Vacuum-plasma-sprayed silicon coatings for biomedical application

Silicon coating was deposited on titanium alloy substrates by vacuum plasma spraying technology. The morphologies and phase composition of the coatings were analyzed by field-emission scanning electron microscopy and X-ray diffraction. The thermal expansion coefficient of silicon coating was measured to be about 3.70 × 10⁻⁶ K⁻¹. The bond strength of coating was approximately 20.6 MPa. The density, open porosity, roughness and Young's modulus of silicon coating were also measured. The as-sprayed silicon coating was treated by deionized water at 60 °C, 80 °C and 100 °C for a period of time and soaked in simulated body fluids to evaluate its bioactivity. The results showed that the water-treated coating could induce apatite to precipitate on its surface in simulated body fluid, indicating that the bioactivity of silicon coating was improved. The increase of temperature and duration of water treatment had a positive effect on the bioactivity of silicon coatings.     

Electrochemical deposition and evaluation of electrically conductive polymer coating on biodegradable magnesium implants for neural applications

In an attempt to develop biodegradable, mechanically strong, biocompatible, and conductive nerve guidance conduits, pure magnesium (Mg) was used as the biodegradable substrate material to provide strength while the conductive polymer, poly(3,4-ethylenedioxythiophene) (PEDOT) was used as a conductive coating material to control Mg degradation and improve cytocompatibility of Mg substrates. This study explored a series of electrochemical deposition conditions to produce a uniform, consistent PEDOT coating on large three-dimensional Mg samples. A concentration of 1 M 3,4-ethylenedioxythiophene in ionic liquid was sufficient for coating Mg samples with a size of 5 × 5 × 0.25 mm. Both cyclic voltammetry (CV) and chronoamperometry coating methods produced adequate coverage and uniform PEDOT coating. Low-cost stainless steel and copper electrodes can be used to deposit PEDOT coatings as effectively as platinum and silver/silver chloride electrodes. Five cycles of CV with the potential ranging from ?0.5 to 2.0 V for 200 s per cycle were used to produce consistent coatings for further evaluation. Scanning electron micrographs showed the micro-porous structure of PEDOT coatings. Energy dispersive X-ray spectroscopy showed the peaks of sulfur, carbon, and oxygen, indicating sufficient PEDOT coating. Adhesion strength of the coating was measured using the tape test following the ASTM-D 3359 standard. The adhesion strength of PEDOT coating was within the classifications of 3B to 4B. Tafel tests of the PEDOT coated Mg showed a corrosion current (I_CORR) of 6.14 × 10^?5 A as compared with I_CORR of 9.08 × 10^?4 A for non-coated Mg. The calculated corrosion rate for the PEDOT coated Mg was 2.64 mm/year, much slower than 38.98 mm/year for the non-coated Mg.     

Differential laser absorption and thermal emission for remote identification of opaque surface coatings

We experimentally and theoretically studied the phenomenon of thermal emission from nonvolatile liquid surface coatings following heating with a pulsed CO(2) laser. The effects of thermal diffusion across the liquid-air and liquid-substrate interfaces as well as the full absorption spectrum of the liquid are addressed theoretically. The differential temporal and intensity characteristics of the thermal emission signal from the heated surface coating, resulting from the differential heat deposition profile for on- and off-resonance excitation, are shown to be useful for the purposes of identifying different surface contaminants. The application of this technique to standoff thermal imaging of contaminated surfaces is discussed.     

