preparation conditions have been optimized using thermogravimmetric analysis (TGA) studies. The formation of the material sample under the reported condition has been confirmed by X-ray diffraction (XRD) analysis. XRD analysis indicates the crystal structure to be orthorhombic with lattice parameter: a = 3.5637 Å, b = 17.7486 Å, c = 12.2884 Å. The phase morphology and surface properties studied using scanning electron microscopy (SEM), suggest a polycrystalline texture with reasonable number of the voids. Complex impedance analysis of the sample has indicated: (i) conduction due to bulk contribution at T ≤ 200 °C, (ii) the presence of grain boundary effects at T ≥ 200 °C, (iii) negative temperature coefficient of resistance (NTCR) behaviour and (iv) evidence of temperature dependent electrical relaxation phenomena in the sample. The DC conductivity (σ_DC) shows typical Arrhenius behaviour when observed as a function of the temperature. The activation energy value has been estimated to be 0.42 eV. σ_DC, as evaluated from complex impedance spectrum, shows a jump of nearly ∼4 orders of magnitude in the value at higher temperature when compared to that of the room temperature value. AC conductivity spectrum obeys Jonscher's universal power law. The results of σ_AC as a function of frequency are also discussed.     

Influence of Al2O3 on low-field spin-polarized tunneling magnetoresistance of (1 − x) La0.7Ca0.3MnO3 + x Al2O3 composites

In this study we report the effect of Al₂O₃ on the low field magnetoresistance (LFMR) of (1 ? x) La_0.7Ca_0.3MnO₃ + x Al₂O₃ composite synthesized through a solid-state reaction method combined with an energy milling method. Based upon a spin-polarized tunneling of conduction electrons at the grain boundaries, we have proposed a phenomenological model to explain the observed electrical transport behavior over the whole temperature range (5  300 K), especially the gradual drop of metal-insulator transition temperature (T_p = T_max) as a function of increasing Al₂O₃ content, while the ferromagnetic–paramagnetic transition temperature (T_C) remains almost constant (T_C = 250 K).     

Aluminum-free glass-ionomer bone cements with enhanced bioactivity and biodegradability

Al-free glasses of general composition 0.340SiO₂:0.300ZnO:(0.250-a-b)CaO:aSrO:bMgO:0.050Na₂O:0.060P₂O₅ (a, b = 0.000 or 0.125) were synthesized by melt quenching and their ability to form glass-ionomer cements was evaluated using poly(acrylic acid) and water. We evaluated the influence of the poly(acrylic acid) molecular weight and glass particle size in the cement mechanical performance. Higher compressive strength (25 ± 5 MPa) and higher compressive elastic modulus (492 ± 17 MPa) were achieved with a poly(acrylic acid) of 50 kDa and glass particle sizes between 63 and 125 μm. Cements prepared with glass formulation a = 0.125 and b = 0.000 were analyzed after immersion in simulated body fluid; they presented a surface morphology consistent with a calcium phosphate coating and a Ca/P ratio of 1.55 (similar to calcium-deficient hydroxyapatite). Addition of starch to the cement formulation induced partial degradability after 8 weeks of immersion in phosphate buffer saline containing α-amylase. Micro-computed tomography analysis revealed that the inclusion of starch increased the cement porosity from 35% to 42%. We were able to produce partially degradable Al-free glass-ionomer bone cements with mechanical performance, bioactivity and biodegradability suitable to be applied on non-load bearing sites and with the appropriate physical characteristics for osteointegration upon partial degradation. Zn release studies (concentrations between 413 μM and 887 μM) evidenced the necessity to tune the cement formulations to reduce the Zn concentration in the surrounding environment.     

Electro-magnetic transport behavior of La0.7Ca0.3MnO3/SnO2 composites

The composites of (1 ? x)La_0.7Ca_0.3MnO₃ (LCMO) + xSnO₂ (x = 0.01, 0.05, 0.10, 0.30, 0.50, 0.60, 0.65 and 0.70) were synthesized by conventional solid-state reaction method. The results of X-ray diffraction (XRD) and scanning electronic microscopy (SEM) indicate that SnO₂ and LCMO coexist in the composites and SnO₂ mainly segregates at the grain boundaries of LCMO, which are in accordance with the results of the magnetic measurements. The detailed electrical characterizations for all the samples showed that a new metal–insulator (M–I) transition temperature (T_P2) appeared at a lower temperature compared with the intrinsic metal–insulator (M–I) transition temperature (T_P1) when x < 0.50 (T_P1 > T_P2). When x > 0.50, T_P1 disappeared, leaving only T_P2. The resistivity percolation threshold of the composites occurred at x = 0.60. Corresponding to the two M–I transition peaks, the curves of magnetoresistance against temperature also showed two peaks for all composites. These phenomena can be explained by the segregation of a new phase related to SnO₂ at the grain boundaries or surfaces of the LCMO grains.     

