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Powder Metallurgy and Metal Ceramics
Journal Prestige (SJR): 0.221  Number of Followers: 7  Hybrid journal (It can contain Open Access articles)ISSN (Print) 1573-9066 - ISSN (Online) 1068-1302 Published by Springer-Verlag  [2468 journals]
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- Tribological Properties of B4C–SiC–hBN Composite Ceramics Sliding
Against AISI 347 Steel Immersed in Emulsion-
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Abstract: The powders of hBN, SiC, and B4C were employed as the raw ingredients to prepare the B4C–SiC–hBN composite ceramics by a vacuum high-pressure sintering method with hBN and SiC contents in the range of 0, 10, and 20 wt.%, respectively. A pin-on-disc testing equipment was used to assess the tribological properties of B4C–SiC–hBN composite ceramics with various hBN and SiC content when sliding against AISI 347 steel immersed in the emulsion. The experiment’s findings indicate that the sliding COF of the B4C/AISI 347 steel pair marginally drops as the sliding distance increases. Besides, the sliding COF of the B4C–10 wt.% SiC–20 wt.% hBN/AISI 347 steel pair rapidly declines. By tribopairs of B4C–SiC–hBN composite ceramics against AISI 347 steel under the condition of lubrication by water-based emulsion, the steady-state friction may move into a state of mix lubrication as the hBN concentration rises, improving the tribological performance. The steady-state COF considerably decreases to 0.01 from 0.386 as the hBN and SiC concentration is increased to 20 wt.% and 10 wt.% from zero, showing a decreasing trend for both the B4C–SiC–hBN pin and AISI 347 steel disc samples’ COWs. The steady-state friction of tribopairs of B4C–SiC–hBN composite ceramics against AISI 347 steel may enter a state of mixed lubrication in the emulsion. The wear resistance of composite ceramics was improved by the addition of hBN and SiC particles because of their lubricating and reinforcing effects. These findings offer valuable insights into the design and development of advanced composite ceramics for various industrial applications that require improved tribological properties.
PubDate: 2023-11-24
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- Wear-Resistant Composites Produced from Tool Steel Waste for Contact
Joints of High-Speed Printing Machines-
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Abstract: The paper examines the effect of doping elements on the structurization and properties of a new antifriction composite produced from grinding waste of the R2AM9K5 high-speed tool steel and CaF2 solid lubricant. The composite is intended for operation at loads of 2.0–3.0 MPa and high rotation speeds (5,000–7,000 rpm) in contact joints of high-speed printing machines. The production process imparted a heterophase structure to the antifriction composite. The composite consists of a metal pearlite–carbide and carbonitride matrix and CaF2 solid lubricant particles being evenly distributed in it. Valuable Mo, Cr, W, V, N, and Co doping elements contained in the R2AM9K5 steel waste particles promote the formation of strengthening phases in the composite’s metal matrix. In combination with CaF2 solid lubricant, these strengthening phases impart high antifriction properties to the material under high-speed friction at speeds up to 7,000 rpm and loads of 2.0–3.0 MPa. Comparative tests of the new R2AM9K5 steel + (4.0−8.0)% CaF2 composite demonstrated significant advantages in the antifriction properties over cast brass, currently used for units of modern rotary printing machines and can perform effectively only under continuous liquid lubrication. The R2AM9K5 steel waste composite containing CaF2 solid lubricant permanently forms a protective antifriction film on the contact surfaces in the friction process, which was confirmed by electron microscopy studies. Under these friction conditions, the film is continuous, uniform, and smooth and is constantly restored on its worn areas, leading to self-lubrication. When the rotation speed increases up to 8,000 rpm, the composite antifriction properties decrease as the film on the contact surfaces becomes discontinuous. The research allowed operating limits to be determined for applying the new composite and proved the effectiveness of industrial grinding waste in developing high-quality structural materials through a reasoned choice of secondary raw materials, considering the nature of doping elements present in them.
