The role of Ce ions in electrochemical corrosion of 304 SS in Ce(NO<Subscript>3</Subscript>)<Subscript>3</Subscript>.6H<Subscript>2</Subscript>O

Effects of temperature and potential on the electrochemical corrosion behavior of alloy AISI 304 (UNS S30400) Stainless steel were investigated in 3 wt.% cerium nitrate (Ce[NO₃]₃.6H₂O) solution. With an increase in electrolyte temperature from ambient temperature to 90°C, the corrosion potential of the alloy shifted towards the noble direction, and the resistance to polarization increased due to the formation of Ce-oxide on the electrode surface. The oxide films formed at the open circuit potential (OCP) and a passive potential of 0.4 V_SCE were examined by x-ray photoelectron spectroscopy (XPS). The oxide film formed at 50°C and a passive potentialof 0.4 V_SCE consists of mixed oxides of Ce and Cr, whereas that at OCP consists of only Cr oxide. The formation of Cr oxides on the electrode surface was primarily due to the nitrate (NO₃ ⁻) ions in Ce(NO₃)₃.6H₂O electrolyte.     

Thermodynamic optimization of the Na<Subscript>2</Subscript>O-B<Subscript>2</Subscript>O<Subscript>3</Subscript> pseudo-binary system

The Na₂O-B₂O₃ system is thermodynamically optimized by means of the CALPHAD method. A two-sublattice ionic solution model, (Na⁺¹)_P(O⁻²,BO₃ ⁻³,B₄O₇ ⁻²,B₃O_4.5)_Q, has been used to describe the liquid phase. All the solid phases were treated as stoichiometric compounds. A set of thermodynamic parameters, which can reproduce most experimental data of both phase diagram and thermodynamic properties, was obtained. Comparisons between the calculated results and experimental data are presented.     

Preparation and optical properties of Y<Subscript>2</Subscript>O<Subscript>3</Subscript>/SiO<Subscript>2</Subscript> powder

Y(NO3)3 and NH3·H2O were used as a raw materials,and nano-Y2O3 powder was successfully synthesized by a precipitation method.Employing TEOS as a raw material,SiO2 powder was successfully prepared by a alkoxide-hydrolysis method,and a Y2O3/SiO2 composite powder was obtained by coating.The Y2O3,SiO2,and Y2O3/SiO2 powders were characterized using X-ray diffraction(XRD),scanning electron microscopy(SEM),and Fourier transform infrared spectrophotometer(FT-IR);the Y2O3 and Y2O3/SiO2 powders were further examined ...     

Kinetics of forward extraction of Ti（IV） from H_2SO_4 medium by P_（507） in kerosene using the single drop technique

The kinetics of forward extraction of Ti(IV) from H2SO4 medium by P507 in kerosene has been investigated using the single drop technique.In the low concentration region of Ti(IV),the rate of forward extraction at 298 K can be represented by F(kmol·m-2·s-1)=10-5.07 [TiO 2 + ][H+]-1 [NaHA 2 ](o)·Analysis of the rate expression reveals that the rate determining step is(TiO)(i)2+ +(HA 2)(i)-[TiO(HA2)](i)+.The values of Ea,H±,S±,and G±298 are calculated to be 22 kJ·mol-1,25 kJ·mol-1,-218 J·mol-1·K-1,and 25 kJ·mol-1,respectively.The experimental negative S± values indicate that the reaction step occurs via SN2 mechanism.     

Phase Relations in the Al<Subscript>2</Subscript>O<Subscript>3</Subscript>-V<Subscript>2</Subscript>O<Subscript>5</Subscript>-MoO<Subscript>3</Subscript> System in the Solid State. The Crystal Structure of AlVO<Subscript>4</Subscript>

Phase relations in the ternary oxide system Al₂O₃-V₂O₅-MoO₃ in the solid state in air have been investigated by using the x-ray diffraction (XRD) and differential thermal analysis/thermogravimetric (DTA/TG) methods. It was confirmed that in the subsolidus area of the Al₂O₃-V₂O₅-MoO₃ system, there exist seven phases, that is Al₂O₃, V₂O_5(s.s.), MoO₃, AlVO₄, Al₂(MoO₄)₃, AlVMoO₇, and V₉Mo₆O₄₀. Seven fields, in which particular phases coexist at equilibrium, were isolated. The crystal structure of AlVO₄ has been refined from x-ray powder diffraction data. Its space group is triclinic, , Z = 6, with a = 0.65323(1) nm, b = 0.77498(2) nm, c = 0.91233(3) nm, α = 96.175(2)°, β = 107.234(3)°, γ = 101.404(3)°, V = 0.42555 nm³. The crystal structure of the compound is isotypic with FeVO₄. Infrared (IR) spectra of AlVO₄ and FeVO₄ are compared.     

