Chao-Sung Lin

Formation of Cerium Conversion Coatings on AZ31 Magnesium Alloys

Cerium conversion coatings, which have been used as protective coatings for aluminum alloys, are now being considered as an alternative to chromium conversion coatings for improving the corrosion resistance of magnesium alloys. This study investigated the evolution of conversion coatings on an AZ31 magnesium plate immersed in 0.05 M cerium nitrate solution. In addition to the expected growth of the conversion coating with immersion time, it was found that there may be an inherent adhesive weakness within the coating layers, which then led to partial detachment of the coatings from the magnesium plate while drying the samples at room temperature. Cross-sectional transmission electron microscopy characterization of conversion coatings revealed a three-layered structure comprising of porous, compact, and fibrous layers sequentially formed on top of the magnesium plate. Furthermore, the weakest bonding was identified as the interface between the compact and the fibrous layers. Based on the identified layer morphology and the respective composition, a possible formation mechanism for cerium conversion coating on magnesium alloy was proposed, which would serve as a basis for improving the adhesive strength of the coating on magnesium substrate.

Formation of Phosphate/Permanganate Conversion Coating on AZ31 Magnesium Alloy

The properties of conversion coating on magnesium can be closely related to its microstructure and composition. This study investigated the evolution and microstructure of phosphate/permanganate conversion coating on AZ31 magnesium alloy. Results show that increasing the solution temperature reduced the growth rate of the coating. The temperature effect lies in the different structure associated with the coating layer contacting the substrate: a porous layer mainly composed of magnesium, aluminum hydroxides/phosphate formed in the solution at 40°C, while a compact magnesium oxide layer formed in the solution at 80°C. The formation mechanism of phosphate/permanganate coating was discussed in detail, with emphasis on the effect of the solution temperature.

Codeposition and Microstructure of Nickel—SiC Composite Coating Electrodeposited from Sulphamate Bath

Ni–SiC composite coatings were electroplated from a nickel sulphamate solution with a SiC suspension, with and without the addition of monovalent thallium ions. Without thallium ions, the incorporated SiC particles did not modify the columnar grain structure of the nickel matrix. Conversely, the nickel matrix exhibited an equiaxed grain structure; meanwhile, the amount of codeposited SiC was markedly increased by adding thallium ions to the solution. Additionally, the density of lattice defects associated with nickel grains substantially decreased when the columnar grains were replaced by equiaxed grains. These distinct grain structures associated with the various coatings were discussed in terms of the inhibition of nickel electrocrystallization by thallium ions as well as the absorption and reduction of the various ionic species absorbed on the surface of the SiC particles.

Superiority of Branched Side Chains in Spontaneous Nanowire Formation: Exemplified by Poly(3-2-methylbutylthiophene) for High-Performance Solar Cells

One-dimensional nanostructures containing heterojunctions by conjugated polymers, such as nanowires, are expected to greatly facilitate efficient charge transfer in bulk-heterojunction (BHJ) solar cells. Thus, a combined theoretical and experimental approach is pursued to explore spontaneous nanowire formation. A dissipative particle dynamics simulation is first performed to study the morphologies formed by rodlike polymers with various side-chain structures. The results surprisingly predict that conjugated polymers with branched side chains are well suited to form thermodynamically stable nanowires. Proof of this concept is provided via the design and synthesis of a branched polymer of regioregular poly(3-2-methylbutylthiophene) (P3MBT), which successfully demonstrates highly dense nanowire formation free from any stringent conditions and stratagies. In BHJ solar cells fabricated using a blend of P3MBT and [6,6]-phenyl-C71-butyric acid methyl ester (PC(71) BM), P3MBT polymers are self-organized into highly crystalline nanowires with a d(100) spacing of 13.30 Å. The hole mobility of the P3MBT:PC(71) BM (1:0.5 by weight) blend film reaches 3.83 × 10(-4) cm(2) V(-1) s(-1) , and the maximum incident photon-to-current efficiency reaches 68%. The results unambiguously prove the spontaneous formation of nanowires using solution-processable conjugated polymers with branched alkyl side chains in BHJ solar cells.

Hydrogen Bubbles and the Growth Morphology of Ramified Zinc by Electrodeposition

Real-time X-ray microscopy was used to study the influence of hydrogen-bubble formation on the morphology of ramified zinc electrodeposit. The experimental results show that when intense hydrogen bubbling occurs at high potential, the morphology of the ramified zinc deposit changes from dense-branching to fern-shaped dendrite. The fern-shaped dendrite results in part from the constricted growth due to hydrogen bubbles but also from the highly concentrated electric field. The fern-shaped dendrite morphology was observed during the early stages of electroplating for both the potentiostatic and galvanostatic modes; however, the deposit plated in the galvanostatic mode densified via lateral growth during the later plating stages. This indicates that potentiostatic plating for which the hydrogen-bubble formation steadily occurs throughout the electrodeposition process is better than galvanostatic plating for fabricating fern-shaped deposits, which are ideal electrodes for Zn-air batteries due to the relatively large specific area

Properties and microstructure of nickel electrodeposited from a sulfamate bath containing ammonium ions

A 70 μm thick Ni layer was electrodeposited from a sulfamate bath containing various amounts of ammonium ions onto a copper plate. The detailed microstructure of the Ni deposits was characterized using a plane-view and cross-sectional transmission electron microscopy (TEM). The textures of the Ni deposits were also determined using conventional X-ray diffraction. Experimental results indicated that ammonium ions suppressed the lateral growth of Ni deposits and favoured out growth, thus leading to the growth of [1 1 0] and [3 1 0] oriented deposits. A structural refinement effect was observed after ammonium ions were added to the sulfamate bath. Ammonium ions also increased the internal stress and hardness of the deposits. A general Hall–Petch relationship was observed for the dependence of deposit hardness on the average grain size of the Ni deposits. The adsorption of atomic hydrogen and the polar NH3 molecule explains the effect of ammonium ions on the electrocrystallization of Ni.

