On the advantages of using a hypoeutectic Sn-Zn as lead-free solder material

Hypoeutectic Sn-Zn may be a better choice than the eutectic Sn-9Zn as a lead-free solder. We checked the non-equilibrium melting behaviors of a series of Sn-Zn alloys (2.5-9 wt.% Zn) by differential thermal analysis, and found that at a heating rate of 5 °C/min, Sn-6.5Zn behaves the same way as the eutectic Sn-9Zn in melting. Dipping and spreading tests were carried out to characterize the wettability of Sn-Zn alloys on Cu. Both tests indicated that Sn-6.5Zn has significantly better wettability to Cu than Sn-9Zn does. The reaction layers formed during the spreading tests were examined. For all samples with 2.5-9 wt.% Zn, two reaction layers are formed at the interface, a thick and flat Cu₅Zn₈ layer adjacent to Cu and a thin and irregular Cu-Zn-Sn layer adjacent to the alloy. The total thickness of the reaction layers between the alloy and Cu was found to remarkably decrease with decrease of the Zn concentration.     

Self-assembled monolayers of alkanethiols on gold: the adsorption and wetting properties of monolayers derived from two components with alkane chains of different lengths

This paper describes the preparation and wetting properties of two-component self-assembled monolayers (SAMs) obtained by the competitive adsorption of one short-chain (HS(CH₂)₁₀Sh) and one long-chain (HS(CH₂)₂₁Lg) alkanethiol onto gold from dilute ethanolic solutions. The four possible combinations of the tail groups CH₃ and CH₂OH were investigated: Sh = CH₃/Lg = CH₂OH, Sh = CH₂OH/Lg = CH₃, Sh = CH₂OH/Lg = CH₂OH, and Sh = CH₃/Lg = CH,. The compositions of these SAMs are not the same as the compositions of the solutions from which they were formed. Although the relationship between the composition of the SAM and the composition of the solution suggests that some phase separation may be occurring within the SAM, contact angles with water and hexadecane show that significant disorder still remains in the interfacial region.     

On Measurement of Food Powder Reconstitution Properties

Dissolution of powdered ingredients is of particular importance to manufacturers and consumers as a benchmark of consumption quality. Standard methods gauging the reconstitution properties of milk powders in the dairy industry are available, although they are relatively crude with poor reproducibility. Since most procedures were developed based on “traditional” dairy powders, they may fail to recognize the important characteristics of specialty products. A critical review is presented that identifies the properties of interests and methods for analysis. It is argued that more reliable techniques tailored for different food products can be developed to predict their behaviors for specific end usage.     

Factors affecting instant properties of powdered cocoa beverages

The increasing number of small and medium scale manufacturers of powder cocoa beverages (PCBs) in Nigeria requires relevant technical data useful in designing new and value added products from cocoa powder. This paper reports a preliminary study carried out to determine how some physical and chemical factors relate to the instant properties of some commercial samples of PCBs produced in Nigeria. The levels of chemical component like moisture, fat and sugar in the PCBs varied from 0.8% to 3.6%, 2.0% to 10.4% and 52.4% to 90.5%, respectively. Physical properties like the bulk density, angle of repose, average particle size and uniformity index of the products varied from 0.49 to 0.81 g/cm³, 25.0° to 37.7°, 0.031 to 0.796 mm and 6.25 to 7.44, respectively. Instant properties such as wettability, dispersibility and solubility ranged from 10.7 to 21.7 s, 50.0% to 94.5% and 44.2% to 76.6%, respectively. These properties differed significantly (p < 0.05) among the 10 commercial samples of PCB studied. Sugar (sucrose) content of products had the most significant (p < 0.05) main effect on their instant properties followed by the fat content. Wetting time showed a significant (p < 0.05) negative linear correlation with sugar content. Agglomeration increased the average particle size, which correlated negatively with uniformity index. The instant properties of fine PCBs (average particle size <0.294 mm) were more predictable than the agglomerated samples.     

激光织构化不同材料表面对润湿性能的影响

采用激光微织构加工技术分别在SAF2507双相不锈钢和碳纤维增强聚醚醚酮(CF/PEEK)表面制备不同形状、面积占有率的微织构凹坑，通过润湿性试验分析时间、液滴体积、微织构形状与面积占有率、液滴种类对润湿性的影响。结果表明：液滴润湿材料表面过程中，固液接触角先随时间迅速减小，后保持在一个较为稳定的值；使用体积较大的液滴测量接触角时，液滴铺展的速度减缓，接触角的测量值变小；CF/PEEK表面的接触角随微织构面积占有率的增大而减小，SAF2507表面的接触角随微织构面积占有率的增大而增大；微织构面积占有率相同的表面，方柱形微织构表面的接触角小于圆柱形微织构表面，润湿效果更好；天然海水在光滑和织构表面的接触角均小于蒸馏水。     

