Main Phase Changes Research Articles

Research for the recovery of Zn and Pb from electric arc furnace dust through vacuum carbothermal reduction

Isothermal kinetic methods were used to investigate reduction process in the Zn and Pb during the vacuum carbothermal reduction of electric arc furnace dust (EAFD). During the experiments, the volatilization ratios of Zn and Pb in EAFD increased with the increase of temperature and holding time, which was 96.29 % and 83.91 % for Zn and Pb respectively at a temperature of 1000 °C and holding time of 60 min. The main phase changes of Zn and Pb in the reduction process were ZnFe2O4 → ZnO → Zn and PbSO4 → PbO → Pb, and the generated Zn and Pb gases escaped and were collected via condensation. In the kinetic study, the volatilization of Zn was controlled by three-dimensional diffusion (Jander) with an apparent activation energy of 19.97 kJ/mol, whereas the volatilization of Pb was controlled by the interfacial chemical reaction with an apparent activation energy of 85.68 kJ/mol. The results show that higher purity of valuable metals Zn and Pb could be obtained, laying a theoretical foundation for the treatment of EAFD pollution.

Numerical simulation of nucleate pool boiling under high pressure using an initial micro-layer thickness model

Micro-layer evaporation is one of the main phase change mechanisms in nucleate pool boiling. However, the influence of pressure on micro-layer evaporation remains unclarified. The objective of this study is to establish an approach to calculate micro-layer evaporation at high pressure. Here, an analytical solution of the governing equations is applied to derive a semi-empirical correlation for the initial micro-layer thickness δ0. After the calibration with measurement under atmospheric pressure, δ0 becomes a function of fluid properties. A nucleation sites tracking method is then implanted in the micro-layer evaporation system for multi-bubble cases. In this study, two single bubble growing cases are employed to validate our initial micro-layer thickness model at high pressure (1.91 MPa, 4.47 MPa). The simulated bubble radius profiles show similar trends with experimental data. Furthermore, the entire multi-bubble evaporation system is also validated against a pool boiling experiment at high pressure (0.51 MPa). The simulated wall superheat is consistent with reported data, with the minimum deviation of about 20%. The contribution of evaporation during nucleate boiling from both the macro and micro region is demonstrated at various operating conditions. Micro-layer supplies about 70% vapor in nucleate pool boiling at 0.51 MPa.

Effect of Al2O3–SiO2 Addition on Gehlenite Growth and the Mechanical Performance of Steel Slag

Steel slag, as industrial solid waste, is difficult to recycle owing to its complex components and poor mechanical properties. However, steel slag can be modified by adding Al2O3–SiO2 through high temperature sintering, which would improve the mechanical properties and expand the scope of its application. The phase changing, morphology evolution and the mechanical properties of the modified steel slag were investigated. The results indicate that the main phase changes to gehlenite occur with increasing temperature. The compressive strength increases to 115 MPa at 1350 °C. The relationship of the quantity of gehlenite and the compressive strength were explored.

Hemodynamic and adaptive correlates of transcranial magnetotherapy in patients with high-grade malignant brain gliomas in the early postsurgery period

The results of this study have demonstrated the possibility of improving the efficiency of restoring hemodynamics and an adaptive status in patients with high-grade brain tumors by using transcranial magnetic therapy (TMT). The convenience and expediency of using the diagnostic criteria of the cardiac analyzer software CARDIOCODE consisted in obtaining complex digital data sets related to the main phase changes in the cardiac performance, energy supply and metabolism, associated with the corrective effect produced by TMT in the early postsurgery period. At the same time, it is noted that acting in concert by the cardiac performance can be provided against the background of the formation of a stable type of an integral reaction of calm activation

Thermal Property Characterization of a Low Supercooling Degree Binary Mixed Molten Salt for Thermal Energy Storage System

