Characterization of physical and biomedical properties of nitrogenated diamond-like carbon films coated on polytetrafluoroethylene substrates

A technique to coat hydrogen-free diamond-like carbon (DLC) films on polytetrafluoroethylene (PTFE) substrates has been developed by sputtering of a negatively biased graphite target in a mixture of argon and nitrogen plasma. The coated films were characterized by various methods to investigate their chemical, electronic features, and particularly their biomedical properties. DLC films produced by this method have up to 20% sp³ carbon bonds depending on the nitrogen concentration in the plasma. Raman spectroscopy revealed that, bond-disorder increases with nitrogen doping. The average grain size of DLC decreases in the nitrogen doped samples by almost 30%. The roughness of the uncoated PTFE substrate surfaces decreased dramatically from 660 nm to 170 nm after DLC coating. However, the nitrogen contents in the plasma have little effects on the roughness, the cluster size, and shapes. Electronic band gap of the samples decreases with adding nitrogen from ~ 2 eV in nitrogen-free samples to ~ 1 eV in nitrogenated samples. Lower adhesion and aggregation of platelets on PTFE surfaces coated with DLC-10% nitrogen and DLC-20% nitrogen have been observed while there is greater adhesion of platelets on DLC-30% nitrogen and DLC-40% nitrogen.     

The effects of tannins on adhesion strength and surface roughness of varnished wood after accelerated weathering

This study evaluated the effect of accelerated weathering on the adhesion strength and surface roughness of beech wood (Fagus orientalis) treated with mimosa and quebracho extracts and coated with polyurethane, water-based, and cellulosic varnishes. Untreated beech wood blocks and beech wood blocks treated with Tanalith-E were used as control samples. Test samples were exposed to accelerated weathering processes of 100 and 300 h. According to the test results, the mean adhesion strength of the wood samples impregnated with mimosa and quebracho tannins decreased by a maximum of 20%, while increases in the mean surface roughness (R _a) were detected. The highest adhesion strength and lowest mean surface roughness were obtained with polyurethane varnish. Moreover, the mean adhesion strength increased with the accelerated weathering up to 100 h and then decreased thereafter. As a result of the weathering process, the mean surface roughness increased and was thus negatively affected.     

Graphene oxide/hydroxyapatite composite coatings fabricated by electrophoretic nanotechnology for biological applications

Graphene oxide (GO) was firstly employed as nanoscale reinforcement fillers in hydroxyapatite (HA) coatings by a cathodic electrophoretic deposition process, and GO/HA coatings were fabricated on pure Ti substrate. The transmission electron microscopy observation and particle size analysis of the suspensions indicated that HA nanoparticles were uniformly decorated on GO sheets, forming a large GO/HA particle group. The addition of GO into HA coatings could reduce the surface cracks and increase the coating adhesion strength from 1.55 ± 0.39 MPa (pure HA) to 2.75 ± 0.38 MPa (2 wt.% GO/HA) and 3.3 ± 0.25 MPa (5 wt.% GO/HA), respectively. Potentiodynamic polarization and electrochemical impedance spectroscopy studies indicated that the GO/HA composite coatings exhibited higher corrosion resistance in comparison with pure HA coatings in simulated body fluid. In addition, superior (around 95% cell viability for 2 wt.% GO/HA) or comparable (80–90% cell viability for 5 wt.% GO/HA) in vitro biocompatibility were observed in comparison with HA coated and uncoated Ti substrate.     

