CuO Melt Research Articles

Low-Temperature Industrial Waste Heat (IWH) Recovery Using a New Design for Fast-Charging Thermal Energy Storage Units

The dynamic melting of CuO–coconut oil was addressed in a latent-heat thermal energy storage unit loaded with copper foam. In a new design, the thermal storage unit is made of a shell-tube-shaped chamber, in which a liquid flow of hot phase-change material (PCM) is allowed to enter the chamber from a port at the bottom and exit at the top. A fin is mounted in the chamber to forward the entrance PCM liquid toward the solid regions. The control equations were solved using the finite element method. The impact of foam porosity, inlet pressure, fin length, and the concentrations of CuO nanoparticles on the thermal charging time of the chamber was investigated. A fast-charging time of 15 min with a foam porosity of 0.95 was achieved. A porosity of 0.95 can provide a maximum thermal charging power of 15.1 kW/kg. The inlet pressure was a significant parameter, and increasing the inlet pressure from 0.5 kPa to 4 kPa reduced the melting time by 2.6 times. The presence of the fin is not advantageous, and even a long fin could extend the thermal charging time. Moreover, dispersed nanoparticles were not beneficial to dynamic melting and extended the thermal charging time.

Thermodynamic Modeling of Cooper Reduction from the B2O3–CaO–FeO–CuO Melt by Carbon Monoxide and Hydrogen

Thermodynamic Modeling of Cooper Reduction from the B2O3–CaO–FeO–CuO Melt by Carbon Monoxide and Hydrogen

Structure dependence of microwave dielectric properties in Zn2-xSiO4-x-xCuO ceramics

In this work, the Zn2-xSiO4-x-xCuO (x = 0, 0.04, 0.08, 0.12, 0.16 and 0.20) ceramics were synthesized through solid state reaction. The dependence of microwave dielectric properties on the structure was investigated through X-ray diffraction (XRD) with Rietveld refinements, Scanning electron microscope (SEM) and Raman spectra. The melting of CuO can reduce the densification temperature of Zn2-xSiO4-x ceramics. In comparison with x = 0, the x = 0.08 ceramics were densified at 1150℃ and the excellent microwave dielectric properties with low dielectric constant (εr = 6.01), high quality factor (Qf = 105 500 GHz) and τf = −28 ppm/°C, were obtained. The εr, Qf and τf value are dominated by covalency of Si-O bond and secondary phase, crystallinity and lattice energy, respectively. This provides a theoretical basis to further adjust the microwave dielectric property (especially τf value) from the structural point of view.

Size of metal drops formed on a bubble of reducing gas at oxide melt barbotage

To estimate the size of the drops formed on individual bubbles of the reducing gas during the oxide melt barbotage, a metal phase formation model was used. This model includes the following stages: formation of bubbles upon injection of gas into the melt; metal recovery on the bubbles surface and its concentration in the form of drops in stern. Equations are presented that make it possible to estimate the limiting sizes of a gas bubble (Rкрп) and drops (rкрк) moving in oxide melt without crushing. Using the densities (p, kg/m3) and surface tension (σ, mJ/m2) of B2O3 - CaO (1) and B2O3 - CaO - CuO (2) melts in the temperature range of 1373 - 1673 K, described by the equations σ1= 87,0 + 0,242T, p1 = 3,2610-3 - 0,91T, σ2= 10,8 + 0,178T, p2 = 3,1910-3 - 0, 70T, respectively , the critical dimensions of a gas bubble (Rкрп)moving in an oxide melt without crushing were calculated. In B2O3 - CaO - CuO melt, critical radius of the bubble varies from 0.047 to 0.053 m depending on temperature, and for the B2O3 - CaO system these values are 0.06 - 0.081 m. Using a technique with thermodynamic equilibrium calculations that allows to describe the features of oxide melt barbotage by various reducing gases, we determined the change of the copper oxides content in B2O3 - CaO - CuO melt depending on the amount of CO introduced at different temperatures. Based on the obtained data, the amount of copper formed during the interaction of Cu2O in the melt with a single CO bubble wascalculated depending on the content of copper oxide and the amount of CO in the bubble. The correlation dependences of the drop size on the content of Cu2O in the melt (CCu O, %), temperature (T, K) and the amount of CO in the bubble (nCO , mol) were obtained by statistical data processing methods.

