Effect of crystallization on the property of hard enamel coating on steel substrate

Crystallization treatment was conducted to improve hardness of an enamel coating on steel. Microstructure change of the enamel steel interface was observed. Phase transformation of the glassy enamel was analyzed, and adhesion of the enamel to steel was evaluated. As crystallization time increases, the as-fired enamel/steel interface roughens, protrudes to form anchor points and develops into dendrites growing into grain boundaries of the steel substrate. An adherence factor η is proposed to predict the adherence of the enamel/substrate interface metallographically. Microhardness of the enamel increases from 582HV_0.05 as-fired to 991HV_0.05 after crystallization treatment at 840 °C for 20 min, which is attributed to the transformation of the vitreous enamel into NaAlSi₂O₆ crystals during the crystallization treatment. Microstructure observation indicates that the white needle-like NaAlSi₂O₆ crystals in the as-fired glassy enamel matrix is increased in number and their morphology change from large aspect ratio into coarsened ones with increasing time at 840 °C crystallization treatment. The as-fired enamel coating exhibits an impact energy of 0.81 J, and the crystallization treatment at 840 °C increases impact energy of the enamel coating from 1.05 to 1.56 J with changing crystallization time from 5 to 20 min. A regression formula of impact energy associated with adherence factor is obtained to evaluate adhesion of the enamel to steel substrate on the basis of metallographic measurement. The aluminum melt corrosion resistance of the enamel is increased with increasing crystallization of its glassy matrix.     

In vitro biological performance of nano-particles on the surface of hydroxyapatite coatings

The biocompatibility of a kind of heat-treated bilayer hydroxyapatite (HA) coatings with nano-particles was investigated, mainly in terms of the immersion in simulated body fluid (SBF) and osteoblast adhesion. Scanning electron microscopy (SEM) was used to observe the morphology of coatings and cellular adhesion. The phases present in the coatings were determined by X-ray diffraction (XRD). Calcium ion (Ca²⁺) concentration in SBF was measured by Atomic absorption spectrophotometer. The results show nano-HA heat-treated at 650 °C for 0.5 h (BBCs) is comparatively stable during immersion in SBF and favor of the adhesion of osteoblasts. Cellular filopodia adhere firmly to the nano-particles and stretch in various direction.     

Coating formation by plasma electrolytic oxidation on ZC71/SiC/12p-T6 magnesium metal matrix composite

Plasma electrolytic oxidation (PEO) of a ZC71/SiC/12p-T6 magnesium metal matrix composite (MMC) is investigated in relation to coating growth and corrosion behaviour. PEO treatment was undertaken at 350 mA cm⁻² (rms) and 50 Hz with a square waveform in stirred 0.05 M Na₂SiO₃.5H₂O/0.1 M KOH electrolyte. The findings revealed thick, dense oxide coatings, with an average hardness of 3.4 GPa, formed at an average rate of ∼1 μm min⁻¹ for treatment times up to 100 min and ∼0.2 μm min⁻¹ for later times. The coatings are composed mainly of MgO and Mg₂SiO₄, with an increased silicon content in the outer regions, constituting <10% of the coating thickness. SiC particles are incorporated into the coating, with formation of a silicon-rich layer at the particle/coating interface due to exposure to high temperatures during coating formation. The distribution of the particles in the coating indicated growth of new oxide at the metal/coating interface. The corrosion rate of the MMC in 3.5% NaCl is reduced by approximately two orders of magnitude by the PEO treatment.     

Laser treatment of white China surface

The surface of gloss fired porcelain with and without raw glaze coating was radiated by a CO₂ laser working at 10.6 μm, a choice resulted from spectroscopic studies of suspensions made of China. The shine of the untreated sample was defined as the distribution of micro-droplets on the surface. The surface alterations due to laser heating were classified by the diameter of the completely melted surface, the ring of the surface at the threshold of melting, and the size of microscopic cracks. The diameter of the laser treated area was in the range of 3 mm, while the incident laser power and the duration of laser heating were varied between 1 and 10 W and 1-8 min, respectively. The different stages of surface modifications were attributed primarily to the irradiating laser power and proved to be rather insensitive to the duration of the treatment. We have found a range of parameters under which the white China surface coated with raw glaze and followed by laser induced melting exhibited very similar characteristics to the untreated porcelain. This technique seems prosperous for laser assisted reparation of small surface defects of unique China samples after the firing process.     

