Bioactive glass coating using aerosol deposition

This work demonstrates the successful deposition of bioactive glass (BG) 45S5 coatings on various metallic and ceramic substrates at room temperature under low vacuum condition by using aerosol deposition (AD). This room temperature and particle impact consolidation-based deposition method enabled us to deposit well-adhered and dense BG coatings directly on metallic and ceramic substrates. In vitro tests with human osteoblast-like cells on substrates with a 45S5 BG coating demonstrated high cell activity on the surfaces. All tested materials exhibited high in vitro biocompatibility as no inhibition in cell proliferation could be observed. The utilization of AD process for achieving non-crystalline BG coatings is promising for practical bio-medical applications, e.g., bioactive coatings on bioinert metallic and ceramic substrates.     

Corrosion resistance of Al2O3-Y2O3-SiC coating on depleted uranium prepared by cathode plasma electrolytic deposition

Al₂O₃-Y₂O₃-SiC composite coatings were prepared on depleted uranium by cathode plasma electrolytic deposition in Al(NO₃)₃, Y(NO₃)₃, SiC nanoparticles and anhydrous ethyl alcohol mixture. The resulting coating consisted of an inner barrier layer and an outer porous layer. The SiC nanoparticles were incorporated into the composite coating and decreased the coating porosity by filling the pores. The potentiodynamic polarization test and neutral salt spray test revealed that the corrosion resistance of depleted uranium was enhanced by the composite coating. Moreover, with increasing the content of SiC nanoparticles in the coating, the coating corrosion resistance was improved gradually.     

Preparation of Al2O3 coating on TiN coating by polymer-assisted deposition to improve oxidation resistance in coking inhibition applications

In order to inhibit the metal catalytic coking and improve oxidation resistance of single TiN coating, the TiN/Al₂O₃ double layer coatings were designed as a chemically inert coating for methylcyclohexane supercritical pyrolysis. Internal TiN coatings were prepared by atmospheric pressure chemical vapor deposition using TiCl₄–H₂–N₂ system. The external Al₂O₃ coatings with different thicknesses were prepared on the TiN surface by polymer-assisted deposition, and the coating with the most suitable thickness was further annealed at different temperatures of 600, 700, 800 and 900 °C. The morphology, elemental and phase composition of TiN/Al₂O₃ coatings were characterized by SEM, EDX and XRD respectively. The chemical state information of the coating elements was based on Ti 2p, Al 2p core level X-ray photoelectron spectroscopy (XPS) spectra. The results indicated that the external Al₂O₃ coating will partially peel off at 900 °C annealing temperature. The thermogravimetric analysis results indicated that all TiN/Al₂O₃ coatings show better oxidation resistance than single-layer TiN coating. The anti-coking test with methylcyclohexane supercritical pyrolysis showed that the TiN/Al₂O₃ coatings can effectively cover the metal catalytic sites and eliminate metal catalytic coking. However, the acid sites of external Al₂O₃ coating slightly promoted coking, so the anti-coking ratios of TiN/Al₂O₃ coatings were smaller than that of TiN. Thus, the addition of external Al₂O₃ coating can greatly improve the oxidation resistance of TiN coatings with little loss of coking resistance.     

Determining the local pressure during aerosol deposition using glass memory

Aerosol deposition (AD) is a dynamic loading process that can be envisioned as a shock wave loading, necessitating the consideration of the elastic/plastic response of solid materials. Due to the dynamic nature of this process, however, experimental determination of the local pressures during the deposition process is difficult. This work addresses this by investigating the compression and subsequent structure modification of a silicate glass after room-temperature AD on a silicate glass substrate with Raman spectroscopy. Clear structural changes in the short- and middle-range order of the silicate glass were observed, both as intertetrahedral angle distribution and as ring statistic. Therefore, the AD induced permanent densification of the glass, equivalent, in a hydrostatic approximation, to a minimal pressure of 10.5 ± 1.5 GPa during the film deposition process. Furthermore, the analysis of the Nd³⁺ photoluminescence of the ⁴F_3/2 − ⁴I_9/2 transition provided complementary information on the glass network modifications occurring during film formation. More than a pure hydrostatic densification, the AD seems to present a very intense shear deformation. This work opens up the perspective of evaluating the mechanical response of film-substrate and of the particles themselves, and provides critical information on the mechanisms responsible for the AD film formation.     

