Wear Resistance of Ti–6Al–4V Alloy Ball Heads for Use in Implants

The effect of thermohydrogen treatment and vacuum ion–plasma nitriding on the determination of the volume and surface structure of ball heads made of Ti–6Al–4V alloy was studied. It was found that the submicrocrystalline structure formed in the head during thermohydrogen treatment makes it possible to achieve hardness values of 39–41 units HRC and a surface roughness of 0.02 μm. It was shown that the creation of a modified layer consisting of ε (TiN) and δ (Ti2N) titanium nitrides on the surface of a ball head and the solid interstitial solution of nitrogen in α-titanium makes it possible to completely eliminate material wear when testing for friction on ultra-high-molecular-weight polyethylene. The equivalent analysis was also conducted with a ball head that had been implanted in a human body for 12 years. It was found that the change in the color of the head, from slightly golden after nitriding to metallic, is due to the formation of an oxynitride nanoscale layer on the surface. It was shown that in contrast with films made of titanium oxide, the film developed in this study has high wear resistance.

Effect of the addition of metakaolin on the carbonation of Portland cement concretes

Carbonation has been a concern of constructors and researchers because, by lowering the pH of the interstitial solution of the concrete, it can favor the post-deposition and subsequent corrosion of reinforced concrete reinforcement. Among the factors that influence carbonation is the use of pozzolanic materials, such as metakaolin. However, there is no consensus as to the positive or negative contribution of these additions. This work evaluated the influence of metakaolin on the mechanical properties, porosity and in particular on the carbonation of concrete, from the addition of 0%, 5%, 10% and 15% of metakaolin, in relation to the cement mass. From the results, it was observed that the addition of metakaolin, while not significantly influencing the porosity, gave the concrete a greater resistance to axial compression, a decrease in the capillary absorption and delayed the advance of the carbonation front in the concrete.

Alkali-Aggregate Reactions in Concrete: Methodologies Applied in the Evaluation of Alkali Reactivity of Aggregates for Concrete

The alkali-aggregate reaction (AAR) in concrete is a group of chemical reactions that involves the reaction of certain minerals present in the aggregates with alkali and hydroxyl ions in the interstitial solution of cement paste in concrete. These reactions form an alkaline hygroscopic gel that absorbs water and expands causing internal stresses with cracking [1]. The AAR mitigation measures oblige the correct evaluation of the alkali reactivity of the aggregates. This is normally assessed by petrographic, chemical or expansion test methods. Several studies regarding alkali reactivity of aggregates for concrete structures in Portugal, including bridges and dams, indicated that their field performance does not correspond to the previously performed evaluation. Presently, Portuguese methodology is based on the LNEC Specification E461-2007, which shows some limitations regarding rock types such as granitoids [2]. This situation motivated the development of a research project, involving medium and long term expansion tests in different conditions, under accelerated and natural exposure conditions, as well as petrographic evaluation of the main Portuguese aggregates used/to be used in concrete. This paper presents the preliminary results of this research.

Le mûrissement à l'eau de chaux des échantillons de béton en laboratoire est-il adapté au cas des bétons contenant des cendres volantes?

In order to study the influence of the maturation type on the behavior of concrete containing fly ash, specimens of mixtures and mortars have been made with a water/binder ratio of 0.40. In all cases, the proportion of fly ash has been constant and equal to 20%. Different maturation types have been studied: the confinement in an aluminum foil, the immersion in a lime saturated solution and the immersion in an NaOH and KOH solution simulating the interstitial solution that is found in concrete. At different times, the composition of the interstitial solution, the resistance to compression, the content of chemically bound water as well as the quantity of portlandite have been measured in order to evaluate the maturation effect. The results show that the maturation type has an influence on the fly ash hydration rate. The data also indicate that it is essential that the specimens have enough water to hydrate themselves. In the case of the confinement of samples, evaporation must absolutely be avoided. In order to qualify mineral additions representatively, and to measure their properties on representative specimens of the conditions usually found in the concrete structure mass, the alkalinity of the interstitial solution must be preserved. Immersion of samples in an NaOH and KOH solution at a concentration simulating that of the interstitial solution is suggested. The maturation in lime water provides enough water for hydration but pulls down the alkalinity of the interstitial solution too rapidly, which reduces the fly ash hydration rate.Key words: maturation, fly ash, cement, lime water, interstitial solution, chemically bound water, resistance, portlandite.[Journal translation]

The Effect of Humic Acids on the Element Release from High Level Waste Glass

ABSTRACTEu and Am doped glasses were interacted with synthetic interstitial clay water (SIC) and corresponding reference leachant, humic acids free interstitial solution (IS) to investigate the influence of humic acids on the leaching behaviour of the waste glass. Static leach tests were carried out at 40°C and 90°C. The release of the lanthanide Eu and the actinide Am from the glass was obviously enhanced by the presence of humic acids. The leaching of transition elements, Fe and Ti strongly depends on the humic acids concentration. The leaching of glass matrix components, Al and B was also influenced by the concentrations of humic acids. However, humic acids have little effect on the leaching of glass matrix element Si.