Surface Oxidation Treatment Research Articles

Selective Laser Melting of High Relative Density and High Strength Parts Made of Minor Surface Oxidation Treated Pure Copper Powder

Pure Copper (Cu) is very difficult to prepare using selective laser melting (SLM) technology. This work successfully prepared the pure Cu with high relative density and high strength by the SLM technology using a surface oxidation treatment. The gas-atomized pure Cu powder was used as the feedstock in this work. Before the SLM process, the pure Cu powder was initially handled using the surface oxidation treatment to coat the powder with an extremely thin layer of Cu2O. The SLMed highly dense specimens contain α-Cu and nano-Cu2O phases. A relationship between the processing parameters (laser power (LP), scanning speed (SS), and hatch space (HS)) and density of Cu alloy in SLM was also investigated. The microstructure of SLMed Cu consists of fine grains with grain sizes ranging from 0.5 to ~30 μm. Tensile testing and detailed microstructural characterization were performed on specimens in the as-SLMed and pure copper state specimens. The mechanical property experiments showed that the specimens prepared by SLM technology containing nano-oxide phases had higher yield strength and tensile strength than that of other SLM-built pure copper. However, the elongation was remarkably decreased compared to other SLM-built pure copper, due to the fine grains and the nano-oxides.

Adoption of the Wet Surface Treatment Technique for the Improvement of Device Performance of Enhancement-Mode AlGaN/GaN MOSHEMTs for Millimeter-Wave Applications.

In this work, a low-power plasma oxidation surface treatment followed by Al2O3 gate dielectric deposition technique is adopted to improve device performance of the enhancement-mode (E-mode) AlGaN/GaN metal-oxide-semiconductor high-electron-mobility transistors (MOSHEMTs) intended for applications at millimeter-wave frequencies. The fabricated device exhibited a threshold voltage (Vth) of 0.13 V and a maximum transconductance (gm) of 484 (mS/mm). At 38 GHz, an output power density of 3.22 W/mm with a power-added efficiency (PAE) of 34.83% were achieved. Such superior performance was mainly attributed to the high-quality Al2O3 layer with a smooth surface which also suppressed the current collapse phenomenon.

Graphene Oxide Surface Treatment on Piassava Fiber Attalea funifera to Improve Adhesion in Epoxy Matrix

ABSTRACT The growing environmental awareness in the last few decades has driven the research and development of composites reinforced with natural fibers as an alternative to replace synthetic fiber composites. However, their hydrophilic character and surface heterogeneity may be considered a challenge to allow reliable and wide application of these materials. One way to overcome this drawback is the modification of the surface of the fiber by chemical and/or physical treatments. Among these treatments, the graphene oxide (GO) has stood out due to its amphiphilic character. In the present work, the influence of GO-treatment in piassava fiber was investigated. The interfacial adhesion between the piassava fiber, both untreated and with GO, and the epoxy resin was evaluated by pullout tests. Fourier transform infrared spectroscopy (FTIR) and Raman spectroscopy were also performed to verify the effectiveness of the GO-treatment on the piassava fiber. The fiber’s surface morphology was further investigated by scanning electron microscopy (SEM). The GO-treatment of the piassava fiber enhanced the interfacial shear strength by ∼171% more than untreated fibers. This could allow new applications of these eco-friendly composites as high-performance materials.

Investigating interfacial adhesion and open-hole compressive (OHC) strength correlations for CFRPs via variations in sizing and oxidative surface treatment

Increasing interfacial shear strength (IFSS) has been observed to improve fracture toughness within carbon fiber/epoxy laminates. However, a direct correlation between IFSS of carbon fiber surface treatments and open-hole compressive (OHC) strength has never been established. Here the effects of systematically altering electrochemical oxidation surface treatments (0, 2 and 3.4 Amps) and sizing deposition levels (Unsized, 1:15 and 1:20 dilution epoxy:water, respectively) to observe the correlation, if any, between microscale IFSS and laminate OHC strength. Increases in OHC strength of up to 30.2% relative to untreated and unsized fibers were observed and attributed to the surface treatments for sized fibers. No changes in OHC strength were observed when the surface treatment was altered for unsized fibers, suggesting a major role of the sizing in governing OHC strength. This is supported by OHC strength increases of up to 49.4% attributed to increased sizing deposition level.