Effect of delay in layering on the incremental adhesion of indirect dental composite resins

Adhesion of the new layer of indirect composite resin (ICR) to the already polymerized one may be affected when the time between the applications of subsequent layers is prolonged. The aim of this study was to compare the shear bond strength and degree of conversion (DC) of two ICR systems with different compositions and adhesive promoters, relayered after four time points. Disk shaped ICR materials (ICR1=Sinfony and ICR2=Targis) (N=96, n=48 per material) were fabricated and processed according to each manufacturer's instructions. They were then randomly assigned to 4 groups. While immediate layering acted as the control group, after 5 min, 24 h and 1-week delay, a new layer of the ICR of the same kind with the substrate was adhered to the substrate in polyethylene molds. The bonded specimens were loaded under shear (1 mm/min) and bond strength was calculated. DC of ICR1 and ICR2 were similar (75±1, 75±2, respectively). Delay in relayering at different timepoints did not significantly affect the adhesion between the incremental layers of ICR1 (32–34 MPa) compared to the control group (34 MPa), but the adhesion between the layers of ICR2 showed decreased bond strength after 24 h (30.9) and especially more after 1 week (25 MPa) compared to immediate layering (38.9 MPa). The effects of ageing before bonding additional layers of ICRs is variable, and depends on the chemical formulation of the ICR as reflected in the different brands.     

Microstructural and mechanical properties of porous Si3N4 carbon coated ceramic brazed with a cobalt-silicon filler

The Co_22.5Si_77.5 (at.%) braze was used to bond porous Si₃N₄ ceramics. The effects of brazing temperature on microstructure and the bonding strength of the joint were studied. The results reveal that no visible reaction layer was observed. The corresponding joint strength was low. In order to improve the joint strength a carbon coated modification of the porous Si₃N₄ substrate was suggested. The impact of this modification on the joint properties was examined. It was established that a SiC reaction layer with a thickness from ∼15 μm to ∼65 μm was formed at the interface and SiC nanowires were observed when the temperature increased from 1280 °C to 1340 °C. The maximum shear strength of the carbon coated and uncoated joints were 115 MPa and 44 MPa, respectively. The significant improvement of the joint strength was attributed to the SiC reaction layer and a strengthening by the presence of SiC nanowires. .     

HF etching effect on sandblasted soda-lime glass properties

Our objective in this work is to study the HF etching chemical treatment effect on the mechanical and optical properties of soda-lime glass eroded with 200 g fixed sand mass. We followed the evolution of these properties in relation to the chemical attack duration.The results show a clear improvement of the measured properties. The strength of the eroded samples is 44.23 ± 0.91 MPa. It increases up to 57.73 ± 1.76 MPa after 15 min of treatment and reaches 181.43 ± 23.69 MPa after 1 h. This last value is much higher than the as received glass strength (117.5 ± 10.48 MPa). The optical transmission of the eroded samples is about 18.5%. During the first 2 min of the chemical treatment, an important drop of the optical transmission (12%) was observed. However, improvement of the transmission was achieved for longer chemical treatment durations. After 8 h of treatment, the optical transmission increases up to 57%. Microscopic observations show that the HF attack causes the opening and the blunting of the surface cracks. In general, the surface state is improved during the chemical treatment.     

Anti-adhesion performance of various nitride and DLC films against high strength steel in metal forming operation

High strength steel (HSS) is widely used for automobile reinforcement parts and the quantity required is rapidly grown. However, the strength and hardness of the steel are relatively high, its formability is very low and adhesion to tool material can be easily found under forming operation. This paper aimed to evaluate the anti-adhesion performance of commercial nitride and DLC films coated on cold work tool steel against HSS in forming operation. The friction coefficient and wear rate of the non-coated ball (SKD11; hardness 60 ± 2 HRC), balls coated with TiN-PVD, TiCN-PVD, AlTiN-PVD, Nitride + CrN and DLC have been evaluated in sliding contact against SPFH 590 (JIS) disk. The scratch and nano-indentation tests were done on each type of coated tools to characterize the adhesive strength between the film and the substrate, and the hardness and the elastic modulus, respectively. The anti-adhesion performance of various films coated tool in metal stamping process was also investigated by performing U-bending experiment. The cold roll carbon steel; SPCC (JIS) was also used to compare a material transfer problem to the case of using HSS (JIS: SPFH590). As the results, for HSS sheet, the adhesion of workpiece material on a non-coated die surface was detected after 49 strokes whereas adhesion could not be found in case of stamping SPCC sheet up to 500 strokes. The TiCN, AlTiN, and Nitride + CrN films showed good anti-adhesion performance when forming HSS, while the TiN and DLC films did not provide the satisfied results.     

