Powder Heat Research Articles

Phase Transitions in SiO2 Nanopowder Synthesized by Electric Arc Plasma

This article deals with the synthesis of the SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> nanopowder in the original plasma system including a water-cooled reactor, arc plasma jet, and feed unit. The operating principle of this electro-plasma system is based on gas evaporation and condensation of the molten material. A continuous material feeding into the plasma jet provides the high yield of the target product due to a complete evaporation of the condensed phase. This article presents the experimental results of the SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> nanoparticle synthesis from high-silica natural material and the investigation of the particle phase composition after the conventional thermal treatment. It is found that the average particle size is about 100 nm at a maximum 25-kW power of the plasma jet; amorphized bonds in the synthesized high-dispersive powder provide the formation of polydisperse clusters of particles. The powder heating up to 1173 K results in crystallization and grouping of the SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> nanoclusters. The high-dispersive SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> powder allows stabilizing the phase transition to a modification of SiO <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$_{2}\alpha $ </tex-math></inline-formula> -tridymite that is not observed in the initial natural quartz.

Effect of nanostructure on phase transformations during heat treatment of 2024 aluminum alloy

In this work, we studied the transformations involving the coherent (θ”/S”), semicoherent (θ’/S’), and incoherent (θ/S) precipitates (θ = Al 2 Cu, S = Al 2 CuMg) formed during the heat treatment of an annealed nanostructured powder of Al 2024 produced by cryogenic milling. These precipitates form over a wide temperature range (300–500 °C) depending on the chemical composition. They influence grain growth during sintering and may facilitate the formation of a fully dense nanostructured material. Mechanical milling was performed for 20 h at a cryogenic temperature to obtain nanostructured particles. The structural evolution and morphology of the particles during the heat treatment were investigated for three particle size ranges (<25, 25–45, and 45–90 μm). Heat treatment of the milled powder was performed at three different temperatures (475, 500, and 525 °C) for 5, 10, 15, and 20 min. Morphological analysis of the as-milled particles using scanning electron microscopy indicated that the milling process was not completed. X-ray diffraction analysis yielded the θ and S volume fractions for the heat-treated and as-milled powders. DSC analysis indicated the precipitation and dissolution of GP (Guinier-Preston zone), coherent, and incoherent precipitates during heating of the as-atomized and milled powders. Accumulation of the deformation energy during milling is suggested to lead to an early transformation of the S and θ phases in the finer powder.

Behaviour of Microwave-Heated Al4SiC4 at 2.45 GHz.

The ongoing development of high-temperature processes with the use of microwaves requires new microwave absorbers that are useful at these temperatures. In this study, we propose Al4SiC4 powders as important and efficient microwave absorbers. We investigated both the behavioural microwave heating and electrical permittivity characteristics of Al4SiC4 powders with various particle sizes at 2.45 GHz. The TE103 single-mode cavity indicated that Al4SiC4 powder samples yielded different heating behaviours and dielectric constants for each particle size compared with SiC. By microwave heating ∅50 mm × 5 mm disks of Al4SiC4 and SiC, we demonstrate that for specific sizes, Al4SiC4 can be heated at a higher temperature than SiC. Finally, the results of the two-dimensional two-colour thermometer show that an energy concentration appears at the interface of the microwave-heated Al4SiC4. These phenomena, which are inconsistent in individual physical property values, can be explained without contradicting microwave heating physics.