Microstructure and plasma corrosion behavior of yttria coatings prepared by the aerosol deposition method

Particle contamination arising from inner ceramic components of the plasma etching equipment has become a serious issue. Yttria (Y₂O₃) coatings prepared via aerosol deposition (AD) have demonstrated superior plasma resistance in the reduction of particle contamination. The superior particle contamination performance of Y₂O₃ coatings prepared by AD has been speculatively attributed to its unique microstructure; however, the relationship between the coatings’ microstructure and plasma corrosion behavior has been insufficiently clarified. Herein, we investigated the relationship between the microstructure and plasma corrosion behavior of Y₂O₃ coatings prepared by the AD method and compared the results with those for coatings prepared by other coating methods. When internal pores are present, these internal pores were selectively plasma corroded; plasma corrosion marks reflecting their pore shape were formed, and the surface roughness increased with increasing plasma exposure time. However, when no internal pores were present, as in the case of the AD coating, the surfaces were homogeneously corroded and maintained their initial surface. As the risk of particle contamination caused by the corrosion of the plasma-resistant coatings is greatly increased with surface roughness, we concluded that the Y₂O₃ coating prepared via AD will contribute greatly to reducing particle contamination.     

Dual layer SiC coating on matrix graphite sphere prepared by pack cementation and fluidized‐bed chemical vapor deposition

A dual layer silicon carbide (SiC) coating including inner porous SiC (p‐SiC) layer and outer dense SiC (d‐SiC) layer was fabricated on the matrix graphite (MG) spheres of high‐temperature gas‐cooled reactor fuel elements by pack cementation and fluidized‐bed chemical vapor deposition process to improve the oxidation‐resistant property. Microstructure of the coating demonstrates different density and structure of the two SiC layers with no obvious boundaries between them. Weight gain curves of oxidation tests at 1773 K for 200 hours show that the coating could effectively protected the MG sphere by isolating the air infiltration with p‐SiC layer as the main functional layer and d‐SiC layer as the transition layer to improve the bond strength. Due to the transition function of p‐SiC layer, the coated spheres could understand more than 50 times thermal shocking tests from 1773 K to room temperature with no stress cracking.     

Controlling the degradation rate of bioactive magnesium implants by electrophoretic deposition of akermanite coating

In order to improve the corrosion resistance and the surface bioactivity of biodegradable magnesium alloys, a nanostructured akermanite (Ca₂MgSi₂O₇) coating was grown on AZ91 magnesium alloy through electrophoretic deposition (EPD) assisted with micro arc oxidation (MAO) method. The crystalline structures, morphologies and compositions of samples were characterized by X–ray diffraction, scanning electron microscopy and energy dispersive spectroscopy. The in vitro bio–corrosion (biodegradability) and bioactivity behaviors of samples were investigated by electrochemical and immersion tests. The experimental results indicated that the nanostructured akermanite coating could slow down the corrosion rate and improve the in vitro bioactivity of biodegradable magnesium alloy. Thus, magnesium alloy coated with nanostructured akermanite may be a promising candidate to be used as biodegradable bone implants.     

镁钙砂表面沉积MgO涂层的动力学分析

采用MgO碳热还原和扩散氧化法在镁钙砂表面沉积MgO涂层,研究了MgO涂层的沉积动力学、微观形貌、生长机制以及涂层厚度对镁钙砂抗水化性能的影响。结果表明：随着反应温度的升高,沉积过程存在两个控制机理,在1400～1500℃之间,为化学动力学控制,反应为一级反应,活化能为97.82 kJ·mol^-1;在1500～1600℃之间,沉积过程为扩散控制,扩散活化能为19.18 kJ·mol^-1;MgO涂层以方镁石和方钙石为基底均呈二维台阶状生长,但二者生长机制并不完全相同;抗水化实验结果显示最佳处理温度为1600℃、沉积时间为6 h,镁钙砂水化质量增加率为0.02%,约是处理前的1/150。     

High temperature performances of tri-layer environmental barrier coating with Si bond layer modified by Yb2O3

