Effect of nitric acid surface treatment on tensile and tribological properties of thermoplastic polyimide composite filled with carbon fibre

Abstract

Polyacrylonitrile based carbon fibres were submitted to nitric acid oxidation treatments to improve the interfacial adhesion of the carbon fibre reinforced polyimide (CF/PI) composite. The carbon fibre surfaces were characterised by X-ray photoelectron spectroscopy. Nitric acid oxidation not only affects the oxygen concentration, but also produces an appreciable change in the nature of the chemical functions, namely the conversion of hydroxy type oxygen into carboxyl functions. Nitrogen concentration of nitric acid oxidation treated carbon fibre is ～1·2 times higher compared with untreated one. The mechanical and tribological properties of the CF/PI composites treated with nitric acid oxidation were investigated. Results showed that the tensile strength of the CF/PI composites improved remarkably due to nitric acid treatment along with enhancement in friction and wear performance.     

Phenol–formaldehyde resins modified by copper nanoparticles

Abstract

Phenol–formaldehyde (PF) resins modified by copper nanoparticles were synthesised by in situ polymerisation process. X-ray diffraction (XRD), transmission electron microscopy (TEM) revealed that nanosized copper particles were well dispersed in the resulting PF resins. The thermal properties of the prepared PF resins were investigated by thermogravimetric analysis (TGA). It was indicated that copper nanoparticles remarkably improved the thermal stability of the PF resins at lower temperature. However, the copper nanoparticles increased the rate of the degradation of the PF resins at the elevated temperature. The toughness and the tribological properties of the friction materials based on the prepared PF resins were also studied. The results showed that copper nanoparticles obviously improved the brittleness and the tribological performances of the friction materials.     

Viscoelastic properties and lap shear strength of EVA/aromatic hydrocarbon resins as hot-melt adhesives

A series of ethylene vinyl acetate (EVA) copolymers were blended with aromatic hydrocarbon resins in the molten state in various ratios and possible relations between viscoelastic and adhesion properties as hot-melt adhesives (HMAs) were investigated. When the softening point of aromatic hydrocarbon resin was high and the concentration of aromatic hydrocarbon resin was low, the tan δ peak height decreased and broadened. This result corresponds to the miscibility of the blend. The single lap shear strength increased with increasing softening point of the aromatic hydrocarbon resin and it reached a maximum value with increasing temperature. A large scatter was observed in lap shear strength values, which were higher at higher test rates and lower temperatures, and under these conditions interfacial failure occurred.     

Interfacial shear strength of wood–plastic composites: a new pullout method using wooden dowels

This preliminary study examined the relationship of interfacial shear strength (IFSS) to modulus of rupture (MOR) for several different wood–plastic composites (WPCs). Plastics utilized were high-density polyethylene (HDPE) and polypropylene (PP). Pine and oak were used as the wood species. Compatibilizers used included maleic-anhydride-grafted polyethylene (MAPE) and maleic-anhydride-grafted polypropylene (MAPP). A strong correlation between IFSS and MOR was observed in a limited composition region. PP/oak WPCs showed poor correlation between MOR and IFSS, probably due to the roughness of the oak surface. Compatibilizer systems incorporating liquid components did not give good results and appeared to be inappropriate for this test method.     

The effects of nanostructure and composition on the hydrophobic properties of solid surfaces

The effects of nanoroughness and chemical composition on the contact and sliding angles on hydrophobic surfaces were studied theoretically and experimentally. A theoretical model based on forces developed at the contact area between a liquid drop and hydrophobic smooth or nanoroughened surface was developed and compared with the existing models, which are based on forces developed at the periphery between the drop and the solid surface. The contact area based model gives rise to an interfacial adhesion strength parameter that better describes the drop-sliding phenomenon. Consequently, relationships were derived describing the dependence between the interfacial adhesion strength of the liquid drop to the surface of a given composition, the mass of the drop, the measured contact angles and the sliding angle. For a given surface chemistry, the sliding angle on a nanometric roughened surface can be predicted based on measurements of contact angles and the sliding angle on the respective smooth surface. Various hydrophobic coatings having different surface nanoroughnesses were prepared and, subsequently, contact angles and sliding angles on them as a function of drop volume were measured. The validity of the proposed model was investigated and compared with the existing models and the proposed model demonstrated good agreement with experimental results.     

