Electrochemical codeposition of Sn–Pb–metal alloy along with detonation synthesis nanodiamonds

In this work, it is shown that the addition of detonation nanodiamonds into electrolytes for electrochemical deposition of the alloy of Sn–Pb results in considerable improvement of coating properties such as microhardness, microporosity, soldering ability and throwing power of the electrolytes.     

High pressure–high temperature growth of diamond crystals using split sphere apparatus

An overview of the application of crystal growth fundamentals in the high pressure–high temperature production of diamond by solvent/catalyst technique is presented. The process, also called temperature gradient process, makes use of a molten catalyst to dissolve carbon from a source (graphite or diamond powder) and transport the dissolved carbon to a growth site where they precipitate on a diamond seed. The pressure and temperature requirements for the process are generally around 5.0–6.5 GPa and 1300–1700 °C, depending on the chemistry of the solvent used and the desired crystal geometry. In spite of major progress in the science and technology of diamond growth, large scale commercial production of diamonds single crystals for jewelry or electronic applications has not been feasible until recently. This has been mainly due to the substantial cost associated with the presses needed, and the difficulties in controlling the growth parameters and catalyst chemistry. The recent developments in the commercial production of diamond single crystals utilizing the Split Sphere pressurization apparatus are discussed.     

Self-healing corrosion protection by nanostructure sol–gel impregnated with propargyl alcohol

Zirconia based nanostructured hybrid sol–gel coating, impregnated with propargyl alcohol (PA) to hinder corrosion of mild steel was studied. Zirconia nano-particles (TPOZ) contained sol–gel was synthesized using 3-glycidoxypropyltrimethoxysilane (GPTMS) as precursor and subsequently optimized for internal cohesion as well as adhesion to the mild steel substrate to assess the consequent effect on suppression of corrosion damage in 0.5 M NaCl solution. Electrochemical Impedance Spectroscopy (EIS) and Scanning Electron Microscopy (SEM) results demonstrated the effect of coating integrity on impeding corrosion. Experiments on mild steel specimens coated with hybrid sol–gel films following mechanical polishing render superior corrosion resistance to mild steel in contrast to those undergoing electrochemical polishing with marked lower surface roughness. Results also proved of beneficial effect of low and exact concentration of PA on sol–gel coat's barrier properties evident from diminished corrosion current and other electrochemical indicators.     

Improvement in adhesion of diamond films on cemented WC substrate with Ti–Si interlayers

Diamond films were deposited on the cemented WC+(3–5)% Co substrates by a microwave plasma chemical vapor deposition system. The substrates were pretreated with various processing steps before diamond deposition, including: polishing, etching for Co removal, Ti coating by DC sputter, and amorphous Si coating by E-gun. The residual stress of the films was determined by both Raman shift and low incident beam angle X-ray diffraction (LIBAD) methods. The adhesion of the films was evaluated by indentation adhesion testing. The film morphology and film–substrate interface structure were examined by SEM and Auger electron spectroscopy, respectively. The results show that Ti–Si can be a good interlayer to improve film adhesion and inhibit diffusion of Co to the substrate surface on diamond nucleation. This is due to the formation of strong TiC and SiC bonding to enhance film adhesion; Si acts as a promoter for diamond nucleation, and the residual stress with application of interlayer is much lower than that interlayer-free. The results also show the existence of an optimum Ti thickness for the best film adhesion.     

Recent IBIC measurements on epitaxial CVD diamond

Frontal IBIC (Ion Beam Induced Current) mesurements have been carried out on new single crystal epitaxial CVD diamond. The sample consists of about 100 μm synthetic diamond grown by microwave CVD on a 300 μm thick, low cost, HPHT diamond substrate (see Balducci et al. – this conference). Both proton and alpha microbeams of energies 3 and 4.5 MeV have been used, with a beam diameter spot of about 1.5–3 μm. Scanned areas varied from 450 μm × 450 μm down to 150 μm × 150 μm and the homogeneity of charge collection efficiency (cce) was suitably monitored. At voltage bias of 80–100 V, the average cce was in the range 42–50%. Depending on the scanned surface area and on the beam type, energy resolutions FWHM from 1.3% to 4.1% FWHM have been obtained, even at counting rates as high as 700 cps.     

