Special Microstructure Research Articles

Ultra-low core loss FeSiAl soft magnetic composites with in-situ double oxidation layers of outer Fe3O4 layer and inner super-thin Al2O3/SiO2 hybrid layer

How to synchronously reduce eddy current loss and hysteresis loss still remains a challenge for achieving low core loss of soft magnetic composite (SMC). In-situ surface oxide effectively combines the formation of insulating layer and the release of internal stress during the molding process. In this study, FeSiAl SMC has been fabricated by powder metallurgy method with in-situ oxidated FeSiAl powder, in which FeSiAl powder are covered by outer Fe3O4 insulating layer and inter super-thin Al2O3/SiO2 hybrid layer. Fe3O4 layer alleviates dilution magnetic effect, ensuring high saturated magnetization and effective permeability. The super-thin Al2O3/SiO2 hybrid layer enhances electrical resistance, reducing eddy loss. Effects of the in-situ oxidation time on insulating layer and soft magnetic performances of SMC are investigated in detail. Synchronous reduction of eddy current loss and hysteresis loss is achieved through high resistance accompanied with proper insulating layer thickness and low coercive force provided by the special microstructure. For powder with 90 min oxidation at 500 °C, core loss of SMC is low up to 64 mW/cm3 at 50 mT and 100 kHz and 363 mW/cm3 at 100 mT and 100 kHz, while the permeability is kept at 50 until 1100 kHz and is stable until 140 °C. Meanwhile, DC bias performance reaches 51.2% at 100 Oe applied field and Q value is 104.8 at 400 kHz.

English

Recently, there has been a high interest in using lightweight aluminum foams for automotive, railway and aerospace operations. Because of its high ductility and deformability, Aluminum foam is generally used for energy absorption for crashworthiness applications. To keep safe and avoid occupant injuries, it is necessary to absorb the kinetic energy generated during impact. Thus, to absorb high kinetic energy, the crash box material needs a special material microstructure, which is light in weight and can absorb further energy than the being one like CaCo3, CBC, or SiC. B4C etc. In particular, the analysis of energy absorption of aluminum foam in automotive for energy absorption applications is limited. The main objective of this exploration is to analyze and optimize the porosity size and voids percentage on impact energy absorption of aluminum foam using a numerical approach. For this purpose, first, fifteen CAD Al foam samples were developed by using Digimat multi-scale material modeling software. Second, cubic elements with circular bubble shape at 5, 10 and 15 void percentage and at 1.5 mm, 2 mm,2.5 mm, 3 mm and 3.5 mm bubble sizes were modeled. Finally, the numerical analysis of impact energy by using ANSYS workbench19.2 Explicit dynamics by applying initial low velocity was performed. The parameters were compared to each other to optimize the proper percentage composition and cell size for the best energy absorption applications. The effects of bubble shape, foaming agent and percentage composition on energy immersion were discussed. In this study, the analysis was fulfilled by determining and comparing the energy absorptions of all the models and, finally, comparing them with existing foaming agents.

A nanocomposite metamaterial with excellent broadband microwave absorption performance and good mechanical property

The microwave absorbers draw great attentions in addressing the electromagnetic pollution issues and the electromagnetic stealth needs. However, it remains a challenge to realize the microwave absorbers with thin thickness, broadband absorption and good mechanical properties simultaneously. Inspired by the special microstructures of papilio palinurus's wing and beetle’s elytra, nanocomposite metamaterial with excellent broadband microwave absorption and good mechanical property was designed and fabricated. The Carbonyl iron-Carbon nanotubes-epoxy nanocomposites were firstly synthesized for fabricating the designed metamaterial. Slab made of the synthesized nanocomposites can realize 7.04 GHz effective absorption bandwidth (i.e., EAB, reflection loss (RL) ≤-10 dB) with thickness of 1.28 mm. Unit cell size parameters optimization of designed metamaterial was then conducted with the multi-population genetic algorithms, in which both the microwave absorption bandwidth and microwave absorption intensity were set as the optimized target. The optimized bioinspired nanocomposite metamaterial possesses 31.7 GHz EAB and −47 dB minimum RL value with thickness of only 6 mm, and its compressive strength is 33.78 MPa. The proposed bioinspired metamaterial strategy in this paper provides an efficient way for designing metamaterials with excellent broadband microwave absorption performance and good mechanical properties.

