Materials with multifunctionality or multiresponsiveness, especially polymers derived from green, renewable precursors, have recently attracted significant attention resulting from their ...technological impact. Nowadays, vegetable‐oil‐based waterborne polyurethanes (WPUs) are widely used in various fields, while strategies for simultaneous realization of their self‐healing, reprocessing, shape memory as well as high mechanical properties are still highly anticipated. We report development of a multifunctional castor‐oil‐based waterborne polyurethane with high strength using controlled amounts of dithiodiphenylamine. The polymer networks possessed high tensile strength up to 38 MPa as well as excellent self‐healing efficiency. Moreover, the WPU film exhibited a maximum recovery of 100 % of the original mechanical properties after reprocessing four times. The broad glass‐transition temperature of the samples endowed the films with a versatile shape‐memory effect, including a dual‐to‐quadruple shape‐memory effect.
A castor‐oil‐based waterborne polyurethane (WPU) with high strength was developed. The PU networks demonstrated high tensile strength up to 38 MPa, excellent self‐healing with a tensile strength of 100 %, and a maximum recovery of 100 % of the original mechanical strength after reprocessing four times. The broad glass‐transition temperature of the samples endows the films with shape‐memory effects.
Kaolinization of 2:1 type clay minerals commonly occurs in the supergene environments of the Earth, which plays critical roles in many geochemical and environmental processes. However, the ...transformation mechanism involved and the specific behavior of 2:1 type swelling and non-swelling clay minerals during kaolinization remain poorly understood. In this study, laboratory experiments on the kaolinization of montmorillonite (swelling), illite (non-swelling), and rectorite (partially swelling) were carried out to investigate the kaolinization mechanism of 2:1 type clay minerals and to evaluate whether swelling and non-swelling layers of 2:1 type clay minerals perform differently or not in their kaolinization processes. The results show that montmorillonite, illite, and rectorite in acidic Al3+-containing solutions can be transformed into kaolinite, whereas such transformation is hard to take place in Al3+-free solutions. Part of the Al3+ in the solutions was exchanged into the interlayer spaces of swelling clay minerals at the early stage and resulted in the formation of hydroxy-aluminosilicate (HAS) interlayers, but they show no influence on the transformation process. Interstratified kaolinite-smectite (K-S), kaolinite-illite (K-I), and kaolinite-rectorite (K-R) formed as the intermediate phases during the transformations of the three different precursor minerals, respectively. The results obtained in this study demonstrate that 2:1 type clay minerals, including both swelling and non-swelling ones, can be transformed into kaolinite via a local dissolution-crystallization mechanism, which starts mainly from the layer edges rather than the basal surfaces. Due to different dissolution rates from domain to domain within a precursor mineral particle, the layers with a low dissolution rate become "splints," while the dissolved elements are concentrated between two "splints," leading to precipitation of kaolinite along the basal surfaces of precursor minerals. The size and stacking order of the newly formed kaolinite strongly depend on the morphology and property of the precursor minerals. These findings not only are of importance for better understanding the transformation procedures between different clay minerals and the mechanisms involved but also provide new insights for well understanding mineral-water interactions that are central to all geochemical processes.
Through billions of years of evolution and natural selection, biological systems have developed strategies to achieve advantageous unification between structure and bulk properties. The discovery of ...these fascinating properties and phenomena has triggered increasing interest in identifying characteristics of biological materials, through modern characterization and modeling techniques. In an effort to produce better engineered materials, scientists and engineers have developed new methods and approaches to construct artificial advanced materials that resemble natural architecture and function. A brief review of typical naturally occurring materials is presented here, with a focus on chemical composition, nano‐structure, and architecture. The critical mechanisms underlying their properties are summarized, with a particular emphasis on the role of material architecture. A review of recent progress on the nano/micro‐manufacturing of bio‐inspired hybrid materials is then presented in detail. In this case, the focus is on nacre and bone‐inspired structural materials, petals and gecko foot‐inspired adhesive films, lotus and mosquito eye inspired superhydrophobic materials, brittlestar and Morpho butterfly‐inspired photonic structured coatings. Finally, some applications, current challenges and future directions with regard to manufacturing bio‐inspired hybrid materials are provided.
Typical, naturally‐occurring materials are reviewed, with a focus on chemical composition, nanostructure, and architecture. The critical mechanisms underlying their properties are summarized, with a particular emphasis on the role of material architecture. A review of recent progress on the nano/micro‐manufacturing of bio‐inspired hybrid materials is then presented in detail.
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•A novel tri-functional bio-based methacrylate prepolymer was prepared from castor oil.•Low VOCs and high reactive UV-curable active bio-based prepolymer was synthesized.•The castor ...oil content of the prepared bio-based prepolymer is greater than 57%.•The castor oil-based prepolymer has promising applications in UV-curable coatings.