Multi-scale simulation approach for identifying optimal parameters for fabrication ofhigh-density Inconel 718 parts using selective laser melting

PurposeDepending on an experimental approach to find optimal parameters for producing fully dense (relative density > 99%) Inconel 718 (IN718) components in the selective laser melting (SLM) process is expensive and offers no guarantee of success. Accordingly, this study aims to propose a multi-scale simulation framework to guide the choice of processing parameters in a more pragmatic manner.Design/methodology/approachIn the proposed approach, a powder layer, ray tracing and heat transfer simulation models are used to calculate the melt pool dimensions and evaporation volume corresponding to a small number of laser power and scanning speed conditions within the input design space. A layer-heating model is then used to determine the inter-layer idle time required to maximize the temperature convergence rate of the solidified layer beneath the power bed. The simulation results are used to train surrogate models to construct SLM process maps for 3,600 pairs of the laser power and scanning speed within the input design space given three different values of the underlying solidified layer temperature (i.e., 353 K, 673 K and 873 K). The ideal selection of laser power and scanning speed of each process map is chosen based on four quality-related criteria listed as follows: without the appearance of key-hole melting; an evaporation volume less than the volume of the d90 powder particles; ensuring the stability of single scan tracks; and avoiding a weak contact between the melt pool and substrate. Finally, the optimal laser power and scanning speed parameters for the SLM process are determined by superimposing the optimal regions of the individual process maps.FindingsThe feasibility of the proposed approach is demonstrated by fabricating IN718 test specimens using the optimal processing conditions identified by the simulation framework. It is shown that the maximum density of the fabricated parts is 99.94%, while the average density is 99.88% and the standard deviation is less than 0.05%.Originality/valueThe present study proposed a multi-scale simulation model which can efficiently predict the optimal processing conditions for producing fully dense components in the SLM process. If the geometry of the three-dimensional printed part is changed or the machine and powder material is altered, users can use the proposed method for predicting the processing conditions that can produce the high-density part.

Correlation between microstructures and tensile deformation behavior of a PM near α Ti–6Al–2Sn–4Zr–2Mo−0.1Si alloy

A powder metallurgy (PM) near α Ti–6Al–2Sn–4Zr–2Mo−0.1Si (wt.%) alloy was fabricated by in-situ dehydrogenation and hot extrusion of a TiH2-based powder compact and heat treatments. Three types of microstructures were obtained in the as-consolidated state and after different heat treatments. They are a basketweave microstructure consisting of a network of inter-penetrating α plates filled with domains of ultrafine β transformed structure (βt) (Type I microstructure), an α/β lamellar microstructure with most β layers being thin and discontinuous plus α layers at prior β grain boundaries (Type II microstructure) and an α/βt lamellar microstructure (Type III microstructure). Although the three types of microstructures render the alloy with a similar yield strength (1085–1109 MPa) and ultimate tensile strength (1217–1239 MPa) due to the balanced effects of various strengthening mechanisms, the Type II microstructure exhibits a significantly lower tensile ductility than the other two types of microstructures (elongation to fracture: 5.5% vs. 13–14%). Examination of dislocations in the tensile deformed specimens reveals that dislocations cutting through the thin β layers in the Type II microstructure during deformation. Such interactions between moving dislocations and thin β layers in the Type II microstructure are expected to be the primary reason for the clearly lower strain hardening rate, premature fracture of grain boundary α layers and low tolerance to strain localization observed in the tensile tests, fracture surface examination and DIC analysis. This correlation between the microstructures and tensile deformation behavior strongly suggests that preventing moving dislocations cutting through thin β layers by turning them into thicker and ultrafine structure strengthened βt lamellae or blocks is critically important in ensuring high tensile ductility of high strength PM near α titanium alloys.

Fabrication of bioinspired edible liquid marble with phase transition and tunable water barrier property.

Based on aphid wax–honeydew marble and the hydrophobic wax structure of lotus and its derived applications with superareophilic and superhydrophobic properties, edible carnauba wax and beeswax particles were mixed and utilized to mimic lotus wax and wrap liquid, thus forming liquid marbles (LMs). Through the utilization of continuous production system (CPS), wax as an interfacial surfactant, water and solid, air-phase or mixed-phase marble content was produced. The edible liquid marble (ELM) could encapsulate water and food droplets. Edible solid marble (ESM) and edible solid hollow marbles (ESHMs) could be fabricated by applying pectin or syrup. Moreover, through the heating of wax powders with different melting temperatures, stable tablets and hollow capsules could be produced. The wax powder as interfacial surfactant could firmly bind with pectin through hydrogen bonds on ESM. The edible LMs can therefore be applied for residue reduction, corrosion reduction, biohazard prevention and cleaning in the food industry. The other phase LMs could act as novel tools in the pharmaceutical and food industries with the above-mentioned water transport, preservation, sustained releasing and selective releasing abilities. Graphic abstract Supplementary InformationThe online version contains supplementary material available at 10.1007/s42242-021-00158-z.

