Fabrication of a SiC/Si/MoSi2 multi-coating on graphite materials by a two-step technique

A SiC/Si/MoSi₂ multi-coating for graphite materials was prepared by a two-step technique. SiC whisker reinforcement coating was produced by pyrolysis of hydrogen silicone oil (H-PSO) at 1600 °C, and then the dense coating was formed by embedding with the powder mixture of Si, graphite and MoSi₂ at 1600 °C in argon atmosphere. The microstructure, thickness, phase and oxidation resistance of the coating were investigated. Research results showed that, the phase of multi-coating was composed of SiC, Si and MoSi₂. The thickness of the coating was about 300 μm. In addition, the coating combined with matrix well, and surface was continuous and dense. The oxidation pretreatment experiment was carried out in the static air at 1400 °C for 4 h before thermal failure tests and the specimens had 0.045% weight gain. Subsequent thermal failure tests showed that, the SiC/Si/MoSi₂ multi-coating had excellent anti-oxidation property, which could protect graphite materials from oxidation at 1000 °C in air for 12 h and the corresponding weight loss was below 1 wt%. Based on the surface morphology changes, oxidation pretreatment experiment and thermal failure tests enhanced densification of multi-coating and the coating had a certain self-healing ability.     

Ablation resistance of HfC–SiC coating prepared by supersonic atmospheric plasma spraying for SiC-coated C/C composites

In order to improve the ablation properties of carbon/carbon composites, HfC–SiC coating was deposited on the surface of SiC-coated C/C composites by supersonic atmospheric plasma spraying. The morphology and microstructure of HfC–SiC coating were characterized by SEM and XRD. The ablation resistance test was carried out by oxyacetylene torch. The results show that the structure of coating is dense and the as-prepared HfC–SiC coating can protect the C/C composites against ablation. After ablation for 30 s, the linear ablation rate and mass ablation rate of the coating are −0.44 μm/s and 0.18 mg/s, respectively. In the ablation center region, a Hf–Si–O compound oxide layer is generated on the surface of HfC–SiC coating, which is conducive to protecting the C/C composites from ablation. With the ablation time increasing to 60 s, the linear ablation rate and mass ablation rate are changed to −0.38 μm/s and 0.26 mg/s, respectively. Meanwhile, the thickness of the outer Hf–Si–O compound layer also increases.     

Preparation and ferroelectric properties of (Na0.5Bi0.5)0.94Ba0.06TiO3 thin films deposited on Pt electrodes using LaNiO3 as buffer layer

(Na_0.5Bi_0.5)_0.94Ba_0.06TiO₃ thin films were deposited on Pt/Ti/SiO₂/Si (1 1 1) and LaNiO₃/Pt/Ti/SiO₂/Si (1 1 1) substrates by a sol–gel process. The phase structure and ferroelectric properties were investigated. The X-ray diffraction pattern indicated that the (Na_0.5Bi_0.5)_0.94Ba_0.06TiO₃ thin film deposited on Pt/Ti/SiO₂/Si (1 1 1) substrates is polycrystalline structure without any preferred orientation. But the thin film deposited on LaNiO₃/Pt/Ti/SiO₂/Si substrates shows highly (1 0 0) orientation (f ≥ 81%). The leakage current density for the two thin films is about 6 × 10^?3 A/cm² at 250 kV/cm, and thin film deposited on LaNiO₃/Pt/Ti/SiO₂/Si substrates possessed a much lower leakage current under high electric field. The hysteresis loops at an applied electric field of 300 kV/cm and 10 kHz were acquired for the thin films. The thin films deposited on LaNiO₃/Pt/Ti/SiO₂/Si substrates showed improved ferroelectricity.     

