Structures at Glassy,Supercooled Liquid,and Liquid States in La-Based Bulk Metallic Glasses

Local atomic structures at glassy, supercooled liquid, and liquid states for La-based bulk metallic glasses (BMGs) have been investigated by in-situ high-temperature X-ray diffraction. It is found that the coordination number of about 15.1 ± 0.1 for the La₆₂Al₁₄Cu_11.7Ag_2.3Ni₅Co₅ alloy does not depend on temperature up to liquid temperature, while it decreases slightly with temperature for the La₆₂Al₁₄Cu₂₄ and La₆₂Al₁₄Cu₂₀Ag₄ alloys. The S(q) data recorded at the supercooled liquid region can be well described by the Debye theory. For the three alloys, the volume expansion coefficient and the slopes of radii variation for the first to third nearest neighboring coordination shells show differences at glassy-to-supercooled liquid transition, while no obvious changes were detected at supercooled liquid-to-liquid transition for them. The linear expansion coefficient value (β = 1.6 ± 0.1 × 10^–5 K^–1) below the glass transition temperature deduced from S(q) data is consistent with that detected by the dilatometer (β = 1.25 × 10^–5 K^–1) for the La₆₂Al₁₄Cu_11.7Ag_2.3Ni₅Co₅ BMG.     

Formation,Structure, and Crystallization Behavior of Cu-Based Bulk Glass-Forming Alloys

We studied Cu-Zr–based alloys having exceptionally high glass-forming ability (GFA) and investigated the influence of Ag and Al addition on their structure and crystallization behavior. Most of the bulk glassy alloys (BGAs) do not contain any crystals, while some samples studied by high-resolution transmission electron microscopy (HRTEM) were found to contain well-developed medium-range order zones and nanoparticles in a bulk form. The crystallization kinetics of Cu₅₅Zr₄₅, Cu₅₀Zr₅₀, Cu_55–x Zr₄₅Ag _x (x = 0, 10, 20), Cu₄₅Zr₄₅Al₅Ag₅, Cu₄₄Ag₁₅Zr₃₆Ti₅, and Cu₃₆Zr₄₈Al₈Ag₈ glassy alloys was analyzed. An influence of the cooling rate on the formation of glassy phase and thermal stability of the Cu-based glassy alloys on heating was also studied. The crystallization kinetics and phase composition of the ribbon-shape and bulk glassy samples of Cu₃₆Zr₄₈Al₈Ag₈ alloys were also analyzed. The results also indicate that the best glass-forming compositions are possibly located at slightly off-eutectic area, owing to the shift of the eutectic point due to the nonequilibrium processing conditions.     

Formation of complex compounds of univalent copper at the Cu<Superscript>0</Superscript>-Cu<Superscript>2+</Superscript> interphase boundary in chloride solutions

Kinetics and a mechanism of formation of compounds of univalent copper at the interphase boundary Cu⁰-Cu²⁺ in the solution containing excess chlorine anions are investigated by the spectrophotometry method. It is shown that the [CuCl₂]^? and [CuCl₃]^2? complex anions are formed during the contact of metal copper with the Cu²⁺ ions. The former ones are characterized by the appearance of the band in the region of 233 nm in the spectra of electron absorption, and the latters ones—in the region of 273 nm. The dependence of intensity of absorption bands on the contact time of the Cu²⁺ ions with copper is used to estimate the kinetic parameters of formation and oxidation of the [CuCl₂]^? and [CuCl₃]^2? ions. A thickness of the reaction layer, in which they are formed, is determined. The formation of the Cu(I) compounds during the contact interaction of copper with the Cu²⁺ ions is confirmed by the results of electrochemical investigations. The mechanism of cathode reduction of copper-containing compounds on a copper electrode is suggested.     