Adhesive properties of modified triticale distillers grain proteins

The adhesive properties of five protein extracts (DDGSae, DWGae, DDGSaa, DWGaa, and P6L) from triticale distillers grain were studied with/without modifications using 0.5 mM NaOH, 1 M urea or 60 μM glutaraldehyde. The dry, wet and soaked adhesion strength was measured using an automated bonding evaluation system (ABES II). The highest (p<0.05) adhesion strength was observed for acetic acid extracted proteins in all modifications. Among three different modifications, glutaraldehyde modification exhibited the greatest improvement. Glutaraldehyde modification increased the adhesion strength of DDGSaa from 2.56, 0.84, 1.11 MPa to 3.86, 2.03, 2.60 MPa for dry, wet and soaked adhesion strength, respectively. Increase in α-helical conformation and molecular weight was observed for glutaraldehyde modified proteins according FTIR and SDS-PAGE results.     

A multi-wall carbon nanotube-reinforced high-temperature resistant adhesive for bonding carbon/carbon composites

Multi-wall carbon nanotubes (MWCNTs) were chemically functionalized by 3-aminpropyltriethoxysilane and used to increase the strength and stiffness of an adhesive for joining carbon/carbon (C/C) composites. The silanized MWCNTs were uniformly dispersed in the adhesive with a good interface adhesion between them. When the content of silanized MWCNTs in the adhesive was 0.2 wt.%, average shear strength of the C/C joint was 10.40 MPa, which was 31% higher than that of neat C/C composites. The adhesive could be cured at room temperature with good heat-resistant property. The MWCNTs reacted with B₄C filler to establish strong B–O–C bond with C/C substrate.     

Characterization of thick and soft DLC coatings deposited on plasma nitrided austenitic stainless steel

Thick and soft a-C:H:Si coatings containing more than 45% hydrogen (thickness: 25–27 μm, hardness: 6 GPa, Young's Modulus 38 GPa and low ratio of sp³ bonds) were deposited by PACVD with a DC pulsed discharge on nitrided (duplex sample) and non-nitrided austenitic stainless steel (coated sample). After deposition, the chemical, microstructural and tribological properties were studied. Finally, the adhesion and the atmospheric corrosion resistance of a-C:H:Si coatings were also investigated.In pin-on-disk tests, the friction coefficient using an alumina pin of 6 mm in diameter as counterpart, under 0.59 GPa Hertzian pressure was 0.05 for the coated samples and 0.076 for the duplex samples. These values were more than one order of magnitude smaller than the friction coefficient of the nitrided sample without coating, which was around 0.65. In the coated samples, the wear loss could not be measured. In ball-on-disk tests under dry sliding conditions, the coatings were tested under different Hertzian pressures (1.29, 1.44 and 1.57 GPa) using a steel ball with a diameter of 1.5 mm as counterpart. Using a normal load of 9 N, the a-C:H:Si coating of the coated samples was broken and detached thus leading to a coefficient of friction of around 0.429. However, in contrast to that, the friction coefficient of the duplex samples remained stable and reached as maximum a value of 0.208.In abrasive tests, mass loss was undetectable in both duplex and coated samples. Furthermore it could be seen that the a-C:H:Si film showed only some smaller grooves and no severe damage or deformation. On the contrary, severe damage was observed in the only nitrided sample. With respect to adhesion, the critical load to break the coating was higher in the duplex sample (27 N) than in the only coated sample (16.3 N). By chemical analysis using the salt spray fog test, the duplex sample remained clean, but the coated sample failed and presented film delamination as well as general corrosion.     