Development of process for aluminising nickel alloy 718 strips for tube bundle support structures in liquid sodium–water steam generators

Abstract

The tubes in liquid sodium–water steam generators of the Indian prototype fast breeder reactor (PFBR) will be supported by corrugated nickel alloy 718 strips. Aluminisation of nickel alloy 718 strips has been chosen for this application because of the excellent performance of aluminide coatings in reducing impact fretting wear of the tubes due to flow induced vibrations and compatibility of the coating with liquid sodium at the operating temperature of the steam generators. Aluminisation of nickel alloy 718 strips for steam generator tube bundle support structures has been developed using a procedure involving thermal spraying of aluminium followed by diffusion heat treatment in vacuum atmosphere. One of the advantages of the technique is that it will coat only the desired surfaces of the strips, whereas in conventional pack cementation process, significant precautions have to be ensured. Furthermore, this process has enabled aluminisation to be carried out at a much lower cost than the conventional process of pack aluminising. The problems encountered during the initial trials and technology development, such as coating thickness and distortion, are discussed. A process flow chart for this procedure to take the job on an industrial scale is also reported. This process (under patenting) has been adopted for the aluminisation of corrugated strips for the support structures of one steam generator module and the steam generator for a test facility during the technology development phase, as also of all the steam generators being fabricated for the PFBR.     

MoS2/ta‐C‐Kombinationsschichten hergestellt durch Laser‐Arc‐Technologie

MoS₂/ta‐C coatings produced by laserarc‐technology A series of MoS₂ and combined MoS₂/ta‐C coatings were prepared by lasercontrolled arc evaporation (Laser‐Arc) in order to study the tribological coating behaviour under vacuum and atmospheric conditions. Very low friction coefficients down to 0.005 were measured under high vacuum. By using a ta‐C underlayer beneath the MoS₂ a increased lifetime up to 5×10⁵ load cycles could be obtained. Also under atmospheric conditions the underlayer had a beneficial effect on coating performance.     

Effect of chromium carbide coating on thermal properties of short graphite fiber/Al composites

A chromium carbide coating was synthesized onto graphite fibers by molten salts method to improve the interfacial bonding and thermal properties of short graphite fiber/Al composites which were fabricated by vacuum pressure infiltration technique. The graphite fiber/Al composites with different thicknesses of chromium carbide coatings were prepared through varying plating times to investigate the influence of chromium carbide layer on the microstructures and thermal properties of the composites. The combined Maxwell–Garnett effective medium approach and acoustic mismatch model schemes were used to theoretically predict thermal conductivities of the composites. The results indicated that the chromium carbide coating formed on graphite fiber surface in molten salts consists mainly of the Cr₇C₃ phase. The Cr₇C₃-coating layer with plating time of 60 min and thickness of 0.5 μm was found to be most effective in improving the interfacial bonding and decreasing the interfacial thermal resistance between graphite fiber and aluminum matrix. The 40 vol% Cr₇C₃-coated graphite fiber/Al composite with Cr₇C₃ thickness of 0.5 μm exhibited 45.4 % enhancement in in-plane thermal conductivity of 221 W m^?1 K^?1 compared to that of uncoated composite, as well as the coefficient of thermal expansion of 9.4 × 10^?6 K^?1, which made it as very interesting material for thermal management applications.     

Electrodeposition of dicalcium phosphate dihydrate coatings on stainless steel substrates

Cathodic reduction of an aqueous solution containing dissolved calcium and phosphate ions results in the deposition of micrometer thick CaHPO₄·2H₂O (dicalcium phosphate dihydrate) coatings on stainless steel substrates. The coating obtained at a low deposition current (8 mA cm^???2) comprises lath-like crystallites oriented along 020. The 020 crystal planes are non-polar and have a low surface energy. At a high deposition current (12 mA cm^???2), platelets oriented along 121? are deposited. CaHPO₄·2H₂O is an important precursor to the nucleation of hydroxyapatite, the inorganic component of bones. Differently oriented CaHPO₄·2H₂O coatings transform to hydroxyapatite with different kinetics, the transformation being more facile when the coating is oriented along 121?. These observations have implications for the development of electrodeposited biocompatible coatings for metal endoprostheses for medical applications.     

