On the importance of some surface and interface characteristics in the formation of the properties of adhesive joints

The importance of some relative surface characteristics which determines the strength of adhesive joints: specific surface of substrate , relative contact area β and specific contact area β in the adhesion interaction process were emphasised. Existing and potential methods of experimental evaluation of these characteristics were shortly analysed. The durability of the adhesive joints in water media significantly increases with growth of specific surface ^* of chemically treated substrate evaluated from the SEM micrographs. Specific surface calculated from the experimental data of hexane adsorption measurements for iron particles (particulate model of steel substrate) is more then ten times greater than respective ^* values. The relative contact area β of the Al₂O₃ particles (in wide range of ) with PE melt was in a roundabout way evaluated by experimental determination of the affect of on kinetic of peel strength formation of adhesive joints: Al₂O₃ filled PE-steel. The speculation was based on the ability of Al₂O₃ to adsorb low-molecular products of contact oxidation of PE which takes place in the process of formation of adhesive joints and determines their strength. The ability of sorption in its turn is proportional to efficient value of β. The availability of the Al₂O₃ surface was evaluated.     

Optimizing fuel assembly placement in a research reactor

Institute for Nuclear Research, Academy of Sciences of the Ukrainian SSR. Translated from Atomnaya Energiya, Vol. 70, No. 4, pp. 257–259, April, 1991.     

Kinetics of Adhesion Interaction of Polyolefins with Metals under Conditions of Contact Thermooxidation. 1. Oxidation Kinetics and Change of Peel Strength

The kinetics of contact thermooxidation (CTO) of a polyethylene layer on a steel surface in connection with the change of peel strength (A) under conditions of free access of oxygen through the polymeric layer was studied. The CTO parameters (oxygen uptake, carbon dioxide evolution, change of carbonyl group content, change of the weight of the layer) and the change in the values of A were found to be kinetically interrelated. The dependence of the rate of change of individual CTO parameters and the magnitude of A on the thickness of the layer being oxidized and temperature can be described by a simple equation. The analysis of constants in this equation allows one to estimate the catalytic effect of the substrate in CTO. The dependence of experimental determined A values on contact time can be satisfactorily described by a simple expression based on the assumption that the magnitudes of A are controlled by two main competitive processes: the accumulation of oxygen-containing groups and oxidative cross-linking, causing the increase of A values, and reactions of oxidative destruction causing the decrease in A.     

Studies of heteropoly acid/polyvinylidenedifluoride–hexafluoroproylene composite membranes and implication for the use of heteropoly acids as the proton conducting component in a fuel cell membrane

Complete polarization curves for a number of heteropoly acids (HPAs), H₃PW₁₂O₄₀, α-H₃P₂W₁₈O₆₂, H₆P₂W₂₁O₇₁, and H₆As₂W₂₁O₆₉ as the only proton conducting component are presented for the first time. Both thin pellets of HPA and composite membranes of 1:1 (w/w) of HPA and polyvinylidenedifluoride–hexafluoropropylene (PVDF–HFP) are investigated. Although the pellets are somewhat variable, the HPA phase changes can be observed by electrochemistry and these materials show promise for solid acid fuel cell performance at >200 °C. The high proton conductivities reported for HPAs at RT are demonstrated in fuel cells using HPA/PVDF–HFP composites with limiting current densities as high as 1.6 A cm⁻² using dry O₂ and H₂. Moderate fuel cell activity is demonstrated for α-H₃PW₁₈O₆₂ at 120 °C and 25%RH. Unfortunately all of the materials studied were somewhat porous and the open circuit potentials observed were somewhat low. We were also able to show that an HPA fuel cell could be shorted by reduction of the HPA to a heteropoly blue under exceptional circumstances.     

Study of blends based on recycled polyethylene wastes

Data covering the physical properties of molten and solid samples of two binary blends of recycled polyethylene wastes, in a wide range of compositions, are reported. While some properties (density, fusion enthalpy) show a linear behaviour with composition other properties (microhardness, yield stress) show a deviation from linearity. Deviation of microhardness additivity of the single components has been interpreted, after analysis of the DSC thermograms, as being due to segregation and recombination of molecular species from both components during crystallization. It is also suggested that the presence of a high oxidation in one low-density polyethylene component, detected by infrared spectroscopy, influences the very low values observed for the melt flow index and melt elongation at break.     

Optimizing fuel-pin assembly location in a research reactor

Nuclear Research Institute, Ukrainian Academy of Sciences. Translated from Atomnaya Énergiya, Vol. 72, No. 6, pp. 624-626, June, 1992.     

Study of blends based on recycled polyethylene wastes

A calorimetric study of binary blends based on recycled, low and high density polyethylene, wastes is presented. The physical properties of these blends were reported previously [1]. A comparison between the first and second differential scanning calorimetry (DSC) traces of blended samples reveals the presence of an intermediate endothermic peak which can be associated to the melting of crystals from mixed molecular species of the single components. Further thermal treatments after the second DSC run at temperatures just below and above the intermediate peak for two compositions (_B = 10 and 30% of high density component) highlight the dependence of the various crystal populations upon annealing. A quantitative analysis of a series of consecutive thermograms for each sample has allowed us an estimation of the relative amount of material associated to the three main endothermic peaks.     

Kinetics of Adhesion Interaction of Polyolefins with Metals under Conditions of Contact Thermooxidation. 1. Oxidation Kinetics and Change of Peel Strength

The kinetics of contact thermooxidation (CTO) of a polyethylene layer on a steel surface in connection with the change of peel strength (A) under conditions of free access of oxygen through the polymeric layer was studied. The CTO parameters (oxygen uptake, carbon dioxide evolution, change of carbonyl group content, change of the weight of the layer) and the change in the values of A were found to be kinetically interrelated. The dependence of the rate of change of individual CTO parameters and the magnitude of A on the thickness of the layer being oxidized and temperature can be described by a simple equation. The analysis of constants in this equation allows one to estimate the catalytic effect of the substrate in CTO. The dependence of experimental determined A values on contact time can be satisfactorily described by a simple expression based on the assumption that the magnitudes of A are controlled by two main competitive processes: the accumulation of oxygen-containing groups and oxidative cross-linking, causing the increase of A values, and reactions of oxidative destruction causing the decrease in A.