Sintering Operation Research Articles

Closed-loop optimized nanometal sintering method

Abstract Intense pulsed-light sintering is suitable for forming conductive patterns as it exhibits high efficiency and processing speed; however, it has problems such as destructive sinter necks and poor forming stability. To overcome these drawbacks, conductive pattern sintering based on noncontact height and temperature sensor feedback is proposed. This method involves using a dual-camera vision system for extracting the surface features of the scanned surface. In addition, a temperature sensor measures the surface temperature distribution of the sample to evaluate the sintering state. The two sets of data are fused using a variable weight method to comprehensively evaluate the sintered state of the conductive patterns and adjust the parameters of the next sintering operation. This system was utilized for printing and sintering microstrip antennas, and their return loss and patterns were determined experimentally and they were found consistent with those obtained using traditional manufacturing methods. Therefore, the sensor feedback of the intense pulsed-light sintering method improves the pass rate and reduces the duration of the production cycle. Moreover, this is an environmentally friendly method because unlike traditional etching processes, it does not generate large amounts of contaminated solutions.

Study of polycrystalline diamonds produced by infiltration method using natural and synthetic diamond powders

Diamond tooling is used to machine a broad range of materials. Due to their strength, diamond tools can be used to machine extremely hard alloys. At the same time, diamond tooling is also widely used to machine soft nonferrous alloys and polymers. This paper examines polycrystalline diamond (PCD) composites which are used in diamond tooling designed for various applications. A few types of diamond composites are known today, which are produced by different techniques. Such materials can be produced both by sintering diamond powders together with activating agents and by converting graphite into diamond using catalyst alloys. Production of such materials is always associated with the use of high pressures and temperatures. Depending on the production technique applied, the composition, properties and application of the resultant PCD composites can vary greatly. This paper looks at the infiltration method, i.e. when the binding melt infiltrates in pressed diamonds under high pressures and temperatures. Even though the obtained specimens have a lower strength than the ones produced by other methods, this technique proves to be optimum. Unlike it is with the other methods, the sintering operation in this one is not technically difficult (the applied pressure does not exceed 4 GPa), and PCD composites of bigger sizes can be produced. A study was conducted in the framework of this research to better understand the key physical and mechanical properties of PCD composites, which were produced by infiltration method using two binding materials (Ni – Si and Mn – Si alloys) and two diamond powders (the ASM grade of synthetic powder and the AM grade of natural powder). A comparative analysis of their properties was also carried out.This research study was carried out as part of the research initiative 2.2. “Material Qualification and Studies” (“Strategic Areas in the Development of Materials and Processing Technology till 2030”).

Modifying the figure of merit of thermoelectric materials with inclusions of porous structures

The overall investigation of devices when it comes to the transformation of heat flux into electrical power, and electrical energy to heat power, significantly involves thermoelectric devices (TEDs). These devices provide the potential to build clean energy using a combination of appropriate materials. It has been recognized that more than 60% of the energy generated worldwide disappears, frequently due to the heat involved (exothermic reactions, friction, combustion, and radiation). Economically feasible TED materials and devices have not been successfully developed for larger-scale industrial use due to their low efficiency, unreliability, and high cost of materials and manufacturing. In this study, simple and inexpensive materials and methods were used to tailor the properties of thermoelectric materials to improve their figure of merit, which may be of great potential for meeting future energy demand. Stoichiometric bismuth telluride (Bi2Te3) powder was compounded with numerous concentrations of sodium chloride (NaCl) salt particles ranging from 0 to 50% by volume. The NaCl was ground to microscale particles, and cylindrical pellets were crafted using cold pressing and sintering operations. Consequently, the NaCl was leached separately within the samples using hot water, which caused porous structures. Testing equipment was designed to measure the three essential parameters of TEDs—electrical conductivity, Seebeck coefficient, and thermal conductivity—before and after the NaCl leaching process. Following that, the figure of merit was also calculated for each concentration. Primarily porous structures containing 20% NaCl had a 37.55% higher figure-of-merit value compared to the base samples (0% NaCl), and an increase of 89.07% in the figure of merit from the solids content of the samples was observed with NaCl inclusions at a concentration of 30% by volume. The existence of both NaCl and pores was sufficient to increase the figure of merit. Inclusions and porosity detrimentally influenced the electrical conductivity, but there was a substantial rise in the Seebeck coefficient and thermal conductivity changes leading to an increase in the figure of merit. The figure of merit obtained from this study is relatively moderate for the latest generation of thermoelectric materials. However, the materials and methods used here were simple, economical, and scalable and have great potential for use with optimized thermoelectric materials in hopes of further improvement in the figure of merit.

