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.     

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.     

UV curable EA-Si hybrid coatings prepared by combination of radical and cationic photopolymerization

A series of UV curable EA-Si hybrid coatings were prepared by a simple approach combining radical and cationic photopolymerization, with epoxy acrylate (EA) as monomer, γ-glycidoxypropyltrimethoxysilane (GPTMS) as inorganic precursor, benzophenone (BP) as free radical photo initiator and a diaryliodonium salt DPIHFP as cationic photo initiator. The chemical structures of EA-Si hybrid coatings were characterized by Fourier transform infrared (FTIR), Raman spectroscopy and X-ray diffraction (XRD). The thermal and optical properties of hybrid coatings were investigated by thermal gravimetric analysis (TGA) and UV–vis transmission spectroscopy, respectively. The results indicated that cross-linked network structure of SiOSi formed in the hybrid coatings, which led to the decrease in crystallinity and of EA-Si hybrid coating. The final conversion of CC bonds was also decreased because of the addition of GPTMS. The thermal stability of EA-Si hybrid coatings was enhanced in the second decomposition stage (300–400 °C) because of the existence of organic–inorganic cross-linked network structures. The transparency of coatings at around 346 nm tended to increase with increasing concentration of inorganic precursor GPTMS.     

Synthesis and properties of hyperbranched polyurethane acrylate used for UV curing coatings

The hyperbranched polyurethane acrylate (HPUA) was synthesized through the addition of hyperbranched polyurethane endcapped by hydroxyl groups (HPU-OH), with the semiadduct urethane monoacrylate (IPDI-HEA). The HPU-OH was prepared by the amidation reaction of diethanolamine with isophorone diisocyanate. The molecular structure of HPUA was characterized by FTIR and ¹H NMR analyses. The number average molecular weight and its polydispersity index were measured by GPC to be 7714 g mol⁻¹ and 1.24, respectively. The HPUA was blended with epoxy acrylate EB600 and difunctional monomer TPGDA in different ratios, and exposed to a UV lamp for photopolymerization in the presence of Runtecure 1104 as a photoinitiator at room temperature. The photopolymerization rate and final unsaturation conversion reached to the highest values with only 5 wt% HPUA addition, whereas decreased as further added. The tensile strength of UV-cured films was improved by adding less than 10 wt% HPUA without damaging the modulus, having the value of 62.56 MPa for EB₉₀HPUA₁₀ film. Besides, the elongation at break increased continuously with the addition of HPUA, reaching to 130% for EB₇₀HPUA₃₀ film. Moreover, the impact strength was greatly enhanced by the addition of HPUA, possessing nearly two times high for EB₇₀HPUA₃₀ film compared with pure EB600 film. However, the T_g decreased as HPUA was added from the DMTA measurements. According to the ratios of T_s/T_g the HPUA has good compatibility with EB600/TPGDA resin.     

Application of laser ablation technique for removal of chemically inert organically modified silicate coatings

Removal of organically modified silicate (Ormosil) coatings from 2024-T3 aluminum alloy substrates has been investigated using a laser ablation technique utilizing a 308 nm excimer laser. Incorporation of UV-absorbing dye molecules containing λ_max in the vicinity of the laser wavelength (butyl-PBD, Furan 2, Morin, HQSA) into the Ormosil thin film was found to facilitate coating removal. Ormosil thin films containing 0.1–0.5 mol% UV-absorbing dye molecules were subjected to laser treatment at various fluences ranging from 0.2 to 0.6 J/cm². The presence of the UV-absorbing dye molecules in the Ormosil thin film was found to facilitate coating removal at a lower fluence as compared to dye-free coatings as determined by scanning electron microscopy. The effectiveness of coating removal was found to depend on several parameters including laser fluence, number of pulses per spot, and dye concentration.     

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.     

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.     

Particle generation by laser ablation during surface decontamination

Laser ablation allows significant number of particles to be generated from the surfaces of cement, chromium-embedded cement, stainless steel, or alumina. The number concentrations and size distributions of the particles were experimentally investigated with respect to applied laser fluence (mJ cm^-2) and wavelength. Based on the measurements, 266-nm laser ablation generates particles most efficiently. Of the three materials tested, cement was the most favorable for material removal, stainless steel was the next, and alumina was the least. The removal of particles from chromium-embedded cement by 532- and 1064-nm-wavelength lasers was less effective than from stainless steel, but more effective than from alumina. For ablation with a 266-nm laser, chromium enhanced the removal above 20 J cm^-2. Comparisons of other characteristics such as the size and removal rate of these particles are also discussed in this paper.     

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.     

