Oxygen-free Copper Substrate Research Articles

Characterization of Water-Based Anti-Corrosion and Anti-Fouling Coating in the Heat Exchanger Tube of Gas Water Heater

Due to the fouling and corrosion issues with gas water heater heat exchangers during use, a water-based coating is created using the sol-gel method and applied to the inner surface of the copper tube of the heat exchangers. The water-based coating can reduce the surface energy of copper that is oxygen-free by 82.40 % and has outstanding hydrophobicity. The coating's adhesion strength was 8.46 MPa, and its wet adhesion reduction rate was only 0.0375 MPa·d-1 when submerged in a bath of water at a constant temperature. Its water contact angle remained above 110° even after being abraded by sandpaper, demonstrating its excellent wear resistance. At a constant temperature of 45 °C, the corrosion experiment was carried out in salt, acid, and alkali solutions. The maximum corrosion rate of the coating was 3.24 × 10-2mg∙(cm2∙h)-1, which was only 20.85 % of that of the oxygen-free copper substrate. The dynamic fouling experiment shows that the coating can effectively inhibit fouling growth, prolong the fouling induction period and reduce the average fouling rate. By factoring in the fouling thermal resistance and the coating thermal resistance, the overall heat transfer coefficient of the copper tube was computed. The results demonstrate that after applying this water-based coating, the copper tube can continue to have a high heat transfer coefficient for an extended period, ensuring the continuous and effective operation of the heat exchanger and having practical application value.

Annealing study on the properties of Cu-based Nb3Sn films under argon pressures for SRF applications

Nb3Sn is an alternative material for future superconducting accelerators. With its higher critical temperature and superheating field than that of niobium, its application in the field of SRF is a great advantage. In this paper, the magnetron sputtering method is applied to prepare the Nb3Sn thin film on the oxygen-free copper substrate by the stoichiometric target—the ratio of 3:1 of niobium to tin, so as to explore the effect of different annealing air pressures on the properties of the film in detail. The film crystal structure, morphology, composition, and superconducting critical temperature were characterized by XRD, SEM, EDS, and MPMS. After in-situ annealing, XRD and MPMS reveal the existence of Nb3Sn crystal. The compact film with good surface properties is free of cracks and tin islands. The superconducting critical temperature reaches 13.6 K. The results show that if annealing was conducted in Ar atmosphere at 1 Pa, the obtained film exhibits better performance with a sharp transition from the superconducting state to the normal state.

Characterization of Ti–Zr–V thin films deposited by DC and unipolar pulsed DC magnetron sputtering

Ternary Ti–Zr–V getter films with approximately equal atomic concentrations were deposited on oxygen free copper substrates by magnetron sputtering using DC and unipolar pulsed DC current modes. The thin film morphologies were studied using scanning electron microscopy, atomic force microscopy, while their chemical and phase compositions were investigated by energy dispersive spectroscopy and X-ray diffraction, respectively. The chemical states within the superficial regions of the films were characterized by X-ray photoelectron spectroscopy in ultra-high vacuum. The results indicate that both current modes promote formation of porous thin films, while the microstructure of the DC film is much finer than that of the unipolar pulsed DC film. Initially, the thin films were covered by oxides of Ti, Zr and V that are reduced upon annealing treatment; those within the DC film present faster reduction kinetics as compared with that of the unipolar pulsed DC film.

Effect of ion-beam surface treatment on photocathode emission

To meet the needs of high-frequency, miniaturized vacuum microwave devices, a new photocathode for microwave vacuum electronic device has been studied. Untreated oxygen-free copper, commonly used for photocathode substrate, exhibits relatively high photoemission characteristics. In this paper, we describe a specialized ion-beam bombardment procedure for textured copper surfaces, thereby improving the photoemission properties relative to untreated copper. The emission characteristics of antimony cesium photocathode on oxygen-free copper substrate before and after surface treatment are studied The photoemission and texture of post-treated oxygen-free copper surface are examined by scanning electron microscope. The results show that the treated surface has a particle-free, robust, uniformly highly-textured all-metal structure. This processing technology does not require to modify the copper machining and brazing, nor normal fabrication procedures of other photocathodes. In the experiment, the maximum photoemission current density of photocathode for the untreated substrate is 60.5 and that for the treated substrate is 146.0 mA/cm<sup>2</sup>, and their corresponding quantum efficiencies are calculated to be 2.67 × 10<sup>–3</sup> and 1.71 × 10<sup>–2</sup>, respectively. So, the quantum efficiency is enhanced by 6.41 times. The analysis indicates that the improvement of the quantum efficiency of the treated photocathode is mainly due to the enhancement of the light absorption rate. The results show that the photoemission is enhanced significantly after the substrate has been treated, and there is still much room for improvement.

