Multi-walled Carbon Nanotubes Content Research Articles

The Effect of Multi-Wall Carbon Nanotubes Addition on the Shielding Properties Against Gamma Radiation

In this work, the effect of Multi-Wall Carbon Nanotubes (MWCNTs) addition on the materials shielding properties against Gamma radiation with an energy of 662 keV from a 137Cs source is investigated. The linear attenuation coefficient of MWCNTs-based materials (gelatin-water mixture) with MWCNTs concentrations of 0%, 5%, and 10% is measured. To isolate the contribution of the MWCNTs unique structure to the shielding capabilities, samples with the same concentrations of activated carbon were fabricated and their linear attenuation coefficients were obtained. Also, the linear and the mass attenuation coefficients are obtained theoretically for the same concentrations using the XCOM program and compared with measured values. It is found that the addition of MWCNTs by 5% or 10% has increased the linear attenuation coefficient by around 5% when compared to the same concentrations of activated carbon. This increase in the shielding apabilities against gamma radiation can be related to the interaction of gamma radiation with the extraordinary geometry and structure of MWCNTs.

Photocurable 3D printed anisotropic electrically conductive materials based on bio-renewable composites

The manufacturing industry is moving towards an environmentally friendlier and more sustainable economy by substituting fossil fuel-based materials for plant-based and related renewable resources obtained materials, such as soybean oil. The combination of these materials with electrically conductive fillers allows the fabrication of conductive tracks and sensors essential for the implementation of the internet of things (IoT) and Industry 4.0 concepts. Here, we've fine-tuned the combination of acrylated epoxidized soybean oil (AESO) and isobornyl methacrylate (IBOMA), considering factors like viscosity, photoreactivity, and physico-chemical properties, with the further addition of multiwalled carbon nanotubes (MWCNT) in varying amounts for selected formulations. The resulted materials obtained in films present gel times between 1 and 30 s, FTIR conversion between 75% and 50%, Tg in the range of 57–123 °C and crosslinking densities between 1.90 and 0.015 mmol/cm3. In addition, good MWCNT dispersion is achieved with conductivities as high as 1.4 × 10-4 S/m. The optimal formulation in terms of 3D printability was obtained for 0.6 wt% MWCNT content and AESO:IBOMA polymer matrix in a 50:50 ratio, showing a good fabrication precision for bulk and hollow structures (average dimensional differences between the model and printed objects of ± 100 mm). The 3D printed samples demonstrate anisotropic electrical conductivity ascribed to a MWCNT orientation that occurs during 3D printing process. The electrical conductivity values can vary in nearly 6 orders of magnitude depending on the orientation with respect to the printed pattern, − 6.6·10-3 S/m for parallel and 5.2·10-9 S/m for perpendicular - demonstrating the suitability for 3D printed electronic applications.

Synergistic effect of Mn2+ with unzipped carbon nanotubes on enhancement of mechanical properties of polyamide 66

Multi-walled carbon nanotubes (MWCNTs) are widely recognized for their exceptional mechanical properties and potential to reinforce composite materials. However, the requirement for high MWCNT concentration remains a challenge in achieving effective reinforcement. In this study, using unzipped multi-walled carbon nanotubes (uMWCNTs) and transition metal filler as a means to significantly enhance the mechanical properties of polyamide 66 (PA66) and incorporating 0.2% w/w of uMWCNTs-Mn as filler allowed us to increase PA66's tensile strength by over 74% and its Young's modulus by over 100%. The structural and functional integrity of uMWCNTs-Mn and PA66 matrix were investigated in detail. This work reveals that the enhancement of mechanical properties is mainly due to the interfacial interaction between uMWCNTs-Mn sheets and the PA66 matrix, the coupling effect of manganese ions, and increases the crystallinity and reduces the size of microcrystals. This work's findings provide a novel approach to the preparation of high-performance composites with low concentrations of carbon nanostructures, which holds significant implications for the development of advanced materials.

