Molten Phase Research Articles

Advances in Robotic Tapping and Plugging of Non-Ferrous Smelting Furnaces: The MIRS Robotic Tapping Machine.

The operation of a metallurgical furnace requires the safe opening and closing of the furnace taphole. In this operation, the molten phase in the furnace is allowed to flow through the tap-hole for transfer to a ladle or another vessel before the tap-hole needs to be safely closed. Until now, non-ferrous tapping operations have largely been performed by an operator. Safe operations around the tap-hole require good process control of the smelting furnace, the proper tap-hole design for the required duty, and high-quality, robust tapping equipment. This paper briefly describes a new robotic tapping and plugging machine for the slag tapping operation on a large copper flash smelting furnace. The operating features and performance aspects are also summarized. Studies that indicate the applicability of this technology in operations other than slag tapping at a flash furnace are described.

Elucidation of subtle degradation mechanisms in composite CO2 separation membranes

Composite membranes for CO2 separation based on CGO (Gd-doped ceria) and the eutectic mixture of Na and Li carbonates, with distinct salt content (around 20 and 40 vol%) and microstructures (starting oxide grain size in the 170–220 nm range), were prepared and tested up to 250 h, at 650 °C, under distinct atmospheres (CO2 gradient or fully immersed in CO2 or Ar), to elucidate degradation mechanisms. Substantial oxide grain growth (50–65%) was observed during endurance tests of membranes with higher and lower oxide content, respectively. These relative changes were unable to explain the observed stability, higher for membranes with lower salt content. Combined microstructural, structural and electrochemical analyses of samples revealed that the solubility of metal oxides in the molten phase plays a crucial role. While ceria is poorly soluble, Gd oxide dissolves easily under acidic conditions (high CO2, membrane feed side) but precipitates under low CO2 (sweep side). Grain growth with formation of regions with distinct Gd content (core-shell CGO grains) explain the degradation of the oxide scaffold. This information provides important guidelines on membrane design, pointing towards oxide scaffolds with large and well percolated grains, also moderate acidity of the molten phase, to improve membrane stability.

Preparing high-strength and low-density proppants with oil-based drilling cuttings pyrolysis residues and red mud: Process optimization and sintering mechanism

This study aimed to assess the feasibility of manufacturing high-strength and low-density proppants from oil-based drilling cuttings pyrolysis residues (ODPR) and red mud (RM). The effects of ODPR and RM content on the performance of the proppants were studied, respectively. The optimum sintering condition was determined by response surface methodology (RSM), and the sintering mechanism was explored based on microstructural analysis of the proppants. The results showed that high-strength and low-density proppants with the breakage ratio of 8.6 % under 52 MPa closed pressure, bulk density of 1.45 g·cm−3, and apparent density of 2.96 g·cm−3 were obtained under the optimum preparation conditions (mass ratio of ODPR: RM: bauxite: MnO2 of 20: 8: 76: 4, sintering temperature of 1342 °C, sintering time of 1.0 h, sintering rate of 4.9 °C·min−1). The performance of the product proppants could meet the requirements of the Chinese Petroleum and Gas Industry Standard “Measurement of properties of proppants used in hydraulic fracturing and gravel-packing operations” (SY/T 5108-2014). ODPR and RM in the raw materials provided the chemical components of Al2O3, SiO2, CaO, BaO, Na2O, and K2O, which were involved in the formation of crystalline phases and molten phases during the sintering process. The performance of high-strength was primarily provided by the framework structure containing the crystalline phases and the dense structure caused by the molten phases. In addition, the Fe2O3 of RM would promote the generation of closed pores and then enhance the lightweight performance of proppants; however, excessive RM incorporation would lead to the formation of connected pores, which had a negative effect on the breakage ratio of proppants. This study not only creates a new pathway for recycling ODPR and RM within the shale gas industry but also provides a novel approach for manufacturing high-strength and low-density proppants.

