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Coating Systems (coating + system)
Selected AbstractsCombined application of extrusion-spheronization and hot-melt coating technologies for improving moisture-proofing of herbal extractsJOURNAL OF PHARMACEUTICAL SCIENCES, Issue 5 2010Hao Chen Abstract The aim of this research was to investigate the moisture-proofing effect and its mechanism for herbal extracts using extrusion-spheronization combined with hot-melt coating. Guizhi Fuling (GF) compound herbal extract with high hygroscopicity was used as a model drug. In the process of extrusion-spheronization, pellets containing 100% GF were prepared, and then coated with hot-melt coating material using a traditional coating pan. The moisture sorption data for GF were determined by storage at a series of different relative humidities. When the pellets were coated with a 96:4 mixture of stearic acid and polyethylene glycol 6000, the cumulative drug release was over 90% at 45,min while the moisture content was 4.9% at 75% RH within 10 days. These pellets have better moisture-proofing than those coated with Opadry AMB at the same coating level due to a different moisture sorption mechanism. The moisture sorption behavior of the hot-melt coating can be attributed to water vapor diffusion via a porous matrix system, while the Opadry AMB coating system involved a swelling controlled system. The Higuchi model was the best fit for the moisture sorption of the hot-melt coating in all formulations whereas the Opadry AMB coating fitted the Nuttanan model. © 2009 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 99: 2444,2454, 2010 [source] Corrosion behaviour of aircraft coating systems in acetate- and formate-based de-icing chemicalsMATERIALS AND CORROSION/WERKSTOFFE UND KORROSION, Issue 3 2009E. Huttunen-Saarivirta Abstract Corrosion behaviour of four coating systems, which are commonly used in aircraft components; namely cadmium-coated and subsequently chromate-treated steel AISI 4340, aluminium-coated steel AISI 4340, anodised aluminium alloy 7075-T6 and chromate-treated aluminium alloy 7075-T6, were investigated in six commercial acetate- and formate-based de-icing chemicals. The results show that the aluminium-coated steel specimens experience least corrosion among the four coating systems; no corrosion is detected in potassium acetate-based de-icing chemicals (Safeway KA HOT, Safegrip and Safegrip+), although some corrosion is observed in the other three chemicals (Safeway SD, Safeway SF and Meltium). In contrast, the coatings in the other three coating systems are damaged in all six de-icing chemicals. The thickness of the coating does not necessarily predict how well the coating will protect the substrate; the thickest coating, several tens of micrometres, is apparent on the cadmium- and chromate-coated steel specimens, while only a few micrometres thin aluminium coating on the steel substrate is the only coating system that can survive the corrosion tests in some of the de-icing chemicals. Comparison of the results from the two test methods used in this research, polarisation measurements and chemical exposure tests, shows that, for each coating system, the extent of corrosion, as evaluated on the basis of weight changes calculated from corrosion current density values and those experienced during chemical exposure tests, is different: the weight changes that materialise during exposure tests are, at least, from one to two orders of magnitude higher than those predicted by calculations. In this paper, these observations are discussed and explanations for them are presented. [source] Application of thermally sprayed coatings of the type WC/CoCr in reverse osmosis processes for seawater desalinationMATERIALS AND CORROSION/WERKSTOFFE UND KORROSION, Issue 11 2008A. Dwars Abstract Seawater desalination based on the reverse osmosis process requires a variety of hydraulic systems. The material concepts of these hydraulic systems are designed to reliably resist the corrosive properties of seawater and brine as well as the tribological loads. Strong tribological loads typically occur during the start-up