Density Composition Research Articles

Development of two-layer whisker-reinforced PcBN materials for cutting tool applications

This study investigates the polycrystalline cubic boron nitride (PcBN) tool materials with a TiN-Zr based binder without additives (BTZ base material) and with whisker additives (SiCw, Al2O3w, Mg2B2O5w) obtained via high-pressure high-temperature (HPHT) sintering at 7.7 GPa and 2000 °C. The whiskers reinforced composite compacts were produced both in one- and two-layer (sandwich-type) forms. The phase composition, microstructure, physical-mechanical properties and cutting performance of the composite compacts were analysed. The results demonstrate that reinforcing with SiCw leads to the formation of BTZ+SiCw composites with a homogeneous microstructure, high hardness, and Young's modulus, enabling the manufacture of one-layer cutting inserts with an extended tool life of up to 11 min when turning Inconel 718 alloy. Similarly, the BTZ+Al2O3w one-layer material, despite exhibiting slightly lower hardness compared to BTZ+SiCw, still displayed satisfactory wear resistance with a tool life of up to 7 min. Notably, the two-layer (sandwich type) s1: BTZ+SiCw/BTZ+Al2O3w composite cutting inserts exhibited the highest durability, with a tool life of up to 13 min when tested on the SiCw-reinforced side and 8 min on the Al2O3w-reinforced side. In contrast, the BTZ+Mg2B2O5w composite was found unsuitable as a working tool component but shows promise as a substrate layer in two-layer configurations. The study indicates the potential for further development of whisker-reinforced two-layer composite PcBN materials to enhance tool performance and longevity.

Non-exchange bias hysteresis loop shifts in dense composites of soft-hard magnetic nanoparticles: New possibilities for simple reference layers in magnetic devices

Exchange bias has been extensively studied in both exchange-coupled thin films and nanoparticle composite systems. However, the role of non-exchange mechanisms in the overall hysteresis loop bias is far from being understood. Here, dense soft-hard binary nanoparticle composites are used not only as a novel tool to unravel the effect of dipolar interactions on the hysteresis loop shift but also as a new strategy to enhance the bias of any magnet exhibiting an asymmetric magnetization reversal. Mixtures of equally sized, 6.8 nm, soft maghemite (γ-Fe2O3) nanoparticles (no bias—symmetric reversal) and hard cobalt doped γ-Fe2O3 nanoparticles (large exchange bias—asymmetric reversal) reveal that, for certain fractions of soft particles, the loop shift of the composite can be significantly larger than the exchange-bias field of the hard particles in the mixture. Simple calculations indicate how this emerging phenomenon can be further enhanced by optimizing the parameters of the hard particles (coercivity and loop asymmetry). In addition, the existence of a dipolar-induced loop shift (“dipolar bias”) is demonstrated both experimentally and theoretically, where, for example, a bias is induced in the initially unbiased γ-Fe2O3 nanoparticles due to the dipolar interaction with the exchange-biased hard nanoparticles. These results open a new paradigm in the large field of hysteresis bias and pave the way for novel approaches to tune loop shifts in magnetic hybrid systems beyond interface exchange coupling.

Effect of synthesis pressure on the properties of PcBN composites

Polycrystalline cubic boron nitride (PcBN) composites were synthesized under high-temperature and high-pressure (HPHT) conditions using TiC, Al and Ti as binders. This study explores the influence of varying synthesis pressures on the microstructure, interfacial bonding, densification, and mechanical properties of PcBN composites. The test results indicate that as synthesis pressure increased, the diffusion of Al and Ti elements to the surface of cBN particles was enhanced. This facilitates the migration of Ti atoms through the Al-rich matrix to the surface layer of cBN, thus accelerating the chemical interaction. At the highest pressure of 6 GPa, the hardness, flexural strength and fracture toughness of the samples achieved their maximum values: 3719 Hv, 1090 MPa, and 7.6 MPa.m1/2, respectively. Additionally, the material exhibits excellent cutting properties. Crack bridging, crack deflection, particle pullout and transgranular fracture were observed during the fracture process of the samples. Indicating strong interfacial bonding between cBN and the binder, which contributes to the material's enhanced toughness.