Deposition of stress-free diamond films on Si by diamond/β-SiC nanocomposite intermediate layers

Stress-free diamond films have been synthesized by using microwave plasma enhanced chemical vapour deposition (MWCVD) technique. Nanocrystalline diamond/β-SiC gradient composite film system was used as an interlayer for the diamond top layers. As a result, Raman phonon line shifts (obtained from diamond top layers) corresponding to diamond are recorded very close to the stress-free value of 1332 cm^− 1. This implies an extraordinarily low biaxial compressive stress state in the diamond films. The interlayer accommodates to a considerable extent, the stress that occurs due to the difference in the thermal expansion coefficient of the diamond film and the underlying substrate.     

Incorporation of hydrogen in diamond thin films

In this investigation, diamond thin films with grain size ranging from 50 nm to 1 µm deposited using hot filament chemical vapor deposition (HFCVD) have been analyzed by elastic recoil detection analysis (ERDA) for determining hydrogen concentration. Hydrogen concentration in diamond thin films increases with decreasing grain size. Raman spectroscopy and X-ray photoelectron spectroscopy (XPS) results showed that part of this hydrogen is bonded to carbon forming C–H bonding. Raman spectra also indicated the increase of non diamond phase with the decrease in crystallite size. Incorporation of hydrogen in the samples and increase of hydrogen content in nanocrystalline sample are discussed. Large separation between filament and substrate used for the synthesis of nanocrystalline film helped to understand the large incorporation of hydrogen in nanocrystalline diamond films during growth. The study addresses the hydrogen trapping in different samples and higher hydrogen concentration in nanocrystallites by considering the synthesis conditions, growth mechanisms for different grain sized diamond films and from the quality of CVD diamond films.     

Oxidation behavior of C–SiC composites with a Si–W coating from room temperature to 1500°C

Oxidation tests of carbon fiber reinforced silicon carbide composites with a Si–W coating were conducted in dry air from room temperature to 1500°C for 5 h. A continuous series of empirical functions relating weight change to temperature after 5 h oxidation was found to fit the test results quite well over the whole temperature range. This approach was used to interpret the different oxidation mechanisms. There were two cracking temperatures of the matrix and the coating for the C–SiC composite. Oxidation behavior of the C–SiC composite was nearly the same as that of the coated C–C composite above the coating cracking temperature, but weight loss of the C–SiC composite was half an order lower than that of the coated C–C composite below the cracking temperature. As an inhibitor, the SiC matrix increased the oxidation resistance of C–SiC composites by decreasing active sites available for oxidation. As an interfacial layer, pyrolytic carbon decreased the activation energy below 700°C. From 800°C to 1030°C, uniform oxidation took place for the C–SiC composite, but non-uniform oxidation took place for the coated C–C composite in the same temperature range. The Knudsen diffusion coefficient could be used to explain the relationship between weight loss and temperature below the coating cracking temperature and the matrix cracking temperature.     

Pt–Ru–Co catalysts for PEMFC synthesized by combustion

In this work the novel use of urea combustion synthesis as a straightforward method for the preparation of a trimetallic alloy, 60 Pt–30 Ru–10 Co (mol%) is described. A novel composition in the Pt–Ru–Co ternary system has been considered for a possible substitution of commercial anode catalysts in PEMFC. The specific surface area (102 m²/g) of the carbon supported catalysts produces anodes which gave power density stable values of 260 mW/cm². The XPS (X-ray Photoelectron Spectrometry) data showed that combustion synthesis produces Platinum and Cobalt segregated in the catalyst’s surface, these metals are layered structured and exhibit different oxidation states.     