A comparative study on gunpowder erosion and promoted ignition combustion of 30SiMn2MoV gun barrel

Various failure mechanisms of gun barrel based on thermal or thermochemical coupling have been proposed, but the understanding of microstructure evolution in the erosion process is still restricted. In this paper, the microstructure of a 30SiMn2MoV gun barrel after gunpowder erosion was investigated and compared with that after promoted ignition combustion test. In the failed barrel, erosion pits and micro-cracks were observed at the beginning of rifling. TEM and EDS analysis showed that erosion pits and micro-cracks were both composed of sulfides, oxides, and molten phases. Molten oxide zone with amorphous structure was observed in the erosion pits and similar molten microstructure was also observed along the grain boundaries of oxide in the propagating eroded cracks. Erosion pits consisting of oxides and eutectic microstructure were observed on the surface of 30SiMn2MoV steel after combustion. By comparing of microstructure, thermodynamic and kinetic characteristics, a barrel erosion mechanism based on the view of micro-combustion was proposed.

Novel molten phase route for composite CO2 separation membranes

Alkali metal nitrates were successfully used as starting chemicals in the production of composite CO2 separation membranes. The easy conversion of nitrates into carbonates after high temperature annealing in CO2 is confirmed using techniques like FTIR (Fourier transform infrared) or selective NO3− electrodes. This conversion shows a step like increase at temperatures in the order of 600 °C, consistent with target utilization temperatures for these membranes. A second but equally relevant consequence of this novel route is the formation of significant concentrations of oxide ions in the molten phase, able to boost the membrane performance, where the ceramic phase modest oxide ion conductivity is rate determining. At 650 °C, a CO2 separation flux enhancement in the order of 60% was reached using nitrates as starting chemicals. A deep analysis of the oxide ion content in molten phases using a variety of analytical techniques, confirmed the specific features of the nitrates as starting chemicals but also showed that even when carbonates are used as precursors, the role of oxide ions in the molten phase can increase significantly the membrane performance.

Effects of calcium, sodium and potassium on ash fusion temperatures of solid recovered fuels (SRF)

Various types of solid recovered fuels (SRFs) were investigated, then the waste was chemically leached and co-fired with coal and sewage sludge. Ashes with different properties and oxide compositions were used to explain the influence of various ash components (mainly sodium, potassium and calcium) on the Ash Fusion Temperatures (AFTs). Oxide compositions and empirical indices were determined and the effect of these data on the measured AFTs was investigated. An attempt to explain the effects of specific oxides on SRF melting temperatures using FactSage thermodynamic equilibrium software is presented. Thermodynamic equilibrium calculations are also used to predict the onset temperature of the molten phase, the percentage of molten phase at different combustion temperatures, and the possible solid phases that may exist at different temperatures. The mechanism of transformation of the inorganic substance of SRF turned out to be more complex than that of the mineral substance of coal, which resulted from the variable composition of the SRF. The character of temperature changes of the studied wastes after leaching in water and acetic acid in most cases is similar to the courses determined experimentally. For all investigated ashes from obtained the leaching of SRF wastes, the melting temperature decreases with the applied leaching. Potassium and sodium are the key elements causig the formation of low-melting silicates. Depending on the type of waste and leaching agent the lower the value of the B/A and α indices and the CaO content in ash, the lower the shrinkage temperature of the ash.