Preparation and characterization of nanostructured Bi<Subscript>2</Subscript>Se<Subscript>3</Subscript> and Sn<Subscript>0.5</Subscript>-Bi<Subscript>2</Subscript>Se<Subscript>3</Subscript>

Nanostructured Bi₂Se₃ and Sn_0.5-Bi₂Se₃ were successfully synthesized by hydrothermal coreduction from SnCl₂·H₂O and the oxides of Bi and Se. The products were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), and field emission scanning electron microscope (FESEM). Bi₂Se₃ powders obtained at 180°C and 150°C consist of hexagonal flakes of 50–150 nm in side length and nanorods of 30–100 nm in diameter and more than 1 μm in length. The product obtained at 120°C is composed of thin irregular nanosheets with a size of 100–200 nm and several nanometers in thickness. The major phase of Sn_0.5-Bi₂Se₃ synthesized at 180°C is similar to that of Bi₂Se₃. Sn_0.5-Bi₂Se₃ powders are primarily nanorod structures, but small amount of powders demonstrate irregular morphologies.     

Evaluation of in vitro and in vivo tests for surface-modified titanium by H<Subscript>2</Subscript>SO<Subscript>4</Subscript> and H<Subscript>2</Subscript>O<Subscript>2</Subscript> treatment

Titanium is widely used as an implant material for artificial teeth. Furthermore, various studies have examined surface treatment with respect to the formation of a fine passive film on the surface of commercial titanium and its alloys and to improve the bioactivity with bone. However, there is insufficient data about the biocompatibility of implant materials in the body. The purpose of this study was to examine whether surface modification affects the precipitation of apatite on titanium metal. Specimens were chemically washed for 2 min in a 1∶1∶1.5 (vol.%) mixture of 48 %HF, 60%HNO₃ and distilled water. The specimens were then chemically treated with a solution containing 97%H₂SO₄ and 30%H₂O₂ at the ratio of 1∶1 (vol.%) at 40°C for 1h, and subsequently heat-treated at 400°C for 1h. All the specimens were immersed in HBSS with pH 7.4 at 36.5°C for 15d, and the surface was examined with TF-XRD, SEM, EDX and XPS. In addition, specimens of commercial pure Ti, with and without surface treatment, were implanted in the abdominal connective tissue of mice for 28 d. Conventional aluminum and stainless steel 316L were also implanted for comparison. An amorphous titania gel layer was formed on the titanium surface after the titanium specimen was treated with a solution of H₂SO₄ and H₂O₂. The average roughness was 2.175 μm after chemical surface treatment. The amorphous titania was subsequently transformed into anatase by heat treatment at 400°C for 1h. The average thickness of the fibrous capsule surrounding the specimens implanted in the connective tissue was 47.1μm in the chemically treated Ti, and 52.2, 168.7 and 101.9μm, respectively, in the untreated commercial pure Ti, aluminum and stainless steel 316L.     

Upconversion luminescence properties of Er<Superscript>3+</Superscript> doped GeS<Subscript>2</Subscript>-Ga<Subscript>2</Subscript>S<Subscript>3</Subscript>-KCl chalcohalide glasses

Er3+ ions doped chalcohalide glasses with the composition of 56GeS2-24Ga2S3-20KCl were fabricated by a melt-quenching method.Under 800 nm laser excitation,strong green emissions centered at 525 nm and 550 nm and weak red emission centered at 660 nm were observed,which were assigned to 2H11/2→4I15/2,4S3/2→4I15/2,and 4F9/2→4I15/2 transitions,respectively.The intensity reached maximum when the Er3+ ions concentration was 0.1 mol%.The possible upconversion luminescence mechanism was proposed from the discussion...     

Up-Date of a Thermodynamic Database of the ZrO<Subscript>2</Subscript>-Gd<Subscript>2</Subscript>O<Subscript>3</Subscript>-Y<Subscript>2</Subscript>O<Subscript>3</Subscript>-Al<Subscript>2</Subscript>O<Subscript>3</Subscript> System for TBC Applications

