Lignin-modified phenolic resin: synthesis optimization,adhesive strength,and thermal stability

Lignin-modified phenolic resin has been prepared by replacing phenol with lignin at different weight percentages. The resin synthesis was optimized by varying the molar ratio of phenol to formaldehyde, the concentration of sodium hydroxide, and the reaction time by measuring parameters such as the gelation time, flow time, solids content, pH, and specific gravity. The thermal stability of lignin-modified phenolic resin was studied by DSC, TGA, and isothermal analysis, and it was found that lignin-modified phenolic resin is thermally more stable than pure phenolic resin. The adhesive strength of lignin-modified phenolic resin was determined by the lap-shear method, which showed that the lignin-modified resin retains 78% of the adhesive strength for wood-wood systems and 86% of the adhesive strength for Al-Al systems.     

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.     

Studies on polycrystalline layered ceramic oxide: LiFeVO4

Abstract

A new polycrystalline layered ceramic oxide, LiFeVO₄, has been prepared by a standard solid state reaction technique. The preparation conditions were optimised using thermogravimmetric analysis (TGA) technique. Material formation under the reported conditions was confirmed by X-ray diffraction studies. A preliminary structural analysis indicated that the crystal structure was orthorhombic with lattice parameters: a=4·3368 Å, b=13·1119 Å and c=16·3426 Å. The phase morphology and surface property were studied by scanning electron microscopy. Complex impedance analysis of the sample indicated bulk contribution to electrical properties at T≤125°C, grain boundary effects at the temperatures ≥125°C, negative temperature coefficient of resistance (NTCR) effect and evidence of temperature dependent electrical relaxation phenomena in the sample. The dc conductivity σ_dc shows typical Arrhenius behaviour when observed as a function of temperature. The activation energy value was estimated to be 0·24 eV. The value of σ_dc, evaluated from complex impedance spectrum, shows a jump of nearly two orders of magnitude at higher temperature (～1·24 × 10^?5 S cm^?1 at 350°C) when compared with that of σ_dc (1·14 × 10^?6 S cm^?1 at 50°C). Alternating current conductivity spectrum obeys Jonscher's universal power law. The results of σ_ac v. temperature are also discussed.     

Analysis of thermoelastic interaction of manufacturing stresses along the interface on interlaminar delamination progression in multi-ply composite laminates

This paper deals with the study of interaction of manufacturing thermal residual stresses and mechanical loading in penny-shaped delaminations embedded between dissimilar, anisotropic fiber composite layers by conducting two sets of three-dimensional thermoelastic finite element analyses with and without residual stress effects. Modified crack closure integral (MCCI) techniques based on the concepts of linear elastic fracture mechanics (LEFM) have been used to calculate the distribution of individual modes of strain energy release rates (SERR) to investigate the interlaminar delamination initiation and propagation characteristics. Asymmetric variations of strain energy release rates obtained along the delamination front are caused by the overlapping stress fields due to the coupling effect of thermal and mechanical loadings. It is found that parameters such as ply sequence and orientation, thermoelastic anisotropy and material heterogeneity, and ply properties of the delaminated interface dictate the interlaminar fracture behavior of multi-ply laminated FRP composites.     

Effect of Structural Parameters on the Thermal Stress of a NiFe2O4-Based Cermet Inert Anode in Aluminum Electrolysis

Inert anode has been a hot issue in the aluminum industry for many decades. With the help of FEA(finite element analysis) software ANSYS,a model was developed to simulate the thermal stress distribution working condition of an inert anode. To reduce its thermal stress,the effect of some parameters on the thermal stress distribution was investigated,including the anode height,the anode radius,the hole depth,the hole radius,and the radius of inner chamfer and outer chamfer. The results showed that in the actual working condition of an inert anode,there existed a large axial tensile stress near the tangent interface between the anode and bath,which was the major cause of anode breaking. Increasing the anode height and reducing the hole depth properly seemed to be beneficial for the stress distribution. With the increase of anode radius,the stress distribution became better first and then deteriorated,the reasonable value was between 0.045 to 0.06m. The hole radius had a significant effect on the stress and a smaller radius would reduce the thermal stress. The effect of the radius of the inner chamfer and the outer chamfer was less than other parameters.     