Estimation of Metal Drop Size on a Reducing Gas Bubble during Oxide Melt Bubbling

In this paper, we use the metal-phase formation model to estimate the drop size formed on individual bubbles of the reducing gas during the oxide melt bubbling. The model includes the following stages: the bubble formation upon gas injection into the melt, metal reduction on the bubble surface, and its drop concentration in the stern. We present equations that estimate the limiting sizes of a gas bubble ( $$R_{{\text{b}}}^{{{\text{cr}}}}$$ ) and a drop ( $$r_{{\text{d}}}^{{{\text{cr}}}}$$ ) moving in an oxide melt without defragmentation. The critical sizes of a gas bubble ( $$R_{{\text{b}}}^{{{\text{cr}}}}$$ ) moving in an oxide melt without defragmentation were calculated using the densities (ρ kg/m3) and surface tension (σ, mJ/m2) of B2O3–CaO and B2O3–CaO–CuO melts that are, respectively, described by the equations: σ1 = 87.0 + 0.242T , ρ1 = 3.26 × 103 – 0.91T, σ2 = 10.8 + 0.178T, ρ2 = 3.19 × 103 – 0.70T in the temperature range of 1373–1673 K. Depending on the temperature, the critical bubble radius varies from 0.047 to 0.053 m in the B2O3–CaO–CuO melt and 0.06–0.081 m in the B2O3–CaO melt. Depending on the CO amount introduced at various temperatures, the change in the copper oxide content in the B2O3–CaO–CuO melt was determined by calculating the thermodynamic equilibrium to describe the features of oxide melt bubbling by various reducing gases. Based on the obtained data, the copper amount produced from the interaction of Cu2O in the melt with a single CO bubble was calculated depending on the copper oxide content and the CO amount in the bubble. The correlation dependences of the drop size on the Cu2O content in the melt ( $${{C}_{{{\text{C}}{{{\text{u}}}_{{\text{2}}}}{\text{O}}}}}$$ , %), temperature (T, К), and the CO amount in the bubble (nCO, mol) were obtained by statistical data processing.

Thermodynamic simulation of the oxidation of radioactive graphite in the Na2CO3–K2CO3–NiO and Na2CO3–K2CO3–CuO melts

The oxidation of radioactive graphite in the Na2CO3–K2CO3–NiO and Na2CO3–K2CO3–CuO melts in the temperature range 373–3273 K is subjected to a thermodynamic simulation. The behavior of radionuclides is studied and the equilibrium constants of the reactions occurring in these systems are calculated.

TEM Observations on 0.65Pb(Zr0.42Ti0.58)O3‐0.35Pb(Ni0.33Nb0.67)O3 Ceramics with CuO Additive

The microstructural properties and the chemical compositions of a 0.65Pb(Zr0.42Ti0.58)O3‐0.35Pb(Ni1/3Nb2/3)O3 (0.65PZT58‐0.35PNN) ceramic system sintered at 900°C for 4 h with 10 mol% CuO additives were studied using transmission electron microscope (TEM) and energy dispersive spectroscopy (EDS). CuO pockets were found as new microstructural constituents. The liquid phase has formed by the partial melting of CuO additives at the sintering temperature by reacting with Pb element in the matrix. The reaction started at the interfaces and then proceeded into the pocket through the diffusion of the Pb element. The presence of the Pb‐rich precipitates during cooling was confirmed by EDS analyses. Cu‐rich crystals in the pocket were observed near the boundaries between the matrix grain and the pocket. Rather smaller Pb‐Cu‐O‐contained particle segments were detected around the center of the pocket, demonstrating that the reaction of melting of CuO has occurred with the Pb element which was diffused from the matrix. Due to the existence of the liquid phase, a dense microstructure was achieved during the sintering process and abnormal grain growth occurred in the process.

