Sintering Of Materials Research Articles

Sodium molybdate‐hexagonal boron nitride composites enabled by cold sintering for microwave dielectric substrates

AbstractTo fulfill the demands of more bandwidth in 5G and 6G communication technology, new dielectric substrates that can be co‐fired into packages and devices that have low dielectric loss and improved thermal conductivity are desired. The motivation for this study is to design composites with low dielectric loss (tan δ) and high thermal conductivity (κ), while still limiting the electrical conductivity, for microwave applications involving high power and high frequency. This work describes the fabrication of high‐density electroceramic composites with a model dielectric material for cold sintering, namely sodium molybdate (Na2Mo2O7), and fillers with higher thermal conductivity such as hexagonal boron nitride. The physical properties of the composites were characterized as a function of filler vol.%, temperature, and frequency. Understanding the variation in measured properties is achieved through analyzing the respective transport mechanisms.

Research on Obtaining Sintered Materials From 410 Stainless Steel Powder

Ferritic steels are used in applications that require good thermal conductivity and/or durability in operation involving heat cycles. They are easy to process due to their high ductility and have magnetic properties.
 The paper presents a series of experimental research on the manufacture of sintered products obtained from 410 stainless steel powder and their characterization from the microstructural and wear resistance point of view.

Construction ceramsite from low-silicon red mud: Design, preparation, and sintering mechanism analysis

Low-silicon red mud (LSRM) is limited in its application in the field of light aggregates for construction. Supplementation sintering materials (SSMs) effectively aids LSRM in preparing sintered construction ceramsite. To produce an LSRM-based ceramsite with economical and effective performance, this study investigated the effect of SSMs (silica fume, bentonite, and glass powder) on the performance of the ceramsite and determined the optimum ratio using the response surface method (RSM). The results indicated that the silica fume (SF) significantly influenced the apparent density (AD) and water absorption (WA) of the ceramsite; with an increase in SF, AD increased and WA decreased. SF and glass powder (GP) were negatively correlated with particle strength (PS), whereas bentonite was positively correlated with PS. The optimum doping values for SF, bentonite, and GP were determined as 19.79, 9.28, and 12 wt%, respectively. Ceramsite could achieve the best performance with an AD of 1254 kg/m3, a WA of 3.13%, and a PS of 13.1 MPa. In addition, the formation of aluminosilicate played a positive role in the fixation of heavy metals and the reduction of the pH value of ceramsite, ensuring its good environmental performance.

Synthesis and characterization of phase pure and Mg-modified AgZnVO4 microwave dielectrics for high-frequency ULTCC applications

A novel low-loss and ultra-low temperature sinterable microwave dielectric material, AgZnVO4, was systematically investigated for the first time. The material exhibited a monoclinic structure with a space group P21/n, obtained by conventional solid-state processing. The material also showed combined microwave dielectric properties of εr = 10.3, Q×f = 42,000 GHz, and τf = –9.2 ppm/°C for specimens sintered at 540 °C. The partial substitution of Mg for Zn in the Ag(Zn1−xMgx)VO4 ceramics effectively improved the densification and reduced the dielectric loss of the ceramics. X-ray diffraction patterns revealed a single solid solution phase of Ag(Zn1−xMgx)VO4. The relative density, dielectric polarizability, packing fraction, lattice energy, and bond valence of the samples were calculated. An excellent combination of the microwave dielectric properties was obtained for Ag(Zn0.97Mg0.03)VO4 ceramic sintered at 540 °C: εr = 10.6, Q×f = 52,000 GHz, and τf = –10 ppm/°C. Additionally, the ceramic exhibited good chemical compatibility with aluminum electrodes, indicating great potential for ultra-low temperature co-fired ceramics (ULTCC) applications, particularly in the microwave and millimeter wave regions.