Effect of oxidation on the optical and surface properties of AlGaN

The chemical properties of Al_xGa_1−xN surfaces exposed to air for different time periods are investigated by atomic force microscopy (AFM), photoluminescence (PL) measurement and X-ray photoelectron spectroscopy (XPS). PL and AFM results show that Al_xGa_1−xN samples exhibit different surface characteristics for different air-exposure times and Al contents. The XPS spectra of the Al 2p and Ga 2p core levels indicate that the peaks shifted slightly, from an AlN to an AlO bond and from a GaN to a GaO bond. All of these results show that the epilayer surface contains a large amount of Ga and Al oxides.     

Carbon nanotubes as reinforcement of styrene-butadiene rubber

This study reports an easy technique to produce cured styrene-butadiene rubber (SBR)/multi-walled carbon nanotubes (MWCNT) composites with a sulphur/accelerator system at 150 °C. Significant improvement in Young's modulus and tensile strength were achieved by incorporating 0.66 wt% of filler without sacrificing SBR elastomer high elongation at break. A comparison with carbon black filled SBR was also made. Field emission scanning electron microscopy was used to investigate dispersion and fracture surfaces. Results indicated that the homogeneous dispersion of MWCNT throughout SBR matrix and strong interfacial adhesion between oxidized MWCNT and the matrix are responsible for the considerable enhancement of mechanical properties of the composite.     

Studies on surface modification of UHMWPE fibers via UV initiated grafting

In this research, the surface of ultra high molecular weight polyethylene (UHMWPE) fiber was modified by high energy ultraviolet (UV) initiated grafting reactions and acrylamide groups were grafted onto UHMWPE chains. The initiating and grafting mechanism of the reactions was studied. Some important factors influencing the grafting effect, e.g. crystallinity of UHMWPE fiber, concentration of the initiating reagent, grafting time and the concentration of grafting monomer (acrylamide) were discussed. Fourier transform infrared (FTIR) was used to manifest the mechanism of the grafting reaction. Scanning electron microscopy (SEM) was used to show the morphology changing of the fiber surface. Single fiber pull-out strength and ILSS tests of the composite showed that acrylamide grafted onto the surface of the fiber could improve the interfacial adhesion between treated fibers and matrices.     

Short-time plasma surface modification of HDPE powder in a Plasma Downer Reactor - process, wettability improvement and ageing effects

The effectiveness of improving the wettability of HDPE powders within less than 0.1 s by plasma surface modification in a Plasma Downer Reactor is investigated. A correlation is revealed between the XPS results (O/C-ratio) and the wettability (contact angle, polar surface tension by capillary rise method). The O₂-content in the plasma feed gas has been adjusted for best wettability properties. XPS results indicate the formation of CO and COOH functional groups on the powder surface. The O/C-ratio increased from 0.0 (no oxygen on the non-treated powder) up to 0.15 for the plasma treated HDPE powder surface. With pure O₂-plasma treatment, a water contact angle reduction from >90° (no water penetration into the untreated PE powder) down to 65° was achieved. The total surface free energy increased from 31.2 to 45 mN/m. Ageing of treated powders occurs and proceeds mostly within the first 7 days of storage. Contact angle measurements and O1s/O2s intensity ratio data support that ageing is mainly a diffusion-controlled process. Nevertheless, XPS results show the presence of oxygen functional groups even after 40 days, which explains why the powder is still dispersible in water without any addition of surfactants.     

Surface modification of Sylgard 184 polydimethylsiloxane by 254 nm excimer radiation and characterization by contact angle goniometry, infrared spectroscopy, atomic force and scanning electron microscopy

The modification of polydimethylsiloxane (PDMS) by narrow band 254 nm excimer radiation under a nitrogen atmosphere was characterized by contact angle goniometry, attenuated total reflectance infrared spectroscopy, atomic force and scanning electron microscopy. UV irradiation results in the formation of the carboxylic acids that influences the wettability of the surface. Continued exposure results in the formation of an inorganic surface (SiO_x (1 < x < 2)) which hinders the ability to continually increase the wettability. The continuity of this inorganic layer is disrupted by the formation of surface cracks. These results have implications in the fabrication and chemical modification of microfluidic or micro-electro-mechanical systems.     

