Papers by Keyword: Current Density

Abstract: The ceramic coating containing anatase TiO₂ and rutile TiO₂ is fabricated on the surface of pure titanium in the electrolyte of C₄H₆CaO₄-NaH₂PO₄ by micro-arc oxidation (MAO) method. The effect of different current density to microscopic structure, elemental composition and phase components of Ceramic Coating are studied with scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), X-ray diffraction (XRD), 3D profilometer and etc. Results indicate that the ceramic coating on pure titanium by micro-arc oxidation is a porous mixed crystal structure which is mainly composed of such elements as Ti, O, Ca and P. With current density increasing, the average pore diameter and roughness on film surface first increase and then decrease, the porosity increases, the ratio of Ca/P then decreases, the relative content of anatase TiO₂ increases and that of rutile TiO₂ decreases.

Abstract: Surfacing in gas-shielded as well as by the open arc burning between consumable electrodes, is usually made in reverse polarity. It is connected with the stable burning of arc and the minimum spatter of electrode metal. In this case, the cathode spot of the welding arc is on the plate, and the anode spot is on the wire end. These conditions of the arc spots existence affect the processes proceeding in the cathode and anode areas of the arc. The article considers the influence of the arc active spots formation conditions and its modes on the cathode and anode voltage breakdowns.

Abstract: Bioinert titanium (Ti) can be modified to bioactive by performing various techniques including anodic oxidation. Where, this method encompasses electrode reactions in combination with electric field driven metal and oxygen ion diffusion to the formation of an oxide film on anode surface. The objective of this study is to evaluate the effect of current density of anodic oxidation upon the characteristic of titanium in sulphuric acid (H₂SO₄) under various conditions. The modified titanium was prepared using anodic oxidation method in 0.3 M of sulphuric acid as electrolyte. The applied voltage and current density of the anodic oxidation parameters were varied from 50 – 200 V and 25 – 75 mA.cm^-2 respectively for 10 min of oxidation process at room temperature. The effects of anodic oxidation on the titanium were characterised using X-ray diffractometer (XRD), field emission scanning electron microscopy (FESEM) and atomic force microscopy (AFM). The results show that by increasing the current density of the anodic oxidation, different mineralogy, surface morphology, and surface profile were produced. At low current density (25 mA.cm^-2), high voltage is needed to produce high crystalline of anatase formed on the titanium surface and only able to produced very low of rutile titanium with 200 V of applied voltage compared to high current density (75 mA.cm^-2) with same applied voltage, very high rutile crystal with mixture of low anatase was observed on the titanium. This modified oxide of titanium has potentially to be applied in biomedical as implant.

Abstract: According to the electromagnetic pump in Magnesium Alloy Casting Experiments Center of University of Science and Technology Liaoning, with the help of ANSYS software, we realized three-dimensional simulation of electric field of the pump by finite element analysis method, and calculated the distribution of electric field generated by five data sets , whose slot length and width were 30mm, 50 mm, 60 mm, 70 mm and 80 mm. We have explored how different runner dimensions affected electric field distribution in electromagnetic field, and simulated the distribution of current density. The optimal size of the runner is 50mm according to the current density distribution.

Abstract: This paper reports on the properties of YBa₂Cu₃O_d (Y123) and YCaBa₄Cu₆Oy (Y146) with non-porous and porous structures. The relationship between calcium doping and critical temperature (T_c) was studied to determine the optimal superconducting properties. A series of heating and grinding via solid state reaction method was used to fabricate the ceramic materials. The electrical properties were investigated via critical temperature, T_C and critical current density, J_C using the resistivity measurement system (RMS). Scanning Electron Microscope (SEM) and X-Ray Diffraction (XRD) were used to analyze the material morphology and structure, respectively. The orthorhombicity increased due to less porosity of the samples. The calcium presence partially replaced larger Ba(II) site and degraded orthorhombicity. The highest critical current density (J_C) was porous YCaBa₂Cu₃Oy which was 2.32 A/cm² compared to 0.75 A/cm² for porous YCaBa₄Cu₆Oy at 60 K. The critical temperature for porous structure was less than non porous structure for Ca doped Y146 system which was 69.9 K and 67.9 K. SEM micrograph unveiled that the Jc was induced significantly by continuity of grain formation via grain size. Pores homogenized the grains surface quality and connectivity due to strain release thus increasing effective cross section of the sample for current density (Jc) over the vast areas.

Abstract: Electro-migration has become a critical reliability issue for high density solder joints in flip chip technology, especially for current crowding and joule heat. Electro-migration force and mean time to failure of flip chip are introduced in this paper. This study employs two-dimensional simulation to investigate the distribution of current density and Joule heating in the flip chip joint. It is found that current crowding and Joule heat effect are very serious in the solder bump. The Joule heat may play important role in the void formation and thermo-migration in solder bump. And the factors that impact the distribution of current density and Joule heat are studied. The results show that the thickness of Al and UBM has great influence on the distribution of current density and Joule heat.

Abstract: Electrochemical chloride extraction – ECE is an effective method to rehabilitate reinforced concrete structure, which has been corroded. This study investigated concentration of chloride remained in concrete and half-cell potential of the steel reinforcement after ECE using interrupting period of electricity current. Efficiency of ECE using Ca (OH)₂ was surveyed with two current density of 0.5 and 1A/m². In this study, ECE treatment was proceeded intermittently in approximately 8 weeks. Results pointed out that chloride concentration decreased to 30 – 60% significantly, especially at in the vicinity of reinforcing steel. Simultaneously, half-cell potential of the steel reinforcement after 4 weeks halted treatment stabilizes in low-corrosion rate.

Abstract: The Ni-Mo alloy coatings with a high content of Mo up to 44.5 at.%, were prepared by galvanostatic electrodeposition in the range of deposition current density, j_dep, from-30 to-240 mA cm^-2 from the nickel plating bath containing potassium pyrophosphate, nickel chloride, sodium molybdate, and sodium bicarbonate. Investigations of hydrogen evolution reaction (HER) were carried out in 5 M KOH solution at room temperature using steady-state polarization and electrochemical impedancy spectroscopy (EIS) measurements. It was found that for the Ni-Mo alloy coatings, the increase in their catalytic properties towards the HER with the increase in the value of j_dep of the coatings, was due to the intrinsic activity.

Abstract: Microarc oxidation (MAO) coatings on ZL108 aluminum alloy were prepared in the silicate-Na₂MoO₄ electrolytes with different current density. The MAO process was studied by measuring the voltage as a function of time. The microstructure, compositions, distribution of element and corrosion resistance of the MAO coatings were investigated by SEM, XRD, EDS, XPS and polarization curve, respectively. With the increasing of current density, the final voltage in the microarc discharge process increased. The results shown that the MAO coatings were mainly composed of mullite, γ-Al₂O₃, Si, little MoO₂ and MoO₃. The micropore size, thickness, compositions, distribution of element of the MAO coatings depended on the current density and the amount of MoO₂ and MoO₃. The corrosion resistance improved as the porosity of the MAO coatings decreasing.

Abstract: Nowadays, more and more scientific studies deal with the formation of electroplating alloy coatings due to the possibility of combination and share content type metal – forming alloy. To produce coatings that fulfil pre-defined specific requirements is possible by a suitable combination of process conditions. The paper deals with the study of tribological properties of Ni-Co coatings that were prepared by electrodeposition technique from sulphate electrolyte on the copper substrate. Effect of current density on the properties of electroplated coatings was determined via a morphology characteristics and micro-hardness of coating′surface. The tribological behaviour of Ni – Co coatings was described by friction coefficient using the pin-on-disc method.