Investigation of the Influence of the Mixing Process on the Powder and Component Properties during Cyclic Reuse of a Polyamide 12 Sinter Material in Selective Laser Sintering

Selective laser sintering (SLS) with polymers is currently in transition to the production of functional components. Nevertheless, the potential to revolutionize conventional production processes is confronted by newly imposed requirements regarding reliability and reproducibility. To ensure that the requirements are fulfilled, the aging mechanisms occurring in polymers are compensated by recycling strategies, such as fraction-based mixing of a defined ratio of new with recycled powder. Although various mixing ratios for the reuse of the material in SLS have been investigated, there is insufficient knowledge of suitable mixing parameters for homogeneous and gentle mixing of the powder fractions. This work therefore focused on the influence of potentially suitable mixing parameters identified in a previous study on the ongoing powder and component properties in SLS using polyamide 12 and a constant refreshing rate. Regarding the powder properties, the intrinsic properties and density of the powders were investigated. Regarding the component properties, mechanical properties, sinter density, and surface quality were investigated. Decreases in the powder density and the component properties were measured by increasing the number of process cycles. Taking into account the determined powder and component properties, the selected mixing parameters enabled a homogeneous and gentle mixing of the powder fractions.

Investigations for Material Tracing in Selective Laser Sintering: Part Ι: Methodical Selection of a Suitable Marking Agent.

Selective laser sintering (SLS) with polymers is currently at the transition stage for the production of functional components and holds great potential to revolutionize conventional production processes. Nevertheless, its application capability is confronted by newly imposed requirements regarding reliability and reproducibility. To safeguard these requirements, a deeper process understanding of material aging mechanisms in polymeric materials is needed. In order to enable the traceability of the materials as well as the identification of defective components with subsequent tracing of the cause, the use of a material marking process represents an alternative. SLS in combination with material marking is proving to be an efficient option for reproducible, high-quality manufacturing based on an increased understanding of the process. In this study, the idea of a marker-based traceability methodology for the purpose of process optimization is presented. Fundamental to the subsequent experimental investigation of the marking agent suitability, this work first focuses on the systematic selection of a suitable marking agent for use in SLS. Based on an analysis of the sinter material to be marked and a set of marking technologies, as well as using the selection methodology, the modified polymer marking technology was evaluated as the most suitable marking technology.

Oxidative modification of industrial basic oxygen furnace slag for recover iron-containing phase: Study on phase transformation and mineral structure evolution

Basic oxygen furnace (BOF) slag is the main co-product in the steelmaking process, its recycling within the iron and steel enterprises is crucial for the industry to ensure greater sustainability. According to the composition characteristics of BOF slag, a method of separating and recovering iron resources by regulating the composition of BOF slag with silica as an additive at high temperature was proposed. In this study, the growth of iron-containing phase during oxidative modification of BOF slag was in-situ observed by ultra-high-temperature confocal scanning laser microscope, and the phase transformation and mineral structure evolution were analyzed by chemical analysis, X-ray diffraction and field emission scanning electron microscopy. The results demonstrated that the increase of oxidation temperature effectively promoted the transformation of iron oxides to (Mg,Fe2+)O·Fe2O3, but too high temperature could lead to the increase of iron-containing melilite phase and reduce the iron recovery. In the oxidative modification process, the appropriate holding time and cooling mode facilitated the growth and development of (Mg,Fe2+)O·Fe2O3 particles, which was conducive to the separation and recovery of iron resources. After BOF slag was oxidized at 1300 ℃ for 240 min and cooled in the furnace (1 ℃/min), the grade of magnetic slag obtained by magnetic separation had a grade of 40.26%, a recovery of 70.95%, and a P and S content of 0.042 and 0.456, respectively, which may be used as an important supplement to the raw materials for sintering. The regulated secondary slag may be used to diversify into higher value-added production. Therefore, the systematic research and development of oxidative modification-crushing-magnetic separation technology may promote the efficient utilization of BOF slag components and heat energy.

Investigation of the Influence of the Mixing Process on the Powder Characteristics for Cyclic Reuse in Selective Laser Sintering

Selective laser sintering (SLS) with polymers is currently at the transition to the production of functional components and thus holds great potential to revolutionize conventional production processes. Nevertheless, the application capability is confronted by newly defined requirements regarding reliability and reproducibility. In order to fulfil the requirements and to increase the process stability, the ageing mechanisms in polymers are compensated by recycling strategies. This involves fraction-based mixing of a defined ratio of new powder with recycled powder. Basically, fraction-based mixing must be preceded by the selection of suitable mixing parameters. The work focused on the influence of the mixing process on the powder characteristics for cyclic reuse in SLS. With regard to the powder characteristics, the particle shape and particle size distribution as well as the bulk and tap density of the powder were investigated. The authors found an influence of the mixing process with increasing mixing time on the powder characteristics of a black polyamide 12 sintering material. A mixing time of 1 h and a mixing intensity of 15 rpm proved to be potentially effective for achieving a gentle and homogeneous mixing of the powders.