Nanoindentation-induced deformation behaviour of tetrahedral amorphous carbon coating deposited by filtered cathodic vacuum arc

The nanoindentation-induced deformation behaviour of a ta-C (tetrahedral amorphous carbon) coating deposited on to a silicon substrate by a filtered vacuum cathodic vapour arc technique was investigated. The 0.17-μm-thick ta-C coating was subjected to nanoindentation with a spherical indenter and the residual indents were examined by cross-sectional transmission electron microscopy. The hard (~ 30 GPa) ta-C coatings exhibited very little localized plastic compression, unlike the softer amorphous carbon coatings deposited by plasma-assisted chemical vapour deposition. However, neither through-thickness cracks nor delamination was observed in the coating for the loads studied. Rather, the silicon substrate exhibited plastic deformation for indentation loads as low as 10 mN and at higher loads it showed evidence of both phase transformation and cracking. These microstructural features were correlated to the observed discontinuities in the load-displacement curves. Further, it was observed that even a very thin coating can modify the primary deformation mechanism from phase transformation in uncoated Si to predominantly plastic deformation in the underlying substrate.     

Facile synthesis of SiOx spheres or dumbbell-shaped β-SiC whiskers on expanded graphite by silicon vapor deposition

A facile method was developed to synthesize SiO_x spheres or dumbbell-shaped β-SiC whiskers on expanded graphite (SiO_x/EG or β-SiC/EG) by silicon vapor deposition without catalyst. With the carbon black atmosphere, the above hybrids were synthesized above 1100 °C in a graphite crucible where silicon powder was placed under the expanded graphite (EG). The growth of SiO_x spheres is controlled by vapor-solid mechanism at 1100 °C and 1200 °C. Namely, the active carbon atoms absorbed SiO (g) and Si (g) to form SiC nuclei. Then, the SiO₂, residual SiO (g) and Si (g) deposited on SiC nuclei to form SiO_x spheres. At 1300 °C and 1400 °C, the same SiO_x spheres formed on EG as well as many dumbbell-shaped β-SiC whiskers. The growth of dumbbell-shaped β-SiC whiskers is controlled by vapor-vapor and vapor-solid mechanism successively. In a word, firstly, the β-SiC whiskers with defects formed via the reaction between Si (g) and CO (g). After that, the SiO₂, residual SiO (g) and residual Si (g) preferentially deposited on defects, then deposited on other parts of β-SiC whiskers to form dumbbell-shaped SiC whiskers.     

Electron field emission from filtered arc deposited diamond-like carbon films using Au and Ti layers

In this work, tetrahedral diamond-like carbon (DLC) films are deposited on Si, Ti/Si and Au/Si substrates by a new plasma deposition technique — filtered arc deposition (FAD). Their electron field emission characteristics and fluorescent displays of the films are tested using a diode structure. It is shown that the substrate can markedly influence the emission behavior of DLC films. An emission current of 0.1 μA is detected at electric field E_DLC/Si=5.6 V/μm, E_DLC/Au/Si=14.3 V/μm, and E_DLC/Ti/Si=5.2 V/μm, respectively. At 14.3 V/μm, an emission current density J_DLC/Si=15.2 μA/cm², J_DLC/Au/Si=0.4 μA/cm², and J_DLC/Ti/Si=175 μA/cm² is achieved, respectively. It is believed that a thin TiC transition layer exists in the interface between the DLC film and Ti/Si substrate.     

Structure and characteristics of amorphous (Ti,Si)–C:H films deposited by reactive magnetron sputtering

The hydrogenated amorphous carbon films doped with Ti and Si ((Ti,Si)–C:H) were deposited on silicon substrates using reactive magnetron sputtering Ti₈₀Si₂₀ composite target in an argon and methane gas mixture. The structures of the films were analyzed by X-ray photoelectron spectroscopy and Visible Raman spectroscopy. The morphologies were observed by atomic force microscope. The friction coefficients of the films were tested on the ball-on-disc tribometer. The results indicate that the sp³/sp² ratios in the films can be varied from 0.18 to 0.63 by changing Ti and Si contents at various CH₄ flow rates. The surface of the films becomes smoother and more compact as the CH₄ flow rate increases. The lowest friction coefficient is as low as 0.0139 for the film with Ti of 4.5 at.% and Si of 1.0 at.%. Especially, the film exhibits a superlow value (μ < 0.01) under ambient air with 40% relative humidity in friction process. The superlow friction coefficient in ambient air may be, attributable to synergistic effects of a combination of Ti and Si in the film.     

