The citrate sol–gel method was utilized for the fabrication of copper-containing films sensitive to NO2 gas. Effect of annealing temperature on the film phase composition, morphology, and sensor response was studied. X-ray diffraction reveals the formation of Cu2Cl(OH)3 phase at 250 °C and the CuO phase at 350 and 500 °C. It was found out that the films annealed at 250 °C and 350 °C showed the best sensor characteristics. The influence of thermal degradation on the probability of percolation effect in films and its connection to a decrease of gas sensitivity was studied. The kinetics of the NO2 gas adsorption on the film’s surface was described following the Elovich model. Activation energy estimated from the ln(S) vs. 1/T plots was 252 and 30 kJ/mol for the films annealed at 250 and 350 °C, respectively.
Copper oxides films as promising materials for gas sensors applications were studied. Copper oxide films were deposited onto Si/SiO2substrates using a citrate sol-gel method with the subsequent temperature treatment at 150-5000C. These films were characterized by means of secondary electron microscopy (SEM) and X-ray-absorption near-edge structure (XANES) spectroscopy. The prepared films were utilized in NO2sensors. The dependences of the NO2response on the operating temperature and NO2concentration (10-200 ppm) were investigated. The maximum NO2response was achieved for the film annealed at 2500C.
To work out the optinu2l chemical composition of wear-resistant cast iron with a pearlitic metallic matrix that is able to restore the relief of a rough surface, we investigated the properties of cast iron with different composition by the method of single-factor experiment.Chilled cast iron with more disperse metallic matrix than pearlite has, and with hard primary phases in the form of cementite and other special carbides is often used at present as wear-resistant material in the light and food industry.Such cast iron with troostite-sorbitic, bainitic, or martensitic metallic matrix has good resistance to abrasive wear but is inefficient, e.g., as working layer of flour-milling rolls with smooth "mat" surface because these alloys are unable to retain and spontaneously restore the relief of the rough surface of the rolls during operation. A fundamentally new type of wearresistant material is economically alloyed high phosphorus cast iron with pearlitic matrix, and with phosphide eutectic in addition to the above-mentioned hard phases. A characteristic feature of the structure of cast iron containing a large amount of phosphorus is the directivity of the columnar cementite crystals in the chilled layer and a certain morphology of the ternary eutectic which is bound to have a beneficial effect on the wear resistance of this material.In the present work we investigated the influence of carbon and the alloying elements on the structure, the wear resistance, the ability to restore the relief of the rough surface, and the mechanical properties of white cast iron of the system Fe-C-Si-P.In working out the basic composition of the cast iron we changed the content of carbon in the range 2.4-4.2%; of silicon 0.17-1.66%; of phosphorus 0.3-0.9%. For studying the influence of the alloying elements we used the basic cast iron with the following composition: 3.5% C, 0.17% Si, 0.32% MN, and negligible additions of other elements (see Table 1).The cast iron for the experiments was produced in an induction furnace with a crucible of 10 and 160 kg capacity, and it was based on steel scrap, with various ferroalloys used for alloying. Carburization was carried out with graphitized coke fines. To determine the structure and properties of the cast iron we cast samples 15 x 120 x 120 mm in size in a sandy-loam mold and a half-mold at 1340-1360°C. The amount, shape, distribution and dimension of the structural components were evaluated according to GOST 3443-87.Wear was determined* according to the decrease in weight of a specimen 10 x 20 x 70 mm in size, rubbing against an abrasive (quartz sand of the fraction 0.2-0.4 mm) with the aid of a rubber wheel 8 mm wide by Haworth's method for 30 min at a speed of 200 rpm (6 m/sec) under a specific load of 3.3 kg/m 2 . The ability of the cast iron of spontaneous restoration of the rough surface under the effect of abrasive particles was evaluated with the aid of a profilometer M296 according to the change of roughness (Ra) of the specimens after wear tests. Hardness was determined according to...
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