Preparation and characterization of sol–gel Al2O3/Ni–P composite coatings on carbon steel

Ceramic films have been applied to improve the resistance against high temperature oxidation of carbon steels. Alumina film was prepared on carbon steel surface by a dip coating technique. Electroless Ni–P plating film has been pre-deposited as an intermediate layer to improve the adherence of the film to carbon steel substrate. The oxidation kinetics of coated sample was investigated by measuring weight gain at 800 °C for 100 h. The surface and cross-section morphology of samples before and after oxidation were characterized by scanning electron microscopy (SEM). The composition and element distribution at the interface of the coated samples were analyzed by energy dispersive spectroscopy (EDS) and EMAX.The results show that the composite coating is uniform. The alumina coating adhesion strength to the substrate is up to 20 ± 2 N in scratch test because the alumina film presents interdiffusion of nickel and aluminum during heat treatment. The oxidation resistance test indicates higher oxidation resistance of as-coated carbon steel comparing to uncoated ones.     

Effect of calcium promoter on a precipitated iron–manganese catalyst for Fischer–Tropsch synthesis

A series of precipitated Fe/Mn Fischer–Tropsch synthesis (FTS) catalysts incorporated with calcium promoter were prepared by the combination of co-precipitation and spray-drying technology. The catalysts were characterized by using N₂ physisorption, CO₂ temperature-programmed desorption and Mössbauer spectroscopy methods. FTS performances of the catalysts were tested in a 1 dm³ continuous stirred tank reactor. It is found that calcium promoter has negligible effect on the textural properties, and the addition of calcium promoter can enhance the surface basicity of the catalyst. An appropriate amount of calcium promoter can promote the reduction and carburization of the catalysts during the reduction and Fischer–Tropsch synthesis (FTS) reaction in syngas, but the excessive addition of calcium promoter will decrease the extent of reduction and carburization. The reaction results indicated that the activities of both FTS and water-gas shift (WGS) decrease with the incorporation of calcium promoter. Calcium promoter can inhibit the hydrogenation ability, suppress the formation of methane, and enhance the selectivities to olefin and higher molecular weight products.     

On the effect of La–Cr–O– phase composition on diesel soot catalytic combustion

A series of samples of La–Cr–O– perovskites were designed as catalysts for diesel soot combustion. They were prepared by using co-precipitation method, at ambient temperature using ammonia followed by a hydrothermal treatment (T = 200 °C, P = 20 atm, t = 24 h). All the chromium-containing precursors were then calcined at high temperature to develop the oxide catalyst. Two phase composition 86%LaCrO₃–(14%) La₂CrO₆ or 94%LaCrO₃–6%La₂O₃ were formed depending on the atmosphere of calcination (oxygen or hydrogen respectively) used. Their respective BET surface areas were 1.1 and 6.5 m² g⁻¹. Highly crystalline, pure phase of LaCrO₃ and La₂CrO₆ powders were also prepared, with BET area of 4 and 3 m² g⁻¹, respectively. The crystalline structure and properties of all samples were characterised by X-ray diffraction (XRD), using Rietveld refinement, and temperature-programmed reduction (TPR) techniques. O₂-TPD measurements performed on all samples showed the presence of suprafacial, weakly chemisorbed oxygen only for LaCrO₃, which contributes actively to soot combustion. TPR study performed on all catalysts showed that while pure LaCrO₃ and La₂O₃ samples did not reduce, the biphasic catalysts showed the presence of oxygen depletion peaks characteristic of lattice oxygen mobility in the samples at ca. 665 °C. Catalytic combustion of diesel soot was studied over all catalysts. The results showed that pure LaCrO₃ exhibited significant catalytic activity which was sensitively affected by the modifier La₂CrO₆ or La₂O₃.     