Understanding the mechanism of two-step, pyrolysis-alkali chemical activation of fibrous biomass for the production of activated carbon fibre matting

Pyrolysis of fibrous biomass followed by alkali (KOH and K2CO3) chemical activation of the pyrolysis char for the production of activated carbon fibre matting material has been investigated. For KOH, activation initially involved the melting of the KOH and reaction with the disorganised/volatile material of the char, producing hydrogen gas and K2CO3 and further developing the existing pore structure of the char. At higher temperatures (>700 °C), pore widening occurs due to physical activation with less reaction of the alkali molten phase with the char. Metallic potassium or other potassium species may also contribute to the pore widening process. Chemical activation with K2CO3 occurs at higher temperatures (>600 °C) and is controlled by the decomposition of K2CO3 to K2O and CO2. The development of surface area and porosity occurs through reaction of the pyrolysis char with K2O and CO2. The production of CO2, enhances the physical activation of the pyrolysis char, leading to widening of pores. KOH activation results in the development of micropores at low temperatures, followed by pore widening at higher temperatures. For K2CO3 activation, pore creation and pore widening occur simultaneously at higher temperature, resulting in a lower micropore volume and a wider pore size distribution.

Dynamic Characteristics of Phase Change Material in a Square Cavity under Various Heating Modes

Phase change material (PCM) is particularly advantageous in developing low-carbon buildings. However, its melting efficiency is severely determined by the dynamics of the molten phase, which is greatly associated with the applied heating orientation. This work aims to describe the dynamic character in the melting process of paraffin under different heating modes. A total of four heating modes are considered for the paraffin enclosed in a square cavity, including side heating, top heating, bottom heating, and around heating. The around heating can be regarded as the combination of the first three heating modes along a single wall. A comparative study of numerical and experimental results of temperature is firstly performed for the side heating case to verify the computational model, which is then extended to study the dynamic state during the melting process of paraffin. The evolutions of the solid/liquid interface and the internal flow field show that the bottom heating can maximally activate the involvement of natural convection of the liquid paraffin and thus has the highest efficiency than the side and top heating. The contribution rate of the bottom heating is about 1.55 times over that of the top heating. This observation is useful to identify the contribution of each heating mode to the heat transfer in the paraffin and guide its practical application.

RETRACTED:Thermal management of a battery pack using a layer of phase change material around the batteries: Changes in the airflow through the battery

In this paper, a battery pack with 27 lithium-ion cylinder batteries is simulated in two dimensions. This consists of 3 rows of 9 batteries. All batteries are made of phase change material, which is placed in a circular chamber. There is airflow at the Reynolds number ranging from 100 to 400. Temperature, airflow, the volume percent of molten phase change material, the highest and average temperatures of the battery pack, ambient air temperature, and volume fraction are all measured from 0 to 3000 s in this research. COMSOL Multiphysics 5.4 software is used for numerical analysis. The results demonstrate that the ambient air temperature at Reynolds number = 100 does not control the temperature of the battery and its temperature has an increasing trend. Also, the temperature of the output air from the battery pack is reduced with the Reynolds number. At 3000 s, the molten phase change material at Reynolds number = 400 is 30.74% lower than that at Reynolds number = 100. At all values of Reynolds number, enhancing the time reduces the amount of molten phase change material.

Multi-parameter heat transfer analysis of molten PCM in an inclined enclosure

• The natural convective heat transfer characters of molten phase change material (mPCM) in an inclined enclosure with forced convection boundary condition on one side and constant heat flux on another side is numerical studied, which is rare in previous literatures. • Heat transfer characters of two side walls and the whole enclosure are investigated separately. • Effects of Reynolds number, Rayleigh number aspect ratio and tilt angles on natural convection inside the enclosure are analyzed, and their influence on heat transfer are compared by quantifying. • A series of dimensionless parameters are conducted to quantitatively evaluate the heat transfer performance of mPCM. The efficiency of the photovoltaic (PV) panel would drop significantly as the absorbed solar radiation converts into heat. To improve the performance of PV, a novel cooling system with phase change material (PCM) and air forced convection cooling is developed, the flow and heat transfer of molten PCM (mPCM) under flow boundary is focused and investigated through numerical method. Three Rayleigh numbers for heat flux boundary (10 4 , 10 5 , and 10 6 ), five Reynolds numbers for forced convection boundary (1 × 10 4 , 1.5 × 10 4 , 2 × 10 4 , 3 × 10 4 and 4 × 10 4 ), three aspect ratios (5, 8, and 10) and tilt angles (30°, 45°, and 60°) for design parameters are considered. A group of dimensionless numbers is performed to describe heat transfer characteristics. It is concluded that different boundary conditions would cause different flow and heat transfer characteristics in the enclosure. Especially for the forced convection boundary, increasing Reynolds number can improve the heat transfer efficiency and reduce the temperature at the same time. Further, the influence of each factor on heat transfer is quantified, as the Rayleigh number increases by two orders of magnitude, Reynolds number increases by 33.33%, aspect ratio enlarged by double variation and tile angle varied by 50%, the heat transfer efficiency changes by 36.53%, 10.76%, 28.45% and 20.34%, respectively.