Preparation of metakaolin-based geopolymer membrane and its application in black liquor treatment

In recent years, inorganic membrane filtration technology has become the most promising treatment option for treating papermaking black liquor and recovering lignin from black liquor. However, the preparation of most inorganic membranes requires sintering or high-cost raw materials, which leads to high cost in the application of black liquor treatment and lignin recovery. For this reason, in this study, a no-sintering, low-cost metakaolin-based geopolymer membranes (MGM) was prepared at room temperature using steel mesh with good ductility and processability as the substrate. The effects of slag doping on the mechanical properties, microstructure and separation properties of MGM were investigated. The results concluded that when the mass ratio of slag to metakaolin is 1:10 (MGM-10), the membrane has the best comprehensive performance. The compressive strength and pure water flux of MGM-10 were 23.94 MPa and 286.62 kg m−2 h−1, respectively. In the application of black liquor treatment and lignin separation and recovery from black liquor, MGM-10 showed excellent separation performance by removing 96% of TSS, 91.75% of COD and 98.97% of BL from black liquor after primary filtration. Compared with ceramic membranes prepared by sintering, MGM has cheaper raw materials and lower energy consumption, which is more promising for industrial scale applications.

Structure and Properties of Mechanically Synthesized Tin Bronze Powders and the Related Sintered Materials

Structure and Properties of Mechanically Synthesized Tin Bronze Powders and the Related Sintered Materials

Preparation and mechanism of silicate-based sintering material from large amount of steel slag

In this paper, silicate-based sintering materials (SBSM) were prepared by high-temperature sintering process with steel slag as the main raw material. By strictly controlling the particle gradation of steel slag, the content of steel slag in SBSM was increased to 70%, to realize the efficient resource utilization of steel slag. The phase composition and micro-morphology of the SBSM were characterized by X-ray diffraction (XRD) and scanning electron microscope (SEM), respectively. The flexural and compressive strength of the SBSM were tested by the full-automatic compression and folding machine. The results show that the main phases of the SBSM are anorthite and quartz, and the existence of anorthite is benefit to improve the mechanical properties of the SBSM. An appropriate proportion of small-size steel slag (more than 100 mesh) can promote the reaction process, and improve the flexural and compression strength of the samples. However, excessive small-size particles of steel slag lead to a large amount of liquid phase in the reaction process, which makes the aggregate react with the matrix. The strength of the sample decreases with the decrease of its resistance to external forces. The water absorption of the samples decreases with the increase of the steel slag with small-size particles.

Upgrading Hopper Cars for Transportation of Sinter and Other Materials

Upgrading Hopper Cars for Transportation of Sinter and Other Materials

Combined carbon content assessment method for powder metallurgy

Powder metallurgy (PM) lacks a clear method to analyse the combined carbon content based on metallography visualisation, and this article describes the creation of such a method for powder materials. Different methods are used to analyse combined carbon within metallurgical samples, and the hardness of components within the automotive industry is related to this question. The main aim of this paper is to determine if optical microscopy provides a reliable means to assess the combined carbon content. For checking these items, the Optical Microscope will be used, density, hardness of sinter material, and particle size laser analysis of powder for creating the observed compact, and SEM microscope. This investigation provides standardised rules that can be implemented within any material laboratory. The analysis of powder particle size, hardness test, density check, and the investigation of the structure of powder element are presented.

Influence of Atmospheric Conditions on Mechanical Properties of Polyamide with Different Content of Recycled Material in Selective Laser Sintering.