A Review of Advances in Fabrication Methods and Assistive Technologies of Micro-Structured Surfaces

Micro-structured surfaces possess excellent properties of friction, lubrication, drag reduction, antibacterial, and self-cleaning, which have been widely applied in optical, medical, national defense, aerospace fields, etc. Therefore, it is requisite to study the fabrication methods of micro-structures to improve the accuracy and enhance the performance of micro-structures. At present, there are plenty of studies focusing on the preparation of micro-structures; therefore, systematic review of the technologies and developing trend on the fabrication of micro-structures are needed. In present review, the fabrication methods of various micro-structures are compared and summarized. Specially, the characteristics and applications of ultra-precision machining (UPM) technology in the fabrication of micro-structures are mainly discussed. Additionally, the assistive technologies applied into UPM, such as fast tool servo (FTS) technology and slow tool servo (STS) technology to fabricate micro-structures with different characteristics are summarized. Finally, the principal characteristics and applications of fly cutting technology in manufacturing special micro-structures are presented. From the review, it is found that by combining different machining methods to prepare the base layer surface first and then fabricate the sublayer surface, the advantages of different machining technologies can be greatly exerted, which is of great significance for the preparation of multi-layer and multi-scale micro-structures. Furthermore, the combination of ultra-precision fly cutting and FTS/STS possess advantages in realizing complex micro-structures with high aspect ratio and high resolution. However, residual tool marks and material recovery are still the key factors affecting the form accuracy of machined micro-structures. This review provides advances in fabrication methods and assistive technologies of micro-structured surfaces, which serves as the guidance for both fabrication and application of multi-layer and multi-scale micro-structures.

Atmospheric plasma sprayed W coating/Detonation sprayed W-steel composite coating/steel substrate-based coating system for the tokamak first wall

To study the manufacturing method of the tungsten armored first wall of tokamak devices, the W-316 L steel (W-SS) composite coatings were fabricated on 316 L steel substrates by detonation spraying (DS) as the interlayer of pure tungsten coatings manufactured by atmospheric plasma spraying (APS). The main characteristics and performance under transient heat shocks of the APS W/DS W-SS /substrate-based three-layer coating system were studied and compared with the APS W/substrate-based coating system. The results showed the porosity of the DS W-SS was about 1.9% with most of the pores smaller than 70 nm. In contrast, the porosity of the APS W reached about 8.6% and most of the pores were up to hundreds of nanometers. The bonding strength tests proved that both the adhesions of APS W to DS W-SS and DS W-SS to the substrate were much higher (almost 1.5 times) than the adhesion of APS W to the substrates. The three-layer specimens performed much better than the APS W/substrate specimens during the transient heat shock tests as expected. Besides, a special microstructure variation occurred on the three-layer specimens before its damage under the tests which was considered helpful to prolong its life-span under high heat flux. In a conclusion, the DS W-SS interlayer improved the service performance of the APS W/substrate-based coating significantly and demonstrates its potential for application in current tokamak experimental devices.

Asymmetric bending characteristics and failure mechanism of bamboo under different loading directions