Simulation of the Die and Punch Behavior During the Compaction Process of Alumina-Based Matrix Composite Using Finite Element Analysis

Background: Compaction in the powder metallurgy process typically involves using a die and punch, applying high pressure to mixed powder to achieve product quality, such as geometry, density, and porosity. This step is critical in the powder metallurgy process. Objective: This study aims to systematically design and manufacture a die and punch for compacting an Alumina-based matrix composite. Specimens were selected according to ASTM C 1421-10 guidelines, and the die and punch were constructed using AISI D3 tool steel alloy. Methods: To ensure satisfactory compaction, the design underwent virtual testing using Finite Element Analysis (FEA) with compaction loads ranging from 2.5 to 20 tons in 2.5-ton increments. The simulation results were validated through experimental testing. Results: The die parts were analyzed for three-dimensional stress and deformation during compaction. Maximum stress distribution was observed in the Alumina powder, followed by the punch, plate, and die. Additionally, compaction behavior and density tests confirmed that a compaction pressure of 548 MPa or more results in high relative density in the Alumina-based matrix composite powder during the compaction process. Conclusion: Both simulation and experimental results indicate that a compaction pressure of 548 MPa or more is necessary to achieve satisfactory compaction of the Alumina-based matrix composite. These findings offer practical implications for optimizing the powder metallurgy compaction process and reducing costs.

Fracture behavior of brittle particulate composites consisting of a glass matrix and glass or ceramic particles with elastic property mismatch

The aim of this work is two-fold: i) elaborating dense and transparent inorganic glass composites with improved fracture properties, and ii) testing the theoretical analysis proposed in [1] and based on Poisson's ratio mismatch. Particulate composites, consisting of glass or ceramic particles embedded in a soda-lime-silica glass matrix, were synthesized and their fracture behavior was studied by means of the Single Edge Precraked Beam (SEPB) and Double Cantilever Drilled (DCDC) methods, using in situ experiments with X-ray tomography where possible. An important effect of the T-stress on the fracture toughness (KIc) was observed in the case of DCDC exdperiments. KIc is increased by about 40 % by incorporating 7 vol. % amorphous silica beads or SrAl2O4:Eu,Dy ceramic particles (SAED) with a 40 μm mean particle size. It is suggested that toughening results from the crack front trapping and pinning at particle sites and from the tortuous crack path in the case of a-SiO2 particles, and from the contribution of the intrinsic fracture surface energy of the ceramic particles, which are cleaved by the propagating crack, in the case of the SAED particles. The thermally induced stress field is believed to play a major role in the case of a-SiO2 particles. Two glass grades possessing Young's moduli similar to the one of the matrix but much larger Poisson's ratios were used to produce glass beads. However, the incorporation of these latter beads in the matrix was found to have a minor incidence on the fracture behavior.

Microstructural analysis and prediction of strength response of black expansive soil

Amelioration studies using waste residues are gaining popularity in the construction sector, as they offer dual effective management and utilization of waste residue. This practice is of interest to the growth of any nation due to environmental protection and the economic advantages it offers. For that reason, this present-day study seeks the sustainable utilization of calcium carbide residue (CCR) and palm oil fuel residue (POFR) in expansive soil amelioration. After an in-depth characterization of the parent soil, several number of California bearing ratio (CBR) tests was performed on the parent and additive-treated soil. For this purpose, a total of twenty mixes were prepared possessing various combinations of CCR, POFR, water, and soil. CBR testing for soaked and unsoaked conditions was carried out to assess the strength performance and effectiveness of the additives. Through this approach, optimal California bearing ratio (CBR) values of 41 and 61% were achieved at trial runs designated Y4 for soaked and unsoaked conditions, indicating a strong mechanical performance. These experimental outcomes were subsequently validated using statistical indicators such as ANOVA (F crit > F) and student t-test (t crit > t stat). A step further, microstructural testing such as transmission electron microscopy (TEM), scanning electron microscopy (SEM), and Fourier transform infrared spectroscopy (FTIR) were performed on the natural soil and soil treated with the optimal level of additives obtained at trial runs designated Y4. The SEM micrographs evidence the transformation of the loosely packed structure of untreated soil into a dense soil composite. Similarly, diverging molecular functional groups were recorded in the FTIR examination with the incorporation of blended CCR-POFR. Finally, the findings suggest that carefully designed mixtures of CCR and POFR can offer a sustainable, efficient approach to soil amelioration, potentially revolutionizing construction practices.