The potential use of green mussel (Perna Viridis) shells for synthetic calcium carbonate polymorphs in biomaterials

Green mussel shells contain a high content of calcium that can be potentially used for starting biomaterials. A powder processing and subsequent calcination-dissolution-precipitation (CDP) technique for recycling the shells into the value-added of precipitated calcium carbonates (PCC) is presented in this paper. In the experimental study, the received green mussel shells were initially washed and ground and followed by heat treatment at different temperatures in an electric furnace. PCC product was precipitated from the blended solution of calcium and carbonate ions derived from the heat-treated ground powder. The precipitating solids were then investigated via XRD, SEM-EDX, and FTIR methods. The XRD Rietveld method confirmed that the raw green mussels were rich in crystalline aragonite, which could be recycled into vaterite and calcite in the PCC product. The current study demonstrated that the green mussel shells are technically possible for the starting materials in biomedical applications.

Case study of spontaneous heating of metal powder – Calorimetric solution

Two samples of mixed metal powders taken from one workplace of surface metallisation were studied with respect to self-heating risk. Irrespective of the similar chemical composition, one of the powders proved significantly increased reactivity in aerial oxygen resulting in self-heating occurrence in situ. As the main reason for the distinct behaviour of the samples, a difference in particle size distribution was found. From a technical point of view, the different grain size of the powders arose from the nonsymmetric branching of the suction piping.

Phase evolution and sinterability of lanthanum phosphate – Towards a below 600 °C Spark Plasma Sintering

Lanthanum phosphate, due to its interesting thermal and mechanical properties is a widely studied material for refractory applications. Sintering processes have already been proposed to densify this material and drive its microstructure. Inspired by recent progress on low temperature sintering, we investigate a low temperature Spark Plasma Sintering (LowT-SPS) using hydrated precursor. First, lanthanum phosphate thermal behaviour was studied using TGA/DTA and XRD analysis on various heat-treated powders. Their SPS behaviour were explored by in situ dilatometry measurements. As hydrated precursor showed a low temperature densification, samples were sintered at temperatures from 160 °C to 350 °C under 400 MPa. Even if dense and nano-scaled microstructures were obtained, a residual hydration was observed. Finally, a well densified and fine-grained monazite type lanthanum phosphate was obtained at 550 °C and under 200 MPa. Its mechanical properties are then compared to conventional and Spark Plasma Sintered materials.

Heating of milk powders at low water activity to 95°C for 15 minutes using hot air-assisted radio frequency processing achieved pasteurization

Salmonella persistence in milk powders has caused several multistate foodborne disease outbreaks. Therefore, ways to deliver effective thermal treatment need to be identified and validated to ensure the microbial safety of milk powders. In this study, a process of hot air-assisted radio frequency (HARF) followed by holding at high temperatures in a convective oven was developed for pasteurization of milk powders. Heating times were compared between HARF and a convection oven for heating milk powders to a pasteurization temperature, and HARF has been shown to considerably reduce the come-up time. Whole milk powder (WMP) and nonfat dry milk (NFDM) were inoculated with a 5-serotype Salmonella cocktail and equilibrated to a water activity of 0.10 to simulate the worst case for the microbial challenge study. After heating the sample to 95°C using HARF, followed by 10 and 15 min of holding in the oven, more than 5 log reduction of Salmonella was achieved in WMP and NFDM. This study validated a HARF-assisted thermal process for pasteurization of milk powder based on previously collected microbial inactivation kinetics data and provides valuable insights to process developers to ensure microbial safety of milk powder. This HARF process may be implemented in the dairy industry to enhance the microbial safety of milk powders.