PubDate: 2023-11-20
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- Method of Determining the Liquid Phase Content in the Pelletized Charge
for Producing Compacts with the Maximum Strength II. Development of the
Method-
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Abstract: Researchers of the Nekrasov Iron & Steel Institute, National Academy of Sciences of Ukraine, conduct studies aimed at developing analytical methods for predicting the strength characteristics of pellets. These studies use analyses of phase interaction mechanisms within free-flowing media to develop theoretical ideas on the formation of strong bonds in the pellets through adhesion. This led to the establishment of local models of adhesion processes for two basic particle interaction schemes: ‘particle + particle’ and ‘particle + liquid phase + particle’. Experimental studies undertaken in laboratory premises of the Nekrasov Iron & Steel Institute for the ‘particle + particle’ interaction scheme provided the foundation for a method to determine the strength characteristics of pellets made from fine-grained materials with zero moisture at compaction pressures ranging from 50 to 220 MPa. The first part of the paper justified methodological prerequisites for experiments to study strong bonds within the compacts for the ‘particle + liquid phase + particle’ interaction scheme. The methodological prerequisites accounted for the mechanical, physical, and physicochemical interactions, both between individual particles of the pelletized material and between the charge components (liquid phase). A generalized analysis of the experimental findings allowed evaluating a range of potential adhesion processes for the ‘particle + liquid phase + particle’ interaction scheme, pinpointing their manifestation, examining their nature, and assessing the effect of a liquid phase introduced into the pelletized charge, considering the compaction pressures applied. This paper focuses on experimental findings for the ‘particle + liquid phase + particle’ interaction scheme, establishing analytical relationships between the strength characteristics of pellets and integral indicators of the adhesive bond mechanism in this interaction scheme (in particular, relationship between the bulk density (ρ0) and moisture content (Wm) for materials in the first group of systematization). Additionally, an analytical relationship between the compaction factor for compacts produced at a pressure (P) of 220 MPa (Kcomp220), considering their loosening, and the bulk density of materials (ρ0) in the first group of systematization was established for the first time. Analysis of the findings led to a hypothesis suggesting that the amount of the liquid phase (in particular, water) introduced into the material should be balanced by its potential displacement during compaction to achieve maximum compact strength. Based on the hypothesis, a novel equation was derived to calculate the amount of liquid binder (water) to promote the most favorable conditions for the adhesion processes, thereby imparting the maximum strength to compacts from materials in the first group of systematization. A comparative analysis between the experimental findings and calculations confirmed that the equation was accurate. Consequently, an analytical method was proposed to determine the moisture content needed in the charge to produce compacts with maximum strength from materials in the first group of systematization (ρpycn ≥ 4.64 × × 10–3).
PubDate: 2023-11-20
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- Effect of MoO3 and TiO2 Powder Particle Sizes on the Phase Composition and
Density of Dysprosium Titanate Pellets-
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Abstract: An important process task is to expand the range of raw materials applied for the synthesis of dysprosium titanate (neutron-absorbing material for VVER-1000 reactors) and to establish and optimize methods for producing powders and pellets with characteristics that meet specific technical requirements, primarily those for the density and structural and phase compositions of the materials. The influence of MoO3 doping additions and TiO2 powders with different particle sizes on the density and phase composition of dysprosium titanate (Dy2O3 · TiO2) pellets was experimentally studied. Titanium oxide powders of two grades were used: powder with spherical 10–30 μm particles (OSCh 7-3 grade as per TU 6-09-3811–79) and powder with an average particle size of ~63 nm (China Rare Metal Material Co., China). The nanosized TiO2 powder intensified the sintering of the pellets, which achieved a density of 6.9 g/cm3 and acquired a single-phase hexagonal structure at 1650°C. The coarse TiO2 powder did not promote high density of the sintered pellets, nor did it facilitate complete synthesis of dysprosium titanate since a significant amount of intermediate dysprosium dititanate (Dy2Ti2O7) and initial dysprosium oxide (Dy2O3) remained in the synthesized material. The introduction of MoO3 intensified the sintering of pellets, increased the pellet density up to 6.7 g/cm3, and led to a single-phase cubic structure of pyrochlore type, regardless of the TiO2 powder grade. The simultaneous use of the nanosized TiO2 powder and MoO3 doping addition increased the density of the sintered dysprosium titanate pellets to 7.1 g/cm3 and promoted a single-phase structure of pyrochlore type.
