Low-pressure-plasma-deposited coatings formed from mechanically alloyed powders

A limiting feature of the low-pressure-plasma-coating process at the present state of the art is the need for ?400 mesh (?37 μm) feed powder for the gun. In this study we demonstrated that mechanically alloyed MCrAltype (where M is cobalt, nickel or iron) powders suitable for low pressure plasma spraying can be prepared using the attritor process.A two-step attriting process was developed which yields a large fraction of ?400 mesh powders. A study of the effects of attritor processing parameters was made on Co29Cr6Al1Y powder that was mechanically alloyed from a blend of cobalt, chromium, CoAl and CoY powders. Coatings deposited onto IN-738 pin specimens by low pressure plasma spraying were hot corrosion tested; these compare favorably with Co29Cr6Al1Y coatings deposited using atomized powders.A three-step attriting process also was developed which is particularly useful in forming MCrAl-type powders using elemental aluminum as a starting ingredient.     

Cr5Si3B and Hf5Si3B: New MAB phases with anisotropic electrical,mechanical properties and damage tolerance

Through a combination of electronic structure,chemical bonding and mechanical property investigations,anisotropic electrical and mechanical properties,and damage tolerant ability of MAB phases Cr_5Si_3B and Hf_5Si_3B are predicted.The anisotropic electrical conductivity is due to the anisotropic distribution of Cr in Cr_5Si_3B and Hf in Hf_5Si_3B,which mainly contribute to the electrical conductivity.The anisotropic mechanical properties are underpinned by the anisotropic chemical bonding within the crystal structures of Cr_5Si_3B and Hf_5Si_3B.The high stiffness is determined by the strong covalent-ionic Cr1 B Cr1 and Cr1 Si bonds in Cr_5Si_3B and the ionic-covalent Hf1 B Hf1 and Si B bonds in Hf_5Si_3B;while the low shear deformation resistance is attributed to the presence of metallic Cr Cr,Hf Hf and Si Si bond.Based on the low Pugh’s ratio,Cr_5Si_3B and Hf_5Si_3B are predicted tolerant to damage.The possible cleavage plane is(0001)and the possible slip systems are1 100|{11 20}and11 20|{0001}for both Cr_5Si_3B and Hf_5Si_3B.     

Synthesis of micron-sized porous CeO2SiO2 composite particles for ultraviolet absorption

Micron-sized porous composite particles composed of CeO₂ and SiO₂ nanoparticles were prepared for a UV absorption application by an aerosol spray-drying process from as-prepared CeO₂ nanoparticles, commercial SiO₂, and a polystyrene latex template. The morphology, structure crystallinity and pore size distribution of the as-prepared porous CeO₂SiO₂ composite particles were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), and Barrett-Joyner-Halenda (BJH) method, respectively. The porous CeO₂SiO₂ composite particles, with diameters of approximately 10 μm, showed a spherical morphology. As the contents of CeO₂ in the precursor was increased from 0.25 wt% to 1.5 wt%, we observed a change in the morphology of the composite particles from compactly packed porous particles to loosely packed porous particles. The as-prepared CeO₂SiO₂ composite particles were composed of meso- and macropores in the range of 3–200 nm. The effect of the CeO₂ content on the porous composite particles in terms of the UV absorption properties was also investigated by UV-visible spectroscopy. When the content of CeO₂ exceeded 0.75 wt% in the precursor, the particles showed higher UV absorption values compared to those of commercial TiO₂ nanoparticles. The as-prepared porous CeO₂SiO₂ composite particles can therefore be promising materials given their high UV absorption value.     

Comparison of properties of Cr3C2-Ni-Cr coatings thermally sprayed from pre-alloyed and mechanically mixed powders

A process for producing powder whose individual particles contain both Cr₃C₂ and Ni-Cr is discussed. The process consists of forming agglomerates which are subsequently sintered, melted in a plasma flame and sized. This powder does not exhibit the segregation and inhomogeneity problems associated with conventional mechanical blends of Cr₃C₂ and Nichrome powders. Plasma-sprayed coatings made from the pre-alloyed powders have uniform microstructures and high hardnesses. At room temperature their wear characteristics are superior to those of plasma-sprayed coatings from conventional blends.     

