Applied Mechanics and Materials Vols. 511-512

Abstract: UV laser dicing has many advantages such as mechanical stress-free and dicing shape-free, but it is seldom used to dice multi-layer MEMS wafers because of the deposition of a lot of debris and heat affected zones around the dicing lines. In this paper, a novel UV laser dicing method for anodically bonded wafers is presented. The heat caused split of the bonded silicon and glass around the dicing line is prevented by fabricating recesses on either the glass wafer or the silicon wafer. The Finite Element Method (FEM) in the ANSYSTM software was utilized to analyze the temperature and thermal stress distributions during the dicing process. The thermal stress is minimized sharply due to the fabrication of the recesses beneath the dicing line. The thicknesses of the glass and silicon wafers are 500μm and 250μm, respectively. The anodically bonding temperature is 360oC, and the bonding voltage is 400V. Dicing experiments show that the huge thermal stress caused by the laser can split the originally bonded silicon from glass around the dicing line. After recesses are fabricated along the dicing line, no heat caused split happens. The experiment results are in a good agreement with the FEM simulation. Compared with other methods, this research can provide a more reliable, flexible and cheaper laser dicing process for thick anodically bonded silicon/glass MEMS wafers, especially for multi-layer wafers with free shape.

Abstract: Microfluidic chip is the most active field and frontier of μTAS. In comparison to other aspects of researches on microfluidic chips, the work on sample pretreatment units are in the preliminary stage. In this study, a microfluidic device for extraction was devised and fabricated. The extraction efficiency of the microfluidic device was investigated by two phase fluid 0.1% Rhodamine-B aqueous solution and Hexyl alcohol. The results demonstrated that the microfluidic chip worked well in the first two days and might be integrated in a complex chip as a potential tool for sample pretreatment.

Abstract: The uranium ore sample is dissolve with H₂SO₄, HF and H₂O₂.Uranium (VI) is reduced to uranium (IV) by titanous. The excess titanous is oxidized with sodium nitrite and excess sodium nitrite is destroyed with urea. Uranium can be determined by ammonium vanadate volumetry in the medium of 6 mol/L sulfuric acid taking o-phenanthroline ferrous sulfate as indicators. The determination limit is 0.03%, the RSD is better than 3%, the recovery is 95~105%. The error is less than 2% compared with the standard sample of uranium ore.

Abstract: LF16 aluminum alloy and Q235 steel were brazed by Zn-Al solder and the Al-Si-Cu solder. Metallographic microscope and scanning electron microscope were used to observe the microstructure of weld joint. The result shows that the strength of the joints, which were welded with Zn-Al solder reached 133.6Mpa. Zn-rich solid solution phase and Al-rich solid solution phase existed in Zn-based solder brazing seam. The Fe element trend was gradual changed, while Al element trended more gently, and generated Fe₂Al₅ intermetallic compounds in the joints in both the brazing joint of Zn-based and Al-based solder.

Abstract: A fast and effective method was developed for sequence determination of Cd and Pb in honey by incomplete digestion-high resolution continuum source graphite furnace atomic absorption spectrometry (HR-CS GFAAS). Cd and Pb in some honey samples using incomplete digestion treatment were measured by HR-CS GFAAS. The factors influencing determination were investigated by single factor experimental design. The optimal determination conditions were found as follows: NH₄H₂PO₄ (10mg/mL) were added as a chemical modifier with the volume of 5μL; pyrolysis temperature 600°C(Cd) and 800°C(Pb); atomization temperature 1100°C(Cd) and 1400°C(Pb). Detection limits (3σ, n=12) were found to be 0.06 μg/L and 0.78 μg/L for Cd and Pb, respectively. The precisions (RSD) for 6 replicate measurements of Cd and Pb in honeys were 3.8% and 2.6%, respectively. Recoveries of added Cd and Pb were varied from 95% to 103%. Therefore, the proposed method was rapid, accurate and stable with a high practical value. It provided scientific basis for multi-element sequence determination in food.

Abstract: In order to acquire axial tensile stress-strain curve of HFRC, specimens of equal cross-sections with embedded screw and pasted with carbon fiber cloth in corresponding length were tested on closed-loop electro-hydraulic servo testing machine which a subsidiary rigid frame was attached to. The effect of fiber volume, steel fiber slenderness ratio, steel fiber type and active admixture on the tensile properties of HFRC with low volume fraction was studied. The results indicate that when total volume proportion is less than 1% the first crack strength and ultimate tensile strength of HFRC can increase more than 15% and about 40% , respectively, the difference of effect of arched steel fiber and crimped steel fiber on the tensile behavior is small. The tensile behavior of HFRC is the best with a combination of slenderness ratio of 80 and 47.1kg/m³ arched steel fiber, 2.6kg/m³ macro-polypropylene fiber and1.0kg/m³ dura fiber and 10% .

Abstract: The uniaxial tensile tests are generally used to measure the yield stress and/or tensile stresses. The majority of the results, resulting from this method and deferred in the literature on the mechanical properties of amorphous materials, were obtained in the ribbons form generally produced by melt spinning. This limitation in the shape of the specimens for tensile tests was inherent in the manufacturing techniques of the amorphous materials which required cooling rates of about 10⁶ °C/s. The fabrication of amorphous coatings by plasma spraying, in tubular form, should improve rigidity of the specimens, increase their size and especially get a more reliable means to the amorphous coatings under the tensile test. Amorphous coatings of NiCrBSi alloys are produced by thermal plasma spraying. The thickness of the resulting amorphous deposit may be up to 500 μm. The uniaxial tensile tests were carried on Instron machine at room temperature. Microstructural studies are investigated by means of X-ray diffraction (XRD), scanning (SEM) and transmission (TEM) electron microscopy. The test methodology used in this study shows that it is possible to obtain a comprehensive assessment of the mechanical properties of the amorphous coatings deposited by thermal plasma in tubular form. Plasma sprayed coatings in tubular form, under the uniaxial tensile test in the amorphous state, crystallized and nanocrystallized, fracture without bursting compared to samples in the form of amorphous ribbon.

Abstract: The preparation of uranium ore gritstone standard substance have been introduced and the contents of U, Th, Ra, K₂O, SiO₂, Fe, A1₂O₃, CaO, MnO, TiO₂, Na₂O, P₂O₅, MoO₃, V ,S and C in it have been determined in this paper. The uranium ore sandstone standard substance was authorized as the first national grade standard substance.

Abstract: Taking the corrosion depth as the evaluation index, the influence law of different factors such as pH and moisture content of sludge, corrosion temperate on metal corrosion behavior was studied by single factor experiment. The corrosion product was characterized by SEM and EDX at last. The results show that the corrosion depth of A3 carbon steel increases with the increase of temperature, moisture content and acidity of sludge. The corrosion product of A3 carbon steel is mainly brown loose substance, the corrosion extent of carbon steel is deep and many elements are soaked into carbon steel. Metal corrosion results from different temperatures and different pH of sludge is non-uniform, while metal corrosion results from different moisture content of sludge is uniform.