PubDate: 2023-11-18
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- Structure and Distribution of Chemical Elements in the Transition Zone in
Deposited VT20 and VT1-0 Alloy Samples-
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Abstract: Buildup (or additive manufacturing) processes enable the production of components where individual sections can possess distinct chemical compositions tailored to their specific purpose. However, the distribution of elements in the fusion zone and its sizes remain inadequately understood. Samples of VT1-0 and VT20 titanium alloys were fused so that the VT1-0 alloy powder was deposited onto the VT20 cast alloy in one case and the VT20 titanium alloy powder was deposited onto the VT1-0 cast alloy in the other. Regardless of the grain-size and chemical compositions of the powders, the chemical composition of the samples met relevant standards for the alloys. The macrostructures were studied employing a Neophot 32 optical microscope. Minimal porosity was revealed in the samples across all deposition options. Microstructural analysis showed that the deposited material formed a uniform structure both longitudinally and transversely. The microstructure in zones with specific chemical compositions resembled that of the associated as-cast alloys. Variations in the sizes and shapes of structural components were observed toward the powder/cast metal fusion line. A distinct transition zone was found in the fusion of titanium alloys with different chemical compositions. The chemical composition in the longitudinal and transverse sections in the powder/cast metal fusion zone was examined with a scanning electron microscope. The chemical composition was established at different distances from the fusion line. The results showed that the chemical elements redistributed and their contents changed. The presence of zones with altered chemical composition was ascertained by microstructural studies. The distribution of chemical elements was qualitatively assessed and found to be uniform.
PubDate: 2023-11-17
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- Comparative Study of the Structure and Properties of Composite Materials
Produced From Hydroxyapatite Glass Ceramics and Carbon Fibers of Different
Types-
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Abstract: A comparative study of the structure and properties of composite materials produced from biogenic hydroxyapatite/glass/carbon fibers, depending on the type of carbon fibers (activated carbon nanostructured fibers or cellulose fibers), was conducted employing scanning electron microscopy, X-ray diffraction, infrared spectroscopy, Brunauer–Emmett–Teller method, helium pycnometry, and in vitro experiments. The potential to produce a biogenic hydroxyapatite/glass/carbon fiber composite by sintering at 800°C, involving the simultaneous formation of carbon nanostructures during thermal destruction and carbonization of cellulose fibers, was ascertained. This method allows preserving the hydroxyapatite phase in the newly formed biogenic hydroxyapatite/glass/carbon fiber composite and ensures the presence of carbon nanostructures. The microstructure of the composites produced with activated carbon nanostructured fibers is characterized by the presence of these fibers, contrastingly to the composite produced with cellulose fibers, which has more homogeneous microstructure. Moreover, as opposed to cellulose fibers, activated carbon nanostructured fibers in the composite significantly increase (by more than three times) the specific surface area of the material and significantly reduce the particle size. Regardless of the carbon fibers used, the biogenic hydroxyapatite/glass/carbon fiber composites are nanostructured and microporous (pores < 2 nm). The resorption rate of the biogenic hydroxyapatite/glass/carbon (activated nanostructured or hydrated cellulose) fiber composites in the physiological solution within the first two days is significantly higher than that of the starting biogenic hydroxyapatite/glass composites because of changes in the porous structure.
PubDate: 2023-11-17
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- Production of Wear-Resistant Cobalt Alloy Powders
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Abstract: To select and optimize the experimental conditions for producing powders from wear-resistant cobalt alloys, the following methods were tested: gas spraying of the KhTN-37 alloy, centrifugal spraying of the KhTN-61 alloy, cryogenic spraying of the KhTN-61 alloy, and ultrasonic plasma atomization of the KhTN-62 alloy melt. The production of particles in different sizes and shapes, the difference between the experimental values of their sizes, and the potential of using individual size fractions taking into account the industrial production requirements were analyzed and summarized. The gas spraying method used for the KhTN-37 alloy did not yield the required amount of suitable powder and was thus inexpedient. The centrifugal spraying method for the production of KhTN-61 alloy powders was characterized by a significant number of spherical/needle particles formed in the sprayed material, affecting its flowability and complicating sieving. In addition, this method did not reliably protect the sprayed material against oxygen. The cryogenic spraying process for producing KhTN-61 alloy powders turned out to be unsuitable because it changed the chemical composition. The method involving melt ultrasonic atomization turned out to be the most acceptable for producing KhTN-62 alloy powders. It yielded a fine spherical powder with the required particle size. The use of this rapidly hardened powder is promising for the development of wear- and oxidation-resistant surface layers on responsible components of friction units in power equipment, particularly in aircraft structures. The high-temperature wear-resistant alloy powders can be recommended for strengthening and restoring the surfaces of components in friction units in aviation equipment and for additive manufacturing of bulk parts (3D printing), possessing high wear resistance at elevated temperatures.