A novel tri-functional castor oil-based methacrylate prepolymer (MCOG) was developed by mercapto castor oil (MCO) and glycidyl methacrylate (GMA) in this study through a two-step method. Primarily, the mercapto castor oil (MCO) was prepared through thiol-ene reaction of castor oil and mercaptoacetic acid, and subsequently an esterification reaction based on above product and glycidyl methacrylate (GMA) was conducted. FT-IR and 1H NMR spectra collectively revealed that MCOG was successfully synthesized. As a dominant component, MCOG was formulated with other additives including a reactive diluent pentaerythritol tri-acrylate (PETA), a photo-initiator (TPO) and another self-made polyurethane acylate prepolymers (B-215) and cured under UV irradiations. UV-curing kinetics of the MCOG/PETA/B-215 film was detailly investigated by tracing the ATR-IR spectroscopy and gel content and it demonstrated that the cured films had more than 95% CC double bond conversion. Moreover, dynamic mechanical property, thermal stability and mechanical property of the cured films were respectively determined by dynamic mechanical analysis (DMA), thermogravimetric analysis (TGA) and tensile measurement. DMA testified that with the increasing of B-215 content, storage modulus, cross-linking density of the cured films dropped, whereas the corresponding glass transition temperatures (Tg) increased. TGA showed that the maximum thermal decomposition temperatures were all above 460 °C. Tensile tests indicated that the better tensile strength was obtained with the content of 20% of the B-215 in the cured film. Additionally, transparency and flexibility of the cured films were respectively analyzed by digital image and scanning electron microscopy (SEM). Besides, these cured films displayed high pencil hardness (5H–6H) and excellent resistance to acidic and alkali solutions.
Wire arc additive manufacturing (WAAM) has been considered as a promising technology for the production of large metallic structures with high deposition rates and low cost. Stainless steels are ...widely applied due to good mechanical properties and excellent corrosion resistance. This paper reviews the current status of stainless steel WAAM, covering the microstructure, mechanical properties, and defects related to different stainless steels and process parameters. Residual stress and distortion of the WAAM manufactured components are discussed. Specific WAAM techniques, material compositions, process parameters, shielding gas composition, post heat treatments, microstructure, and defects can significantly influence the mechanical properties of WAAM stainless steels. To achieve high quality WAAM stainless steel parts, there is still a strong need to further study the underlying physical metallurgy mechanisms of the WAAM process and post heat treatments to optimize the WAAM and heat treatment parameters and thus control the microstructure. WAAM samples often show considerable anisotropy both in microstructure and mechanical properties. The new in-situ rolling + WAAM process is very effective in reducing the anisotropy, which also can reduce the residual stress and distortion. For future industrial applications, fatigue properties, and corrosion behaviors of WAAMed stainless steels need to be deeply studied in the future. Additionally, further efforts should be made to improve the WAAM process to achieve faster deposition rates and better-quality control.
•Effects of carbonate and phosphate on ferrihydrite transformation were investigated.•Carbonate can override the retarding impact of P on the ferrihydrite transformation.•Carbonate promoted the ...formation of more crystalline rhombic hematite particles.•Phosphate and carbonate serve a different role in the cycling of nutrients & metals.
In soils and rhizospheres, iron (oxyhydr)oxides and oxyanions like carbonate and phosphate occur ubiquitously and their interaction have important implications for nutrients and metals cycling. An elevated activity of carbonate in soils and sediments (e.g., pCO2, ∼2%) above current atmospheric CO2 (∼0.04%) is observed. The level of agronomic soil test phosphorus (P) in intensively managed agricultural soils can be up to several hundred mg kg−1. Although it is known that the transformation of iron (oxyhydr)oxides is suppressed by phosphate adsorption, it is unclear how increasing carbonate activities exert the reaction process. Here, the effects of carbonate on the transformation of ferrihydrite were evaluated at pH 7.5 in the presence of phosphate using experimental geochemistry, Fe K-edge X-ray absorption spectroscopy, transmission electron microscopy-energy dispersive X-ray spectroscopy, and Fourier transform infrared spectroscopy. Our results, for the first time, showed that the inhibitory effect of phosphate on ferrihydrite transformation was retarded by carbonate, and it transformed into hematite. Under pCO2 = 408 ppm (0.213 mM carbonate), an increase in phosphateo from 0 to 0.5 mM decreased the transformation rate of ferrihydrite from 0.009 to 0.003 d−1. However, the suppression was drastically perturbed when carbonate was added to the phosphate-ferrihydrite system. When 11.42 mM carbonate (pCO2 = 20000 ppmv) was present, the rate increased from 0.009 to 0.033 d−1 without phosphate and from 0.003 to 0.018 d−1 with 0.5 mM of phosphate. Moreover, carbonate promoted the formation of more crystalline rhombic hematite particles, while phosphate modified the morphology of hematite from rhombic to ellipsoidal-like with rough surfaces. The distinctive difference of the influence of carbonate and phosphate on the transformation kinetics, products distribution, and morphologies come from the interaction between carbonate/phosphate and ferrihydrite. Although phosphate formed strong inner-sphere complexes on the ferrihydrite surface, which inhibited the direct contact and dissolution of ferrihydrite, co-adsorbed carbonate still promoted the olation reaction, facilitating the formation of hematite. These results suggest that as an important geochemical process, the increasing activity of carbonate or pCO2 can override the retarding impact of phosphate on the transformation of ferrihydrite and control the occurrence/crystallization of hematite in the subsurface soils under the scenario of climate change.