Evaluation of the dielectric, and piezoelectric properties and optimizing the figure of merit of the 0–3 KNN-0.8ZnO/PVDF-HFP piezoelectric composite by the Taguchi method

Piezoelectric ceramic and composite materials are attractive for various applications, but they can be challenging to process. In this research, KNN-0.8ZnO with high density (ρth=95 %), favorable microstructure, and suitable dielectric and piezoelectric properties (K=875, d33=125 pC/N, tanδ=0.01) was first synthesized. Additionally, polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP) copolymer, known for its advantageous piezoelectric and mechanical properties, was selected as the polymer phase. subsequently, the KNN-0.8ZnO/xPVDF-HFP composite samples with a 0–3 connectivity pattern were made with the cold sintering method. The Taguchi design of experiment (DOE) was employed to determine the optimal condition for maximizing the figure of merit (FOM). Furthermore, an analysis of variance (ANOVA) was carried out to evaluate the significance of individual factors on each measured property. Phase identification was performed using X-ray diffraction (XRD) analysis, while the microstructure was examined using scanning electron microscopy. Among the different composite samples fabricated using the L9 orthogonal array (OA) of the Taguchi method, the KNN-0.8ZnO/20PVDF-HFP composite containing 20 wt% polymer phase, that was cold-sintered under a pressure of 400 MPa at 200 ͦC for 2 h, exhibited the highest FOM value of 1.945Pm2/N. This result aligns with the optimal conditions predeicated by the Taguchi DOE method. The compressive strength of the KNN-0.8ZnO/20PVDF-HFP composite was assessed through a compression test, yielding a value of 207 MPa, while the elastic modulus was approximately 3 GPa. The findings of this study demonstrate that the cold sintering method is an effective approach for producing dense piezoelectric composites with favorable electrical and mechanical properties, along with a high FOM for energy harvesting applications.

Mechanical, Corrosion and Wear Characteristics of Cu-Based Composites Reinforced with Zirconium Diboride Consolidated by SPS

This study aimed to investigate the physical, mechanical, corrosion, and tribological properties of Cu-based composites with varying zirconium diboride content. The composites were successfully consolidated using spark plasma sintering (SPS) at temperatures of 850 °C and 950 °C and a pressure of 35 MPa. The effect of the ZrB2 content and the sintering temperature on the properties of the Cu-based composites was investigated. Scanning electron microscopy (SEM), electron backscatter diffraction (EBSD), and X-ray diffraction were used to analyse microstructure evolution in copper matrix composites. Microhardness tests were used to evaluate mechanical properties. Wear behaviour was evaluated using a ball-on-disc method. Corrosion properties were estimated on electrochemical tests, such as potentiodynamic polarisation. The results demonstrated an enhancement in the density and porosity of the composites as the sintering temperature increased. A uniform dispersion of ZrB2 was observed in the copper matrix for all composites. With an increase in the content of the ZrB2 reinforcement phase, there was an increase in microhardness and an improvement in the wear resistance of the sintered composites. A reduction in densification and corrosion resistance of Cu-based composites was observed with increasing ZrB2 content.