Hard silicon carbonitride films obtained by RF-plasma-enhanced chemical vapour deposition using the single-source precursor bis(trimethylsilyl)carbodiimide

Amorphous silicon carbon nitride (Si/C/N) coatings were prepared on steel substrates by RF plasma-enhanced chemical vapour deposition (RF-PECVD) from the single-source precursor bis(trimethylsilyl)carbodiimide (BTSC). The films were characterised by X-ray diffraction (XRD), ellipsometry, FTIR, glow discharge optical emission spectroscopy (GDOES), optical microscopy, AFM, hardness measurements, scratch-, tribological- and corrosion-tests. The results of these studies show that the coatings obtained on the RF-powered electrode (cathode) were black, thick (>20 μm) and hard (21–29 GPa), while those grown on the grounded electrode (anode) were yellow, thin (<4 μm) and soft (∼5 GPa). Coatings on the anode contained around 19 at.% oxygen and exhibited silicon predominantly bonded to oxygen. In contrast, the oxygen content of the films deposited on the cathode was below 2 at.%. Silicon atoms in these coatings are co-ordinated predominantly to nitrogen and carbon. The surface of all coatings was very smooth with a maximum rms roughness between 2 nm and 5 nm for an area of 5 μm × 5 μm. Scratch and tribological tests reveal a brittle nature of the cathode-coatings and rather weak adhesion to the metal substrates. Salt-spray tests indicate an excellent corrosion resistance of the material.     

Effect of XeF laser treatment on structure of nanocrystalline diamond films

Nanocrystalline diamond (NCD) films were deposited on Si substrates by microwave plasma-enhanced chemical vapor deposition (MPECVD) using methane/hydrogen/oxygen (30/169/0.2 sccm) as process gases. Subsequently a thin (0.33 μm) and a thick (1.01 μm) NCD films were irradiated with XeF excimer laser (λ = 351 nm) with 300 and 600 mJ cm^? 2 of energy densities in air. The NCD films became rougher after laser irradiations. Fraction of graphitic clusters decreased but oxygen content increased in the thin NCD film after laser irradiation. Opposite phenomena were observed for the thick NCD films. Effect of laser irradiation to oxygenation and graphitization of NCD films was correlated with structural properties of free surface and grain boundaries of the thin and thick NCD films.     

Morphology of water-based chemical solution deposition (CSD) lead titanate films on different substrates: Towards island formation

This study aims at the deposition of PbTiO₃ (PT) islands prepared by a water-based chemical solution deposition (CSD). Two aqueous citrato-based PbTiO₃ precursor solutions, either with or without peroxide, are deposited by spin coating. The effect of different substrates on the formation of separated grains or islands is examined. It is observed that spin coating of a 0.6 M precursor solution on a Pt(1 1 1)/IrO₂/Ir/SiO₂/Si substrate gives the best results towards island formation. For this substrate, crystallizations are carried out between 600 °C and 900 °C. A final crystallization at 800 °C results in the highest degree of separation for the islands, while keeping the platinized substrate intact. The deposition of diluted precursors shows that it is possible to form islands from a precursor solution with a concentration down to 0.3 M. Solutions with a lower concentration result in irregularly shaped structures.     

Reactivity between liquid Si or Si alloys and graphite

The fundamental issues of the reaction at liquid Si/graphite interfaces between Si melting point (1412 °C) and 1600 °C are studied on the basis of results obtained with polycrystalline graphite concerning the growth kinetics of the interfacial reaction layer and the microstructure and morphology of this layer. Experiments were also performed using vitreous carbon substrates. Results are also reported for Si–Al alloys at 1000 °C. The elementary process controlling the growth kinetics is determined and a model is proposed to describe the different stages of the interfacial reaction.     