掺杂聚苯胺导电膜的制备及对核设施表面铀的去污

制备了掺杂导电聚苯胺可剥离膜，首次采用涂膜、电解联用去污方法，进行涂膜电解去除渗透到核设施金属材料内部形成氧化物的铀。在膜中，聚苯胺、盐酸、EDTA-2Na含量各为4％、0．5％～1%、1％；电解电压2．3V、电解时间25min～30min时，其去污率可达99％，优于其它的方法。     

Laser ablation protection of polymer matrix composites by adhesive inorganic coatings

Further utilization of polymer matrix composites (PMCs) in the aerospace industry is threatened by the development of laser weapons, resulting from weak oxidation resistance, low operation temperature and poor anti-laser ablation performance of the PMCs. Preparing an adhesive inorganic coating on the surface of components is an effective method to improve the laser irradiation resistance. Anti-laser ablation coatings composed of ZrO₂ as pigment and sodium silicate as binder with different curing agents (including SiO₂ and Na₂SiF₆) are fabricated on the PMCs substrate with brush painting. Influence of the different curing agents on anti-laser ablation of the coatings at the laser wavelength of 1064 nm is investigated. The rear surface temperature of substrate with coatings, containing SiO₂ and Na₂SiF₆, decreases from 240 to 60 and 70 °C, respectively, when testing at 1000 W for 5 s. After irradiation test at 1000 W for 10 s, the coating with SiO₂ as curing agent shows slight molten state on the surface, while the coating with Na₂SiF₆ is broke down, because coating containing SiO₂ possesses more compact microstructure and fewer cracks than that with Na₂SiF₆.     

Drug loading and release of Tobramycin from hydroxyapatite coated fixation pins

This paper evaluates the loading and release properties of Tobramycin incorporated by adsorptive loading from a solution into plasma sprayed and biomimetically coated Hydroxyapatite (HA) fixation pins. The aim of this study is to contribute towards designing a functional implant surface offering local release of the antibiotic agent to prevent post-surgical infections. Cathodic arc deposition is used to coat stainless steel fixation pins with a bioactive, anatase phase dominated, TiO₂ coating onto which a HA layer is grown biomimetically. The loading and release properties are evaluated by studying the subsequent release of Tobramycin using high performance liquid chromatography and correlated to the differences in HA coating microstructure and the physical conditions under loading. The results from these studies show that a dual loading strategy consisting of a solution temperature of 90 °C and a pressure of 6 bar during a loading time of 5 min release a sufficient amount of Tobramycin to guarantee the inhibition of Staphylococcus aureus up to 2 days for plasma sprayed HA coatings and for 8 days for biomimetic coatings. The present study emphasizes the advantages of the nanoporous structure of biomimetically deposited HA over the more dense structure of plasma sprayed HA coatings in terms of antibiotic incorporation and subsequent sustained release and provides a valuable outline for the design of implant surfaces aiming for a fast-loading and controlled, local drug administration.     

Amorphous silica containers for germanium ultrapurification by zone refining

We have studied the wetting behavior of molten germanium on silica ceramics and amorphous silica coatings in vacuum at a pressure of 1 Pa and a temperature of 1273 K. The results demonstrate that the wetting of rough surfaces of ceramic samples and coatings by liquid Ge is significantly poorer than that of the smooth surface of quartz glass. The contact angle of polished glass is ~100°, and that of the ceramics and coatings increases from 112° to 137° as the total impurity content of the material decreases from 0.120 to 1 × 10^–3 wt %. Using experimental contact angle data, we calculated the work of adhesion of molten Ge to the materials studied. Its value for the surface of the ceramics and coatings decreases from 0.45 to 0.20 J/m² with decreasing impurity content, whereas the work of adhesion to a smooth glass surface is 0.55 J/m². We have fabricated fused silica test containers coated with high-purity amorphous silica. Using horizontal zone refining, we obtained germanium samples with a carrier concentration difference on the order of 10¹¹ cm^–3.     

