Preparation of PbS thin films: A new electrochemical route for underpotential deposition

Nanostructured thin films of lead sulfide have been synthesized by a new electrochemical approach based on the underpotential deposition (UPD) of Pb and S from the saturated solution of PbS containing excess of PbS particles as a source of Pb²⁺ and S²⁻ at various temperatures.We have demonstrated that this new electrochemical route is a simple method with several advantages, including better control of the growth conditions and a one-step process to obtain the nanostructures of PbS. Scanning probe microscopy studies indicate that the growth of PbS nanofilms follows a two-dimensional layer-by-layer growth kinetics at the beginning of electrodeposition but a three-dimensional growth dominates after the formation of the first few layers. The results of morphological and structural investigations reveal that PbS nanostructures grown by this method are single-crystalline in cubic structure and have a preferential orientation along the [2 0 0] direction. The optical absorption spectra of PbS nanostructures show the blue-shift with respect to those of the bulk counterpart, which are attributed as quantum-size effect.     

Electrolytic Co-deposition of Ni-CrAlY Composite Coatings Using Different Deposition Configurations

With the aim of seeking an alternative low-cost process for the fabrication of MCrAlY coatings, an electrolytic co-deposition process was employed to form a composite coating consisting of a Ni matrix and CrAlY particles. Three configurations were investigated in the co-deposition process, including a vertical setup, a horizontal arrangement, and a rotating barrel. The CrAlY volume fractions in the resultant composite coatings were compared. The advantages and disadvantages of each configuration were discussed. Among the three configurations studied in this paper, the rotating barrel demonstrated the best overall performance, with the capability of producing coatings with more uniform CrAlY particle incorporation of up to 40 vol.%.     

The effect of micro-alloying addition of Cr on age hardening of an Mg–Zn alloy

This work reports a chemical method called “co-deposition route” for fabricating ND (nanodiamond)/Cu composite at a molecular-level mixing. The main procedure of “co-deposition route” includes four steps. ND particles have been functionalized by HF acid before co-deposition. SEM, HRTEM (high-resolution transmission electron spectroscopy), XRD (X-ray diffraction), EDS (energy-dispersive spectrum analysis) and optical microscope were carried out to characterize the as-prepared composite powders and bulk composites. Results indicated that copper matrix composite with a homogeneous dispersion of functionalized ND particles can be prepared. The modification of ND particles was performed by HF (30 vol%) acid at 70 °C, and CF bond was successfully detected by XPS (X-ray photoelectron spectrum) and IR (Infrared spectroscopy). The properties of relative density, microhardness and electric conductivity of ND/Cu composites have been measured. With the comparison of conventional methods, it showed that the as-prepared ND/Cu composites with good combined performances have a promising future for industry application.     

Co-deposition of Al-Cr-Ni alloys using constant potential and potential pulse techniques in AlCl3-NaCl-KCl molten salt

To improve the oxidation resistance of TiAl intermetallic compound under high temperature condition, cathodic co-deposition of Al-Cr and Al-Ni alloy was carried out by constant potential control or potential pulse control in AlCl₃-NaCl-KCl molten salt containing CrCl₂ and/or NiCl₂ at 423 K. Cathodic reduction of Ni and Cr starts at potential of 0.8 and 0.15 V versus Al/Al³⁺ in the molten salt, respectively. The co-deposition of Al, Cr, and Ni occurred at potentials more negative than −0.1 V to form a mixture of intermetallic compounds of Cr₂Al, Ni₃Al, and Al₃Ni. Concentration of Cr in the deposit was enhanced to 43 at% at −0.1 V; however, concentration of Ni in the deposit was 6 at% at the same potential. The concentration of Ni further decreased with more negative potential to 1 at% at −0.4 V. The potential pulse technique enhanced the Ni concentration in the deposit to about 30 at%, due to anodic dissolution of Al content from the deposit at the higher side of potential on the potential pulse electrolysis.     

