Application and evaluation of environmentally compliant spray-coated ormosil films as corrosion resistant treatments for aluminum 2024-T3

An epoxide modified silicate sol–gel film spray coated on an aluminum alloy 2024-T3 coupon was demonstrated to provide exceptional barrier and corrosion protection when compared to chromate-based surface treatments. Surface characterization indicated that the applied film was 2.2 μm thick and crack free. Potentiodynamic evaluation revealed that the film provided a continuous barrier of protection over a broad potential range. Comparison with standard Alodine-1200 type surface treatment indicated several orders of magnitude improvement in barrier protection and enhanced protection under accelerated corrosion test.     

Improving the corrosion protection properties of organically modified silicate–epoxy coatings by incorporation of organic and inorganic inhibitors

Organically modified silicate (ORMOSIL)–epoxy coatings were formed on aluminium alloy 2024-T3 in order to protect the substrates from corrosion. Organic and inorganic compounds, all known for their corrosion inhibition ability, were incorporated into the polymer matrix for the improvement of the corrosion resistance. The ORMOSIL–epoxy coatings were deposited via the dip-coating process. The properties of the coatings were investigated after 24 h of curing at 90 °C. The morphology of the coatings was examined by scanning electron microscopy (SEM). Their composition and structure were investigated by Fourier transform infrared spectroscopy (FT-IR) and energy dispersive X-ray analysis (EDX). The corrosion resistance of these coatings was investigated using electrochemical impedance spectroscopy (EIS). The results showed that the most effective corrosion protection ability was provided by the inorganic inhibitors and that an important role can be attributed to the cation in the nitrate salt.     

Design and preparation of composite coatings with increased reflectivity under high-energy continuous wave laser ablation

High-energy continuous wave (CW) laser ablation can cause severe damage to structural materials in an extremely short time, which generates considerable concern in terms of material safety. For the purpose of reducing or even eliminating such laser-induced damage, a novel composite coating consisting of a boron-modified phenolic formaldehyde resin incorporating ZrC and SiC has been designed and prepared. The experimental results reveal that ZrC and SiC are rapidly oxidized to ZrO₂ and SiO₂ respectively, leading to the formation of a white ceramic layer consisting of ZrO₂ particles and melted SiO₂. After ablation at 1000 W/cm² for 50 s, elemental analysis indicates that no Si can be found in the central ablation zone because of gasification. A relatively compact ZrO₂ layer is formed through the sintering of adjacent ZrO₂ particles, which effectively improves the reflectivity of the coating from 7.3% (before ablation) to 63.5% (after ablation). The high reflectivity greatly reduces the absorption of laser energy. In addition, no obvious ablation defects are observed in the composite coating. The excellent anti-laser ablation performance of the coating makes it a promising system for protecting a material against the effects of long-term CW laser ablation.     

Study of cationic UV curing and UV laser ablation behavior of coatings sensitized by novel sensitizers

To improve the laser ablation performance of cycloaliphatic epoxide cationic UV curable coatings, two novel reactive sensitizers were synthesized and characterized and their effect on coating properties examined. The sensitizers were synthesized based on the reaction between naphthalene or anthracene derivatives and monomers or oligomers used in the coating system. HPLC and GC-MS confirmed the formation of the desired products. Three coating systems based on cycloaliphatic epoxide with either oxetane or polycaprolactone polyol were formulated with the reactive sensitizers. The sensitized coatings had higher conversion during UV curing in the oxetane containing formulation and did not deter the curing in the polyol containing formulation. Better UV laser ablation performance was observed in all sensitized coatings compared to the controls. Coatings with the anthracene based sensitizer even had better laser ablation performance than a commercial polyimide. The sensitized coatings had higher hardness, T_g and crosslink density while the adhesion and solvent resistance were not affected. An optimal amount of sensitizer was found for each coating formulation in terms of UV curing behavior. The relationship between coating T_g and laser ablation behavior was investigated and it was found that the higher the T_g and crosslink density, the poorer the laser ablation performance.     