Liquid phase deposited titania coating to enable in vitro apatite formation on Ti6Al4V alloy

A recently developed “GRAPE^® technology” provides titanium or titanium alloy implants with spontaneous apatite-forming ability in vitro, which requires properly designed gaps and optimum heat treatment in air. In this study, titanium alloy and commercially pure (cp) titanium substrates were thermally oxidized in air before aligning pairs of specimens in the GRAPE^® set-up, i.e., titanium alloy and cp titanium substrates were aligned parallel to each other with optimum gap width (spatial design). A liquid phase deposition (LPD) technique was employed for titania coatings on titanium alloy substrate. Then, they were soaked in Kokubo’s simulated body fluid (SBF, pH 7.4, 36.5 °C) for 7 days to confirm the in vitro apatite formation on the substrates under the specific spatial design. Anatase-type titania coatings fabricated by using LPD technique led to the deposition of apatite particles within 7 days and showed apatite X-ray diffraction. On the other hand, thermally oxidized titanium alloy substrate in air and non-treated specimens did not show any apatite X-ray diffraction. These results indicated that the heterogeneous nucleation of apatite induced on anatase-type titania coating prepared by LPD technique when it was aligned parallel to thermally oxidized cp titanium substrate with optimum gap width.     

Characterisation, corrosion resistance and in vitro bioactivity of manganese-doped hydroxyapatite films electrodeposited on titanium

This work elucidated the corrosion resistance and in vitro bioactivity of electroplated manganese-doped hydroxyapatite (MnHAp) film on NaOH-treated titanium (Ti). The NaOH treatment process was performed on Ti surface to enhance the adhesion of the MnHAp coating on Ti. Scanning electron microscopy images showed that the MnHAp coating had needle-like apatite crystals, and the approximately 10 μm thick layer was denser than HAp. Energy-dispersive X-ray spectroscopy analysis revealed that the MnHAp crystals were Ca-deficient and the Mn/P molar ratio was 0.048. X-ray diffraction confirmed the presence of single-phase MnHAp, which was aligned vertically to the substrate. Fourier transform infrared spectroscopy indicated the presence of phosphate bands ranging from 500 to 650 and 900 to 1,100 cm^?1, and a hydroxyl band at 3,571 cm^?1, which was characteristic of HAp. Bond strength test revealed that adhesion for the MnHAp coating was more enhanced than that of the HAp coating. Potentiodynamic polarisation test showed that the MnHAp-coated surface exhibited superior corrosion resistance over the HAp single-coated surface. Bioactivity test conducted by immersing the coatings in simulated body fluid showed that MnHAp coating can rapidly induce bone-like apatite nucleation and growth. Osteoblast cellular tests revealed that the MnHAp coating was better at improving the in vitro biocompatibility of Ti than the HAp coating.     

Nanoceria coating imperfections and their effect on the high-temperature oxidation resistance of a 304 stainless steel

The microemulsion method was employed in this work for synthesizing nanocrystalline cerium oxide particles. Average nanoparticle sizes of 3.45 nm were produced by these means. XPS determinations indicated that both Ce³⁺ and Ce⁴⁺ are present in the synthesized nanoceria particles, with an average amount of 22.8 % of Ce³⁺ ions. It was found that the nanocrystalline cerium oxide coatings lead to significant improvements (of 1–2 orders of magnitude) in the high-temperature oxidation resistance of 304 SS. In addition, it was found that by decreasing the nanoparticle mean size from 10 to 3.45 nm, the effect of the coating protection was drastically improved. The experimentally determined parabolic rate constants k _p at 1073 and 1273 K for 304 SS indicated a reduction of up to two orders of magnitude when nanoceria coatings with 3.45 nm in mean size were applied. Also, the scale thickness was reduced from 15 to 5 μm when oxidized at 1073 K for 442 h. Coatings with purchased nanoceria particles (10 nm) were not as effective as the coatings with synthesized nanoceria. Apparently, at increasing nanoceria sizes, the oxidation protection is significantly reduced. In addition, it was found that the method of dipping for coating 304 SS does not provide a uniform coverage with nanoceria particles. Fe-rich ‘islands’ develop during high-temperature oxidation indicating that some regions do not exhibit the protection that nanoceria can provide. In contrast, relatively thick-coating regions on the steel substrate exhibit minimal oxidation, and the resultant scale is fine grained and uniform.     

