Vitreous phosphate coatings on silicate glasses

Translated from Steklo i Keramika, No. 4, pp. 14–15, April, 1991.     

Properties of hydroxyapatite prepared by the hydrolysis of tricalcium phosphate

Non-stoichiometric hydroxyapatite was prepared by the hydrolysis of α-tricalcium phosphate. The apatite was obtained as a powder and hardened with and without stirring during the hydrolysis. The apatite had a general formula, characteristic dehydration and pyrolysis behaviour similar to that of precipitated non-stoichiometric hydroxyapatite. In addition, it exhibited some new phenomena (i.e. thermal reaction between lattice H₂O and PO₄^3? above 473 K, formation of ESR centres above 473 K and disappearance at 873–973 K, and a slight weight loss at 873–973 K). Apatite particles were composed of aggregates of cylindrical rods or thin blades grown along the c-axis or {100} faces of apatite structure. Hardened apatite materials with various porosities above 55% and bulk densities below 1.4 g cm^?3 were obtained by using different water-soluble additives. The strength of the hardened materials was 20–500 kg cm^?2 in compression and 10–120 kg cm^?2 in bending. The strengths were improved at least two to three times by impregnating the hardened materials with methyl methacrylate polymer.     

Characterization of composite titanium nitride coatings prepared by reactive plasma spraying

Reactive plasma spraying (RPS) technology has been used to produce high thickness (>100 μm) films of composite Ti-TiN-Ti_xN_y coatings. Reactively sprayed coatings obtained from SP700 (Ti-4.5Al-3V-2Mo-2Fe) and Ti6242 (Ti-6Al-2Sn-4Zr-2Mo) powders, deposited onto flat substrates of Ti-6Al-4V, have been investigated. X-ray diffraction (XRD) and micro-hardness measurements have been used to characterize the crystallographic features and differences between the hardness of cross-section and surface. Scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS) techniques have been used to determine the morphology and surface chemical composition of the coatings. Back-scattered electron imaging has revealed the distribution of Ti and TiN in the composite material. Obtained results evidenced a sharp interface between the coating and substrate in terms of the profile of chemical composition. The presence of unmelted Ti particles as well as the formation of nitrides was observed.     

Influence of organics on ZnO coatings prepared by chemical solution deposition

Highly c-axis-oriented ZnO thin films were prepared on soda–lime–silica glass substrates by chemical solution deposition process using a zinc-naphthenate precursor as a starting material. In order to investigate the effect of pyrolysis temperature on properties of the films such as crystallinity, surface morphology and transmittance in visible spectra region, the precursor films were pyrolyzed at 300 °C or 500 °C, followed by final heat treatment at 600 °C. Highly transparent films in visible spectra region were obtained. The relationship between residual organics and properties of the annealed films was discussed.     

两种电化学方法对制备羟基磷灰石涂层的差异性研究

通过恒电流和脉冲电流技术在钛基表面制备磷酸钙,然后经热碱处理得到羟基磷灰石(HAP)涂层。利用X射线衍射(XRD)、红外光谱(FT-IR)和扫描电镜(SEM)等手段对涂层的结构及形貌进行了表征,并对涂层的耐腐蚀性进行了研究。结果表明,恒电流与脉冲电流技术均可在钛基表面电沉积羟基磷灰石涂层,所得的2种涂层均具有良好的生物相容性;与恒电流方法制得的涂层相比,脉冲电流技术制得的涂层更均匀、致密,与基体结合强度较高,在模拟体液中表现出较好的耐腐蚀性。     

Properties of amine‐containing coatings prepared by plasma polymerization

Two monomers, ethylenediamine (EDA) and diaminocyclohexane (DACH), were plasma‐polymerized in continuous‐wave (CW) and pulse modes. The influence of different plasma parameters on the deposition rate and film composition were investigated in detail and the changes in aminofunctionalization with varying pulse parameters were examined by FTIR, ESCA, and chemical‐derivatization techniques. It was shown that a varying duty cycle does not produce a considerable effect on the retention of amine groups into the film, while power and t_on play a significant role in the polymerization process. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 979–990, 2004     

Organic coatings for marginally prepared steel surfaces

The present study, carried out in the frame of a common research programme between the Institute of Chemistry, Faculty of Engineering at the University of Genoa and AGIP CORM Department about alternative surface preparation methods, is a preliminary contribution to the development of a series of rust-prevention coatings that can be applied directly in order to protect steel structures exposed to aggressive environments. The use of ‘rust converters’ may be considered a tool for alternative surface preparation but it is necessary to control the amount of loose rust layers and to ensure their complete removal. The poor adhesion level of converted layers is a problem not yet solved and it does not allow for a subsequent coating and/or finishing step. The application of the ‘surface tolerant’ coating systems seems to be a more useful way to protect steel structures without sandblasting and all its related economic and environmental disadvantages. The application of these systems on marginally prepared steel surfaces shows promising reliability both for the intrinsic protective power and for the adhesion to the metallic substrata. Their use during repainting maintenance is a reliable proposition and a profitable way to overcome not only technical problems but also subsequent environmental pollution and related constraints.     