A new low temperature modification of TaTe2—Comparison to the room temperature and the hypothetical 1T-TaTe2 modification

A new low temperature modification of TaTe₂ is reported (structural data at T = 150 K: C2/m (no. 12), Z = 18, a = 14.792(1) Å, b = 10.8829(9) Å, c = 9.3005(7) Å, β = 110.693(1)°). Temperature dependent single crystal X-ray diffraction, magnetic susceptibility, resistivity, specific heat capacity and differential scanning calorimetry measurements all show a phase transition at T_PT ≈ 170 K. The structural change is mainly reflected by a shift of only 2/9 of the Ta atoms by 0.283 Å, which leads to clustering of the Ta atoms. The bonding patterns were derived from the Crystal Orbital Hamiltonian Population and from the Electron Localization Function based on Density Functional Theory calculations, respectively. Differences to the room temperature modification and to the hypothetical 1T-TaTe₂ structure are elaborated. It is suggested, that the room temperature structure might show a dynamic type of disorder, with the X-ray structure analysis reflecting the time averaged structure.     

Design of polymeric capsules for self-healing concrete

Up to now, glass capsules, which cannot resist the mixing process of concrete, have been mostly used in lab-scale proof-of-concept to encapsulate polymeric agents in self-healing concrete. This study presents the design of polymeric capsules which are able to resist the concrete mixing process and which can break when cracks appear. Three different polymers with a low glass transition temperature T_g have been extruded: Poly(lactic acid) (PLA) (T_g = 59 °C), Polystyrene (PS) (T_g = 102 °C) and Poly(methyl methacrylate/n-butyl methacrylate) (P(MMA/n-BMA)) (T_g = 59 °C). After heating the capsules prior to mixing with other components of the mix, to shift from a brittle state to a rubbery state, their survival ratio considerably increased. Moreover, a part of the capsules, which previously survived the concrete mixing process, broke with crack appearance. Although some optimization is still necessary concerning functional life of encapsulated adhesives, this seems to be a promising route.     

Improvement of dry float–sink separation of smaller sized spheres by reducing the fluidized bed height

In this study, the influence of the fluidized bed height on the float–sink of different sized spheres in a gas–solid fluidized bed was investigated. Fluidized beds with heights h = 200, 150, 100 and 50 mm were prepared using a cylindrical column of inner diameter = 290 mm and a mixture of zircon sand and iron powder as the fluidized medium. Float–sink experiments were carried out using density adjusted spheres of diameter D_sp = 40, 30, 20 and 10 mm. It was found that the float–sink performance at D_sp ?20 mm is not affected by the height of the bed, and the sharpness of separation (the density range where spheres neither float nor sink completely) is less than or equal to 200 kg/m³. In the case of D_sp = 10 mm, the sharpness of separation is a larger value (1100 kg/m³ at h = 200 mm), whereas it decreases with decreasing h and is 400 kg/m³ at h = 50 mm. The fluctuation of the surface height of the fluidized bed was visually recorded. The fluctuation is reduced by reducing h. The fluctuation vs. h correlates with the sharpness of separation at D_sp = 10 mm vs. h. These results indicate that the dry float–sink separation of smaller sized spheres is improved as the fluctuation of fluidized bed surface is decreased by reducing the fluidized bed height.     

Study on the ITO work function and hole injection barrier at the interface of ITO/a-Si:H(p) in amorphous/crystalline silicon heterojunction solar cells

For this study we focused on the front contact barrier height of HIT (ITO/a-Si:H(p)/a-Si:H(i)/c-Si(n)) solar cell. The ITO films with low resistivity of 1.425 × 10^?4 Ω cm were deposited by pulsed DC magnetron sputtering as a function of substrate temperature (T_s). There were improvement in Φ_ITO from 4.15 to 4.30 eV and delta hole injection barrier from 0 to 0.129 eV for the HIT solar cell. The results show that the high values of Φ_ITO and the delta hole injection barrier at the front interface of ITO/p-layer lead to an increase of open circuit voltage (V_oc), fill factor (FF) and efficiency (η). The performance of HIT device was improved with the increase of T_s and the best photo voltage parameters of the device were found to be V_oc = 635 mV, FF = 0.737 and η = 14.33% for T_s = 200 °C.     

A facile assembly of polyimide/graphene core–shell structured nanocomposites with both high electrical and thermal conductivities

Polyimide/reduced graphene oxide (PI/r-GO) core–shell structured microspheres were fabricated by in-situ reduction of graphene oxide (GO), which was coated on the surface of PI microspheres via hydrogen bonding and π–π stacking interaction. The highly ordered 3D core–shell structure of PI/r-GO microspheres with graphene shell thickness of 3 nm was well characterized by scanning electron microscope (SEM), transmission electron microscopy (TEM) and Raman spectra. The glass transition temperature (T_g) of PI/r-GO microspheres was slightly increased because of the interaction of r-GO and PI matrix while the temperature at 5% weight loss (T_5%) of PI/r-GO microspheres was decreased due to the side effect of reductant hydrazine hydrate. The PI/r-GO nanocomposites exhibited highly electrical conductivity with percolation threshold of 0.15 vol% and ultimate conductivity of 1.4 × 10⁻² S/m. Besides, the thermal conductivity of PI/r-GO nanocomposites with 2% weight content of r-GO could reach up to 0.26 W/m K.     