Influence of the oxide phase on the process of inflation of composition from highly dispersed porous iron

The article describes a new technology for the production of steel parts for structural purposes. The technology is based on molding mixtures of iron powders, iron oxide powders and a binder. Technological processes include the processes of vacuum reduction of iron oxide and a binder material with subsequent sintering of the mixture. The study of the features of the brass infiltration process is carried out on highly porous iron-based blanks with pore sizes less than 1 μm with various percentages of the starting components. The analysis of the structures and mechanical properties of materials obtained on the basis of the developed technology has been performed. The mechanism of infiltration of highly iron-based preforms based on iron obtained by casting from the compositions “iron-iron oxide-phenol-formaldehyde resin” obtained in three stages is established. Recommendations have been developed for the pilot production of products of complex shape from iron-based metal powders, including of casting molding operations, oxide reduction and sintering operations, followed by brass infiltration and heat treatment of the products. The introduction of new technology makes it possible to produce products of complex shapes with a high level of mechanical properties, improved dimensional accuracy and lower cost.

Optimization of Siderite Ore Sintering Operation Conditions

Research was сarried out on a pilot plant on sintering of various size siderite ore and limonite taken in various ratios. To study impact of a number of process factors on the sintering process performance and the obtained agglomerate quality at the minimum number of the carried out experiments, one of the experiment planning methods was used, and regression equations were derived. With these equations the effect of the ore size, siderite ore and limonite ratio, solid fuel consumption, sintered layer height on the agglomeration unit performance and the agglomerate metallurgical properties was reviewed. The obtained work results have great practical importance, as they allow optimization of siderite ore sintering operation conditions and production of high quality agglomerate. They may be used at a variety of the country agglomeration factories, where siderite ores will be used as iron ore component of the sinter burden.

Reinforced Al-Matrix Composites with Ni-Aluminides, Processed by Powders

The paper addresses issues of interest related to the uniform distribution of the reinforcement phase and the continuity of the metal matrix, for two ways of obtaining the powder composites, the hot extrusion and the spark plasma sintering (SPS) respectively. The reinforcement phase is the nickel aluminides obtained by mechanical alloying in ball mills, and the metal matrix is made of aluminum powders. Prior to extrusion, the mixture of aluminum powders and nickel aluminides was pressed and subsequently sintered in environments with high carbon potential, so that in the final product, nickel aluminides, carbide and aluminum oxides were found as reinforcement phases. The obtained results confirmed the hypothesis that, from a blank product with a random distribution of the reinforcement phase, a product with an ordered distribution of the reinforcement phase is obtained after extrusion and that for the same initial proportion of nickel aluminides as reinforcement phase, the composite hardness obtained by hot extrusion is higher compared to that obtained by SPS, the difference being determined by the increase of the proportion of the reinforcement phase by the appearance of aluminum carbide and aluminum oxides during the sintering operation in the high carbon environment.