Sol–gel synthesis of tantalum oxide and phosphonic acid-modified carbon nanotubes composite coatings on titanium surfaces

Carbon nanotubes used as fillers in composite materials are more and more appreciated for the outstanding range of accessible properties and functionalities they generate in numerous domains of nanotechnologies. In the framework of biological and medical sciences, and particularly for orthopedic applications and devices (prostheses, implants, surgical instruments, …), titanium substrates covered by tantalum oxide/carbon nanotube composite coatings have proved to constitute interesting and successful platforms for the conception of solid and biocompatible biomaterials inducing the osseous regeneration processes (hydroxyapatite growth, osteoblasts attachment). This paper describes an original strategy for the conception of resistant and homogeneous tantalum oxide/carbon nanotubes layers on titanium through the introduction of carbon nanotubes functionalized by phosphonic acid moieties (P(O)(OH)₂). Strong covalent CP bonds are specifically inserted on their external sidewalls with a ratio of two phosphonic groups per anchoring point. Experimental results highlight the stronger “tantalum capture agent” effect of phosphonic-modified nanotubes during the sol–gel formation process of the deposits compared to nanotubes bearing oxidized functions (OH, CO, C(O)OH). Particular attention is also paid to the relative impact of the rate of functionalization and the dispersion degree of the carbon nanotubes in the coatings, as well as their wrapping level by the tantalum oxide matrix material. The resulting effect on the in vitro growth of hydroxyapatite is also evaluated to confirm the primary osseous bioactivity of those materials. Chemical, structural and morphological features of the different composite deposits described herein are assessed by X-ray photoelectron spectroscopy (XPS), scanning (SEM) and transmission (TEM) electronic microscopies, energy dispersive X-rays analysis (EDX) and peeling tests.     

A simple method to ameliorate hierarchical porous structures of SiO2 xerogels through adjusting water contents

In this contribution, hierarchical micro-/meso-porous SiO₂ xerogels were successfully prepared through a Stöber methodology coupled with following drying process. The SiO₂ xerogels were consisted of nanoparticles of 20–40 nm in size with different contents of water. Fourier transform infrared spectroscopy proved that SiOC₂H₅ and SiOH groups could be formed in SiO₂ xerogels. Further analyses declared that the amount of the SiOC₂H₅ groups decreased while the concentration of SiOH was firstly increased and then suffered a decline with improving contents of water. Besides, the SiO₂ xerogels was endowed with controllable micro-/meso-porous structure. Furthermore, the formation mechanism of the micro-/meso-porous SiO₂ xerogels was tentatively put forward. As a consequence, SiO₂ xerogels with controllable hierarchical micro-/meso-porous structure could act as the smart material for huge development in catalytic fields.     

Surface modification of Cr3C2–NiCr cermet coatings by direct diode laser

Thermal spraying has emerged as an important tool of increasingly sophisticated surface engineering technology, and it is being used widely to repair and surface modification in metallic parts. The Cr₃C₂–NiCr sprayed coatings are frequently used as wear resistant coatings against abrasion and erosion at high temperature up to 1173 K, and in corrosive environments. Hardness and microstructure of Cr₃C₂–NiCr cermet coatings fused by direct diode laser process was compared with that formed by high-velocity oxygen fuel spraying (HVOF) process. The effect of beam characteristics (power density, power, scanning speed, etc.) was examined on the surface modification of sprayed coatings. In this study, we treated Cr₃C₂–25%NiCr cermet coatings by laser irradiation process and examined its hardness compared with that formed by HVOF process. Consequently, the average hardness of laser-treated Cr₃C₂–25%NiCr cermet coatings has been found out to be higher than that of HVOF coatings. Laser remelting improved markedly the wear resistance of HVOF sprayed Cr₃C₂–25%NiCr cermet coatings.     

