Improved Adhesion Strength Research Articles

Influence of Ground Temperature on Shotcrete-to-Rock Adhesion in Tunnels

Long and deep tunnels are increasingly designed and built worldwide, often in severe geothermal environments characterized by high temperature in the rocks. This issue cannot be ignored because high temperature definitely affects the strength of the adhesion between the concrete and the surrounding rocks, whatever the lining cast in place, segmental or sprayed using shotcrete. The causes of geothermal heat and the effect of the temperature on tunnel linings during and after their construction are recalled and discussed in this paper. Both temperature and humidity are shown to be the most relevant factors affecting adhesion strength, whose loss is related to the microdamage in the shotcrete layers closest to the rock. Possible ways to improve adhesion strength and to minimize the high-temperature detrimental effect are also presented and discussed.

TiO2 Nanotube Layers: Homogeneous Anodic TiO2 Nanotube Layers on Ti–6Al–4V Alloy with Improved Adhesion Strength and Corrosion Resistance (Adv. Mater. Interfaces 12/2019)

TiO₂ Nanotube Layers: Homogeneous Anodic TiO₂ Nanotube Layers on Ti–6Al–4V Alloy with Improved Adhesion Strength and Corrosion Resistance (Adv. Mater. Interfaces 12/2019)

Strengthening the Electrodes for Li-Ion Batteries with a Porous Adhesive Interlayer through Dry-Spraying Manufacturing.

The manufacturing technologies for electrodes have a great influence on the performance of Li-ion batteries. Manufacturing procedures largely determine the microstructure of electrodes, and thus affect how active materials are involved in the electrochemical reactions. However, the usage of solvent in the dominant slurry-casting method weakens its competence on obtaining desired microstructures and properties. In this study, an improved adhesion strength is achieved during the fabricaion of graphite anodeswithour solvent-free manufacturing method. Through dry-spraying an interfacial "adhesion enhancer" layer between the current collector and the electrode coating, the mechanical strength (from 0.5 kPa to over 83.0 kPa) and electrochemical performance (from 24.2% to 92.4% as the capacity retention in 100 cycles) are significantly improved. Results here demonstrate a simple and economical route to practically control the microstructure of electrodes during manufacturing and potentiate the strategy enabled by dry-spraying to design and manufacture advanced batteries.

Study the effect of thermal annealing on adhesion strength of Silver-Tantalum Oxide thin film deposited by reactive magnetron sputtering

Stainless steel (SS) are extensively used for healthcare, hygiene and surgical applications due to their excellent corrosion resistance and adequate mechanical strength. Among this class SS 316 L is employed most widely, due to highest corrosion resistance, good mechanical properties, resistance to sensitization and ease of fabrication. To incorporate antimicrobial characteristic in SS 316 L based surgical tools a nanocomposite layer comprising of Silver (Ag) and Tantalum oxide (TaxOx) has been deposited by using Physical Vapor Deposition (PVD) magnetron sputtering. Delamination of ceramic layers on SS 316 L substrate is one of the major limitation arising from insufficient crystallization and poor adhesion strength. PVD magnetron sputtering has been employed to develop 5.49 µm thick Ag-TaxOx nanocomposite layer on SS 316 L. Substantially improved adhesion strength has been achieved by controlling thermal treatment. The microstructure, surface and phase analysis of as-sputtered and annealed thin films has been carried out to determine the characteristics of the developed layer. A nanocomposite layer on SS 316 L substrate comprising of Ag and TaxOx has been achieved by releasing O2 during deposition. Thermal treatment was performed at 300, 400, 500 and 600 °C which progressively increased the crystallinity and segregation of Ag at the surface. Highest adhesion strength was achieved by annealing the coated samples at 400 °C, which exhibited four-fold increased adhesion strength when compared to as-deposited layer. The precipitation of a new phase Silver tantalum oxide (AgTaO3) was observed for the samples annealed at temperature above 400 °C, which may be responsible for the decrease in adhesion strength.