Environmental barrier coatings (EBCs) have been expected to be applied on the surface of ceramic matrix composites (CMCs). However, the oxidation and propagation cracking of the silicon bond layer are the most direct causes to induce the failure of EBCs under high temperature service environment. The modification of silicon bond layer has become an important method to prolong the service life of EBCs. In this work, the Yb₂O₃ have been introduced to the silicon bond layer, and three kinds of tri-layer Yb₂SiO₅/Yb₂Si₂O₇/(Si-xYb₂O₃) EBCs with modified Si bond layer by different contents of Yb₂O₃ (x = 0, 10 vol%, 15 vol%) were prepared by vacuum plasma spray technique. The thermal shock performance and long-term oxidation resistance of the EBCs at 1350 °C were investigated. The results showed that the addition of appropriate amount of Yb₂O₃ (10 vol%) can improve the structural stability and reduce the cracks of the mixed thermal growth oxide (mTGO) layer by forming the oxidation product of Yb₂Si₂O₇ during long-term oxidation. The excessive addition of Yb₂O₃ increased the stress during thermal shock as well as accelerated the oxygen diffusion during long-term oxidation, leading to the failure of EBCs. Moreover, the distribution uniformity of Yb₂O₃ deserves further consideration and improvement.     

管道等离子喷涂Cr_2O_3复合涂层及其耐蚀性能

采用等离子喷涂技术在X70管线钢表面喷涂Cr_2O_3复合涂层,利用X射线衍射仪、扫描电镜、维氏硬度计、划痕仪、电化学工作站等方法表征了涂层相关特征与性能。结果表明,相成分主要是Cr_2O_3和TiO_2,硬度可达4.928GPa,结合力可达46.15N,粘结层+陶瓷层试样腐蚀速率显著降低,对基体有很好的耐蚀保护作用。     

铝合金表面电解沉积稀土转化膜工艺研究

研究了一种通过电解沉积方法在防锈铝LF21表面上生成铈盐转化膜的工艺,应用正交实验研究了有关因素对成膜过程的影响并获得了最佳的技术参数用极化曲线、交流阻抗和中性盐雾试验等方法测试了该工艺形成膜层的耐蚀性能及其组成一结果表明：经过电解沉积稀土转化膜处理后,防锈铝的阳极腐蚀过程受到了阻滞,自然腐蚀电位负移;与经过化学转化膜处理后相比,其耐蚀性能有显著提高,可通过400h的中性盐雾实验,亲水性能亦有明显提高。     

Mechanical integrity of ceramic coatings on Kapton made by a dry aerosol deposition of lunar mare simulant

The purpose of this paper is to demonstrate the use of lunar regolith and the dry aerosol deposition (DAD) method to produce ceramic coatings on polyimide polymer, and to test their mechanical integrity. Ceramic films were produced on Kapton substrates using a custom-built DAD system and lunar mare simulant (LMS) feedstock. Ultrafine grains and impact densification were confirmed using atomic force and electron microscopy. Mechanical properties of the DAD–LMS Kapton samples were evaluated with indentation, tensile, and mandrel bend tests. DAD–LMS coatings tripled the hardness and doubled the indentation modulus of the Kapton surface. Coatings 3–16 µm thick did not have a predictable effect on the ultimate tensile strength or elongation to failure; however, the apparent modulus of elasticity did increase. The coatings were able to withstand significant bending before damage, with critical bend radii of 5 and 1.5 mm for 7.5 µm and 120 nm thicknesses, respectively. Modest heat treatment was shown to reduce the bending strain of coated substrates. Advanced ceramic coatings are of interest for the protection of space and satellite polymers from micrometeoroid impacts, radiation, and atomic oxygen. Lunar posts and habitats will require the development of space manufacturing techniques and in situ resource utilization.     

Room temperature impact-induced deposition of pure SiC coating layer by vacuum kinetic spraying

This study successfully manufactured a thick, pure SiC coating layer with a thickness of 83.3 μm using vacuum kinetic spray process and investigated the unique impact-induced deposition behavior at room temperature. The simulated result of SiC particle collides with the metallic matrix, or predeposited SiC layer confirmed that particle shock pressure could increase up to the maximum pressure of 27.2 GPa. Moreover, the particles were predicted to fracture to submicrometer size after plastic deformation and those characteristics also matched microstructural observations made with a transmission electron microscope. The SiC coating layer formed an unexpected microstructure composed of bent lattices, fractured submicrometer-sized particles, and amorphous layers. Correlating the microstructure and simulation results suggested that a pure SiC coating layer could be formed using mechanical anchoring and amorphous bonding at room temperature.     