The thermodynamic database of the ZrO₂-Gd₂O₃-Y₂O₃-Al₂O₃ system is up-dated taking into account new data on lattice stabilities of ZrO₂, Gd₂O₃ and Y₂O₃ and heat capacity measurements for the monoclinic phase Gd₄Al₂O₉ and phase with garnet structure Gd₃Al₅O₁₂. New data for the heat capacities of Gd₂Zr₂O₇ (pyrochlore) and GdAlO₃ (perovskite) as well as on the enthalpy of formation of fluorite solid solutions (Zr_1−x Gd _x )O_2−x/2 were found to be in good agreement with calculated results. In comparison with the previous assessment, taking into account new experimental data resulted in a change of the melting character of the Gd₄Al₂O₉ phase from a peritectic one to a congruent one in the Gd₂O₃-Al₂O₃ system. Correspondently, in the ternary system ZrO₂-Gd₂O₃-Al₂O₃, the melting character of the three-phase assemblage Gd₂O₃ (B), Gd₄Al₂O₉ and GdAlO₃ changed from eutectic to transition type U. The T ₀-lines for T/M and F/T diffusionless transformations and driving force of partitioning to equilibrium assemblage T + F were calculated in the ZrO₂-Gd₂O₃-Y₂O₃ system.     

Magnetoresistance of the La<Subscript>0.7</Subscript>Ca<Subscript>0.3</Subscript>MnO<Subscript>3</Subscript> single crystal

The dependence of the resistance ρ of the La_0.7Ca_0.3MnO₃ single crystal on the temperature (in a range of 77 < T < 410 K) and magnetic field H is studied. The dependence of the magnetoresistance Δρ/ρ of the ferromagnetic phase on the field is shown to be determined by the competition of two mechanisms. In low magnetic fields, the magnetoresistance is positive Δρ/ρ > 0 and is determined by changes in the resistance with changing magnetization orientation with respect to the crystallographic axes; in high magnetic fields, the magnetoresistance is negative Δρ/ρ < 0, since it is the suppression of spin fluctuations in the magnetic field that plays the principal role. The phase transition from the ferromagnetic to paramagnetic state is a first-order transition close to the second-order one. In the transition range, the magnetoresistance is determined by the resistivity in the zero field ρ(T) and by the shift of the transition temperature T _C(H) in the magnetic field. In the paramagnetic state, the resistivity ρ(T) has an activation character; similarly to the magnetoresistance of other lanthanum manganites, the magnetoresistance of this single crystal is controlled by a change in the activation energy in the magnetic field.     

Influence of Sb<Subscript>2</Subscript>O<Subscript>3</Subscript> doping on the properties of KBT-NBT-BT lead-free piezoelectric ceramics

0.144(K0.5Bi0.5)TiO3-0.85(Na0.5Bi0.5)TiO3-0.006BaTiO3(KBT-NBT-BT) lead-free piezoelectric ceramics were prepared using a conventional solid state method.The influence of Sb2O3 doping on the crystal phase,surface microstructure and properties of the KBT-NBT-BT lead-free piezoelectric ceramics were investigated using X-ray diffraction(XRD),scanning electron microscope(SEM) and other analytical methods.The results show that all compositions are of pure perovskite structure solid states.Sb2O3 doping does not influence the microstructure of KBT-NBT-BT lead-free piezoelectric ceramics obviously in the Sb2O3 doping range of 0.1-0.5 wt.%.Sb2O3 functions as a donor when doped small amount,while functions as a acceptor when doped large amount.The piezoelectric strain constant(d33) increases first and then decreases;the dielectric constant(ε3T3/ε0) and the dielectric loss(tanδ) decrease continuously when the amount of Sb2O3 dopant increases.When the doping amount of Sb2O3 is 0.1 wt.%,the KBT-NBT-BT piezoelectric ceramics with good comprehensive properties are obtained,whose d33,ε3T3/ε0 and tanδ are 147 pC/N,1510 and 4.2%,respectively.     

Microwave-assisted synthesis of CePO<Subscript>4</Subscript> nanorod phosphor with violet emission

Monoclinic and hexagonal CePO4 nanoparticles and nanorods were successfully synthesized from Ce(NO3) 3·6H2O and Na3PO4·12H2O solu-tions at pH 1-5 by a 180 W microwave radiation for 60 min.The products were characterized by X-ray diffraction(XRD) ,Fourier transform infrared(FTIR) spectroscopy,and scanning electron microscopy(SEM) .XRD patterns revealed that the products are hexagonal CePO4 structures at pH 2-5,and monoclinic CePO4 structures at pH 1.SEM characterization shows that these products were nanoparticles,short nanorods,and long nanorods,controlled by the pH of the precursor solutions.Optical properties of the nanorods were also investigated by ultraviolet-visible(UV-vis) and photoluminescence(PL) spectroscopy.     