Diamond growth on Ir/CaF2/Si substrates

A new multi-layered structure of heteroepitaxial (1 0 0) and (1 1 1) Ir grown on CaF₂-buffered (0 0 1) and (1 1 1) Si wafers by UHV electron-beam evaporation was prepared for the deposition of diamond films. A two-step process of bias-enhanced nucleation and a subsequent growth by controlling the α growth parameter was performed to deposit (0 0 1) and (1 1 1) diamond films by chemical vapor deposition, respectively. Scratching or seeding by fine diamond powders was also attempted on the (1 1 1) substrates to enhance the diamond nucleation density. Raman spectroscopy, X-ray diffraction, scanning electron microscopy and high-resolution transmission electron microscopy were used to characterize the Ir/CaF₂/Si substrates as well as the diamond films grown on top of iridium layer. Heteroepitaxial relationship between the deposited diamond grains and (0 0 1) substrates has been observed.     

TaB2–SiC–Si multiphase oxidation protective coating for SiC-coated carbon/carbon composites

To improve the oxidation resistance of the carbon/carbon (C/C) composites, a TaB₂–SiC–Si multiphase oxidation protective ceramic coating was prepared on the surface of SiC coated C/C composites by pack cementation. Results showed that the outer multiphase coating was mainly composed of TaB₂, SiC and Si. The multilayer coating is about 200 μm in thickness, which has no penetration crack or big hole. The coating could protect C/C from oxidation for 300 h with only 0.26 × 10^?2 g²/cm² mass loss at 1773 K in air. The formed silicate glass layer containing SiO₂ and tantalum oxides can not only seal the defects in the coating, but also reduce oxygen diffusion rates, thus improving the oxidation resistance.     

Fabrication and characterization of in-situ duplex plasma-treated nanocrystalline Ti/AlTiN coatings

Plasma nitriding and plasma-assisted PVD duplex treatment was adopted to improve the load-bearing capacity, fatigue resistance and adhesion of the AlTiN coating. Ion etch-cleaning was applied for better adhesion before plasma nitriding. After plasma nitriding Ti interlayer was in-situ deposited by high power impulse magnetron sputtering (HIPIMS), followed by the AlTiN coating through in-situ deposition by advanced plasma-assisted arc (APA-Arc). The microstructure and properties of the duplex-treated coating were carefully characterized and analyzed. The results show that the thicknesses of the nitriding zone, the γ′-Fe₄N compound layer, the Ti interlayer and the AlTiN top layer with nanocrystalline microstructures are about 60 μm, 2–3 μm, 100 nm and 6.1 μm, respectively. The nitriding rate is about 30 μm/h and the AlTiN coating deposition rate reaches 6.1 μm/h. The interfacial adhesion of the Ti/AlTiN coating is well enhanced by ion etch-cleaning and a Ti interlayer, and the load-bearing capacity is also improved by duplex treatment. In addition, the instinct hardness of the Ti/AlTiN coating reaches 3368HV_0.05 while the wear rate coefficient of 5.394×10⁻⁸ mm⁻³/Nm is sufficiently low. The Ti/AlTiN coating, which possesses a high corrosion potential (E_corr=−104.6 mV) and a low corrosion current density (i_corr=4.769 μA/cm²), shows highly protective efficiency to the substrate.     

Electrophoretic deposition for fabrication of YSZ electrolyte film on non-conducting porous NiO–YSZ composite substrate for intermediate temperature SOFC

Electrophoretic deposition (EPD) of YSZ electrolyte films onto porous NiO–YSZ composite substrates that had been pre-coated with graphite thin layers was carried out in the following two means for solid oxide fuel cell application: one was EPD based on electrophoretic filtration by which YSZ films were formed on the reverse sides without the graphite layers; the other was EPD on a graphite thin layer pre-coated on the substrates. Dense YSZ electrolyte thin films were successfully obtained in both means, although it was difficult to form YSZ films that were strongly adherent to the substrates using the latter means. The densification of YSZ films was assisted by shrinkage of the substrates during co-firing. A single cell was constructed on ca. 5 μm thick dense YSZ films fabricated using the EPD based on electrophoretic filtration. Maximum power densities over 0.06, 0.35, 1.10 and 2.01 W/cm² were attained, respectively, at 500, 600, 700 and 800 °C on the cell.     