A promising ternary nanohybrid of Copper@Zinc oxide intercalated with polyaniline for simultaneous antistatic and antibacterial applications

In this study, a facile and cost-effective approach has been developed for fabricating antibacterial and antistatic waterborne polyurethane (WPU)-based coatings by using Polyaniline-Copper@Zinc oxide (P-Cu@ZnO) ternary nanohybrid as a multifunctional additive. The solid-state reaction of copper acetate and zinc acetate salts led to the synthesis of copper clusters on the ZnO nanoparticles (Cu@ZnO). The obtained Cu@ZnO nanoparticles were intercalated with polyaniline (PANI) chains to prepare the P-Cu@ZnO nanohybrid. FTIR, XRD, UV–Vis, and FESEM analyses were used to characterize the structural, crystallographic, and morphological properties of the synthesized nanohybrid. Adding P-Cu@ZnO nanohybrid to the WPU matrix not only improved adhesion strength of the coatings but also enhanced their scratch resistance compared to the pristine WPU coating. Moreover, incorporation of the obtained nanohybrid into the WPU coatings caused electrical surface resistance of the obtained coatings to reach 1.2 × 10+8 Ω/sq, so, these coatings gained the optimum electrical surface resistance to be counted as an antistatic coating. Also, the results of the colony counting test showed that the modified coatings could reduce the Staphylococcus aureus and Escherichia coli bacteria growth by about 86% and 74%, respectively.

Homogeneous Anodic TiO2 Nanotube Layers on Ti–6Al–4V Alloy with Improved Adhesion Strength and Corrosion Resistance

AbstractHexagonal TiO2 nanotubes (TNTs) arrays are generally fabricated on Ti‐based substrates for some biomedical purposes, but the TNT layers constructed on conventionally processed Ti alloys are usually inhomogeneous because the substrates typically contain both the α and β phases. In this work, high‐pressure torsion (HPT) is applied to obtain a saturated single α‐phase microstructure in Ti–6Al–4V alloys via strain‐induced β phase dissolution. Homogeneous anodic TNT layers with three different morphologies, one‐step nanoporous, one‐step nanotubular, and two‐step nanoporous structures, are electrochemically fabricated on the ultrafine‐grained (UFG) Ti–6Al–4V alloy substrates after HPT processing, whereas the TNT layers prepared on coarse‐grained substrates are normally inhomogeneous. More notably, the TNT layers show significantly improved adhesion strength to the UFG substrate as well as better corrosion resistance compared to those on the conventionally processed Ti–6Al–4V substrates. X‐ray diffraction analysis, scanning electron microscopy in combination with electron backscatter diffraction, and transmission electron microscopy indicate that the improvement is due to a larger dislocation density in the UFG substrate as well as strain‐induced β phase dissolution.

Optimization of cellular lightweight concrete using silica sand of sandblasting waste based on factorial experimental design

Sandblasting is a surface treatment that serves to clean the surface, improves adhesion strength and bonding performance, which in the process produces silica sand waste. Silica sand of sandblasting waste can be used as a lightweight concrete type of Cellular Lightweight Concrete (CLC). The experimental design was used factorial to find out factors influencing the compressive strength of lightweight concrete and to find the optimum composition of lightweight concrete with maximum compressive strength. The results showed that Portland cement composition and the ratio of foam significantly influenced the compressive strength of lightweight concrete with silica sand waste of sandblasting as aggregate. The optimum compressive strength of 86.13 kg/cm2 was found in the composition of Portland cement by 40%, silica sand 40% and volume ratio foam to mortar 0.6.

Improving the molecular weight and synthesis of a renewable biomimetic adhesive polymer

Renewable materials are in demand to replace the petroleum-based glues we use on a daily basis. Such substitutions will not take place until bio-based adhesives can meet or exceed the performance of current materials. Work presented here examines several chemical parameters in order to improve the molecular weight and synthetic strategy for a polymer that combines polylactic acid with mussel mimicking catechol, (“catechol-PLA”). Altering the polymerization time as well as the deprotection time and temperature afforded better control over both molecular weights and yields. Dispersity and molecular weight were shown to both be parameters tunable to improve adhesion strength. Cross-linking with iron improved the adhesion of low molecular weight polymers, bringing performance up to that of the longer chain counterparts. Such cross-linking and molecular weight effects were seen to alter the balance of adhesive and cohesive interactions. Such development and understanding of renewable polymer systems may help to hasten future competition with petroleum-based adhesives.