and shutdown of multi-stage high-pressure pumps. Thermally sprayed coatings can be used to increase the wear resistance and also the tribological properties of bearings. Also in pressure exchangers for energy recovery, high tribological loads occur on the surfaces of rotors which operate with a clearance gap of 40,100 µm. Today, thermally sprayed coatings are used for the surface protection of these rotors. To resist the various tribological loads, the material pairs are optimized for each case. Thermally sprayed coatings with high surface hardness have proven to be particularly successful. A coating system, based on a CoCr matrix, has been developed especially for these applications. [source] Werkzeugbeschichtungen für die Trockenbearbeitung,MATERIALWISSENSCHAFT UND WERKSTOFFTECHNIK, Issue 10 2006E. Abele PVD coating; tribology; dry machining; tool wear Abstract Bei der Trockenbearbeitung wirkt an der Werkzeugschneide ein Belastungskollektiv aus mechanischen, thermischen und chemischen Einflussgrößen. Im Vergleich zur konventionellen Bearbeitung unter Verwendung von Vollstrahl-Emulsionskühlung erhöht die Trockenbearbeitung die auf den Schneidkeil wirkenden Belastungen. Eine sehr gute Möglichkeit die Schneide vor thermischen, abrasiven und tribo-oxidativem Verschleißangriff zu schützen stellt die Verwendung von PVD Beschichtungen dar. Neu entwickelte PVD Beschichtungen aus CrxAlyYzN, CrxAlyBzN und CrxAlySizN- wurden sowohl im tribologischen Modelltest als auch im realen Zerspanungstest auf ihre Eignung zur Trockenbearbeitung untersucht. In diesem Paper wird neben der verwendeten Beschichtungstechnologie detailliert auf die Schichteigenschaften eingegangen. Im Zusammenhang mit dem im Zerspanungstest gemessenen Verschleißverhalten und der Prozesskräfte werden anschließend Rückschlüsse auf das weitere Optimierungspotential dieser Schichtsysteme gezogen. Tool coatings for dry machining During dry machining a strain collective consisting of mechanical, thermal, and chemical loads is imposed upon the cutting edge. Compared to conventional machining using cooling lubrication fluids, the loads are increased in dry cutting. A feasible solution to protect the cutting edge from thermal wear, abrasion, and tribo-oxidation is the application of hard coatings. Newly developed CrxAlyYzN, CrxAlyBzN and CrxAlySizN PVD coatings were both evaluated in tribological model tests and machining tests concerning their suitability for dry cutting applications. Herein, the used coating technology and the coating properties are described in detail. The measured tool wear and the process forces give further hints for the optimization of the coating system. [source] Engineering and Design of Wear and Corrosion Resistant PVD Coatings Regarding the Exceptional Properties of Magnesium SubstratesPLASMA PROCESSES AND POLYMERS, Issue S1 2007Holger Hoche Abstract Although magnesium alloys were popular in the first half of the 20th century, the bad corrosion properties prevented their breakthrough in industrial mass production. Since the technology for the production of high purity alloys was introduced in the 1970s, magnesium alloys became more and more in the focus of industrial attention. Today magnesium alloys are state-of-the-art in construction parts in automotive industry. Despite its outstanding properties like good castability, low density and nearly unlimited availability the negative aspects like weak corrosion and wear behaviour still limit the application of magnesiums in industry, due to the need of sufficient surface protection (E. Aghion, B. Bronfin, Mater. Sci. Forum2000, 350,351, 19). Today, plasma electrolytic anodisations are state-of-the-art (H. Haferkamp, "Magnesiumkorrosion,Prozesse, Schutz von Anode und Kathode", in: Moderne Beschichtungsverfahren, F.