控制结晶法制备球形磷酸铁的团聚尺寸模型

磷酸铁是制备锂离子电池正极材料磷酸铁锂的主要前躯体之一,磷酸铁的形貌和粒度大小对磷酸铁锂材料的电化学性能有较大影响.为了更好地实现磷酸铁的可控制备,有效改善磷酸铁锂的电化学性能,文中采用硝酸铁和磷酸反应合成磷酸铁的液相结晶控制工艺,研究了反应结晶釜中反应物浓度、温度、搅拌速度与沉淀物颗粒粒径之间的关系,结果表明:沉淀物...     

Calcium phosphate cements based on alpha-tricalcium phosphate obtained by wet method: Synthesis and milling effects

Calcium phosphate cements present many advantages for their use as bone substitute, among which biocompatibility and bioactivity. However, these cements generally have low mechanical strength compared to the bones of human body. This work aims to develop a method to produce calcium phosphate cements based on alpha-tricalcium phosphate and to evaluate the influence of milling time (0–16 h) on their particle size and mechanical properties. The obtained powder was characterized by particle size analysis and X-ray diffraction. The proposed method allowed to obtain highly pure alpha-tricalcium phosphate. The milling resulted in different average particle size, showing a decrease of around 83% with 16 h of milling. Specimens were prepared and evaluated by apparent density, microstructure by scanning electron microscopy and compressive strength. The variation of the average particle size influenced the compressive strength whose best result was obtained for the sample without additional milling.     

Calcium phosphate grafts produced by rapid prototyping based on laser cladding

Rapid prototyping based on laser cladding by powder injection has been used to produce calcium phosphate three-dimensional grafts without using molds. Precursor material comprising of hydroxyapatite (HA) powder was irradiated by means of an infrared Nd:YAG laser. The processing parameters and the thermal history of the processed material have been assessed and the process has been optimized to obtain solid parts. Processing by laser cladding lead to complete dehydroxylation of the precursor HA, the obtained microstructure is composed by an alpha-tricalcium phosphate (α-TCP) matrix with nucleated tetracalcium phosphate (TTCP) grains, in coexistence with oxyapatite and amorphous calcium phosphate. The produced bioceramic grafts were observed to be bioactive, leading to calcium-deficient hydroxyapatite precipitation and promoting pre-osteoblastic cell attachment and proliferation during “in vitro” cell culture test.     

Properties of ceramic coatings of phosphate ceramics

Conclusions The phosphate ceramic coatings made from Al₂O₃ and ZrO₂ containing ortho- and metaphosphate of aluminum, in terms of properties (adhesion, thermal-shock resistance, and impact strength) are 1.5-3 times better than other coatings based on Al₂O₃ and ZrO₂.The low thermal conductivity, the appreciable bonding strength with metals and alloys, and the high thermal-shock resistance enable us to recommend the coatings for protecting metals and alloys from the action of high-temperature gas currents.Translated from Ogneupory, No. 1, pp. 41–45, January, 1971.     

Microstructure and properties of niobium carbide composite coatings prepared by plasma spraying

Niobium carbide composite coatings were prepared on titanium alloy surface by plasma spraying NbC–Al₂O₃, Nb–SiC and Nb–SiC–Al composite powders, respectively. The phase composition, microstructure and formation mechanism of the three composite coatings were analyzed and their microhardness, toughness and scratch resistance were compared. The phases of the NbC–Al₂O₃ system did not change during the plasma spraying process, and new phases (Nb₂C, NbC and Nb₃Si) were formed in the Nb–SiC and Nb–SiC–Al systems. TEM results of the Nb–SiC composite coating indicate that the new phases nanocrystalline Nb₂C, submicron NbC and nanocrystalline Nb₃Si were formed during the plasma spraying process. Compared with the NbC–Al₂O₃ composite coating, the microstructure of the Nb–SiC and the Nb–SiC–Al composite coatings were uniform, and the porosity were relatively low, and the hardness was higher. The Nb–SiC–Al composite coating was denser than the Nb–SiC composite coating, the lamellar structure was obvious and the number of pores in the coating was the least, which is attributed to the better molten state of the composite powder by the addition of the Al to the Nb–SiC system. The Nb–SiC–Al composite coating had better toughness and scratch resistance.     