Standardized methodology for in vitro assessment of bone-to-bone adhesion strength

Advancement of adhesives technology has been limited in orthopedics, which still has a striking reliance on metal hardware to help facilitate fracture healing. Despite an obvious clinical need, bone adhesives are not currently available on the market. Testing the bone adhesion strength and other aspects of the adhesive performance is extremely complex. This paper presents standardized methodology for in vitro assessment of bone-to-bone adhesion strength. Two test configurations (lap shear and butt joint) were used to comparatively assess the adhesion strength of four commercially available adhesive material, poly(methyl methacrylate) cement (CMW), glass-ionomer cement (FUJI), dimethacrylate resin (SB) and cyanoacrylate resin (VB), which were allowed to set under two environmental conditions (air and water). Under dry conditions, both test configurations generally yielded similar measurements of adhesion strength, which was around 1.1, 2.8 and 9.1 MPa for CMW, FUJI and VB, respectively. The dry adhesion strength for SB measured using the butt configuration (2.5 MPa) was 43.2% higher compared to that measured using lap shear (1.4 MPa). In a wet environment, the measured adhesion strength generally decreased and was dependent on the test configuration used. The failure mode of the samples adhered using CMW was adhesive, while that using FUJI, SB and VB was a combination of both adhesive and cohesive, independent of the test configuration and the setting condition. This proposed methodology is comparable to ASTM standards and can be used to study the effect of different biomaterial formulations as well as test parameters on the bone-to-bone adhesion strength, in a reproducible manner.     

Brazing of silicon nitride ceramic composite to steel using SiC-particle-reinforced active brazing alloy

Silicon carbide particles have been introduced as reinforcements in a commercially available active metal braze filler alloy (Incusil ABA, Wesgo Metals) used for the joining of ceramic-to-metal. The effect of particle reinforcement of the braze filler on the flexural strength of ceramic to metal joints has been investigated at room temperature and at elevated temperatures. An average four point flexural strength of nearly 400 MPa is achieved at room temperature when using Incusil ABA + 30 vol.% SiC (sandwich foil system) compared to 330 MPa with Incusil ABA alone. At a test temperature of 250 °C relaxation of residual stresses in the joints results in an average flexural strength of approximately 520 MPa when using Incusil ABA + 10 vol.% SiC. These values compare with an average room temperature flexural strength of nearly 800 MPa for the ceramic composite. The reaction products of the braze alloy at the joint interface were identified by SEM.     

Fault-tolerant hybrid epoxy-silane coating for corrosion protection of magnesium alloy AZ31

In this work, a hybrid epoxy-silane coating was developed for corrosion protection of magnesium alloy AZ31. The average thickness of the film produced by dip-coating procedure was 14 μm. The adhesion strength of the epoxy-silane coating to the Mg substrate was evaluated by pull-off tests and was found to be higher than 16 MPa both in dry and wet conditions. The hybrid epoxy-silane coating showed high corrosion resistance both when intact and when punched through by a needle. The low frequency impedance of intact coating was higher than 1 GΩ cm² after one month of immersion in 3.5% NaCl solution. Both, artificially induced defects and corrosion sites that appeared on the metal surface did not propagate. Their passivation behavior, that we call fault-tolerance, was observed by EIS, SVET-SIET and SEM-EDS. It was ascribed to the good adhesion, high coating integrity and corrosion inhibiting effect provided by diethylenetriamine used as epoxy hardener.     

Low temperature tensile lap-shear testing of adhesively bonded polyethylene pipe

This work studies the lap-shear strength performance of polyethylene pipeline bonded with acrylic adhesive in the temperature range -10 to +20 °C. Single lap shear test samples were firstly prepared at 20 °C under various clamping pressures and curing times to determine suitable conditions under which to prepare and test further samples at temperatures of -10, -5, 0, +5 and +20 °C. It was found that a decrease in curing/testing temperature to zero degrees resulted in a steady reduction in the lap-shear strength performance of the bonded joints from a mean value of 2.72 MPa at +20 °C to 1.15 MPa at 0 °C. Below zero degrees the strength of the bonded substrates was significantly reduced; no samples bonded at -5 °C had sufficient strength to test and only one sample bonded -10 °C was tested, which had very low strength of 0.105 MPa.     