-W. Bach, T. Duda, Eds., Wiley-VCH, Weinheim 2000, ISBN 3-527-30117-8, 242; M. Thoma, Metalloberfläche1984, 38, 393; T. W. Jelinek, Galvanotechnik2003, 94, 46; A. Kuhn, Galvanotechnik2003, 94, 1114). They provide acceptable corrosion resistance and protect the magnesium from mechanical damage due to their high hardness. On the other hand, their high porosity limits their use in combination with electrochemically noble materials, leading to galvanic corrosion (J. Senf, "Untersuchung und Beschreibung von Magnesiumdruckgusslegierungen unter tribologischer, korrosiver und mechanisch-korrosiver Beanspruchung, Berichte aus der Werkstofftechnik", Shaker Verlag, Germany 2001, ISBN 3-8265-8428-7). In addition, the high surface roughness of the plasma electrolytic anodisations restricts their use in tribological applications, particularly under sliding conditions (H. Hoche, "Grundlegende Untersuchungen zur Entwicklung von PVD-Beschichtungen auf Magnesiumlegierungen im Hinblick auf die Erhöhung der Verschleißbeständigkeit und unter Berücksichtigung des Korrosionsverhaltens", Dissertation, TU-Darmstadt D17, Shaker Verlag, Germany 2004). In order to achieve smooth surfaces with high quality, the PVD technology moves into the centre of interest. Since the 1980s PVD coatings are well established and widely used for different industrial applications, mainly for steel and tool coatings. The authors were the first who carried out serious studies on the development of PVD coatings for magnesium alloys in 1999 (J. Senf, "Untersuchung und Beschreibung von Magnesiumdruckgusslegierungen unter tribologischer, korrosiver und mechanisch-korrosiver Beanspruchung, Berichte aus der Werkstofftechnik", Shaker Verlag, Germany 2001, ISBN 3-8265-8428-7; H. Hoche, "Grundlegende Untersuchungen zur Entwicklung von PVD-Beschichtungen auf Magnesiumlegierungen im Hinblick auf die Erhöhung der Verschleißbeständigkeit und unter Berücksichtigung des Korrosionsverhaltens", Dissertation, TU-Darmstadt D17, Shaker Verlag, Germany 2004). The extensive research activities lead to the recent development of a coating system, which provides both, good wear properties as well as good corrosion behaviour. [source] Characteristics of paint systems prepared from dammar with the addition of natural pigmentPOLYMERS FOR ADVANCED TECHNOLOGIES, Issue 3 2009N. M. Omar Abstract Adhesion and electrochemical properties of paint system prepared from dammar binder or binder from Dipterocarpus grandifolius with the addition of natural pigment have been investigated. In this work, carotenoid pigment obtained from Capsicum annum (dried chili pepper) was added into the mixture of dammar resin and acrylic polyol resin to form the organic paint system. Five different paint systems were formulated on the basis of various concentrations of dammar resin, and their viscosities were measured by using Brookefield Viscometer. The paint systems were proofed on Aluminum steel Q-panels as a substrate. The cured paint systems were then evaluated by using the crosshatch adhesion method to test their adhesion properties according to ASTM D3359 standards. The corrosion potential property of paint was characterized by using electrochemical impedance spectroscopy (EIS) while the coated substrate was exposed to 3% NaCl for 30 days. Comparative results have been presented in terms of number of damage grids for the crosshatch test in each sample at different viscosity conditions and also regarding the ability of the coated sample to resist the corrosion potential. The result shows that the paint system with a composition of 35% dammar (CD35%) possessed the best adhesion performance compared to other CD paint compositions. Furthermore, CD35% also had higher corrosion resistance after 30 days of exposure in the 3% NaCl solution. The decrease in coating resistance values is associated with the electrolyte penetration into the coating system. The results showed that the developed organic paint system prepared from dammar improved the adhesion and electrochemical properties of a paint system. Addition of natural pigment to the formulation may enhance the attractiveness and vibrancy of the color. Copyright © 2009 John Wiley & Sons, Ltd. [source] Progress toward a biomimetic leaf: 4,000 h of hydrogen production by coating-stabilized nongrowing photosynthetic Rhodopseudomonas palustrisBIOTECHNOLOGY PROGRESS, Issue 4 2010Jimmy L. Gosse Abstract Intact cells are the most stable form of nature's photosynthetic machinery. Coating-immobilized microbes