How Cu doping improves the interfacial wettability between Ag and SnO2 of Ag/SnO2 contact material

There are two major weaknesses for the AgSnO2 contacts used in the low voltage switch devices. One is poor workability, which causes the AgSnO2 materials to hardly deform into the required shape. Another is the increased contact resistance after arcing, which, in turn, causes an unfavorable temperature rise in the switches. In this article, the nanocomposited AgSnO2 materials were developed to overcome the weaknesses. The nanosized SnO2 powders with or without CuO additive were prepared by the chemical precipitation method. The SnO2 powders and Ag powders were high energy milled together to obtain AgSnO2 composite powders, which were then sintered, hot pressed and extruded. It was found that the SnO2 particles mainly distribute in the interior of Ag grains with Ag film on the grain boundary. The hardness of AgSnO2 composites and the wetting angle of Ag melt on SnO2 particles decreased with the addition of a small amount of CuO. By the combining effect of Ag film on grain boundary and the addition of CuO, the elongation and workability of the AgSnO2 materials improved. The experiments of rapid solidification revealed that more SnO2 particles with CuO addition were engulfed in the Ag matrix than those without CuO, which inhibited the redistribution of SnO2 particles on the contact surface during the arcing process. The industrial type test in the 45A contactor suggested that the nanocomposited AgSnO2 materials are suitable to be used as contacts in low voltage switches.

Arc erosion behaviors of AgSnO2 contact materials prepared with different SnO2 particle sizes

This study was undertaken to clarify the effect of the mixing condition of SnO2 and glass partieles on the densification behavior, the microstructure and the electrical properties of the glass composites containing semiconductive SnO2 particles prepared by a mechano-chemical process. The relationship between the electrical properties of the glass composites and the dispersion state of the SnO2 particles in a glass matrix was discussed based on the results of the quantitative analysis of SnO2 particle dispersion by the computer-assisted image analysis of SEM photographs.The results are summarized as follows:(1) The homogeneity of the mixing state of SnO2 and glass particles mainly depends on the degree of pulverization of the glass particles because the SnO2 aggregates formed during the mechano-chemical synthesis of the SnO2-Sb2O3 powder mixture are easily disintegrated during ball or attrition-milling. Therefore, when the mixing condition in which glass particles are effectively pulverized, such as in attrition milling, is applied, homogeneous mixing is easily achieved, and densely sintered glass composites with homogeneously dispersed SnO2 particles are obtained at low firing temperatures.(2) The electrical conductivity and the temperature coefficient of resistivity (TCR) of the glass composites fired at low temperatures largely depend on the degree of densification. The glass composites well densified at low firing temperatures, such as an attrition-milled sample, show a high electrical conductivity and a small negative TCR at low firing temperatures.On the other hand, the electrical conductivity and TCR of the glass composites fired at high temperatures are significantly influenced by the SnO2 particle dispersion in a glass matrix. When comparing the densely sintered glass composites, the electrical conductivity becomes higher, and TCR approaches zero when the highly aggregated SnO2 particles form networks in the glass matrix.

