Analysis of Intermetallic Phases Formed on Surface Vapor Oxidized H13 Hot Work Steels in Molten Aluminum

In this paper, the author dipped surface vapor oxidized H13 steel specimens into 700℃ molten aluminum liquid for a certain period of time. Analyze the intermetallic phases formed on the H13 samples surface with optical microscope and X-ray diffraction method. The observation of immersion test sample's cross-section shows that Fe3O4 film will protect die substrate from molten aluminum erosion. The identification of the intermetallic phases reveals that they consist of 2parts, which is named as the composite layer and the compact layer. Further investigations are made in order to know the phase constituents of the 2 layers, they are Al8Fe2Si (outer composite layer), (AlCuMg) and Al5Fe2 (compact layer),respectively. The experimental results show that on the same specimen, a convex surface with bigger radius of curvature is more likely to be molten and the melting loss speed is also faster than a flat and smooth surface. The thickness of compact layer on a smooth surface is much bigger than that of the convex surface. Therefore, the author supposes the compact layer is favorable in stabilizing the die surface material from further melting loss, as their formation on the die surface, the melting loss speed will decrease.     

Effect of surface free energy on the adhesion of biofouling and crystalline fouling

Pipelines and heat exchangers using seawater as coolant suffer from biofouling. Biofouling not only reduces heat transfer performance significantly, but also causes considerable pressure drop, calling for higher pumping requirements. It would be much more desirable if surfaces with an inherently lower stickability for biofouling could be developed. In this paper, a cost-effective autocatalytic graded Ni-Cu-P-PTFE composite coating with corrosion-resistant properties was applied to reduce biofouling formation. The experimental results showed that the surface free energy of the Ni-Cu-P-PTFE coatings, which were altered by changing the PTFE content in the coatings, had a significant influence on the adhesion of microbial and mineral deposits. The Ni-Cu-P-PTFE coatings with defined surface free energy reduced the adhesion of these deposits significantly. The anti-bacterial mechanism of the composite coatings was explained with the extended DLVO theory.     

The Structure of the Irreversibly Bound Adhesion Promoter-Substrate Interfacial Layer of γ-Aminopropylsilanetriol on Crystalline Si, as Measured by XPS and FTIR

The irreversibly bound interfacial layer deposited by the γ-aminopropysilanetriol adhesion promoter onto a crystalline silicon substrate, which remains even after profuse washing, was found by XPS to have resulted from the fragmentation and rearrangement of the original γ-aminopropylsilanetriol molecule. A mechanism is proposed, involving the homolytic scission of the terminal N-C bond. One of the subsequent reactions is believed to involve hydrogen loss by abstraction and the formation of a terminal vinyl group, which bonds to the substrate. Support for this mechanism is found in IR spectroscopy of this layer.     

The role of the surface free energy in the selection of a suitable excipient in the course of a wet-granulation method

Pellets containing metronidazole were produced in a centrifugal granulator, with hydroxypropylcellulose (Klucel LF®) as binding agent, and corn starch, microcrystalline cellulose (Vivapur 101®) and lactose as excipients. The wettability of the pharmaceutical powders was assessed by means of contact angle measurements, and the dispersive and polar surface energies were determined. The spreading coefficients, the work of adhesion and the work of cohesion were calculated and correlated with the pellet properties (friability, bulk and tapped density, and porosity). The aim was to investigate the role of the surface free energy of one- and two-component powder compositions in pellet production. The interactions between the particles were found to be connected with the measured pellet parameters. It was concluded that, in the course of the growth of the pellets, the particle sizes of the pharmaceutical powders and the interactions between them are important. If the work of cohesion of the binder is lower than the work of cohesion of the substrate and the work of adhesion, then the optimal amount of the binding agent is that which coats the particles uniformly in minimal quantity and in continuous layer.     