A novel method, epoxidation/reduction of vegetable oils, is developed to prepare bio‐based polyols for the manufacture of polyurethanes (PUs). These polyols are synthesized from castor oil (CO), ...epoxidized soybean oil, and epoxidized linseed oil and their molecular structures are characterized. They are used to prepare a variety of PUs, and their thermomechanical properties are compared to those of PU made with petroleum‐based polyol (P‐450). It is shown that PUs made with polyols from soybean and linseed oil exhibit higher glass transition temperatures, tensile strength, and Young's modulus and PU made with polyol from CO exhibits higher elongation at break and toughness than PU made with P‐450. However, PU made with P‐450 displays better thermal resistance because of tri‐ester structure and terminal functional groups. The method provides a versatile way to prepare bio‐polyols from vegetable oils, and it is expected to partially or completely replace petroleum‐based polyols in PUs manufacture.
A novel method to produce bio‐based polyols from vegetable oils is developed using an epoxidation/reduction route. Using castor oil, epoxidized soybean oil, and epoxidized linseed oil, a variety of polyols are synthesized and used to prepare polyurethanes (PUs) with variable properties. The thermomechanical behaviors of these versatile PUs are compared to those of PUs made with a petroleum‐based polyol.
A new substrate integrated waveguide (SIW) leaky-wave antenna is investigated for endfire-radiation with a narrow beam and sidelobe suppression. Maximum directivity conditions for endfire-radiation ...from line sources with different amplitude distributions are theoretically discussed as a design aid. Interestingly, for endfire beams it is seen that designs that have a lower sidelobe level can also have a higher directivity, contrary to what is normally encountered for broadside beams. An SIW leaky-wave antenna with tapered transverse slots on only the top and bottom planes is presented. Compared with a previous leaky-wave antenna having uniform transverse slots on the top plane, the presented leaky-wave antenna has a main beam that can radiate exactly at endfire and also has a lower sidelobe level. The design of the low sidelobe antenna is based on the leaky mode, which loses physical significance as the beam is scanned to the endfire direction. Nevertheless, the antenna retains a good beam shape and a low sidelobe level when it radiates at endfire. A prototype is made, and measured results are consistent with theoretical and simulated results.
Additive manufacturing of WC-Co hardmetals: a review Yang, Yankun; Zhang, Chaoqun; Wang, Dayong ...
International journal of advanced manufacturing technology,
05/2020, Letnik:
108, Številka:
5-6
Journal Article
Recenzirano
Odprti dostop
WC-Co hardmetals are widely used in wear-resistant parts, cutting tools, molds, and mining parts, owing to the combination of high hardness and high toughness. WC-Co hardmetal parts are usually ...produced by casting and powder metallurgy, which cannot manufacture parts with complex geometries and often require post-processing such as machining. Additive manufacturing (AM) technologies are able to fabricate parts with high geometric complexity and reduce post-processing. Therefore, additive manufacturing of WC-Co hardmetals has been widely studied in recent years. In this article, the current status of additive manufacturing of WC-Co hardmetals is reviewed. The advantages and disadvantages of different AM processes used for producing WC-Co parts, including selective laser melting (SLM), selective electron beam melting (SEBM), binder jet additive manufacturing (BJAM), 3D gel-printing (3DGP), and fused filament fabrication (FFF) are discussed. The studies on microstructures, defects, and mechanical properties of WC-Co parts manufactured by different AM processes are reviewed. Finally, the remaining challenges in additive manufacturing of WC-Co hardmetals are pointed out and suggestions on future research are discussed.
In this paper, the influence of interlayer on titanium/steel dissimilar metal resistance spot welding is reviewed from the aspects of macroscopic characteristics, microstructure and interface bonding ...properties of the joint. Previous studies have demonstrated that TiC, FeTi and Fe2Ti intermetallic compounds with high brittleness are formed in the joint during titanium/steel welding, which reduces the strength of the welded joint. Researchers proposed different interlayer materials, including Cu, Ni, Nb, Ta, 60%Ni-Cu alloy and BAg45CuZn. Firstly, adding an interlayer can weaken the diffusion of Fe and Ti. Secondly, the interlayer elements can combine with Fe or Ti to form solid solutions or intermetallic compounds with lower brittleness than Fe–Ti compounds. Finally, Cu, Ni, Ag, etc. with excellent ductility can effectively decrease the generation of internal stress, which reduces the formation of defects to improve the strength of the joint.
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