Microstructural and biological properties of nanocrystalline diamond coatings

In this study, the microstructural, mechanical, adhesion, and hemocompatibility properties of nanocrystalline diamond coatings were examined. Microwave plasma chemical vapor deposition (MPCVD) was used to deposit nanocrystalline diamond coatings on silicon (100) substrates. The coating surface consisted of faceted nodules, which exhibited a relatively wide size distribution and an average size of 60 nm. High-resolution transmission electron microscopy demonstrated that these crystals were made up of 2–4 nm rectangular crystallites. Raman spectroscopy and electron diffraction revealed that the coating contained both crystalline and amorphous phases. The microscratch adhesion study demonstrated good adhesion between the coating and the underlying substrate. Scanning electron microscopy and energy dispersive X-ray analysis revealed no crystal, fibrin, protein, or platelet aggregation on the surface of the platelet rich plasma-exposed nanocrystalline diamond coating. This study suggests that nanocrystalline diamond is a promising coating for use in cardiovascular medical devices.     

A stable suspension of single ultrananocrystalline diamond particles

As the result of successful disintegration of tight aggregates in detonation nanodiamond by stirred-media milling with microbeads, stable colloid of nanodiamond particles with a mean core size of 4 nm is obtained for the first time, but the colloid is colored deep black. X-ray diffraction, Raman scattering, HRTEM, UV–vis absorption spectra and viscosity data were used to characterize the colloid. It was suggested that the reason for the unexpected black color of the suspension is a result of graphitic partial surface (π-electrons formation of 4 nm diamond particles) induced by strong collision with beads during milling process. π-electrons are a reason of double electric layer formation and high viscosity of the suspension. Theoretical estimations fitted experimental data.     

A compression test for adhesion evaluation of diamond coatings

A key requirement of an effective coating is its adequate adhesion to the substrate. Thus, reliable test methods to evaluate coating adhesion and to characterize the deposition parameters affecting it are necessary for the systematic development of such coatings. The conventional technique for measuring diamond coating adhesion, the scratch test, is unreliable because of wear of the stylus and influences of the substrate. Thus, a noncontact technique (compression test) of evaluating the adhesion of diamond coatings on brittle substrates was modelled and developed. This method utilizes the differences in Young's modulus between the coating and the substrate via application of an external load in order to generate interfacial stresses and debond the coating. An innovative three-dimensional numerical model, based on combining the variational and boundary integral approaches, was utilized to link the indirect (i.e. load) to the direct (i.e. debond shear stress or elastic energy of delamination) characteristics of adhesion. Factors affecting the adhesion strength of the diamond coatings are discussed in relation to the process parameters. This test offers an excellent alternative to conventional techniques for measuring the adhesion strength of diamond coatings on brittle substrates.     

Coating films prepared by photoreactions of the surface‐modified diamond powder and PET film with a binder agent

The surface‐modified diamond and PET film underwent photopolymerization rapidly with a binder agent to afford coating films of interpenetrating network (IPN) structure. The coating films thus formed exhibit higher tensile strength, thermal stability, and adhesion strength to the PET film. The inert surfaces of pristine diamond (PD) and PET film were modified by different chemicals and procedures to introduce epoxide and methacryloyl groups, respectively, on their surfaces. A coating agent consisting of an epoxide group containing modified diamond (called ED), a binder agent, and photoinitiators was prepared. After applying the coating agent to the substrate (a glass plate or a methacryloyl group containing PET film, MMA‐PET) and degassing under reduced pressure, the thin film of the coating agent was exposed to UV light (λ_max; 365 nm) at room temperature to yield a coating film of IPN‐structure. The tensile strength and thermal properties of the ED‐containing free coating film (called free film) increased with the amount of ED embedded, whereas the strength of the PD‐containing free film decreased with the amount of PD embedded. The adhesion strength of the coating film on the MMA‐PET improved significantly by the free radical polymerization of the methacryloyl groups on the MMA‐PET and the acrylate resin in the binder agent. The surface photoreactions of ED and MMA‐PET with the binder agent were confirmed by modeling. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Mechanical properties of nanocrystalline diamond/amorphous carbon composite films prepared by microwave plasma chemical vapour deposition