HAp/Ti<Subscript>2</Subscript>Ni coatings of high bonding strength on Ti–6Al–4V prepared by the eutectic melting bonding method

Eutectic melting bonding (EMB) method is a useful technique for fabricating bioactive coatings with relatively high crystallinity and bonding strength with substrate on titanium substrates. Using the EMB method, hydroxyapatite/Ti₂Ni coatings were prepared on the surface of Ti–6Al–4V at a relatively low temperature (1,050 °C) in a vacuum furnace. The coatings were then characterized in terms of phase components, microstructure, bonding strength and cytotoxicity. The results showed that the coatings were mainly composed of HAp and Ti₂Ni, and the thickness of the coatings was approximately 300 μm. X-ray diffraction analysis showed that the coatings exhibited relatively high crystallinity. The tensile bonding strength between the coatings and the substrates was 69.68 ± 5.15 MPa. The coatings had a porous and rough surface which is suitable for cell attachment and filopodia growth. The cell culture study showed that the number of MG-63 cells increased, and the cell morphology changed with the incubation time. This study showed that the EMB method can be utilized as a potentially powerful method to obtain high quality hydroxyapatite coatings with desired mechanical and biocompatibility properties on Ti-alloy substrates.     

Notch Sensitivity of Fatigue Behavior of a Hi-Nicalon™/SiC-B4C Composite at 1,200 °C in Air and in Steam

The effect of holes on the fatigue life of a non-oxide ceramic composite processed via chemical vapor infiltration (CVI) was examined at 1,200 °C in laboratory air and in steam. The effect of holes on tensile strength at 1,200 °C was also evaluated. The composite comprised laminated woven Hi-Nicalon? fibers in an oxidation inhibited matrix, which consisted of alternating layers of silicon carbide and boron carbide. Fiber preforms had pyrolytic carbon fiber coating with boron carbon overlay applied. Unnotched specimens and specimens with a center hole having a radius to width ratio of 0.24 were tested in tension-tension fatigue at 0.1 Hz and at 1.0 Hz. The fatigue stresses ranged from 100 to 140 MPa in air and in steam. Fatigue run-out was defined as 10⁵ cycles at 0.1 Hz and as 2?×?10⁵ cycles at 1.0 Hz. The net-section strength was less than the unnotched ultimate tensile strength. Comparison of notched and unnotched data also revealed that the fatigue performance was notch insensitive in both air and steam environments. Composite microstructure, as well as damage and failure mechanisms were investigated.     

Beschichtungen für Life Science

Coatings for Life Science Thin film technologies being well known from semiconductor industry and corresponding technologies for microstructures are successfully used in Life Science (medical technology, pharmaceutical research or biology). These technologies are the base of the complex and miniaturized life science products. Life Science is a strongly growing part of microsystems technology enabling innovations like the cochlear implant replacing the human ear or new products like the retina implant, the latter being shortly before market entrance. Since 1960 the use of plastic material in this field grew rapidly and still today it is a growing market for plastic material manufacturers. The reasons are cheap production and easy way to sterilize plastic material disposables.Unfortunately in many cases plastic materials do not possess the desired surface properties. But an additional (functional) coating may lead to the necessary properties. Low pressure vacuum technology as a sub group of vacuum coating technology is well suited for this surface modification. Normally process temperatures are only between 20 °C – 60 °C. Ceramic and metal based products in Life Science can be modified, too. There is a wide range of coating applications e.g. diamond like coatings on stents leading to decreased thrombus formation. In this overview basics of vacuum coating technology and plasma technology are described and examplarily some aspects and applications in Life Science are shown.     