Study on ablation behavior and mechanism of C/SiC composite irradiated by a laser with various parameters

C/SiC composite has been widely used as a high-temperature material for engineering components due to its excellent thermal properties. Facing the rapid development and threat of high-energy laser, study on the ablation resistance under laser irradiation is strongly required. In this work, a continuous high-energy laser was applied to explore the laser ablation behavior and mechanism of C/SiC composite. From the results, C/SiC composite shows different morphologies when irradiated at various laser power densities for 500 and 700 W/cm². We divided the ablation area into three regions; the central, transition, and edge regions, where the formation of SiO₂, SiO, and the breakage of carbon fiber were observed. The generated highly reflective SiO₂ layer reduces the absorption of laser energy, which is beneficial to lower the back-surface temperature and reduce the damage of composite. In addition, we put forward the ablation physical models and ablation mechanisms irradiated at different power densities. The work provides a basis for the laser ablation resistance of C/SiC composites under different conditions.     

脉冲激光轰击法连续制备纳米铜研究

采用脉冲激光轰击法连续制备了纳米铜及表面活性剂原位修饰的油溶性纳米铜,用UV-Vis研究了不同表面活性剂不同浓度对纳米铜／乙醇溶胶的紫外-可见光谱的影响,从而确定各表面活性剂的最佳浓度,用TEM研究了不同表面活性剂对纳米铜溶胶分散稳定性的影响,确定了最佳表面活性剂为平平加O,傅立叶红外光谱发现纳米铜／乙醇溶胶中乙醇分子基团振动波长受纳米铜颗粒的影响而出现红移现象,分散性实验表明：平平加O表面修饰纳米铜具有良好的油溶性。     

A comparative investigation on micro-channel by using direct laser ablation and liquid-assisted laser ablation on zirconia

In this work, direct laser ablation (DLA), liquid-assisted laser ablation in water (LALA-W) and in ethanol (LALA-E) is applied to fabricate single micro-channels on the zirconia ceramic by using a picosecond laser. To assess the machining ability of them, micro-channels fabricated are characterized and compared the differences in morphology, geometric profile, chemical and phase composition. The morphological results indicate that both LALA-E and DLA can fabricate microchannel with obvious recast layer and cracks, and LALA-W can fabricate microchannel with a porous surface, and almost no recast layer and cracks. The results of geometric characteristics show that LALA-W can fabricated micro-channels with “U” shape profile with 52.74% enhancement in depth compared to that “V” shape by DLA and LALA-E. The XPS results demonstrate that LALA-W can exhibit the smallest oxygen vacancies with 50.01% than that of LDA 53.81% and LALA-E 54.56%. For XRD results, after machining by all three processes, the zirconia ceramic undergoes the tetragonal→monoclinic phase transformation, resulting in an increase in monoclinic phase. While LALA-W exhibits the smallest increase in monoclinic phase from 9.9% to 12.7%, and has the most tetragonal phase content of 58.8%.     

Research on the ablation mechanism and ablation threshold of CMC-SiCf/SiC by using dual-beam coupling nanosecond laser

Due to the excellent properties of high hardness, oxidation resistance and high temperature resistance, silicon carbide fiber silicon carbide ceramic matrix composite (CMC-SiC_f/SiC) is a typical difficult-to-process material, and is a high-performance advanced material in the aerospace field. In this paper, two groups of ablation experiments (experiment 1 and experiment 2) were performed on CMC-SiC_f/SiC using a dual-beam coupling nanosecond laser, and the ablation morphology was observed by confocal laser microscope. The dual-beam coupling angle of experiment 2 is obtained by experimental method. And through the method of calculation, we get the dual-beam coupling angle of experiment 1 and experiment 2. According to the dual-beam coupling ablation mechanism, based on the theoretical calculation model of non-destructive method D²-lnP₀, combined with the Equivalent Diameter Calculation Method (EDCM) and Equivalent Area Calculation Method (EACM), the laser ablation threshold corresponding to different beam waist size was calculated and compared. The results show that the ablation region of CMC-SiC_f/SiC surface can be divided into three parts: ablation boundary, recast layer area and SiO₂ coverage area. When the pulse energy increases gradually from 300 μJ to 1500 μJ, the variation trend of hole depth is first increase, second decrease, increase again, and finally decrease. The angle between two laser beams affects the waist radius, which in turn affect the laser ablation threshold. The waist of the dual-beam coupling is elliptical, and the orifice of the ablation hole is elliptical. When the waist radius of nanosecond laser is 57 μm, the laser ablation threshold is calculated to be 3.12 J/cm². The main factors affecting the laser ablation threshold are laser pulse repetition frequency (f), beam waist radius (ω₀), laser pulse width (τ), minimum laser power (P_th), and laser wavelength (λ).     

