Papers by Keyword: Bonding Mechanism

Abstract: Here, we report the bonding mechanism and electronic structure of single-walled carbon nanotube and oxygenated single-walled carbon nanotube functionalized by cellulose chain using first-principles density functional theory. Analysis of the optimized molecular configuration and charge redistribution of the nanohybrid indicates that the cellulose chain binds with the prototype single-walled carbon nanotube and oxygenated single-walled carbon nanotube via physisorption. The cellulose chain adsorption on the single-walled carbon nanotube preserved its electronic structure. On the other hand, the electronic structure of the oxygenated single-walled carbon nanotube and cellulose complex reveals that the electronic states of the cellulose tend to populate in the forbidden gap, thus, lowering the bandgap of the overall complex. The electronic structure of the complex can be considered as the superposition of its constituents in which no significant hybridization of the orbital characters is observable. The findings confirm that cellulose is indeed suitable for the non-covalent functionalization of single-walled carbon nanotubes and provide new insights into the electronic structure of the oxygenated single-walled carbon nanotube/cellulose complex.

Abstract: In tri-layered Cold Roll Bonded (CRB) composite sheets of dissimilar metals, uneven thickness reduction of the different layers have been observed. This has been explained by the difference in yield strength/flow stress of the metals. The aim of this research was to study if these observations also depend on different parameters such as stacking sequence and initial sheet thickness, as opposed to only material properties. Hence, tri-layered CRB composite sheets consisting of AA6082 and IF-steel were produced with two different stacking sequences, St/Al/St vs Al/St/Al. Two different layer thicknesses of the intermediate layer were used. Rolling was performed in a single pass achieving approximately 55-65% total thickness reduction. Comparisons between the samples are given, focusing on the reduction of thickness achieved in each layer, the roll bonded interface characteristics and the bond strength of the joints. The overall thickness reduction achieved in each layer was found to be similar for both metals in both stacking sequences for the considered material combination. The stacking sequence is statistically found not to have any effect on the bond strength of the joints. The thickness of the intermediate layer does not significantly affect the overall bond strength of the composite sheet for both stacking sequences. These findings are opposed to earlier results found in the literature.

Abstract: One kind of Al₂O₃ ceramic-lined steel pipe was prepared with the gravitational separation SHS method by using the reaction system of Al-Fe₂O₃-Cr₂O₃. The element line scans of transition structure and the element plane scans of ceramic coating far away from transition layer were analyzed by Scanning Electron Microscopy and Energy Dispersive Spectroscopy, and then they were used to discuss the coating structure and interface bonding mechanism, and investigate the element composition distribution of coating. All of these were closely related to improving the properties of ceramic-lined steel pipe. The results showed that a transition layer was formed between metal pipe and ceramic coating, it was due to the gravitational separation and molecular diffusion motion of the reaction products in molten state; in the transition structure the amount of the reaction elements was gradually transitional from the direction of the coating-transition layer-steel pipe, which could reduce the stress difference between the layers; in the coating far away from the transition layer, only small amount of Fe embedded in the ceramic was left in the form of Fe-Cr alloy, while Cr was uniformly enriched in the Al₂O₃ ceramic, these all have great influence on the anti-corrosion ability of coating.

Abstract: Boron (B) has great potential to be the primary fuel in energetic systems for its high heating values per unit volume and mass. The existence of B₂O₃ layer on its surface holding the combustion of B back has limited its extensive utilization. Adding magnesium (Mg) into B can improve its poor combustion performance according to the previous research. A new technique, cryomilling, was employed to prepare Mg and B (Mg/B) composite powders. The powders were cryomilled with a ball-to-powder ratio (BPR) of 80: 1(w/w) and an impeller rotation speed of 400 rpm, 500 rpm and 600 rpm. The cryomilling time is 5 h, 6 h and 7 h. A small amount of ferrum (Fe) is introduced into the powders in spite that the main phases are Mg and B. The effects of cryomilling parameters, such as cryomilling time and rotation speed on Mg/B composite powders were investigated. The results show the amount of active Mg and B is over 80%. The bonding mechanism during the process is analogous to mechanical alloy.

Abstract: This paper analyzed the failure modes of single layer electroplated uperabrasive products. The bonding force is the primary factor that dominates the grinding quality and tool life. So the understanding of bonding mechanism is of great importance for improving efficiency and quality in the applications of these abrasive products. In this paper, the experimental setup similar to an inclined micro-threading process is designed to observe and measure the failure mode and maximum bonding force respectively. The relationship between maximum bonding force and bonding layer thickness is established through the experiment. In addition, failure modes are analyzed by comparing the morphology before and after the high speed bonding force test for electroplated layer.

Abstract: To develop a new industrial briquette composite binder, response surface methodology was used to arrange experiments, with modified peat(MP），mixed wastes(WS)，modified clay 2(C2) and clay 1(C1) as raw materials. The experimental data was firstly processed utilizing the method of multi-factorial total probability formula evaluation. Then based on the regression analysis and model building, the optimum formula was obtained. Finally, the bonding mechanism was analyzed through a systematical study by means of both ESEM and TG-DTA. The results indicated that the briquette prepared according to the optimum formula, namely 4.4% of MP, 6.5% of WS, 2% of C1, 1% of C2, and correlative key parameters of briquetting technics, namely forming water 13%, drying temperature 180°C and drying time 2.5h had excellent performances, which could meet the demand of industrial production in enterprises.