Phase Change Nanoelectromechanical Relay for Nonvolatile Low Leakage Switching

AbstractThe design, modeling, and experimental validation of a highly scalable phase change electromechanical relay are present. The Phase Change NEMS Relay (PCNR) is a nonvolatile mechanical relay actuated by the volumetric expansion of phase change material. GeTe is used as the active phase change material, and nonvolatile relay states are changed by converting it between amorphous and crystalline phases, which differ in volume by 10%. Phase conversion is induced by Joule heating an adjacent metal layer. Finite element analysis (FEA) models are developed to predict actuator temperature distributions and quench times for varied actuation pulses. Additional models are developed to simulate actuator deflection including reflow of molten phase change material during an actuation pulse. The smallest fabricated device has a heater footprint of 3 µm × 1 µm, with a 20 nm air‐gap. The FEA model, which calculates the actuation voltage, energy, and ON–OFF current ratio for this device to be 1.1 V, 42 nJ, and 108, respectively, are experimentally verified. A PCNR scaled down to a 15 nm × 5 nm heater footprint with a 2 nm air‐gap is predicted to actuate at 400 mV and 1.7 pJ.

Multi-Layers Composite Plasma Coatings Based on Oxide Ceramics and M-Croll

The paper considers the influence of the parameters of the plasma spraying process on the technological characteristics of multilayer coatings based on nickel-chromium, nickel-chromium-aluminum-yttrium materials, oxide ceramics, intended for operation at high temperature and additional dynamic loads. The design of plasma coatings during their application (with subsequent high-energy processing) under such conditions requires a comprehensive solution – both the use of high-quality powder ingredients and the optimization of technological parameters. The plasma process of applying powder materials has been improved to obtain the maximum values of their utilization factors. The technological characteristics that affect the properties of plasma coatings are optimized, namely: the flow rates of the plasma-forming and materials-transporting gases, the flow rate of supplied powder materials, the current and voltage of the electric arc of the plasma torch, the distance from the plasma torch nozzle exit to the substrate. The paper presents the results of studies of the structure of coatings, performed using scanning electron microscopy. Their analysis has made it possible to form general regularities obtained by the action of radiation of compression plasma flows on coatings formed by air plasma. The considered structures are created using the processes of melting, compaction and high-speed cooling of plasma coatings. The main optimization indicators are the maximum local compaction and spillage of the obtained compositions with the absence of defects and destruction from the impact of compression plasma flows. The main effect during the action of radiation of a compression plasma flow on previously formed coatings is thermal. It contributes heating of the near-surface layer. When the coating is exposed to radiation of compression plasma flows, a remelted layer of oxides with a thickness of about 12–15 µm is created, smoothing the relief of the formed surface and creating a network of cracks on the surface, diverging into the depth of the coating. The liquid-phase processes occurring in the molten phase of the near-surface layers after exposure to compression plasma radiation change the structure of the layers and contribute to the modification of their mechanical properties. By smoothing the surface, increasing the density of the surface crystallized layer and minimizing macro-defects – pores or macrocracks – the mechanical characteristics of the coatings increase.