Dual layer structural thermoplastic polyester powder coating film and its weathering resistance

Micro FTIR analysis was performed to the point with a 50–80 μm spatial resolution to verify the exact structure of a new blend thermoplastic powder coating film. Resistance to certain artificially accelerated conditions and actual outdoor exposure were examined to confirm the performance of the film as a protective coating for use in the telecommunication field. The new blend powder coating film consists of primary polyethylene terephthalate (PET) and secondary polyvinyl butyral (PVB) resins, and has a distinct dual phase structure. Specifically, it forms a continuous PVB phase in a surface layer with a thickness of approximately 100–150 μm. Good corrosion resistance was confirmed in artificially accelerated testing using salt water spray, heat cycle, and accelerated UV tests. Actual outdoor exposure in a metropolitan area (Shinkiba in Tokyo) and a coastal area (Miyake Island) revealed good weathering performance throughout the study period. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Effect of phase composition on the oxidation resistance of ZrB2-SiC coatings

ZrB₂-SiC-Al₂O₃ (ZSA) and ZrB₂-SiC-Si (ZSS) coatings were prepared on the surface of C/C composites by atmospheric plasma spraying. During oxidation at 1200 ℃ for 10 h, the formation of B₂O₃ in the ZSA coating volatilizes gradually, no glass phase is able to seal cracks and holes, resulting in poor oxidation resistance. On the other hand, the ZSS coating produces a large amount of borosilicate glass phase and still gains 0.8% weight after 10 h. During oxidation at 1500 ℃, a low viscosity SiO₂ glass phase forms on the ZSA coating, due to the presence of Al₂O₃ and this glassy phase has a good ability to seal defects. However, the rapid volatilization of B₂O₃ in the ZSS coating leads to the formation of large holes in the coating, and to progressively increased viscosity of SiO₂ glass phase, resulting in decreased oxidation resistance.     

High-temperature interactions of desert sand CMAS glass with yttrium disilicate environmental barrier coating material

A calcium-magnesium aluminosilicate (CMAS) glass was prepared by melting a sample of desert sand to evaluate the high-temperature interactions between molten CMAS and yttrium disilicate (Y₂Si₂O₇), an environmental barrier coating (EBC) candidate material. Cold-pressed pellets of 80?wt% Y₂Si₂O₇ powder and 20?wt% CMAS glass powder were heat treated at 1200?°C, 1300?°C, 1400?°C and 1500?°C for 20?h in air. The resulting phases were evaluated using powder X-ray diffraction. In the second set of experiments, free standing hot-pressed Y₂Si₂O₇ substrates with cylindrical wells were filled with CMAS powder to a loading of ~35?mg/cm² and heat treated in air at 1200?°C, 1300?°C, 1400?°C and 1500?°C for 20?h. Scanning electron microscopy, energy-dispersive spectroscopy and electron microprobe analysis were used to evaluate the microstructure and phase compositions of specimens after heat treatment. An oxyapatite silicate (Ca₂Y₈(SiO₄)₆O₂) phase was identified in all specimens after CMAS exposure regardless of heat treatment temperature. Apatite appeared to form by dissolution of Y₂Si₂O₇ into molten CMAS, reacting with CaO in the melt according to the reaction 4Y₂Si₂O₇ +?2CaO → Ca₂Y₈(SiO₄)₆O₂ +?2SiO₂, and followed by precipitation of the apatite phase.     

Fabrication of high-quality alumina coating through novel,dual-particle aerosol deposition

High-quality alumina (Al₂O₃) coating has an extensive demand in the fields of optoelectronics, solar cells, and corrosion/impurity resistant coatings and cutting tools. The quality of alumina coating depends on its hardness and transparency. To obtain hard and highly transparent alumina coating, which is also a widely used ceramic material, a novel, aerosol deposition approach is presented in which the starting powder, used to fabricate Al₂O₃ ceramic coatings, is composed of angular and spherical Al₂O₃ particles. Films fabricated using angular:spherical Al₂O₃ particle mixtures with ratios of 10:0, 7:3, 5:5, 3:7, and 0:10, showed significant variation in surface roughness and microstructure. The dramatic morphology modulation of the 3:7 angular:spherical Al₂O₃ mixture film, resulting from the superposition hammering effect caused by the aerosol mixture, improved transmittance (84.7%) and hardness (13.6 GPa). Previous studies used high-energy approaches to optimize Al₂O₃ film properties. This dual-particle approach, however, produces Al₂O₃ film with excellent transmittance and hardness while achieving a fast coating speed (32 mm² × μm/min) without additional thermal treatment. Our proposed approach provides a novel and energy efficient method to produce transparent Al₂O₃ films with superior durability.     