Adhesion improvement of diamond coatings on cemented carbide with high cobalt content using PVD interlayer

At present, diamond coating is usually deposited on cemented carbide (WC-Co) tool with low Co content (Co ≤ 6 wt.%). It is more difficult to deposit diamond coating on WC-Co with high Co content because of the strong catalytic effect of Co. However, WC-Co tools with high Co content (Co ≥ 6 wt.%) are more widely used in difficult-to-cut materials machining because of their higher strength and better ductility. In this paper, the research was carried out on the adhesion performance of diamond coating on WC-Co (Co 10 wt.%). The deposition of diamond coating was conducted in hot filament chemical vapor deposition (HFCVD) system with the presence of the strong carbon-forming metallic interlayer (Nb, Cr or Ta), which was prepared using physical vapor deposition (PVD) on WC-Co substrate after chemical etching through a two-step process (Murakami solution and Caro's acid), which is a general way to treat the WC-Co substrate before growth of diamond coating. The results showed that the diamond films grown on the above treated WC-Co substrate have higher nucleation density, purity and adhesion strength than those on WC-Co substrates pretreated only using PVD interlayer or chemical etching. The PVD interlayer restrains the diffusion of Co as a result of high substrate temperature during the diamond film deposition, and consequently prevents the formation of the loosened layer induced by the removal of Co binder phase in the WC-Co substrate. The results also indicated that Nb interlayer leads to the most adhesion improvement of diamond films on the WC-Co inserts among the Nb, Ta and Cr interlayers.     

Preparation of silicon carbide ceramics using chemical treated powder by DCC via dispersant reaction and liquid phase sintering

Dense silicon carbide ceramics using chemical treated powder by DCC via dispersant reaction method and liquid phase sintering was reported. Ammonium peroxydisulfate ((NH₄)₂S₂O₈) and ammonium carbonate ((NH₄)₂CO₃) were used as acid and base solutions to treat the silicon carbide powder, respectively. Influence of silicon carbide powder with chemical treatment on the preparation of silicon carbide suspension was studied. It was indicated that 50 vol% and 52 vol% silicon carbide suspensions with viscosities of 0.71 Pa s and 0.80 Pa s could be prepared using acid and base treated powders. Influence of silicon carbide powder with chemical treatment on the coagulation process and properties of green bodies and sintered ceramics were studied. It was indicated that silicon carbide green bodies with compressive strength of 1.13 MPa could be prepared using base treated powder. Dense silicon carbide ceramics with relative density above 99.3% and flexural strength of 697 ± 30 MPa had been prepared by DCC via dispersant reaction and liquid phase sintering using Al₂O₃ and Y₂O₃ as additives at 1950 °C for 2 h.     

Microstructural,mechanical and thermal shock properties of triple-layer TBCs with different thicknesses of bond coat and ceramic top coat deposited onto polyimide matrix composite

In this study, a triple-layer thermal barrier coating (TBC) of Cu-6Sn/NiCrAlY/YSZ was deposited onto a carbon-fiber reinforced polyimide matrix composite. Effects of different thicknesses of YSZ ceramic top coat and NiCrAlY intermediate layer on microstructural, mechanical and thermal shock properties of the coated samples were examined. The results revealed that the TBC systems with up to 300 µm top coat thicknesses have clean and adhesive coating/substrate interfaces whereas cracks exist along coating/substrate interface of the TBC system with 400 µm thick YSZ. Tensile adhesion test (TAT) indicated that adhesion strength values of the coated samples are inversely proportional to the ceramic top coat thickness. Contrarily, thermal shock resistance of the coated samples enhanced with increase in thickness of the ceramic coating. Investigation of the TBCs with different thicknesses of NiCrAlY and 300 µm thick YSZ layers revealed that the TBC system with 100 µm thick NiCrAlY layer exhibited the best adhesion strength and thermal shock resistance. It was inferred that thermal mismatch stresses and oxidation of the bond coats were the main factors causing failure in the thermal shock test.     