Robust synthesis and characteristics of novel one-dimensional gadolinium oxide nanorods decorated multiwalled carbon nanotubes based antibacterial nanocomposites for health care applications

A facile and scalable chemical method for synthesizing one-dimensional (1D) gadolinium oxide nanorods decorated multiwalled carbon nanotubes (MWCNTs) based nanocomposites (GNR) as antibacterial agents for biomedical applications is introduced in this paper. The hybrid nanocomposite was obtained by using gadolinium nitrate hexahydrate as gadolinium precursor and MWCNTs as resource material with hydrogen peroxide as a reducing agent and citric acid and cytosine as a reducing agent and stabilizers. The advanced nanocomposite was further studied using sophisticated techniques like XRD, FTIR, XPS, UV–Visible spectroscopy, Thermal Studies /TG-DTA analysis, SEM, TEM and EDS analysis. SEM and TEM studies reveal the simultaneous existence of nanorods and nanotubes in the prepared hybrid nanocomposite material. This kind of morphological orientation has significantly improved the nanocomposite’s antibacterial properties. The XPS studies depicts the binding energy of gadolinium oxide and MWCNTs. Different concentrations of nanocomposite and MWCNTs were tested against Gram −ve and gram +ve bacterial strains: Escherichia Coli, Staphylococcus Aureus, Klebsiella pneumonia, and Micrococcus luteus, respectively by disc diffusion method. Nanocomposite showed better performance against both types of bacteria, especially against gram +ve bacteria, in which MWCNTs did not establish any bacterial zone of inhibition. We believe that the developed advanced nanocomposite has enormous potential for healthcare applications based on these antibacterial properties.

Studying the Incorporation of Multi-Walled Carbon Nanotubes in High-Performance Concrete

The current work aimed to study nanomodified HPC with multi-walled carbon nanotubes (MWCNT). The effect of MWCNT concentration, from 0% to 0.6% of cement weight, was evaluated on HPC multi-level output properties, namely, the flowability, mechanical strength, electrical resistivity, and microstructure. In addition, a tentative, simplified, and more cost-effective method based on dispersion of a high-pH solution of hydroxide was also adapted to disperse the MWCNT before incorporation in fresh HPC mixtures. Adding 0.2–0.6% MWCNT reduced HPC workability even with a higher superplasticiser dosage. The electrical resistivity was 484.58 Ω m for the HPC without MWCNT at 28 days of curing, while the samples with 0.2%, 0.4%, and 0.6% MWCNT presented 341.41 Ω m, 363.44 Ω m, and 360.34 Ω m, respectively. The use of 0.2–0.6% MWCNT in HPC decreased the flexural and compressive strength by 20% and 30%, respectively. The HPC performance decrease with MWCNT seemed to be related to relatively significant agglomerations of the long MWCNTs, namely, in HPC-0.6% samples. New developments are needed to state a simple and cost-effective dispersion method for MWCNT incorporation in HPC. In addition, smaller dosages of MWCNT are suggested for future research works.

Mechanical and thermal properties of high volume‐fraction carbon nanotube/epoxy composites, and property enhancement byUVozone treatment of carbon nanotubes

AbstractA new method to fabricate carbon nanotube/epoxy composites, consisting of well dispersed and highly concentrated CNTs in an epoxy resin, has been developed. In this method, multiwalled carbon nanotubes (MWNTs) were dispersed into water with the assistance of cationic polymers to form a MWNT sheet by filtration. An epoxy resin was impregnated into the MWNT sheet by vacuum assisted impregnation using a filtration system, followed by autoclave cure, resulting in a MWNT/epoxy composite with a MWNT content of 33 wt%. It was revealed that the composite has a tensile modulus of 8.37 GPa and a tensile strength of 130 MPa. An application of a UV ozone (UV/O3) treatment to the MWNTs increased the XPS O/C ratio from 0.03 to 0.10, resulting in the improvement of the tensile strength to 171 MPa. These results indicate the effectiveness of the UV/O3treated MWTNs for mechanical property enhancement.

