Research on Electrostatic Monitoring of Tribo-Contacts with Dynamic Adaptive Fusion Method

Electrostatic monitoring is a unique and rapid developing technique applied in the prognostics and health management of the tribological system based on electrostatic charging and sensing phenomenon. It has considerable advantages in condition monitoring of tribo-contacts with high sensitivity and resolution. Unfortunately, the monitoring result can be affected due to the switch of operating conditions that reduces its accuracy. This paper presents a dynamic adaptive fusion approach, moving window local outlier factor based on electrostatic features to overcome the influence. Life cycle experiments of rolling bearings and railcar gearbox were carried out on an electrostatic monitoring platform. The MWLOF method was used to extract and analyze the experimental data, combined with the Pauta criterion to judge wear faults quantitatively, and compare with other feature extraction results. It is verified that the proposed method can overcome the influence of changes in working conditions on the monitoring results, improve the monitoring sensitivity, and provide an accurate reference for friction and wear faults.

Structural, Magnetic and Electronic Properties of Nanostructured Magnetic Materials

<p>This thesis was motivated by the different properties exhibited by magnetic nanoparticles when compared with the bulk. For example the coercivity and magnetocrystalline anisotropy vary with the particle size and the finite particle size can affect the spin-wave dispersion. When the nanoparticle radius becomes small enough it is possible to observe superparamagnetism with negligible hysteresis. The transport properties can also be different in nanoparticle composites when compared with the bulk. It is particularly interesting if the nanoparticles have a degree of electronic spin polarization because it is then possible to observe spin-dependent tunnelling. This thesis reports the results from a study of the structural, magnetic, and electronic properties of two partially electronically spin-polarized nanostructured compounds, iron-nickel alloy and magnetite, that were made using a new arc-discharge method, ion implantation and annealing, and a co-precipitation method. It was found that permalloy powders could be made by arc-discharge where there were a range of particle sizes from nms to 10s of microns. Magnetoresistance was observed where it is due to the ordinary magnetoresistance and spin-dependent tunnelling between the particles. It was also possible to make magnetite using the arc-discharge process and the powders contained nanoparticles, large faceted nanoparticles, and larger particles in the 10s of micron range. The temperature dependence of the saturation magnetization changes at 127 K, which can be attributed to the charge-ordering Verwey transition. A large magnetoresistance was observed and attributed to spin-dependent tunnelling between the magnetite particles. It was less than predicted due to a spin-disordered interfacial region. The electrical resistance was modelled in terms of small nanoparticles coating the larger particles and electrostatic charging during tunnelling between small nanoparticles. Magnetite powders were also synthesized via a chemical co-precipitation method where nanoparticles with diameters of ~14 nm were observed. The Verwey transition was only observed in the zero-field cooled field-cooled magnetization for the arc-discharge powders. It was observed for the magnetite powders made using both methods in the temperature dependence of the saturation moment. The saturation magnetic moment for powders made using both methods has a power law dependence on temperature with an exponent of 3/2 at low temperatures and a higher value above the Verwey transition temperature 2. There was also a large magnetoresistance due to spin-dependent tunnelling for magnetite nanoparticle made using a chemical co-precipitation method and the electrical resistance could be modelled in terms of electrostatic charging during tunnelling. NixFe₁₋x nanoparticles were made for the first time by ion beam implantation. Small superparamagnetic nanoparticles occurred after implantation. The saturation moment after implantation did not follow the Bloch’s T³/² for x=0.82, which is likely to be due to spin-waves propagating in the nanoparticle/NiyFe₁₋ySizOn matrix. A bi-modal particle size distribution of mostly spherical nanoparticles was observed for x=0.82 after annealing. An x=0.45 sample showed large asymmetric NixFe₁₋x nanoparticles with minimal smaller nanoparticles. The different nanoparticle morphologies is likely to be due to the different nucleation centres and the different initial concentration profiles. The saturation moment had an exponent of 3/2 at low temperatures and there was a contribution from surface disordered spins. A higher Ni fluence with x=0.53 lead to the formation of superparamagnetic nanoparticles that had a higher blocking temperature, indicating the formation of larger nanocrystallites. There was an enhancement in the permeability.</p>

Structural, Magnetic and Electronic Properties of Nanostructured Magnetic Materials