Properties improvement of atmospheric plasma sprayed tungsten coating by annealing

Tungsten coatings were deposited onto oxygen-free copper substrate by atmospheric plasma spraying technique. Annealing treatment was adopted to modify the inherent defects and improve the performance of the plasma sprayed tungsten coating. The effect of annealing under vacuum and hydrogen atmosphere on the properties of plasma sprayed tungsten coating was studied. The results show that the tungsten grains grow up after annealing treatment, the coatings are transformed from a disorganized structure into a columnar crystal structure with an orderly arrangement. Annealing treatment at a certain temperature can decompose and reduce the tungsten oxide in the coating into pure tungsten, thereby reducing the oxygen content and improving the purity of the coating. As a result, the thermal conductivity, microhardness and other performances of the APS-W coating are improved after annealing.

Properties of Active Water Cooling Atmospheric Plasma Spraying Tungsten Coating

Tungsten coating was deposited onto an actively water-cooled oxygen-free copper substrate by atmospheric plasma spraying technique. The properties of the microstructure, porosity, microhardness and oxidation of the active water cooling atmospheric plasma spraying tungsten coating were characterized and measured. High heat load and thermal response tests using an electron beam facility have been carried out on the tungsten coated mock-ups under the water cooling condition. The heat flux is changed from 3 to 10 MW/m2 under the condition that the water flow rate is 2.5, 2.0 and 1.5 m3/h, respectively. It is demonstrated that the mock-ups successfully withstood a heat flux of 15.5 MW/m2 at steady state.

Transient High Heat Load Performance of Atmospheric Plasma Sprayed Tungsten Coating

Tungsten coatings on oxygen-free copper substrates were fabricated by atmospheric plasma spraying (APS) technique. The properties of the microstructure, porosity, microhardness and oxidation of the coatings were characterized and measured. In order to evaluate the thermal properties of the APS-W coating, a high current pulsed electron beam facility was introduced to carry out the transient high heat load tests. Three power densities of 0.2, 0.5 and 1.0 GW/m2 and total pulse duration of 5 ms were performed on the coating surfaces. The surface temperature and behavior of the APS-W coatings under the transient high heat load were investigated. Obvious melting and re-solidification were found on the treated APS-W coatings, and cracks were also observed on coating surface.

Feasibility study on surface finishing of miniature V-grooves with magnetic compound fluid slurry

Towards the development of a novel polishing technique for the high-precision surface finishing of miniature V-grooves, the feasibility of finishing linear V-grooves generated on an oxygen-free copper substrate using a magnetic compound fluid (MCF) slurry was experimentally investigated, and the fundamental finishing characteristics were elucidated. First, a polishing apparatus was constructed by installing an MCF unit for generating a rotary magnetic field and rotating an MCF carrier onto a polisher, along with a wave maker used for vibrating the workpiece. Then, polishing experiments were performed to clarify the fundamental polishing characteristics, including the effects of the polishing time on the material removal, the form accuracy (i.e. the form retention rate and symmetry error), and the surface roughness at different polishing locations/positions in the polishing zone. Thereafter, the fundamental characteristics were examined by investigating the distribution of abrasive particles in the polishing zone, the relative velocity of abrasive particles compared to the V-groove, and the impact angle of abrasive particles against the V-groove side surface. Finally, the effect of the MCF carrier rotation speed nc on the characteristics was elucidated, and an appropriate value of nc was proposed. The main results can be summarized as follows. (1) At the majority of locations in the polishing zone, the surface quality Ra at higher positions on the V-grooves was better than that at lower ones. At locations where abrasive particles moved from the right/left side to left/right side of the grooves, the surface quality Ra on the right/left side was better than that at the left/right side. The final surface roughness after 150min of polishing was in the range of 15–50nm Ra, indicating that a mirror-like surface could be successfully achieved for a miniature V-groove using the proposed technique. (2) The V-groove form accuracy, i.e. form retention rate η and symmetry error ɛ, deteriorated during polishing, and the final form accuracy differed with the location. Nevertheless, the η and ɛ values at the location where the form accuracy was the lowest were greater than 99.47% and less than 0.17, respectively. (3) Increasing the MCF carrier rotational speed nc deteriorated the form accuracy but improved the surface quality Ra. Taking into account the balance between the form accuracy and surface quality Ra, nc should be set at 10rpm under the experimental conditions in the current work.