Ferromagnetic resonance studies in Co/SiO2 multilayers

The uniaxial in-plane and out-of-plane anisotropies of [Co/SiO₂] × 10 multilayers have been studied by ferromagnetic resonance, magnetometry and transmission electron microscopy. The surface and volume anisotropy constants are in the range of values typical for multilayers with Co and transition metals of the iron group. The influence of the intermixed Co-SiO₂ region is discussed.     

Antibacterial activities of surface modified electrospun poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) fibrous membranes

Poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) membrane, with its excellent chemical and mechanical properties, has good potential for broad applications. However, due to its hydrophobic nature, microbial colonization is commonly encountered. In this work, electrospun PVDF-HFP fibrous membranes were surface modified by poly(4-vinyl-N-alkylpyridinium bromide) to achieve antibacterial activities. The membranes were first subjected to plasma pretreatment followed by UV-induced surface graft copolymerization of 4-vinylpyridine (4VP) and quaternization of the grafted pyridine groups with hexylbromide. The chemical composition of the surface modified PVDF-HFP electrospun membranes was studied by X-ray photoelectron spectroscopy (XPS). The morphology and mechanical properties of pristine and surface modified PVDF-HFP fibrous membranes were characterized by scanning electron microscopy (SEM) and tensile test, respectively. The antibacterial activities of the modified electrospun PVDF-HFP fibrous membranes were assessed against Gram-positive Staphylococcus aureus (S. aureus) and Gram-negative Escherichia coli (E. coli). The results showed that the PVDF-HFP fibrous membranes modified with quaternized pyridinium groups are highly effective against both bacteria with killing efficiency as high as 99.9999%.     

Influence of chemical composition of filler's surface on the burning of foam plastics

The influence of additives such as TiO₂, Al₂O₃ and their mechanical mixture as well as aluminium oxide, the surface of which contains phosphorous and titanium-oxide nanostructures, on the combustibility of foam plast (trade mark PEN-I), produced on the basis of epoxide novolak block-copolymers, was studied. It was stated that the incorporation both phosphorous-containing and titanium-containing oxides in the composition results in significant (in two to five times) decreasing of the samples’ combustibility. The probable mechanism of inhibition of burning process for those combustion retarders was discussed.     

Oxygen plasma functionalization of poly(p-phenilene sulphide)

Surface effects during plasma activation of poly(p-phenilene sulphide)—PPS have been studied. Samples that were exposed to weakly ionized highly dissociated oxygen plasma created an inductively coupled radiofrequency discharge with the power of 100 W. The electron density and temperature were measured with a double Langmuir probe and were 4 × 10¹⁵ m⁻³ and 3 eV, respectively, while the neutral atom density was measured with a fiber optics catalytic probe and was 4 × 10²¹ m⁻³. The surface tension was determined by measuring the contact angle of deionized water, while the appearance of surface functional groups was detected by XPS. The surface tension of untreated PPS was 7 × 10⁻³ N/m or/and increased to 7 × 10⁻² N/m in few seconds of plasma treatment. It remained fairly constant for longer plasma treatments. The XPS survey spectrum showed little oxygen on untreated samples, but its concentration increased to about 20 at.% in few seconds. Detailed high resolution XPS C 1s peak showed that the carbon was left fairly stable during plasma treatment. The main functional groups formed were rather sulphate in sulphite groups, as determined from high resolution S 2p peak. Namely, a strong transition from sulphide to sulphate state of sulfur was observed. The spontaneous deactivation of the polymer surface was measured as well. The deactivation was fairly logarithmic with the characteristic decay time of several hours.     