Comparison of electrolyte fabrication techniques on the performance of anode supported solid oxide fuel cells

A comparison of three solid oxide electrolyte fabrication processes, namely dip coating, screen printing and tape casting, for planar anode supported solid oxide fuel cells (SOFCs) is presented in this study. The effect of sintering temperature (1325–1400 °C) is also examined. The anode and cathode layers of the anode-supported cells, on the other hand, are fabricated by tape casting and screen printing, respectively. The quality of the electrolytes is evaluated via performance measurements, impedance analyses and microstructural investigations of the cells. It is found that the density of the electrolyte increases with the sintering temperatures for all fabrication methods studied. The results also show that with the process and fabrication parameters considered in this study, both dip coating and screen printing do not yield a desired dense electrolyte structure as proven by open circuit potentials measured and SEM photos. The cells with tape cast electrolytes, on the other hand, provide the highest performances regardless of the electrolyte sintering and cell operating temperatures. The best peak performance of 0.924 W/cm2 is obtained from the cell with tape cast electrolyte sintered at 1400 °C. SEM investigations and measured open circuit potentials reveal that almost fully dense electrolyte layer can be obtained with a tape cast electrolyte particularly sintered at temperatures higher than 1350 °C. Impedance analyses indicate that the main reason behind the significantly higher performances is due to not only increased electrolyte density but a decrease in the interface resistance of the anode functional and electrolyte layer is also responsible. This can be explained by the load applied during the lamination step in the fabrication of the tape cast electrolyte, providing better powder compaction and adhesion.

Interdiffusion between gadolinia doped ceria and yttria stabilized zirconia in solid oxide fuel cells: Experimental investigation and kinetic modeling

Interdiffusion between the yttria stabilized zirconia (YSZ) electrolyte and the gadolinia doped ceria (CGO) barrier layer is one of the major causes to the increment of ohmic resistance in solid oxide fuel cells (SOFCs). We present in this work experimental investigations on CGO-YSZ bi-layer electrolyte sintered at 1250 °C or 1315 °C and element transport as a function of sintering temperature and dwelling time. In order to quantitatively simulate the experimental observations, the CALPHAD-type thermodynamic assessment of the CGO-YSZ system is performed by simplifying the system to a CeO2–ZrO2 quasi-binary system, and the kinetic descriptions (atomic mobilities) are constructed based on critical review of literature data. The CGO-YSZ interdiffusion is then modeled with the DICTRA software and the simulation results are compared with the experimental data under different sintering or long-term operating conditions. The corresponding ohmic resistance of the bi-layer electrolyte is predicted based on the simulated concentration profile. The results implies that the interdiffusion across the CGO-YSZ interface happens mainly during sintering at high temperature, while during long-term operation at relatively lower temperature the impact of interdiffusion on cell degradation is negligible.

Investigation of Pr0.2Ce0.8O2-δ@Li2CO3 nanocomposite electrolytes as intermediate temperature ionic conductors: a thermal, structural, and morphological insight

Pr0.2Ce0.8O2-δ@Li2CO3 (PDC-LC) nanocomposite electrolytes were prepared through the co-precipitation of Pr-doped cerium/lithium complex carbonate and its pre-firing and sintering operations. The structural and thermal properties of PDC-LC nanocomposite were investigated by means of X-ray diffraction, thermogravimetric analysis, Raman spectroscopy, and electrochemical impedance spectroscopy. The remarkable presence of oxygen vacancies and the influence of the interfacial interactions between PDC crystallites and amorphous Li2CO3 were deliberately probed by Raman spectroscopy and FEG-SEM, respectively. It was observed that there is a long-range interaction between the PDC crystallites and Li2CO3 phase, which resulted in the tight binding of $$ {\mathrm{CO}}_3^{2-} $$ ions on the facets of PDC nano-crystals and may be well characterized by the shift and broadening of the characteristic Raman spectroscopic peaks of $$ {\mathrm{CO}}_3^{2-} $$ ions in the samples. The X-ray diffraction results confirm the successful incorporation of praseodymium into ceria phase that presented the sole crystalline structure contrarily to the lithium carbonate present as an amorphous phase in the as-prepared samples. The oxygen ionic conductivity behaviors of PDC-LC phase were measured at the intermediate operating temperature range (300–500 °C). However, AC conductivity measurements demonstrated that the conductivities in air atmosphere increased linearly with temperature. The Arrhenius plot of total conductivity showed two different slopes indicating two distinct conduction mechanisms. The interfacial interactions between the PDC and LC phase inside the PDC-LC nanocomposite were responsible for oxygen ionic conductivity.