RETRACTED:Lithium-ion batteries investigation regarding different fins distribution associated electrochemical effects and various voltage types

The passive heat control system of a battery connected to a solar system using materials with phase change materials is investigated. The effect of fins with peak and valley configurations on cylindrical lithium-ion batteries is assessed. In this study, the temperature distribution on the battery is determined by solving the thermal equations of the battery and using the previous references. Then, the fins and their configurations on the battery are determined by using the temperature distribution. These configurations are in the form of maximum length on the center and maximum length on the sides of the battery. The effect of the distance of the fins in different configurations is investigated. For this purpose, the solution is done using the finite element method. The simulation results show that the maximum amount of battery temperature occurs in its middle. The use of shorter fins enhances this and also reduces the volume fraction of molten phase change materials for a long time. Using this cooling method, the blade along with the phase change materials improves the performance of the charging process in a solar system.

Effect of sodium carbonate addition on carbothermic reduction of ilmenite concentrate

The enhanced reduction mechanism and kinetics of different Na2CO3 additions in the carbothermic reduction of ilmenite concentrate were investigated. The reduction process was carried out at different heating rates in a thermogravimetry facility, and the kinetics was studied using the Starink method. The results indicate that Na2CO3 addition enhanced the reduction effect as well as reduced the initial temperature of the reaction and the activation energy by increasing reactant activity in reactant form; however, it deteriorated the late-stage kinetic conditions by generating a molten phase, thereby reducing the reaction rate in the late stages of reduction. The average apparent activation energies of ilmenite concentrate with 0%, 3%, and 6% Na2CO3 are 447, 289, and 430 kJ/mol, respectively. The results from kinetics parameters confirm that Na2CO3 addition accelerated the reduction kinetics; however, excessive addition worsened the reduction kinetics.

A novel latent heat storage unit by introducing jet breakup of phase change material

To enhance the heat transfer performance in discharging process, the jet breakup of molten phase change material was introduced into a real scale heat storage unit by numerical method. In order to fully understand its performance, this paper conducted a numerical simulation on discharging process under different temperatures and flow rates of heat transfer fluid. The results showed that the heat transfer performance of this novel unit is superior to the conventional type due to the counterflow and the large heat transfer surface area. When increasing the mass flow rate of heat transfer fluid from 1.29 kg/s to 2.58 kg/s, the preheating time was shortened by 14.9%. When reducing the heat transfer fluid temperature from 38 °C to 18 °C, the preheating time was increased by 10.5%. However, the counterflow could also make small size droplets outflow the unit.

An experimental and numerical study on the leakage of molten phase change material through a micropore under gravity

This work presents an experimental and numerical study on the leakage of phase change materials through a micropore under gravity during the melting process. The effects of the pore size, wettability and physical properties of phase change materials on the packaging performance of composite phase change materials are discussed in details. The leakage process is divided into four stages, including breaking through the pore, wetting, necking and rupture. Dimensional analysis shows that the leakage process is mainly governed by the dimensionless Bond number (Bo) and Ohnesorge number (Oh). The results demonstrate that increasing the pore size significantly enhances the potential of leakage because of the increase of Bo. With a fixed Bo, the leakage can be efficiently suppressed by increasing Oh, which gives rise to a larger viscous resistance. Furthermore, it is discovered that reducing the contact angle could also prevent the leakage, as the larger surface tension is provided.

