Currently microstructured heat exchangers are widely used in heat dissipation systems to increase the cooling intensity of high-power electronic components. They also hold promise for electromechanical sensors and microfluidic chips for laboratory-on-a-chip (LOC). This research aims to address key manufacturing challenges associated with maintaining the characteristic dimensions of microstructures at high aspect ratios. A combined method for fabricating precision metal microstructures is presented on the basis of ultraviolet dry film photolithography with electrochemical deposition from copper and nickel sulfate electrolytes. A comparative analysis of the metal particle deposition rate and the edge effect characteristics during the fabrication of nickel and copper microstructures leading to the fusion of elements into dense dendritic formations is carried out. The influence of the conductive frame shape on the quality, geometry, and uniformity of layer growth on the substrate during horizontal deposition in an electrochemical metallization system is noted. Square-type microstructures with height of 100 ± 5 μm, characteristic size of 180 ± 5 μm, and interelement pitch of 90 ± 5 μm is obtained, while maintaining vertical sidewalls, good adhesion to the substrate, minimization of defects during metal deposition and precise reproducibility of the microstructure geometry. The developed technology ensures the formation of mechanically stable microstructures capable of withstanding extreme hydrodynamic loads.
The method of calculation of the drying process of thin flat materials on the basis of the equation of drying kinetics, which establishes the relationship between the values determining the heat exchange by the heat transfer coefficient and moisture exchange by the relative drying rate, is presented. On the basis of the drying kinetics equation, the heat exchange process is fully described by moisture exchange data. An experimental method for calculating the material temperature during the period of falling drying rate for drying porous ceramics, sheet asbestos and woollen felt is considered. The dependence of relative drying rate on relative moisture content and an experimental method for calculating the heat transfer coefficient for the period of falling drying rate are given. A method for determining the drying rate from the value of drying rate during the period of constant rate and relative drying rate is proposed. Equations for calculating drying intensity and heat flux density are presented. Comparison of calculated values of drying parameters according to the obtained formulas with experimental ones for drying of ceramics, asbestos and felt is given. Experimental data processing methods and formulas obtained are of practical importance for calculating the kinetics of drying various wet materials.
The structural features and mechanical properties of composite carbon coatings formed from plasma flows of complex composition generated by pulsed electric arc and spark evaporation in the presence of molecular nitrogen were investigated. The nitrogen concentration in the coating was varied by changing its partial pressure in the residual atmosphere of the vacuum chamber. It was found that nitriding of carbon coatings doped with zirconium and silicon at a nitrogen partial pressure of 0.08 Pa leads to an increase in dispersion, a decrease in their roughness and the size of individual structural formations. The features of chemical interaction processes were determined using X-ray photoelectron spectroscopy. Nitriding promotes an increase in the degree of structural ordering of sp2-clusters, the formation of compounds based on CNx, nitrides of alloying elements and an increase in the ratio of sp3/sp2-hybridized carbon atoms, which leads to an increase in the nanohardness of composite carbon coatings to 15.3 GPa. It has been shown that the formation of hard phases based on alloying element carbides and nitrides leads to increased friction coefficients and volumetric wear of the counterface during nitriding of composite carbon coatings. The chemical composition of the composite carbon coatings has been determined, providing an optimal combination of nanohardness and tribological properties due to the highest proportion of clusters based on Csp2–N-bonds, which are transformed during friction into graphite, which acts as a solid lubricant. The obtained results can be used to modify the surface of metalworking tools and specialized equipment parts in order to improve their mechanical characteristics and increase their service life.
Experimental equipment for producing charcoal from sawmill residues using thermochemical conversion of biomass in an oxygen-free environment has been developed. This equipment features thermal conversion of wood raw materials in a pyrolysis chamber equipped with microwave sources. The pyrolysis equipment includes a unit for producing generator gas from organic waste, a wood pyrolysis unit, a pyrolysis chamber purging system with inert gas, an afterburner for the generator gas and pyrolysis gas mixture, a combustion product temperature control unit, a heat exchanger, a smoke exhauster, a pyrolysis unit control and monitoring system, and a chimney. Magnetrons were used as microwave sources. A description of the testing methodology for the equipment for producing charcoal in the presence and absence of a microwave field is provided. Hardwood (split maple firewood) was used in the tests. The results of the study indicate that the use of microwave technology can increase the rate of thermochemical destruction of wood, increase the productivity of equipment for the production of charcoal, and also obtain a higher yield of charcoal per unit mass of the original wood, raw material or product with a higher calorific value and lower ash content.For example, the productivity of the experimental pyrolysis unit without microwaves was 1.42 kg/h, while with microwaves, it was 1.73 kg/h, an increase of 22 %. The developed technology for producing charcoal by thermal pyrolysis in the presence of microwaves offers economic and energy-efficient potential.
Thin films with a quasi-amorphous finely dispersed structure and a crystallite size of 1–3 nm were obtained using the magnetron sputtering method of a composite target of MoSi2 + 20 wt.% SiC compound. A study was conducted on the influence of temperature and duration of annealing on the surface electrical resistance, structure and phase composition of these films, which made it possible to establish a relationship between the structural-phase state and the value – of the surface resistance of the films. It was determined that annealing of freshly deposited films at a temperature above 700 °C leads to a decrease in their surface resistance by 2.5–3 times, and at a heat treatment temperature of 900 °C this characteristic is stabilized. Based on the results of electron diffraction analysis and resistive properties of the films, it was found that the change in surface electrical resistance is due to the evolution of the structure from quasi-amorphous to polycrystalline. It was shown that the formation of stable phases of MoSi2 and Mo5Si3 of the tetragonal modification, as well as SiC of the hexagonal modification after heat treatment ensures stabilization of the electrical properties of the films. It was found that the a temperature of 900 °C and a heat treatment duration of 3 hours can be considered as optimal annealing modes, at which stabilization of the surface resistance, structure and phase composition of the films can be achieved. The results obtained can be used to produce highly efficient thin-film IR emitters used as light sources in gas microanalyzers.