Technology of sub-100 nm InAlN/GaN HEMTs on silicon with suppressed leakage current

Due to the thin InAlN barrier layer, leakage current is a serious problem in InAlN/GaN high-electron-mobility transistors (HEMTs). The InGaN back-barrier can raise the conduction band of the GaN buffer layer and enhance the carrier confinement, resulting in a reduced buffer leakage current. The surface oxidation treatment prior to gate deposition can form an oxide layer and reduce the barrier leakage current. In this study, using both technologies, a record low off current (Ioff) and a record high on/off current (Ion/Ioff) ratio are achieved on InAlN/GaN HEMTs on silicon substrate. The InAlN/GaN HEMT with a 70-nm rectangular gate presents a low Ioff of 7.15 × 10−8A/mm, a high Ion/Ioff ratio of 2.20 × 107, an average subthreshold swing (SS) of 69 mV/dec, and a low drain-induced barrier lowering (DIBL) of 90 mV/V. The InAlN/GaN HEMT with a 70-nm T-shaped gate exhibits a low Ioff of 3.26 × 10−8 A/mm, a high Ion/Ioff of 4.5 × 107, an average SS of 60 mV/dec, and a DIBL of 30 mV/V. To the best of our knowledge, these are record values among the reported InAlN/GaN HEMTs on Si. RF measurements present that current/power gain cutoff frequency (fT/fmax) of 215/45 GHz and 130/160 GHz are achieved on the 70-nm InAlN/GaN HEMTs with rectangular and T-shaped gate, respectively.

Carbon micro- and nanofibrous materials with high adsorption capacity for water desalination

This work demonstrates the adsorption capacity of carbon micro- (CF) and nanofibrous (CNF) adsorbents differing in specific surface area, fiber diameter and open porosity in the removal of NaCl from water. The effect of the adsorption conditions, i.e. contact time, initial salt concentration, and oxidative surface treatment on the adsorption kinetics and equilibrium salt uptake capacity was investigated. Adsorption experiments were carried out by batch-mode experiment at room temperature. The study showed that activated CNF exhibit high adsorption capacity for NaCl, namely 827.5 mgNaCl/gCNF, and this value is over 40 times higher than that of activated carbon and exceeds the values reported for CNT and GO. The adsorption kinetics followed the pseudo-second-order kinetic model and was largely controlled by the intramolecular diffusion rate. The equilibrium data showed a good correlation with the Langmuir and Freundlich isotherms, which supported the complex interaction of salt with the carbon surface. It was shown that salt ions can be attached to the fibrous surface both by ion-exchange mechanisms and electrostatic interactions. The carbon fibrous adsorbents present a new approach to water desalination through the mechanism of adsorption and continuous crystallization, and may be used for the elaboration of new type membranes for water purification and desalination.

Effect of graphene oxide surface treatment on the interfacial adhesion and the tensile performance of flax epoxy composites

The high stiffness and damping properties of flax fibres promote the integration of biocomposites in structural applications. However, the strength of flax/epoxy composites is still limited compared to glass/epoxy composites. Graphene oxide (GO) has proved to be a promising building block for nanocomposites due to its high toughness, stiffness and tunable interfacial interactions with polymers. This study aims to understand the potential of GO-based surface treatment of flax fibres to modify the interfacial adhesion and tensile performance of flax fibre/epoxy composites. GO-modification improves the interfacial shear strength of elementary flax fibre/epoxy by 43%. The interfacial improvement is also established by the 40% higher transverse bending strength compared to untreated flax/epoxy composites. The tensile moduli of GO-modified flax/epoxy composites are on average 2 GPa higher than for untreated flax fibre/epoxy composites in all strain ranges. The quasi-static longitudinal tensile strength of unidirectional composites is not affected by GO-modification.