Microstructure, adhesion and tribological properties of CrN/CrTiAlSiN/WCrTiAlN multilayer coatings deposited on nitrocarburized AISI 4140 steel

In this study, the CrN/CrTiAlSiN/WCrAlTiN multilayer coatings have been deposited on polished AISI 4140 steel substrates (named only-coating specimens) and plasma nitrocarburized specimens (named duplex specimens) by cathodic multi-arc evaporation. The microstructure and composition of the specimens were studied using X-ray diffraction (XRD), scanning electron microscopy (SEM) with Energy dispersive X-ray analysis (EDX), and transmission electron microscope (TEM) techniques. The micro-hardness and nano-hardness were measured by Vickers hardness tester and nanoindentation, respectively. The adhesion and tribological behavior were evaluated using the Rockwell-C indentation and micro-tribometer, respectively. The results showed that plasma nitrocarburizing gives rise to a modified layer due to diffusion of nitrogen/carbon, leading to surface hardness, H, of 13.0 GPa, compared to H = 6.8 GPa for the untreated steel. Notably, it shows that the super-hardness (H = 47.9 GPa) multilayer coating consists of a bottom CrN layer, a middle CrTiAlSiN layer, and an outmost superlattice WCrTiAlN layer. The nitrocarburizing pretreatment considerably improves adhesion strength of the duplex specimen compared with the only-coating one. The improved mechanical and tribological properties of the duplex specimen are mainly related to the gradient in the hardness profile of the diffusion nitrocarburized layer.

Heating behavior and adhesion performance of induction-heated multilayered thermoplastic polyurethane adhesive film

ABSTRACT A multilayer thermoplastic urethane (TPU) adhesive system was developed to achieve higher heat generation efficiency and adhesion by using the same amount of nickel particles in an induction heating process. The results of the present study show that a higher heat generation efficiency and peel adhesion strength were achieved with a higher density of nickel particles in the core layer, even for a constant 20 phr nickel particle content in the 200 μm film. The heat generation mechanism of the 70 nm nickel particles was confirmed as hysteresis heat loss by calculating the magnetic penetration skin depth. The results of the scanning electron microscope (SEM) and Fourier transform infrared (FT-IR) analysis show that the observed failure mode was substrate failure in the peel adhesion test, and the nickel particles of the core layer were spread on the TPU adhesive film at the top and bottom. In conclusion, the multilayer structure, including the high-density susceptor core layer at the center of the adhesive film, can be employed for industrial applications to enable highly efficient heat generation and improvement in adhesion strength.

Kinetic stabilization of cellulose nanocrystals in a photocurable prepolymer for application as an adhesion promoter in UV-curable coatings

Cellulose nanocrystals (CNC) at low loading levels were shown to reinforce a photocurable coating resulting in improved adhesion. A polyether polyol containing CNC at loading levels of up to 1.8 wt% was grafted with 3-isopropenyl-α,α-dimethylbenzyl isocyanate to functionalize it with a photocurable group. The nanoparticles were kinetically stabilized in the rapidly forming prepolymer of high viscosity. Photoinitiators and a difunctional reactive diluent were added to produce optically transparent coatings and free films upon irradiation by ultraviolet (UV) light. This allowed evaluation of the effects of CNC at low loading levels in a glassy polymer matrix obtained through a rapid cure system. Incorporation of CNC nanoparticles in the polymer matrix resulted in an average improvement in adhesive strength of 154% while enhancing tensile strength by an average of 16%. The technique described could be used as a new approach to reduce adhesive failure in UV-curable coatings without sacrificing their mechanical strength.

Enhancement of the Epoxy Coating Corrosion/Cathodic Delamination Resistances on Steel by a Samarium Based Conversion Coating

Samarium (III) (Sm)-based conversion layer was developed on carbon steel for improvement of the epoxy coating adhesion properties, corrosion protection performance, and cathodic delamination resistance. The post-heating and pre-heating actions impact on the Sm (III) film properties was studied. The morphology and chemistry of the Sm (III) film were examined by scanning electron microscopy, atomic force microscopy, contact angle, and X-ray photoelectron spectroscopy. The outcomes from these analyses proved that both pre-heating and post-heating actions altered the morphology and chemistry of the Sm (III) film. The pull-off test indicated that Sm (III) film could enhance the adhesion between the epoxy/steel through increasing the surface roughness and enhancing the surface free energy. The improvement in adhesion strength led to a decrease in the cathodic delamination rate up to 78%. Although both pre-heating and post-heating actions improved the corrosion protection performance of the epoxy film, the pre-heating method had a much higher impact on the epoxy film corrosion resistance enhancement. An excellent corrosion protective performance was observed in the samples preheated at 65°C after 1000 h exposure to salt spray test.

