Microstructural Evolution and Wear Behavior of SiCp/7085 Composites Manufactured by Ultrasonic Stirring Casting

In this work, SiCp/7085 composites with a volume fraction of 10% were fabricated by ultrasonic stirring casting. The evolution of the microstructure and wear properties of SiCp/7085 composites, as well as the mechanism of ultrasonic action in the process of preparation, when the ultrasonic treatments last for 0 min, 5 min, 10 min, and 15 min, respectively, were studied using the optical effects (OM), scanning electron microscope (SEM), and X-ray diffraction (XRD). The experimental results show that the high temperature and high pressure formed by the cavitation of ultrasound can effectively eliminate the cluster of particles, improve the distribution of SiC particles, increase the interfacial wettability of the composites, and form MgAl2O4 and MgO on the particle surface, thereby ultimately improving the wear resistance of the composites. Because the particles in the melt are affected by the segregation effect of ultrasonic standing wave field, there exists an optimal value for the ultrasonic treatment time. When the melt is treated with the ultrasonic wave with an amplitude of 12 μm and a treatment duration of 10 min in the test conditions given in this paper, the composites have the most uniform distribution of particles, the best wear resistance, a large and stable friction coefficient, and the minimum weight loss of sample wear: 12 mg. The change of wear resistance is consistent with the variation of solidification structure and interface properties.

Effect of Hybrid Ultrasonic and Mechanical Stirring on the Distribution of m-SiCp in A356 Alloy

The present study details the micro-scale silicon carbide particle (m-SiCp) homogeneous distribution in an A356 alloy through hybrid ultrasonic-stirring melt treatment under different operation conditions. Ultrasonically excited fluids were studied by particle image velocimetry to estimate the efficiency of the acoustic streaming in different distances to the sonotrode. Distinct particle approaches to introduce the melt and stirring techniques were performed to determine a successful route to promote a homogenous distribution of reinforcement particles. Results showed that the addition of m-SiCp in the semisolid state significantly improved particle wettability, preventing rapid sedimentation. The combination of ultrasonic induced streaming and mechanical stirring is an effective tool for the homogeneous distribution of m-SiCp along the casting specimen.

Biogenic Nanoparticles of Calcium Carbonate - Preparation and Behaviour

Calcium carbonate is one of the most widespread natural material. Biogenic calcium carbonate nanoparticles are biocompatible. Currently, they are of great interest for their possible applications, especially in medicine. The aim of this introductory experimental study is to present a simple preparation of biogenic nanoparticles of calcium carbonate from natural resources with a subsequent specific behaviour of nanoparticles in aquatic environment. Different type of shells were used for the preparation of nanoparticles. All structures were burned at 850°C and then grounded to powder. The obtained powders were left in normal laboratory environment for 2 weeks and then placed in beakers with distilled water. Subsequently, two homogenization routes were used - stirring at 1000 rpm for 5 minutes and ultrasonic stirring for 5 minutes. One part of the particles was separated at the bottom of the beaker, but small formations started to create a fractal structure on the surface of water. These formations gradually increased. Crystalline interconnected structures built up with nanoparticles were confirmed by a subsequent analysis by a scanning electron microscope. EDX analysis confirmed the presence of calcium carbonate.

Study on Mechanical Properties and Fire Resistance of Epoxy Nanocomposite Reinforced with Environmentally Friendly Additive: Nanoclay I.30E

The main purpose of this study is to complete the research process of dispersing nanoclay I.30E (montmorillonite) into epoxy Epikote 240 by mechanical method combined with energy-saving ultrasonic method. We investigate appropriate dispersion conditions such as stirring speed, mechanical stirring temperature, ultrasonic stirring time, and ultrasonic stirring capacity, which affect the mechanical properties and fire resistance of nanocomposite materials. The nanoclay contents studied were 1, 2, 3, and 4% by weight, and the methods used in this study are FE-SEM; XRD; and flame-retardant evaluation methods: LOI, UL 94HB. The mechanical properties were studied: tensile strength, flexural strength, compression strength, and impact resistance Izod. The dispersion method was recommended to stir mechanically at a speed of 3000 rpm at 80°C for 8 hours and then conduct ultrasonic vibrations for 6 hours at 65°C. The results showed that epoxy Epikote 240/nanoclay I.30E nanocomposite material had mechanical properties and improved fire retardancy with a small amount of nanoclay I.30E added (2% by weight): tensile strength of 63.5 MPa (increased by 13.59%), flexural strength of 116.80 MPa (increased by 34.63%), compressive strength of 179.67 MPa (increased by 15.11%), impact resistance Izod of 12.81 KJ/m2 (increased by 80.16%), oxygen limit of 23.7%, and combustion rate of 24.5 mm/min; according to UL 94HB, the combustion rate reached 22.59 mm/min.

Preparation of Ag/SnO2 Contact Material by Chemical Deposition

In order to improve the dispersion of SnO2 in Ag matrix, Ag/SnO2 contact materials wasprepared by optimized chemical deposition process. The micro-morphology and phase of theAg/SnO2 contact materials were tested by metallographic microscope and XRD. The results showedthat the combination of mechanical stirring and ultrasonic stirring can effectively improve thedispersion of SnO2 in Ag matrix, the Vickers hardness, conductivity and density of the Ag/SnO2contact materials with 88% Ag content are 114.4HV, 77.4% IACS and 9.75g/cm3 respectively. Theseprovide data reference for preparation of Ag/SnO2 contact materials with uniform SnO2 distributionin Ag matrix.

SYNTHESIS, CHARACTERIZATION AND ELECTROCHEMICAL PERFORMANCE OF ACTIVATED CARBON SUPPORTED MnO2 FOR ELECTROCHEMICAL CAPACITOR

MnO2 was synthesized by adding activated carbon into KMnO4 solution and stirred in a magnetic or ultrasonic stirrer. The obtained MnAC samples were characterized by means of XRD, TGA, TPR-H2, SEM and BET. All samples are amorphous and have porous structure. MnAC-M prepared by magnetic stirring have higher manganese content, earlier reduction temperature, smoother surface area while MnAC-U prepared by ultrasonic stirring have larger specific surface area and pore volume.