Synthesis and photoinitiating behavior of benzophenone-based polymeric photoinitiators used for UV curing coatings

Three benzophenone-based type II polymeric photoinitiators, poly(2-(4-benzophenone methylene ether)-1,3-dihydroxypropane maleate)) (PBM), poly(2-(4-benzophenone methylene ether)-1,3-dihydroxypropane succinate)) (PBS), and poly(2-(4-benzophenone methylene ether)-1,3-dihydroxypropane-co-2-(phenyl-methylene-ether)-1,3-dihydroxypropane maleate)) (PBPM) used for free radical UV curing systems, were prepared through the step-growth polymerization of 4-(2,3-epoxypropyloxy) benzophenone (EBP) with maleic anhydride and succinic anhydride, as well co-polymerization with phenyl glycidyl ether and maleic anhydride, respectively. The molecular structures were characterized with ¹H NMR and FT-IR spectroscopy, and GPC analysis. For equimolar EBP and MA reaction system, the M_n led to the maximum of 6868 g/mol with the PDI of 1.22. The UV spectroscopy analysis showed that the synthesized polymeric photoinitiators possess higher UV absorption intensity in the wavelength range of 300–400 nm compared with benzophenone (BP). The photoinitiating activity was examined based on the photopolymerization of tripropyleneglycol diacrylate (TPGDA) in the presence of triethylamine as a coinitiator by using Photo-DSC method. It was found that PBM and PBS showed higher photoinitiating efficiency than BP in the photopolymerization of TPGDA. Moreover, the side BP moiety incorporated into the polymeric chain possessed higher initiating activity than end-capped BP moiety. Moreover, PBM with higher molecular weight was more efficient to photoinitiate TPGDA UV-cured. The side chromophore group distribution in the molecular chain also affected the photoinitiating activity. The highest photopolymerization rate at the peak maximum was obtained by the photoinitiation with PBM prepared with the molar feed ratio of 1.0 of EBP to MA.     

Development of photoluminescent powder coatings by UV curing process

The use of thermal curing powder coatings have obtained a wide acceptance, but is limited to the metal substrates applications, because they need high temperatures for the film curing. Safety sings in edifications use, generally, PVC substrates, that are unable to support typically curing temperatures (150–200 °C). In order to prepare a photoluminescent powder coating by UV curing process, an experimental technique was development and the influence of some preparative conditions were studied. To achieve the better results, photoluminescent pigment percentage, conditions of ultra-centrifugal mill and thickness of deposition coating were varied in order to increase the luminance decay time.     

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.     

紫外固化粉末涂料的合成及固化研究

用E-12、E-20环氧树脂与丙烯酸反应,合成了可紫外光固化的环氧丙烯酸酯预聚物,并对产物进行固化研究。讨论了催化剂的种类、反应温度、反应时间等对合成产物的影响,光引发剂的种类、光照时间等对固化产物的影响。结果表明:环氧树脂与丙烯酸以甲苯为溶剂、四丁基溴化铵为催化剂,在110℃下反应180 min为较适宜的反应条件;环氧丙烯酸酯以TPO为引发剂,120 w/cm的紫外灯光照15 s为较宜适的固化条件。     

Fabrication of micro-scale textured grooves on green ZrO2 ceramics by pulsed laser ablation

The green ZrO₂ ceramics were fabricated by cold isostatic pressing. Pulsed laser ablation with a wavelength of 1064 nm was performed to fabricate micro-scale textured grooves on the surface of green ZrO₂ ceramics. The influence of laser parameters on surface quality was studied. The heat-affected zone around the machined grooves and micromorphology of laser-irradiated surface were investigated. Results showed that micro-scale textured grooves with a width of 30–50 µm and a depth of 15–50 µm on the green ZrO₂ ceramic surfaces were successfully fabricated by pulsed laser ablation. The laser parameters had a profound influence on the surface quality of micro-scale textured grooves. Better surface quality could be obtained with frequency below 40 Hz, power below 6 W, and scanning velocity above 200 mm/s. A sintering layer was found on the laser-irradiated surfaces when frequency was above 60 Hz, power was above 10 W, and scanning velocity was below 150 mm/s. Analysis of this sintering layer revealed clear melting and resolidification of ZrO₂ particles.     

One-step synthesis of γ-Fe2O3 nanoparticles by laser ablation

A Nd:YAG pulsed laser was used to ablate a 0.5-mm-diameter iron wire in a sealed chamber in a mixed gas flux of N₂ and O₂ to generate pure γ-Fe₂O₃ nanoparticles at atmospheric pressure. Structural characteristics and sizes of the prepared nanoparticles were determined by X-ray diffraction and TEM. The effects of laser power density, total mixed gas pressure and the oxygen ratio on the mean particle size were investigated, respectively. The results showed that the mean particle size decreased with the increase of the laser power density, total gas pressure and the oxygen ratio, respectively. Besides, the nanoparticle formation mechanism by laser ablation of iron wires was also discussed.