Ba2.5Pb1.5B12O22: Structural Transformation from Centrosymmetric to Noncentrosymmetric Space Group via Introducing Pb into Ba2B6O11

A new congruent-melting lead barium borate, Ba2.5Pb1.5B12O22 was synthesized via the high-temperature solid-state reaction under atmospheric pressure. It crystallizes in the noncentrosymmetric space group Cmc21 with a unit cell of...

The impacts of lead recycling activities to human health and environment in Dong Mai craft village, Hung Yen, Vietnam

Lead (Pb) recycling activities in Dong Mai village, Chi Dao commune, Van Lam district, Hung Yen province have been taking place for more than 30 years. The development of recycling activities contributed to the improvement of the local economics. However, along with economic development, Dong Mai craft village is facing to serious pollution. Soil, air and water polluted by lead (Pb) caused food containing Pb at higher levels than allowed limit from 20 to 40 times. The pollution had the bad effect on human health in this village. The investigation results showed that 100 % of employee who participated on melting lead and 63.5 % of local children were poisoned by Pb. Besides, the local people got diseases relating to skin, eyes, etc. This situation requires the provincial authorities to find immediate solutions to reduce the impacts of Pb recycling activities to environment and human. Hoạt động tái chế chì của thôn Đông Mai, xã Chỉ Đạo, huyện Văn Lâm, tỉnh Hưng Yên đã diễn ra hơn 30 năm nay. Sự phát triển của nghề tái chế đã làm góp phần cải thiện kinh tế của địa phương. Tuy nhiên, cùng với sự phát triển kinh tế, làng nghề Đông Mai đã và đang đối mặt với ô nhiễm môi trường nghiêm trọng. Môi trường đất, nước không khí bị ô nhiễm bởi chì (Pb) dẫn đến thực phẩm nhiễm chì ở hàm lượng cao hơn mức cho phép từ 20- 40 lần. Sự ô nhiễm gây ra những ảnh hưởng xấu tới sức khỏe của người dân làng nghề. Kết quả điều tra cho thấy 100% công nhân tham gia nấu chì và 63.5% trẻ em địa phương bị nhiễm độc chì. Bên cạnh đó, người dân địa phương còn bị mắc của các loại bệnh ngoài da, bệnh về mắt, …. Tình trạng này đòi hỏi chính quyền địa phương phải tìm ra giải pháp khẩn cấp để giảm thiểu tác động của những hoạt động tái chế chì tới môi trường và con người.

HIGH RELIABILITY HIGH MELTING LEAD-FREE MIXED BIAGX SOLDER PASTE SYSTEM

In the current work, a mixed solder powder BiAgX solder paste system with the melting temperature above 260°C and the comparable or even better reliability to the high lead solders has been studied. The mixed solder powder paste system is composed of a high melting first alloy solder powder as majority and the additive solder powder as minority. The additive solder is designed to react aggressively with various surface finish materials before or together with the melting of the majority solder to form a controllable IMC layer. The IMC layer of the mixed powder system is controllable by the species and the quantity of the additive solder and it is observed to be insensitive to thermal aging and thermal cycling in current tests while the high lead ones do show a considerable increase in IMC layer thickness. Microstructure investigation shows the fishbone shape IMC layer interlocks the bonding interface between solder and components. Both micron-sized and nano-sized Ag-rich precipitations in the joints have been observed to be well distributed in the joint. The exposed Ag-rich particles and the surrounding stepwise pattern in Bi matrix on the fracture surface indicate that these Ag-rich particles constrain the dislocation movement in Bi matrix thus enhance the strength and the ductility of the joint. Under thermal aging and thermal cycling, both the micron-sized and nano-sized Ag-rich precipitations exhibit only discernible and localized coarsening. The stable interfacial IMC together with the existence of the well dispersed Ag-rich particles are attributed to the promising reliability in BiAgX solder paste system.

Synthesis and Determination of Thermodynamical Properties of the Compounds of the system Ca-Mg-Bi

ABSTRACTBismuth is an element obtained as a sub-product in lead production; Mexico occupies the second position in the world in production of this element. Bismuth is used as iron, aluminum and copper alloying, in the pharmaceutical industry, in the cosmetics industry, etc. Bismuth is separated from lead by the Kroll-Betterton Process in which a Ca-Mg alloy is added to the melting lead to form the intermetallic compounds Ca3Bi2, Mg3Bi2 and Ca2MgBi2 which float to the surface of the bath. Unfortunately, there is little thermodynamical information of the compounds of the system Ca-Mg-Bi which can be used to study and optimize the Kroll-Betterton process in a theoretical way. In this work there were synthesized the compounds Ca3Bi2, Mg3Bi2 and CaMg2Bi2 using powders of pure elements (Ca, Mg and Bi) in the required amounts and melted under an inert atmosphere. After synthesis, the samples were characterized by X-Ray Diffraction to ensure the formation of the desire compounds. Later, calorimetric technique was used to determine the thermodynamical properties of the compounds. The results obtained by X-Ray Diffraction show the formation of Mg3Bi2 and Mg2CaBi2 species; however, there is no crystallographic information of the compound Ca3Bi2. The heating curves obtained by calorimetry show endothermic peaks, due to the presence of phases changes as is indicated in the Ca-Bi, Mg-Bi and Ca-Mg-Bi phases diagrams.

Study on Surface Quality of Lead Clad Tin Bimetal Continuous Casting by Air Pressing Core-Filling

To provide theoretical basis and practical guidance of preparing copper clad aluminum composite rods by directly continuous casting, low melting point materials of lead and tin were selected to prepare composite rods of external diameter Φ12mm and inner diameter Φ8mm through adopting air pressing core filled continuous casting processing. The orthogonal tests consisting of three factors of melting lead temperature, continuous casting speed and inflation pressure at three different levels were designed to obtain arrangements of optimal process parameters that affected surface quality of bimetal casting rods in principle. The experiments showed that composite rods have excellent surface quality under the condition of melting lead temperature,375 , continuous casting speed, 10 mm/min, and inflation pressure, 0.03MPa.