Improved Workability of the Nanocomposited AgSnO<Subscript>2</Subscript> Contact Material and Its Microstructure Control During the Arcing Process

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.     

Effect of La2Sn2O7 content on Ag-La2Sn2O7/SnO2 arc erosion behavior and mechanism

La₂ Sn₂ O₇/SnO₂ powder was synthesized by chemical co-precipitation method,and Ag-La₂ Sn₂ O₇/SnO₂ composites were prepared by hot-pressing sintering.The electrical resistivity,density,Brinell hardness and flexural strength of Ag-La₂ Sn₂ O₇/SnO₂ composites were measured.Moreover,the effect of La₂ Sn₂ O₇ content on the arc erosion beha...     

Processing copper and silver matrix composites by electroless plating and hot pressing

A simple process was developed to fabricate ceramic-reinforced copper and silver matrix composites by electroless plating and hot pressing at 873 K and 300 MPa, in air. Composites were produced containing 10 to 40 vol pct ceramic reinforcements of different sizes and shapes including silicon carbide whiskers (SiC _w ), alumina particles (Al₂O_3p ), carbon short fibers (Carbon _sf ), and Saffil short fibers (Saffil _sf ) (3.8 pct SiO₂-96.2 pct Al₂O₃) uniformly distributed within the matrix. The hardness and bending strength of the composites were much higher than those of the pure matrices. The electrical conductivity, measured by a four-point probe method, was similar to that of traditional CdO/Ag electrical contact materials. The surface morphologies and cross-sectional microstructures of the arc-eroded Al₂O_3p /Ag composites were similar to those of conventional CdO/Ag and SnO₂/Ag and exhibited a good arc-erosion resistance. These composites combine the high strength and elevated-temperature stability of the ceramic reinforcements with the good electrical and thermal conductivity of the two metallic matrices.     

Synthesis and Characterization of Al–Al/(SiO<Subscript>2</Subscript>)<Subscript>np</Subscript> Composite by Powder-in-Tube Method

In this study, a macro-nanocomposite of Al–Al/(SiO₂)_np was synthesized using powder-in-tube method. Pure aluminum cylinders were cast and then machined to prepare tubes. Nanocomposite powders of Al/(SiO₂)_np were prepared by mixing 1 and 2 wt% SiO₂ nano-particle with aluminum. Then macro-nanocomposites were prepared by compaction of the nanocomposites inside the tubes. The effects of reinforcement weight fraction, volume fraction of nanocomposite in the macro-nanocomposites and hot extrusion on the microstructure and mechanical properties were investigated. Scanning electron microscope (SEM) and optical microscope (OM) were used for microstructural examinations. Mechanical properties were investigated using tensile and compression tests at room temperature. The results revealed that when 25 vol% of the powder-in-tube composite was the nanocomposite reinforced with 2 wt% of nano-particle, the tensile strength was increased by 10.8%. Tensile strength was improved by up to 24% when 64 vol% of nanocomposite reinforced with 1 wt% of nano-particle was employed. Additionally, significant increase in compressive strength was achieved. This is noteworthy that coupling of a pure aluminum sheath with the nanocomposite enhanced the strength with limited loss of ductility. Micrographs showed integrated composites in which the interface between the sheath and the core had no defects.     

Development of Wear-Resistant Cu-10Cr-3Ag Electrical Contacts with Nano-Al<Subscript>2</Subscript>O<Subscript>3</Subscript> Dispersion by Mechanical Alloying and High Pressure Sintering