Particle size-dependent properties of a char produced using a moving-bed pyrolyzer for fueling pulverized coal injection and sintering operations

Pyrolytic chars are a potential high-quality fuel for use in iron ore sintering and pulverized coal injection (PCI) operations of blast furnace. In this study, industrial char produced from a moving-bed pyrolyzer was screened into four particle size ranges and compared with coke used in an industrial sintering process and a PCI coal used in an industrial blast furnace, and their basic compositions, micropore structures, functional group distributions, carbonaceous structures, reactivities, and gas release behaviors during combustion were analyzed. Furthermore, the mechanism underlying the particle size-dependent properties of the char was analyzed by comparing it with a char prepared under laboratory-simulation conditions. Results demonstrate that char particles larger and smaller than 3 mm (the turning point) have different structures and properties. More specifically, particles larger than 3 mm have stable properties, better developed pore structures, carbonaceous structures that are more ordered, superior reactivities, and lower releases of SO2 and NOx. Therefore, they represent a desirable option for use in fueling sintering and PCI operations. Char particles smaller than 3 mm were further investigated by screening them into particle size ranges, and results showed that they had significantly varied compositions and structures, which further confirmed their unsuitability for use in the two operations. Finally, the particle-size-dependent properties of the char can be explained by the differing residence times, the radial variations in pyrolysis degrees, and the mechanical (or thermal) stresses experienced by the different raw coal particles within the pyrolyzer.

Surface topography of nickel-based superalloy manufactured with direct metal laser sintering (DMLS) method

In the present study, a nickel-based powder, which is extensively utilized in aero-engine applications, was utilized in direct metal laser sintering operation to investigate the surface topography of additively manufactured products. Laser power, scanning speed and layer thickness were used as variable in the process and the role of each variable was investigated considering surface parameters such as surface roughness and waviness. In order to determine the surface parameters, 2D profile topography and 3D areal topography measurements were carried out from the product surfaces. According to the results, surface quality is improved increasing laser power while reducing scanning speed and layer thickness. In addition, 2D measurements predict the surface parameters lower than 3D measurements because profile topography considers only a limited number of sections from the surface however, areal topography includes all points on the surface while calculating the surface parameters.

Optimisation of spark plasma sintering parameters of Al-CNTs-Nb nano-composite using Taguchi Design of Experiment

Optimisation of process parameters is usually undertaken to achieve more efficient and cost-effective process conditions. This work deals with the optimisation of spark plasma sintering process parameters which include sintering temperature, pressure, dwell time and heating rate for the development of Al-CNTs-Nb nano-composite. Taguchi Design of Experiment (DOE) was used to design the sintering operation, while analysis of variance (ANOVA) was used to investigate the contribution of the factor variables to the response variables of density and micro-hardness. The admixed powders were consolidated as designed with SPS machine, while the sintered compacts were characterised using optical microscope, Vickers hardness tester and Archimedes-based density tester. The results obtained were a maximum density of 2.68 g cm−3 (99.3% relative density) and maximum micro-hardness of 38.57 HV (0.37 GPa), while the optimal SPS parameters were sintering temperature of 630 °C, pressure of 30 MPa, dwell time of 10 min and heating rate of 200 °C/min. This work has achieved a 20% improvement in micro-hardness which is good for so many engineering applications.

Particulate matter filtration of the flue gas from iron-ore sintering operations using a magnetically stabilized fluidized bed

This study proposes a novel process for the separation of particulate matter (PM) from the flue gas emitted from iron-ore sintering operations using a magnetically stabilized fluidized bed (MSFB) with sintered ore as a filter medium. The deactivated sintered ore can still be used as a raw material for subsequent sintering operations. Sintered ore and sintered ash samples were characterized by x-ray diffraction, x-ray fluorescence, and laser diffraction analyses. The effects of collector size (150–300, 300–450, and 450–600 μm), applied magnetic flux density (48–160 Gs), bed height (5, 7.5, and 10 cm), and gas velocity ratio (1.40, 1.51, and 1.62) on PM filtration are investigated. The experimental results indicate that PM filtration efficiency increases with increasing magnetic field strength and bed height. However, a high gas velocity ratio has negative effects on PM removal performance, while collector size has little influence. A comparative study of the MSFB for magnetic sintered ash and non-magnetic coal-fired ash filtration demonstrates that sintered ash is more effectively captured due to magnetic retention. This indicates that this technology has good prospects for the purification of flue gas from iron-ore sintering operations.