Tribological roles of nanometre thick Ag layers on Hertzian macroscopic contacts

Abstract

Tribological performance of subnano to nanometre thick Ag layers deposited on Si(111) has been examined under ultra high vacuum conditions to understand effect of surface thin layers on the wear and friction characteristics. The slider was made of a diamond sphere 3 mm in radius. As a result, a minimum of the coefficient of friction 0·007 was observed over a film thickness range of 1·5–10 nm. The sliding planes were observed by Auger electron spectroscopy, reflection high energy electron diffraction (RHEED), synchrotron orbital radiated X-ray diffraction (SOR-XD) and scanning tunnelling microscopy (STM). No worn particles were found after 100 reciprocal sliding cycles, and the very low friction coefficient lasted for at least 1000 sliding cycles. Observations using STM on the sliding surfaces confirmed that the stacking Ag(111) planes slid. The SOR-XD and RHEED verified that a tribo-induced orientation of polycrystal film occurs as Ag(111) sliding planes are oriented parallel to the sliding direction on the track. The friction force of as deposited epitaxial Ag films as a function of the load was constant. On the other hand, in the 5 nm thick Ag films annealed to form complete single crystals, the friction coefficient showed a strong load dependency. At a load of 250 mN or more, the annealed films showed a low and static friction coefficient. These results suggested that the shearing resistance of nanometre thick Ag layers exhibits a strong anisotropic performance within the thickness range of nanometres, along with an orientation of Ag during sliding. Experimental results of sliding tests were discussed on the contribution of surface atoms to the friction, an extraordinarily low wear rate of the Ag layers, and the relationship between the nanoscopic structure and macroscopic tribological performance.     

Friction and wear behaviour of plasma sprayed WC–12Co coating sliding against Si3N4 under lubrication of ionic liquids

Abstract

The friction and wear behaviour of a WC–12Co coating prepared by plasma spraying sliding against a Si₃N₄ ceramic ball, under the lubrication of liquid paraffin and ionic liquids 1-methyl-3-butylimidazolium hexafluorophosphate and 1-methyl-3-hexylimidazolium hexafluorophosphate at room temperature, was investigated using an SRV tester. The morphology and elemental distribution of the worn coating surfaces were characterised by means of scanning electron microscopy (SEM) equipped with an energy dispersive X-ray analyser (EDXA) attachment, and the chemical state of typical elements in the boundary lubricating film on the worn coating surface was analysed by means of X-ray photoelectron spectroscopy (XPS). The SEM/EDXA analysis shows that phosphorus is uniformly distributed on the worn coating surface lubricated by ionic liquids. The XPS results also indicate that the boundary lubricating film is mainly composed of CoF₂ and PF_x and the tribochemical reaction products contribute to reducing the friction and wear of the plasma sprayed WC–12Co coating.     

Effect of heat treatment on tensile properties of friction stir welded joints of 2219-T6 aluminium alloy

Abstract

The effect of post-weld heat treatment (PWHT) on the tensile properties of friction stir welded (FSW) joints of 2219-T6 aluminium alloy was investigated. The PWHT was carried out at aging temperature of 165°C for 18 h. The mechanical properties of the joints were evaluated using tensile tests. The experimental results indicate that the PWHT significantly influences the tensile properties of the FSW joints. After the heat treatment, the tensile strength of the joints increases and the elongation at fracture of the joints decreases. The maximum tensile strength of the joints is equivalent to 89% of that of the base material. The fracture location characteristics of the heat treated joints are similar to those of the as welded joints. The defect free joints fracture in the heat affected zone on the retreating side and the joints with a void defect fracture in the weld zone on the advancing side. All of the experimental results can be explained by the hardness profiles and welding defects in the joints.     

The Use of Conductive Organic Coatings for Metallisation of Printed Circuit Boards

The use of intrinsically conductive organic coatings as replacements for electroless copper in the metallisation of printed circuit boards is described. A comparison of traditional metallisation technologies with that of the new method is reported. The suitability of the new method for pattern, panel and selective plating is discussed. The benefits of the new technology with respect to through-hole quality, process control and effluent treatment are also reported.     

Superconducting Bi(2223) thick film on Ba2HoNbO6: a new perovskite ceramic substrate

Abstract

Barium holmium niobate Ba₂HoNbO₆ (BHNO) has been developed as a new substrate for (Bi,Pb)₂Sr₂Ca₂Cu₃O_x (Bi(2223)) superconductor film. Ba₂HoNbO₆ has a cubic perovskite structure with lattice constant a = 8·26 Å. The dielectric constant and loss factor of this material are in a range suitable for its use as a substrate for microwave applications. The Bi(2223) superconductor shows no detectable chemical reaction with BHNO, even under extreme processing conditions. Dip coated Bi(2223) thick film on Ba₂HoNbO₆ substrate had T _c(0) of 109 K and current density of around 4 × 10³ A cm ^{- 2} at 77 K and in zero magnetic field.