Electrical transport and magnetoresistance in La2 / 3Ca1 / 3MnO3/CuO composites

The electrical transport and magnetoresistance properties were experimentally studied for composites according to the nominal composition (1 − x)La_2 / 3Ca_1 / 3MnO₃/xCuO which were fabricated using a special chemical route (x is molar ratio). The composites display different transport behaviors for the range of x < 6% and > 6%. The introduction of CuO causes a large shift of the insulator–metal transition temperature (T_p) toward low temperature for x < 6%, while the T_p is almost independent on x for x > 6%. We also show that the magnetoresistance near T_p can be substantially increased through the introduction of CuO. The largest magnetoresistance with a value as high as ∼90% is obtained in the x = 20% composite for a rather small magnetic field (0.3 T). It is interesting to observe another transition in MR₀ vs. T curve at temperature range of 170∼200 K for the composites with CuO addition. Based on structural and microscopic analysis, unusual observations of transport and magnetoresistance are discussed.     

Structural and magnetic study of thin films based on anisotropic ternary alloys FeNiPt2

L1₀ ordered (Fe–Ni)₅₀Pt₅₀ alloy films with perpendicular magnetic anisotropy were successfully prepared by interdiffusing FePt(0 0 1) and NiPt(0 0 1) layers co-deposited on MgO(0 0 1) substrates by MBE. The [0 0 1] growth direction corresponds to the epitaxy of the alloy on the substrate and is the interesting growth orientation to get a perpendicular magnetization. The X-ray diffraction shows a high L1₀ chemical order (S = 0.7 ± 0.1). The easy magnetization direction is perpendicular for all samples. The MFM images display highly interconnected stripes corresponding to up and down orientations of the magnetization. Large uniaxial magnetic anisotropy (K_u = 9.10⁵ J/m³) and suitable magnetic transition temperature (T_C = 400 K) are obtained. The addition of Ni changes the spin–orbit interaction in the FePt compound system, hence causes a decrease of anisotropy, saturation magnetization and coercivity.     

Effect of V2O5 additive to 0.4SrTiO3–0.6La(Mg0.5Ti0.5)O3 ceramics on sintering behavior and microwave dielectric properties

The effect of V₂O₅ addition on the microwave dielectric properties and the microstructures of 0.4SrTiO₃–0.6La(Mg_0.5Ti_0.5)O₃ ceramics sintered for 5 h at different sintering temperature were investigated systematically. It was found that the sintering temperature was effectively lowered about 200 °C by increasing V₂O₅ addition content. The grain sizes, bulk density as well as microwave dielectric properties were greatly dependent on sintering temperature and V₂O₅ content. The 4ST–6LMT ceramics with 0.25% V₂O₅ sintered at 1400 °C for 5 h in air exhibited optimum microwave dielectric properties of ɛ_r = 50.7, Q × f = 15049.6 GHz, T_f = −1.7 ppm/°C.     

Local solid particle behavior inside the upper zone of a circulating fluidized bed riser

The solid phase behavior is studied in the upper zone of a circulating fluidized bed riser with glass particle of mean diameter 107 μm, using a Phase Doppler Anemometer. Superficial gas velocities U_g > U_c are investigated covering the turbulent and the fast fluidization regimes and this for three static bed heights (H_s = 50 mm, H_s = 100 mm and H_s = 150 mm). The results show that the mean axial particle velocity lateral profile shapes found parabolic for H_s = 50 mm, devolve to a concave shape for H_s = 100 mm and H_s = 150 mm, creating a particles speeding zone between the core and the annulus zones. For both axial and transversal standard deviations of particle velocities in the core region, the values for the three static bed heights unite to form two stages of evolutions with U_g, where the transition velocity between these stages is found associated to the appearing of a significant entrainment of solid particles. At this transition velocity, the transversal movement originally directed toward the center riser, undergo a change toward the wall beginning near the wall and spreading into a large part of the section riser with increasing U_g. A discussion on the boundary between the turbulent and fast fluidization regimes is made based on these results.     

Magnetic moments and exchange interaction in Sm(Co, Fe)5 from first-principles

The electronic structure, magnetization and exchange interaction in Sm(Co_1?xFe_x)₅ with x = 0–1 are studied from a first-principles density functional calculation. The dependence of the magnetization on Fe content shows a 3d-like Slater–Pauling relationship in these alloys. As the Fe content x increases from 0 to 1.0, the magnetization increases from 7.8 μ_B to 10.6 μ_B (x = 0.8) and then decreases to 10.0 μ_B (x = 1). The effective exchange interaction parameters show a peak value around x = 0.6, which is ascribed to the exchange parameters between Fe and Co being larger than those for Co–Co and Fe–Fe pairs. The estimated T_C from the calculated exchange parameters range between 890 K and 1357 K in Sm(Co_1?xFe_x)₅ using a multi-sublattices mean field model.