The effect of the variation of δ-ferrite content of weld seams on the resistance to hot cracking and corrosion in HNO3 solution of weld joints for a high SiN stainless steel was studied, while weld joints were made with five types of welding wires with different contents of δ-ferrite as filler so that to adjust the Cr and Ni equivalent for the weld seams. Which were then characterized by means of optical microscopy (OM), X-ray diffraction (XRD), scanning electron microscopy (SEM), and electron probe microanalysis (EPMA) in terms of the influence of δ-ferrite on properties of the weld seams. The results demonstrated that the significant increase in the content of δ-ferrite could reduce the cracking sensitivity of the weld metal. However, if δ-ferrite rich in Cr to certain extent, the possibly existed galvanic effect between which and the austenitic matrix may lead to preferential corrosion of δ-ferrite. As the δ-ferrite content continued to increase, the corrosion rate of the weld seams accelerated. Notably, when the δ-ferrite content exceeded a critical threshold, the δ-ferrite began to form an interconnected network within the columnar dendrite. This morphological transformation resulted in a phenomenon of corrosive spreading, where the corrosion front propagated rapidly across the material. Consequently, the corrosion rate exhibited a slight increase during the latter stages of the process.
With the rapid development of communication technologies and portable flexible electronic devices, the problems related with electromagnetic radiation and heat accumulation have been increasingly aggravated, posing significant threats to surrounding electronic equipment and human health. Therefore, the development of flexible multifunctional composite films with high electromagnetic interference (EMI) shielding performance and excellent fire safety has been considered an urgent necessity. In this study, a multifunctional tunable sandwich-structured composite film was successfully prepared, comprising polyvinyl alcohol-ammonium polyphosphate (PVA-APP) as a flexible flame-retardant outer layer, a silver nanowire (AgNWs) conductive network as the inner layer, and polydimethylsiloxane (PDMS) as the encapsulation layer. The composite film exhibits outstanding performance in electromagnetic shielding, flame retardancy, and hydrophobicity. The sandwich structure was designed to significantly enhance the shielding stability of the internal AgNWs layer. When the carrying capacity of the AgNWs is 0.50 mg/cm², the EMI shielding effectiveness of this film reaches 53.12 dB. Furthermore, the vertical burning test results in accordance with UL-94 standard reveal that the composite film also exhibits self-extinguishing property with a V-0 flame-retardant grade. Additionally, the PDMS encapsulation layer endows the composite film excellent hydrophobicity and self-cleaning properties, even when the film was subjected to bending or placed in a humid environment its EMI shielding performance remains stable. In conclusion, the film is characterized by its simple fabrication process and excellent comprehensive performance, making it highly promising in applications for components with curved surfaces and flexible foldable electronic devices.
The phosphoric acid dihydrogen aluminum (AP) was modified by in situ organic-inorganic hybridization technique, and then the graphite-based lubrication coatings were applied on TA1 pure titanium surfaces by taking AP and hybridized AP as binding agent respectively. The prepared hybridized AP was characterized by means of infrared spectroscopy, X-ray photoelectron spectroscopy, and X-ray diffraction. The high-temperature tribological performance of different coatings was assessed via RTEC MFT-5000 multifunctional friction and wear tester at 700 oC to 900 oC, which then were characterized by means of scanning electron microscopy and three-dimensional white light contour interferometry. The results indicated that AP was successfully hybridized with phenyltrimethoxysilane (PTMS), forming a chemical structure with P-O-Si as the skeleton. The coating with hybridized AP exhibited optimal lubrication performance at high temperatures when the PTMS content was 10%. Specifically, by tribological test at 850 oC, the coating with hybridized AP presented coefficient of friction 0.1219 and wear rate 0.57 × 10-3 mm3·N-1·m-1, which were reduced by 77% and 82%, respectively, compared to those with simple AP. It follows that the reticulated material generated in the hybridized AP binder can enhanced the high-temperature tribological properties of the lubricated coatings containing laminated graphite. Furthermore, this reticulated material can fill the holes and cracks within the coating, thereby reducing the wear rate and improving wear resistance of coatings.
Radioactive gaseous iodine produced during the operation of nuclear reactors needs to be handled safely and efficiently. In this study, a nano-silver loading activated carbon fiber material Ag0@ACF was successfully synthesized by hydrothermal modification and in situ reduction methods, and then the Ag0@ACF material was characterized by SEM-EDS, XRD, BET, and XPS to evaluate the iodine adsorption performance of Ag0@ACF. The results show that the nano-silver particulates were uniformly loaded on the microporous activated carbon fiber material, the acquired Ag0@ACF composite exhibited high specific surface area and high reactivity. Its adsorption capacity of gaseous elemental iodine and methyl iodine reached 2.25 g/g and 0.48 g/g, respectively, the adsorption performance was increased by 2.5 times and 3.5 times in contrast to the blank activated carbon fiber material. With the increase of modifier concentration, the adsorption capacity of Ag0@ACF for gaseous iodine increases. The material still showed excellent adsorption performance (I2: 2.30 g/g, CH3I: 0.51 g/g) even at 130 oC. Through the analysis of material adsorption kinetics and mechanisms, the adsorption of Ag0@ACF materials for gaseous iodine is a chemical reaction between nano-silver and iodine to form a stable AgI, which is a stable chemical adsorption behavior. The highly reactive silver nanoparticles combined with the rich porous structure of activated carbon fiber materials can achieve rapid and efficient capture of gaseous iodine.