Nickel-based single-crystal superalloy is a typical kind of difficult-to-machine material, which has no grain boundary and has excellent high temperature mechanical properties, making it the best choice for the manufacturing of hot end components of aviation engine and gas turbine. Micro-grinding which uses tool with a diameter of less than 1 mm to remove material is the final procedure of machining micro-parts, and its machined surface quality directly affects the service life of workpiece. In this paper, micro-grinding experiments of nickel-based single-crystal superalloy with only one grain were carried out, which considered the influence of crystal anisotropy. Firstly, the reasons for the anisotropy of single-crystal material were analyzed theoretically. Secondly, the influence of different crystal planes and different crystal orientations in the same crystal plane on micro-grinding surface quality was analyzed. Then, the influence of micro-grinding parameters and micro-grinding tool-wear on micro-grinding surface quality was analyzed. Finally, a preliminary exploration and research on the generation and restraint process of the subsurface recrystallization of micro-grinding workpiece was conducted through simulating the high-temperature application environment of nickel-based single-crystal superalloy. The experimental results show that the grinding surface roughness along (100) crystal plane is higher than that along (110) crystal plane and (111) crystal plane, and the grinding surface roughness along (110) crystal plane is higher than that along (111) crystal plane. When grinding in the (001) crystal plane, the grinding surface roughness along [110], \( \left[\overline{1}10\right] \), \( \left[\overline{1}10\right] \), \( \left[1\overline{1}0\right] \) crystal orientations is the lowest, and that along [100], [010], \( \left[\overline{1}00\right] \), \( \left[0\overline{1}0\right] \) crystal orientations is the highest. The subsurface recrystallization layer thickness of the workpiece grinding along the [110], \( \left[\overline{1}10\right] \), \( \left[\overline{1}10\right] \), \( \left[1\overline{1}0\right] \) crystal orientations and under high temperature is larger, and that along the [100], [010], \( \left[\overline{1}00\right] \), \( \left[0\overline{1}0\right] \) crystal orientations is smaller. With the decreases of spindle speed (vs), and the increase of feed rate (v w ), grinding depth (a p ) and degree of grinding wheel wear, micro-grinding surface quality becomes worse gradually. It is appropriate when the extended length of micro-grinding tool is 18 mm. When the micro-grinding workpiece of nickel-based single-crystal superalloy was insulated at 760 °C for 4 h and the furnace cooling was used, the thickness of recrystallization layer is smaller, which is nearly 1.6 μm. The service life of single-crystal components can be improved. So this is a good guide and reference to the machining of nickel-based single-crystal superalloy micro components.

Effect of strengthening phase on material transfer behavior of Ag-based contact materials under different voltages

Sulfurization of planar MoO3 optical crystals: Enhanced Raman response and surface porosity

SUMMARYThe chemical changes occurring from 0 to 24 and/or 48 hr post‐mortem were followed in longissimus dorsi muscle from 18 pork carcasses. In an attempt to induce soft, watery pork, one side from each of 13 carcasses was placed at 37°C immediately after slaughter, and the other side of each carcass was subjected to ‐29°C. Values for pH, glycogen, total reducing sugars, and lactic acid differed markedly at 0 time. Carcasses from Poland China pigs showed a stoichiometric relationship between the post‐mortem decrease in glycogen and the corresponding accumulation of lactic acid and total reducing sugars. This relationship was less apparent in Hampshire pigs. The 37°C treatment did not consistently result in soft, watery and pale muscle, as was expected from other reports. This suggests that exposure of muscle to a low pH at a high temperature per se does not necessarily cause the soft, watery, and pale appearance. A loss in fibrillar water‐binding capacity as a result of low pH values and high muscle temperatures confirmed earlier investigations. However, the decrease in fibrillar water‐binding capacity as a result of the low pH at high muscle temperatures did not usually make the muscle appear soft and watery. Results indicate that even though a loss in fibrillar water‐binding capacity occurs as a consequence of a low pH and high temperature, and is a characteristic frequently encountered in soft, watery muscle, low fibrillar water‐binding capacity by itself is not the primary causal factor in making pork muscle appear soft and watery. Post‐mortem levels of ATP, creatine phosphate, lactic acid, total reducing sugars and glycogen are reported and compared with literature values.

Improved fracture resistance of the Ag/SnO2 contact materials using Cu nanoparticles as additive

In electrical apparatuses containing an arc chute, arc occurs initially on the contacts arranged between the insulating walls spaced at a relatively wide distance from each other, after which the electromagnetic forces drive the arc into the area occupied by the chute plates. Electric arc is a complex phenomenon, in which a large number of physical interactions occur within a very short period of time. An analysis and calculation of arc processes in the arc quenching devices of electrical apparatuses imply simultaneous consideration of thermal gas dynamic, kinetic, electrical (network), arc, and mechanical processes. This adds much difficulty to a search of acceptable models that would satisfy all these requirements. The difficulties of solving the equations that are based on the general principles of thermodynamics and the laws of continuum mechanics are connected, in particular, with the validity of boundary and initial conditions, which are usually selected with due regard for experimental data (it should be noted that the experimental techniques in studying an arc are quite sophisticated and costly). In the course of many years, many electric arc modeling methods have been developed. The following three basic types of electric arc models should be pointed out: a physical model, a black box model, and a parametric model. These models cannot show all physical processes in an electric arc, but they can describe the variations of the main parameters. The physical processes accompanying the arc motion can slow down or even stop its displacement, which may lead to an emergency. Therefore, it is very important to select the arch chute parameters in such a way that it would offer the lowest resistance to the arc motion. In this regard, it is of primary importance to estimate the electric arc channel radius. The article is devoted to calculating the electric arc channel radius. The calculations presented in the article can be useful in selecting the parameters of arc chute plates.

