Enhancement effect of nonferromagnetic particles on the viscosity of magnetorheological fluid under a dynamic magnetic field

This study aims to investigate the effect of nonferromagnetic particle content on the properties of the magnetorheological fluid (MRF) under a dynamic magnetic field. A magnetic-induced viscosity calculation model under the temperature field was built. The influence on the viscosity of the MRF made in-house was analyzed by adding different proportions of nonferromagnetic particles, such as glass powder. Experiments show that a certain proportion of glass powder can increase the viscosity of the MRF. When the powder content is less than 10%, viscosity increases as the glass powder content increases. Conversely, viscosity decreases as the glass powder content increases when the content is more than 10% but less than 20%. These results indicate that adding micron glass powder to the MRF can increase the magnetic saturation limit of the MRF under the dynamic magnetic field and improve its settlement resistance by 25.6%.When 10% glass powder is added to the MRF containing 60% iron powder, sedimentation resistance increases by 25.6%. When the magnetic field intensity is 640 mT, the viscosity of the MRF increases by 6.6 times.

Exopolysaccharide anchoring creates an extreme resistance to sedimentation

By evolving strains of E. coli that hyper-resist sedimentation, we discovered an uncharacterized mechanism that bacteria can use to remain in suspension indefinitely without expending energy. This unusual phenotype was traced to the anchoring of long colanic acid polymers (CAP) that project from the cell surface. Although each characterized mutant activated this same mechanism, the genes responsible and the strengths of the phenotypes varied. Mutations in rcsC, lpp, igaA, or the yjbEFGH operon were sufficient to stimulate sedimentation resistance, while mutations altering the cps promoter, cdgI, or yjbF provided phenotypic enhancements. The sedimentation resistances changed in response to temperature, growth phase, and carbon source and each mutant exhibited significantly reduced biofilm formation. We discovered that the degree of colony mucoidy exhibited by these mutants was not related to the degree of Rcs pathways activation or to the amount of CAP that was produced; rather, it was related to the fraction of CAP that was shed as a true exopolysaccharide. Therefore, these and other mutations that activate this phenotype are likely to be absent from genetic screens that relied on centrifugation to harvest bacteria. We also found that this anchored CAP form is not linked to LPS cores and may not be attached to the outer membrane. IMPORTANCE Bacteria can partition in aqueous environments between surface-dwelling, planktonic, sedimentary, and biofilm forms. Residence in each location provides an advantage depending on nutritional and environmental stresses and a community of a single species is often observed to be distributed throughout two or more of these niches. Another adaptive strategy is to produce an extracellular capsule, which provides an environmental shield for the microbe and can allow escape from predators and immune systems. We discovered that bacteria can either shed or stably anchor capsules to dramatically alter their propensity to sediment. The degree to which the bacteria anchor their capsule is controlled by a stress sensing system, suggesting that anchoring may be used as an adaptive response to severe environmental challenges.

A STUDY ON OPERATIONAL PROPERTIES OF ANTI-WEAR ADDITIVES FOR MOTOR LUBRICATING OILS DEPENDING ON THEIR PROCESSING AND SEDIMENTATION

The article presents studies on the dependence of sedimentation resistance of the anti-wear additive solid component for marine diesel trunk-type internal combustion engines on the technological conditions of its manufacturing. A friction modifier, molybdenum diselenide, which has optimal anti-wear properties, was selected as a solid component. The authors consider the process of sedimentation of a given substance, stabilized in the volume of an additive solution with unsaturated acids, at different times of rotary stirring, and under the influence of subsequent treatment of the prepared solution with ultrasound. The mass of the solution solid component is studied as irretrievably precipitated over various periods of storage time of the additive solutions, subjected to rotary stirring and additional ultrasonic treatment. The recommended storage time of the considered anti-wear additive with a 10% content of molybdenum diselenide has been established.

The Synthesis and Study of Metal Powder Stabilizer Properties in Lubrication Compositions

Introduction. Modern manufacturing technologies of powder materials allow obtaining particles sized 0.1–0.5 μm. Powders with such dispersion have a very high surface energy and, consequently, unique properties. Powders with a given size can be used as an additive to motor oil to form the surface film with high tribological properties. However, the widespread use of ultra-nanoscale powder materials as additives to motor oil limits sedimentation and aggregation of the particles. As a result, the dimensions of the metal crystals increase to dozens of microns and their particles are then retained by oil filters of engines that leads to efficiency decrease and even to clogging oil-conducting channels and to setting the friction surfaces of the parts. The most technically competent solution for increasing sedimentation resistance of the lubricant composition is the use of chemical stabilizers forming the thinnest film at the surface of metal particles, which not only hinders particle aggregation, but also keeps them suspended for a long time. Materials and Methods.As stabilizers of dispersed metal powders in lubricant compositions, organic compounds of various classes are used. The analysis of several stabilizers of disperse metal powders is given in the paper and new compositions are proposed: apinezon MN, polyethylene glycol sebacate and commodity stabilizer apiezon L. The methods of stabilizers synthesis and examination of their activity are described. Results. The stabilization activity of the developed preparations was compared to the basic version: oleic acid. Addition of the ester of ethylene glycol sebacate had no stabilizing effect on the lubricant composition. The synthesized MN and Mg reagent apeizon L show stabilizing properties with respect to metallic powders of the lubricant composition, comparable with the properties of oleic acid. Discussion and Conclusion.Since apiezon greases are a mixture of hydrocarbons, their corrosivity is much lower than that of oleic acid, they can be recommended for practical use.