Sulfur dioxide gas sensing at room temperature based on tin selenium/tin dioxide hybrid prepared via hydrothermal and surface oxidation treatment

In this paper, a novel SnSe/SnO2 nanoparticles (NPs) composite has been successfully fabricated through hydrothermal method and surface oxidation treatment. The as-prepared sample was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM). A series of morphological and structural characteristics confirm that the SnSe/SnO2 NPs composite shows a core–shell structure with a SnO2 shell with thickness of 6 nm. The prepared SnO2 NPs and SnSe/SnO2 NPs composite were applied as gas-sensing materials, and their gas-sensing properties were investigated at room temperature systematically. Experimental results show that the response value of the SnSe/SnO2 composite sensor toward 100 × 10–6 SO2 is 15.15%, which is 1.32 times higher than that of pristine SnSe (11.43%). And the SnSe/SnO2 composite sensor also has a detection limit as low as 74 × 10–9 and an ultra-fast response speed. The enhanced gas-sensing performance is attributed to the formation of p–n heterojunction between SnSe and SnO2 and the appropriate SnO2 shell thickness.

Engineering the interfacial chemistry and mechanical properties of cellulose-reinforced epoxy composites using atomic layer deposition (ALD)

Automotive and aerospace industries require new lightweight materials that enhance payload and improve efficiency via vehicle weight reduction. Employing composites, such as fiber-reinforced polymers, is a common approach to reducing vehicle component weight. In this work, we examine the use of atomic layer deposition (ALD) to alter the interfacial chemistry in cellulose-reinforced epoxy composites. As produced, most cellulosics are hydrophilic and immiscible in industrially relevant hydrophobic polymers. In this study, a variety of ALD-derived surface modification schemes are explored to improve resin permeation within a fibrous, cellulose-based paper preform and to increase interfacial adhesion between the epoxy and the cellulose preform. Specifically, we consider surface modification of the cellulose paper with the ALD precursors trimethylaluminum (TMA) and titanium tetrachloride (TiCl4) with a water oxidant to form aluminum oxide and titanium oxide-based surface chemistries. Few cycle ALD treatments (2-cycles) combined with an additional post-deposition heating step are found to make the cellulose preforms more hydrophobic. X-ray photoelectron spectroscopy verifies the presence of the metal oxide surface treatments and points towards high concentration of adsorbed adventitious carbon as the source for surface hydrophobicity. Tensile testing of laminated epoxy composites made from these cellulosic preforms indicates two mechanical property regimes depending on surface treatment: (1) high toughness and high strain for preforms that underwent only an ALD coating and (2) high modulus and high strength for preforms ALD coated and then heated at 120 °C in air. ALD treatments resulted in an 80% increase in toughness and a 47% increase in strain at break. ALD treatments with post-deposition heating resulted in a 16% increase in the elastic modulus and a 27% increase in the ultimate tensile strength. Here we propose a combination of cellulose/epoxy mechanical interlocking and interfacial adhesion as mechanisms to explain the difference in mechanical properties of the explored composites.

Formation of a corrosion-resistant coating on zinc by a duplex plasma electrolytic oxidation and conversion surface treatment

A two-step, environmental-friendly process is proposed to improve the corrosion resistance of zinc. The first step involves plasma electrolytic oxidation (PEO), to produce a uniform 6 μm thick ZnO layer in a short processing time of 30 s. This is followed by a conversion treatment by immersion in 1 M sodium bicarbonate solution for 1 h at open circuit potential. The morphology, thickness and phase composition of the surface layers were analysed using scanning electron microscopy and X-ray diffraction. The electrochemical tests (potentiodynamic polarisation and electrochemical impedance spectroscopy) showed enhanced corrosion resistance of the PEO coating after the conversion treatment. The improved corrosion resistance was attributed to the sealing of defects during the conversion treatment and the partial conversion of the ZnO layer into a protective patina. The PEO and duplex treatments also imparted a mechanically durable coating with higher scratch resistance compared to the conversion treatment.