Abstract: The aluminum phosphate adhesive was prepared by aluminum dihydrogen phosphate and ceramic fillers. The mullite, silica and silicon powders were added as the fillers to improve the mechanical property and high temperature property. The specimens were prepared by joining the mullite ceramic/ceramic by phosphate adhesive. The strengths of the specimens treated at different temperatures were studied. The results indicated that the tensile strength at room temperature was 2.02 MPa, and it reached 5.06 MPa when the specimen was treated at 800°C. The bonding effect and bonding property at high temperature were discussed through the SEM analysis. Besides, the bonding mechanism was also explored.

Abstract: Cold gas dynamic spraying (CGDS) is a relatively new branch of surface engineering that involves modification of the surface of substrates to provide specific engineering advantages, which the substrate alone cannot provide. Cold spraying, as a metal deposition technique, involves spraying of typically 10-40 μm particles which are accelerated by a propellant gas to 300-1200 m/s at a temperature well below the melting point of material, and upon impact deform and adhere to the substrate. The deposition process in cold spraying occurs in a solid state which results in reduced oxidation and absence of phase changes; whereas, in thermal spraying deposition occurs of molten or semi molten particles. Over the last decade the interest in cold spraying has increased substantially. Considerable effort has been invested in process developments and optimization of coatings like copper. However, bonding in cold spraying is still a matter of some debate. The most prevalent theory is that when a particle travels at a minimum required velocity the particle deforms at a very high strain rate upon impact and during this deformation thermal softening dominates over work hardening in impact zone and a material jet is produced. This material jet removes oxides from the surface of the materials and the metal-to-metal contact is established between the freshly exposed surfaces. However, precisely how this high strain rate deformation behaviour of material promotes bonding is still unclear and requires further investigations. This article provides a comprehensive review of the current theories of bonding in cold spraying based on numerical modelling of impact and experimental work. The numerical modelling of the impact section reviews adiabatic shear instability phenomena, critical velocity, critical particle diameter, window of deposition of particles, particle impact on various substrates and the role of adhesion and rebound energy. The review of the experimental section describes the shear lip formation, crater formation on the substrates, role of surface oxides, characterization of bond formation, role of substrate preparations, coating build up mechanisms and contributions of mechanical and metallurgical components in bonding. Cold spraying of copper and aluminium has been widely explored in the last decade, now it is of growing interest to the scientific and engineering communities to explore the potential of titanium and its alloys. Titanium and its alloys are widely utilized in many demanding environments such as aerospace, petrochemical, biomedical etc. Titanium components are very expensive to manufacture because of the costly extraction process of titanium and their difficult to machine properties. Therefore, additive manufacturing from powder and repair of titanium components are of great interest to the aerospace industry using technologies such as cold gas spraying. Titanium coating as a barrier layer has a great potential for corrosion resistant applications. Cold spraying has a great potential to produce oxygen-sensitive materials, such as titanium, without significant chemical degradation of the powder. In-flight oxidation of materials can be avoided to a great extent in cold spraying unlike thermal spraying. This review article provides a critical overview of deposition efficiency of titanium powder particles, critical velocity, bond strength, porosity, microhardness, microstructural features including microstrain and residual stress, mechanical properties reported by various research groups. A summary of the competitor warm sprayed titanium coating is also presented in this article.

Abstract: Cold spray (CS) is an emerging revolutionary technology for deposition of metal or composite powders at a low temperature. High quality deposits can be produced without heating related defects, such as oxidation, phase transformation and residual tensile stress due to the shrinkage during fast cooling. The present contribution demonstrates the state of the art of CS process. Since nozzle is a key component in the CS equipment to prompt the efficiency of particle acceleration, the progress of its design is summarized. Major issues regarding to the successful adhesion of particles and corresponding interaction with substrates and existing deposits are discussed, in terms of numerical simulation and experimental observation. Current implemented CS applications are presented, and potential industrial applications are discussed. Keywords: cold spray; coatings; rapid manufacturing; particle impact; bonding mechanism; nozzle design

Abstract: Adding B-ion additive or Mg-ion additive to Al-phosphate binder to get different binders, and viscosity of Al-phosphate binders and dry strength of their no-bake sand were tested, bonding mechanism among sands of Al-phosphate no-bake sand was discussed by SEM and EDS. Results indicate that Mg-ion additive can increase binder’s viscosity and dry strength of its no-bake sand more obviously than B-ion additive, adding Mg-ion additive and B-ion additive simultaneously is more obvious. Location crack produced is changed from sand surface to binding bridge inner while adding Mg-ion additive and B-ion additive simultaneously ,and fracture mode is changed from adhesive fracture mainly to cohesive fracture mainly, dry strength is improved from 0.86MPa to 2.38MPa.