In this paper, LiNO3–NaCl binary mixed molten salt with high phase change enthalpy was selected as phase change materials (PCM). LiNO3 was used as the main phase change material, and NaCl was used as the additional material to change the properties and reduce the supercooling degree of molten salts. LiNO3–NaCl binary mixed molten salts with different mass proportion were prepared by static melting method. The optimum eutectic ratio of the mixed molten salt was obtained through analysis of the experiment results. The influence of NaCl on phase change temperature, decomposition temperature, supercooling degree and phase change latent heat were tested and analyzed. The properties of the phase change materials were characterized by thermogravimetric analyzer and simultaneous differential scanning calorimeter (TGA/DSC), scanning electron microscopy (SEM) and X-ray diffraction (XRD). The phase transition temperature, latent heat and supercooling degree of the binary mixed molten salts showed nonlinear variation with the increase in NaCl mass fraction. When the mass ratio was 88:12 for LiNO3–NaCl, the phase change temperature was the lowest of 222.6 °C, the phase change latent heat was the highest of 389.3 J·g−1 and the supercooling degree was 1.2 °C. The optimum eutectic crystallization degree was achieved. At the same time, the decomposition temperature of the mixed molten salt was increased from 560 °C to 620 °C with the addition of NaCl, which greatly increased the applicable temperature range of LiNO3.

Ductility and Toughness Improvement of Injection-Molded Compostable Pieces of Polylactide by Melt Blending with Poly(ε-caprolactone) and Thermoplastic Starch.

The present study describes the preparation and characterization of binary and ternary blends based on polylactide (PLA) with poly(ε-caprolactone) (PCL) and thermoplastic starch (TPS) to develop fully compostable plastics with improved ductility and toughness. To this end, PLA was first melt-mixed in a co-rotating twin-screw extruder with up to 40 wt % of different PCL and TPS combinations and then shaped into pieces by injection molding. The mechanical, thermal, and thermomechanical properties of the resultant binary and ternary blend pieces were analyzed and related to their composition. Although the biopolymer blends were immiscible, the addition of both PCL and TPS remarkably increased the flexibility and impact strength of PLA while it slightly reduced its mechanical strength. The most balanced mechanical performance was achieved for the ternary blend pieces that combined high PCL contents with low amounts of TPS, suggesting a main phase change from PLA/TPS (comparatively rigid) to PLA/PCL (comparatively flexible). The PLA-based blends presented an “island-and-sea” morphology in which the TPS phase contributed to the fine dispersion of PCL as micro-sized spherical domains that acted as a rubber-like phase with the capacity to improve toughness. In addition, the here-prepared ternary blend pieces presented slightly higher thermal stability and lower thermomechanical stiffness than the neat PLA pieces. Finally, all biopolymer pieces fully disintegrated in a controlled compost soil after 28 days. Therefore, the inherently low ductility and toughness of PLA can be successfully improved by melt blending with PCL and TPS, resulting in compostable plastic materials with a great potential in, for instance, rigid packaging applications.

Effect of multi-element addition of Alnico alloying elements on structure and magnetic properties of SmCo 5 -based ribbons

Abstract New SmCo5 + x wt% Alnico composite ribbons melt-spun at 40 m/s are designed by multi-element addition of Alnico alloy into SmCo5 matrix, and their structure and magnetic properties are investigated. The results show that the main phase in x ≤ 2.5 ribbons is Sm(Co,M)5, whereas the main phase changes into Sm(Co,M)7 at x = 4.0–8.5, and simultaneously that the content of Al-rich and amorphous phases increases with increasing x. The hard magnetic properties of the ribbons are found to improve with an increase in Alnico content, and particularly the average magnetic properties reach maximum, i.e., Hc = 19.6 ± 1.2 kOe, Mr = 47.7 ± 3.4 emu/g and M2T = 59.1 ± 5.6 emu/g, at x = 4.0. The main reasons for such improvement are that the finer grains divided by three grain boundaries exist in main phase, the dispersed Al-Ni and Al-Co-rich phases distribute in grains and grain boundaries, and the Fe-rich Alnico alloying elements dissolve into Sm(Co,M)7 matrix phase. However, when x > 4.0, the gradually increasing Al-Co and amorphous phases lead to the reduction of hard magnetic properties.