PubDate: 2023-11-17
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- Improvement of the Bond Strength in Al Laminates via APB Process Using Tin
Particles-
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Abstract: Aluminum metal matrix composites (AMMCs) are a new modern group of composite materials that are becoming more popular in industrial progress. As a solid welding method to fabricate metal matrix composites, accumulative press bonding (APB) is one of the most capable processes. One of the major disadvantages of the APB process is the weak bonding strength. This study utilizes tin (Sn) particles as filler metal to enhance the bonding strength of aluminum laminates. Thus, AA1060 bars with different content of Sn particles (interlayer filler material) were manufactured at various pressing temperatures and APB steps. The peeling test was used to evaluate the bonding strength. It was found that by increasing the number of APB steps, Sn content, and pressing temperature, better bonds of higher strength and quality were generated. The bonding strength was improved to 424 N for a sample fabricated with 15 wt.% of Sn particles at 300°C. Scanning electron microscopy (SEM) was used to examine the peeling surface of Al/Sn composite samples.
PubDate: 2023-11-17
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- Electrocaloric Effect of Sm-Doped 0.5BZT–0.5BCT Lead-Free Ceramics
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Abstract: The use of refrigeration technology is widespread in national security, industrial and agricultural production, biomedicine, and everyday life. High efficiency, environmental friendliness, and low cost make solid-state refrigeration based on electrocaloric effect (ECE) a promising refrigeration technology. Lead-free ferroelectric ceramics (1–x)Ba(Zr0.2Ti0.8)O3–x(Ba0.7Ca0.3)TiO3 (BZT–BCT) are promising materials for electrocaloric refrigeration in the field. In this paper, Sm-doped 0.5BZT–0.5BCT ceramic was fabricated by the conventional solid-state reaction method. The effect of Sm-doping contents (0, 1.0, 2.0, 2.5, and 3.0 mol.%) on the phase structures, dielectric properties, ferroelectricity, and electrocaloric properties of 0.5BZT–0.5BCT ceramics was systematically examined. The results indicate that all ceramics have a pure perovskite structure with no other secondary phase available. High relative densities are observed in all lead-free ferroelectric ceramics and all of the samples show transgranular fracture with no clear grain boundaries seen. The ceramics’ ferroelectric hysteresis loops become thinner as the Sm doping content increases. At that, remanent polarization Pr decreases, indicating that more polar nanoregions (PNRs) are formed in BZT–BCT lead-free ceramics through Sm doping. The increase in Sm doping content resulted in a change in the dielectric permittivity and electrocaloric temperature that first increased and then decreased. The maximum dielectric permittivity is 5,518 when the doping content of Sm is 2.5 mol.% and the maximum electrocaloric temperature change ΔTmax of 0.109 K at 4 kV/mm was obtained when Sm doping content was 2 mol.%. The results show that an appropriate Sm doping is favorable for improving the dielectric, ferroelectric, and electrothermal properties of lead-free ceramics 0.5BZT–0.5BCT.
PubDate: 2023-11-17
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- Microwave Sintering of 3D Printed Composites from Polymers Reinforced with
Titanium Nitride Particles-
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Abstract: The production of intricate samples from polymer–ceramic composites employing fused deposition modeling was studied. The samples were subjected to high-temperature heat treatment in microwave furnaces to yield titanium nitride ceramics. The conditions for making polymer–ceramic materials from polypropylene and titanium nitride powders and 3D printing conditions for associated intricate parts were examined. The TiN–polypropylene composite was produced at a temperature of 190°C through extrusion of a previously prepared homogeneous mixture with a reinforcement content of 10, 20, 40, 46, 50, and 60 vol.% TiN. Using fused deposition modeling, a gear-shaped part made of the polymer–ceramic material was printed. The printed samples with 20 and 40 vol.% TiN were heat-treated in microwave furnaces in air in a carbon black backfill and in a nitrogen flow. Following the heat treatment in microwave furnaces, the samples preserved their initial shape. The composite samples treated in a carbon black backfill in air exhibited a porosity of ~38% and those treated in a nitrogen flow showed a porosity of ~22%. The samples subjected to microwave heat treatment in a carbon black backfill in air underwent sintering and partial oxidation. After microwave heat treatment in a nitrogen flow, the titanium nitride samples showed higher density and bimodal structure with titanium nitride grains varying from several micrometers to 400–200 nm. The microhardness of the samples heat-treated in a carbon black backfill was 6.5–8.5 GPa and that of the samples treated in a nitrogen flow was 16 GPa.