Bamboo has a special microstructure, its fiber content decreases gradually from the outside to the inside. This kind of gradient distribution results in obviously asymmetric bending characteristics of bamboo, and shows different bending properties and failure modes in different bending directions. In this study, bending properties of moso bamboo (Phyllostachys pubescens) in three different directions (type A: outward bending, type B: tangential bending, type C: inward bending) were tested. Digital image correlation (DIC) and scanning electron microscopy (SEM) were used to analyze the failure process, strain field change and failure morphology of bamboo, and summarized the failure mechanism of bamboo bending in different directions. Results indicated that the tangential bending have the highest modulus of rupture (MOR) and modulus of elasticity (MOE), and the inward bending has the best flexural toughness. The failure mechanism of the three bending directions was different. For type A, the initial crack appeared in the parenchyma tissue in the tensile region where the fiber content was less, so the crack rapidly expanded inside the parenchyma tissue, forming a neat failure section, then led to low toughness of bamboo. For type B, the initial crack appeared in the parenchyma tissue in the tensile region. Due to the moderate fiber content in the tensile region, the fiber bridging phenomenon appeared in the fracture section, led to the higher elastic modulus and strength of the type B. For type C, the initial crack appeared in the parenchyma tissue in the compression region. Because of the more fiber content in the tensile region, the cracks in this part propagated transversely and formed the failure morphology of interlayer separation, which increased the toughness of the specimen. This study is helpful to understand the asymmetric bending characteristics of bamboo, and provide guidance for the use of bamboo as a structural material and the preparation of composite materials.

Special hot working plastic deformation behavior and microstructure evolution mechanism of single-phase BCC structure AlFeCoNiMo0.2 high-entropy alloy

The single-phase body-centered cubic (BCC) structured high-entropy alloys are considered to be typically difficult-to-deform processing alloy because they can still crack during hot deformation at high temperatures and low strain rates. However, we found that the hot working formability of this type of alloy is very sensitive to temperature, and there is a unique microscopic transformation. In this paper, the as-cast single-phase BCC-structured AlFeCoNiMo0.2 high-entropy alloy was investigated with the single-pass hot-compression simulation experiment (deformation of 0.6), at temperatures and strain-rate ranges of 900 – 1150 ℃ and 0.001 – 0.1 s−1, respectively. The hot-deformation behavior and microstructure-evolution mechanisms were studied. The Arrhenius constitutive relation model was revised and established. The processing maps of Prasad, Gegel, Malas, and Murty with different instability criteria were constructed. The optimal thermal-processing parameters (temperatures of 1070 – 1150 ℃ and strain rates of 0.001 – 0.1 s−1) were provided. It was great to find that the alloy has a narrow temperature window effect of hot working with the Ruano-Wadsworth-Sherby (R-W-S) deformation-mechanism map established by incorporating the dislocation quantity. The deformation mechanisms of the alloy at 900 °C, 1000 °C, 1050 °C, and 1100 °C were predicted. The single-phase (BCC) structure of the alloy has strong stability during hot deformation. In a narrow range of hot-working temperatures, the microstructure has a necklace-like structure, and its substructure has a strong textured effect, impeding grain-boundary slip. In the optimized processing interval, discontinuous dynamic recrystallization (DDRX) occurs, and the necklace-like structure disappears. The recrystallization mechanism is related to grain-boundary sliding, caused by dislocation sliding.

A Novel Process to Produce Ti Parts from Powder Metallurgy with Advanced Properties for Aeronautical Applications

Titanium and its alloys have excellent corrosion resistance, heat, and fatigue tolerance, and their strength-to-weight ratio is one of the highest among metals. This combination of properties makes them ideal for aerospace applications; however, high manufacturing costs hinder their widespread use compared to other metals such as aluminum alloys and steels. Powder metallurgy (PM) is a greener and more cost and energy-efficient method for the production of near-net-shape parts compared to traditional ingot metallurgy, especially for titanium parts. In addition, it allows us to synthesize special microstructures, which result in outstanding mechanical properties without the need for alloying elements. The most commonly used Ti alloy is the Ti6Al4V grade 5. This workhorse alloy ensures outstanding mechanical properties, demonstrating a strength which is at least twice that of commercially pure titanium (CP-Ti) grade 2 and comparable to the strength of hardened stainless steels. In the present research, different mixtures of both milled and unmilled Cp-Ti grade 2 powder were utilized using the PM method, aiming to synthesize samples with high mechanical properties comparable to those of high-strength alloys such as Ti6Al4V. The results showed that the fine nanoparticles significantly enhanced the strength of the material, while in several cases the material exceeded the values of the Ti6Al4V alloy. The produced sample exhibited a maximum compressive yield strength (1492 MPa), contained 10 wt.% of fine (milled) particles (average particle size: 3 μm) and was sintered at 900 °C for one hour.