Phase Change of Carbon Atoms in Surface Layer Under Nanocutting During Diamond Lapping Process

Lapping is still an efficient and economical way in diamond shaping process, which is important in both industrial and scientific applications. It has been known that the material removal originates from the phase change or amorphization of diamond crystal carbon atoms that are chemically activated by stress, forming a top layer of amorphous carbon atoms. In this paper, the phase change of amorphous carbon atoms undergoing the nanocutting of amorphous layer during diamond lapping process is studied by molecular dynamics (MD) simulation. Two regions, the debris layer and cutting surface underneath, are studied. In the debris layer, the change of sp2 carbon atoms is directly affected by impact, while underneath the cutting surface the changes of carbon atoms are almost not affected; the change speed of amorphous carbon atoms is higher than that of pristine crystal ones; the main phase change is transformation of sp3 into sp2; cutting depth to different extent affects the phase changes of sp3 and sp2 carbon atoms. Our study expands the understanding of diamond lapping process.

Simulation for a New Type of Photovoltaic (PV) Fresh Air and Domestic Hot Water System

A new type of photovoltaic (PV) fresh air and domestic hot water system is established to improve indoor air quality and to provide living hot water. And a phase change energy storage water tank heating system is established to optimize heating with non-continuous energy forms, such as solar energy. A 600mm * 485mm * 250mm phase change material is selected as the storage container, decanoic acid is as the main phase change material, and aluminium alloy box is as the package material. We establish a real scale model of the system and apply the FLUENT software to explore and optimize the design scheme employed in the heating system. Effective hot-melt method is used in dealing with the enthalpy of the phase change material. The system will be an effective way to solve the indoor air quality problem and to achieve the optimal allocation of energy.

Preparation of nitrogen-doped graphene/palmitic acid shape stabilized composite phase change material with remarkable thermal properties for thermal energy storage

Palmitic acid (PA) is one of the main phase change materials (PCMs) for medium temperature thermal energy storage systems. In order to stabilize the shape and enhance the thermal conductivity of PA, the effects of adding nitrogen-doped graphene (NDG) as a carbon nanofiller were examined experimentally. NDG was dispersed in liquid PA at various mass fractions (1–5wt%) using high power ultrasonication. The dropping point test shows that there was clearly no liquid leakage through the phase change process at the operating temperature range of the composite PCMs. The thermal stability and thermal properties of composite PCM were investigated with a thermogravimetric analyzer (TGA) and differential scanning calorimeter (DSC), respectively. The thermal conductivity of the PA/NDG composite was determined by the laser flash method. The thermal conductivity at 35°C increased by more than 500% for the highest loading of NDG (5wt%). The electrical conductivity of composite PCMs was increased significantly by using NDG. The thermal cycling test proved that the PA/NDG composites PCMs had good thermal reliability and chemical durability after 1000 cycles of melting and freezing. The thermal effusivity of the PA/NDG composite PCMs was larger than that of pure PA, which is advantageous for latent heat thermal energy storage (LHTES).

Effect of carbon nanospheres on shape stabilization and thermal behavior of phase change materials for thermal energy storage

Stearic acid (SA) is one of the main phase change materials (PCMs) for medium temperature thermal energy storage systems. In order to stabilize the shape and enhance the thermal conductivity of SA, the effects of adding carbon nanospheres (CNSs) as a carbon nanofiller were examined experimentally. The maximum mass fraction of SA retained in CNSs was found as 80wt% without the leakage of SA in a melted state, even when it was heated over the melting point of SA. The dropping point test shows that there was clearly no liquid leakage through the phase change process at the operating temperature range of the composite PCMs. The thermal stability and thermal properties of composite PCMs were investigated with a thermogravimetric analyzer (TGA) and differential scanning calorimeter (DSC), respectively. The thermal conductivity of the SA/CNS composite was determined by the laser flash method. The thermal conductivity at 35°C increased about 105% for the highest loading of CNS (50wt%). The thermal cycling test proved that form-stable composite PCMs had good thermal reliability and chemical durability after 1000 cycles of melting and freezing, which is advantageous for latent heat thermal energy storage (LHTES).

Preparation, phase transformation and microstructure of ZrxTi1−xO2 (x=0.1–0.9) fine fibers

Zr x Ti 1− x O 2 ( x = 0.1–0.9) fibers were prepared by the sol–gel dry-spinning method. Polyacetylacetonatozirconium (PAZ) and tetrabutyl titanate (C 16 H 36 O 4 Ti) were used as raw materials. The green fibers were obtained from the amorphous spinnable solution and then heat-treated to convert into polycrystalline fibers. The main phase changes from TiO 2 to zirconium titanate (ZT) and then tetragonal ZrO 2 with increasing ZrO 2 content. The crystallization temperature varied with the molar ratio of Zr:Ti. The heat-treated fibers at 1050 °C have few pores and no cracks with diameters of 10–20μm and lengths of 1–5 cm.