Cluster-glass behavior in the two-dimensional triangular lattice Ising-spin compound Li2Mn3O7

We present the detailed structural and magnetic properties of ${\mathrm{Li}}_{2}{\mathrm{Mn}}_{3}{\mathrm{O}}_{7}$ from powder x-ray diffraction (XRD), dc susceptibility, heat capacity, ac susceptibility, thermoremanent magnetization, magnetic memory, and exchange bias effect. Rietveld refinement of XRD data reveals that this compound has a rhombhohedral structure composed of a layered triangular lattice. Onset of spin-glass transition was confirmed by dc magnetization and ac susceptibility measurements. Dynamic scaling laws were used to analyze and classify the glassy behavior of the compound. Magnetic field dependence of irreversible temperature follows the Almeida-Thouless line, which is characteristic for an Ising spin-glass system. Fitting of the frequency-dependent freezing temperature with a power law results in $z{\ensuremath{\nu}}^{\ensuremath{'}}=4.06\ifmmode\pm\else\textpm\fi{}0.06$, which indicates the critical exponent of the sluggish spin dynamics and ${\ensuremath{\tau}}_{0}=4.2\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}8}$ s is a characteristic time scale for a single spin-flip. Further evidence of cluster-glass behavior comes from the frequency dependence of the freezing temperature fitted with the Vogel-Fulcher law, which considers interaction between bigger magnetic entities. Values of fitting parameters are ${E}_{a}/{k}_{B}=27.62$ K and ${T}_{0}=9.57$ K, which confirm cluster-glass behavior. The presence of magnetic relaxation below freezing temperature and the magnetic memory effect confirms the nonequilibrium dynamics of the system through a number of metastable states. Moreover, observation of the exchange bias effect reflects the presence of intrinsic phase inhomogeneity. These results indicate that the triangular lattice causes a disordered ground state as a result of competing exchange interactions.

Effect of Powder Heat Treatment on Chemical Composition and Thermoelectric Properties of Bismuth Antimony Telluride Alloys Fabricated by Combining Water Atomization and Spark Plasma Sintering.

In this work, Bi0.5Sb1.5Te3 materials were produced by an economically viable and time efficient water atomization process. The powder samples were heat treated at different temperatures (673 K, 723 K, 743 K, 773 K, 803 K, and 823 K) followed by spark plasma sintering (SPS). It was found that the Te evaporated slightly at 723 K and 743 K and became dominated at 773 K, 803 K, and 823 K, which severely influences the thermoelectric properties. The electrical conductivity was significantly improved for over 803 K heat treated samples due to the remarkable improvement in hole concentration. The power factor values for the 803 K and 823 K samples were significantly larger at T > 350 K compared to other samples. Consequently, the peak ZT of 0.92 at 350 K was obtained for the 803 K sample, which could be useful in commercial thermoelectric power generation.

Enhancing Graphene Retention and Electrical Conductivity of Plasma-Sprayed Alumina/Graphene Nanoplatelets Coating by Powder Heat Treatment