Deposition and characterization of diamond-like carbon films by microwave resonator microplasma at one atmosphere

Diamond-like carbon (DLC) films have been deposited at atmospheric pressure by microwave-induced microplasma for the first time. Typical precursor gas mixtures are 250 ppm of C₂H₂ in atmospheric pressure He. Chemically resistant DLC films result if the Si (100) or glass substrate is in close contact with the microplasma, typically at a standoff distance of 0.26 mm. The films deposited under this condition have been characterized by various spectroscopic techniques. The presence of sp³ CH bonds and ‘D’ and ‘G’ bands were observed from FTIR and Raman spectroscopy, respectively. The surface morphology has been derived from SEM and AFM and shows columnar growth with column diameters of approximately 100 nm. Likely due to the low energy of ions striking the surface, the hardness and Young's modulus for the films were found to be 1.5 ± 0.3 GPa and 60 ± 15 GPa respectively with a film thickness of 2 μm. The hypothesis that a high flux of low energy ions can replace energetic ion bombardment is examined by probing the plasma. Rapid deposition rates of 4–7 μm per minute suggest that the method may be scalable to continuous coating systems.     

Bias-enhanced nucleation of oriented diamonds on cone-like Si

Uniform distribution of bias-enhanced nucleation of diamond has been improved on Si substrate of an area of 1 × 1 cm² by using a dome-shaped Mo counter electrode in a microwave plasma chemical vapor deposition reactor. A nucleation density of 10⁹ cm² can be reached within a few minutes when the bias voltage of − 100 V is applied on the substrates. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) show that a single-crystalline diamond in a few nanometered size can be deposited on a volcano-shaped cubic SiC which is epitaxially formed on a Si cone. Examination reveals a large fraction of diamond nuclei are oriented along with one side of SiC on each Si cone. The Si cone formed on the Si substrate is due to plasma etching. The diamond nuclei have a shape close to rhombus in TEM. With further growth, secondary nucleation of diamond occurs on top of diamond nuclei and SiC which grows with Si cones. As a result, polycrystalline diamonds are deposited on each Si cone.     

Structure and dielectric properties of barium titanate thin films for capacitor applications

BaTiO₃ is a typical ferroelectric material with high relative permittivity and has been used for various applications, such as multilayer ceramic capacitors (MLCCs). With the tendency of miniaturization of MLCCs, the thin films of BaTiO₃ have been required. In this work, BaTiO₃ thin films have been deposited on Pt-coated Si substrates by RF magnetron sputtering under different deposition conditions. The films deposited at the substrate temperature from 550 °C–750 °C show a pure tetragonal perovskite structure. The films deposited at 550 °C–625  °C exhibit (111) preferential orientation, and change to (110) preferential orientation when deposited above 650 °C. The film morphologies vary with working pressure and substrate temperature. The film deposited at 625 °C and 4.5 Pa has the relative permittivity of 630 and the loss tangent of 2% at 10 kHz.     

Synthesis and characterization of CuO-hybrid silica nanocomposite coatings on SS 304

Pure and CuO-dispersed hybrid silica nanocomposite coatings were generated using sols synthesized from acid catalyzed hydrolysis and condensation of n-propyl trimethoxysilane and tetraethoxysilane in combination with copper nitrate. Coatings were initially deposited on soda lime glass substrates by dip coating followed by heat treatment at 150, 250 and 350 °C for 2 h in air and characterized. Coatings were subsequently deposited by dip coating on stainless steel 304 substrates. An optimized heat treatment temperature of 250 °C was chosen based on the contact angles of coatings on soda lime glass substrates and results of thermogravimetric/differential thermal analysis on the dried gels obtained from the sol synthesized from the combination of n-propyl trimethoxysilane and tetraethoxysilane. Gels heat-treated at 250 °C were characterized by X-ray diffraction, X-ray photoelectron spectroscopy and transmission electron microscopy for crystallinity. Characterization of the coatings was carried out with respect to thickness, water contact angle and adhesion. Corrosion testing of coatings on SS 304 was studied by potentiodynamic polarization measurements and electrochemical impedance spectroscopy after 1 h and 24 h exposure to 3.5% NaCl. The corrosion resistances of CuO-dispersed hybrid silica coatings after 1 h and 24 h exposure to 3.5% NaCl solution were higher than that of pure hybrid silica coatings, both of which had thicknesses ranging from 140 nm–200 nm.