Optimizing electromechanical performance of multilayered multiwalled carbon nanotube/silicone rubber composites via filler content distribution modulation

AbstractDielectric elastomers are widely used as electroactive polymer materials due to their high energy density, high strain, and low loss. However, the practical applications are limited sometimes by their low electromechanical strain ability due to relatively low dielectric permittivity for polymers. Herein, multiwalled carbon nanotube (MWCNT) filled silicone rubber (SR) composites with a five‐layered structure are prepared with the outer two layers of neat SR while the middle three layers are MWCNT filled SR, in which the former functions as insulating layers while the latter acts as the dielectric permittivity enhancement layers. Further, by differing the MWCNT content within the middle three layers, we find that as the concentration distribution increases from 1:1:1 to 1:2:1 and 1:3:1, both Young's modulus and dielectric permittivity gradually improve while dielectric loss remains extremely low even though the total MWCNT content reaches 1.6 wt%. With the combined effects of dielectric permittivity and modulus, the composite with evenly distributed MWCNT content (1:1:1) shows the highest actuation strain under a given electric field strength. Meanwhile, the electric breakdown strength of the composite 1:1:1 is also the highest, leading ultimately to a maximum actuation strain of 10.87% at the breakdown strength of 14.6 kV/mm.

Kenaf Fiber and Hemp Fiber Multi-Walled Carbon Nanotube Filler-Reinforced Epoxy-Based Hybrid Composites for Biomedical Applications: Morphological and Mechanical Characterization

This study used a hybrid combination of kenaf and hemp fibers and the multi-walled carbon nanotube (MWCNT) reinforcements in the matrix phase to synthesize the composites. A kenaf/hemp fiber blend with MWCNTs in epoxy was used for the specific concentration. The procedure used three composite materials chosen from pilot trials. The ratio of MWCNT filler particles was altered up to the agglomeration limit based on initial trials. Two specimens (2 and 3) were supplemented with MWCNTs in a concentration range of 0.5 wt. % to 1 wt. %, with the fiber concentration being maintained in equilibrium with the epoxy resin, all of the materials were tested under the same conditions. The hybrid nanocomposite was characterized for its morphological and mechanical properties; the tensile properties were higher for 1% MWCNTs concentration (specimen 2), while the flexural properties were higher for 0.5% MWCNTs, with values of 43.24 MPa and 55.63 MPa, correspondingly. Once the MWCNT concentration was increased to 1 wt. %, the maximum impact strength was achieved (specimen 3). In the limits of the Shore-D scale, the kenaf fiber and hemp fiber matrix composite (specimen 1) gained a hardness index of 84. Scanning electron microscopy was carried out to analyze the morphological features of the fractured samples and to assess the adhesion between the fiber, matrix, and surface. Among the various fillers tested, the kenaf fiber/hemp/MWCNT composite (specimen 3) demonstrated superior binding and reduced the incidence of fiber pull-out, breakage, and voids. In addition to the comparative analysis, the addition of 0.5 wt. % MWCNTs resulted in better mechanical properties compared to the other two combinations.

Investigation of the electrical sensing properties of cementitious composites produced with multi-wall carbon nanotubes dispersed in NaOH

The use of nanomaterials, such as carbon nanotubes, in cement-based composites has been a topic of considerable attention in recent years due to their potential to monitor civil structures and infrastructures. One of the main challenges is the adequate and efficient dispersion of the carbon nanotubes due to their nanoparticle size and the high adhesion forces developing among them. The most common strategy to tackle this challenge is to use sonic treatments that are unfeasible for field-scale implementations. Alternatively, specific chemicals (i.e. surfactants) facilitating nanotube mixing are used, but this often results in poor mechanical properties, reduced electrical conductivity and high environmental impact of the composites. This works has as the main aim to analyze the self-sensing properties of the cementitious composites developed with NaOH as the dispersing agent. For this purpose, the work investigates electrical and sensing properties of cement-based nanocomposites with different contents of multi-wall carbon nanotubes (MWCNT), namely 1%, 1.5%, and 2% with respect to cement weight, previously dispersed in NaOH aqueous solution. The composites' fresh and electrical properties are evaluated, and a microstructural analysis is carried out. The major findings of the work reveal that cement paste samples with different contents of MWCNT presented increasing sensing properties up to 2%, and that the dispersing strategy was promising despite its simplicity.

Mechanical Characterization of MWCNT-Reinforced Cement Paste: Experimental and Multiscale Computational Investigation.

