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Nitrogen (N) pollution of water courses is a major concern in most coastal watersheds in eastern China with intensive agricultural production. We use hydrogeological and dual-isotopic approaches to analyze the N concentrations, pollution, transformations, and sources of surface water and groundwater in an agricultural watershed of the Jiaozhou Bay (JZB) area. Results showed that dissolved total N (DTN) concentrations in sub-rivers (SRs) ranged from 6.0 to 25.3 mg N L−1 in the dry season and 9.1–26.7 mg N L−1 in the wet season, which indicated a positive relationship with the percentages of agricultural land. Meanwhile, the dominant dissolved N species in SRs changed from nitrate (NO3−, 64–100%) to dissolved organic N (DON, 52–77%) from the dry season to the wet season and the increased DON concentrations showed a positive relationship with the planted proportions of vegetable production systems. The NO3− concentrations of groundwaters ranged from 10.6 to 121.4 mg N L−1, which were over the limit for drinking water by the World Health Organization. Isotopic analysis indicated that most NO3− originated from the microbiological conversion via nitrification, whereas the deletion of denitrification was insignificant in this area. The results of the stable isotope analysis in R mixing model showed the contributions of potential NO3− sources which were in order of manure fertilizers (20.6–69.0%) > soil organic matter (19.5–53.2%) > chemical fertilizers (5.5–34.3%) > atmospheric deposition (1.3–18.8%). This study suggests that the management of crop productions and reasonable manure fertilizer application should be implemented to protect the quality of aquatic systems in the JZB area. [ABSTRACT FROM AUTHOR]

Sn-Bi solder was proposed as one of the most promising substitutes for lead solder due to its lower melting temperature, good wettability, good yield strength and cost efficiency. With Ag elements added, the mechanical properties of Sn-Bi solder were improved obviously. There are two ways that are commonly used to add the reinforced particles into the solder. The first way (Way I) is to blend the reinforced particles with solder powders together, and then followed by pressure forming, sintering, cooling, crystallization and serious machining methods under inert atmosphere to make the solder paste. Another way (Way II) is to directly add the reinforced nano or micro particles into the solder paste by sufficient mechanical-stirring. In this research we would like to get fully understanding on the effects of these two ways of Ag addition on the mechanical properties of Sn-Bi-Ag solder joints during aging. Sn57.6Bi0.4Ag solder stands for the Way I and the doped Sn58Bi + 0.4Ag solder stands for the Way II. These two kinds of joints were compared via micromorphology observation, thermal failure analyses as well as balls shear strength measurement after different aging time (under 100 °C, from 0 to 800 h). The mechanical properties of Sn57.6Bi0.4Ag and the doped Sn58Bi + 0.4Ag solder joints during aging were shown to be associated with the changes of micromorphology, the dissolution of IMCs, as well as the flatness of the joints' interface. Before long-time aging, the doped Sn58Bi + 0.4Ag solder joints showed better mechanical performance than Sn57.6Bi0.4Ag solder joints. During aging, Sn56.7Bi0.4Ag solder joints had better performance in preventing the dissolution of Ni-Sn IMCs into the solder side, having smoother interfaces, comparing with Sn58Bi + 0.4Ag solder joints. The degenerated phenomenon of Ag nanoparticle reinforcement seriously happened in the doped Sn58Bi + 0.4Ag solder joints. After longtime aging, Sn57.6Bi0.4Ag solder joints had better mechanical properties than the doped Sn58Bi + 0.4Ag solder joints. [ABSTRACT FROM AUTHOR]