Leaching of chalcopyrite with ferric ion. Part III: Effect of redox potential on the silver-catalyzed process

This study examines the effect of redox potential on silver-catalyzed chalcopyrite leaching. Leaching tests were carried out in stirred Erlenmeyer flasks with 0.5 g chalcopyrite mineral, 1 g Ag/kg Cu and 100 mL of a sulphate solution of Fe³⁺/Fe²⁺ (with redox potential ranging between 300 and 600 mV Ag/AgCl) at pH 1.8, 180 rpm and 35°C or 68 °C. Unlike uncatalyzed leaching, an increase of the redox potential increased copper dissolution in the presence of silver ions, as the regeneration of Ag⁺ requires a high concentration of oxidizing agent, Fe³⁺. Additionally, the high reactivity of the mineral surface when silver was present could have been responsible for inhibiting the nucleation of hydrolysis products of Fe³⁺ on it. Excessive addition of silver transformed the chalcopyrite surface into copper-rich sulphides such as covellite, CuS, and geerite, Cu₈S₅, preventing the formation of CuFeS₂/Ag₂S galvanic couple and the recycling of silver ions.     

Study of the kinetics of silver ions cementation onto copper from sulphuric acid solution

The kinetics of silver cementation with copper from sulphuric acid solution has been studied with a rotating cylinder. Two independent methods have been used to monitor the concentration of Ag⁺ ions in the solution: atomic absorption spectrophotometry (AAS) method and a continuous method with the use of an ion-selective electrode. The reaction has been found to follow first-order kinetics with respect to silver ion concentration. The initial rate of the reaction is limited by diffusion through the mass transfer boundary layer. The rate constant for initial period of cementation is independent of the absence or the presence of oxygen in the solutions and is independent of the presence of Cu²⁺ ions up to the concentration of 2×10⁻⁴ M. After the initial period of cementation a rate enhancement has been observed. In solutions containing 20 mg/L of Ag⁺ ions, the rate enhancement is associated with changes in the structure of the deposit which involve an increase in the effective surface area during the process. However, the rate enhancement phenomenon in the absence of oxygen at 100 mg/L of Ag⁺ is attributed not only to an increase in the effective surface area but also to a chemical reaction between Cu⁺ and Ag⁺ ions.     

Thermal properties and interfacial reaction between the Sn-9Zn-<Emphasis Type="Italic">x</Emphasis>Ag lead-free solders and Cu substrate

The thermal properties and interfacial reaction between the Sn-9Zn-xAg lead-free solders and Cu substrate, such as solidus and liquidus temperatures, heat of fusion, intermetallic compounds, and adhesion strength, have been investigated. Two endothermic peaks appear in the DSC curve when the Ag content in the Sn-9Zn-xAg solder alloy is above 1.5 wt pct. The solidus temperatures of the Sn-9Zn-xAg solder alloys are around 197 °C, but the liquidus temperatures decrease from 225.3 °C to 221.7 °C and 223.6 °C with increasing the Ag content in the solder alloy from 1.5 to 2.5 and 3.5 wt pct, respectively. Three intermetallic compounds, namely, Cu₆Sn₅, Cu₅Zn₈, and Ag₃Sn are observed at the Sn-9Zn-xAg/Cu interface. The Cu₅Zn₈ is formed close to the Cu substrate, Ag₃Sn is adjacent to it, and Cu₆Sn₅ is nearest the Sn-9Zn-1.5Ag solder alloys. A bi-structural Cu₆Sn₅ layer with hexagonal η-Cu₆Sn₅ and monoclinic η′-Cu₆Sn₅ is found at the Sn-9Zn-1.5Ag/Cu interface due to Ag dissolution. A maximum adhesion strength of 10.7±0.8 MPa is obtained at the Sn-9Zn-2.5Ag/Cu interface as soldered at 250 °C for 30 seconds.     

Calculation of the acid-base equilibrium constants at the alumina/electrolyte interface from the ph dependence of the adsorption of singly charged ions (Na<Superscript>+</Superscript>, Cl<Superscript>−</Superscript>)

A procedure was proposed for the calculation of the acid-base equilibrium constants at an alumina/electrolyte interface from experimental data on the adsorption of singly charged ions (Na⁺, Cl⁻) at various pH values. The calculated constants (pK ₁⁰= 4.1, pK ₂⁰= 11.9, pK ₃⁰= 8.3, and pK ₄⁰= 7.7) are shown to agree with the values obtained from an experimental pH dependence of the electrokinetic potential and the results of potentiometric titration of Al₂O₃ suspensions.     