Multifunctional flower-like Ni particles/silicon carbide nanowires for infrared radar compatible stealth performance

Alongside the rapid development of detection systems and improved detection accuracy, infrared/radar-compatible stealth materials have become the emphasis of current stealth technology research. Versatile flower-like Ni particles/silicon carbide nanowires (SiC NWs) composites for infrared radar stealth compatibility have been successfully prepared. Due to its special microstructure in combination with the multiple loss mechanisms of dielectric and magnetic, the minimum reflection loss (RLmin) achievable with the paraffin matrix mixture is −49.26 dB at a composite content of 50 wt%, which has a thickness of 1.9 mm and an effective absorption bandwidth (EAB) of 4.85 GHz. By increasing the absorbent content to 60 wt%, the EAB in the Ku band can attain 5.0 GHz at 1.8 mm thickness. Petal-shaped Ni particles are introduced to improve the impedance matching characteristics, increase interfacial polarisation and multiple scattering of electromagnetic (EM) wave, and enhance the microwave absorption properties. Simultaneously, the pure SiC NWs material can protect against infrared radiation emitted from the hand for more than 15 min, and the infrared (IR) reflectivity is improved in all three bands after the composite metal Ni particles. A novel formulation guide for the design of versatile and high-performance EM wave absorbing and infrared stealth materials is provided by this work.

Novel Co3O4-CuO-CuOHF porous sheet for high sensitivity n-butanol gas sensor at low temperature

In this study, porous sheet-like nanostructured Co3O4-CuO-CuOHF composites with great n-butanol sensing properties were synthesized by the biotemplate method and hydrothermal method. The effect of various contents of Co3O4-CuO-CuOHF sensor performance was systematically investigated, in which the best performance was achieved for the composite with 0.03 g Co3O4 addition. The response of the best content Co3O4-CuO-CuOHF composite sensor to 100 ppm n-butanol at 180 ℃ is 120, which is 8 times higher than that of the CuO-CuOHF sensor. The composite sensor has excellent selectivity for n-butanol and responds 3.75–25 times higher to n-butanol than other target gases. It is detectable up to 500 ppb n-butanol and has potential promise for low concentration detection. Furthermore, it has outstanding stability and resistance to humidity. The gas sensing mechanism was analyzed by UV–visible diffuse reflectance spectroscopy, EPR oxygen vacancies and X-ray photoelectron spectroscopy, which indicated that the abundant oxygen vacancies, the physical adsorption of polar hydroxyl bonds, the electronegative fluorine substitution and the special microstructure of the composite contributed to its gas-sensitive performance.

Enhanced Photothermal Steam Generation and Gold Using the Efficiency of Ultralight Gold Foam with Hierarchical Porosity

Controlling the optical properties of metal plasma nanomaterials through structure manipulation has attracted great attention for solar steam generation. However, realizing broadband solar absorption for high-efficiency vapor generation is still challenging. In this work, a free-standing ultralight gold film/foam with a hierarchical porous microstructure and high porosity is obtained through controllably etching a designed cold-rolled (NiCoFeCr)99Au1 high-entropy precursor alloy with a unique grain texture. During chemical dealloying, the high-entropy precursor went through anisotropic contraction, resulting in a larger surface area compared with that from the Cu99Au1 precursor although the volume shrinkage is similar (over 85%), which is beneficial for the photothermal conversion. The low Au content also results in a special hierarchical lamellar microstructure with both micropores and nanopores within each lamella, which significantly broadens the optical absorption range and makes the optical absorption of the porous film reach 71.1-94.6% between 250 and 2500 nm. In addition, the free-standing nanoporous gold film has excellent hydrophilicity, with the contact angle reaching zero within 2.2 s. Thus, the 28 h dealloyed nanoporous gold film (NPG-28) exhibits a rapid evaporation rate of seawater under 1 kW m-2 light intensity, reaching 1.53 kg m-2 h-1, and the photothermal conversion efficiency reaches 96.28%. This work demonstrates the enhanced noble metal gold using efficiency and solar thermal conversion efficiency by controlled anisotropic shrinkage and forming a hierarchical porous foam.