Growth of YBCO single crystals by the self-flux technique

Preparation of high purity, highly perfect and homogeneous YBa2Cu3O6+ δ (YBCO) single crystals is a lengthy procedure that consists of five major steps. They are (a) fabrication of BaZrO3 ceramic crucibles, (b) self-flux growth of YBCO crystals using BaZrO3 crucibles, (c) setting of the oxygen content in the crystals, (d) removal of twins and homogenisation of oxygen content, and (e) formation of oxygen vacancy ordered superstructures by low temperature annealing. To obtain BaZrO3 ceramic impervious to the BaO–CuO melt, the volume of the grain boundary glass phase must be reduced to a very low level through the use of high purity starting materials and precise BaO:ZrO mole ratio control. The best quality YBCO crystals are obtained by slow cooling of YO1.5–BaO–CuO melt in the primary crystallisation region of YBCO. Oxygen content in heavily twinned orthorhombic YBCO is inhomogeneous due to the stress caused by twins. Therefore, homogenisation annealing must be carried out after removal of twin boundaries or, alternatively, under conditions where YBCO is tetragonal. In high purity YBCO, randomly distributed oxygen vacancies are the main source of charge carrier scattering. However, ordered superstructures of oxygen vacancies with significantly lower scattering rates can be generated by careful annealing at low temperatures.

Transmission Electron Microscopy Microstructure of (K0.5Na0.5)NbO3 Ceramics with CuO Addition

The microstructures in Na0.5K0.5NbO3 (NKN) ceramics sintered at 960 °C with CuO additives were investigated with transmission electron microscopy (TEM). As a new microstructural constituent, CuO pockets have been observed at the grain boundaries of NKN and also inside the NKN matrix. The melting of CuO is caused by the element Na from the matrix, which forms Na–Cu–O eutectoid compounds whose melting point is lower than the sintering temperature. The kinetics of melting reaction largely depends on the size of the pocket. The interaction starts at the interfaces between the pocket and the matrix and advances into the interior of the pocket. The smaller pocket would melt earlier during the sintering process, flow into triple junctions between matrix grains, and participate in sintering via liquid phase sintering. In the larger pockets, the melting starts at the interfaces. Thus the outer areas are melted, but the CuO particles in the center remained unmelted. The NKN matrix then grows further into the pocket through liquid phase sintering, leaving low-angle grain boundaries behind that interface with the remaining CuO particles. The unmelted CuO particles in the pocket remain as the second-phase particles.

Rapid synthesis of submicron crystalline barium zirconate BaZrO 3 by precipitation in aqueous basic solution below 100 °C

Pure crystalline BaZrO 3 powders can be produced by precipitation in highly basic aqueous solution. The influence of several synthesis parameters is studied. At high OH − concentration ([NaOH] = 20 mol/l), it is possible to obtain the well-crystallized stoichiometric perovskite phase at relatively low temperature (∼80 °C), after a short reaction time (15 min) and without requiring any precaution to avoid the presence of CO 2. This synthesis method yields spherical particles, whose size can be controlled by changing the concentration of the Ba + Zr solution. No calcination treatment is necessary since the precipitate is crystalline. Suitable choice of the synthesis parameters ([NaOH] = 20 mol/l, [Ba + Zr] = 1 mol/l, reaction time = 15 min) yields a sub-micron precipitate with excellent densification behaviour. Corrosion tests in BaO–CuO melt show that ∼98% dense BaZrO 3 obtained by sintering at 1650 °C for 13 h could be used for crucibles in the synthesis of YBa 2Cu 3O 7 superconducting single crystals.

Thermodynamic reassessment of the Cu-O phase diagram

Parts of the copper-oxygen equilibrium phase diagram were reassessed using the calculation of phase diagram technique (CALPHAD). The model parameters were optimized to yield the best fit between calculated and experimentally determined phase equilibria at elevated oxygen pressures up to 11 MPa. The Cu-O liquid phase is represented by the two-sublattice model for ionic liquids containing copper on the cation sublattice with formal valences of Cu+1, Cu+2, and Cu+3. The presence of Cu+3 ions in the liquid phase, corresponding to a formation of Cu2O3 species, was the key assumption of this model. Congruent melting of CuO at 1551 K under an oxygen pressure of ∼126.8 MPa is predicted, which is considerably below previous theoretical values.