Cu-10Cr-3Ag (wt pct) alloy with nanocrystalline Al₂O₃ dispersion was prepared by mechanical alloying and consolidated by high pressure sintering at different temperatures. Characterization by X-ray diffraction and scanning electron microscopy or transmission electron microscopy shows the formation of nanocrystalline matrix grains of about 40 nm after 25 hours of milling with nanometric (<20 nm) Al₂O₃ particles dispersed in it. After consolidation by high pressure sintering (8 GPa at 400 °C to 800 °C), the dispersoids retain their ultrafine size and uniform distribution, while the alloyed matrix undergoes significant grain growth. The hardness and wear resistance of the pellets increase significantly with the addition of nano-Al₂O₃ particles. The electrical conductivity of the pellets without and with nano-Al₂O₃ dispersion is about 30 pct IACS (international annealing copper standard) and 25 pct IACS, respectively. Thus, mechanical alloying followed by high pressure sintering seems a potential route for developing nano-Al₂O₃ dispersed Cu-Cr-Ag alloy for heavy duty electrical contact.     

Structural,Optical and Impedance Studies of Hydrothermally and Solvothermally Prepared SnO<Subscript>2</Subscript> Nanocrystallites for Conducting Electrode Application

Nanocrystalline SnO₂ powders were synthesized by hydrolysis and solvolysis of SnCl₂ followed by a fast nucleation process in Teflon lined autoclave. The as prepared samples were calcined at 400 ^°C for 4 h to attain stable phase. The X-ray diffraction pattern confirms tetragonal crystal structure for both hydrothermally and solvothermally prepared nanoparticles and the average crystallite size is calculated to be 14 and 30 nm respectively. Williamson–Hall plot (W–H plot) reveals low value of strain induced broadening using uniform deformation model. Absorption co-efficient of prepared SnO₂ was determined using UV–Visible absorption spectrum. Nyquist plane plot shows the decreased electrical resistance of SnO₂ with increasing the applied potential resulting in increased conductivity. The increasing conducting behavior of tin oxide nanoparticles can be used as conducting layer in photoelectrodes.     

Wettability of Mn<Subscript>x</Subscript>Si<Subscript>y</Subscript>O<Subscript>z</Subscript> by Liquid Zn-Al Alloys

The wettability of Mn_xSi_yO_z by liquid Zn-Al alloys was investigated to obtain basic information on the coating properties of high-strength steels with surface oxides in the hot-dip galvanizing process. In this study, the contact angles of liquid Zn-Al alloys (Al concentrations were 0.12 and 0.23 wt pct) on four different Mn_xSi_yO_z oxides, namely MnO, MnSiO₃, Mn₂SiO₄, and SiO₂, were measured with the dispensed drop method. The contact angle did not change across time. With an increasing Al concentration, the contact angle was slightly decreased for MnO and Mn₂SiO₄, but there was no change for MnSiO₃ and SiO₂. With an increasing SiO₂ content, the contact angle gradually increased by 54 wt pct to form MnSiO₃, and for pure SiO₂ substrate, the contact angle decreased again. Consequently, the MnSiO₃ substrate showed the worst wettability among the four tested oxide substrates.     

Micro-structural Analysis and Densification Behavior of Al–ZrB<Subscript>2</Subscript> Powder Metallurgy Composite During Upsetting

The performance of the product components in application greatly depends on the morphological parameters and inherent capabilities of the material. In the present study, Al–ZrB₂ composite is made out of powder metallurgy route. Incremental weight% (0, 2, 4 and 6 wt%) of ZrB₂ were added into Al matrix to produce different composites. Composites were prepared by cold axial compaction followed by pressureless sintering at 550 °C for 1 h in controlled atmosphere (Ar gas). Hardness increased with the amount of ZrB₂ in the composite. To enhance the properties further, composites were deformed at 25, 400 and 500 °C respectively. The size, shape and orientation of the grains in the deformed composites were analyzed and correlated with the mechanical properties. The mechanical adhesion of ZrB₂ particle with the Al matrix was examined in different composites during different temperature conditions of deformation process. The fracture strain of the composites decreased with increase of ZrB₂ in the composite.     