Whether do nano-particles act as nucleation sites for C-S-H gel growth during cement hydration?

In this study, three modelling experiments were designed to investigate whether nano-particles incorporated in the cement paste act as nucleation sites for CSH gel growth during cement hydration. The nano-particles with (nano-SiO₂) and without (nano-TiO₂) pozzolanic reactivity were used. In the first experiment, both the cement and nano-particles were dispersed in water to prepare dilute cement paste, in which the cement and nano-particles can contact each other. In the second one, the cement particles were laid inside a filter paper funnel and immersed in tap and ultrapure water with nano-particles dispersed, in order to separate the cement particles with nano-particles by using the filter paper. In the third one, large clinker particle was embedded in resin, surface-polished and then exposed upside down in ultrapure water with and without nano-particles dispersed. After hydration for 7 days, the hydration products in the paste or the nano-particle dispersion were observed by using TEM and the hydrated surface of the embedded clinkers were detected by using SEM. Based on the experimental results and the detailed discussions by using the classic nucleation theory, it was found that there may have no nucleus function of the nano-particles for the CSH gel precipitation during cement hydration, at least in the hydrating system with nano-silica and nano-TiO₂ addition. It was proposed to more reasonably explain the observations in the three modelling experiments by using the topochemical reaction instead of the through-solution mechanism for the CSH gel formation.     

Phase constitutions of MoSiN anti-oxidation multi-layer coatings on CC composites by fused slurry

To improve the oxidation resistance of MoSi fused slurry coating fabricated in vacuum, MoSiN multi-layer coatings were synthesized on C/C composites in nitrogen atmosphere by fused slurry using same Mo and Si element powders. The phase compositions and microstructures were characterized by X-ray diffractometry (XRD), optical microscopy (OM), scanning electron microscopy (SEM) with energy-dispersive spectroscopy (EDS). The results indicate that the MoSiN coating contains SiC inner layer and MoSi₂/Si main layer, which was similar with MoSi coating. Additionally, a thin outer layer with nano-filiform morphology has been found on the coating surface, which consists of SiC, Si₃N₄, AlN, Al₂O₃ and sialon phase. Oxidation experiments show that the MoSiN multi-layer coating exhibits excellent oxidation resistance at 1400 °C and anti-oxidizing potential ability at 1450 °C.     

Poly (hydroxyethyl methacrylate-glycidyl methacrylate) films modified with different functional groups: In vitro interactions with platelets and rat stem cells

Copolymerization of 2-hydroxyethylmethacrylate (HEMA) with glycidylmethacrylate (GMA) in the presence of α-α′-azoisobisbutyronitrile (AIBN) resulted in the formation of hydrogel films carrying reactive epoxy groups. Thirteen kinds of different molecules with pendant NH₂ group were used for modifications of the p(HEMA-GMA) films. The NH₂ group served as anchor binding site for immobilization of functional groups on the hydrogel film via direct epoxy ring opening reaction. The modified hydrogel films were characterized by FTIR, and contact angle studies. In addition, mechanical properties of the hydrogel films were studied, and modified hydrogel films showed improved mechanical properties compared with the non-modified film, but they are less elastic than the non-modified film. The biological activities of these films such as platelet adhesion, red blood cells hemolysis, and swelling behavior were studied. The effect of modified hydrogel films, including NH₂, (using different aliphatic CH₂ chain lengths) CH₃, SO₃H, aromatic groups with substituted OH and COOH groups, and amino acids were also investigated on the adhesion, morphology and survival of rat mesenchymal stem cells (MSCs). The MTT colorimetric assay reveals that the p(HEMA-GMA)-GA-AB, p(HEMA-GMA)-GA-Phe, p(HEMA-GMA)-GA-Trp, p(HEMA-GMA)-GA-Glu formulations have an excellent biocompatibility to promote the cell adhesion and growth. We anticipate that the fabricated p(HEMA-GMA) based hydrogel films with controllable surface chemistry and good stable swelling ratio may find extensive applications in future development of tissue engineering scaffold materials, and in various biotechnological areas.     