Er~(3+)-Yb~(3+)-Na~+:ZnWO_4 phosphors for enhanced visible upconversion and temperature sensing applications

The crystal structure and surface morphology of the Er³⁺/Yb³⁺/Na+:ZnWO₄ phosphors synthesized by solid state reaction method were analyzed by X-ray diffraction(XRD) and field emission scanning electron microscopy(FESEM) analysis.The frequency upconversion(UC) emission study in the developed phosphors was investigated by using 980 nm laser diode excitation.The effect of codoping in the Er³⁺:ZnWO₄ phosphors on the UC emission intensity was studied.The UC emission bands that are exhibited in the blue(490 nm),green(530,552 nm),red(668 nm) and NIR(800 nm) region correspond to the ⁴F_7/2→⁴I_15/2.²H_11/2,⁴S_3/2→⁴I_15/2,⁴F_9/2→⁴I_15/2 and ⁴I9/2→⁴I_15/2 transitions,respectively.The temperature sensing performance of the Er³⁺-Yb³⁺-Na+:ZnWO₄ phosphors was investigated based on the 2 H_11/2→⁴I_15/2 and ⁴S_3/2→⁴I_15/2 thermally coupled transitions of the Er³⁺ions.The photometric study was also carried out for the developed phosphors.     

Thermodynamics of MnO-SiO<Subscript>2</Subscript>-Al<Subscript>2</Subscript>O<Subscript>3</Subscript>-MnS Liquid Oxysulfide: Experimental and Thermodynamic Modeling

The activities of MnO and MnS in a MnO-SiO₂-Al₂O₃(or AlO_1.5)-MnS liquid oxysulfide solution were investigated by employing the gas/liquid/Pt-Mn alloy chemical equilibration technique under a controlled atmosphere at 1773 K (1500 °C). Also, the sulfide capacity, defined as C _S = (wt pct S)(pO₂/pS₂)^1/2, in MnO-SiO₂-Al₂O₃ slag with a dilute MnS concentration was obtained from the measured experimental data. As X _SiO2/(X _MnO + X _SiO2) in liquid oxysulfide increases, the activity coefficient of MnO decreases, while that of MnS first increases and then decreases. As X(AlO_1.5) in liquid oxysulfide increases, the activity coefficient of MnS increases, while no remarkable change is observed for the activity coefficient of MnO. The behavior of the activity coefficient of MnS was qualitatively analyzed by considering MnO + A _x S _y (SiS₂ or Al₂S₃) = MnS + A _x O _y (SiO₂ or Al₂O₃) reciprocal exchange reactions in the oxysulfide solution. The behavior was shown to be consistent with phase diagram data, namely, the MnS saturation boundary. Quantitative analysis of the activity coefficient of the oxysulfide solution was also carried out by employing the modified quasichemical model in the quadruplet approximation.     

Improving luminescence and thermometric performance of Ba2CaWO6:Er3+ by tri-doping with Yb3+ and Na+

The Er³⁺doped double perovskite Ba₂ CaWO₆ crystal is a promising ratiometric thermometer based on the fluorescence intensity ratio(FIR) of transitions from ² H_11/2 and ⁴ S_3/2to the lowered ⁴ I_15/2 level.However,the Ca²⁺vacancy defect caused by the charge difference between rare-earth ions and the substituted alkaline-earth ions gives rise to the non-radiative probability and limits the t...     

The redox equilibria of copper ions in the molten silicate fluxes as a measure of basicity

The redox equilibria of copper ions in the molten NaO_0.5-SiO₂, NaO_0.5-NaF-SiO₂, NaO_0.5-CaO-SiO₂, CaO-CaF₂-SiO₂, CaO-MgO-SiO₂, and CaO-SiO₂ systems have been measured in order to seek a new measure of flux basicity. The Cu²⁺/Cu⁺ ratio decreases with increasing the content of basic oxide. The correlations between the Cu²⁺/Cu⁺ ratio and other refining indexes, such as carbonate, sulfide, and phosphate capacities, CaO activity, and theoretical optical basicity are discussed.     