Solid reaction mechanism of CaHPO4·2H2O ＋ CaCO3 with and without yttria

The effect of yttria on the solid reaction mechanism of a CaHPO₄·2H₂O + CaCO₃ system at different temperatures was experimentally studied. The samples with and without yttria were subjected to thermogravimetric/differential scanning calorimetry measurement. The samples were heat treated at the temperatures corresponding to the peaks on the DSC spectra, and the resulted phase compositions were identified by X-ray diffraction. The transformation mechanism was deduced by comparing the phases obtained at different temperatures. The results show that the transformations at below 1073 K are not affected by yttria, but all those at above 1073 K are completely altered. The formation temperature of hydroxyapatite decreases by 134 K, and the decomposition temperature increases by 38 K. The polymorphous transformation of Ca₃(PO₄)₂ from β phase to α phase increases by 47 K. The thermodynamic properties of the transformations at above 1073 K are also modified by the addition of yttria; that is, the endothermal peaks are substituted by exothermal peaks.     

Synthesis and Characterization of New Bismuth Lead Vanadate Pb<Subscript>2</Subscript>BiV<Subscript>3</Subscript>O<Subscript>11</Subscript>

It has been shown that BiVO₄ and Pb₂V₂O₇ react with each other, forming a new compound of the formula Pb₂BiV₃O₁₁ at molar ratio equal to 1:1. This compound has also been obtained from PbO, Bi₂O₃, and V₂O₅, mixed at a molar ratio of 4:1:3. It melts congruently at a temperature of 725 ± 5 °C and crystallizes in the triclinic system with unit-cell parameters: a = 0.710076 nm, b = 1.41975 nm, c = 1.42972 nm, α = 134.552°, β = 97.2875°, γ = 89.6083°, and Z = 4.     

The effect of heat treatment on the corrosion resistance of 440C stainless steel in 20% HNO<Subscript>3</Subscript> + 2.5% Na<Subscript>2</Subscript>Cr<Subscript>2</Subscript>O<Subscript>7</Subscript> solution

The effect of heat treatment on the corrosion resistance of 440C stainless steel was investigated in a 20% HNO₃ + 2.5% Na₂Cr₂O₇ solution using electrochemical noise (ECN) measurements, electrochemical impedance spectroscopy (EIS), and scanning electron microscopy (SEM) examinations. The noise resistance (Rn), which has been found to be inversely related to the localized corrosion rate, was measured to be 5.7E + 08 Ω-cm², 4.2E + 08 Ω-cm², and 3.7E + 04 Ω-cm² for the oil-quenched, air-quenched, and vacuum furnace cooled (VFC) samples, respectively, after 1200 s exposures. The Rn for all heat treat conditions stabilized within a range of 1.0E + 07 Ω-cm² to 3.2E + 08 Ω-cm² after 2 h exposures. The EIS response showed a polarization resistance (R _p) on the order of 6.6E + 04 Ω-cm², 5.3E + 04 Ω-cm², and 1.1E + 04 Ω-cm² for the oil-quenched, air-quenched, and VFC samples, respectively, after 2 h exposures. The EIS data are in good agreement with ECN data and indicate that after longer exposures, general corrosion mechanisms dominate and the corrosion rates are comparable. SEM examinations of specimens subjected to 1200 s exposures revealed that severity of pitting and intergranular corrosion damage was consistent with trends in the Rn data. Specifically, the electrochemical noise data as well as SEM examinations of specimens revealed a higher localized corrosion resistance of the hardened specimens during the early stages of passivation. This greater resistance to localized corrosion can be attributed to an increased stability of the natural passive film resulting from a higher concentration of chromium atoms in solution for the martensite phase.     

Surface modification of LiNi<Subscript>1/3</Subscript>Co<Subscript>1/3</Subscript>Mn<Subscript>1/3</Subscript>O<Subscript>2</Subscript> with Cr<Subscript>2</Subscript>O<Subscript>3</Subscript> for lithium ion batteries

Cr 2 O 3-coated LiNi 1/3 Co 1/3 Mn 1/3 O 2 cathode materials were synthesized by a novel method. The structure and electrochemical properties of prepared cathode materials were measured using X-ray diffraction (XRD), scanning electron microscopy (SEM), charge-discharge tests, cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS). The measured results indicate that surface coating with 1.0 wt% Cr 2 O 3 does not affect the LiNi 1/3 Co 1/3 Mn 1/3 O 2 crystal structure (α-NaFeO 2 ) of the cathode material compared to the pristine material, the surfaces of LiNi 1/3 Co 1/3 Mn 1/3 O 2 samples are covered with Cr 2 O 3 well, and the LiNi 1/3 Co 1/3 Mn 1/3 O 2 material coated with Cr 2 O 3 has better electrochemical performance under a high cutoff voltage of 4.5 V. Moreover, at room temperature, the initial discharging capacity of LiNi 1/3 Co 1/3 Mn 1/3 O 2 material coated with 1.0 wt.% Cr 2 O 3 at 0.5C reaches 169 mAh·g 1 and the capacity retention is 83.1% after 30 cycles, while that of the bare LiNi 1/3 Co 1/3 Mn 1/3 O 2 is only 160.8 mAh·g 1 and 72.5%. Finally, the coated samples are found to display the improved electrochemical performance, which is mainly attributed to the suppression of the charge-transfer resistance at the interface between the cathode and the electrolyte.     