Effects of coexisting oxoanions on SO<sub>3</sub> decomposition activity of molten-phase potassium metavanadate catalysts

Molten-state potassium metavanadate (KVO3) supported on mesoporous SiO2 materials have emerged as active catalysts for SO3 decomposition over a moderate temperature range (≤650 °C), which is a potential O2 evolution reaction useful for solar thermochemical water splitting. The molten phase formed at ≥520 °C contained tetrahedral VO42−, which plays a vital role in accelerating the SO3 uptake and conversion to SO2/O2. The present study aimed to reveal how the SO3 decomposition activity is affected by adding other oxoanions such as borate (BO33−), carbonate (CO32−), and phosphate (PO43−) into the melt. Although borate showed a deteriorating effect, phosphate tended to improve the catalytic activity when the P/V molar ratio was equal to or less than 0.5. The addition of phosphate produced a mixed phosphate vanadate with a composition of KV2PO8, which consists of infinite tetrahedral PO4 and pyramidal VO5 linked by vertex sharing. Because of the congruent melting at temperature as low as ∼530 °C, KV2PO8 may be expected as another candidate of active molten phase catalyst for SO3 decomposition.

Pyrite as prospective absorber material for monograin layer solar cell

FeS2 monograin powders as absorber materials in monograin layer solar cells were grown in the molten phase of two different flux materials - in liquid sulphur (S) and in potassium iodide (KI) at different temperatures - at 500 °C, 550 °C, 600 °C in S and at 740 °C in KI. The cooling temperature profiles were modified to preserve the pyrite phase of material until room temperature was reached. FeS2 microcrystals, synthesized in sulphur and recrystallized in molten KI as flux, had cubic structure of pyrite phase with stoichiometric composition, confirmed by X-ray diffraction, Raman, and energy dispersive X-ray analyses, respectively. The grown FeS2 crystals exhibited n-type conductivity determined by hot probe measurements. The powder crystals were fixed in monograin membranes for making heterostructures with p-type nickel oxide (NiO) buffer layer. Charge carrier concentrations 6.2 × 1016 and 2.5 × 1017 cm−3, were found from capacitance-voltage measurements using FeS2/NiO heterostructures and FeS2/Pt Schottky diodes, respectively.

Raman analysis of intermediate phases during melting and freezing in long-chain n-alkanes

Structural changes of the n-alkanes (n = 18, 20, 21, 22) have been investigated by Raman spectroscopy during the melting from solid phase to the intermediate transition phase to the molten phase. With increasing temperature docosane (C22) undergoes an orthorhombic-hexagonal (rotator, R) phase follow by an alpha (α) phase. In addition, the α phase as an intermediate transition between the solid and liquid phases is observed in heneicosane (C21). For eicosane (C20) and octadecane (C18) the transition from solid to liquid phase is almost instantaneous unlike docosane (C22) and heneicosane (C21) where the intermediate transitions are observed. During freezing from the liquid phase, the even n-alkanes show the rotator phase (R) a few degrees lower than melting and just before the crystalline solid phase. The intermediate phase transition temperature can be spectrally determined with the 1100–1350 cm−1 Raman region of the CH2 band.

The Role of Temperature on the Degree of End-Closing and Filling of Single-Walled Carbon Nanotubes.

Carbon nanotubes (CNTs), owing to their high surface area-to-volume ratio and hollow core, can be employed as hosts for adsorbed and/or encapsulated molecules. At high temperatures, the ends of CNTs close spontaneously, which is relevant for several applications, including catalysis, gas storage, and biomedical imaging and therapy. This study highlights the influence of the annealing temperature in the range between 400 and 1100 °C on the structure and morphology of single-walled CNTs. The nitrogen adsorption and density functional theory calculations indicate that the fraction of end-closed CNTs increases with temperature. Raman spectroscopy reveals that the thermal treatment does not alter the tubular structure. Insight is also provided into the efficacy of CNTs filling from the molten phase, depending on the annealing temperature. The CNTs are filled with europium (III) chloride and analyzed by using electron microscopy (scanning electron microscopy and high-resolution transmission electron microscopy) and energy-dispersive X-ray spectroscopy, confirming the presence of filling and closed ends. The filling yield increases with temperature, as determined by thermogravimetric analysis. The obtained results show that the apparent surface area of CNTs, fraction of closed ends, and amount of encapsulated payload can be tailored via annealing.