Relaxor-like behavior of the dielectric response of dense ferroelectric composites

We study experimentally and theoretically the influence of size effects and structural factors on the dielectric and ferroelectric properties of the dense ferroelectric composites. The composites have the form of the tape-casted films with 28 vol% of nanosized or submicron BaTiO3 particles dispersed in the polyvinyl butyral. We measured and analyzed the temperature dependences of the capacitance and dielectric losses in the temperature range (−200 – +200)oC and frequency range (102–105) Hz. The nonmonotonic temperature dependences of dielectric permittivity of the studied composite films have a wide plateau-like maxima located between 80oС and 160oС, in contrast to the relatively sharp maximum near the Curie temperature (∼124oC) observed in the fine-grained and coarse-grained ceramics, sintered from the same nanosized or submicron BaTiO3 particles at 1250oC. The shift of the dielectric permittivity and losses maxima (in more than 40oC) and their strong frequency dispersion do not agree with the behavior expected for the systems with a weak interaction between ferroelectric particles and a polymeric matrix. In contrast, we reveal the relaxor-like behavior of the composite dielectric response. To explain the observed results, we propose the analytical model, which considers the strong dipole-dipole cross-interaction of the BaTiO3 particles in the dense nanocomposite. The analytical model is corroborated by the structural studies of the BaTiO3 nanosized and submicron particles by X-ray phase analysis and static 137Ba NMR spectra, as well as by the finite element modelling of the composite polar properties, which confirms the strong cross-interactions between the dipole moments of single-domain nanoparticles and/or between the domain walls of different submicron polydomain particles.The obtained results may be useful for development of cheap and flexible lead-free dense ferroelectric nanocomposites with relaxor-like behavior of the dielectric response, which are promising for non-volatile memory and energy-saving elements, modulators, electrical converters and piezoresistive elements.

Pseudo-Core-Shell Permalloy (Supermalloy)@ZnFe2O4 Powders and Spark Plasma Sintered Compacts Based on Mechanically Alloyed Powders.

Soft magnetic composite cores were produced by spark plasma sintering (SPS) from Ni3Fe@ZnFe2O4 and NiFeMo@ZnFe2O4 pseudo-core-shell powders. In the Fe-Ni alloys@ZnFe2O4 pseudo-core-shell composite powders, the core is a large nanocrystalline Permalloy or Supermalloy particle obtained by mechanical alloying, and the shell is a pseudo continuous layer of Zn ferrite particles. The pseudo-core-shell powders have been compacted by SPS at temperatures between 500-700 °C, with a holding time of 0 min. Several techniques were used for the characterisation of the powders and sintered compacts: X-ray diffraction, scanning electron microscopy, energy dispersive X-ray spectroscopy, magnetic hysteresis measurements (DC and AC), and electrical resistivity. The electrical resistivity is stabilised at values of about 7 × 10-3 Ω·m for sintering temperatures between 600-700 °C and this value is three orders of magnitude higher than the electrical resistivity of sintered Fe compacts. The best relative initial permeability was obtained for the Supermalloy/ZnFe2O4 composite compacts sintered at 600 °C, which decreases linearly for the entire frequency range studied, from around 95 to 50. At a frequency of 2000 Hz, the power losses are smaller than 1.5 W/kg. At a frequency of 10 kHz, the power losses are larger, but they remain at a reduced level. In the case of Supermalloy/ZnFe2O4 composite compact SPS-ed at 700 °C, the specific power losses are even lower than 5 W/kg. The power losses' decomposition proved that intra-particle losses are the main type of losses.

Silicon oxycarbide composites reinforced with silicon nitride and in situ formed silicon carbide

Dense SiOC-Si3N4 composites have been obtained employing mixtures with 10 % of Si3N4 (SN10) or 5 % Si3N4- and an extra amount of carbon-5 % carbon nanofibers- (SN5N5) using spark plasma sintering (SPS). SPS produces densification at 1300/1400 °C and delays the carbothermal reaction of SiO2/Si3N4 up to 1600 °C. It is observed the formation of a percolating network of SiC nanodots/nanowires widespread all over the matrix decorated with graphene-like carbon generated by Joule heating during SPS. The evolution of the Cfree is studied by conventional/non-conventional Raman parameters. In this sense, SN5N5–16 and SN10–17 show a Cfree phase composed by large highly tortuous and ordered graphene layers with the highest degree of interconnection and crystallinity determinant for understanding the highest thermal and electrical conductivities (1.91 WmK−1 and 33.6 Sm−1). Finally, this material displays a low coefficient of thermal expansion (1.26×10−6 K−1), remarkable resistance against oxidation to 1400 °C and high absorptance (95.8 %).