Low Temperature Diffusion Bonding of Ti-6Al-4V to Oxygen Free Copper with High Bonding Strength Using Pure Ag Interlayer

Abstract Diffusion bonding of Ti-6Al-4V (TC4) to oxygen free copper (OFC) at low temperature was carried out using silver foil as interlayer. Results show that the interlay can prevent the formation of brittle Ti-Cu compounds and improve the interfacial microstructure and bonding strength of the TC4/OFC joint. Moreover, adding the silver interlayer greatly lowers the bonding temperature. The composition of the joint from the TC4 side to the OFC side is TC4 substrate, AgTi compound, Ag interlayer, Ag-Cu solid solution and OFC substrate. The tensile strength of the joint bonded at 700 °C for 1 h under 10 MPa bonding pressure has an excellent value of 150 MPa, higher than those previously reported in literatures. Fracture failure takes place in the Ag/OFC interface and ductile fracture can be observed on the fracture surface. It is suggested that the ductile properties of the AgTi compounds are superior to that of Ag-Cu solid solution in this joint.

Performance characterization and improvement of tungsten coating atmospheric plasma sprayed with submicron powder

Tungsten coatings were deposited on oxygen free copper substrate via atmospheric plasma spray technique with submicron W powder (600nm on average). The properties of the tungsten coating such as microstructure, density, microhardness, oxygen content and thermal conductivity were characterized and measured. The results show that spraying with submicron W powder can achieve a relatively dense, high thermal conductivity tungsten coating. In order to improve the performance of tungsten coating, vacuum annealing was applied to the as-sprayed tungsten coatings. The results show that annealing in vacuum after deposition at suitable temperature can significantly improve the quality of the tungsten coating by increasing the grain size and decreasing the porosity. The oxygen content also decreased due to the decomposition of tungsten oxide in vacuum annealing. Compared with the as-sprayed W coating, the thermal conductivity of the annealed W coating was doubly improved.

Influence of Ti Layer on the Structure and Properties of Al/Cu Thin Film

Titanium and aluminum films were deposited on oxygen-free copper substrates by electron beam evaporation method to obtain Al/Cu and Al/Ti/Cu layer composites. Evolution of microstructure and properties of Al/Cu and Al/Ti/Cu thin film during heat treatment processes were investigated by XRD, SEM and electrical properties analysis. The introduce of Ti layer can prevent the formation of Cu-Al intermetallic compounds, and has no obvious influence on the electrical resistivity of Al/Cu thin film, which can be used as a pad in microelectronic package and devices.

Microstructures and Thermal Properties of Cold-Sprayed Cu-Cr Composite Coatings

Copper-based composites for thermal conductive components were prepared via the cold spray process, and the deposition efficiency and adhesion morphology of feedstock powders on Cu substrate were evaluated. Cu-based composites were fabricated using Cu-Cr mixed powders with their mixture ratio of 20, 35, 50, and 65 mass% Cr onto oxygen-free copper substrate with N2 carrier gas. Cu-Cr composite coatings were investigated for their Cr content ratio, microstructures, and thermal conductivity. The Cr content ratio in the coating was approximately 50-60% of feedstock mixture ratio due to the low formability of the hard particles. Transmission electron microscopy characterizations revealed that an oxygen-rich layer exists at the Cr particle/Cu substrate interface, which contributes to the deposition of the Cr particles. After the heat treatment at 1093 K, the coatings showed denser cross-sectional structures than those before the heat treatment, and the thermal conductivity was improved as a result of the recrystallization of Cu matrix.

Microfluidic baker's transformation device for three-dimensional rapid mixing

We developed a new passive-type micromixer based on the baker's transformation and realized a fast mixing of a protein solution, which has lower diffusion constant. The baker's transformation is an ideal mixing method, but there is no report on the microfluidic baker's transformation (MBT), since it is required to fabricate the complicated three-dimensional (3D) structure to realize the MBT device. In this note, we successfully fabricate the MBT device by using precision diamond cutting of an oxygen-free copper substrate for the mould fabrication and PDMS replication. The MBT device with 10.4 mm mixing length enables us to achieve complete mixing of a FITC solution (D = 2.6 × 10(-10) m(2) s(-1)) within 51 ms and an IgG solution (D = 4.6 × 10(-11) m(2) s(-1)) within 306 ms. Its mixing speed is 70-fold higher for a FITC solution and 900-fold higher for an IgG solution than the mixing speed by the microchannel without MBT structures. The Péclet number to attain complete mixing in the MBT device is estimated to be 6.9 × 10(4).

Fabrication of thick W coatings by atmospheric plasma spraying and their transient high heat loading performance

Both tungsten coatings with or without a W/Cu graded interlayer on an oxygen-free copper substrate were fabricated by atmospheric plasma spraying. High purity argon gas was used for cooling the substrate and preventing the coating from oxidation. The thickness of both coatings is ∼1 mm. XRD and EDS measurements of the coatings show that minimal oxidation occurred during the deposition process. Transient high heat load tests by electron beam with a pulse duration of 5 ms were performed on both coatings. The single pulse loading was applied on the virgin surfaces at several power densities (from 0.22 to 0.9 GW/m 2). Although the weight loss of the W/Cu FGM (functionally graded materials) based coating was slightly lower than that of the pure W coating, their transient high heat loading performances were quite similar.