An Experimental and Modeling Study of Synthesis, Consolidation and Aging Behavior of AA2014 Composite Reinforced by TiB2 via Powder Metallurgy Method

Aluminum 2014 alloy composite reinforced with TiB2 particulates with different volume% of TiB2 (5, 10 and 15%) has been successfully synthesized by P/M route. The composite powders were consolidated by cold uniaxial compaction pressure followed by sintering at 590 °C in N2 atmosphere. The Al 2014–TiB2 composites were aged at 160 °C between 0 and 8 h followed by microstructural characterization and hardness evaluation. Scheil cooling and equilibrium calculations were performed using FactSage for qualitative understanding of the microstructural evolution during sintering and aging operations. In addition, the thermo-physical properties such as hardness, density and transverse rupture strength of the sintered samples were evaluated.

Studying the Efficiency of Lime-Soda Sinter Process to Extract Alumina from Colored Kaolinite Ores Using Factorial Technique of Design of Experiments

As the increasing demand for alumina in recent years with the result diminishing reserve of bauxite, the need to secure a domestic raw material base is driving research in new technologies to process low grade ores into alumina, with the intention that these technologies will lead to a significant reduction of bauxite and alumina transportation costs, allow the extraction of more valuable components from the ore and reduce environmental impact. Clays are types of the low-grade aluminum ores, they're also well abundant which make them a potential substitutes for Bauxite. In this work, lime soda sinter process was adopted for extracting alumina from kaolinitic claystone from Al-Ga'ara formation (Duekhla) quarry in western Iraq. The operation efficiency of sintering was studied in which the whole process has been done with three stages: the sintering process for the raw materials, leaching and carbonizing processes to precipitate and separate the alumina from the leach pregnant solution . Factorial technique of Design of Experiments (DOE) module in Minitab was used as a principal methodology to examine the sintering efficiency over alumina extraction. The results obtained showed that the optimum parameters for the sintering operation were CaO/SiO2 molar ratio of 2.2, Na2O/Al2O3 molar ratio of 1.2, sintering temperature at 1213 °C for 90 min. The sintered materials were leached with sodium carbonate solution, and sodium aluminate solution was obtained. By bubbling carbon dioxide gas into this extract solution aluminum hydroxide [Al(OH)3] has been precipitated and on calcination at 1200 °C for 2 hrs, alpha alumina (α-Al2O3) was obtained with purity of 98.5 %.

Numerical simulation and experimental analysis of the sintered micro-parts using the powder injection molding process

This paper discusses in detail the development of numerical simulations capable of simulating structural evolution and macroscopic deformation during a powder injection molding process. A sintering model based on elastic-visco-plastic constitutive equations was proposed, and the corresponding parameters such as sintering stress, bulk and shearing viscosities were identified from dilatometer experimental data. As a complement to this experimental study, a finite element simulation of the sintering operation was performed. The simulations were based on constitutive equations identified from specific experiments performed for each blend at different sintering heating rates and loadings. Finally, the numerical analyses, performed on the 3D micro-structured components, allow the numerical predictions to be compared with experimental results of sintering stage. They show that the FE simulation results have better agreement with the experimental ones at high temperatures.