Preparation of Soft Magnetic Composite Using Cold Sintering Technique

Soft magnetic composites are powder metal products under development as an alternative to 2D laminates in electric motor applications. The 3D design of SMCs offers greater energy efficiency but poses a challenge to maintain adequate strength properties required for application. Soft magnetic composites are fabricated through compaction and heat treatment of iron particles coated with insulated coating to form a dense compact. The soft magnetic properties of the compact are affected by the properties of the iron powder, density of compact as well as the efficacy of forming uniform thin insulating coating at the particle boundary. Additionally, the strength of the compact is also affected by the nature of the insulating boundary at the particle interfaces. We report a low temperature process that involves cold sintering phenomenon to densify and strengthen soft magnetic composites. Iron powders have been modified using a co-precipitation method that forms a hydrated copper/iron oxalate coating on individual iron particles. Warm compaction of the modified iron powders at 100°C resulted in a highly dense soft magnetic composite which demonstrated ~ 3x improvement in strength. The compacts can be further heat treated in air at higher temperatures to form high strength oxide coating iron based soft magnetic composites. Results of the AC and DC magnetic measurements of fabricated cold sintered toroid compacts made as a function of heat treatment temperature reveal that DC permeability increased with heat treatment temperature. Analysis of AC core loss data showed that hysteresis power losses dominated the performance at lower heat treatment temperatures (< 300°C) beyond which dynamic core losses significantly increased.

Synergistic effect of YAG particulate reinforcement on microstructural and thermo-mechanical properties of pressureless sintered MgAl2O4 spinel ceramic composites

Yttrium aluminum garnet (YAG) powders, synthesized through a partial wet chemical process, exhibit controlled morphology, high phase purity, and uniform homogeneity etc. This process involves the precipitation of aluminum ions onto Y2O3 particles. The transformation process of the Al-compound/Y2O3 precursor structure leads to the direct crystallization of pure YAG at 900 °C, passing through an intermediate stage where hexagonal YAH phase forms. A comprehensive study was conducted on the impact of preformed YAG as a reinforcing phase on the densification, mechanical, and thermo-mechanical properties of MgAl2O4-YAG composite, sintered under pressureless sintering in temperature range of 1500 °C–1600 °C. The inclusion of YAG particulate up to 5.0 wt% significantly enhances the densification, hardness, fracture toughness, flexural strength and high-temperature mechanical behavior of magnesium aluminate spinel (MAS) ceramics, however, increasing the YAG content beyond 5.0 wt% causes a reduction in these properties. The optimized addition of YAG particulate contributes to reducing the average grain size and refining the microstructure of the spinel ceramic matrix.

In situ oxidative growth to form compact TiO2–Ti3C2 heterojunctions for photocatalytic hydrogen evolution

Solar photocatalytic hydrogen production shows promise in addressing global energy and environmental concerns. The limited efficiency of photocatalysts is mainly due to ineffective separation and transfer of photogenerated charges. To improve this, we enhance the TiO2–Ti3C2 heterojunction by in-situ oxidation through interfacial engineering, resulting in a more compact composition. Subsequently, we anchor single-atom Pt at the TiO2–Ti3C2 interface through photo-Ti3C2 reduction. The in-situ growth of TiO2 on Ti3C2 introduces an interfacial driving force for carrier separation and provides a channel for electron transfer from TiO2 to Ti3C2. This further facilitates transfer onto Pt, shortening the migration distance and enhancing the photocatalytic efficiency. The best Pt/TiO2–Ti3C2 composite demonstrates an impressive hydrogen precipitation efficiency of 767 μmol g−1 h−1, surpassing TiO2 and Pt/TiO2 by factors of 12 times and 1.46 times, respectively. Furthermore, we developed a higher efficiency photocatalyst using the molten salt method to avoid the risks associated with conventional hydrofluoric acid etching. This research opens up new possibilities for the preparation of MXenes interface-modified catalysts, offering a valuable avenue for future exploration in the field.