Protective abilities of nanocomposite coatings containing Al2O3 nano-particles loaded by CeCl3

The protective ability of hybrid nano-composite oxysilane coatings, deposited via sol–gel method on AA2024-T3 – aluminium alloy, were studied by linear voltammetry (LVA) and electrochemical impedance spectroscopy (EIS) methods in 0.05 M solution of NaCl. Cerium chloride (CeCl₃) was incorporated as an inhibitor into a sol–gel hybrid matrix in two different routes: directly and via filled porous Al₂O₃ nano-particle aggregates with diameters up to 500 nm. The influences of the inhibitor concentration, as well as the influence of nano-particles on the barrier properties and the susceptibility against corrosion, were evaluated and EIS spectra were fitted by appropriated equivalent circuits. The values for C_coat, R_coat, C_oxy and R_oxy were achieved and their evolution over time was investigated. The investigated coatings possess highly expressed barrier properties (10⁶ to 10⁷ Ω cm²). Despite of the chloride ions inside of the matrix, some samples illustrated a significant durability of over 4000 h during exposure to the corrosion medium before first signs of corrosion appeared. The electrochemical results were compared with the neutral salt spray test. Thus, it was proved that the potential of these coatings is to be used as anticorrosive protective materials and are candidate to replace Cr(VI)-based anti-corrosion coatings.     

Cerium cinnamate as an environmentally benign inhibitor pigment for epoxy coatings on AA 2024-T3

An environmentally friendly inhibitor, cerium cinnamate (CeCin), was studied as an additive to an epoxy coating. The effects of corrosion inhibition on AA 2024-T3 provided by cerium cation and cinnamate anion were investigated by electrochemistry impedance spectra (EIS) and polarization tests. It was found that cerium ion and cinnamate group have synergistic inhibiting effects. The EIS results show that CeCin is an effective inhibitor pigment for improving the corrosion resistance of epoxy coatings on AA2024-T3, as reflected by the much higher coating resistance than that of the blank epoxy coating. The inhibiting effect of CeCin during the onset of corrosion in defects of the epoxy coating was verified using scanning vibrating electrode technique (SVET), which is in agreement with the EIS results.     

The application of synchrotron-based spectroscopic techniques to the study of chromate conversion coatings

This work utilized synchrotron spectroscopic techniques such as extended X-ray absorption fine structure (EXAFS), X-ray absorption near edge structure (XANES) and synchrotron infrared microspectroscopy (SIRMS) to understand the chemistry, formation, structure and aging of protective chromate conversion coatings (CCC). We shall discuss issues related CCC formed on aluminum-copper alloys. SIRMS combined with argon ion sputtering demonstrated spatial and depth chemical variations of the CCC formed on AA2024-T3. XANES indicated that in the first stages of CCC formation the thickness depends on the Cu content of the substrate and that thinner CCC appears to contain less Cr⁶⁺ for protection. Micro-XANES shows that even monolayer coverage of chromate can protect the alloy surface. EXAFS and XANES measurements were used to monitor the structural changes of the CCC with time. It was observed that a slight decrease in the Cr(VI)Cr(III) ratio occurred during the first 24 h following coating. The structure of the CCC is in close agreement with a Cr mixed oxide. EXAFS data appeared to indicate an increase in ordering in the CCC structure with time.     

The mechanical properties of C/C-ZrC-SiC composites after laser ablation

Considering practical environment, the bending property of C/C-ZrC-SiC, C/C-SiC and C/C composites after ablation was worthily studied. Results revealed that C/C-ZrC-SiC composites had a better laser ablation resistance and higher bending strength retention compared with C/C-SiC and C/C composites. The mass loss rate and ablated depth of C/C-ZrC-SiC composites was − 0.09% and 190.377 μm, respectively. The retention of bending strength of C/C-ZrC-SiC composites was 217.67 ± 44.12 MPa, whose strength decreased by 3.57% compared with that of as-prepared C/C-ZrC-SiC composites. The excellent anti-ablation property and residual bending strength of C/C-ZrC-SiC composites were attributed to the lowest ablative temperature and the effective protection of the ZrO₂ grain and ZrO₂-SiO₂ layer, which were formed by oxidation of ZrC-SiC, evaporation of SiO₂, migration of liquid ZrO₂-SiO₂ and the infiltrated as well as grown ZrO₂. However, the fracture behavior transformation of composites from pseudo-plastic rupture to brittle rupture was induced by the ablation damage.     