Computational approaches could provide a viable and cost-effective alternative to expensive experiments for accurately evaluating the nonlinear constitutive behavior of cementitious nanocomposite materials. In the present study, the mechanical properties of cement paste reinforced with multi-wall carbon nanotubes (MWCNTs) are examined experimentally and numerically. A multiscale computational approach is adopted in order to verify the experimental results. For this scope, a random sequential adsorption algorithm was developed to generate non-overlapping matrix-inclusion three-dimensional (3D) representative volume elements (RVEs), considering the inclusions as straight elements. Nonlinear finite element analyses (FEA) were performed, and the homogenized elastic and inelastic mechanical properties were computed. The use of a multiscale computational approach to accurately evaluate the nonlinear constitutive behavior of cementitious materials has rarely been explored before. For this purpose, the RVEs were analyzed both in pure tension and compression. Young's modulus as well compressive and tensile strength results were compared and eventually matched the experimental values. Moreover, the effect of MWCNTs on the nonlinear stress-strain behavior of reinforced cement paste was noted. Subsequently, three-point bending tests were conducted, and the stress-strain behavior was verified with FEA in the macro scale. The numerical modeling reveals a positive correlation between the concentration of MWCNTs and improved mechanical properties, assuming ideal dispersion. However, it also highlights the impact of practical limitations, such as imperfect dispersion and potential defects, which can deteriorate the mechanical properties that are observed in the experimental results. Among the different cases studied, that with a 0.1 wt% MWCNTs/CP composite demonstrated the closest agreement between the numerical model and the experimental measurements. The numerical model achieved the best accuracy in estimating the Young's modulus (underestimation of 13%), compressive strength (overestimation of 1%), and tensile strength (underestimation of 6%) compared to other cases. Overall, these numerical findings contribute significantly to understanding the mechanical behavior of the nanocomposite material and offer valuable guidance for optimizing cement-based composites for engineering applications.

Enhanced sensing performance of EVA/LDPE/MWCNT piezoresistive foam sensor for long-term pressure monitoring

Conductive polymer composites (CPCs) with piezoresistive properties are smart detecting systems with high sensitivity, fast response, and low energy consumption. To enhance their sensitivity and cope with their high filler content requirements, solid CPCs are normally transformed into blends and foams, which reduces the elastic modulus, enabling larger deformations, wider detection range, and increased sensitivity. However, providing reversible and durable sensing properties remains challenging as it depends on the phase morphology, foam cell structure, and particle dispersion. To this end, we use multi-walled carbon nanotube (MWCNT) as a conductive filler with a high aspect ratio and develop CNT-filled ethylene vinyl acetate/low-density polyethylene (EVA/LDPE) blend foams. We fix the foam structure using chemical foaming and crosslinking agents in a compression molding process. To optimize the piezoresistive behavior, we follow a step-wise tuning approach, studying the blending morphology, the foaming attributes, the particle dispersion and affinity, thereby selecting the most promising formulations for further investigations. The least mechanical and electrical hysteresis is obtained at minimum foam density, which is obtained at a compromised crystallinity and crosslinking density. The higher affinity of MWCNT to EVA and the faster crosslinking of the EVA phase results in uniformly dispersed small cells at EVA-rich formulations and 4 phr MWCNT content. The final foam sensor demonstrates an impressive response and recovery times of less than 200 ms and remarkable durability thanks to the optimized cell morphology and mechanical properties. These findings expand the application of carbon-filled polyolefin foams in pressure monitoring, particularly in wearable sensors for strain and motion sensing.

Reinforcing potential of MWCNTs on mechanical and machining performance of hot-pressed ZTA-MgO ceramic cutting inserts