Preparation and characterization of GDC-Li2SO4/Li2CO3 nanocomposite electrolytes for applications in intermediate solid oxide fuel cells

Abstract Gd0.1Ce0.9O1.95/Li2CO3-Li2SO4 (GDC/LCS) nanocomposite electrolytes were prepared through nano-powders mixing, prefiring and sintering operations. The phase components and microstructures of the as-prepared nanocomposite were characterized by XRD, FESEM, TG-DSC and IR spectroscopy. AC impedance spectroscopy and DC polarization method were utilized to measure their electrical conductivities under different conditions. It has been found that the GDC/LCS nanocomposite have a very homogeneous microstructure, where the LCS is mostly in amorphous state due to the strong interfacial interactions between the GDC and LCS. In addition, their overall electrical conductivity was found to increase with temperature in air, featured with a sharp activation energy change from 1.01 to 0.30 eV around 520 °C, and reach 108.7 mS/cm at 600 °C, while their protonic and oxide ionic conductivities were 16 mS/cm in H2 and 5 mS/cm in air at the same temperature, respectively. The single cell built up of the GDC/LCS nanocomposite showed an open-circuit voltage of 1.01 V and peak power density of 272 mW/cm2 at 600 °C.

Thermodynamic stability of SFCA (silico‐ferrite of calcium and aluminum) and SFCA‐I phases

AbstractSilico‐ferrite of calcium and aluminum (SFCA) and SFCA‐I phases form in iron ore sintering operations. Their behavior in blast furnaces, with sinter being a significant component of blast furnace burden, is of critical importance to the ironmaking process. They have complex disordered crystal structures and form over a range of composition. In the present work, enthalpies of formation from oxides for five different SFCA compounds and one SFCA‐I phase were measured by oxide melt solution calorimetry in molten lead borate solvent at 800°C. The enthalpies of formation from binary oxides are zero within experimental error for SFCA phases and slightly endothermic for SFCA‐I, confirming that SFCA phases are stabilized, not by energetics, but by their configurational entropies resulting from atomic site disorder. In addition, enthalpies of drop solution into a molten slag at 1450°C were measured for SFCA phases and show good agreement with values predicted using the heats of formation and previously measured drop solution enthalpies for the binary oxides. This agreement confirms data consistency and shows that the presence of variable amounts of SFCA relative to binary oxides in a sinter will have negligible effect on the heat balance in the blast furnace.

Mechanical performance of Cr-alloyed PM steel after different sintering and heat treatment operations

Main benefits of the PM technology versus conventional steel making processes in the manufacture of structural steel parts are high material utilization, low energy consumption and short production time. These benefits are fully exploited by choosing the right combination of material and processing route to get the required mechanical properties at a low production cost. Powder grades pre-alloyed with Cr are robust and cost effective materials which are suitable for high performance PM steel components. This paper presents mechanical properties of Cr-alloyed PM steel obtained after different processing routes, including high temperature sintering, sinter-hardening and heat treatment by low pressure carburizing. Static mechanical data are presented as well as results from plane bending fatigue tests. Microstructures are also shown and correlated with the mechanical properties obtained for the respective processing routes.

Sustainable Recycling of Ferrous Metallic Scrap Using Powder Metallurgy Process

Powder metallurgy (PM) process can be used for transforming the oxidized ferrous metallic scrap to usable products. The present study establishes an optimized PM-based recycling process to obtain considerably higher physical and mechanical properties of products (cylindrical samples in the present work). To this end, seven parameters including a source of metallic scrap, the quantity of carbothermic reducing agent, and PM process parameters were used to build a Taguchi L18 orthogonal array. In situ reduced and sintered samples made under these 18 conditions were characterized for physical, mechanical, and microstructural characteristics. The gray relational analysis (GRA) approach was used to arrive at the most optimal parametric setting. The grinding sludge as a source of scrap material led to the highest sintered density, hardness, and mechanical strength under these conditions: compaction pressure of 900 MPa, a sintering temperature of 1150 °C, stoichiometrically added graphite (for carbothermic reduction), 90 min of sintering time, and ratio of heating-to-cooling rate of 5/7. This analysis also corroborated with the earlier findings that simultaneous reduction of metal oxides and densification occur in the sintering operation. This newly established PM-based recycling process with GRA-optimized parametric settings improves the product characteristics of interest by approximately 14 % compared to those of the initial optimal setting obtained from L18 outcomes. This was confirmed by analytical prediction as well as confirmatory experiments.