Soil contaminated with PAHs and nitro-PAHs: contamination levels in an urban area of Catania (Sicily,southern Italy) and experimental results from simulated decontamination treatment

This study is aimed at investigating the levels of polyaromatic hydrocarbons and nitro-polyaromatic hydrocarbons in polluted urban soils and the potential application of microwave heating as decontamination treatment. The soil samples were collected from an area of 0.05 km² of Catania (Sicily, southern Italy) rural site. HPLC in fluorescence and electrochemical–fluorescence detection mode were used for selective separation, identification and quantification of pollutants in soil samples. A bench-scale microwave treatment was performed irradiating a contaminated soil using different operating powers for removing both kinds of contaminants. Results reveal that soil pollutant concentrations were sometimes higher than those found in other locations. Polyaromatic and nitro-polyaromatic hydrocarbon levels observed suggest a strong contribution from incomplete combustion of gasoline or other fuels also due to the vicinity to the airport. Many polyaromatic hydrocarbon derivatives are more carcinogenic than the initial contaminant form and may have toxicological significance, even if present at much lower concentrations than their parent compounds. Thus, the environmental levels of these pollutants need to be monitored and removed. Contaminant removals from simulated microwave remediation show that the treatment is effective. Results also showed that contaminant features, especially polarity, significantly influence the dielectric properties of the soil and thus the final temperature reachable during the heating processes and the contaminant removals.     

Laser surface modification of titanium substrate for pulsed laser deposition of highly adherent hydroxyapatite

Biomedical implant devices made out of titanium and its alloys are benefited by a modified surface or a bioactive coating to enhance bone bonding ability and to function effectively in vivo for the intended period of time. In this respect hydroxyapatite coating developed through pulsed laser deposition is a promising approach. Since the success of the bioactive ceramic coated implant depends mainly on the substrate-coating strength; an attempt has been made to produce micro patterned surface structure on titanium substrate for adherent hydroxyapatite coating. A pulsed Nd-YAG laser beam (355 nm) with 10 Hz repetition rate was used for surface treatment of titanium as well as hydroxyapatite deposition. The unfocussed laser beam was used to modify the substrate surface with 500–18,000 laser pulses while keeping the polished substrate in water. Hydroxyapatite deposition was done in a vacuum deposition chamber at 400°C with the focused laser beam under 1 × 10⁻³ mbar oxygen pressure. Deposits were analyzed to understand the physico-chemical, morphological and mechanical characteristics. The obtained substrate and coating surface morphology indicates that laser treatment method can provide controlled micro-topography. Scratch test analysis and microindentation hardness values of coating on laser treated substrate indicate higher mechanical adhesion with respect to coatings on untreated substrates.     

Kostenstruktur von Plasmaverfahren

Cost Structure of Plasma Processes — The share of investment costs and operating expense in vacuum coating processes At a first glance coating costs of plasma processes seem to be dominated by high investments. Here it is shown that operating costs are at least of the same importance. Thus, it is reasonable to accept coating costs as only one contribution amongst others to the overall production costs. The example ?solar cells”? shows that further enhancement of the coating process is less effective compared to an increase of energy conversion efficiency. On the other hand it appears more effective for cost reduction of hard coatings to decrease energy consumption and to increase the deposition rate instead of minimization of investment costs for the coating machine. The cost structures of depositions from the liquid phase and plasma processes are of the same order but growing environmental demands clearly favor the latter one (no liquid waste, etc.). The commonly used argument, that it is always preferable to run coating processes at atmospheric pressure without the use of (expensive) vacuum equipment rather than under vacuum conditions needs to be reconsidered particularly when noble gases are necessary at atmospheric pressure to obtain equal qualities of the coatings.