Ultrafast fabrication of W/Cu composites using flash sintering

When the proportion of reinforcing phases is high and the wettability between the secondary phase and the metal is poor, preparing fully dense particle-reinforced metal matrix composites becomes challenging. This study employs the flash sintering method to prepare fully dense WCu20 composite materials within a few tens of seconds. It is found that during the “thermal runaway' process of flash sintering, the Cu phase undergoes rapid melting and solidification, and the core mechanism of material densification is that pressure causes Cu liquid to quickly fill the gaps between tungsten particles. Pressure not only promotes the contraction of the framework formed by tungsten particles but also facilitates the complete filling of gaps within the tungsten frameworks by the Cu liquid and promotes the rapid expulsion of bubbles from the Cu liquid, thereby achieving rapid densification of WCu20 composite materials. Moreover, an increase in the temperature enhances the fluidity of the Cu liquid, which aids in filling the gaps between tungsten particles and promotes the discharge of bubbles from the Cu liquid. Flash sintering is a common technique for the sintering and densification of metal powders, suitable for the rapid preparation of various metal matrix composites.

Development of pyrargyrite Ag3SbS3 absorber films through sulfurization of Ag–Sb stacks for thin-film photovoltaics

Pyrargyrite Ag3SbS3, which consists of naturally abundant and non-toxic elements, has attracted attention as a promising solar cell material. A two-stage fabrication method has been developed to synthesize Ag3SbS3 thin films through a solid-state reaction between Sb and Ag metallic layers by sulfurizing at 250–350 oC. The Ag3SbS3 film prepared at a sulfurization temperature of 250 °C contained Ag2S and Sb2S3 secondary phases with non-stoichiometric composition, distinct grain growth, a bandgap energy of 1.4 eV, and an electrical resistivity of 5.74 × 10−4 Ω cm. Through sulfurization of the stacks at 300 °C, the Ag2S and Sb2S3 secondary phases disappeared, and dominant Ag3SbS3 films were obtained with a minor AgSbS2 secondary phase. A compact and uniform near-stoichiometric Ag3SbS3 composition with large grains was obtained with an increased bandgap energy of 1.64 eV and electrical resistivity of 6.19 × 104 Ω cm. A further increase in the sulfurization temperature to 350 °C resulted in an increase in the crystallite and grain sizes of Ag3SbS3 with a decreased bandgap energy of 1.62 eV and electrical resistivity of 2.90 × 104 Ω cm. AgSbS2 remained as a minor secondary phase in this film. Thin-film solar cells prepared with the Ag3SbS3 absorber synthesized at a sulfurization temperature of 300 °C exhibited an open-circuit voltage of 473.85 mV, short-circuit current density of 1.47 mA/cm2, fill factor of 41.6 %, and an efficiency of 0.3 %. These results demonstrate that Ag3SbS3 is a potential candidate for thin-film solar cells.

Study on the Corrosion Resistance Of Thermal Sprayed Aerospace Coatings Under The Action Of High Current Pulsed Electron Beam

Aluminum-based amorphous alloys have excellent mechanical properties and corrosion resistance and are currently used in the form of coating materials for the protection of aircraft surfaces. In this study, AlCoCe alloy and powder are prepared, and then AlCoCe alloy coating is prepared on Q235 substrate by supersonic flame thermal spraying technology, and finally, the surface remelting modification treatment is carried out on the coating by current pulsed electron beam, and the transformation behavior of microstructure of the coating and the change of the corrosion resistance in this process are analyzed by structural characterization and corrosion experiment, to make clear the relationship between the structure of the coating and its corrosion resistance performance. After 15 current pulsed electron beam pulses, the coating surface formed a layer of dense and homogeneous composition of the amorphous structure of the treatment layer, when the number of pulses is higher, due to the heat of the substrate leads to a decrease in the cooling rate, which in turn will lead to the emergence of a crystalline structure of the surface treatment layer.