Measurement of reduction kinetics in Nb 2O 5-doped SrTiO 3 by use of a new technique of liquid film migration

To investigate the reduction kinetics of Nb 2O 5-doped SrTiO 3, which has previously been difficult because of its low diffusivity, we have developed a new technique for the measurement of chemical diffusivity using the phenomenon of liquid film migration. 0.2 mol%-Nb 2O 5-doped SrTiO 3 powder compacts were sintered in air and then annealed at various temperatures and for various periods of time in 95N 2/5H 2. During the annealing the surface of individual grains was reduced and the thickness of the reduced layer varied with the annealing temperature and time. As a CuO melt was infiltrated into the annealed samples, liquid film migration occurred and eventually stopped when the reduced layer was swept. It was therefore possible to measure the thicknesses of the reduced layers under different annealing conditions. Based on the measured migration thicknesses, the chemical diffusion coefficient, D chem, during reduction of 0.2 mol%-Nb 2O 5-doped SrTiO 3 was determined to be D chem = 4.6 × 10 4 exp [ − ( 489 ± 118 kJ ) / R T ] (cm 2 s −1). Comparing the diffusion coefficient and activation energy with previous data showed that the reduction was governed by the diffusion of Sr ions. The present investigation demonstrates a new technique for the study of oxidation/reduction kinetics in systems where the lattice parameter varies with oxygen partial pressure.

Off-stoichiometric Melt Growth of LuBa2Cu3O6 + x Crystals

Superconducting LuBa2Cu3O6 + x crystals up to 5 × 5 × 0.2 mm in dimensions were grown by spontaneous crystallization during slow cooling of Lu2O3–BaO–CuO melts and were characterized by thermal analysis, x-ray diffraction, and electron probe x-ray microanalysis.

Crystal growth of SrCu 2O 3 under high pressure

In the Sr–Cu–O system, several high-pressure phases have been described in the literature. Single crystal growth is complicated by the strong reactivity of CuO with conventional crucible materials. This problem could be solved essentially by using a new compound crucible, consisting of a single crystalline MgO inset in a sealed platinum capsule. The markedly prolonged standing time of the improved crucible allows growth of single crystals from a SrO–CuO melt for the first time. After an assessment of the relevant part of the SrO–CuO phase diagram, single crystals of the spin ladder compound SrCu 2O 3 with dimensions up to 2 mm could be grown.

Growth and Electric Transport of Ca-doped PrBa2Cu3O7-δSingle Crystals

Crystal growth of Ca-doped PrBa 2 Cu 3 O 7-δ (Pr-123) single crystals by slow cooling of Pr 3 O 11 -CaCO 3 -BaCO 3 -CuO melts (self-flux technique) in ambient air atmosphere was studied. As the first approach the growth of Ca-free crystals in Al 2 O 3 and ZrO 2 crucibles was investigated. The best quality crystals with the average size of 5 x 5 x 0.2mm 3 were obtained from Al 2 O 3 crucibles for Ba/Cu = 0.41 and 15 wt.% (2.41 mol.%) of stoichiometric Pr-123 solute in the melt. Next, using CaCO 3 as calcium source (0.09 -12.68 wt.%), the good quality Pr 1-x Ca x Ba 2 Cu 3 O 7-δ crystals with 0 ≤ x ≤ 0.26 were grown in the Al 2 O 3 crucibles from the solution with fixed value of Ba/Cu = 0.41. The oxygenated single crystals with size up to 5 x 8 x 0.2 mm 3 were used for electric transport investigations from four-probe resistivity measurements. The temperature dependence of resistivity of Ca-doped Pr-123 crystals is typical for systems with locallized states and, in principle, follows the Mott law for variable-range hopping (VRH).