Sn-Ag-Cu composite solder has been prepared by adding Ni nanoparticles. Interfacial reactions, the morphology of the intermetallic compounds (IMC) that were formed, the hardness between the solder joints and the plain Cu/immersion Ag-plated Cu pads depending on the number of the reflow cycles and the aging time have all been investigated. A scallop-shaped CuSn IMC layer that adhered to the substrate surface was formed at the interfaces of the plain Sn-Ag-Cu solder joints during the early reflow cycles. A very thin CuSn IMC layer was found between the CuSn IMC layer and the substrates after a lengthy reflow cycle and solid-state aging process. However, after adding Ni nanoparticles, a scallop-shaped (Cu, Ni)-Sn IMC layer was clearly observed at both of the substrate surfaces, without any CuSn IMC layer formation. Needle-shaped AgSn and sphere-shaped CuSn IMC particles were clearly observed in the β-Sn matrix in the solder-ball region of the plain Sn-Ag-Cu solder joints. Additional fine (Cu, Ni)-Sn IMC particles were found to be homogeneously distributed in the β-Sn matrix of the solder joints containing the Ni nanoparticles. The Sn-Ag-Cu-0.5Ni composite solder joints consistently displayed higher hardness values than the plain Sn-Ag-Cu solder joints for any specific number of reflow cycles-on both substrates-due to their well-controlled, fine network-type microstructures and the homogeneous distribution of fine (Cu, Ni)-Sn IMC particles, which acted as second-phase strengthening mechanisms. The hardness values of Sn-Ag-Cu and Sn-Ag-Cu-0.5Ni on the Cu substrates after one reflow cycle were about 15.1 and 16.6 Hv, respectively-and about 12.2 and 14.4 Hv after sixteen reflow cycles, respectively. However, the hardness values of the plain Sn-Ag-Cu solder joint and solder joint containing 0.5 wt% Ni nanoparticles after one reflow cycle on the immersion Ag plated Cu substrates were about 17.7 and 18.7 Hv, respectively, and about 13.2 and 15.3 Hv after sixteen reflow cycles, respectively. [ABSTRACT FROM AUTHOR]

In order to identify the effect on the properties and behavior of tin-zinc-bismuth (Sn-8 wt% Zn-3 wt% Bi or Sn-13.6 at.% Zn-1.6 at.% Bi) based solders produced by adding nickel (Ni) nano-particles, the interfacial microstructure between plain and composite solders with newly developed immersion silver (Ag) plated copper (Cu) substrates has been investigated as a function of reaction time, at various temperatures. For plain Sn-8Zn-3Bi solder joints, a scallop-shaped Cu-Zn-Ag intermetallic compound layer was found to adhere to the surface of the immersion Ag-plated Cu substrate. However, after addition of Ni nano-particles into the Sn-8Zn-3Bi solder, Cu-Zn-Ag (at the bottom) and (Cu, Ni)-Zn (at the top) intermetallic compound layers were observed at the interfaces. In addition, these intermetallic compound layer thicknesses increased substantially with increases in the temperature and reaction time. In the solder ball region, needle-shaped α-Zn rich phase and spherically-shaped Bi-particles appeared to be homogeneously distributed throughout a beta-tin (β-Sn) matrix. However, after the addition of Ni nano-particles, needle-shaped α-Zn rich phase appeared that exhibited a fine microstructure, due to the heterogeneous nucleation of the Ni nano-particles. The calculated activation energy for the Cu-Zn-Ag intermetallic compound layer for the plain Sn-8Zn-3Bi solder/immersion Ag-plated Cu system was 29.95 kJ/mol-while the activation energy for the total [Cu-Zn-Ag + (Cu, Ni)-Zn] intermetallic compound layers formed in the Sn-8Zn-3Bi-0.5Ni (Sn-13.6 at.% Zn-1.6 at.% Bi ~1 at.% Ni) composite solder/immersion Ag-plated Cu system was 27.95 kJ/mol. Addition of Ni nano-particles reduces the activation energy which enhanced the reaction rate as we know that lower the activation energy indicates faster the reaction rate. [ABSTRACT FROM AUTHOR]

In this research, the interactions of SnInAg solder on Kovar leadframes (Fe29Ni17Co) with Au/Ni UMB was studied, to reveal the whiskers growth mechanism. Samples were prepared by reflow process and aging, with SnInAg solder paste on the substrate. Scanning electron microscope was used to observe the morphology and the cross-sectioned structure of the whiskers. Focused ion-beam was used for the preparation of the transmission electron microscope (TEM) samples, and energy dispersive X-ray and TEM were then used to distinguish the different intermetallic compound (IMC) phases. It was found that, a special solder thickness range would be needed for the growth of whiskers. The root cause of this strip whiskers growth region was studied. It is worthy to mention that, the Sn-Cu reactions, which was reported by many former researches, was not the main source of the compressive stress here. It was found that the Au-Sn reactions, the IMCs transformation during the aging process, and the oxidation layer growth were dominating the whiskers growth. Effects of cracks on the whiskers growth were carefully observed and discussed, and it was found that cracks under a certain width could exempt the breaking of the oxidation layer at the solder surface, thus help the whiskers growth. On the other hand, wide cracks might accommodate the deformation of the solder layer and prohibit the whiskers from being erupted out. [ABSTRACT FROM AUTHOR]