Organic-inorganic composites for novel optical transformation induced by high-energy laser ablation

High-energy continuous-wave (CW) laser has been considered as a significant technology in recent decades. Such laser can destroy conventional materials in an extremely short time, necessitating their protection. In this study, zirconium carbide (ZrC) and silicon carbide (SiC) particle-modified short silicon carbide fiber-reinforced phenolic resin matrix composites (SiC/BPF-ZS) with significant anti-laser performance were designed and prepared. Our results showed that the ceramic particles and SiC fibers rapidly oxidized, leading to the formation of a ceramic coating composed of ZrO₂ and SiO₂. Owing to the formation of the ceramic coating, the reflectivity of the composites improved significantly from 15.8% to 73.2% after ablation at 500 W/cm² for 30 s. Additionally, the SiC fibers played an important role in the formation of a high-reflectivity coating during laser ablation. Contrast experiments indicated that SiC fibers lead to better performance than the carbon fibers. The high reflectivity and low mass ablation rate are demonstrated to be the key factors improving the anti-laser ablation performance of the SiC/BPF-ZS composites.     

Effect of the experimental setup in the behaviour of sol–gel coatings

Electrochemical behaviour of the sol–gel-coated AA2024-T3 samples was evaluated using electrochemical impedance spectroscopy (EIS) in a three-electrode arrangement cell using Na₂SO₄ 0.1 M solution as electrolyte. The effect of the reference electrode leakage was examined using as reference a low-leakage Ag/AgCl electrode and a platinum wire. The results show that very low-chloride concentrations in solution are able to induce heavy dissolution of intermetallic precipitates. That corrosion process masks information on the barrier properties of sol–gel coatings otherwise available through EIS measurements.     

2024铝合金化学镀Ni-P加速剂的研究

研究了硫脲、碘酸钾以及两者复合后对2024铝合金化学镀Ni-P合金镀层沉积速率的影响。结果表明:硫脲、碘酸钾都可以促进Ni-P合金在铝合金表面的沉积,且当镀液中硫脲、碘酸钾的质量浓度分别为3mg/L和20mg/L时,沉积速率都达到了最大值;并且当两者复合以后,镀层沉积速率又明显提高;当镀液中硫脲和碘酸钾的质量浓度比为1:5时,沉积速率达到最高值,此时镀层质量良好,耐蚀性高。     

Effects of reflectivity on laser-ablation resistance of the laser-cladding repaired Nd2O3 modified SiO2 coatings on C/C composites

To repair the damaged SiC coated C/C composites, a double-layer coating including a SiO₂-Nd₂O₃ external layer (∼60 μm) and a Si-SiC inner layer (∼240 μm) was prepared by a slurry-based laser cladding technique, and the laser-ablation tests under two heat fluxes (23.89/39.81 MW m⁻²) were performed. The spectrophotometer, X-ray diffraction, scanning electron microscopy and 3D profilometer were used for characterization. For avoiding the secondary damage of laser-ablation, the laser-reflection of the repaired area was enhanced, which was conducive to the mitigation of mass and linear ablation. Combined with Finite Element Analysis, by raising the reflectivity, the surface and back temperature of samples could be reduced greatly by 1224 K and 983 K respectively, and plenty of ablation reactions could be avoided. Therefore, the SiO₂-Nd₂O₃ coating possessed an excellent laser-ablation resistance and protected the C/C substrates from thermal damage and oxidation effectively.     