Alternative conceptions of ‘physical and chemical change’ concepts to minimize their effects on further learning should be handled at lower secondary school in that these concepts are formally introduced at grade 6. This study aimed to investigate the effect of storylines embedded within context-based learning approach on grade 6 students’ understanding of ‘physical and chemical change’ concepts. To probe the students’ conceptions, Chemical and Physical Change Concept Questionnaire (CPCCQ) was employed as pre- and post-test. The results indicated that most of the students tended to pay more attention to ‘reversibility’ criterion in distinguishing ‘chemical change’ concept from ‘physical change’ one. Finally, it can be deduced that the storylines embedded within the context-based learning approach not only resulted in a better meaningful learning but also increased student achievement level. To give an opportunity for the students to grasp the relevance of chemistry/science to their lives, the meaning of each daily life concept should be bridged with that in a chemistry context. Key words: alternative conception, context-based learning approach, chemical change, physical change, science education, storylines.

Adsorption behavior of molecules on Zn2SnO4(1 1 1) crystal plane and its effect on electrical conductivity

Mechanical characteristics of the Ag/SnO2 electrical contact materials with Cu2O and CuO additives

Aircraft tires face extremely complex conditions during landing and the sharp temperature rise that is caused by the friction in a short period of time during landing may bring about serious destruction to the tread compound and thus threat on the safety of the aircraft. Our research described here focused on the high-temperature stability of a carbon black enhanced natural rubber (NR) composite at high temperatures (300-400 °C) in short time (0-100 s) ranges and its effect on the mechanical properties, and a deep investigation of the corresponding mechanisms. The experimental results confirmed that the thermal experience at 300-400 °C for 60 s did not remarkably affect the mechanical properties of the NR composite. However, serious damage to the mechanical properties of the NR composite occurred at 400 °C after thermal treatment for longer than 60 s. The analysis of the cross-linking density, hardness, and surface morphologies of the NR composite illustrated that the mechanical loss was related to the chemical and physical changes of the NR composite. Physical and chemical changes took place in the NR composites with increasing the heat treatment temperature, which seriously reduced the mechanical properties of the NR composites. Further analysis showed that more oxygen participated in the decomposition process of the NR with increasing the treating temperature from 300 to 400 °C, which led to more intensive decomposition of the NR and finally resulted in a remarkable decrease in mechanical properties of the NR composite.

The effects of oxide additives on the mechanical characteristics of Ag–SnO2 electrical contact materials

The use of metal nanoparticles as seed layers forcontrolling the microstructures of tin oxide (SnO2) filmson temperature controllable micromachined platforms has beeninvestigated. The study is focused on SnO2 due to itsimportance in the field of chemical microsensors. Nanoparticleseeds of iron, cobalt, nickel, copper and silver were formed by vapour deposition on the microhotplates followed by annealing at 500 °C prior to self-aligned SnO2 deposition.Significant control of SnO2 grain sizes, ranging between20 and 121 nm, was achieved depending on the seed-layer type. Acorrelation was found between decreasing the SnO2 grain sizeand increasing the melting temperature of the seed-layer metals,suggesting the use of high temperature metals as being appropriate choices as seed layers for obtaining a smaller SnO2 grainstructure. Smaller grain diameters resulted in high sensitivityin 90 ppm ethanol illustrating the benefits of nanoparticleseeding for chemical sensing. The initial morphology, particlesize and distribution of the seed layers was found to dictatethe final SnO2 morphology and grain size. This papernot only demonstrates the possibility of depositingnanostructured oxide materials for chemical microsensorapplications, but also demonstrates the feasibility ofconducting combinatorial research into nanoparticle growthusing temperature controllable microhotplate platforms. Thispaper also demonstrates the possibility of usingmulti-element arrays to form a range of different types ofdevices that could be used with suitable olfactory signalprocessing techniques in order to identify a variety of gases.