Effects of calcining temperature on SnO<Subscript>2</Subscript> sensors for CO and NO<Subscript>x</Subscript> gases

Nitrogen oxides (NO_x) and carbon monoxide (CO) are among the most dangerous chemical species to human health present in the atmosphere. Acute CO toxicity leading to unconsciousness, respiratory failure or death can occur after 1 hr of exposure when ambient CO levels reach 1000 ppm, whilst increase of NO_x emissions can contribute to acid deposition, pollution of groundwater, eutrophication of surface waters, and tropospheric ozone and ecosystem damage. In this work, pure SnO₂ sensors for CO and NO_x were prepared by spin coating solutions derived from a washed Gel-precipitate followed by a calcining step. SnO₂ sensors of nanometer grain size prepared by this process showed good sensitivity to CO and NO_x gases. The increase of calcining temperature not only affected grain size and surface morphology, but also caused a decrease in sensitivity of the SnO₂ sensors.     

Obtaining ZrO<Subscript>2</Subscript> + CeO<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> + TiO<Subscript>2</Subscript>/Ti compositions by plasma-electrolytic oxidation of titanium and investigating their properties

Regularities of the effect produced by Ce₂(SO₄)₃ salt introduced in an aqueous electrolyte containing Zr(SO₄)₂ on the plasma-electrolytic formation of oxide coatings on titanium, their composition, and structure are studied. ZrO₂ + CeO _x + TiO₂ three-phase oxide coatings with a thickness about 10 μm are obtained. The coatings involve ZrO₂ cubic phase. The ZrO₂-to-TiO₂ phase ratio in the coatings can be controlled. The zirconium content in the coatings reaches 20 at %, while that of cerium is 3–5 at %. The surface layer (∼3-nm thick) contains Ce³⁺ (∼30%) and Ce⁴⁺ (∼70%). Pores in the surface part of coatings have diameters around or smaller than 1 μm and are regularly arranged. The obtained systems have a certain catalytic activity with respect to the oxidation of CO to CO₂ at temperatures above 400–450°C. The coatings are corrosion-resistant in chloride-containing environments. The thickness h of coatings depending on the charge Q supplied to the cell is described by the equation h = h ₀(Q/Q ₀) ⁿ , where n = 0.35 and h ₀ is the thickness of the coating formed at Q ₀ = 1 C/cm².     

Optical properties of Fe<Subscript>2</Subscript>NiAl and Fe<Subscript>2</Subscript>MnAl Heusler alloys

Results of the investigation of the optical properties and of the calculations of the electronic structure of Fe₂NiAl and Fe₂MnAl alloys are presented. The main attention is paid to the ellipsometric study of the spectral dependence of the real (ɛ₁) and imaginary (ɛ₂) parts of the dielectric constant in the range of wavelengths λ = 0.3–13 μm. An anomalous behavior of the optical conductivity σ(ω) at IR frequencies has been revealed in Fe₂MnAl, which differs substantially from that in Fe₂NiAl. The results obtained are discussed based on the calculations of the electronic structure of the alloys.     

Solvothermal synthesis and thermoelectric properties of skutterudite compound Fe（0.25）Ni（0.25）Co（0.5）Sb3

Nanostructured skutterudite-related compound Fe_0.25Ni_0.25Co_0.5Sb₃ was synthesized by a solvothermal method using FeCl₃, NiCl₂, CoCl₂, and SbCl₃ as the precursors and NaBH₄ as the reductant. The solvothermally synthesized powders consisted of fine granules with an average particle size of tens of nanometers. The bulk material was prepared by hot pressing the powders. Transport property measurements indicated a heavily doped semiconductor behavior with n-type conduction. The thermal conductivity is about 1.83 W·m⁻¹·K⁻¹ at room temperature and decreases to 1.57 W·m⁻¹·K⁻¹ at 673 K. The low thermal conductivity is attributed to small grain size and high porosity. A maximum dimensionless figure of merit of 0.15 is obtained at 673 K.