Effect of heat treatments on <Emphasis Type="Italic">In-Situ</Emphasis> Al<Subscript>2</Subscript>O<Subscript>3</Subscript>/TiAl<Subscript>3</Subscript> composites produced from squeeze casting of TiO<Subscript>2</Subscript>/A356 composites

In-situ Al₂O₃/TiAl₃ intermetallic matrix composites were fabricated via squeeze casting of TiO₂/A356 composites heated in the temperature range from 700 °C to 780 °C for 2 hours. The phase transformation in TiO₂/A356 composites employing various heat-treatment temperatures (700 °C to 780 °C) was studied by means of differential thermal analysis (DTA), microhardness, scanning electron microscopy (SEM), electron probe microanalysis (EPMA), and X-ray diffraction (XRD). From DTA, two exothermic peaks from 600 °C to 750 °C were found in the TiO₂/A356 composites. The XRD showed that Al₂O₃ and TiAl₃ were the primary products after heat treatment of the TiO₂/A356 composite. The fabrication of in-situ Al₂O₃/TiAl₃ composites required 33 vol pct TiO₂ in Al and heat treatment in the range from 750 °C to 780 °C. The hardness (HV) of the in-situ Al₂O₃/TiAl₃ composites (1000 HV) was superior to that of nonreacted TiO₂/A356 composites (200 HV). However, the bending strength decreased from 685 MPa for TiO₂/A356 composites to 250 MPa for Al₂O₃/TiAl₃ composites. It decreased rapidly because pores occurred during the formation of Al₂O₃ and TiAl₃. The activation energy of the formation of Al₂O₃ and TiAl₃ from TiO₂ and A356 was determined to be about 286 kJ/mole.     

Microstructural Evolution and Mechanical Properties of Nanointermetallic Phase Dispersed Al<Subscript>65</Subscript>Cu<Subscript>20</Subscript>Ti<Subscript>15</Subscript> Amorphous Matrix Composite Synthesized by Mechanical Alloying and Hot Isostatic Pressing

The structure and mechanical properties of nanocrystalline intermetallic phase dispersed amorphous matrix composite prepared by hot isostatic pressing (HIP) of mechanically alloyed Al₆₅Cu₂₀Ti₁₅ amorphous powder in the temperature range 573 K to 873 K (300 °C to 600 °C) with 1.2 GPa pressure were studied. Phase identification by X-ray diffraction (XRD) and microstructural investigation by transmission electron microscopy confirmed that sintering in this temperature range led to partial crystallization of the amorphous powder. The microstructures of the consolidated composites were found to have nanocrystalline intermetallic precipitates of Al₅CuTi₂, Al₃Ti, AlCu, Al₂Cu, and Al₄Cu₉ dispersed in amorphous matrix. An optimum combination of density (3.73 Mg/m³), hardness (8.96 GPa), compressive strength (1650 MPa), shear strength (850 MPa), and Young’s modulus (182 GPa) were obtained in the composite hot isostatically pressed (“hipped”) at 773 K (500 °C). Furthermore, these results were compared with those from earlier studies based on conventional sintering (CCS), high pressure sintering (HPS), and pulse plasma sintering (PPS). HIP appears to be the most preferred process for achieving an optimum combination of density and mechanical properties in amorphous-nanocrystalline intermetallic composites at temperatures ≤773 K (500 °C), while HPS is most suited for bulk amorphous alloys. Both density and volume fraction of intermetallic dispersoids were found to influence the mechanical properties of the composites.     