A new generation cutting insert was manufactured by multi-walled carbon nanotube (MWCNT) reinforcement (0–0.25 weight percentage (wt%)) into zirconia toughened alumina (ZTA)- magnesium oxide (MgO) ceramic matrix using a powder metallurgy route. The hot-press sintering technique was used to compact the uniformly mixed ZTA-MgO-MWCNT powders, sintered at 1500 °C followed by morphological, mechanical and functional characterizations. The relative densities of the samples were between 98 % and 99 %. The mechanical properties of the matrix were improved up to 0.15 wt% MWCNTs. The highest microhardness was ~2366 HV0.5 for 0.15 wt% due to grain refinement by synergistic pinning between spinel (MgAl2O4) and MWCNTs. Similarly, the highest indentation fracture toughness was ~7.33 MPa.m1/2 for 0.15 wt% MWCNT content due to micromechanical interlocking mechanism from a combined effect of MWCNT size variation and inter-particle distance between MWCNTs featuring proper crack bridging and crack deflection. To function as a cutting insert, the sintered samples up to 0.15 wt% was selected and shaped according to SNGN120408 cutting tool geometry. For minimum cutting force with high surface roughness, the optimized parameters were observed as a cutting speed of 300 m/min, feed rate of 0.12 mm/rev and 0.2 mm depth of cut using the design of experiment technique while machining AISI 4340 steels. Furthermore, regression models were developed to correlate the machinability with machining conditions. The comparative study suggested that the significant improvement of cutting force (~26.4 %), surface roughness (~55.3 %) and tool life (~29.4 %) was achieved for ZTA-MgO-0.15 wt% MWCNT ceramic tool with respect to ZTA-MgO inserts depending upon self-lubrication phenomenon alongside with the retention of proper tool geometry for a longer tool life ~44 min. The morphological and Raman spectra analysis of the worn region justifies the self-lubricating phenomenon at the interface by breaking and rolling of MWCNTs.

Influence of carbon nanotubes on the plasma electrolytic oxidation process of aluminum under “soft” sparking conditions

Plasma electrolytic oxidation of aluminum (PEO) was performed with dispersed multi-walled carbon nanotubes (MWCNTs) into the electrolyte. The effect of the carbon nanotubes concentration, as well as that of the electrical processing conditions, on the PEO process was investigated. From the point of view of the electrical response of the process, results show that the “soft” sparking regime appears earlier in presence of MWCNTs. The process time at which the transition to the “soft” regime occurs decreases linearly with the increase in the MWCNTs concentration. Over a concentration threshold, depending on the applied pulse bipolar current waveform, the PEO process is inhibited. The dispersion of MWCNTs in the electrolyte results in thicker but more porous alumina layers. More specifically, the proportion of the α-alumina phase relative to the γ-alumina phase decreases with the increase in the MWCNTs concentration. Results are explained by considering the increased coating growth kinetics and lower heat accumulation from MWCNTs addition. Finally, the present study gives new insights into the right management of the PEO process under “soft” sparking regime with dispersed carbon-based nanoparticles in the electrolyte.

Correlation analysis of pore structure and frost resistance of carbon nanotube concrete based on gray relational theory

AbstractIn order to explore the micro‐pore structure improvement mechanism of multi‐walled carbon nanotubes (MWCNT) on the frost resistance of concrete, five kinds of MWCNT concrete with different contents were prepared and the frost resistance test and mercury intrusion test were carried out. The results show that when the content of MWCNT is 0.1 wt%, the mass loss rate and compressive strength loss rate of concrete after freezing and thawing are 15.97% and 23.85% lower than that of ordinary concrete, respectively, indicating that this content is best amount to improve the frost resistance of concrete in this study. Moreover, 0.1 wt% MWCNT can significantly optimize the internal pore structure of concrete, and the average pore diameter growth rate and harmful pore ratio are 30.1% and 64.45%, respectively, after 200 freeze–thaw cycles. The proportion of more harmful pores has the greatest influence on compressive strength and relative elastic modulus, and the gray correlation degree is more than 0.8. Finally, the mathematical models of compressive strength‐pore parameters and relative dynamic elastic modulus‐pore parameters of MWCNT concrete after freeze–thaw cycle are established considering pore structure parameters and pore size distribution.