have the potential to revolutionize the design of photoabsorbers for conversion of sunlight into fuels. Multi-layer adhesive polymer coatings could spatially combine photoreactive bacteria and algae (complementary biological irradiance spectra) creating high surface area, thin, flexible structures optimized for light trapping, and production of hydrogen (H2) from water, lignin, pollutants, or waste organics. We report a model coating system which produced 2.08 ± 0.01 mmol H2 m,2 h,1 for 4,000 h with nongrowing Rhodopseudomonas palustris, a purple nonsulfur photosynthetic bacterium. This adhesive, flexible, nanoporous Rps. palustris latex coating produced 8.24 ± 0.03 mol H2 m,2 in an argon atmosphere when supplied with acetate and light. A simple low-pressure hydrogen production and trapping system was tested using a 100 cm2 coating. Rps. palustris CGA009 was combined in a bilayer coating with a carotenoid-less mutant of Rps. palustris (CrtI,) deficient in peripheral light harvesting (LH2) function. Cryogenic field emission gun scanning electron microscopy (cryo-FEG-SEM) and high-pressure freezing were used to visualize the microstructure of hydrated coatings. A light interaction and reactivity model was evaluated to predict optimal coating thickness for light absorption using the Kubelka-Munk theory (KMT) of reflectance and absorptance. A two-flux model predicted light saturation thickness with good agreement to observed H2 evolution rate. A combined materials and modeling approach could be used for guiding cellular engineering of light trapping and reactivity to enhance overall photosynthetic efficiency per meter square of sunlight incident on photocatalysts. © 2010 American Institute of Chemical Engineers Biotechnol. Prog., 2010 [source] General Corrosion and Galvanic Corrosion Properties of Differently PVD Treated Magnesium Die Cast Alloy AZ91,ADVANCED ENGINEERING MATERIALS, Issue 12 2003H. Hoche Developing PVD coating systems with better corrosion resistance leads to a duplex process, consisting of a plasma anodisation and an Al2O3 top coating which can both be performed in a modified commercial PVD unit. The tested specimens were investigated by means of optical microscopy, SEM and EDX. Furthermore a novel immersion technique to determine the time dependent corrosion behavior of coated magnesium alloys is introduced. [source] Self-Healing Polymer CoatingsADVANCED MATERIALS, Issue 6 2009Soo Hyoun Cho Self-healing coatings that autonomically repair and prevent corrosion of the underlying substrate are created through dispersion of microencapsulated healing agents in a polymer film. Following a damage event, these healing agents are released into the damaged region, passivating the substrate. This approach to self-healing coatings is quite general, and is effective for both model and industrially important coating systems. [source] Water-borne melamine,formaldehyde-cured epoxy,acrylate corrosion resistant coatingsJOURNAL OF APPLIED POLYMER SCIENCE, Issue 1 2008Sarvat Zafar Abstract Organic protective coatings are widely used in corrosion control. However, environmental standards establish that the volatile organic compounds either must be removed or controlled at the lowest possible levels. The carcinogenic environmental impact of volatile organic compounds has led to the substitution of solvent-borne coatings by water-borne coating systems. Among recently developed water-borne coatings, epoxy- and acrylic-based coatings have a special significance over other reported water-borne systems. Keeping in mind, the importance of water-borne coatings in the present work, we report the synthesis of water-borne epoxy,acrylate (EpAc) and melamine,formaldehyde (MF) as well as formulation of their anticorrosive coatings. The structural elucidation of MF-cured EpAc was carried out by FTIR, 1H NMR, and 13C NMR spectroscopic techniques. The coatings of EpAc-MF were applied on mild steel strips and were evaluated for physicochemical, physicomechanical characterization, and the anticorrosive performance under different environmental conditions. The present coating system EpAc coatings exhibited superior performance as compared to the reported water-borne epoxy,acrylatecoatings. The presence of melamine,formaldehyde in the resin increases the scratch hardness, impact resistance, alkali resistance, and thermal stability of these coatings. EpAc-MF-1 was found to cure at ambient temperature and exhibit good physicomechanical properties. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 [source] Ciprofloxacin-releasing bioabsorbable polymer is superior to titanium in preventing Staphylococcus epidermidis attachment and biofilm formation in vitroJOURNAL OF BIOMEDICAL MATERIALS RESEARCH, Issue 1 2006Sanna-Mari Niemelä Abstract Antibiotic coating systems have been successfully used to prevent bacterial attachment and biofilm formation. Our purpose was to evaluate whether bioabsorbable polylactide-co-glycolide (PLGA) 80/20 on its own, and PLGA together with ciprofloxacin (PLGA+C) have any advantages over titanium in preventing Staphylococcus epidermidis attachment and biofilm formation in vitro. Cylindrical specimens of titanium, PLGA, and PLGA+C in triplicate were examined for S. epidermidis ATCC 35989 attachment and biofilm formation after incubation with a bacterial suspension of about 105 cfu/mL for 1, 3, 7, 14, and 21 days, using scanning electron microscopy. Growth inhibition properties of PLGA and PLGA+C cylinders were tested on agar plates. On days 1, 3, and 21, no bacterial attachment was seen in 19.5, 9.2, and 41.4% of the titanium specimens; in 18.4, 28.7, and 34.5% of the PLGA specimens; and in 57.5, 62.1, and 57.5% of the PLGA+C specimens, respectively. During the whole study period, no biofilm was observed on 74,93% of the titanium specimens, 58,78% of the PLGA specimens, and 93,100% of the PLGA+C specimens. PLGA+C showed clear bacterial growth inhibition on agar plates, while PLGA and titanium did not show any inhibition. PLGA+C bioabsorbable material was superior to titanium in preventing bacterial attachment and biofilm formation and may have clinical applicability, for example, in prevention of infection in trauma surgery or in the treatment of chronic osteomyelitis. © 2005 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 2006 [source] Osteointegration of titanium and hydroxyapatite rough surfaces in healthy and compromised cortical and trabecular bone: in vivo comparative study on young, aged, and estrogen-deficient sheepJOURNAL OF ORTHOPAEDIC RESEARCH, Issue 9 2007Veronica Borsari Abstract The osteointegration rate of titanium (Ti; TI01) and duplex Ti plus HA (HT01) coating systems with high surface roughness was investigated in healthy, aged, and oestrogen-deficient sheep. After having evaluated the bone quality, TI01 and HT01 rods were implanted in the tibial diaphyses (two implants for each tibia) and epiphyses (1 implant for each tibia) of five young (YOUNG), five aged (AGED), and five aged and ovariectomized (OVX) sheep. The iliac crest trabecular bone volume (BV/TV) and number (Tb.N) in OVX sheep were respectively 33.5% and 28.5% lower than in YOUNG sheep (p,<,0.005) and lower than in the AGED group (BV/TV, ,17%; Tb.N, ,13.5%; not significant); in the OVX group the trabecular separation was 77.9% higher than in YOUNG (p,<,0.05) and 30.9% higher than in AGED animals. Lumbar vertebrae L5 bone mineral density was significantly lower in AGED (8.9%, p,<,0.05) and OVX sheep (19.3%, p,<,0.0005) when compared with YOUNG animals. Five samples of five sheep from each group were analyzed for each observation. At 3 months, in cortical bone both affinity index and pushout test results showed no significant differences between the two materials in each group of animals. In trabecular bone, the affinity index of HT01 was significantly higher than that of TI01 in each group of animals (YOUNG, 90.7%; AGED, 76.9%; OVX, 49.9%) with no significant differences between groups. In conclusion, the performance of TI01 and HT01 surfaces was high not only in YOUNG, but also in OVX animals and, therefore, they might be useful for aged and osteoporotic patients. © 2007 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 25:1250,1260, 2007 [source] Preparation and characterization of a customized