Determination of interfacial properties between AlN and aluminum beneath salt at high temperature

Aluminum nitride is of interest as a material for electrolysis cells in the aluminum industry due to its chemical stability when in contact with molten aluminum and/or cryolite-based salt melts. It has also been considered in combination with electrically conductive materials (i.e. AlN/Al-composite) as a material for drained cathode systems in Hall-Heroult processes. Knowledge of the interfacial properties of AlN in contact with molten aluminum and/or cryolite-based melts is therefore important. This paper reports observations of the wettability of AlN by aluminum under salt cover at high temperature using an X-ray technique. Results obtained in this work combined with previously published data are used for the assessment of the work of adhesion of molten aluminum on AlN under vacuum as well as under a cryolitic salt. Scanning electron microscopy examination of metallographic sections was used to confirm the nature of the interfaces. The measured contact angle between AlN and molten aluminum beneath a salt cover at 850 °C is 136° demonstrating the non-wettability of AlN by liquid aluminum under these conditions. The work of adhesion of molten aluminum on AlN is higher under vacuum than under salt. Previously published data allowed the determination of the interfacial properties between liquid aluminum and AlN under a salt cover. The interfacial energy between molten aluminum and salt is 773 mN/m at 850 °C. The work of adhesion of aluminum on AlN is 217 and 1322 mN/m under salt and under vacuum, respectively.     

Control of the Surface Properties in Polymer Blends

We report on the preparation of amphiphilic diblock copolymers containing a hydrophilic segment, poly(acrylic acid)(PAA), and a polystyrene hydrophobic part. We analysed, by means of contact-angle measurements, how the hydrophilic segments usually bury themselves under the hydrophobic when exposed to air to reduce the surface free energy of the system. In contrast, in contact with water, the hydrophilic blocks have a tendency to segregate to the interface. We first describe the parameters that control the surface reconstruction when the environmental conditions are inversed from dry air to water vapour. Then, annealing time, temperature, composition and size of the diblock copolymers, and size of the matrix that influenced the surface migration process are the main parameters also considered. Finally, the density of the carboxylic functions placed at the surface was determined using the methylene blue method.     

Model Development for MEOR Process in Conventional Non‐Fractured Reservoirs and Investigation of Physico‐Chemical Parameter Effects

A three‐dimensional multi‐component transport model in a two‐phase oil‐water system was developed. The model includes separated terms to account for the dispersion, convection, injection, growth and death of microbes, and accumulation. For the first time, effects of both wettability alteration of reservoir rock from oil wet to water wet and reduction in interfacial tension (IFT) simultaneously on relative permeability and capillary pressure curves were included in a MEOR simulation model. Transport equations were considered for the bacteria, nutrients, and metabolite (bio‐surfactant) in the matrix, reduced interfacial tension on phase trapping, surfactant and polymer adsorption, and effect of polymer viscosity on mobility of the aqueous phase. The model was used to simulate effects of physico‐chemical parameters, namely flooding time schedules, washing water flowrate, substrate concentration, permeability, polymer and salinity concentration on Original Oil In Place (OOIP) in a hypothetical reservoir.     

Review: Polymers,Surface-Modified Polymers,and Self Assembled Monolayers as Surface-Modifying Agents for Biomaterials

Biocompatibility and nontoxicity of biomaterials are of utmost importance when foreign bodies come in contact with a biological system. Irrespective of the nature of material, nonspecific protein adsorption is the first process observed at surface–biological system interfaces followed by cellular processes. Nonspecific protein adsorption leads to deleterious cellular processes such as biofouling and finally immunological host response. Hence, surface modification becomes mandatory for preventing undesirable implant failure and inflammatory responses. Various polymers, surface-modified polymers and surfaces withself assembled monolayers, have been tested to tune surface properties for a given application. Surface functional groups and surface structures of polymers and copolymers regulate surface hydrophobicity, nonspecific protein adsorption, biomaterial stability, and antifouling property, etc. Self assembled monolayers are formed by covalent linkage with more controlled surface structure and smoothness. Mixed and hybrid self assembled monolayers containing both hydrophilic and hydrophobic groups result in moderate wettability. Further, we have discussed different methods of surface modification using polymers, modified polymers, and self assembled monolayers for improved surface biocompatibility and nonfouling properties.     

氮气保护对无铅焊接工艺温度窗口的影响

无铅化电子组装中无铅焊料的高熔点、低润湿性给实际生产带来了很大挑战。为了改善润湿性,可适当提高焊接温度,但由于PCB及元件的工艺温度限制,导致了焊接工艺温度窗口变窄。氮气保护可以改善无铅焊料润湿性、防止氧化、提高焊接品质,更重要的是可以降低焊接峰值温度,扩大焊接工艺温度窗口。