Studies on Improvement of Adhesive Strength of Composite Panels by Different Adhesion Process Methods

Studies on Improvement of Adhesive Strength of Composite Panels by Different Adhesion Process Methods

Electrodeposited Cu/MWCNT composite-film: a potential current collector of silicon-based negative-electrodes for Li-Ion batteries.

With the aim of developing the potential high theoretical capacity of Si as a negative electrode material for Li-ion batteries, a new type of composite current collector in which multi-walled carbon nanotubes (MWCNTs) are immobilized on a Cu surface was developed using an electroplating technique. For the Si electrode with a flat-Cu substrate, voltage plateaus related to the stepwise electrochemical lithiation were observed below 0.27 V (vs. Li/Li+), whereas the Cu/MWCNT substrate distinctly decreased the overvoltage to enhance charge/discharge capacities to approximately 1.6 times that obtained in the flat-Cu system. Field-emission scanning microscopy revealed that MWCNTs immobilized on the Cu surface extended inside the active material layer. Adhesion strength between the substrate and electrode mixture layer was reinforced by MWCNTs to increase the reversibility of change in electrode thickness before and after cycling: the expansion ratio was 200% and 134% for flat-Cu and Cu/MWCNT systems, respectively. Electrochemical impedance analysis demonstrated that MWCNTs served as an electron conduction pathway inside the electrode. By controlling the upper cutoff voltage from 2.0 V to 0.5 V, synergetic effects including improved adhesion strength and a more developed conduction pathway became noticeable: a reversible capacity of 1100 mA h g−1 with 64% capacity retention was achieved even after the 100th cycle. The results indicate that the Cu/MWCNT is a promising current collector for expansion/contraction-type active materials for rechargeable batteries.

Aqueous Binder for Nanostructured Carbon Anode Materials for Li-Ion Batteries

Water soluble hydrophilic polymer poly-N-vinylformamide (PNVF) has been adopted as new binder for selected anode materials based on nanostructured carbon aerogels (CAGs) derived from different types of starch (rice, maize, potato) as well as for graphite as a reference. The results suggest that PNVF can be promising, fluorine free and volatile organic compounds (VOC) free binder for some anode materials especially when taking into consideration its beneficial properties, cost reduction as well as environmental friendliness. PNVF enhances chemical and physical interactions with tested carbons improving adhesion strength of the created composites and thus capacity retention of the formed electrodes during extensive cycling under high current load. Herein, we show that although the binder is only a small part of the entire electrode composition, it has a huge impact on the properties and efficiency of lithium-ion battery. Thereby, every anode material require properly selected binder for the suitable operation and performance of the cell.

Fabrication of functionally-graded yttria-stabilized zirconia coatings by 355 nm picosecond dual-beam pulsed laser deposition

This article presents the design, fabrication, and characterization of functionally-graded yttria-stabilized zirconia (YSZ) coatings by using a novel dual-beam pulsed laser deposition method based on a 355 nm ps laser. Graded coatings were fabricated by mixing YSZ and the substrate material (stainless steel). The two materials were ablated and deposited on a substrate inside a vacuum chamber, in a way that the mixture composition gradually changes from stainless steel to YSZ, along the coating's growth direction, following a predesigned linear composition profile. The Rockwell indentation method was employed for the adhesion strength analysis based on the interfacial crack radius (c) and indentation load (P). When a load P is applied on the sample surface, a crack with a radius c will be formed. Hence, by using more than one loads and measuring the generated crack diameters, dP/dc can be estimated, which is considered as a critical parameter and is proportional to the coating's adhesion strength. The graded coating was found to provide improved adhesion strength (dP/dc = 9.41 N/μm) over pure YSZ coatings (dP/dc = 8.35 N/μm and 8.43 N/μm). In this study, the thermal barrier effects of the coatings were examined by measuring the thermal conductivity values of the coatings using a high-power multi-mode fiber laser as an impulsive heat source and an infrared camera, and the deposited YSZ coatings showed a low thermal conductivity (∼1.14 W/m·K).