Processing,microstructure, and mechanical properties of cast <Emphasis Type="Italic">in-Situ</Emphasis> Al(Mg,Mn)-Al<Subscript>2</Subscript>O<Subscript>3</Subscript>(MnO<Subscript>2</Subscript>) composite

Cast particulate composites, containing in-situ generated reinforcing particles of alumina, have been developed by solidification of slurry obtained by dispersion of externally added manganese dioxide particles (MnO₂) in molten aluminum, and alumina is formed by reaction of manganese dioxide with molten aluminum. The chemical reaction also releases manganese into molten aluminum. Magnesium is added to the melt in order to help wetting of alumina particles by molten aluminum and to retain the particles inside the melt. The present work aims to understand the influence of key parameters such as processing temperature, time, and the amount of MnO₂ particles added on the microstructure and mechanical properties of the resulting cast in-situ composites. The sequence of addition of MnO₂ particles and magnesium has significant influence on the microstructure and mechanical properties. Increasing processing temperature and time increases the extent of reduction of MnO₂ particles, generating more alumina particles as well as releasing more manganese to the matrix alloy. Alumina helps to nucleate finer and sometimes blocky MnAl₆ in the matrix of the composite and thereby results in relatively higher ductility and increased strength in the composite as compared to the base alloy of similar composition. Even in the presence of relatively higher porosity of 8 to 9 vol pct, one observes a percent elongation not below 7 to 8 pct, which is considerably higher than those observed in cast Al(Mg)-Al₂O₃ composite synthesized by externally added alumina particles.     

Investigation of Microstructure,Mechanical and Wear Behaviour of B<Subscript>4</Subscript>C Particulate Reinforced Magnesium Matrix Composites by Powder Metallurgy

In the present study, magnesium and magnesium matrix composites reinforced with 10, 20 and 30 wt% B₄C particulates were fabricated by powder metallurgy using hot pressing technique. The microstructure, mechanical properties and wear behaviour of the samples were investigated. Microstructure characterization showed generally uniform distribution of B₄C particulates. XRD investigations revealed the presence of Mg, B₄C and MgO phases. The mechanical properties of the investigated samples were determined by hardness and compression tests. Hardness and compressive yield strength significantly increased with increasing B₄C content. The reciprocating wear tests was applied under loads of 5, 10 and 20 N. Wear volume losses decreased with increasing B₄C content. Abrasive and oxidative wear mechanisms were observed.     

Enhancing physical and mechanical properties of Mg using nanosized Al<Subscript>2</Subscript>O<Subscript>3</Subscript> particulates as reinforcement

A magnesium-based composite with 1.1 volume percentage of nanosized Al₂O₃ particulates reinforcement was fabricated using an innovative disintegrated melt deposition technique followed by hot extrusion. Al₂O₃ particulates with an equivalent size of 50 nm were used as reinforcement. Microstructural characterization of the materials revealed grain refinement of magnesium matrix due to incorporation, retention, and uniform distribution of reinforcement. Physical properties characterization revealed that the addition of nano-Al₂O₃ particulates as reinforcement improves the dimensional stability of pure magnesium. Mechanical properties characterization revealed that the presence of nano-Al₂O₃ particulates as reinforcement leads to a significant increase in microhardness, dynamic elastic modulus, 0.2 pct yield strength (YS), ultimate tensile strength (UTS), and ductility of pure magnesium. The results revealed that the combined tensile properties of these materials are superior when compared to Mg reinforced with much higher volume percentage of SiC. An attempt is made in the present study to correlate the effect of nano-Al₂O₃ particulates as reinforcement with the microstructural, physical, and mechanical properties of magnesium.     

Wear of Plasma Sprayed Conventional and Nanostructured Al<Subscript>2</Subscript>O<Subscript>3</Subscript> and Cr<Subscript>2</Subscript>O<Subscript>3</Subscript>, Based Coatings