Crystal-field levels of Nd3+ in a new langasite compound Nd3CrGe3Be2O14

We report on the crystal-field (CF) levels of Nd³⁺ in Nd₃CrGe₃Be₂O₁₄, a representative of recently synthesized Be-containing langasites. They are the first in the family to contain two magnetic subsystems, 1D chromium and Kagome-like rare-earth ones. High-resolution broad-band temperature-dependent spectra allow us to find all five CF Kramers doublets of the ground ⁴I_9/2 CF multiplet and 38 levels of the excited ⁴I_{11/2, 13/2, 15/2}, ⁴F_3/2, ⁴F_5/2 + ²H_9/2, ⁴F_7/2 + ⁴S_3/2 and ⁴F_9/2 CF multiplets. These data form a basis for a future exploration of this interesting two-sublattice magnet with frustrated interactions. Optical transitions between Kramers doublets of Nd³⁺ indicate magnetic activity of 1D-chromium chains at T < 20 K.     

Temperature Dependence of Diffuse Scattering in PZN

Structural disorder seems to relate to the useful physical properties of ferroelectrics and relaxors. One such material is PZN, PbZn_1/3Nb_2/3O₃.\hbox{PbZn}_{1/3}\hbox{Nb}_{2/3}\hbox{O}_{3}. To explore what aspects of the disorder are specific to the polarized state, the temperature dependence of diffuse scattering in PZN has been investigated. The data were collected using both neutron and X-ray single crystal experiments in a range of temperatures from 50 K to 500 K (−223 °C to 227 °C). It has been found that some features, like the diffuse scattering from the B-site ordering, remain unchanged with change of temperature in terms of both intensity and peak shape. However, other diffuse scattering features evolve with T, for example the size effect scattering around the Bragg peaks. The size-effect becomes less pronounced with increasing temperature, with the diffuse scattering becoming more symmetric around the Bragg peaks. The diffuse rods caused by the planar domains change only slightly with temperature. This finding indicates that the planar domains persist into the paraelectric state but that the correlation between lead displacement and the average separation of adjacent lead atoms becomes weaker, suggesting that this size effect may be crucial to the ferroelectric properties.     

Effect of Li+ ion concentration on upconversion emission and temperature sensing behavior of La2O3:Er3+ phosphors

The effects of Li~+ co-doping concentration on the structure, upconversion luminescence and temperature sensing behavior of Er~(3+):La_2O_3 phosphors were investigated. X-ray diffraction and scanning electron microscopy observations reveal that Li~+ ion co-doping can change the lattice parameter of La_2O_3 host and increase the particle size of the samples. The optical investigation shows that co-doping of Li~+ ions can enhance the upconversion emission of Er~(3+) ions in La_2O_3 matrix effectively. Most importantly, the temperature sensing sensitivity of the samples is found to be dependent on Li~+ co-doping concentration,when the emission intensity ratio of the(~2H_(11/2)→~4 I_(15/2)) and(~4 S_(3/2)→~4 I_(15/2)) transitions of Er~(3+) is chosen as the thermometric index. Both of the optimum upconversion luminescence and temperature sensing sensitivity are obtained for 7 mol% Li~+ co-doped sample. When the Li~+ concentration is beyond 7 mol%,both the quenching in upconversion intensity and the degradation of temperature sensitivity are observed, which may be due to the serious distortion in local crystal field around Er~(3+) ions caused by the excess Li~+ ions.     

A thermodynamic study of digenite solid solution (Cu2-δS) at 600 to 1000°C and a statistical thermodynamic critique on general nonstoichiometry