Influence of dope composition of polyethersulfone membrane blend with cellulose nanocrystal and carboxylated multi-walled carbon nanotube on humic acid rejection

A full factorial experimental design was employed to investigate the dope composition of a membrane made of cellulose nanocrystal (CNC), multi-walled carbon nanotube (MWCNT), and polyethersulfone (PES) for its ability to reject humic acid (HA). Four factors were screened, including PES composition, polyvinylpyrrolidone content, CNC content, and carboxylated MWCNT content. The membranes were tested for HA rejection using a 10-ppm aqueous feed solution. The results indicated that the percentage of MWCNT had the most significant impact, contributing 72.31% to the overall contribution. The fabricated membranes exhibited high HA removal capacity of up to 90% for the membrane embedded with MWCNT. The model's predicted values agreed reasonably with the experimental data, indicating the model's validity. This study provides insights into the development of CNC/MWCNT/PES membranes for efficient HA rejection in water treatment applications.

Multi-Walled Carbon-Nanotube-Reinforced PMMA Nanocomposites: An Experimental Study of Their Friction and Wear Properties.

This manuscript presents an experimental investigation of the friction and wear properties of poly (methyl methacrylate) (PMMA) nanocomposites reinforced with functionalized multi-walled carbon nanotubes (MWCNTs). The aim of this study is to evaluate the potential of MWCNTs as a reinforcement material for enhancing the tribological performance of PMMA. Three types of multi-walled carbon nanotubes, i.e., pristine, hydroxyl functionalized, and carboxyl functionalized, were utilized in this study. The nanocomposite samples were prepared by dispersing varying concentrations of MWCNTs (0.1 wt.%, 0.5 wt.%, and 1 wt.%) within the PMMA matrix via a 3D mixing approach, followed by injection molding/compression molding. The resulting nanocomposite films were characterized using scanning electron microscopy (SEM) to observe the dispersion of MWCNTs within the PMMA matrix. The friction and wear tests were conducted using a pin-on-disk tribometer under dry sliding conditions. The effects of functionalization and MWCNT content on the tribological behaviors of the nanocomposites were analyzed. The nanocomposites exhibited lower friction coefficients and reduced wear rates compared to pure PMMA. The lowest friction coefficient and wear rate were achieved at an optimum MWCNT loading of 0.5 wt.%. It was further revealed that the amount of MWCNT reinforcement, average load, and track diameter significantly affect the coefficient of friction (COF) and rate of wear. The COF and wear rate are best at a filler loading of 0.5 wt.%, a 20 Kg load, and 90 mm. The improved tribological performance of the MWCNT-reinforced PMMA nanocomposites can be attributed to the effective transfer of load between the MWCNTs and the PMMA matrix, as well as the reinforcement effect of the MWCNTs. The MWCNTs acted as reinforcing agents, enhancing the mechanical properties and wear resistance of the nanocomposites.

Enhanced Energy Harvesting Performance of Triboelectric Nanogenerators via Dielectric Property Regulation.

Triboelectric nanogenerators (TENGs) hold great application prospects and research values in the field of energy harvest. The friction layer of TENGs plays an important impact role in their output performance. Therefore, composition modulation of the friction layer is of great significance. In this paper, the xMWCNT/CS composite films with multiwalled carbon nanotubes (MWCNTs) as a filler and chitosan (CS) as a matrix were prepared and a TENG based on the xMWCNT/CS composite films (xMWCNT/CS-TENG) was constructed. The introduction of the conductive filler MWCNT significantly improves the dielectric constant of the films due to the Maxwell-Wagner relaxation. As a result, the output performance of the xMWCNT/CS-TENG is greatly enhanced. The best values of an open-circuit voltage of 85.8 V, a short-circuit current of 8.7 μA, and a transfer charge of 29 nC were obtained in the TENG with an optimum MWCNT content of x = 0.8 wt % under an external force of 50 N and a frequency of 2 Hz. The TENG can sensitively perceive human activities such as walking. Our results evidence that the xMWCNT/CS-TENG is a flexible, wearable, and eco-friendly energy collector, holding great prospects in health care and body information monitoring.