Growth of multi-walled CNTs emitters on an oxygen-free copper substrate by chemical-vapor deposition

Field emission properties of carbon nanotubes directly grown on a well-polished oxygen-free copper substrate by chemical-vapor deposition (CVD) were studied. Ni was sputtered on the copper substrate as catalyst, and the reactant gas was acetylene. From scanning electron microscopic and transmission electron microscopic images, the as-grown carbon nanotubes are seen to be bamboo structure with branches. Efficient field emission of CNTs is measured by a diode configuration, and the maximum current is 4.8 mA corresponding to a low electric field of 6.7 V/μm (the emission area is about 3.14 mm 2). The diffusion between nickel and copper substrate is found to cause the loss of catalyst based on X-ray diffraction pattern of the surface of the substrate.

Study on the Plasma-Sprayed Molybdenum as Plasma Facing Materials in Fusion Reactor

Molybdenum has many prominent properties, such as high melting point, good thermal properties, low erosion rate and so on, which make it promising candidate materials for plasma facing materials in the next fusion reactor. In the present work, molybdenum coatings were deposited onto the oxygen-free copper substrates by atmospheric plasma spraying. Different interlayers were introduced between the coatings and substrates. SEM, EDS and XRD were used to investigate the photographs and compositions of these coatings. The bonding strength of the coatings was tested to investigate the effect of interlayers on adhesion of the coatings at room temperature and it was found that the coating without interlayers showed the highest bonding strength. Water quenching method was used to evaluate the adhesion of the coatings under thermal cycling conditions and the results showed that the molybdenum coating with two interlayers possessed of the highest resistance of thermal cycling wrack.

Fabrication and Evaluation of Plasma-Sprayed Molybdenum for Plasma Facing Materials

Molybdenum has many prominent properties, such as high melting point, good thermal properties, and low erosion rate and so on, which make it promising candidate materials for plasma facing materials in the next fusion reactor. In this paper, Molybdenum coatings were deposited onto the oxygen-free copper substrates by atmospheric plasma spraying. The spraying parameters had been carefully selected. Different interlayers were induced between the substrate and the coating. SEM and XRD were used to investigate the photographs and compositions of these coatings. The micro-hardness and bonding strength were also tested. Thermal behaviors of the coatings were evaluated by thermal shock tests. The coatings with interlayers showed better resistance of thermal shock but lower bonding strength compared to coatings that without interlayers.

Study on Interfacial Characterization and Mechanical Properties of Plasma-Sprayed Tungsten Coatings

Tungsten has the highest melting point among all metal, which makes it withstand thermal shock and erosion in high temperature environments. In this study, Tungsten coatings were sprayed onto the oxygen-free copper substrates by plasma spraying using inert gases protection. XRD, SEM and EDS were used to identify the phases, morphologies and compositions of the coatings. Vickers micro-hardness and bonding strength of the tungsten coatings were also measured. The results revealed that the hardness distribution of the tungsten coatings was different along the thickness direction. The tungsten coating without any interlayer showed higher bonding strength than that of the other two coatings with NiCrAl and W/Cu interlayers, respectively.

Microstructure and Bonding Strength of Tungsten Coating Deposited on Copper by Plasma Spraying

Tungsten coatings with different interlayers onto the oxygen-free copper substrates were fabricated by atmosphere plasma spraying. The effects of different interlayers of NiCrAl, NiAl and W/Cu on bonding strength were studied. SEM, EDS and XRD were used to investigate the photographs and compositions of these coatings. The tungsten coatings with different initial particle sizes resulted in different microstructures. Oxidation was not detected in the tungsten coating, but in the interlayer, it was found by both XRD and EDS. The tungsten coating deposited directly onto the copper substrate presented higher bonding strength than those with different interlayers.

Effect of Iron Plating Conditions on Reaction in Molten Lead-Free Solder

To demonstrate the dissolution of plated iron in molten lead-free solder and the effect of iron-plating conditions on reactions in molten lead-free solder, the reaction test between Sn-3.0Ag-0.5Cu (mass%) solder and plated iron was performed. An Iron-plated copper plate, which was made by electroplating iron onto an oxygen-free copper substrate, was used as the test piece. The reaction test was carried out by using an oven in normal air. The solder was placed on the test piece and it was put into an oven held at 400, 430 and 460°C. The interface between the solder and plated iron was particularly examined. It was found that the intermetallic compound of FeSn 2 was formed at the interface regardless of the plating conditions. The results showed that the grain size of plated iron decreased with the increased current density and the dissolution thickness of plated iron in molten lead-free solder increased with the increased current density in the rack plating. In the barrel plating, the grain size was rather small in all the test pieces and the dissolution thickness was rather thick. Thus it has been made clear that the dissolution of plated iron in molten lead-free solder is attributable to the grain size of plated iron.