PubDate: 2023-11-17
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- Interaction in the Ni–Sc–Zr Ternary Alloys Along the 77.8 at.% Ni
Section. Electrochemical Properties of the Alloys-
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Abstract: The interaction of Sc2Ni7 and Zr2Ni7 compounds (with C2/m and P63/mmc crystal structures and congruent melting temperatures of 1270 and 1438°C) in the ternary Ni–Sc–Zr system was studied employing physicochemical analysis methods (metallography, X-ray diffraction, differential thermal analysis, and electron microprobe analysis). The section between the compounds was shown to be quasibinary of peritectic type, with peritectic points of 1340 ± 13°C and 14 at.% Sc. At the peritectic temperature, about 10 at.% Zr dissolves in the Sc2Ni7-based phase and about 8 at.% Sc in the Zr2Ni7-based phase. Electrochemical studies conducted through cathodic polarization of the ternary Sc2Ni7 and Zr2Ni7 alloys using a PI-50-1 potentiostat, with a three-electrode electrochemical cell consisting of a working ceramic anode, a platinum cathode, an electrolyte (a 3% NaCl aqueous solution), and a silver chloride Ag/AgCl/KCl reference electrode, did not reveal any tendency to hydrogenation in their solid solutions. The influence of preliminary cathodic reduction of the 77.8 at.% Ni–8 at.% Sc–Zr sample on its subsequent anodic dissolution was determined. The initial surface of the 77.8 at.% Ni–8 at.% Sc–Zr sample was found to be much more resistant to anodic oxidation than the surface preliminary subjected to cathodic reduction because of a significant decrease in its oxide component.
PubDate: 2023-11-17
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- Two Typical Microstructures of Ti–6.6Al–1.7Mo–2.3V–1.9Zr Alloy
Fabricated by Vacuum Hot Pressing of Powders with the Spherical Shape of
Particles-
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Abstract: Two typical microstructures of Ti–6.6Al–1.7Mo–2.3V–1.9Zr (TA15) titanium alloy were successfully fabricated by vacuum hot pressing using TA15 metallic powders of two different sizes with the spherical shape of particles. The size of prior β grains was consistent with the size of the as-received TA15 alloy powder. The microstructure of TA15 alloys differed depending on the size of the initial powder, forming Widmanstätten patterns for the sample from coarse powder or equiaxed microstructure for fine powder. The microstructure evolution during the vacuum hot pressing included solid-state phase transition and powder compact. In the temperature-rise period, the solid-state phase transition occurred (α → β). The anterior β-grain only grew to the original powder interface, which means that it would not coarsen causing its size to exceed that of the original powder. The solid-state phase transition occurred (β → α) when the temperature decreased during the subsequent cooling process. The nuclei of grain boundaries α appeared at the grain boundary of the anterior β-grain. Then the nuclei of grain boundaries α grew together enclosing the anterior β-grain. The grain boundaries α belonged to a certain anterior β-grain and could provide nucleation sites for the α-colonies of the two adjacent anterior β-grains. Finally, the α colonies grew into the anterior β-grain forming the Widmanstätten structure. The two typical microstructures will likely affect the mechanical properties of the TA15 alloys. An improvement in tensile properties was evident in the TA15 alloys (equiaxed microstructure) fabricated from a fine powder compared to their predecessors, consisting of colonies α microstructure fabricated from the coarse powder. To be specific, the tensile strength increased from 849 to 898 MPa and the ductility growth was from 5.5 to 6.5%.