The price of material is an important factor when selecting the additive polymer procedure. In selective laser sintering (SLS), the price can be reduced by the recycling of material, i.e., with different shares of original and recycled material, as well as by the orientation of the product during manufacturing. Numerous tests warn that orientation in the direction of z axis should be as low as possible to reduce the total price of the product. The product also has to satisfy the influence of atmospheric conditions to which it is exposed during its lifetime, i.e., UV radiation and humid environment. UV light, with sun being its most common source, and average humidity in different parts of the world can be approximately from 20% to 90%, depending on time, day and geographic location. In this work, the test specimens have been made of original, mixed and 100% recycled material and then exposed to the influences of UV radiation and water absorption. After having been exposed to atmospheric conditions for a longer time, the mechanical properties of the polyamide products made by selective laser sintering were tested. The results show that exposure to UV radiation reduces tensile elongation at all ratios of recycled material and orientation of 70–90% except in the z direction, while in flexural deformation it is the other way around. The effect of water was observed only between the 7th–14th day of absorption with a decrease in strength until the deformation did not change.

Iron Ore Sinter Macro- and Micro-Structures, and Their Relationships to Breakage Characteristics

A systematic analysis of industrial iron ore sinter product and associated sinter returns was undertaken. The samples were characterised through identification of the major macro- and micro-structural types present in these materials. Examination of the breakage surfaces of the particles indicates a strong correlation between mechanical sinter strength and sinter microstructure. Preferential breakage was observed to occur in sinter materials having high porosity and those microstructures consisting of isolated hematite grains in a glass matrix. The bulk of the sinter product consisted of material with a microstructure of magnetite and silico-ferrite of calcium and aluminium (SFCA). The phases formed and the reaction sequences responsible for the formation of the principal microstructure types are explained by the non-equilibrium solidification of melts in the “Fe2O3”-Al2O3-CaO-SiO2 system.

Immobilization of iodine waste at low sintering temperature: Phase evolution and microstructure transformation

The treatment of radioiodine produced from nuclear industry is a key priority. It is significant to understand the phase evolution and microstructure transformation of the matrix in the field of radioiodine immobilization. In this work, the iodine wastes (silver-coated silica gel doped with iodine waste) were immobilized by B2O3-Bi2O3-ZnO at different low sintering temperatures (500, 550, and 600 ℃, respectively). The effect of iodine content in silver-coated silica gel on the phase evolution for the sintered matrix was investigated. Based on the FT-IR results, the changing of microstructure transformation affects by temperature and composition were also studied. These results demonstrate that the simulated iodine waste was gradually immobilized in the glassy phase as the sintering temperature increased. Moreover, under the effect of sintering temperature and material composition, part of B-O-B in [BO3] unit transformed into B-O-B in [BO4], resulting in more iodine wastes were immobilized in the glassy phase. This work mainly reveals the phase evolution and microstructure transformation of the iodine waste matrix sintered at low sintering temperatures.

Effects of suspension processing conditions on the multi-scale structural changes of photocured SiO2 bodies during sintering process: An operando observation using optical coherence tomography

The relationships between the processing methods of photocurable SiO2 suspensions, powder dispersion states, material processability, and the structural changes of photocured SiO2 bodies during their sintering into transparent glass components were investigated. Using an inter-particle photo-cross-linkable SiO2 suspension as the model system, three series of suspensions with different dispersion states but the same compositions were designed via different powder processing routes. The effects of the differences in the particle dispersion states on the real-time multi-scaled structural changes of photocured bodies during sintering were elucidated via operando observation using an optical coherence tomography (OCT) system equipped with an infrared image furnace. The photocured body prepared using the well-dispersed suspension starts to gradually densify from the outside, finally reaching a fully densified state. Furthermore, during the densification process, the photocured body warped, and then the structure recovered owing to the earlier densification at the bottom region of the sample, where the infrared light was focused for heating. Contrastingly, when the suspension contained agglomerates, an un-densified area was observed in the sintering material in the form of microstructures, which remained in the material after sintering. The in-line transparency of the sintered SiO2 material was consistent with those of the microstructures observed using OCT.