Al-alloy 7075 based composites 7075-xTiB2 (x = 0%, 3%, 6%, 9%, 12%, 15%, mass fraction) were prepared by hot pressing sintering. The effect of TiB2 particle content and the post solution treatment temperatures on the microstructure and mechanical properties of the composites were studied. The results show that by hot press sintering at 600 oC, the density of 7075-6%TiB2 composites can reach 98.17%; TiB2 particles could effectively inhibit the growth of α-Al, and the average grain size of 7075-6%TiB2 composite was significantly refined, decreasing from 57.53 μm to 38.12 μm; TiB2 particles are mainly located at the grain boundaries, which hinder the diffusion of solute atoms, slow down their diffusion rate, and inhibit the growth of η(MgZn2) and S(Al2CuMg) phases at the grain boundaries; Correspondingly, the mechanical properties of the hot-press sintered 7075-6%TiB2 composite reached the peak, and the yield strength and tensile strength were (205 ± 5) MPa and (338 ± 6) MPa, respectively, due to the joint action of fine crystal strengthening and dispersion strengthening. With the increase of solution temperature within the range 460-520 oC, the yield strength and tensile strength of hot-pressed 7075-6%TiB2 composites first increase and then decrease. When the solution temperature is 500 oC, more small strengthening phases (η, S) are precipitated inside the composite matrix, and the dispersion strengthening effect is significant. Compared with the as hot-pressed 7075-6%TiB2 composite, the yield strength and tensile strength are increased by 39.5% and 25.4%. It should be also mentioned that the composite 7075-6%TiB2 being subjected to solution treated at 500 oC showed better mechanical properties than those of 7075 Al-alloy.
As an advanced technique capable of finely regulating the properties of materials, the controllable grafting technique has gradually become a research hotspot in the field of material science and technology due to its high flexibility and customization. In this study, the regenerated cellulose membrane was surface grafted with poly glycidyl methacrylate (PGMA) via controllable grafting technique by taking 2-bromoisobutyryl bromide (BIBBr) as initiator and CuBr as catalyst. The effect of several key parameters on the grafting effect were systematically investigated, including dosages of initiator BIBBr, monomer GMA and catalyst, CuBr as well as the reaction temperature. The aim is to introduce epoxy groups in a controllable manner and pave the way for downstream separation and purification. The results show that the amount of initiator BIBBr is directly related to the density of the surface grafted initiator, which can effectively control the grafting rate of GMA. By the optimized conditions, i.e., the dose of initiator BIBBr, which is 3 times of the hydroxyl equivalent, the dose of GMA 17.83 mmol, and of CuBr 0.18 mmol, while the reaction at 60 °C, the grafting reaction may result in a grafting rate up to 10.51% (mass fraction) with an epoxy value 12.63 μmol/g. This study provides an important reference for the functional design of cellulose membranes.
Understanding the material removal mechanism during the sliding wear process of β-SiC materials from an atomic scale perspective will helpful reduce the occurrence of adhesive contact failure and wear in micro-electromechanical system devices. Therefore, the influence of abrasive radius, depth of pressing, sliding speed, service temperature and substrate crystal plane etc. on the SiC microstructure evolution and material removal behavior during the sliding wear of β-SiC materials was studied by means of molecular dynamics method. Results show that the atomic-scale removal mechanism of β-SiC materials in sliding wear lies in the fact that the abrasive grains and the extrusion zone are affected by the dual coupling of high stress and high temperature. It is very easy for the material to be continuously removed from the surface under the induction of horizontal friction force, resulting in the accumulation of grinding debris in front of the abrasive grains and on both sides of the edge of the close contact zone. As the service temperature and pressure depth increase, the number of wear chip atoms produced by wear also increases. However, as the sliding speed increases, the accumulation of wear atoms in front of the abrasive grains and on both sides of the contact edge indeed decreases. Furthermore, the plastic deformation in sliding wear of β-SiC is mainly dominated by the nucleation, growth, proliferation and sliding of dislocations from the cubic crystal structure to the sphalerite crystal structure and within the substrate. Moreover, the concentration degree of Von Mises stress distribution in the β-SiC substrate is positively correlated with the regions where dislocation defects occur within the substrate. The results show that in sliding wear, with the increase of abrasive radius, depth of pressing and sliding speed, the larger the peak value of the radial distribution function, the more amorphous atoms will be produced by β-SiC. However, as the service temperature rises, the number of amorphous atoms produced by β-SiC indeed decreases. In addition, the crystal plane selectivity of the β-SiC substrate has significant anisotropic characteristics for the horizontal friction force, microstructure evolution, wear chip number, atomic vector displacement, temperature field and stress field distribution in sliding wear.
A S-type heterojunction composite photocatalyst of g-C3N4/CdS was synthesized by hydrothermal method. The composite material was characterized by SEM, XRD, PL, and XPS. Its photocatalytic performance was evaluated by work function test and free radical trapping test. Under a simulated sunlight irradiation (Xenon lamp), the degradation rate of methylene blue reached 99.62% when in a 10 mg/L methyl blue suspension with addition of with photocatalytic material* containing g-C3N4-1%CdS, which was 12.11 times higher than that of blank g-C3N4. After three cycles, the photocatalytic degradation rate of the catalyst still reached 82.64%, indicating good stability. The enhanced photocatalytic activity may be attributed to the formation of a S-type heterojunction between g-C3N4 and CdS, where electrons transfer from CdS to g-C3N4, creating a built-in electric field that facilitates rapid separation of photogenerated electrons and holes in space, resulting in a strong redox capability of the catalyst. This study may provide a valuable reference for the design and development of high-performance photocatalytic materials.