Uniform growth of carbon nanotubes on carbon fiber cloth after surface oxidation treatment to enhance interfacial strength of composites

The uniform growth of carbon nanotubes (CNTs) on the surface of carbon fiber cloth (CFC) was carried out using quasi-vacuum chemical vapor deposition (CVD). It was found that the oxidation of CFC by H2O2 was critical to the uniform growth of CNTs. A large number of oxygen-containing functional groups were introduced on the surface of the fiber during oxidation, the content of activated carbon had increased by 27.06%, which could improve the wettability of the fiber and the binding property to the catalyst precursor. After prepared into composites, the interlaminar shear strength (ILSS) was increased by 6.28%, as measured by the short beam test. The analysis of the fracture surfaces revealed that the growth of CNTs enhanced the mechanical interlocking and improved the mechanical properties. For the CNTs-grown CFC/epoxy composite, the strength and toughness can be increased and the stress concentration can be reduced due to the long-distance diffusion of destructive cracks from the resin matrix to the carbon fiber. Finally, the mechanism of improvement in composite performance was explained from the perspective of multiscale enhancement.

A General in Situ Deposition Strategy for Synthesis of Janus Composite Fabrics with Co(CO3)0.5OH·0.11H2O Nanoneedles for Oil–Water Separation

For a fixed porous framework, developing an efficient composite material with selective removal of oil and water from an oil–water mixture is of significance but challenging because of the effect of its decreased pore size and porosity and single wettability. Herein, a Janus fabric via a general strategy of surface hydrophobization, oxidation treatment, and chemical bath deposition is constructed. The obtained composite fabric consists of a hydrophilic Co(CO3)0.5OH·0.11H2O nanoneedle/cotton fiber side and a hydrophobic cotton fiber side, which endows it with a unidirectional water transportation capability and exhibits an effective separation for both light and heavy oil–water mixtures under gravity. Especially using the water wetted composite fabric as a separation cell, the built-in lyophobic layer originating from fluid passed through the nonwetting region of wetted fabric decreases the unfavorable contact between lyophobic interface and separated liquid, and the permeation flux is enhanced by 214.5% for water and by 112.5% for oil, respectively, compared to that in the pristine fabric, whereas it has no effect on the separation efficiency of a heavy oil–water mixture. Meanwhile, the Janus composite fabric exhibits an excellent oil–water separation stability and durability and is easily recycled for long-term use. The facile Janus material synthesis strategy is available on various substrates including melamine sponge, Ni foam, cellulose paper, and other nanosheet arrays on cotton fabric. Thus, this work provides a route to develop multifunctional materials for potential application in quick oily wastewater remediation.

Wetting Behavior of Zn-Al Liquid on Si-Containing Steel After Surface Oxidation and Reduction Treatment

In the hot-dip galvanization of steel products, surface oxidation–reduction treatment has been proposed recently to improve the wettability of liquid Zn-Al alloy on Si, Mn-containing high-strength steel. During surface oxidation–reduction treatment, an iron-oxide layer with a nanoscale thickness is formed on the steel surface, which is reduced to a metallic iron layer. Although elemental Si and Mn in steel react with oxygen in the atmosphere to form oxide phases, these oxides are expected to be trapped under a reduced iron layer. However, optimum oxidation–reduction conditions have been explored to achieve a good wettability of the liquid Zn-Al alloy on the steel surface. In this study, the dynamic wetting behavior of liquid Zn-Al alloy on the surface of the Si-containing steel after oxidation–reduction treatment was observed by the sessile drop method. It was found that the wettability of the liquid Zn-Al alloy on Si-containing steel depends significantly on the oxidation–reduction condition of steel, despite the Si content in steel being fixed. A porous structure formed in the reduced iron layer accelerates liquid Zn-Al alloy wetting through a capillary force, whereas oxide phases exposed to the steel surface prevent liquid alloy wetting.