PubDate: 2023-11-17
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- Mechanical and Functional Properties of Composite Coatings with Fine
Reinforcements Produced from Galvanic Processing Waste-
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Abstract: The potential of wastewaters from the galvanic industry treated to remove toxic heavy-metal contaminants for the manufacture of commercial products lies in the development of processes for their reuse. This research addresses the feasibility of employing galvanic waste in the production of powder coatings. Powder waste generated through the resource-saving ferritic method and electroerosion dispersion method is significantly safer for the environment than that generated through reagent methods. Coatings resulting from wastewater treatment exhibit mechanical properties that meet current industry standards. The introduction of 15 wt.% spent polyvalent iron oxide sorbent into paint coatings enhances their mechanical performances. Specifically, the rebound strength increases from 20 to 40 cm/kg and tensile strength from 5 to 7.4 mm, the bending strength decreases from 8 to 5 mm, and the corrosion resistance of the coatings improves by 1.5 times compared to the standard samples. These improvements are attributed to the introduction of chemically and thermally stable crystalline phases possessing ferromagnetic properties into the coatings. As a result, these coatings increase shielding against electromagnetic radiation in the megahertz range by three times compared to the standard coatings. A significant research finding is the potential for reusing ferromagnetic waste from the galvanic industry in specialized materials.
PubDate: 2023-11-16
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- Adsorption of Water Vapors on Magnetite Powders Prepared by Chemical
Precipitation and Thermolysis Methods-
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Abstract: A comparative study of the morphology and physicochemical properties of magnetite synthesized by chemical precipitation for 5 min, 30 min, and 1 h and by thermolysis in nitrogen and hydrocarbon atmospheres was conducted. Regardless of the synthesis method, duration, and atmosphere, the powders were found to have spherical particles, uniform particle size distribution, and ability to agglomerate. The chemical precipitation method produced powders within a narrower size range, specifically up to 56 nm, in contrast to the thermolysis method, characterized by a particle size of up to 84 nm. Gravimetric analysis of the kinetic laws of water vapor adsorption on the synthesized powders in an air flow with a relative humidity ranging from 60 to 100% showed that the adsorption process was most intensive in the initial stage (within 30 min). The adsorption of water vapors and the process speed were significantly influenced by the synthesis method and duration and by the thermolysis atmosphere. Magnetite produced by chemical precipitation exhibited adsorption properties more than an order of magnitude higher than those of the powders produced by thermolysis. This can be attributed not only to the specific surface area but also to the material’s greater affinity for water molecules. A hydrocarbon atmosphere for thermolysis reduced the adsorption properties of magnetite by half compared to nitrogen. This may be associated not only with the potential passivation or catalytic poisoning of the powder surface but also with the influence of the carbon component on the reduction of pore volume and the promotion of magnetite adsorption capacity for polar molecules of the gaseous water phase.
PubDate: 2023-11-14
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- Enhanced Study of Magnetic Properties of Polyvinyl Alcohol-Coated
Superparamagnetic Iron Oxide Nanoparticles Below Blocking Temperatures-
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Abstract: Superparamagnetic iron oxide nanoparticles (SPIONs) coated with the synthetic hydrophilic biocompatible polymer polyvinyl alcohol were synthesized using the aqueous method. Static and dynamic magnetization processes were investigated for surface-modified SPIONs by analyzing the magnetization study at constant and varying magnetic fields. The magnetization on the applied magnetic field (M–H) and the magnetization dependent on temperature (M–T) were investigated. The temperature dependence of the complex susceptibility of SPIONs was investigated by measuring the in-phase (natural) and out-of-phase (imaginary) components of the susceptibility value at a frequency of 10 Hz and a very low magnetizing field. The XRD study shows diffraction peaks consistent with the magnetite (Fe3O4) phase of SPIONPs. FTIR, DSC, and TGA studies confirm the functional groups and stability of the coated nanoparticles. The magnetizing field cycle study at various constant temperatures (10, 100, and 300 K) shows the high magnetization value of polyvinyl alcohol-coated SPIONs with superparamagnetic states at and above 300 K. The effect of interparticle interaction on blocking temperature has been interpreted from FC/ZFC curves drawn at different DC magnetizing field values by varying temperature between 10 and 300 K.