Some aspects of the analysis of coal by X-ray fluorescence spectroscopy

Bituminous coal samples from 84 distinct sources were analysed by conventional British Standards (BS) methods for phosphorus, sulphur, chlorine, ash and the ash-forming elements (calcium, silicon, aluminium, iron, sodium, magnesium, potassium, titanium and manganese). In most cases four determinations were made per element per source. Samples were crushed to ?212 μm (72 BS mesh) and pressed into aluminium cups at 20 t in^?2 (309 MPa) without binder or backing. Two pellets from each sample were analysed by wave-length dispersive X-ray fluorescence techniques, using a spectrometer equipped with a rhodium rube; the X-ray count took 60 s. The X-ray results were calibrated against the conventional results using multiple regression. The accuracy obtained was comparable with routine ‘wet chemical’ techniques. The X-ray technique is suitable for the routine determination of large numbers of samples.     

High resolution XPS characterization of chemical functionalised MWCNTs and SWCNTs

High resolution XPS analysis of chemical functionalised multi-wall carbon nanotubes (MWCNTs) and single wall carbon nanotubes (SWCNT) was done with ESCA300 (overall instrument resolution of 0.35 eV). Information to the degree of functionalisation was ascertained by argon ion bombardment of the samples followed by XPS analysis to detect the functional groups, the percentage atomic concentration of various elements present and whether or not the detected functional groups imposed a chemical shift on the CNT atoms. The results show that true chemical functionalisation was achieved and by argon ion bombardment these functional groups can be altered relative to the C 1s carbon atoms of the CNT. The choice of chemicals used for functionalisation, the techniques employed and the types of nanotubes treated are important factors in chemical characterisation. The carbon atom on the nanotube ring to which the functional group (atom) is bonded, the chirality of the CNT, the electronegativity of the functional group, the bond type and whether the CNT is single-wall or multi-wall, or cut (short) could play a role in determining the chemical shift on the CNTs atoms. These investigations are relevant to chemical functionalisation of carbon nanotubes for various applications for example DNA sensors and other biomedical sensors.     

Thermodynamic Criteria for the Maximum and Minimum Strength of Fibre-Reinforced Composite Materials

The overall performance and reliability of composite materials are, in most cases, dependent upon the behaviour of the reinforcement-matrix interface, particularly upon its ability to transfer stress.

A theory for predicting thermodynamic conditions for the maximum and zero-adhesion at the reinforcement-matrix interface is tested in this paper, based on experimental data. Proposed is a model of the relationship between mechanical properties of composite materials (tensile strength, flexural strength, Young's modulus and impact resistance) and energetic properties of matrix and reinforcement expressed by the energy ratio a = γ_l/γ₂.     

Numerical Analysis of the Constrained Blister Test

The constrained blister test is investigated through finite element analysis to determine the applicabilities and the limitations of the new technique. Numerical results confirm that the strain energy release rate asymptotically approaches a constant value. These results also show that the test technique and the approximate solution for strain energy release rate are applicable for some practical cases.     

Softening and melting mechanisms of polyamides interfering with sliding stability under adhesive conditions

The thermal stability of polymers is a main issue when used as friction elements under dry sliding. Cast polyamide grades processed with either natrium or magnesium catalysors are slid on a small-scale and a large-scale test configuration to reveal the effect of softening or degradation on the sliding stability and to investigate possibilities for extrapolation of friction and wear rates between both testing scales. The combination of softening and afterwards transition into the glassy state is detrimental for the sliding stability of natrium catalysed polyamides, characterised by heavy noise during sliding. A transfer film formed under continuous softening also provides high friction. Melting during initial sliding is necessary for stabilisation in both friction and wear, and eventual softening of a molten film near the end of the test then not deteriorates the sliding stability. Softening of magnesium catalysed polyamides is favourable for the formation of a coherent transfer film resulting in more stable sliding than natrium catalysed polyamides. The differences in softening mechanisms of both polyamide grades is correlated to structural changes investigated by thermal analysis and Raman spectroscopy: the γ crystalline structure prevails in magnesium catalysed samples and the α crystalline structure is predominant in natrium catalysed samples. For internal oil lubricated polyamides, a time dependent degradation of the polyamide bulk deteriorates the supply of internal oil lubricant to the sliding interface, resulting in high friction and wear under overload conditions. As the degradation mechanisms during sliding are strongly correlated to the test set-up, extrapolation is only possible for friction in a limited application range, while wear rates cannot be extrapolated.