Microstructure and mechanical properties of aluminum matrix composites with different volume fractions of surface-oxidized nanodiamonds

Nanodiamonds (NDs) have the characteristics of both diamonds and nanomaterials. However, it is difficult to disperse NDs, and this is why there is less research regarding NDs in the field of aluminum matrix composites. In the present work, NDs were modified via surface oxidation, and ND/Al matrix composites were successfully prepared via mechanical ball milling and vacuum sintering. The effects of different volume fraction of NDs (1%, 3%, 5%, 7%) after surface oxidation on the ND/Al matrix composite were analyzed using a metallographic microscope, scanning electron microscope, infrared spectrometer, X-ray diffractometer, microhardness tester, and universal testing machine. The results show that the optimal temperature of surface oxidation treatment is 673 K, which effectively purifies the surface of ND and introduces appropriate C=O functional groups. NDs are uniformly distributed in the aluminum matrix, and no harmful Al4C3 phase is formed. With an increase in the volume fraction of NDs, the grain size of the matrix first decreases and then increases, and the ultimate compressive strength first increases and then decreases. The volume fraction of ND with better comprehensive performance is 3% and the yield strength increased by 19%.

Low temperature heating and oxidation to prevent spontaneous combustion using Powder River Basin coal

Powder River Basin coal, a subbituminous coal, was studied for its low temperature oxidation tendency after a simple surface oxidation treatment. The influence of the heating temperature on the coal properties was studied. The tendency of this dried coal to oxidize at low temperatures was successfully eliminated by lightly oxidizing the coal in the air at 100 to 200 ºC. The surface reactions during the process were also studied. We found that the passivation treatment appears to consume the functional groups that are prone to low temperature oxidation, such as aliphatics. The passivation effect was weakened when the oxidation temperature went above 200 °C, as decomposition happens. The oxidation reactions are monitored through two different methods: analyzing the CO2 and water produced using quadrupole mass spectrometry (QMS) and analyzing the heat release at oxidation using the differential scanning calorimetry (DSC). Gas chromatography–mass spectrometry (GC-MS) was used to analyze the coal tar material produced from low temperature heating. Scanning electron microscopy (SEM), Surface area measurements, and Fourier Transform Infrared Spectroscopy (FTIR) are used for surface characterization of the solids.

Carbon nanofibers-based nanocomposites with silicon oxy-carbide matrix

The subject of the study were nanocomposites made by infiltration of carbon nanofibers in the form of mat (CNF) with a poly(methylphenylsiloxane) resin (PMPS) solution followed by heat-treatment up to 1000 °C. The nanocomposites were studied using scanning electron microscopy (SEM-EDS), X-ray diffraction (XRD), Raman spectroscopy and by means of surface measurement tests. The morphology, microstructure, structure and selected properties of the nanocomposites were analysed. The influence of the CNF oxidative surface treatment on interface properties in CNF/resin and CNF/resin-derived ceramics nanocomposites was investigated. The high surface tension occurring at the nanofiber/resin interface required preliminary chemical treatment of carbon nanofiber surface. The surface chemical state of CNF had a significant influence on their interaction with the resin and formation of SiOC protective layer on nanofibers surface. The SiOC phase formed on the CNF surface at 1000 °C improved thermal stability of the nanocomposites in air. Due to the formation of the free carbon phase during resin heat-treatment the resulting ceramic nanocomposite matrix showed a lower electrical resistance compared to pure carbon mats.

Titanium(III) Sulfide Nanoparticles Coated with Multicomponent Oxide (Ti–S–O) as a Conductive Polysulfide Scavenger for Lithium–Sulfur Batteries

In spite of the high specific capacity and energy density of Li–S batteries based on low-cost sulfur as the active material, their practical use has not yet been realized due to the undesirable formation of soluble polysulfides (PS) during electrochemical cycles and their shuttling effect. In order to minimize this serious issue caused by the active material dissolution, transition metal compounds such as oxides, nitrides, and sulfides have alternatively been used to capture the PS and also to provide electron pathways in the S electrode. However, high-performance additive materials having both high affinity to PS and high electronic conductivity have not been developed thus far. Herein, we report the preparation and application of a new additive material—titanium(III) sulfide (Ti2S3) nanoparticles covered with multicomponent (Ti–S–O) oxide (MO–Ti2S3), which can be synthesized on a large scale using an inductively-coupled thermal plasma synthesis method followed by a simple surface oxidation treatment. MO–Ti2S3 shows much higher PS affinity than other titanium compounds and electronic conductivity that is comparable to that of carbon black. Furthermore, MO–Ti2S3 shows much higher resistance to heat and oxidation while having charge–discharge stability when compared with TiS2. Finally, we show that the cyclability and specific capacity of the Li–S battery can be significantly enhanced by incorporating MO–Ti2S3 in the cathode when compared to utilizing C species.