cellulose acetate butyrate dispersion for controlled drug deliveryJOURNAL OF PHARMACEUTICAL SCIENCES, Issue 6 2002Siva Vaithiyalingam Abstract The purpose of the present experiment was to prepare and characterize the aqueous-based pseudolatex system of cellulose acetate butyrate (CAB) for controlled drug delivery. Aqueous pseudolatex systems are advantageous over organic-based coating systems because these systems are devoid of criteria pollutants such as carbon monoxide, nitrogen oxides, nonmethane volatile organic compounds, and sulfur dioxide. Pseudolatex was prepared with CAB and polyvinyl alcohol (stabilizer) by a polymer emulsification technique. The stability of pseudolatex was evaluated. Particle size was measured and rheological experiments were conducted. The glass transition temperature, microscopic free volume, permeation coefficient, and mechanical properties of plasticized pseudolatex films were estimated. Surface roughness of coating on inert Nu-Pareil® beads (Ingredient Technology Corp., Mahwah, NJ) was measured as a function of coating weight gain. The CAB Pseudolatex was found to be stabilized by steric forces. From intrinsic viscosity, the thickness of the stabilization layer was estimated. An increase in polymeric particles proportionately decreased the thickness of the stabilization layer. All the essential properties of a coating membrane such as microscopic free-volume fraction, permeability coefficient, mechanical properties, and glass transition temperature were fairly controllable as a function of plasticizer concentration. The pseudolatex dispersion of CAB was stable with negligible sedimentation volume and a particle size of 300 nm. Because CAB is water insoluble and non-ionizable, this pseudolatex can be used for pH-independent coating. The films obtained were strong and flexible for controlled drug delivery applications. Coating with the CAB dispersion reduced the surface roughness of beads but it remained stable as a function of increase in coating weight gain. © 2002 Wiley-Liss, Inc. and the American Pharmaceutical Association J Pharm Sci 91:1512,1522, 2002 [source] Hybrid Miniemulsion Polymerization of Acrylate/Oil and Acrylate/Fatty Acid SystemsMACROMOLECULAR REACTION ENGINEERING, Issue 3 2008Juchen Guo Abstract Acrylate,alkyd hybrid latex via miniemulsion polymerizations show promise as water-borne coating systems. However, poor homogeneity of the particles caused by the immiscibility of the alkyd in polyacrylate limits monomer conversion and film formation. To resolve this problem, the hybrid miniemulsion polymerization of acrylate in the presence of linoleic acid and sunflower seed oil was carried out. Products were characterized by solvent extraction, dynamic light scattering, gel permeation chromatography (GPC), differential scanning calorimeter (DSC), and transmission electron microscopy (TEM). The results provide clear evidence that substituting a fatty acid or natural oil with smaller molecular size (weight) for a conventional alkyd improves the grafting efficiency, and enhances the homogeneity of the hybrid polymer particles in water-borne latex systems. [source] Corrosion behaviour of aircraft coating systems in acetate- and formate-based de-icing chemicalsMATERIALS AND CORROSION/WERKSTOFFE UND KORROSION, Issue 3 2009E. Huttunen-Saarivirta Abstract Corrosion behaviour of four coating systems, which are commonly used in aircraft components; namely cadmium-coated and subsequently chromate-treated steel AISI 4340, aluminium-coated steel AISI 4340, anodised aluminium alloy 7075-T6 and chromate-treated aluminium alloy 7075-T6, were investigated in six commercial acetate- and formate-based de-icing chemicals. The results show that the aluminium-coated steel specimens experience least corrosion among the four coating systems; no corrosion is detected in potassium acetate-based de-icing chemicals (Safeway KA HOT, Safegrip and Safegrip+), although some corrosion is observed in the other three chemicals (Safeway SD, Safeway SF and Meltium). In contrast, the coatings in the other three coating systems are damaged in all six de-icing chemicals. The thickness of