Nanocrystalline diamond films (NCD) have been deposited by microwave plasma chemical vapour deposition from CH₄/N₂ mixtures with varying methane content. They consist of diamond nanocrystallites with sizes of 3–5 nm embedded in an amorphous matrix with grain boundary widths of 1–1.5 nm. The CH₄ content in the gas phase has almost no influence on the microscopic structure but a strong effect on the macroscopic structure and morphology. The mechanical and tribological properties of these films have been investigated by nanoindentation, nano tribo tests, and nano scratch tests. The hardness of a 4-μm-thick film deposited with 17% methane was about 40 GPa, the indentation modulus 387 GPa, and the elastic recovery 75%. Ball-on-disk tests against an Al₂O₃ ball revealed, after initially higher values, a friction coefficient of ≤0.1. Tribo tests and scratch tests proved a strong adhesion and a protective effect on silicon substrates. Finally, the correlations between the macroscopic structure of the films and their mechanical and tribological properties are discussed.     

UV-Light Absorption Properties of Cr-Doped Polyethyleneglycol (PEG)/γ-Glycidoxypropyltrimethoxysilane (GPTMS)/Chelated-Titanium Coating Materials Prepared by the Sol–Gel Process

New hybrid inorganic–organic glass coating materials, which contain polyethyleneglycol/γ-glycidoxypropyltrimethoxysilane/titanium(IV)-n-propoxide(2-methoxyethylacetoacetate)/chromium(III)nitrate [PEG/GPTMS/Ti(OR)(2-MEAA)/Cr³⁺] have been developed for UV-light absorption by using the sol–gel process. The effect of agitation time and temperature on UV-light absorption was investigated. The titanium complex was characterized by ¹H-NMR and FTIR spectroscopies. UV–Vis spectroscopy was used to investigate the optical properties of the coating materials. The results show that the coated glass has very low transmission in the UV region (300–400 nm) compared to the uncoated glass, especially at 150, 200, 250 and 300°C treatment temperatures after 1- and 18-hour agitation times. The UV-light transmission of the coated glass was not different from the uncoated glass between 80–100°C and 350–500°C.     

A simulation study on gas-to-liquid (natural gas to Fischer–Tropsch synthetic fuel) process optimization

A simulation study on gas-to-liquid (natural gas to Fischer–Tropsch synthetic fuel) process was carried out in order to find optimum reaction conditions for maximum production of synthetic fuel. Optimum operating condition for GTL (gas-to-liquid) process was determined by changing reaction variable such as temperature. During the simulation, overall synthetic process was assumed to proceed under steady-state conditions. It was also assumed that physical properties of reaction medium were governed by RKS (Redlich–Kwong–Soave) equation. ATR (auto-thermal reforming) in synthesis gas production unit and slurry phase reaction over Co-based catalyst in FTS (Fischer–Tropsch synthesis) unit were considered as reaction models for GTL process. The effect of reaction temperature on CO conversion and C₅–C₂₀ hydrocarbon yield in FTS unit was mainly examined. Simulation and experimental results showed that optimum reaction temperature in FTS unit was 255 °C. Simulation results were also compared to experimental results to confirm the reliability of simulation model. Simulation results were reasonably well matched with experimental results.     

Comparison of the chemical composition of boron-doped diamond surfaces upon different oxidation processes

In spite of the high stability of polycrystalline diamond, oxidation of the hydrogenated surface is relatively easy to perform. This results in the introduction of ether (C–O–C), carbonyl (CO) and hydroxyl (C–OH) groups on the surface. For further surface functionalization, it is important to quantify the presence of each group on the diamond surface when different oxidation processes are used. In this paper, we investigate the composition of oxidized boron-doped diamond surfaces using X-ray photoelectron spectroscopy (XPS) when electrochemical, photochemical or oxygen plasma methods were employed to introduce oxygen functionalities on as-deposited diamond interfaces. Cyclic voltammetry and C–V measurements were additionally performed to identify more clearly the formation of C–OH, C–O–C and/or CO functions.