Force Measuring System for High-Precision Surface Characterization under Extreme Conditions

Force measuring is used in various surface characterization techniques such as indentation, scratch tests, tribological analysis, determination of gas content, etc. The main problems related with force measurement under extreme conditions have been analysed. A strategy that should be followed to solve these problems has been discussed and several examples of successive solutions that recently were developed by the authors are presented. The need to carry out the characterization under extreme conditions poses serious problems for the designers of the measuring systems that may include the incompatibility of the sensors with the test conditions, undesirable interactions with other components, stability, precision and uncertainty issues, the measurement range, etc. Resolving these problems must be based on a global approach in which the characterization system is considered as a whole, while the designer must analyse and solve the possible conflicts between the subsystems. The way how an appropriate force measuring system can be selected is described. The proposed method is illustrated by an example in which an indirect force measurement using optical fibre displacement sensor was used. Another example describes measuring system developed for vacuum high-temperature nanoindentation. At high temperature, proper heat management based on non-contact heating and laminar flow cooling system is mandatory to avoid experimental data being affected by external noise and thermal drift

Triboemission: Unveiling hidden tribological processes

Resumen del trabajo presentado a Ibertriva (X Iberian Conference on Tribology / XI Iberian Vacuum Conference), celebrada en Sevilla (España) del 26 al 28 de junio de 2019.Injection of concentrated mechanical energy into materials at a tribological interface brings about a number of activated electronic and vibrational states, which trigger cascades of physico-chemical reactions including chemical reactions between the activated material and the environment. Many of these reactions end up emitting electrons, ions, gas molecules, electromagnetic radiation, etc. that is collectively known as triboemission. Born at the buried surfaces of a tribological interface triboemission carries valuable information about hidden tribological processes: energy dissipation, mechanical behaviour of materials (plastic flow, fracture, etc.) and tribochemical reactions (Fig. 1). This work summarizes the results of our recent studies of triboemission of gases, triboelectrification and triboluminescence aimed at establishing links between triboemission and material degradation, both structural and chemical. The research findings led us to the development of innovative methods for non-destructive in situ and real-time evaluation of integrity of tribological materials and coatings, characterization of tribochemical transformation of lubricants, as well as other characterization methods far beyond the tribology area

Development of a composite friction modifier with carbon nanotubes for applications at the wheel–rail interface

Wear of wheels and rails is a major problem in railway transportation industry. Solid lubricants constitute a cost-efficient alternative to control wear and friction at the wheel–rail interface, especially when a fine-tuned balance between traction force and energy consumption is sought. In this work, composite friction modifiers (CFMs) composed of a vinyl ester matrix reinforced with molybdenum disulfide and carbon nanotubes were developed. The total solid additive content was less than a half in comparison with a commercial product available on the market, which was used as a reference. A benchmarking study of the CFM was carried out by means of tribological tests in a twin-disc machine at a contact pressure of 1.1 GPa and different slip values. The results indicated that the developed CFM reduce coefficient of traction by 10% compared to unlubricated conditions that is similar to the reference. However, the total mass loss of steel components due to wear under CFM lubrication was lower than in the reference test

Time-Resolved Characterization of Dynamic Tribochemical Processes for Dicationic Imidazolium Ionic Liquid

Dynamic tribochemical processes for dicationic ionic liquid containing a geminal imidazolium cation head group bridged by a poly(ethylene glycol) and a bis(trifluoromethylsulfonyl)imide anion were studied using time-resolved mechanically stimulated gas emission mass-spectrometry (MSGE-MS). In comparison with similar monocationic imidazolium ionic liquids with short alkyl or long polyether side chains, the dicationic ionic liquid had a lower coefficient of friction on Ti6Al4V alloy and smoother behavior. The analysis of volatile decomposition products suggested multiple tribochemical reactions in which both anionic and cationic moieties are involved. The tribochemical degradation of cations was mainly through the detachment of the side and bridging chains from the imidazolium head groups. The absence of volatile products containing nitrogen implies that the imidazole group remained unchanged. Hydrogen and water desorption were attributed to the reactions of hydrogen fluoride being a product of anion degradation with titanium and titanium oxide, respectively.: The authors are grateful to M. Mahrova for providing the synthesized IL. The authors acknowledge the help of O. Sanchez in measuring the surface profiles. This work was supported by the Ministry of Economy and Competitiveness of Spain through the grant BIA2016-79528-R.We acknowledge support by the CSIC Open Access Publication Initiative through its Unit of Information Resources for Research (URICI)

Rapid assessment of the photocatalytic activity in construction materials: pros and cons of reductive inks (Rz and NBT) versus hydroxyl radical determination and Rhodamine photo‐bleaching

Resumen del trabajo presentado al 3rd International Conference on Catalysis and Chemical Engineering, celebrado en Houston (USA) del 25 al 27 de febrero de 2019