the coating does not necessarily predict how well the coating will protect the substrate; the thickest coating, several tens of micrometres, is apparent on the cadmium- and chromate-coated steel specimens, while only a few micrometres thin aluminium coating on the steel substrate is the only coating system that can survive the corrosion tests in some of the de-icing chemicals. Comparison of the results from the two test methods used in this research, polarisation measurements and chemical exposure tests, shows that, for each coating system, the extent of corrosion, as evaluated on the basis of weight changes calculated from corrosion current density values and those experienced during chemical exposure tests, is different: the weight changes that materialise during exposure tests are, at least, from one to two orders of magnitude higher than those predicted by calculations. In this paper, these observations are discussed and explanations for them are presented. [source] Investigation on the oxidation behaviour of gamma titanium aluminides coated with thermal barrier coatingsMATERIALS AND CORROSION/WERKSTOFFE UND KORROSION, Issue 7 2008R. Braun Abstract In the present study, the applicability of thermal barrier coatings (TBCs) on ,-TiAl alloys was investigated. Two alloys with the chemical compositions of Ti-45Al-8Nb-0.2B-0.15C and Ti-45Al-1Cr-6Nb-0.4W-0.2B-0.5C-0.2Si were used. Before TBC deposition, the specimens were pre-oxidised in laboratory air or low partial pressure oxygen atmosphere. Yttria partially stabilised zirconia top coats were then deposited using electron-beam physical vapour deposition (EB-PVD). The oxidation behaviour of the ,-TiAl specimens with TBC was studied by cyclic oxidation testing in air at 850 and 900,°C. Post-oxidation analysis of the coating systems was performed using scanning electron microscopy with energy-dispersive X-ray spectroscopy (EDS). No spallation of the TBC was observed for pre-oxidised specimens of both alloys when exposed to air at 850,°C for 1100 cycles of 1,h dwell time at high temperature. SEM micrographs of the thermally grown oxide scale revealed outer mixed TiO2/Al2O3 protrusions with a columnar structure. The protrusions contained small particles of zirconia and a low amount of about 0.5 at% zirconium was measured by EDS analysis throughout this outer oxide mixture. The TBCs exhibited excellent adherence on the oxide scale. Intercolumnar gaps and pores in the root area of the TBC were filled with titania and alumina. Below the outer columnar oxide scale, a broad porous zone of predominant titania was observed. The transition region between the oxide scale and substrate consisted of a discontinuous nitride layer intermixed with alumina particles and intermetallic phases rich in niobium formed at the nitride layer/substrate interface. When thermally cycled at 900,°C, the oxide scales on the alloy Ti-45Al-8Nb-0.2B-0.15C pre-oxidised in low partial pressure oxygen spalled off after 540 cycles. For the sample with TBC, spallation was observed after 810 cycles. Failure occurred in the thermally grown oxide near the oxide/nitride layer interface. Microstructural examinations revealed again oxide scales with columnar structure beneath the zirconia top coat and good adherence of the TBC on the thermally grown oxides formed at 900,°C. [source] Novel repair method for technical enamels based on sol,gel and sol-dispersion coatings,MATERIALS AND CORROSION/WERKSTOFFE UND KORROSION, Issue 2 2008S. Benfer The aim of the work presented here is the development of a novel repair method for technical enamels by using chemical nanotechnology. Good adhesion of coatings requires good wettability of the substrate by the repair solution. This was achieved by different pre-treatments of the steel substrates. Low sintering temperatures of the coatings can be ensured by the use of nanoparticle-based systems. Based on liquid metal alkoxides, a colloidal alumina sol and metal salts homogeneous sols with up to seven enamel compounds were prepared. The sols were brush coated onto plain and partly enamelled steel substrates and sintered in a furnace, by inductive heating or