<p>This thesis was motivated by the different properties exhibited by magnetic nanoparticles when compared with the bulk. For example the coercivity and magnetocrystalline anisotropy vary with the particle size and the finite particle size can affect the spin-wave dispersion. When the nanoparticle radius becomes small enough it is possible to observe superparamagnetism with negligible hysteresis. The transport properties can also be different in nanoparticle composites when compared with the bulk. It is particularly interesting if the nanoparticles have a degree of electronic spin polarization because it is then possible to observe spin-dependent tunnelling. This thesis reports the results from a study of the structural, magnetic, and electronic properties of two partially electronically spin-polarized nanostructured compounds, iron-nickel alloy and magnetite, that were made using a new arc-discharge method, ion implantation and annealing, and a co-precipitation method. It was found that permalloy powders could be made by arc-discharge where there were a range of particle sizes from nms to 10s of microns. Magnetoresistance was observed where it is due to the ordinary magnetoresistance and spin-dependent tunnelling between the particles. It was also possible to make magnetite using the arc-discharge process and the powders contained nanoparticles, large faceted nanoparticles, and larger particles in the 10s of micron range. The temperature dependence of the saturation magnetization changes at 127 K, which can be attributed to the charge-ordering Verwey transition. A large magnetoresistance was observed and attributed to spin-dependent tunnelling between the magnetite particles. It was less than predicted due to a spin-disordered interfacial region. The electrical resistance was modelled in terms of small nanoparticles coating the larger particles and electrostatic charging during tunnelling between small nanoparticles. Magnetite powders were also synthesized via a chemical co-precipitation method where nanoparticles with diameters of ~14 nm were observed. The Verwey transition was only observed in the zero-field cooled field-cooled magnetization for the arc-discharge powders. It was observed for the magnetite powders made using both methods in the temperature dependence of the saturation moment. The saturation magnetic moment for powders made using both methods has a power law dependence on temperature with an exponent of 3/2 at low temperatures and a higher value above the Verwey transition temperature 2. There was also a large magnetoresistance due to spin-dependent tunnelling for magnetite nanoparticle made using a chemical co-precipitation method and the electrical resistance could be modelled in terms of electrostatic charging during tunnelling. NixFe₁₋x nanoparticles were made for the first time by ion beam implantation. Small superparamagnetic nanoparticles occurred after implantation. The saturation moment after implantation did not follow the Bloch’s T³/² for x=0.82, which is likely to be due to spin-waves propagating in the nanoparticle/NiyFe₁₋ySizOn matrix. A bi-modal particle size distribution of mostly spherical nanoparticles was observed for x=0.82 after annealing. An x=0.45 sample showed large asymmetric NixFe₁₋x nanoparticles with minimal smaller nanoparticles. The different nanoparticle morphologies is likely to be due to the different nucleation centres and the different initial concentration profiles. The saturation moment had an exponent of 3/2 at low temperatures and there was a contribution from surface disordered spins. A higher Ni fluence with x=0.53 lead to the formation of superparamagnetic nanoparticles that had a higher blocking temperature, indicating the formation of larger nanocrystallites. There was an enhancement in the permeability.</p>

Can Surface Coating of Circular Saw Blades Potentially Reduce Dust Formation?

Coating of steel is a frequently applied approach to increase the resistance of moving machine parts towards abrasion, surface oxidation, and corrosion. Here, we show that plating circular saw blades with certain metals can help to reduce the electrical charging of wood dust during cutting, which has significant implications for occupational safety, healthcare, and lifetime of filter systems. With the example of beech wood planks, machine net energy consumption EV (J cm−3) and cumulated field strength E→V (kV m−4) as caused by electrically charged particles were compared for cutting of 10- and 20-mm deep grooves (800 mm length) using saw blades of different toothing (24, 60 teeth) and surface coating (Cu, Ag, and Cr). To ensure uniform feed per tooth (fz = 0.063 mm), saw blades were operated at different rotation speeds (4000 vs. 1600 rpm). The results demonstrate that the extent of electrostatic sawdust charging can be manipulated to a certain extent by the type of saw blade plating. Coating with chromium turned out to be most effective in shifting the electrostatic charge of the wood particles towards neutralization. Lowering of rotation speed using circular saw blades of higher toothing was an additional measure significantly reducing electrostatic charging of wood dust. Hence, cutting with a chrome-coated blade with 60 teeth can be specifically recommended as the reduction of electrical saw dust charging is not associated with higher machine power consumption.

Microbial Biofilms in the Food Industry—A Comprehensive Review

Biofilms, present as microorganisms and surviving on surfaces, can increase food cross-contamination, leading to changes in the food industry’s cleaning and disinfection dynamics. Biofilm is an association of microorganisms that is irreversibly linked with a surface, contained in an extracellular polymeric substance matrix, which poses a formidable challenge for food industries. To avoid biofilms from forming, and to eliminate them from reversible attachment and irreversible stages, where attached microorganisms improve surface adhesion, a strong disinfectant is required to eliminate bacterial attachments. This review paper tackles biofilm problems from all perspectives, including biofilm-forming pathogens in the food industry, disinfectant resistance of biofilm, and identification methods. As biofilms are largely responsible for food spoilage and outbreaks, they are also considered responsible for damage to food processing equipment. Hence the need to gain good knowledge about all of the factors favouring their development or growth, such as the attachment surface, food matrix components, environmental conditions, the bacterial cells involved, and electrostatic charging of surfaces. Overall, this review study shows the real threat of biofilms in the food industry due to the resistance of disinfectants and the mechanisms developed for their survival, including the intercellular signalling system, the cyclic nucleotide second messenger, and biofilm-associated proteins.