Effect of multi-walled carbon nanotubes on the microstructure and properties of Sn-58Bi solder alloys

The influence of multi-walled carbon nanotube (MWCNT) content on the melting properties, wettability, microstructure, and intermetallic compounds (IMCs) of Sn-58Bi-xMWCNT (x = 0, 0.01, 0.02, 0.03, 0.05, and 0.10 wt.%) and the effects of MWCNT on the tensile strength of Cu/Sn-58Bi-xMWCNT/Cu solder joint were analyzed. The results show that MWCNT addition at a small trace amount into Sn-58Bi solder could increase the spreading area of Sn-58Bi solder, refine the solder matrix microstructure, inhibit the growth of interfacial IMCs, and significantly improve the tensile strength of Sn-58Bi solder joints. However, the melting point and melting range remained the same or slightly changed. The wettability of Sn-58Bi alloys increased first and then decreased with the addition of MWCNT. The spreading area and the tensile strength of solder joint were the maximum when the MWCNT content was 0.01 wt.%, and they were 42.23 mm2 and 50.07 MPa, respectively. The reason may be related to the improved microstructure of solder alloys and the morphology of IMCs due to MWCNT addition at trace level.

Effects of the Ratio of Nano-Cu to Hydroxylated MWCNTs on Anticorrosion and Surface Conductivity of Cu/MWCNT Epoxy Coatings on a Steel Substrate

Epoxy coatings provide an economical and practical solution for combating steel corrosion. However, epoxy coatings have poor conductivity, resulting in the accumulation of electrostatic charges. The surface conductivity and anticorrosion properties of epoxy coatings can be improved by adding nano-Cu and hydroxylated multi-walled carbon nanotubes (MWCNTs). This paper investigates the impact of MWCNTs at different concentrations (2.5, 5%) and the ratio of nano-Cu to MWCNTs on the surface conductivity and anticorrosion properties of epoxy coatings on a steel substrate. The findings from the four-probe method of measuring surface resistance indicated that the surface resistivity of steel coated with an epoxy composite of 5% MWCNTs and 65% nano-Cu (Cu65/MWCNT5) was significantly lower, approximately by one order of magnitude, compared to steel coated with a 5% MWCNT (MWCNT5) epoxy coating. When the Cu65/MWCNT5-coated steel was immersed in a 3.5 wt % NaCl solution for 30 days, it was observed that there was a minimal effect on its surface resistivity. The inclusion of a high content of MWCNTs facilitates a more uniform distribution of Cu particles within the epoxy coatings, thereby improving the anticorrosion properties of these coatings on a steel substrate. This was further corroborated by the results of the polarization curves and electrochemical impedance spectroscopy, demonstrating that the Cu65/MWCNT5 epoxy coating on a steel substrate offers exceptional anticorrosion and barrier protection properties. The corrosion rate of steel with a Cu65/MWCNT5 epoxy coating was three orders of magnitude lower than that of steel with a Cu65/MWCNT2.5 epoxy coating, at 4.79 × 10−7 mm/year.

Multifunctional ultra-high performance fibre-reinforced concrete with integrated self-sensing and repair capabilities towards in-situ structure monitoring

Achieving continuous in-situ monitoring of repaired concrete structures has always been a great challenge. Ultra-high performance fibre-reinforced concrete (UHPFRC), featuring superior mechanical capacity, excellent erosion resistance, and long-life cycle, is expected to realize durable, cost-effective, and aesthetically pleasing repairs and possesses tremendous potential for intrinsic self-sensing. This paper presents the multifunctionality of UHPFRC with integrated self-sensing and repair capabilities using multi-walled carbon nanotube (MWCNT). An experimental evaluation on the bond performance and self-sensing properties, including the bond strength and failure patterns by the three-point bending, splitting tensile, and slant shear tests, electrical properties via alternating current impedance spectroscopy test, and electromechanical properties under three-point bending, was conducted through the designed composite layer between concrete substrate and UHPFRC. The microstructure of the interfacial zone was analysed to reveal the bonding mechanism. Results indicate that the addition of MWCNT improved the bond strength between concrete substrate and UHPFRC as MWCNT can enhance the adhesion and cohesion of the interfacial zone through inactive filling effect, as well as the frictional and mechanical interlocks through increased mechanical properties of repair UHPFRC. Moreover, the repair UHPFRC showed remarkable sensing capabilities for the initial cracking, deflection hardening or softening, and fibre pull-out and debonding processes of the composite layers. The optimal content of steel fibre and MWCNT in multifunctional UHPFRC should be 2 vol.% and 0.2 wt.%, respectively, considering the synergistic damage sensing and bonding properties.