Effects of half-wave and full-wave power source on the anodic oxidation process on AZ91D magnesium alloy

Anodic films have been prepared on the AZ91D magnesium alloys in 1 mol/L Na₂SiO₃ with 10 vol.% silica sol addition under the constant voltage of 60 V at room temperature by half-wave and full-wave power sources. The weight of the anodic films has been scaled by analytical balance, and the thickness has been measured by eddy current instrument. The surface morphologies, chemical composition and structure of the anodic films have been characterized by scanning electron microscopy (SEM), energy dispersion spectrometry (EDS), X-ray diffraction (XRD) and transmission electron microscopy (TEM). The results show that the thickness and weight of the anodic films formed by the two power sources both increase with the anodizing time, and the films anodized by full-wave power source grow faster than that by half-wave one. Furthermore, we have fitted polynomial to the scattered data of the weight and thickness in a least-squares sense with MATLAB, which could express the growth process of the anodic films sufficiently. The full-wave power source is inclined to accelerate the growth of the anodic films, and the half-wave one is mainly contributed to the uniformity and fineness of the films. The anodic film consists of crystalline Mg₂SiO₄ and amorphous SiO₂.     

Study on the surface bioactivity of novel magnetic A-W glass ceramic in vitro

Novel magnetic A-W glass ceramic (M GC) in the system MgO-CaO-SiO₂-P₂O₅-CaF₂-MnO-ZnO-Fe₂O₃ was synthesized by doping Mn-Zn ferrite to apatite-wollastonite glass ceramic. The phase composition was investigated by XRD. The magnetic property was measured by VSM. The in vitro bioactivity was tested by immersion in simulated body fluid. The result shows apatite, wollastonite, fluorapatite and Zn_0.75Mn_0.75Fe_1.5O₄ are the main phases of M GC. Under a magnetic field of 10,000 Oe, the saturation magnetization and coercive force of the material are 6 emu g⁻ and 180 Oe, respectively. After soaking in SBF for 14 days, the surface of M GC is coated by a hydroxycarbonate apatite layer.     

In vivo bone regeneration using a novel porous bioactive composite

Many commercial bone graft substitutes (BGS) and experimental bone tissue engineering scaffolds have been developed for bone repair and regeneration. This study reports the in vivo bone regeneration using a newly developed porous bioactive and resorbable composite that is composed of bioactive glass (BG), collagen (COL), hyaluronic acid (HYA) and phosphatidylserine (PS), BG-COL-HYA-PS. The composite was prepared by a combination of sol-gel and freeze-drying methods. A rabbit radius defect model was used to evaluate bone regeneration at time points of 2, 4 and 8 weeks. Techniques including radiography, histology, and micro-CT were applied to characterize the new bone formation. 8 weeks results showed that (1) nearly complete bone regeneration was achieved for the BG-COL-HYA-PS composite that was combined with a bovine bone morphogenetic protein (BMP); (2) partial bone regeneration was achieved for the BG-COL-HYA-PS composites alone; and (3) control remained empty. This study demonstrated that the novel BG-COL-HYA-PS, with or without the grafting of BMP incorporation, is a promising BGS or a tissue engineering scaffold for non-load bearing orthopaedic applications.     

Pre-treatments applied to oxidized aluminum surfaces to modify the interfacial bonding with bis-1,2-(triethoxysilyl)ethane (BTSE): Part I. High-purity Al with native oxide

A remote microwave-generated H₂ plasma and heating to 250 °C were separately used to modify high-purity oxidized aluminum surfaces and to assess whether these treatments can help enhance adhesion with bis-1,2-(triethoxysilyl)ethane (BTSE) coatings. Different initial oxide surfaces were considered, corresponding to the native oxide and to surfaces formed by the Forest Products Laboratory (FPL) treatment applied for either 15 or 60 min. BTSE is applied from solution at pH 4, and competing processes of etching, protonation (to form OH groups) and coupling (to form AlOSi interfacial bonds) occur at the solid-liquid interface. Scanning electron microscopy (SEM) was used to determine how the topographies of the modified Al surfaces changed with the different pre-treatments and with exposure to a buffer solution of pH 4. Secondary-ion mass spectrometry (SIMS) was used to determine the direct amount of AlOSi interfacial bonds by measuring the ratio of peak intensities 71-70 amu, while X-ray photoelectron spectroscopy (XPS) was used to determine the overall strength of the silane coating adhesion by measuring the Si 2p signals before and after application of an ultrasonic rinse to the coated sample. Measured Al 2p and O 1s spectra helped assess how the different pre-treatments modified the various Al oxidized surfaces prior to BTSE coating. Pre-treated samples that showed increased AlOSi bonding after BTSE coating corresponded to surfaces, which did not show evidence of significant etching after exposure to a pH 4 environment. This suggests that such surfaces are more receptive to the coupling reaction during exposure to the BTSE coating solution. These surfaces include all H₂ plasma-treated samples, the heated native oxide and the sample that only received the 15 min FPL treatment. In contrast, other surfaces that show evidence of etching in pH 4 environments are samples that received lower amounts of AlOSi interfacial bonding. Overall, heating improved the BTSE adhesive bonding for the native Al oxide, while H₂ plasma treatment improved the BTSE bonding for surfaces that had initially been FPL-treated for 15 and 60 min.     