Effects of La2O3 on microstructure and wear properties of laser clad γ/Cr7C3/TiC composite coatings on TiAl intermatallic alloy

The effects of La₂O₃ addition on the microstructure and wear properties of laser clad γ/Cr₇C₃/TiC composite coatings on γ-TiAl intermetallic alloy substrates with NiCr–Cr₃C₂ precursor mixed powders have been investigated by optical microscopy (OM), scanning electron microscopy (SEM), X-ray diffraction (XRD) and energy-dispersive spectrometer (EDS) and block-on-ring wear tests. The responding wear mechanisms are discussed in detail. The results are compared with that for composite coating without La₂O₃. The comparison indicates that no evident new crystallographic phases are formed except a rapidly solidified microstructure consisting of the primary hard Cr₇C₃ and TiC carbides and the γ/Cr₇C₃ eutectics distributed in the tough γ nickel solid solution matrix. Good finishing coatings can be achieved under a proper amount of La₂O₃-addition and a suitable laser processing parameters. The additions of rare-earth oxide La₂O₃ can refine and purify the microstructure of coatings, relatively decrease the volume fraction of primary blocky Cr₇C₃ to Cr₇C₃/γ eutectics, reduce the dilution of clad material from base alloy and increase the microhardness of the coatings. When the addition of La₂O₃ is approximately 4 wt.%, the laser clad composite coating possesses the highest hardness and toughness. The composite coating with 4 wt.%La₂O₃ addition can result the best enhancement of wear resistance of about 30%. However, too less or excessive addition amount of La₂O₃ have no better influence on wear resistance of the composite coating.     

Effects of He (90%)/H2 (10%) plasma treatment on electric properties of low dielectric constant SiCOH films

In microelectronics industry, integration of the low dielectric constant (low-k) material films is a continuing issue due to the decreasing device feature size. To improve electric properties, various post-deposition treatments of the low-k material films can be used. In this work, we used room temperature treatment of He/H₂ plasma and investigated the effects of plasma treatment on the electrical properties of low-k SiOCH films. Plasma treatment time changed from 300 to 1800 s. After treatment, the dielectric constant was decreased from 2.9 to 2.48, and the thickness of the low-k SiCOH films changed by only ～5%. The leakage current densities of the low-k SiCOH films were decreased to ～10^?11 A/cm², with treatment time ≥600 s. The breakdown occurred only around 2 V for films plasma-treated for 600 and 900 s. However, for 1800 s treatment time, the breakdown voltage was enhanced dramatically and breakdown occurred at applied voltage higher than 40 V. The surface composition change of the films after treatment was investigated by X-ray photoelectron spectroscopy (XPS). As the plasma treatment time was increased, the intensities of CC/CH and CSi peaks were decreased while the intensities of SiO and CO peaks were increased. It is thought that increase of oxygen content of the SiCOH film, after plasma treatment, contributed to leakage current reduction and breakdown voltage increase.     

Studies on optimization of silica nanoparticles dosage in cementitious system

Optimization of silica nanoparticles (SNPs) dosage in cementitious system was carried out analytically as well as experimentally by understanding the early stage hydration reaction of tricalcium silicate (C₃S). XRD and TGA results show the maximum nucleation effect of SNPs at 8 h, when the rate of product formation was higher than the control (∼66% additional CSH and ∼61% more CH with 10% SNPs addition). While at 24 h of hydration, ∼25% additional CSH was formed and CH content reduced by ∼32% with 10% addition showing the pozzolanic effect of SNPs. Further, FTIR results reveal that SNPs accelerate the polymerization in silicate chain and with 10% SNPs addition more crystalline (probably tobermorite like) structure is formed. This is responsible for the formation of highly compact and dense microstructure at 24 h as observed in electron micrographs, which may be responsible for the slow hydration rate at later age. XRD, FTIR and TGA studies on C₃S revealed that up to 5% addition of SNPs is beneficial, whereas higher dosages do not contribute significantly. Based on these investigations, studies were performed on cement paste, mortar and concrete samples, which revealed that 2–3% addition of SNPs is the optimum quantity for significant contribution in strength properties.     