Modeling storm-time electrodynamics of the low-latitude ionosphere–thermosphere system: Can long lasting disturbance electric fields be accounted for?

Storm-time ionospheric disturbance electric fields are studied for two large geomagnetic storms, March 31, 2001 and April 17–18, 2002, by comparing low-latitude observations of ionospheric plasma drifts with results from numerical simulations based on a combination of first-principles models. The simulation machinery combines the Rice convection model (RCM), used to calculate inner magnetospheric electric fields, and the coupled thermosphere ionosphere plasmasphere electrodynamics (CTIPe) model, driven, in part, by RCM-computed electric fields. Comparison of model results with measured or estimated low-latitude vertical drift velocities (zonal electric fields) shows that the coupled model is capable of reproducing measurements under a variety of conditions. In particular, our model results suggest, from theoretical grounds, a possibility of long-lasting penetration of magnetospheric electric fields to low latitudes during prolonged periods of enhanced convection associated with southward-directed interplanetary magnetic field, although the model probably overestimates the magnitude and duration of such penetration during extremely disturbed conditions. During periods of moderate disturbance, we found surprisingly good overall agreement between model predictions and data, with penetration electric fields accounting for early main phase changes and oscillations in low-latitude vertical drift, while the disturbance dynamo mechanism becomes increasingly important later in the modeled events. Discrepancies between the model results and the observations indicate some of the difficulties in validating these combined numerical models, and the limitations of the available experimental data.

Effect of nitrogen content on structure and magnetic properties of Nd 16Fe 84− xB xN y alloys prepared by mechanical alloying

The structure and magnetic properties of Nd 16Fe 84− x B x N y alloys prepared by mechanical alloying using pyrolytic boron nitride (p-BN) as starting material have been investigated. By increasing the content of boron and nitrogen, the magnetic main phase changes from Nd 2Fe 17 to Nd 2Fe 14BN δ , and finally transforms into the paramagnetic Nd 1.1Fe 4B 4 phase. The nitrogen and boron contents determine the component of phases and magnetic properties. The enhancement of the Curie temperature of the Nd 2Fe 14BN δ phase originates from the increase of the interstitial nitrogen content in the Nd 2Fe 14B lattice.

On the convective instability of real models of the upper mantle and shear flows beneath the continental lithosphere

The convective instability of realistic upper mantle models is investigated by a new method, taking into account the dependence of viscosity, thermal diffusivity and the coefficient of the thermal expansion on depth. Two main phase changes in the upper mantle, at depths of about 420 and 630 km, are also considered. It is found that the dependence of viscosity on depth and the presence of phase changes strongly affect the stability of the models considered. However, the dependence of the physical parameters on depth does not explain the considerable increase in the horizontal scale of convective cells. A thermomechanical model of the continental upper mantle beneath the crust, moving with a constant velocity, is also constructed, in which a complex profile of the effective viscosity is presented. The stability of the thermomechanical model is investigated. The picture of instability is very complicated because the mechanisms of thermal and convective instabilities are combined. The regions of stability and instability in the model are given in the plane ( Ra c, q) of the critical Rayleigh number Ra c against the wavenumber q. The increments of the convective instabilities have been calculated, and it is shown that the horizontal scale of convection is governed by the thickness of the asthenosphere.

Aging in Au-Ni alloys

Measurements have been made of changes in some physical properties of quenched alloys of 70% Au-30% Ni when they were annealed at low temperatures. Changes in the electrical resistance, volume, and Young's modulus were observed to occur. They indicate that there is at least one metastable precipitate formed on low temperature annealing; it occurs about 10 4 times earlier than the main phase change which has been well studied previously. There is a critical temperature above which this low temperature phase is unstable; this is about 225°C. Exact description of the low temperature phase is not possible, but it does seem to be either (1) clusters of Au-rich or Ni-rich atoms or (2) regions of high geometrical order. Quenched-in vacancies are presumed to control the rate of the reaction but the precipitate is not thought to be simply clusters of vacancies.