The effects of radio-frequency CF4 plasma on adhesion properties of vertically aligned carbon nanotube arrays

In this paper, vertical aligned carbon nanotube arrays (VACNTs) were modified by radio-frequency tetrafluoromethane (CF4) plasma for different times, and the corresponding adhesion performance of VACNTs was investigated. Scanning electron microscopy and Raman spectroscopy showed that the VACNTs remained intact alignment after CF4 plasma treatment, but the defects and amorphous carbon increased with increasing time. X-ray photoelectron spectroscopy showed that various functional groups were introduced with increasing time, such as CO bonds, CO bonds, semi-ionic covalent CF bonds, covalent CF bonds before 90 s, CF2CF2 after 90 s. The water contact angle was drastically decreased before 90 s and then obviously increased until 180 s. The adhesion tests showed that the adhesion of the VACNTs firstly increased and then decreased, and the best adhesion strength of 29.3 N/cm2 was obtained at 90 s, which improved about 39% compared with the pristine VACNTs. It can be seen that the polar/non-polar groups plays a significant role on the adhesion behavior, and a great improvement of adhesion strength is obtained for the VACNT containing the polar groups on the surface after 90 s CF4 plasma treatment.

Weldability modification of conductive silver adhesion for piezoelectric composite material by co-doping of metal material and oxide material

The weldability is essential for the practical applications of conductive adhesion. In this paper we focused on the weldability through microstructure, bonding strength, and shear strength of welding spot with co-doping of metal material Al and oxide material ZnO. When Al and ZnO doped separately, it can be seen from the results that Al-doping would increase the volume resistivity and adhesion strength for welding spot, and a proper amount of ZnO-doping would decrease the volume resistivity and improve adhesion strength for welding spot. Co-doping with Al and ZnO could decrease volume resistivity and enhance adhesion strength of welding spot concurrently, and the typical properties were 1.119 × 10−4 Ω cm for volume resistivity, 34.84 MPa for shear strength, and 17.00 MPa for bonding strength with addition of 4 wt% Al and 7 wt% ZnO.

Effect of PSO and TiB2 content on the high temperature adhesion strength of SiBCNO ceramic

In the present work, SiBCNO-based ceramic as high temperature adhesives are fabricated by polymer derived ceramic route. The effect of polysiloxane (PSO) and TiB2 on the microstructure and high temperature strength is studied, and the toughing effect of TiB2 is discussed. The highest adhesion strength of the joint (S12) reached up to 18.95 MPa at room temperature and 12.3 MPa at 1000 °C in vacuum after pyrolysis at 1000 °C in air for 2 h. It is interesting to find that the crystallization of nano-SiO2 reinforces the strength and thermal stability of glass phase with the addition of PSO, besides, the TiB2 plays the important role in improving adhesion strength by bearing load and facilitating the formation of stable SiO2-B2O3-TiO2 glass.

Infiltration brazed core-shell WC@NiP/NiCrBSi composite cladding

In this study, a novel Ni-P-coated WC/NiCrBSi composite cladding was prepared on a carbon steel substrate through high-temperature vacuum brazing technique with the aim of improving the wear properties of the surface. In order to improve the wettability of WC particles by a liquid phase (NiCrBSi alloy), Ni-P layer was deposited on carbide particles by electroless plating. This layer assisted to fabricate a thick coating with very low porosity, improving adhesion strength between ceramic particles and the matrix. The morphology, crystal structure and microstructure of coated carbides and the resultant composite cladding were characterized by field emission scanning electron microscopy (FESEM) equipped with energy dispersive X-ray spectroscopy (EDS), and X-ray diffraction (XRD) analysis. Thin electroless plated Ni-P shell with a thickness about 50–150 nm, were coated on WC particles. In the claddings, a uniform and homogenous distribution of WC particles in Ni-based matrix was observed. The pin on disk wear test was carried out to investigate the wear behavior of the fabricated cladding reinforced with and without Ni-P coated WC particles. The results indicated that the resistance against crack initiation and propagation significantly improved by using Ni-P layer in the sintered cladding. This cladding exhibited very low wear weight loss than conventional brazed cladding.