Computational simulation of microstructure evolution during solidification of ductile cast iron

Abstract

This paper presents a thermomicrostructural model for the simulation of the solidification process of an eutectic ductile cast iron. The thermal balance is written at a macroscopic level and takes into account both the structural component being cast and its mould. Models of nucleation and growth represent the evolution of the microstructure, and the microsegregation of silicon is also considered. The resulting formulation is solved using a finite element discretisation of the macrodomain, in which the evolution of the microstructure is taken into account at the Gauss integration points. The numerical results are presented in terms of cooling curves and are compared with available experimental values. Furthermore, the sensitivity of the response with respect to changes in the cooling rate and nucleation parameters are investigated. The agreement between experimental and computational values is acceptable in both quantitative and qualitative aspects. Ways to improve the computational model are suggested.     

Relationship between chemical structure of imidazoline inhibitors and their effectiveness against hydrogen sulphide corrosion of steels

Abstract

Seven homologous imidazoline type inhibitors were synthesised, all being derivatives of cyclopentyl- and cyclohexylnaphthenic acids. The protective effectiveness of these compounds was investigated by applying the potential sweep method to the carbon steel St3S and austenitic steel 1H18N9T in a 2% solution of sodium chloride in contact with a hydrocarbon phase and saturated with hydrogen sulphide gas. It was found that the inhibitors investigated and their mixtures present high protective effectiveness at a concentration of 25 ppm, reaching values of 99% for carbon steel and 80% for austenitic steel at 40°C. This protective effectiveness was improved by increasing the length of the substituent chain. Consequently, the least effective compounds were those with the shortest chain substituted at the imidazoline ring. Inhibitors under study were chemisorbed on the electrode surface of the steel and this chemisorption process obeyed the Frumkin adsorption isotherm. Values of the Gibbs free energy of adsorption of inhibitors were determined, and also the equilibrium constants of adsorption and constants of attraction.     

Artificial neural network approach for estimating weld bead width and depth of penetration from infrared thermal image of weld pool

Abstract

In this article an artificial neural network based system to predict weld bead geometry using features derived from the infrared thermal video of a welding process is proposed. The multilayer perceptron and radial basis function networks are used in the prediction model and an online feature selection technique prioritises the features used in the prediction model. The efficacy of the system is demonstrated with a number of welding experiments and using the leave one out cross-validation experiments.     

Ionic Polymer–Metal Composite of Thermo-Responsive Selemion AMV Coated with Gold Foils

Highly dehydrated gold foil-coated Selemion AMV exhibited large bending under electrical stimulation. It bore a relatively well-controllable bending characteristic by the control of electrical stimulation. Conventional ionic polymer–metal composite bending mechanisms could not explain its bending behavior. We speculated that Joule heat played a central role in the bending induction. Employing the classical lamination theory, the influence of Joule heat on its bending behavior was theoretically investigated. The results calculated roughly agreed with the experimental results. Hence, we concluded that the Joule heat was the primary cause of bending induction.     

Effect of tin on melting temperature and microstructure of Ag–Cu–Zn–Sn filler metals

Abstract

To develop low melting point filler metals for brazing TiNi shape memory alloy (SMA) and stainless steel (SS), a series of Ag–22Cu–Zn–Sn (wt-%) filler metals have been studied. Using differential thermal analysis (DTA) analysis, the melting temperatures of Ag–22Cu–Zn–Sn filler metals were determined. The results show that the increase of zinc and tin contents drastically decreases the solidus and liquidus temperatures of the Ag–22Cu–Zn–Sn filler metals and the melting temperatures of the Ag–22Cu–18Zn–Sn filler metals with 5–8 wt-%tin are < 650°C. Metallographic observations indicate that the increase of zinc and tin in the Ag–22Cu–Zn–Sn filler metals helps the formation of eutectic structure and inhibits the formation of α-Ag and α-Cu solid solutions, but the increase of tin also causes the formation of Ag₃Sn and Cu₄₁Sn₁₁ brittle compounds. The results of mechanical property tests of the laser brazed joints of TiNi SMA and SS show that the proper increase of zinc and tin in Ag–22Cu–Zn–Sn filler metals is favourable for improving the strength of the laser brazed joints of TiNi SMA and SS.