Additively-manufactured multiphase coatings with laser protection ability for the repairing of MoSi2-SiC/SiC coated C/C composites

The Si-SiC-MoSi₂ and Si-SiC coatings were proposed to repair the damaged MoSi₂-SiC/SiC coated C/C composites by laser directed energy deposition. Laser ablation was used to assess the repair effect. Results showed that both the repaired coatings with dense structure could restore the geometric size of damaged area. Compared with the Si-SiC-MoSi₂ coating, the Si-SiC repaired coating with higher laser reflectivity and more free Si could reduce the heat generation and enhance the heat dissipation during ablation, which lowered the maximum temperature by 347.49 K and 810.77 K under 300 W and 500 W ablation for 7 s separately, beneficial to avoid the secondary laser damage of the repaired area.     

Calcium phosphates of biological importance based coatings deposited on Ti-15Mo alloy modified by laser beam irradiation for dental and orthopedic applications

Ti-15Mo alloy samples were irradiated by pulsed Yb:YAG pulsed laser beam under air and atmospheric pressure. Sequentially, calcium phosphate coatings were deposited on the irradiated surfaces by the biomimetic method. The formation of calcium phosphates (CaP) under biological medium and SBF (Synthetic/Simulated Body Fluid) occurs in the presence of Ca²⁺ and PO₄^3- ions, as well as ions such as: Mg^2+, HCO₃^-, K⁺ and Na⁺, which facilitates the mimicking of the biological process. The biomimetic calcium phosphates-based surfaces were submitted to heat treatment conditions at 350?°C and 600?°C. The present study correlates four conditions of fluency (1.91, 3.17, 4.16 and 5.54?J/cm², respectively) as established have a sufficient energy to promote ablation on the laser beam irradiated surfaces. Likewise, it has been demonstrated the processes of fusion and fast solidification from the laser beam irradiation, under ambient atmosphere, inducing the formation of stoichiometric (TiO₂₎ and non-stoichiometric titanium oxides (TiO, Ti₃O, Ti₃O₅ and Ti₆O) with different oxide percentages depending on the fluency applied. Besides that, laser modification has allowed a clean and reproducible process, providing no traces of contamination, an important feature for clinical applications. The morphological and physico-chemical analysis indicated the formation of a multiphase coatings depending on the heat treatment temperature performed to 350?°C (ACP1–2, CDHA, HA phases) and 600?°C (CDHA, HA and β-TCP phases). It is worth noting multiphasic bioceramic systems has been gaining attention for biomedical applications. The laser beam irradiation associated to bioactive coatings of calcium phosphates of biological interest have shown to be promising and economically feasible for use in clinical applications.     

The use of laser ablation inductively coupled plasma-mass spectrometry (LA ICP-MS) for the analysis of fly ash

Two methods were used to analyse fly ash for trace elements using laser ablation inductively coupled plasma-mass spectrometry. Individual particles in polished blocks proved difficult to analyse because of the fine grain size of the particles. Identification of particles was one problem and another was loss of sensitivity for key trace elements with a very small diameter (10 μm) laser beam. Analysis using transects covering many particles mounted on slides proved more successful. Statistical analysis of the data using major elements to measure the variation in key components in the ash showed: (1) that the glass is an important location for V, Cr, Cu and Zn; (2) Cr and V are thought to be concentrated in magnetite, although the major source in the ash is the glass; and (3) As, U, Pb, Tl, Mo, Se and probably Ge and Ga to a lesser extent, have a major association with the surfaces of the ash particles.     

Ablation behavior of C/SiC with YSZ and ZrB2 coatings under high-energy laser irradiation