Structural Evolution and Internal Stress of Nickel-Phosphorus Electrodeposits

The properties of nickel-phosphorus (Ni-P) electrodeposits can be best related to their phosphorus content and microstructure. This study systematically investigated the microstructural evolution and mechanical propertiesof the deposits plated from nickel sulfamate baths containing 0-40 g dm - 3 phosphorous acid (H 3 PO 3 ). Experimental results indicate that coarse nickel grains were substantially refined with the incorporation of phosphorus into the deposit. For example, as the deposit phosphorus content was increased from 0 to 14 wt %, the structure of the deposit changed in sequence from a coarse column to a mixture of column and lamella, followed by a well-defined lamella, and finally to a homogeneous amorphous matrix dispersed with nanosized grains. Accompanied with this structural evolution, the deposit exhibited a distinct change in deposit hardness and internal stress. These properties and microstructure relationships are discussed in terms of the lattice defects in the grains and proton discharge during electronlating.

A study of TiNiV ternary shape memory alloys

Abstract The TiNiV ternary shape memory alloys, obtained by equal substitution of V for both Ti and Ni, are investigated focusing on their basic transformation behavior, shape memory effect, pseudoelasticity and wear characteristic. Experimental results reveal that the Ti 49.25− x /2 Ni 50.75− x /2 V x ( x =0–4 at%) alloys exhibit a B2↔B19′ one stage martensitic transformation. The transformation temperatures will drop down about 10°C by adding 1–2 at% V due to the effect of solid-solution strengthening. There appear many (Ti,V) 2 Ni second-phase particles within the matrix of Ti 47.75 Ni 49.25 V 3 and Ti 47.25 Ni 48.75 V 4 alloys. The oxygen atoms in the matrix will be easily absorbed by the (Ti,V) 2 Ni second-phase particles to form the (Ti,V) 4 Ni 2 O oxide. This decreased oxygen content in the matrix will contribute to raise the transformation temperatures for both Ti 47.75 Ni 49.25 V 3 and Ti 47.25 Ni 48.75 V 4 alloys. The shape memory effect and pseudoelasticity of Ti 49.25 Ni 50.75 alloys can be improved by the addition of 1–2 at% V due to solid-solution strengthening. The energy storage efficiency ( E 2 / E 1 + E 2 ) can also be increased by the addition of V. However, the Ti 47.75 Ni 49.25 V 3 and Ti 47.25 Ni 48.75 V 4 alloys exhibit a worse shape memory effect due to the formation of second-phase particles. The wear mechanisms of Ti 49.25− x /2 Ni 50.75− x /2 V x alloys are found to be similar to those of TiNi binary alloys. The Ti 49.25 Ni 50.75 , Ti 48.75 Ni 50.25 V 1 , Ti 48.25 Ni 49.75 V 2 alloys have a better wear resistance than the Ti 47.75 Ni 49.25 V 3 and Ti 47.25 Ni 48.75 V 4 alloys, due to their higher hardness and pseudoelastic behaviors of the B2 structure.

Corrosion of CrN and CrN/TiN coated heat-resistant steels in molten A356 aluminum alloy

Abstract The components of the equipment for processing aluminum melts into molded parts can be severely corroded by molten Al. In this study, a 6-μm CrN coating or a 4-μm CrN/TiN multilayer coating for providing physical and chemical barriers between molten reactive Al and the steel substrate were deposited by cathodic arc evaporation onto 10-mm-thick heat-resistant steel plates. Dipping tests were conducted in a 700°C A356 melt for 1–21 h at intervals of 3 h. The damage of the coated steel was evaluated by plane-view and cross-sectional metallography. Experimental results indicate that after a certain incubation period, the coated steel was locally attacked; forming hemispherical pits on both CrN and CrN/TiN coated steel samples. The incubation time for obvious pitting on the CrN coated steel was shorter than that for the CrN/TiN coated steel. Once the obvious pits were formed, the pitted areas increased with dipping time, regardless of the type of coating. Macroparticles were observed on the surface of both the CrN and CrN/TiN coatings. Both the CrN and CrN/TiN coatings exhibited a columnar structure that hardly changed after 21 h of dipping. The different incubation times of the distinct coatings were discussed in terms of the grain structure, macroparticles and thermo-mechanical stress associated with the physical vapor deposition-coated steels.

Electrodeposition of Nickel-Phosphorus Alloy from Sulfamate Baths with Improved Current Efficiency

In this study, nickel-phosphorus (Ni-P) deposits were electroplated from the nickel sulfamate bath containing phosphorous acid using a pulse current, with emphasis on the effect of current density, duty cycle, and frequency of the pulse current. Experimental results show that both the deposit phosphorus content and current efficiency were substantially enhanced by employing the pulse current, preferentially at low duty cycles. The underlying difference for the dc and pulse currents on the effect of deposit phosphorus content and current efficiency can be explained by the detailed half-reactions relevant to incorporation of phosphorus into Ni-P alloys. Less variation in surface proton, Ni 2+ and H 3 PO 3 concentration due to the diffusion recovery during the time off of a pulse current is believed to play an important role in the improvement of the plating process.