Multi-impregnating pitch-bonded Egyptian dolomite refractory brick for application in ladle furnaces

A method of preparation of multi-impregnated pitch-bonded Egyptian dolomite refractory brick for ladle furnace is described. Brick samples were prepared from blend of calcined dolomite mineral and coal tar pitch. The blend was hot mixed and pressed under a compression force up to 151 MPa. Green bricks were baked for 2 h at temperatures up to 1000 °C. Voids in the baked bodies were filled with carbon by multiple impregnations using low-softening point coal tar pitch. Each impregnation step (30 min) was followed by calcination at 1000 °C. Brick samples containing 8–12 wt.% coal tar pitch binder and pressed under 108–151 MPa acquired quantify crushing strength. However, multi-impregnating favored the mechanical strength of the baked brick samples and improved their hydration resistance (>45 days). Dolomite brick samples containing 10 wt.% coal tar pitch and pressed at 108 MPa gave high hydration resistance (more than 60 days in normal condition) compared to the hydration resistance of the commercial bricks (30 days). The prepared brick samples have acceptable density, chemical stability, outstanding resistance and good mechanical properties would meet the requirements of Ladle furnace (LF) for steel making industry. In addition, estimation of production cost of the brick indicates it is competitive with the market price based on durability and service life time aspects.     

Hydrothermally crystallized Sr-containing bioactive glass film and its cytocompatibility

Sr-containing bioactive glass film with the Sr/(Ca+Sr) atomic ratio of 20% was sol-gel coated on titanium substrate, followed by hydrothermal treatment in a mixed phosphate solution (8 mM CaHPO₄ and 2 mM SrHPO₄) and other media at 120 or 140 °C. X-ray diffraction (XRD) analysis confirms amorphous nature of the gel powder calcined at 610 °C, but small peaks of Ca_1.8Sr_0.2SiO₄ or Ca_1.5Sr_0.5SiO₄ are also present. The absorption bands of Si-O-Si, PO₄ and OH groups and a weak absorption band of NO₃ groups appear in FT-IR spectrum of the calcined gel powder. Hydroxyapatite (HA) is detected for the hydrothermally treated sample by XRD and Raman analyses. Sr-containing HA nanocrystallites are formed on the film through a dissolution and precipitation mechanism in the hydrothermal treatment. The appearant bonding strength is 21±1 MPa for the both samples. In the test with MC3T3-E1 cells, the two coated samples exhibit larger viability, higher ALP levels and better cell morphology than the polished sample.     

Complex ceramic architectures by directed assembly of ‘responsive’ particles

Surface functionalization of alumina powders with a responsive surfactant (BCS) leads to particles that react to a chemical switch. These ‘responsive’ building blocks are capable of assembling into macroscopic and complex ceramic structures. The aggregation follows a bottom up approach and can be easily controlled. The directed assembly of concentrated suspensions leads to highly dense (∼99%) ceramic components with average 4-point bending strength of ∼200 MPa. On the other hand, the emulsification of suspensions with concentrations from 7 to 43 vol% and 50 vol% decane results in emulsions with different properties (stability, droplet size and distribution). The oil droplets provide a soft template confining the alumina particles in the continuous phase and at the oil/water interfaces. Aggregation of these emulsions followed by drying and sintering leads to macroporous (pore sizes ranging from 30 to 4 μm) alumina structures with complex shapes and a wide range of microstructures, from closed cell structures to highly interconnected foams with total porosities up to 83%. Alumina scaffolds with ∼55% porosity can reach crushing strength values above 300 MPa in compression and ∼50 MPa in 4-point bending.