Burning loss of graphene in the high-temperature plasma-spraying process is a critical issue, significantly limiting the remarkable performance improvement in graphene reinforced ceramic coatings. Here, we reported an effective approach to enhance the graphene retention, and thus improve the performance of plasma-sprayed alumina/graphene nanoplatelets (Al2O3/GNPs) coatings by heat treatment of agglomerated Al2O3/GNPs powders. The effect of powder heat treatment on the microstructure, GNPs retention, and electrical conductivity of Al2O3/GNPs coatings were systematically investigated. The results indicated that, with the increase in the powder heat treatment temperature, the plasma-sprayed Al2O3/GNPs coatings exhibited decreased porosity and improved adhesive strength. Thermogravimetric analysis and Raman spectra results indicated that increased GNPs retention from 12.9% to 28.4%, and further to 37.4%, as well as decreased structural defects, were obtained for the AG, AG850, and AG1280 coatings, respectively, which were fabricated by using AG powders without heat treatment, powders heat-treated at 850 °C, and powders heat-treated at 1280 °C. Moreover, the electrical conductivities of AG, AG850, and AG1280 coatings exhibited 3 orders, 4 orders, and 7 orders of magnitude higher than that of Al2O3 coating, respectively. Powder heat treatment is considered to increase the melting degree of agglomerated alumina particles, eventually leaving less thermal energy for GNPs to burn; thus, a high retention amount and structural integrity of GNPs and significantly enhanced electrical conductivity were achieved for the plasma-sprayed Al2O3/GNPs coatings.

Effects of Ti particles and T6 heat treatment on the microstructure and mechanical properties of A356 alloy fabricated by compocasting

In this study, the effects of the addition of Ti powder and T6 heat treatment on the microstructure and the mechanical properties of A356-based composite containing 0.5, 1.5, and 5 wt% Ti fabricated by compocasting were studied. Stirring was carried out at a temperature of 610 °C with a stirring speed of 300 rpm for 10 min. The solution treatment was done at a temperature of 540 °C for 2 h. Then, age hardening was conducted at 170 °C for 7 h. The microstructures and mechanical properties of samples after T6 heat treatment were investigated. After the addition of titanium powder, a reaction layer created on the surface of the titanium powder by diffusion of Ti atoms across the Al melt/Ti interface. Increasing the weight percent of the Ti particles resulted in an increment of silicon nucleation and a decrement of the silicon size. Also, the porosity content increased with increasing the weight percent of Ti. The eutectic Si structure was transformed from a coarse needle-like structure to a short plate-like one by T6 heat treatment. Among all samples, the A356/0.5 wt% Ti composite after the T6 showed the highest ultimate tensile strength (UTS) (306.9 MPa). Compared to the A356 alloy, the hardness and tensile strength of the A356/0.5 wt% Ti composite improved more than 83% and 53%, respectively, due to the presence of Ti and Al3Ti phases. For the A356/Ti composites, the fracture surface was mainly covered by cleavage features.

Исследование тепловых свойств изотермических плит при спекании капиллярного сердечника

This paper mainly introduces the sintering process of the monolithic capillary wick and analyzes the influence of different copper powder particle size, filling rate, copper powder shape and heat source size on the heat transfer performance of the isothermal plate. The experimental results show that: (1) For the isothermal plate sintered with spherical copper powder, the capillary force of large particle size copper powder is small, but the flow resistance is also small, and the performance of the isothermal plate sintered with large particle size copper powder is better. (2) In the case of low filling rate, the isothermal plate is dried due to insufficient return fluid. In the case of high filling rate, on the one hand, the thickness of the liquid film at the evaporation end of the isothermal plate is large, resulting in additional thermal resistance. On the other hand, the thin film evaporation mode will be transformed into pool boiling mode, which will reduce the heat transfer performance. (3) Spherical copper powder sintered plate with regular shape has the best performance, while dendritic copper powder sintered plate has relatively high thermal resistance. (4) The heat source area has a great influence on the thermal resistance of the plate. Under the same heating power, the thermal resistance of the small area heat source is much higher than that of the large area heat source; The thermal resistance of sintered copper plate is lower than that of pure copper plate under two heat source areas.