Equilibrium phase relationships in the system Cu-O under high oxygen pressure

The equilibrium phase relationships near the liquidus line of the system Cu2O-CuO-O2 (a part of wider system Cu-O) were determined under pure oxygen pressure from 0.001 to 11 MPa by three experimental methods: differential thermal analysis (DTA), thermogravimetry (TG), and thermobarometry (TB). The coordinates of the eutectic point between solid Cu2O and CuO were found to be PO2=0.069±0.001 MPa and T=1364±1 K. It was proved experimentally that, at least at temperatures up to 1526 K and oxygen pressures up to 11 MPa, CuO melts incongruently with liberation of gaseous oxygen and with the temperature dependence of PO2 obeying an Arrheniustype equation. The conditions for congruent melting of CuO were analyzed using the model, and it was found that congruent melting of CuO should occur at ≈ 1620 K under oxygen pressure ∼1000 MPa.

Growth of high quality YBCO single crystals using BaZrO 3 crucibles

High density BaZrO 3 ceramic crucibles have been successfully fabricated and used to grow high quality YBa 2Cu 3O 7− x (YBCO) single crystals by the BaO–CuO self flux method. The ceramic crucibles are inert and insoluble in the Y 2O 3–BaO–CuO melt, have a long lifetime, and can be used repeatedly for crystal growth runs. The crystals grown using the crucibles have not only high chemical purity (99.99–99.995%), but also a high degree of crystalline perfection as characterized by an extremely sharp X-ray rocking curve (FWHM=0.007°), very weak magnetic flux pinning and a magnetic irreversibility line that lies about 20 K below the line for the best YSZ crucible grown crystals.

Liquid phase epitaxy for the production of YBa2Cu3O7-δ coated conductor

Abstract The liquid phase epitaxy (LPE), which is performed under ambient pressure with simple growth apparatus, allows us to fabricate high-Jc YBa 2 Cu 3 O 7- δ (YBCO) crystalline thick films at high growth rate. We propose that the LPE growth of YBCO films on single crystalline oxide fibers is another way to produce YBCO-coated conductors for power application. In the conventional case of using BaO–CuO melt as a solvent, by which the YBCO crystals grow at about 1000°C, YBCO coating on yttria-stabilized zirconia (YSZ) or SrTiO 3 (STO) single crystalline fibers has not been successfully achieved because of their reaction with the solvent. Recently we have discovered that BaF 2 added as a solution decreases the crystallization temperature of YBCO down to 900°C and suppress the reactivity with no degradation of superconductivity of the YBCO crystal. The YBCO-coated fibers are successfully prepared using this solution. The behavior of critical current under magnetic fields shows that these YBCO-coated fibers have the potential to be used under a high magnetic field at the temperature of liquid nitrogen.

Investigation of phase equilibria near the eutectic in the Nd 2O 3(CeO 2)CuO system

The phase diagram of the Nd 2O 3CuO binary system has been investigated. It has been found that in the Nd 2O 3CuO system at the temperature 1026 °C the solid-solid dissociation reaction CuO(s) → Cu 2O(s) + O 2(g), and the eutectic forms between the Nd 2CuO 4 and Cu 2O phases at 1035 °C. The temperature dependence of the solubility of the Nd 2CuO 4 phase in a CuO melt has been determined within 1035–1215 °C. The specified isobaric section of the ternary Nd 2O 3CuOCu 2O system in air has been constructed in coordinates of the initial Nd 2O 3 and CuO oxides.

Effects of Melt Chemistry and Platinum Doping in the Refinement of Y2Ba1Cu1OyParticles for the System Y-Ba-Cu-O

Effects of melt chemistry and platinum doping in the refinement of Y2Ba1Cu1Oy(211) particles were investigated for the system Y-Ba-Cu-O. The shapes of the 211 particles in the present study changed from needlelike in a (CuO + BaCuO) melt to nearly spherical in a CuO melt. Platinum plays a small role in the growth inhibition of 211 particles. Barium atoms clearly had no effect on the role of Pt in refining 211 particles, and Pt was found to affect the refinement as an elementary atom rather than as part of a Pt-related compound. The main role of Pt in the refinement process for the system Y-Ba-Cu-O seems to lie in changing the interfacial energy of the 211 particles.