Mechanistic investigation of aluminide coating formation by low-pressure chemical vapor deposition method on NiCoCrAlY coating in presence of nickel-ceria composite layer

In this study, a hybrid coating comprised of NiCoCrAlY fabricated by HVOF method, Ni–CeO₂ composite coated by electrodeposition, and aluminide coating applied by low pressure chemical vapor deposition (LPCVD) method are investigated. To elucidate the formation process of aluminide coating, the microstructure and properties of the applied coatings were examined by field emission scanning electron microscopy (FESEM), X-ray diffraction (XRD), and EDS analyses. It was concluded that the desired β-NiAl phases are uniformly created within a single step on the surface. Furthermore, with the extending of the coating duration from 2 to 4 h, the thickness of the aluminide coating was increased from 14 to 25 μm. The thickness values were increased even further in the presence of Ni–CeO₂ coating, where the growth mechanism was also changed. Within 4 h, a coating with a thickness of roughly 50 μm was obtained. Moreover, in the presence of Ni–CeO₂ coating, it was observed that the inward diffusion of aluminum was predominant at the beginning of the process, whereas with longer processing durations, the outward diffusion of the nickel becomes dominant instead.     

High-voltage all-solid-state lithium metal batteries prepared by aerosol deposition

High-energy-density and safe rechargeable batteries are key components to realizing a low-carbon society. All-solid-state Li-metal batteries have the potential to achieve both high safety and high energy densities. However, the large interfacial resistance between solid electrolytes and cathodes is the major challenge for developing all-solid-state Li-metal batteries. Here we deposited a Li-rich layered metal oxide Li_1.2Mn_0.54Ni_0.13Co_0.13O₂ (LMNC) thin film (6 µm thick) on an Al-doped Li₇La₃Zr₂O₁₂ (LLZO) substrate at room temperature by aerosol deposition. The LMNC particles were coated with Li₃BO₃ (LBO), which acted as a binder to hold LMNC and LLZO together at heating. As a result, good interfacial contact was achieved between LMNC and LLZO. Yet reactions between LMNC and LBO would occur at heat treatment temperatures above 600 °C. The highest discharge capacity of the all-solid-state Li/LLZO/LBO-LMNC cell at 0.1 C and 60 °C was 223 mAh g^-1. The main reason for the cell capacity decay was the cracking of the LBO-LMNC cathode layer during cycling. Searching for a more suitable binder material with a high fracture toughness is crucial for further developing the aerosol-deposited LLZO-based all-solid-state Li metal batteries.     

Enhancement of mechanical properties of hydroxyapatite coating prepared by electrophoretic deposition method

The addition of bio-inert ceramics such as alumina and zirconia can significantly improve the mechanical properties of hydroxyapatite bioactive coatings and increase their biocompatibility. In the present study, the surface of a titanium substrate was coated by the electrophoretic deposition method (EPD). Moreover, the reaction bonding process has been used to precipitate the nanocomposite containing the hydroxyapatite (HA), alumina, yitteria-stabilized zirconia (YSZ). The coating process was performed by an electrical power supply and a suspension of hydroxyapatite, aluminum, and YSZ nanopowders. For preparing a suspension consisting of 50% isopropanol and 50% acetone, 0.6 g/L of iodine was used as a stabilizer. Green and sintered coatings were analyzed by FE-SEM and XRD. In addition, the mechanical properties such as bonding strength, hardness, and toughness were measured. The hardness, bonding strength, and toughness of the HA coating were 107 ± 10.3 HV, 10.8 ± 3.2MPa, and 0.72MPa√m, respectively, while those of the HA-Al₂O₃-YSZ nanocomposite coating were 213 ± 1.8 HV, 35 ± 1.6MPa, and 1.6MPa√m, respectively.