Effects of extracted-vanadium residue and MgO on the basic sintering characteristics of high-chromium vanadium–titanium magnetite

Extracted-vanadium residue (EVR), formed during the smelting and extraction of High-chromium vanadium-titanium magnetite (HCVTM), should be used cyclically, and its use as a sintering material to prepare sinters for blast-furnace smelting is a viable option. The effects of EVR and MgO on the fundamental sintering characteristics of HCVTM, such as assimilative temperature, liquid phase fluidity index, adhesive phase strength, and crystal stock consolidation strength, were studied using X-ray diffraction and scanning electron microscopy, as well as phase composition analysis and microstructure analysis. The assimilative temperature (the lowest reaction temperature between sintering materials and CaO) of HCVTM by adding 0–8 wt% EVR decreased. The liquid phase fluidity index of HCVTM with six wt% EVR is best. The adhesive phase strength decreased from 1162 to 356 N. However, the crystal stock consolidation strength increased to the highest value of 2170 N by adding six wt% EVR. Based on the primary sintering characteristics effect of EVR on HCVTM, the optimum EVR amount is six wt%. After adopting the six wt% EVR added HCVTM with relatively good properties, the assimilative temperature of mixed ores increased from 1290 to 1320 °C with MgO added percent of 0–3 wt%. The liquid phase fluidity index decreased as a whole from 0.88 to 0.796–0.828, and the crystal stock consolidation strength also reduced from 2170 to 1090 N, indicating that both the liquid phase fluidity index and the crystal stock consolidation strength have changed slightly as a result of the addition of >1% MgO. However, adding 1% MgO improved the adhesive phase strength to a high value. The perovskite formation is restrained as Ti4+ diffuses into the liquid phase with the increase of MgO. Based on the effect of the fundamental sintering characteristics of EVR and MgO on HCVTM, a sintering blending ratio of 6 wt% EVR and one wt% MgO is recommended.

The Synergetic Effect of Soil Amendments on Reducing Bioavailable Heavy Metals and Greenhouse Gas Emissions from Upland Soil

Heavy metal pollution and greenhouse gas (GHG) emissions from soil are two major detrimental sources in the agriculture environment because of concerns about crop safety and global warming. Applying amendments on site is a common technique used for heavy metal remediation and the reduction in GHG emissions. This study aims to evaluate the effect of different amendments on the reduction in both bioavailable heavy metals and GHG emissions from soil. Four different amendments, namely bottom ash (BA), sintered material (SM), sintered material combined with lime (SM + L), and FeO (SM + FeO) were applied to upland fields, followed by maize (Zea mays L.) cultivation from April to October. Subsequently, SM + FeO treatment demonstrated the highest bioavailability reduction efficiency for As at 79.1%, and SM + L treatment had a high efficiency for the reduction in Cd and Pb by 64.6% and 41.4%, respectively. SM + FeO treatment also reduced bioaccumulated As and Pb in maize grain by 59.3% and 66.2%, respectively. Furthermore, SM + FeO treatment demonstrated the highest reduction efficiency for cumulative N2O emissions by 70.7%, compared to the control soil. Among the four different amendments, the efficiency of heavy metal and GHG emission reduction was in the following order: SM + FeO > SM + L > SM > BA. Overall, SM combined with FeO is a promising amendment for reducing and managing both heavy metal pollution and GHG emissions in soil.

Experimental and molecular dynamics examination of the interface interaction between magnesium oxide and magnetite in a high temperature oxidation environment

The formation mechanism of sintering neck between magnesium oxide and magnetite under high temperature oxidation environment requires more investigation due to the limitations of high-temperature process monitoring techniques. Through a series of roasting experiments, this research quantitatively investigated the impact of MgO on the roasted microstructure and consolidation behavior of magnetite based on previous research. The results showed that with the increase of MgO content in pellets, the consolidation index of pellets decreased from 0.71 to 0.50, and the porosity increased from 7.24% to 13.57%. The existence of MgO could hinder the interface interaction, reduce the consolidation index and increase the porosity. Furthermore, molecular dynamics simulations were performed to investigate the crystal transformation and migration behavior from a molecular standpoint. The simulation findings revealed that the creation of the sintering neck was caused by atom migration and diffusion. Mg2SiO4 has minimal influence on the migration of the atoms, while MgO and MgFe2O4 have a large impact on pellet consolidation. This work gave new ideas for evaluating porous sintering materials, which may lead to additional research into the interface interaction between heterogeneous oxide during the sintering material formation process.