PubDate: 2023-10-20
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- Generalized Method for Normalizing the Degree of Thixotropy/Rheopexy to
Evaluate the Structure of Powder Suspensions-
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Abstract: The structure of suspensions used to apply films by colloidal methods determines their key properties: thickness, surface roughness, and density. Direct structural studies of thin suspensions are significantly complicated, especially when the task is to determine changes in the structure induced by mechanical loads present in the film development process. This problem can be addressed through rheological studies. For this purpose, a method for normalizing the degree of thixotropy/rheopexy was devised to serve as a quantitative parameter for evaluating the structure of fluids based on their rheological properties. The trapezoidal integration method for calculating the flow curve area was demonstrated. The developed normalization method relies on a modified standard score equation that accommodates the peculiarities of flow curves. The normalized degree of thixotropy/rheopexy was employed to assess the structures of suspensions with identical compositions but subjected to varying maximum shear rates (200, 500, and 800 sec–1) to plot the flow curves. The nonnormalized degrees of thixotropy for these suspensions differed by 11 to 12 times. The developed parameter allowed the deviation to be reduced to 16–19%. The normalized degree of thixotropy/rheopexy, along with the flow behavior index and effective viscosity, was used for the indirect evaluation of structural changes in suspensions with higher nanopowder content based on the rheological properties. This approach enabled the identification of four structural states of suspensions: isolated agglomerates, enlargement of the agglomerates accompanied by rheopectic flow, transition to Newtonian flow after the agglomerates deformed in the flow direction, and evolution of a regular network structure signified by thixotropic flow.
PubDate: 2023-10-17
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- Complex Permittivity in the AlN–SiC Composite in the 1–100 GHz
Microwave Frequency Range-
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Abstract: The dependences of the real and imaginary parts of complex permittivity in AlN–SiC composites, with a silicon carbide content ranging from 20 to 50%, are characterized over a frequency range of 1–100 GHz. The SiC particles have average sizes of 0.8 and 2.3 μm. As the frequency increases from 1 to 100 GHz, the general trend shows a consistent decrease in the real part ε′ in inverse proportion to the frequency raised to the 1/5 power. The imaginary part ε″ first increases in direct proportion to the frequency raised to the 1/2 power when the frequency raises from 1 to 3 GHz, reaches its maximum in the 6–8 GHz range, and then monotonically decreases in inverse proportion to the frequency raised to the 1/5 power at frequencies greater than 8 GHz. Throughout the entire frequency range, ε′ and ε″ are found to be frequency-dependent. However, at frequencies above 8 GHz, the ε″ / ε′ = tgδ ratio remains constant and is not frequency-dependent. Analytical expressions are proposed for these dependences, allowing ε′ and ε″ to be calculated at any frequency within this range. To plot these dependencies, at least one experimental data point with reliable ε′ and ε″ values should be obtained, preferably between 2 and 5 GHz. This is particularly important for ε″, as it changes uniquely over the 1–10 GHz frequency range. To specify ε″ values at frequencies below 8 GHz, two methods are proposed. The first method employs geometric construction of the inscribed circle for ε″ as a function of frequency, enabling rapid determination of ε″ in the 4–8 GHz frequency range for AlN–SiC composites containing 20 to 50% SiC. The maximum deviation from true ε″ does not exceed 3%. The second method involves calculated parabolas, also inscribed in the frequency dependence of ε″. Over the 6–8 GHz range, the deviation of ε″ does not exceed 3% for SiC contents below 40%.
PubDate: 2023-10-17
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- Method of Determining the Liquid Phase Content in the Pelletized Charge
for Producing Compacts with Maximum Strength I. Experimental Study-
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Abstract: The development of analytical methods for predicting the strength characteristics of pellets produced by the compaction of fine-grained materials remains a significant and relevant area. To advance this area, the mechanisms of phase interactions in bulk media were analyzed. The analysis was then used to develop local models of adhesion processes for two basic particle interaction schemes: ‘particle + particle’ and ‘particle + liquid phase + particle’. For each local model, the types, nature, and combination of adhesion processes that occurred simultaneously were theoretically established, and the factors and indicators that determined the occurrence and intensity of adhesive bonding were justified. The experimental studies conducted in the laboratory premises of the Nekrasov Iron and Steel Institute of the National Academy of Sciences of Ukraine were analyzed to evaluate the nature and extent of influence exerted by the selected factors, determining the adhesion processes, on changes in the strength characteristics of compacts. Considering the results obtained and the analytical dependences established for the ‘particle + particle’ interaction scheme, a method for predicting the strength characteristics of pellets produced from fine-grained materials with zero moisture was developed. This paper justifies the methodological conditions for experiments intended to create strong bonds within the compacts under the ‘particle + liquid phase + particle’ interaction scheme, taking into account the mechanical, physical, and physicochemical interaction processes between individual particles of the pelletized material and between the charge components (liquid phase). A generalized analysis of the experimental findings was carried out to estimate the range of potential adhesion processes inherent in the ‘particle + liquid phase + particle’ interaction scheme, identify their manifestation, study the nature of their interaction, and evaluate the effect of introducing the liquid phase into the pelletized charge, considering the applied compaction pressures. The collected array of experimental data will enable a detailed cross-correlation analysis to determine the influence of various factors on the adhesion processes and the formation of strong bonds within the compacts. The analysis will also help establish the dependence of strength characteristics of compacts on integral indicators contributing to the formation of adhesive bonds and describe the dependence by analytical methods. The results will be used to develop a method to determine the moisture content in the charge required to produce compacts with maximum strength from materials that belong to the first of the four groups of systematization. The classification of materials into specific groups of systematization is determined by their pycnometric density.