Carbon fiber-reinforced silicon carbide (C/SiC) composites are important candidates for laser protection materials. In this study, ablation mechanism of C/SiC coated with ZrO₂/Mo and ZrB₂–SiC/ZrO₂/Mo under laser irradiation was studied. ZrB₂–SiC multiphase ceramic and ZrO₂ ceramic were successfully coated on C/SiC composite by atmospheric plasma spraying technology with Mo as transition layer. Phase evolution and morphology of composite were investigated by X-ray diffraction, scanning electron microscopy, and transmission electron microscopy. Moreover, ablation behavior of the composite was investigated by laser confocal microscopy. Results showed that ablation mechanism of C/SiC composite was controlled by phase transformation, thermal reaction, and thermal diffusion, with solid–liquid transition of ZrB₂ and ZrO₂ being dominant factor. Endothermic reaction and good thermal diffusivity of coatings were also important factors affecting ablation performance. Reflectivity effect of ZrO₂ coating was limited under high-energy laser irradiation. Compared with ZrO₂/Mo single-phase-monolayer coating, designed ZrB₂–SiC/ZrO₂/Mo coating showed better ablation performance, and breakdown time of C/SiC increased from 10 to 40 s. The depletion of liquid phase in molten pool was identified as an important factor responsible for rapid failure of C/SiC. The coating failed when the entire liquid phase was consumed within molten pool, followed by rapid damage of C/SiC substrate. Results of this study can provide theoretical guidance and research ideas for design and application of laser protective materials.     

Growth of multi-morphology amorphous silicon oxycarbide nanowires during the laser ablation of polymer-derived silicon carbonitride

Multi-morphology amorphous SiOC nanowires were successfully prepared within the interfacial interstices between the unaffected SiCN ceramic and the bracket during the laser ablation of polymer-derived SiCN ceramic in a low-pressure argon atmosphere. Laser irradiation experiments were performed using a continuous-wave CO₂ laser, and the gas source for the growth of amorphous SiOC nanowires was provided by the laser ablation of the SiCN ceramic. X-ray photoelectron spectroscopy shows that the amorphous SiOC nanowires possess a SiO₂ dominated nanostructure, and the formation of amorphous SiOC nanowires is attributed to the good diffusivity of CO in SiO₂. The morphologies of the amorphous SiOC nanowires include straight nanowires, beaded nanowires, helical nanowires, and branched nanowires, and these are determined by the flowing state of the reactant gases, the laser power, and the surface morphology of the SiCN ceramics. Each amorphous SiOC nanowire with specific morphology can be uniformly distributed in separate regions, which makes it possible to control the growth of amorphous SiOC nanowires in different morphologies.     

Laser ablation behavior of flake graphite and SiO2 particle-filled hyperbranched polycarbosilane matrix composite coatings

Composite coatings consisting of flake graphite and SiO₂ fillers in a hyperbranched polycarbosilane (HBPCS) matrix were designed and prepared to meet the requirements of laser protection. The laser ablation behavior of the composite coatings were investigated. Control experiments were designed to study the performance of SiO₂ during laser irradiation. The results show that the introduction of SiO₂ changes the anti-laser protective mechanism and can improve the anti-laser property of the coating. High power laser irradiation results in pyrolysis of HBPCS and the formation of SiC particles. Chemical reactions between SiO₂, graphite, and SiC play an important role in consuming energy, and provide an excellent cooling effect to the substrate, leading to decreased temperature. SiC particles formed on the surface of the laser ablation area act as a shield to prevent the laser from irradiating deeper layers of the coating. Due to the cooling effect and thermal stability of SiC, the proposed coating shows a good anti-laser property.     

Investigations of nanoparticle generation during surface decontamination by laser ablation at low fluence

Through laser ablation processes, significant amounts of particles can be generated from a surface of cement, stainless steel, or alumina. The minimal laser fluence (mJ cm^-2), or threshold energy, required to produce a detectable amount of particles (100 particles cm^-3) was investigated experimentally. The threshold energy was wavelength-dependent and was found to be the greatest for a pure material, alumina, then for a complex mixture, cement, and least for a simple mixture, stainless steel. The threshold energy requirement for three tested materials was found to be significantly higher for the IR (1064-nm) laser; it was 2.4–10.1 times higher than for the UV (266-nm) laser and 9.1–15.2 times higher than for the Vis (532-nm) laser. Interestingly, the UV laser has a higher threshold energy (1.5–4.0 times higher) than the Vis does. A log–log linear model was found to correlate particle production with the laser fluence of all three wavelengths. Of the three materials tested, stainless steel produced the most particles at a given fluence while alumina produced the fewest. Hypotheses of the particle generation mechanisms based upon the observations are also given here.