WEAR OF COATING WITH A SHEAR MODULE ARBITRALLY CHANGING BY DEPTH

The protection of the working surfaces of mechanisms in sliding contact conditions is often carried out by applying protective multilayer and functionally graded coatings, which prevent wear of the working surfaces and reduce the temperature heating of the contact. The problem of grinding the surface of oxidized and other materials with a functionally graded change in properties along the depth of the product leads to the need to control the wear rate and contact heating from friction. The effectiveness of studying the processes of wear, grinding, polishing and early diagnostics of thermoelastic instability of sliding contact is facilitated by mathematical modeling of the process of wear of products made of functionally graded materials. The thermoelastic contact problem of the wear of a functionally graded coating with an arbitrarily varying shear modulus with a hard abrasive, taking into account the heating of the contact from friction, is considered. The solutions of the problem are constructed in the form of Laplace convolutions. Analysis of the obtained solutions in the complex plane makes it possible to determine the regions of thermoelastic stability and instability of the solutions in the space of dimensionless parameters of the problem. Unstable solutions give rise to the concept of thermoelastic instability of a sliding contact. The constructed analytical solutions made it possible to study the effect of the functionally graded inhomogeneity coefficient of the coating material on the thermoelastic instability regions of the sliding contact, temperature, displacements, stresses and wear of the functionally graded coating material.

A Hybrid Microbial-Enzymatic Fuel Cell Cathode Overcomes Enzyme Inactivation Limits in Biological Fuel Cells

The construction of optimized biological fuel cells requires a cathode which combines the longevity of a microbial catalyst with the power density of an enzymatic catalyst. Laccase secreting fungi were grown directly on the cathode of a biological fuel cell to facilitate the exchange of inactive enzymes with active enzymes with the goal of extending the lifetime of laccase cathodes. Additionally, a functionally graded coating was developed to increase enzyme loading at the cathode. Directly incorporating the laccase producing fungus at the cathode extends the operational lifetime of laccase cathodes while eliminating the need for frequent replenishment of the electrolyte. Additionally, the hybrid microbial-enzymatic cathode addresses the issue of enzyme inactivation by using the natural ability of fungi to exchange inactive laccases at the cathode with active laccases. Finally, enzyme adsorption was increased through the use of a functionally graded coating containing an optimized ratio of titanium dioxide nanoparticles and single walled carbon nanotubes. The hybrid microbial-enzymatic fuel cell combines the higher power density of enzymatic fuel cells with the longevity of microbial fuel cells and demonstrates the feasibility of a self-regenerating fuel cell in which inactive laccases are continuously exchanged with active laccases.