Effects of hot extrusion on compressive strength and densification of aluminium-based metal matrix composites

ABSTRACT Metal matrix composites (MMC) made from powder metallurgy (PM) require post-processing to improve the mechanical properties or achieve the final shape. In this experimental study, Aluminium metal matrix composite (Al-MMC) was first fabricated through PM, followed by a hot extrusion process to study the effects of extrusion on compressive strength and density. Hot extrusion of Al-MMC results in microstructure refinement, enhanced dispersion of reinforcement particles and improved mechanical properties. The experimental findings revealed that hot extrusion of Al-MMC resulted in densification, reflected as an average improvement of 5% in the density. An average improvement of up to 22% was observed in the compressive strength of the Al-MMC. Therefore, hot extrusion can be considered an effective post-processing method for enhancing the Al-MMC fabricated through PM. It was also found experimentally that the extrusion ratio also affects the mechanical properties and performance of Al-MMC. It was revealed that the compressive strength is enhanced with an increase in extrusion ratio. It is also important to note that the PM process is one of the processes which offers reasonable control over the utilisation of starting material. Hence, reinforcement retention is higher than other methods like stir casting.

Modeling of Chemical Vapor Infiltration for Fiber-Reinforced Silicon Carbide Composites Using Meshless Method of Fundamental Solutions

In this study, the Method of Fundamental Solutions (MFSs) is adopted to model Chemical Vapor Infiltration (CVI) in a fibrous preform. The preparation of dense fiber-reinforced silicon carbide composites is considered. The reaction flux at the solid surface is equal to the diffusion flux towards the surface. The Robin or third-type boundary condition is implemented into the MFS. From the fibers’ surface concentrations obtained by MFS, deposition rates are calculated, and the geometry is updated at each time step, modeling the pore filling over time. The MFS solution is verified by comparing the results to a known analytical solution for a simplified geometry of concentric cylinders with a concentration set at the outer cylinder and a reaction at the inner cylinder. MFS solutions are compared to published experimental data. Porosity transients are obtained by a combination of MFSs with surface deposition to show the relation between the initial and final porosities.

Utilization of waste face masks to reinforce magnesite mine tailings for sustainable subgrade construction

The disposal of magnesite mine tailings (MMT), a by-product of magnesite mining, raises significant environmental concerns due to its adverse effects on soil, water and air quality. Likewise, the improper disposal of used face masks exacerbates environmental burdens. The innovative use of polypropylene fibres (PPF) derived from disposable face masks to reinforce. This study explores the compaction and strength characteristics of PPF-MMT composites with varying fibre content to develop a sustainable composite for subgrade construction. The findings indicate that the addition of PPF increases optimal moisture content and decreases maximum dry density. Shear strength analysis reveals a linear failure envelope for both MMT and PPF-MMT, with initial angle of internal friction improvement at lower PPF content (0.25% and 0.5%) but a decline at higher contents (0.75% and 1%). Importantly, PPF-MMT consistently exhibits a unique strain-hardening behaviour across all stress levels, distinguishing it from MMT, which only transitions to strain-hardening at higher stresses. Under vertical load, MMT shows contraction, while the PPF-MMT composite initially contracts but later dilates due to increased fibre-MMT interaction during horizontal displacement. Furthermore, California bearing ratio (CBR) tests demonstrate increased dry CBR with PPF, reaching a peak of 33.85% at 0.5% fibre content. The soaked CBR tests affirm the remarkable durability of PPF-MMT, maintaining significantly higher values than MMT even after 60 days of soaking. The study concludes that 0.5% fibre content as optimum dosage.