A very accurate experimental method to determine the composition of metal-saturated sulfides has been developed and applied to Cu_2-δS. The technique consists of using a high-sensitivity thermobalance which operates in a controlled atmosphere of H₂-H₂S gas. By this method it was shown that Cu-saturated Cu_xS is stoichiometric(x= 2.0000 ± 0.0002) between 700 and 1000°C. The free energy of formation for Cu₂S was found to be: 2Cu(s) + 1/2 S₂(g) = Cu_2.0000S(s), ΔG⁰ = -30,610 + 6.80T (cal/mole). The sulfur partial pressure was determined over nonstoichiometric Cu_2-δS for sulfur contents up to 21 pct. From the result, thermodynamic functions such as activity of copper, heats and entropies of solution were calculated as a function of nonstoichiometric composition. It was thermo-dynamically demonstrated that previous models dealing with nonstoichiometric oxides (or sulfides) based on the law of mass action,i.e., δ = const ie 67 01 (or ie 67 02), are inconsis-tent as they fail to satisfy the Gibbs-Duhem relation and also fail to account for the dis-sociation pressure over the stoichiometric composition. To resolve this dilemma, a sta-tistical thermodynamic method of constructing the grand partition function was introduced. Stoichiometry and nonstoichiometry of the Cu_2-δS were then explained by postulating an ionic crystal consisting of Cu⁺, Cu²⁺, Cu⁰ and neutral vacancies in the copper sublattice and S²⁻ and neutral vacancies in the sulfur sublattice. Formerly Postdoctorate Fellow, National Research Council of Canada, Ottawa, Ontario     

Synthesis and characterization of Ca0.9Mg0.1TiO3:Pr3+,Ag+ phosphor

Ca_(0.9)Mg_(0.1)TiO_3:Pr~(3+),Ag~+ phosphors were synthesized by solid-state reaction technique. The crystalline phase and luminescence performances of Ca_(0.9)Mg_(0.1)TiO_3:Pr~(3+),Ag~+ were observed by X-ray powder diffractometer(XRD), transmission electron microscope(TEM), photoluminescence spectrometer and brightness meter, respectively. The addition of Ag~+ can diminish in the crystal particle sizes of Ca_(0.9)Mg_(0.1)TiO_3:Pr~(3+). Because Ag+ can reduce the concentration of the undesirable defects in the phosphor, luminescence intensity of Ca_(0.9)Mg_(0.1)TiO_3:Pr~(3+),Ag~+ is 2.3 times as high as that of Ca_(0.9)Mg_(0.1)TiO_3:Pr~(3+)at the same preparation condition. The effect of Ag+ on the persistent afterglow properties is to deepen the energy storage traps and enhance the energy transfer efficiency from Ca_(0.9)Mg_(0.1)TiO_3 to Pr~(3+). The persistent afterglow properties of Ca_(0.9)Mg_(0.1)TiO_3:Pr~(3+),Ag~+ are better than those of Ca_(0.9)Mg_(0.1)TiO_3:Pr~(3+) at the same preparation condition. In conclusion,Ca_(0.9)Mg_(0.1)TiO_3:Pr~(3+),Ag~+ phosphor with molar ratio of Ag~+to Pr~(3+) 3:1 obtained at 900 ℃ for 4 h exhibits the optimal photoluminescence performances.     

The oxidation of thiosulfates with copper sulfate. Application to an industrial fixing bath

This paper presents the transformation of thiosulfate using Cu(II) salts, such as copper sulfate, at pH between 4 and 5. The nature and kinetics of this process were determined. In the experimental conditions employed, the reaction between thiosulfates and Cu(II) ions produces a precipitate of CuS and the remaining sulfur is oxidized to sulfate, according to the following stoichiometry: 1 mol thiosulfate reacts with 1 mol Cu²⁺ and 3 mol H₂O, generating 1 mol copper(II), 1 mol sulfate and 2 mol H₃O⁺. In the kinetic study, the apparent reaction order was ≈ 0 with respect to H₃O⁺ concentration, in the interval 1.0 · 10^? 4–1.0 · 10^? 5M H₃O⁺; of order 0.4 with respect to Cu²⁺ in the interval 0.21–0.85 g L^? 1 Cu²⁺; and of order 0 with respect to S₂O₃^2? in the interval 0.88–2 g L^?1 S₂O₃^2?. The apparent activation energy was 98 kJ mol^? 1 in the interval 15–40 °C. On the basis of this behavior an empirical mathematical model was established, that fits well with the experimental results. The thiosulfate transformation process using copper(II) sulfate was applied to an industrial fixing bath that proceeded from the photographic industry; after this, the resulting effluent contained less than 10 mg L^? 1 of thiosulfates.