摩擦喷射电沉积制备Ni-Al2O3纳米复合镀层

采用摩擦喷射电沉积工艺制备了N i-A l2O3纳米复合镀层。研究了电压、镀液中纳米颗粒含量、镀液喷射速度、镀笔相对运动速度等工艺参数对镀层沉积速度以及镀层中纳米颗粒含量的影响。结果表明,电压对镀层沉积速度影响较大,电压、镀液中纳米颗粒含量对复合含量的影响较大。扫描电镜及能谱测试显示,该纳米复合镀层表面较为平整、致密,纳米颗粒在镀层中呈均匀弥散分布,含量在2%~5%。     

Wet abrasive wear behavior of WC-based cermet coatings prepared by HVOF spraying

In this study, three kinds of WC-based cermet coatings including WC–CoCr coating, WC–Ni coating and WC–Cr₃C₂–Ni coating were prepared by the high-velocity oxygen-fuel (HVOF) spraying process. Scanning electron microscopy (SEM), energy disperse spectroscopy (EDS) and Vickers hardness tester were used to analyze the microstructure and mechanical properties of these coatings. The WC–CoCr coating presented the highest average microhardness of 1205 HV_0.3, and then followed by the WC–Cr₃C₂–Ni coating (1188 HV_0.3) and the WC–Ni coating (1105 HV_0.3). The abrasive wear behavior of the WC-based coatings under the conditions of different applied loads and sediment concentrations were studied by a wet sand-rubber wheel tester. The results indicated that the abrasive wear loss rates of all the coatings increased with the increment of applied load or sediment concentration. In addition, the coatings with higher microhardness appeared to have higher abrasive wear resistance. The abrasive wear resistance of the WC-based coatings was 4–90 times higher than that of AISI 304 stainless steel under the same testing condition. The abrasive wear mechanism of the WC-based coatings was deduced to be the extrusion and removal of binder phases, as well as the fragmentation and peel-off of hard phases.     

Novel coatings from soybean oil phosphate ester polyols

Novel coatings with excellent properties have been formulated from polyols derived from the renewable resource soybean oil. Partially and fully epoxidized soybean oils (ESBO) were converted to novel soybean oil phosphate ester polyols (SOPEP) which were successfully incorporated into solventborne and waterborne bake coatings. Thermally cured waterborne alkyd coatings were produced with improved coating adhesion, low volatile organic compounds (VOC), excellent impact resistance, good hardness, less severe curing conditions, and lower cost. Solventborne alkyd coatings gave similar results. Soybean oil phosphate ester polyols appear to offer the coatings industry a low cost route to tough, durable, environmentally compliant, high performance coatings. Presented at the 27th International Waterborne, High-Solids, and Powder Coatings Symposium, on March 1–3, 2000, in New Orleans, LA. 430 West Forest Avenue, Ypsilanti, MI 48197.     

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.     

热化学反应法制备金属基陶瓷涂层的现状和发展

热化学反应法制备金属基陶瓷涂层具有工艺简单、成本低廉、涂层与金属表面结合力特强等优点。从工艺与界面2个方面叙述了热化学反应法制备陶瓷涂层的特征,以及其机理的研究进展。对基体的前处理、陶瓷粒子的选取及涂层的硬化技术进行了介绍。综述了热化学反应法制备陶瓷涂层的发展及现状。     

Evaluation of the corrosion resistance of phosphate coatings obtained by anodic electrochemical treatment

The corrosion resistance of phosphate coating obtained by anodic electrochemical treatment at 4–6 mA/cm² is addressed in this paper. The corrosion performance of these coatings is also compared with the coatings obtained by chemical treatment. The regenerated phosphoric acid under the influence of anodic current causes a large variation in morphological features of the coatings. Immersion and salt spray tests indicate the ability of these coatings to act as a barrier film on mild steel. Polarization and electrochemical impedance spectroscopic (EIS) studies indicate that the corrosion resistance of phosphate coatings obtained by anodic treatment decreases with increase in current density employed for deposition. In spite of their higher coating weight, the corrosion resistance of phosphate coatings obtained by anodic treatment is inferior to those obtained by chemical treatment. The porosity or discontinuities created due to the dissolution of the coating under the influence of anodic current are considered responsible for the inferior corrosion resistance of these coatings. The study concludes that anodic treatment has only a limited scope for preparing phosphate coatings with improved corrosion resistance.