Heterogeneous oxidation of highly boron-doped diamond electrodes and its influence on the surface distribution of electrochemical activity

The electrochemical active surface area (EASA) of polycrystalline boron-doped diamond (BDD) electrodes is heterogeneous and can be affected by numerous factors. There is a strong need for proper consideration of BDD heterogeneity in order to improve this material's range of application in electrochemistry. Localized changes in surface termination due to the influence of oxidation agent result in increased surface resistance. The observed behavior of this characteristic feature varies among individual grains, depending on their crystallographic orientation. Still, there is not much information about this key factor in terms of its influence on the electrochemical response of BDD. In this study we compared two approaches towards BDD surface oxidation, namely: anodic polarization at potentiostatic and potentiodynamic conditions. The surface impedance measurements via Nanoscale Impedance Microscopy (NIM) allowed the confirmation of diversified propensity for the modification of surface termination in BDD. We showed that the NIM studies provide a deep understanding on the electrical characterization and variation of surface resistance in BDD electrodes. In order to evaluate the actual heterogeneity of electrochemical activity distribution, voltammetry, dynamic electrochemical impedance spectroscopy (DEIS) and scanning electrochemical microscopy (SECM) studies were performed. For each investigated electrode, departure from the Randles-Sevcik equation was observed, with its level depending on the surface heterogeneity and oxidation treatment, justifying the standardization of pre-treatment procedure and development of non-standard model for diffusion transport in proximity of BDD electrode.

Production and anodising of highly porous Ti–Ta–Zr–Co alloy for biomedical implant applications

ABSTRACTIn the present study, beta-type low elastic modulus Ti–Ta–Zr–Co alloy foams were manufactured by powder metallurgy-mechanical alloying based space holder route for hard tissue implant purposes. Ta was included to the alloy for low elastic modulus beta-Ti phase stabilisation in order to prevent stress shielding effect between implant and bone. Zr was introduced for corrosion resistance. Co addition was lowered the sintering temperature of the alloy, provided easier machining, and introduced aging capacity. Electrochemical anodisation (oxidation) surface treatment was carried out to produce a surface oxide film in order to improve the corrosion resistance and bioactivity. Corrosion properties of the surface passive oxide film were investigated in artificial saliva. Digital radiography and computed tomography studies were used for three-dimensional defect and pore structure characterisation.

Physical and electrical characterizations of AlGaN/GaN MOS gate stacks with AlGaN surface oxidation treatment

The impacts of inserting ultrathin oxides into insulator/AlGaN interfaces on their electrical properties were investigated to develop advanced AlGaN/GaN metal–oxide–semiconductor (MOS) gate stacks. For this purpose, the initial thermal oxidation of AlGaN surfaces in oxygen ambient was systematically studied by synchrotron radiation X-ray photoelectron spectroscopy (SR-XPS) and atomic force microscopy (AFM). Our physical characterizations revealed that, when compared with GaN surfaces, aluminum addition promotes the initial oxidation of AlGaN surfaces at temperatures of around 400 °C, followed by smaller grain growth above 850 °C. Electrical measurements of AlGaN/GaN MOS capacitors also showed that, although excessive oxidation treatment of AlGaN surfaces over around 700 °C has an adverse effect, interface passivation with the initial oxidation of the AlGaN surfaces at temperatures ranging from 400 to 500 °C was proven to be beneficial for fabricating high-quality AlGaN/GaN MOS gate stacks.