Pre-treatments applied to oxidized aluminum surfaces to modify the interfacial bonding with bis-1,2-(triethoxysilyl)ethane (BTSE): Part II. Anodized 7075-T6 Al alloy

The methods of X-ray photoelectron spectroscopy (XPS), secondary-ion mass spectrometry (SIMS), and scanning electron microscopy (SEM) have been used to investigate aspects of the bonding of bis-1,2-(triethoxysilyl)ethane (BTSE) onto anodized samples of 7075-T6 aluminum alloy that have been subjected to the various pre-treatments considered in Part I. The oxide layer thins when this sample is subjected to a Forest Products Laboratory (FPL) treatment; topographical changes are detected by SEM after only 5 min, and the “scallop structures” increase in size for longer times of the FPL treatment. These 7075-Al surfaces adsorb more BTSE than the high-purity Al samples considered in Part I, although the interfacial bonding indicated by the [AlOSi]⁺/[Al₂O]⁺ SIMS ratios measured for the former samples are constant for different times of FPL treatment, unlike the situation for high-purity Al. Heating anodized 7075-Al samples, either before or after FPL treatment, has no significant effect on the subsequent BTSE adsorption, but a H₂ plasma treatment can enhance the interfacial Al-O-Si bonding with a decrease in the total BTSE polymerization.     

A comparative study of the physical properties of Sb2S3 thin films treated with N2 AC plasma and thermal annealing in N2

As-deposited antimony sulfide thin films prepared by chemical bath deposition were treated with nitrogen AC plasma and thermal annealing in nitrogen atmosphere. The as-deposited, plasma treated, and thermally annealed antimony sulfide thin films have been characterized by X-ray diffraction (XRD), energy dispersive X-ray spectroscopy, scanning electron microscopy, atomic force microscopy, UV-vis spectroscopy, and electrical measurements. The results have shown that post-deposition treatments modify the crystalline structure, the morphology, and the optoelectronic properties of Sb₂S₃ thin films. X-ray diffraction studies showed that the crystallinity of the films was improved in both cases. Atomic force microscopy studies showed that the change in the film morphology depends on the post-deposition treatment used. Optical emission spectroscopy (OES) analysis revealed the plasma etching on the surface of the film, this fact was corroborated by the energy dispersive X-ray spectroscopy analysis. The optical band gap of the films (E_g) decreased after post-deposition treatments (from 2.36 to 1.75 eV) due to the improvement in the grain sizes. The electrical resistivity of the Sb₂S₃ thin films decreased from 10⁸ to 10⁶ Ω-cm after plasma treatments.     

Formation of functional groups on graphite during oxygen plasma treatment

Improved sample wettability was obtained by oxygen plasma functionalization of pyrolytic graphite. The samples were exposed to highly dissociated oxygen plasma with the density of 1 × 10¹⁶ m⁻³, the electron temperature of about 5.5 eV and the density of neutral oxygen atoms of 8 × 10²¹ m⁻³ for 20 s. The surface wettability was measured by a contact angle of water drop. The contact angle dropped from original 112° down to about 1°. The functional groups were detected by XPS analyses. The survey spectrum showed a substantial increase of oxygen concentration on the surface, while high-resolution analyses showed additional oxygen was bonded onto the graphite surface in the form of C-O polar functional group responsible for the increase of the surface energy.