Study of an on-line precision microgroove generating process on silicon wafer using a developed ultra-thin diamond wheel-tool

This study presents a novel and economical method for precisely developing an ultra-thin diamond grinding wheel-tool and using the finished wheel-tool to on-line fabricate crisscross microgrooves on silicon wafer. The wheel-tool blank is made of diamond grain of 0-2 μm grade via a designed micro co-deposition. A non-continuous cathode design, in which current crowding effect can be suppressed, is used to obtain a diamond wheel-tool with good surface characteristics. With abrasive content of 8 g/l, a suitable interval chip-pocket of 2-3 μm can be generated. The grinding wheel blank is thinned and dressed simultaneously down to a thickness of 15 μm using micro wire Electro Discharge Dressing (w-EDD). The finished wheel-tool is directly utilized to grind the crisscross microgrooves on the silicon wafer using ‘high-speed and fast-shallow grinding’ technique. A grinding depth of 0.5 μm per stroke is exactly controlled to ensure that the removal mechanism transfers to a ductile grinding mode. The width, depth and surface roughness R_a of the microgrooves are 15 μm, 9 μm and 0.087 μm, respectively.     

多层分步镀方法制备用于氢气分离的Pd-Ag 膜

用基于化学镀方法的钯银共沉积和分步沉积两种方法制备了PdAg膜。对比研究了两种方法制备的钯银膜的形貌、相结构、成分均匀性和致密性。实验结果表明共沉积法获得的钯银膜是树枝状的、成分不均匀、且致密性很差。分步沉积获得的钯银膜成分均匀、沿侧面生长趋势好,更适合制备超薄致密的用于氢气分离的钯银合金膜。多层分步镀形成Pd-Ag合金需要更高的温度和更长的时间热处理。Ag层的交替使得Pd的晶粒减小,并且最终沉沉积的膜表面更光滑。     

Preparation of ZrC-SiC composite coatings by chemical vapor deposition and study of co-deposition mechanism

In this work, the ZrC-SiC composite coatings were co-deposited by chemical vapor deposition (CVD) using ZrCl₄, MTS, CH₄ and H₂ as raw materials. The morphologies, compositions and phases of the composite coatings were characterized by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS) and X-ray diffraction (XRD). The results indicated that the morphologies, compositions and phases of the composite coatings were related to the deposition temperature, the flow rate of the carrier H₂ gas, and the ratio of C/Zr. Moreover, the co-deposition mechanism of the composite coatings was also studied. It was found that different deposition temperatures resulted in different deposition mechanisms. At temperatures in the range of 1150–1250 °C, the ZrC-SiC co-deposition was controlled by the surface kinetic process. At temperatures in the range of 1250–1400 °C, the ZrC-SiC co-deposition was controlled by the mass transport process.     

Co-deposition mechanism of nanodiamond with electrolessly plated nickel films

The co-deposition behavior and mechanism of nanodiamond with electrolessly plated nickel films was investigated. Due to the variation of complexing agents, various composite films with 0.9-8.0% nanodiamond were plated from electroless nickel plating baths which contained the same amount of nanodiamond (5.0 g dm⁻³) and sodium hypophosphite. In addition, composite films with 0-14% nanodiamond, semi-brilliant, were successfully fabricated from the bath which contained only citrate as a complexing agent. The plating bath was very simple and was sufficiently stable without any decomposition until termination of the plating reaction occurred due to consumption of the reducing agent. When the adsorbed amount of Ni-complex on the nanodiamond particles was large, a large amount of nanodiamond was co-deposited with the nickel. The results are interpreted to indicate that the adsorbed Ni-complex precipitates the incorporation of nanodiamond particles into the nickel matrix. In addition, incorporation becomes more probable when the adsorbed amount of Ni-complex on the nanodiamond particles was large.     

Co-deposited composite coatings with a ceramic matrix destined for sliding pairs

Composite layers with electrolytic oxide coatings matrix on aluminium and its alloys or composite with its matrix are widely applied in production of machine parts destined for sliding pairings. These layers so far have been produced with a two-stages method, i.e. through anodizing and metallising. So produced layers have disadvantageous surface fractions of hard, abrasive acting aluminium oxide and plastic, friction softening metal. Only 1 unit of metal accrues in the friction surface for every 200 area units of aluminia, because there is metal in the pores of the oxide cells only. The new method elaborated by the author, named co-deposition, changes those proportions. The friction-softening metal is deposited through the entire oxide cells' volume, which changes significantly the useful properties of the composite layers. The results of metallographic and tribological investigations of layers produced with the two-stage method and the co-deposition method are presented in this paper.