Elimination of in-plane mechanical anisotropy and enhancement of strength-ductility of rolled Mg sheets via electric-associated twinning and recrystallization

A novel method referred as electric-associated corrugated wide limit alignment (E-CWLA) was proposed to address the contradiction between strength and plasticity of hot-rolled Mg sheets. The counterpart without electricity was known as CWLA. A huge number of tensile twins (TTs) was induced in CWLAed sample R300, and dynamic recrystallization (DRX) occurs. Strong transverse direction (TD)-titled texture accounts for the huge difference in yielding strength between different loading directions, which are closely related to Schmid factors of prismatic <a> and pyramidal <c+a> slips, resulting in different ultimate tensile strength (UTS) and ductility of R300 along different directions. E-CWLAed sample E300 presents good in-plane mechanical isotropy with the maximum UTS of 272.1 MPa, yielding strength of 213.6 MPa and elongation of 22.7%, increasing by 32%, 53% and 83% compared with the as-received sheets, respectively. Regardless loading direction, basal and non-basal slips possess similar SFs and greatly facilitates uniform plastic deformation and mechanical isotropy of E300. The special microstructure including lots of fine grains, some large grains and TTs results in a bimodal basal texture with very weak TD-titled component promotes its good deformation compatibility. Electricity contributes little to TTs formation of E300, and its thermal effect promoting dislocation mobility and DRX and the athermal effect increasing DRX nucleation rate are responsible for final grain size distribution.

Facile and Tunable Synthesis of Nitrogen-Doped Graphene with Different Microstructures for High-Performance Supercapacitors

Heteroatom-doped graphene is of great interest for energy storage applications due to its improved local electronic structures compared with undoped graphene. However, a tunable method for the preparation of heteroatom-doped graphene with a special microstructure is still worth developing. Herein, a novel nitrogen-doped graphene with different microstructures is facilely synthesized via an in situ interlamination self-assembling method that employs the in situ formed Fe3(PO4)2 and organoamine as the catalyst and carbon source, respectively. By tuning the alkyl chain length in organoamine, octylamine and dodecylamine, bubble-like and sheet-like nitrogen-doped graphene are obtained, respectively. In three-electrode supercapacitor tests, besides the double-layer capacitance, the as-prepared graphene electrode material indeed exhibits pseudocapacitance due to the N-rich feature, delivering a good rate capability (166 F g–1 at 20 A g–1) and cyclic performance (96% capacitance retention over 20,000 cycles at 20 A g–1). More importantly, the symmetrical supercapacitor studies reveal the promising practicality due to the achieved excellent energy and power densities together with long-term cyclability. Thereby, this work establishes a new milestone for the facile synthesis of heteroatom-doped graphene with a desired microstructure for energy storage and other applications.

A review of microstructured optical fibers for sensing applications

Microstructured optical fibers, including not only photonic crystal fibers but also new types of fiber with different configurations on the cross section, are elaborately designed and they usually have special application purposes among which sensing is one of the most common. In this review we first summarize fabrication methods and transmission mechanisms of microstructured fibers. And then application examples using fibers with special and novel microstructures in strain/pressure/bending/twist, temperature, flow rate, electric/magnetic field, humidity, gas, refractive index and chemical/biochemical analyte sensing based on various principles are introduced. Finally, state of the art and developing trends as well as challenges faced by sensing technology based on microstructured optical fibers were discussed.

