Applied Mechanics and Materials Vols. 543-547

Abstract: In the assembly of electronic products, developing good organic acid fluxes plays an important role in improving the solderability of lead-free solders. In this paper, a variety of fluxes containing 5% (mass fraction) organic acid activators were prepared. Effects of different activators on the spreading rates of Sn-0.3Ag0.7Cu solder were studied. The results show that: activity of monobasic acids are weak except for benzoic acid; dibasic acids and polybasic acids have relatively strong activity but serious corrosion and slightly less activity persistence. Compounding palmitic acid and adipic acid in the mass ratio of 1:2 as the activator, the average spreading rate of Sn-0.3Ag0.7Cu solder is 71.11% in maximum. Compounding succinic acid and adipic acid in the mass ratio of 3:7 as the activator, the average spreading rate is up to 72.49% in maximum. And solder spots are in-erratic, bright and plump, meeting the quality requirements of electronic micro-connection.

Abstract: By means of chemical composition testing, scanning electron microscopy observation, metallographic observation and hardness gradient detection etc, analysis of the typical failure samples from a well-known brand GD8020×1100 ball screw unit in the fatigue test was carried on. Results show that there is no obvious surface wear of the ball screw, showing the normal contact fatigue failure. But severe surface wear happens on the raceway of nut A with obvious flaking and many local cracks; which is the main reason leading to the failure of ball screw unit. So effective measures to avoid earlier failure of the ball screw unit can be put forward by controlling the steel quality strictly and improving the hardness and depth of the hardened layer on the raceway of nut A.

Abstract: Copper corrosion in air containing sulfur dioxide atmosphere was described in detail, for which was one of the most primary atmospheric corrosion.In the first, effection from the synergy of pure sulfur dioxide gas and mixed gas on copper corrosion was set out, together with the introduction of certain corrosion products and formation mechanism. Besides, initial copper corrosion behaviors in variety gas concentration as well as different film thickness were summarized using electrochemical method. The research prospects were depicted in the last.

Abstract: A fire can cause serious damage to steel framed buildings so most of countries have fire regulations specifying fire resistance for structural elements. Fire resistance generally has been evaluated by a limited size testing facility. However, the size of columns and beams are different based on various conditions. Especially, the height of column and boundary condition are the main factors that govern the fire resistance of structural elements. To make a basic database for the H-section made of an ordinary grade structural steel, SM 400, an analysis was conducted by using mechanical and thermal properties with a proper theory. The fact findings suggested that the fire resistance for longer and fixed to fixed column were required a new guide line for covering of fire protective materials.

Abstract: In this study, NaCl solution was investigated the basic characteristics of phase change materials. The volumes of NaCl solution (as coolant) were studied in storage-transportation of frozen pork. The mathematical models were established between the coolant volumes and cargo capacity. A theoretical basis was provided for the srorage-transportation of fresh foods when NaCl solution was the coolant of phase change materials. The volumes of coolant were optimized in the sorage-srorage-transportation of fresh foods. The logistics costs would be reduced because of our results.

Abstract: Research on beneficiation of a barite ore was conducted according to the properties of the ore. The gravity preconcentration and flotation experiments were carried out. The results showed that direct flotation is the better way to concentrate the valuable mineral without the gravity preconcentration. The flotation results show that a barite concentrate assaying 98.21% BaSO₄ can be obtained with the recovery of 80.71%. The agent used in the flotation is water glass as depressant at 500 g/t, sodium oleate as collector at 700 g/t. In the closed circuit, one rougher, three cleanings and one scavenging operations were employed.

Abstract: Ti/Al/TiC mixed powders were used as the raw materials for the fabrication of functionally graded material (FGM) in situ synthesis by spark plasma sintering. The sample was analyzed by SEM combined with Metallographic microscope and Energy Disperse Spectroscopy. The results show that dense Ti₂AlC/TiC functionally graded material (FGM) was produced by spark plasma sintering. Micro-hardness tester is used to character the distribution of hardness on the material .The results show that the Vickers hardness of every layer increases with TiC content and temperature increasing.

Abstract: Functional floating bead (F-FB), prepared by anchoring the organic sulfonic acid on the surface of the blackberry-like structural FB, was used as both the inorganic substrate and the in situ dopant for the in situ chemical oxidative polymerization of pyrrole to obtain the polypyrrole/functional floating bead (PPy/F-FB) composites. The encapsulating morphologies were revealed with the scanning electron microscopy technique. The PPy/F-FB composites were characterized with Fourier transform infrared spectroscopy and thermogravimetric analysis. Based on the cyclic voltammetry of the composites, it was found that the composites performed typical electrochemical supercapacitor behavior.

Abstract: In this work, carbon nanotube/polycarbonate (CNT/PC) nanocomposites containing 1wt% CNT were prepared by a two-step method of twin-screw extruder mixing followed by injection molding at different temperatures. The microstructure, which has strong impact on the electrical properties of the composite, was affected by the injection molding conditions. This work is focused on the effect of injection molding temperature on the volume resistivity of CNT/PC nanocomposites. The microstructure of the composites was investigated by scanning electron microscopy (SEM). It was found that the volume resistivity of CNT/PC nanocomposites was decreased from 10¹³ to 10⁵ Ω·cm with the increasing injection molding temperature.

Abstract: This paper studied the recovering of Fe and TiO2 minerals from a refractory ore in Yunnan province. The grade of Fe in raw ore is 27.25% and the grade of TiO2 in raw ore is 5.79%. Through technological mineralogy study, we found that the Fe was mainly in the forms of Hematite and limonite, and the Ti was mainly in the forms of ilmenite and anatase. Through the process of strong magnetic separation and shaking table separation, the minerals of Fe and Ti were recovered. Finally, we got two products. They were Fe concentrate with the grade of 44.30%, recovery of 62.65%, and Ti concentrate with the grade of 43.60%, recovery of 32.55%.