An ever increasing demand for high-performance ceramic coatings has made it inevitable for developing techniques with precise control over the process parameters to enable the fabrication of coatings with the desired microstructure and improved structural properties. The literature on plasma sprayed nanostructured ceramic coatings such as of Al₂O₃, Cr₂O₃, and their composites obtained using reconstituted nano sized ceramic powders has been reviewed in this study. Ceramic coatings due to their enhanced properties are on the verge of replacing conventional ceramic coatings used for various applications like automotive systems, boiler components, power generation equipment, chemical process equipment, aircraft engines, pulp and paper processing equipment, land-based and marine engine components, turbine blades etc. In such cases, the advantage is greater longevity and reliability for realizing the improved performance of ceramic coatings. It has been observed that the plasma sprayed nanostructured ceramic coatings show improvement in resistance to wear, erosion, corrosion, and mechanical properties as compared to their conventional counterparts. This article reviews various aspects concerning the plasma sprayed ceramic coatings such as (i) the present understanding of formation of plasma-spray coatings and factors affecting them, (ii) wear performance of nanostructured Al₂O₃, Cr₂O₃ and their composite ceramic coatings in comparison to their conventional counterparts, and (iii) mechanisms of wear observed for these coatings under various conditions of testing.     

Deoxidation of Liquid Copper with Reducing O<Subscript>2</Subscript>/CH<Subscript>4</Subscript> Flames

The rate of deoxidation of molten copper during top blowing with various reducing gases has been investigated using thermogravimetry. It was observed that the rate of deoxidation increases with an increasing flow rate of H₂ or CO and that H₂ is a more effective reducing reagent than CO. The rate of deoxidation using methane was measured for O₂/CH₄ ratios from 1.5 to 2.0. As expected, the deoxidation rate decreased with an increasing O₂/CH₄ feed ratio because the flame became less reducing. For all tests, initially there is a linear decrease in mass as oxygen is removed. However, for some experiments, after some time, a sudden acceleration in the rate of mass loss occurs. Using video and X-ray imaging, it was found that this pattern corresponded to gas evolution from within the molten copper. This finding can be explained by the sudden water vapor evolution because the hydrogen dissolved in the copper reacts with the remaining oxygen, and “boiling” takes place, leading to an enhanced stirring of the copper.     

Tribological Properties of TiO<Subscript>2</Subscript> Reinforced Nickel Based MMCs Produced by Pulse Electrodeposition Technique

Nickel–TiO₂ composite coatings were prepared under pulse current conditions by co-deposition of TiO₂ particles and nickel from a Watts type bath. The effect of TiO₂ particle concentration was studied on microhardness, friction coefficient and wear resistance. The morphological features and the structures were studied by scanning electron microscope, X-ray diffraction analysis and 3D profilometry facilities. A wide particle size range (between 95 and 140 nm) was chosen to provide a high dispersion and load bearing ability for the co-deposited layers. It was determined that increasing the particle concentration in the electrolyte dramatically increased the co-deposited TiO₂ particles in the coating. The results showed that the high concentration of TiO₂ particles in the electrolyte yielded the highest amount of particles co-deposited in the plating layer. The influence of the co-deposited TiO₂ volume on microstructure and tribological properties in the coating were investigated. The wear tests were carried out using a constant load by a reciprocating ball-on disk configuration. Wear loss and friction coefficients of Ni/TiO₂ composites were decreased by increasing TiO₂ content in the electrolyte because of the increasing content of TiO₂ in the deposited layer. The change in wear mechanisms by changing TiO₂ content was also determined.     

Conversion and Distribution of Lead and Tin in NaOH-NaNO<Subscript>3</Subscript> Fusion Process

Oxidizing alkali fusion process has been studied to extract amphoteric metals. Transformation and distribution behaviors of typical amphoteric metals Pb and Sn in the NaOH-NaNO₃ fusion process are systemically studied by theoretical analysis and experimental verification done in this work. Functions of NaOH and NaNO₃ in the fusion process were also investigated. The results show the fused products, Na₂PbO₃ and Na₂SnO₃, are captured in the flux, and Na₂PbO₄ is speculated to reduce to Pb(II) in the following leaching process. By measuring solubility data of NaOH-Na₂SnO₃-PbO-H₂O system, a strategy of crystallization is proposed to separate Sn with Pb in concentrated alkaline solution, and slice Na₂Sn(OH)₆ is obtained as a product.