CO2 reduction to CH4 with H2 on photoirradiated TS-1

CO₂ reduction on reduced titanium silicalite (TS-1) with photoirradiation in the presence of H₂ was investigated in a closed circulation system. CO₂ was reduced to give CH₄ under u.v. irradiation, which TS-1 absorbs. The amount of the carbon species on TS-1 after photoirradiation indicated that all Ti atoms in the framework may act as a photocatalytic site. Infrared spectrum of TS-1 after the reaction showed that CH₂ and CH₃ were left on TS-1.     

Effect of annealing temperature on the microstructure and photoluminescence of low resistivity Si/SiN/TaN thin films using magnetron sputtering

A lot of studies have been devoted to the porous Si, erbium-doped Si and Si-embedded in dielectric matrix of SiO or SiN together with long-time conventional furnace annealing. Besides, it is noted that these Si nanostructured films were highly resistive and non-conducting. In this paper, we have investigated the effect of annealing temperature on the microstructure and photoluminescence of low-resistivity Si/SiN/TaN nanocomposite thin films which are deposited by magnetron sputtering and followed by rapid thermal annealing (RTA). All samples are of luminescence and staying low resistivity at about 1462–2162 μΩ cm which increases with increasing annealing temperatures. The asymmetric broad photoluminescence (PL) peak covered the wavelengths of 400–700 nm. The wide visible PL spectra can be deconvoluted into three bands of blue (~ 455 nm), green-yellow (~ 525 nm), and orange emissions (~ 665 nm), which correspond to the emission origins from unsatisfied states in imperfections of interface between the Si:O and SiN:O, located states related to the mixed SiO or SiN bonds in SiN:O layer and nc-Si embedded in SiN:O matrix. The detailed mechanism of broad visible PL was investigated in terms of microstructure and bonding configuration evolution. The relationship between the annealing temperature, microstructure and PL behavior of Si/SiN/TaN multilayer films is discussed and established.     

Characteristics evaluation of calcium carbonate particles modified by surface functionalization

Calcium carbonate (CaCO₃) particles were modified by a direct blending method using different coupling agents. The changes in the CaCO₃ particles were determined using different techniques. Compared with pristine particles, the modified CaCO₃ particles show good dispersion, particularly those modified by γ-methacryloxypropyl trimethoxy silane. Results of the thermogravimetric analysis indicated that the coupling agents were adsorbed or anchored on the surface of the CaCO₃ particles, thereby hindering aggregation. The formation of covalent bonds [CaOSi] or [CaOTi] was verified using Fourier transform infrared spectroscopy and X-ray diffraction. The modified CaCO₃ particles showed more stable colloidal dispersion in ethyl acetate than that of pristine CaCO₃ particles. Some silane or titanate coupling agents can be combined with CaCO₃ by covalent bonds, thereby changing the surface properties of CaCO₃ and enhancing dispersion in many organic media. The hydroxyl groups on the surface of CaCO₃ particles can interact with silanol groups or titanate coupling agents forming an organic coating layer.     