First-time synthesis of an unparalleled Al72Cr15Ni13 decagonal quasicrystalline phase with the help of mechanical alloying and annealing procedures: A comparative study

An X-ray diffractometer, a field-emission scanning electron microscope, and a high-resolution transmission electron microscope were utilized to characterize the structural and microstructural evolutions of the AlCrNi alloy powders. The single-phase Cr (Al, Ni) nanostructured solid-solution was synthesized through the high-energy planetary ball milling in 96 h. It was turned out that the decagonal quasicrystal obtains after the annealing treatment at 1035 °C. The formation of the decagonal quasicrystalline phase in the AlCrNi alloy system was first investigated in the present article. A differential thermal analyzer was employed for the examination of the thermal performance of the AlCrNi alloy powders. The specific surface area of the mechanically alloyed and heat-treated AlCrNi alloy powders was determined through the BET analysis without any further alkali leaching. The specific surface area of the AlCrNi alloy powders containing the decagonal quasicrystalline phase possesses a high value of 1.75 m2g−1.

Temperature dependent crystal structure re‐determination and electronic properties of UI3

AbstractIn this work, we have re‐investigated the structural and physical properties of UI3 by means of temperature dependent powder neutron diffraction, heat capacity and magnetic measurements. We confirm that UI3 crystallizes in the PuBr3 structure type, space group Cmcm. We did not observe any temperature dependent structural phase transition in the temperature range from 10 to 300 K. We further report the first quantum chemical calculations of UI3 by density functional theory (DFT). The calculated structural and electronic properties demonstrate the pronounced two‐dimensional anisotropic effects present in UI3 due to its layered structure.

Features of Structural-Phase Transformations during Oxidation of Metals with Bulk Submicrocrystalline Structure and Fine Metal Powders

The oxidation processes for compact and powdery samples of titanium, copper, and molybdenum with different volume structure and dispersivity were studied using thermal analysis, electron microscopy, and X-ray diffraction. It is established that producing of metals with a modified structure under conditions of high-energy impact (severe plastic deformation, electric explosion of a thin wire) in accordance with intermediate annealing leads to an increase in the content of oxygen in the form of solid solutions and oxides; the oxide component’s share, form and localization within the material depend on physicochemical properties of both metal and oxide . It is shown that the structural-phase transformations of the oxide component during heating of fine-grained metals and powders have a significant effect on the parameters of the oxidation process of such materials. The thermally induced effects in the oxygen-containing components might play a critical role for the structure stability during long-term use of such materials under cyclic thermomechanical impacts.

Corrosion Behavior of P/M Plain Carbon Steel under the Influence of Various Heat Treatment Processes

Abstract The present research work focuses on the effects of heat treatment on corrosion behavior of sintered plain carbon steel (Fe-0.5%C). Investigation on corrosion mechanism has been carried out on three different heat-treated (annealing, normalizing, and hardening) powder metallurgy plain carbon steel specimens. Aqueous immersion and electrochemical pickling corrosion tests were conducted on the heat-treated specimens. It has been found that the heat treatments have enhanced the percentage of theoretical density as well as the hardness of the specimen compared with the as-sintered specimen. The corrosion resistance of the oil-quenched specimen was found to be higher than that of the other heat-treated specimens. Larger grains are observed in the case of as-sintered and annealed specimens, and more iron carbides are observed in the normalized and oil-quenched specimens. Intergranular and pitting types of corrosion have been observed in the scanning electron microscopy images of corroded specimens.

Smart thermal behavior of tripeptide leucyl-leucyl-leucine towards vapors of binary mixture of benzene and tetrachloromethane

A new method for the determination of benzene vapors in a two-component mixture was proposed. This method is based on smart behavior of L-leucyl-L-leucyl-L-leucine (LLL) crystals, which are able to remember the included benzene. This memory is revealed as the sequential endo- and exothermic effects on the DSC curve under heating of LLL powder saturated with vapors of benzene in the temperature range above the endset point of benzene release. The enthalpies of endo- and exothermic effects are proportional to the benzene content in its binary vapor mixture with tetrachloromethane used to saturate the LLL powder. The reasons of the LLL memory are explained and the possibility to control the polymorphic state of the tripeptide using organic vapors was shown. The observed specific properties of LLL tripeptide may be used for qualitative and quantitative analysis of benzene in its mixture with other organic substances.