Distinct microstructure and property evolution of 0.76(Bi0.5Na0.5)TiO3-0.24SrTiO3 ferroelectric ceramics synthesized with different TiO2 reactants

Single phase 0.76(Bi0.5Na0.5)TiO3–0.24SrTiO3 ferroelectric ceramics have been synthesized with homogenous anatase and hierarchical rutile TiO2 raw reactants (BNST-A and BNST-R). Either calcined powder persists the microstructure characteristics of raw reactants. As the result, when the sintering temperature increases from 1000 to 1200 °C, the average grain size and density of BNST-A increase from 0.49 to 1.48 μm and 5.02 to 5.61 g/cm3, while those of BNST-R from 0.86 to 1.44 μm and 5.37 to 5.61 g/cm3. BNST-A illustrates a predominant ergodic relaxor state, and BNST-R prefers a non-ergodic relaxor state, as evidenced by the distinct polarization-electric field loops and current-electric field curves. Especially, such a distinct ferroelectric state is independent of sintering temperature. It is believed that the special hierarchical microstructure of rutile TiO2 reactant is beneficial to form denser ceramics with larger grains, and thus suppresses the contributions of polar nanoregions and defect-induced built-in field to ferroelectric property, leading to non-ergodic relaxor state. This work clearly demonstrates the nonnegligible effects of TiO2 reactants on the microstructure and properties of BNST ferroelectric ceramics.

Role of Diatom Microstructure in Determining the Atterberg Limits of Fine-Grained Diatomaceous Soil

The presence of diatoms in diatomaceous soil gives it geotechnical properties that are unusual compared with common clays. The most typical physical property of diatomaceous soil is its abnormally high Atterberg limits compared to fine-grained soil without diatoms. For diatomaceous soil, the Atterberg limits are associated with many factors, such as diatom content, diatom crushing degree, etc. In the study reported here, it was ascertained that more diatoms lead to higher plastic and liquid limits. Once the diatoms are crushed, the plastic and liquid limits decrease. The pore fluid salt concentration barely influenced the Atterberg limits of diatomaceous soil. Additionally, the porous diatom microstructure and trimodal pore size distribution of diatomaceous soil were investigated via scanning electron microscopy, transmission electron microscopy, and mercury intrusion porosimetry. The underlying mechanism of abnormally high liquid and plastic limits of diatomaceous soil is revealed as the water stored in the special diatom microstructure. However, water in diatoms has no contribution to plasticity. Also discussed is the applicability of the current soil classification systems for diatomaceous soil. The findings of this study can help for a better understanding of Atterberg limits of diatomaceous soil and provide suggestions for the classification of diatomaceous soil.

Effect of prior-austenite grain size on the microstructure and mechanical properties of ultrafine-grained dual-phase layer-structured steel produced by hot rolling of intercritical annealed bainite

In this study, ultrafine-grained (UFG) ferrite/martensite (F/M) layer-structured (LS) steels were fabricated by hot rolling of intercritical annealed bainite steels with a rolling reduction of 75% to ease the strength-toughness trade-off dilemma, and the effect of prior-austenite grain (PAG) size of the bainitic steels on the microstructure and mechanical properties were systematically studied. The results showed that the layer thickness of martensite and ferrite was not affected by the PAG size, but the spacing of parallel lamellae bands (PLS), which evolved from the packet of bainite, decreased with the decrease of PAG size. The PLS had negligible influence on strength and ductility, but the decrease of the PLS led to the increase of delamination and both room temperature (RT) and cryogenic toughness enhancement. By reducing the PLS to introduce more delamination in this steel, the RT and cryogenic impact energy were increased 5.7 times (301 J) and 21 times (102 J at −196 °C), but without the sacrifice of strength (over 1.5 GPa) and ductility (total elongation of about 14%), compared with the initial bainite steel with the same composition respectively. The significantly improved toughness, especially the cryogenic toughness, was considered to result from the special UFG dual-phase layered structure as strain localization could be restrained and ductile fracture could be promoted by this special microstructure even at −196 °C. The cryogenic toughness improvement with the decrease of the spacing of PLS was confirmed to originate from the ductile crack path increase induced by delamination.