Surface modification on polyethylene terephthalate films with 2-methacryloyloxyethyl phosphorylcholine

In this study, the surface of polyethylene terephthalate (PET) was modified to improve the protein and cell adhesion behavior with low temperature ammonia plasma treatment followed by 2-methacryloyloxyethyl phosphorylcholine (MPC) grafting. The x-ray photoelectron spectroscopy (XPS) results showed that the COO^?, NCO and POH groups were successfully incorporated onto the sample surface after MPC grafting. Furthermore, formation of new bonds, N and NH on the sample surface grafted with MPC was recorded by Fourier transform infrared spectroscopy (FTIR). A large number of spherical particles at submicron to nanometer scale were also observed on the surface by atomic force microscopy (AFM). The cell adhesion experiments on PET film surfaces were evaluated and the highly hydrophilic surfaces could not promote cell adhesion and spreading. All results achieved in this study have clearly indicated that the method combining low temperature ammonia plasma treatment and MPC grafting is an effective way of producing a suitably hydrophilic PET surface with the capability of weakening the protein adsorption greatly.     

Synthesis,crystal structure,luminescent properties and photo degradation of mer-tris(8-Hydroxy-quinolinato-N,O)-indium(iii) hydrate 0.5 methanol solvate

Tris-(8-hydroxyquinioline) aluminium (Alq₃) is widely used in organic light emitting diodes as an emission and electron transport layer. In this study the effect of solvent molecules, in the solid state crystal lattice, on the photoluminescence properties of synthesized mer-tris(8-Hydroxy-quinolinato-N, O)-indium(iii) hydrate 0.5 methanol solvate (mer-[In(qn)₃]⋅H₂O⋅0.5 CH₃OH) was studied. Single crystals were obtained through a recrystallization process and single crystal X-ray diffraction was performed to obtain the unit cell structure. The main absorption peaks were assigned to ligand centered electronic transitions, while the solid state photoluminescence excitation peak at 440 nm was assigned to the 0–0 vibronic state of In(qn)₃. Broad emission at 510 nm was observed and was ascribed to the relaxation of an excited electron from the S₁–S₀ level. A powder sample was annealed at 130 °C for 2 h. A decrease in intensity was observed and could possibly be assigned to a loss of solvent species. To study the photon degradation, the sample was irradiated with an UV lamp for ∼15 h. The emission data was collected and the change in photoluminescence intensity with time was monitored. High resolution X-ray photoelectron spectroscopy (XPS) scans of the O-1s peak revealed that after annealing the binding energy shifted to lower energies indicating a possible loss of the H₂O and CH₃OH present in the crystal. The O-1s peak of the degraded sample indicated the possible formation of CO (∼532.5 eV), COH and OCOH (∼530.5 eV) on the phenoxide ring.     

High contrast glasses for all-solid fibers fabrication

We present composition development of borosilicate glasses for fabrication of high refractive index contrast, all-solid photonic crystal fibers. An oxide system composed of SiO₂B₂O₃Al₂O₃Li₂ONa₂OK₂O was adjusted to match thermal properties of selected highly nonlinear, lead bismuth gallium silicate glass. A high difference of refractive index of 0.376 is achieved at a wavelength of 1550 nm. We proved experimentally that the developed pair of glasses enables to draw optical fibers, and we propose a design of a photonic crystal fiber structure for broadband supercontinuum generation.     

Surface aspects of discolouration in Bisphenol A Polycarbonate (BPA-PC), used as lens in LED-based products

The surface-related reactions during discolouration of Bisphenol A Polycarbonate (BPA-PC), used as LED lens plates, under thermal stress are studied. X-ray photoelectron spectroscopy (XPS) has been used to monitor the changes in the surface chemistry of BPA-PC plates over a temperature range of 100–140 °C for a period up to 3000 h. Increasing time under thermal stress is associated with the discolouration, and increase in the yellowing index (YI) of PC plastic lens. The XPS results show that discolouration is associated with oxidation at the surface, finding a significant increase in the signal ratio O_1s/C_1s in the XPS spectra of degraded specimens. During thermal ageing, the CH concentration decreases and new oxide features CO and OCO form, with the latter being a support for oxidation at the surface being a major reaction during discolouration. Results also show that irradiation with blue light during thermal ageing accelerates the kinetics of discolouration and the increased O_1s/C_1s ratio in XPS spectra.