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Here we describe the improvement of pesticide residue extraction from tomatoes by an improved QuEChERS method. Through Plackett–Burman design, 4 significant variables out of 11 potential variables were identified that could influence the relative deviation of measurements. The 11 variables were: amount of sample, C18, Na2SO4, NaCl, MgSO4, NaAc, GCB (graphitized carbon black), and PSA (primary–secondary amine); ACN volume; percentage of FA (formic acid); and centrifugation time. The amounts of GCB, Na2SO4, PSA and sample were significant variables, which were further optimized using a Box–Behnken design to predict the optimum extraction conditions. The method presented recoveries between 72.5 and 119.7%, with relative standard deviations ranging from 1.17 to 14.62% for all real samples spiked with pesticides at three different fortification levels. Overall, methods met the requirements of national standard for pesticide residue analysis. The results indicate that the improved QuEChERS method is suitable for the routine monitoring of 20 pesticides which often are detected in tomato samples.

To improve friction and wear performance and service life of the disc-brake pair material of a drilling rig, a new type of asbestos-free frictional material with better performance for disc-brake blocks is developed, and its wear mechanism is investigated by friction and wear experiments. Topography and elementary components of the brake block’s wear surface are analyzed by employing SEM and EDAX patterns, revealing its tribological behaviour and wear mechanism. When the frictional temperature is lower, the surface film of the brake block is thinner, dense, smooth with plasticity, and divided into the mixture area, Feabundant area, carbon-abundant area and spalling area. The mixture area consists of various constituents of frictional pairs without ploughing and rolling trace. The Fe-abundant area mainly consists of iron and other constituents. The carbon-abundant area is the zone where graphite and organic fibre are comparatively gathered, while the spalling area is the zone where the surface film is spalled and its surface is rough and uneven, with a loose and denuded state. During the period of high frictional temperature, the frictional surface is also divided into the mixture area, Feabundant area and spalling area. In this case, the mixture area consists of abrasive dust from friction pairs, and the surface film is distributed with crumby hard granules, exiguous oxide, carbide granules and sheared slender fibre. The Fe-abundant area is mostly an oxide layer of iron with a flaky distribution. Fracture and spalling traces as well as an overlapping structure of multilayer surface films can be easily found on the surface film. The components of the spalling area are basically the same as that of the matrix. At the beginning of wear, the hard peaks from the friction surface of the disc-brake plough on the surface of the brake block. With increasing frictional temperature, the friction surface begins to soften and expand, and oxidized wear occurs at the same time. During the high-temperature wear period, severely influenced by friction heat, obvious softening and plastic flow can be found on the friction surface of the brake block, its anti-shearing ability is weakened, and adhesive wear is intensified. Thermal decomposition of cohesive material in the brake block is simultaneously strengthened, so that constituents shed due to loss of adhesion. Organic fibre is in a flowing state and obviously generates drawing, shearing, carbonization and oxidization. In addition, thermal cracking, thermal oxidization, carbonization and cyclization of organic substances on the surface of brake block can make the friction surface produce pores or cracks, thus fatigue wear occurs.

Mechanisms of abrasive erosion for polymers, including polyurethane, styrene-butadiene rubber, nylon-6 and polytetrafluoroethylene, have been investigated using a special abrasive erosion test machine designed by the authors. Based upon some observations of the abraded surfaces of test samples using scanning electron microscopy (SEM), the mechanisms of abrasive erosion for the polymers examined could be summarized as follows: a microcutting action of the abrasives with a certain kinetic energy; microdelamination of the surface layer of the materials resulting from initiation and propagation of microcracks; mechanochemical and thermal decomposition of materials; and surface peeling, resulting from plastic fracture expanded from local plastic deformation of the material. The influence of these factors on the wear rate of the abrasive erosion has been studied, and the relevant wear-rate equations are presented.