Heterogeneous deformation behavior of hybrid manufactured TC11 titanium alloy via directed energy deposition

Hybrid manufacturing technique by combining of the conventional manufacturing techniques with the additive manufacturing technique has an attractive potential to fabricate the large and complex components. In this study, hybrid manufactured TC11 titanium part was produced by depositing TC11 alloy on a rolled TC11 plate via directed energy deposition (DED) process. Microstructure, microhardness and tensile properties of hybrid manufactured TC11 samples were examined. The deformation behavior of the hybrid manufactured TC11 samples was also investigated using in-situ tensile test and digital image correlation (DIC). The results demonstrate that the hybrid manufactured TC11 sample can be divided into three zones: the laser deposition zone (LDZ), the heat affected zone (HAZ) and the rolled substrate zone (SZ). The gradient microstructure is formed in the HAZ along the deposition direction due to the different thermal conditions. A special bimodal microstructure consisting of coarse primary α (αp) phase platelet and ultrafine lamellar α phase has been generated in the upper HAZ. The texture of α phase shows the highest intensity in the easily-activated orientation in the LDZ with larger Schmid factor leading to fracture when loading along the deposition direction. The small grains size with super fine αs in the HAZ results in the highest strength and microhardness.

Highly permeable and durable mixed-matrix reverse osmosis membranes filled with cellulose nanofibers-hybridized Ti3C2Tx

Exploration of optimized nanomaterial fillers has been highly realized as a key to improve the comprehensive performance of reverse osmosis (RO) membranes. In this study, a new kind of high-separating efficient mixed-matrix RO membrane is proposed by filling cellulose nanofibers (CNFs)-hybridized Ti3C2Tx with an enlarged layer distance and enhanced negative electronegativity due to a strong hydrogen-bond-interaction. Therefore, the two-phase monomer interfacial polymerization (IP) process of the polyamide (PA) membranes was mediated to change the RO membrane surface from a leaf-like to a nodular-like morphology with additional water molecular channels, increased hydrophilicity and enhanced roughness. With such a special microstructure, the maximum water flux of the Ti3C2Tx-CNFs/PA membrane was elevated up to 64 L m−2 h−1, 1.4 times that of the pristine PA membrane without reducing the salt rejection (98.8 %) at all. In addition, the incorporation of Ti3C2Tx-CNFs was also found to elevate the antifouling and chlorine resistance of the RO membrane effectively. Interestingly, the Ti3C2Tx-CNFs/PA membrane exhibited both organic protein and inorganic salt pollution resistance. At a chlorination intensity of 10,000 ppm·h, the salt rejection of the PA membrane at this time had dropped to 67.4 %, while that of the TC10/PA membrane still remained at 92.3 %, which could be ascribed to the chlorine adsorption/substitution reaction on the surface of Ti3C2Tx-CNFs and the protective effect on the membrane surface. This study thus has validated the beneficial effects of nanomaterial incorporation and pointed out a new perspective for promoting the real applications of high-performance and long-life RO membranes.

Swelling–shrinkage mechanisms of diatomaceous soil and its geohazard implication

Current understanding of soil behaviors from classic soil mechanics is constantly challenged by a variety of unusual soils, one of which is diatomaceous soils (DSs). It is well understood that this biological-origin soil has fundamentally different geotechnical features from that of common fine-grained soils because of the presence of diatom fossils. Recently, increasing geohazards and engineering disasters associated with DS swelling–shrinkage are reported but the exact role of diatoms in determining soil swelling–shrinkage, the underlying mechanisms, and the geohazard implications, have not yet been revealed. This study systematically investigates the swelling–shrinkage behavior of natural DS as well as artificial mixture of diatoms and clay minerals (kaolinite and montmorillonite). The swelling–shrinkage behaviors are explained from the perspectives of mineralogy and microstructure as revealed through X-ray diffraction, scanning electronic microscopy, and transmission electron microscopy. Diatoms have a special microstructure with inter-frustule pores, and the intra-skeletal and skeletal pores in DS make the soil characterized by a high void ratio and water content. In addition, the presence of diatoms curbs the swelling–shrinkage of DS but this may be overwhelmed by the high stress generated due to the swelling of montmorillonite. The wetting–drying cycles subjected to DS result in fissure development, a higher level of swelling–shrinkage behavior, and ultimately in related geohazards such as landslides. The distinct swelling–shrinkage behavior of DS makes the previous classification inapplicable; thus, more rational classification methods are adopted. This study enhances the understanding of the swelling–shrinkage behavior of DS and the control of related geohazards.