PubDate: 2023-10-16
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- Interaction of Lanthanum, Yttrium, and Gadolinium Oxides at 1600°C
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Abstract: Phase equilibria and structural transformations in the La2O3–Y2O3–Gd2O3 system at 1600°C were studied by X-ray diffraction, electron microscopy, and petrography in the entire composition range. Fields of solid solutions based on hexagonal (A) modification of La2O3, cubic (C) modification of Y2O3, and monoclinic (B) modification of La2O3 (Gd2O3) were identified in the system. The starting materials were La2O3, Gd2O3, and Y2O3 (99.99%) powders. Samples were prepared with concentration steps of 1–5 mol.%. Weighed portions of the oxides were dissolved in HNO3 (1 : 1) solutions. This was followed by evaporation of the solutions and decomposition of the nitrates at 800°C for 2 h. The samples were heat-treated in three stages: 1100°C (168 h), 1500°C (70 h), and 1600°C (10 h) in air in furnaces with FeCrAl (H23U5T) and molybdenum disilicide (MoSi2) heating elements. X-ray diffraction analysis was carried out using the powder method with a DRON-3 diffractometer at room temperature (Cu-Kα radiation). The scanning step was 0.05–0.1° at angles 2θ = 15–90°. The isothermal section of the La2O3–Y2O3–Gd2O3 phase diagrams at 1600°C was characterized by three single-phase (A-La2O3, B-La2O3 (Gd2O3), C-Y2O3) and two two-phase (A + B, B + C) regions. The solubility limits were determined, and composition dependences of the lattice parameters for the phases formed in the system were plotted. No ordered perovskite-type phase was found in the system at 1600°C. A continuous series of solid solutions based on the monoclinic modification of B-La2O3(Gd2O3) formed in the system and occupied the largest area of the isothermal section. Yttrium oxide stabilized the total mutual solubility of lanthanum and gadolinium oxides. With the addition of heavier ions, the lattice parameters of the B modification reduced and the lattice volume and, accordingly, density increased. The lattice of solid solutions based on the B modification of rare-earth metal oxides became more densely packed with a higher concentration of yttrium oxide.
PubDate: 2023-10-16
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- Influence of Deformation Temperature on the Formation of Contacts in
Titanium Powder Ribbons Produced by Symmetric and Asymmetric Rolling-
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Abstract: The influence of various rolling methods on the mechanical properties of titanium ribbons was studied. Ribbons produced by asymmetric rolling showed 100% density and higher strength compared to ribbons produced through symmetric rolling. The temperature sensitivity of contact formation and mechanical behavior of ribbons rolled asymmetrically was determined by thermal variations in the plastic deformation mechanisms specific to titanium. In this regard, three temperature ranges were identified: low, intermediate, and high. In the low-temperature range (<100 °C), the elastic modulus and proportionality limit were significantly higher than those from symmetric rolling, although still inferior to the properties of the compact material. In the intermediate-temperature range (100–300°C), the elastic modulus and proportionality limit in the rolling direction matched those of compact titanium but were approximately three times greater than those found for samples tested transversely. In the high-temperature range (>300°C), the elastic modulus in both longitudinal and transverse directions was comparable to that of the compact material, while the proportionality limit surpassed the compact material significantly, owing to the deformation substructure observed in the ribbons. Asymmetric rolling significantly enhanced the mechanical properties of titanium ribbons compared to symmetric rolling. This enhancement was due to the shear strain component that facilitated contact formation at particle boundaries. Under optimal deformation conditions, the ribbons achieved a strength limit of ~800 MPa, comparable to the strength of ribbons produced conventionally. The plasticity of the ribbons did not exceed 1.5% because of their propensity for interparticle fracture.
PubDate: 2023-10-16
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