an IR emitter. Thin (single layer,,,1µm) crack-free layers were obtained on nearly all substrates independent of the sintering conditions investigated. The local sintering methods (IR emitter, inductive heating) allow to produce multiple coating systems in short times. Electrochemical impedance spectroscopy (EIS) provides evidence of the protective effect of these layers compared to the bare substrate, but as a result of their chemical composition the layers are not stable in the electrolytic environment for longer times. The thickness of such multiple coatings (20 layers, ,,8 µm) is still small compared to that of a technical enamel. Therefore, sol dispersion systems containing powder particles and sol components are applied on top of the sol,gel layers to increase the thickness of the sintered layers. [source] Modelling the influence of reactive elements on the work of adhesion between a thermally grown oxide and a bond coat alloyMATERIALS AND CORROSION/WERKSTOFFE UND KORROSION, Issue 3 2006I. J. Bennett Abstract The durability of thermal barrier coating systems is primarily determined by the degree of adhesion between the thermally grown oxide (TGO) and the bond coat. Failure of the TBC is often the result of delamination at this interface. Adhesion can be improved by the addition of reactive elements (RE) to the bond coat alloy. REs include oxide forming elements such as Y, Zr and Hf. The so-called reactive element effect has been attributed to a direct improvement of the bonding between the TGO and the bond coat. A macroscopic atom model has been developed to allow the work of adhesion between two compounds (e.g. an oxide and a metal compound) to be estimated. By calculating the work of adhesion across a number of different interfaces, the influence of reactive elements and impurities present in the substrate can be assessed. It has been found that the REs have a limited direct influence on the work of adhesion and can even result in a weaker interface. A large reduction in the work of adhesion is calculated when S and C are present at the interface. REs have a high affinity for both S and C. This indicates that the RE effect is primarily that of impurity scavenging, preventing diffusion of impurities to the interface. A number of experiments are reported, which demonstrate the RE effect and support the modelling results. [source] Beschichtungen auf direkt befahrenen Tiefgaragenbodenflächen von Weißen Wannen.BETON- UND STAHLBETONBAU, Issue 7 2006Physikalische Beanspruchungen, Planungsgrundlagen, alternative Beschichtungsvarianten Nach DIN 1045-1 müssen direkt befahrene Parkdecks mit zusätzlichen Maßnahmen ausgeführt werden, zu denen man unter anderem rißüberbrückende Beschichtungen mindestens der Klasse OS 11 nach Instandsetzungsrichtlinie des DAfStb zählt. Die auf dem Markt verfügbaren rißüberbrückenden Beschichtungssysteme mit Allgemeinem bauaufsichtlichem Prüfzeugnis sind für die Beschichtung von Betonoberflächen mit extremen Wassergehalten (Wassersättigungsgrade bis 90 %), wie sie häufig in Bodenplatten Weißer Wannen vorkommen, nicht geeignet. Schadensfälle aus der Baupraxis zeigen, daß gelegentlich an eignungsgeprüften OS-11-Systemen osmotisch induzierte Blasenerscheinungen, vorzugsweise bei rückseitig durchfeuchteten Bodenplatten wasserundurchlässiger Tiefgaragengeschosse, auftreten. Daher werden die physikalischen Beanspruchungen der Beschichtung (osmotische Transportvorgänge, Kapillardrücke, hydrostatische Drücke und Gasdrücke) quantitativ abgeschätzt und dem Leistungsvermögen (Beanspruchbarkeit) der marktüblichen Systeme gegenübergestellt sowie alternative Beschichtungsvarianten vorgestellt. Ferner werden baupraktische Empfehlungen zur Vermeidung von Beschichtungsschäden erläutert. Coatings on directly vehicle-carrying floor slabs of watertight concrete constructions in underground carparks physical stresses , design codes , alternative coating systems According to DIN 1045-1 directly vehicle-carrying park decks have to be realized with additional measures (crack-bridging coating systems). At least surface protection system 11 (SPS 11) according to the Guidelines for the Protection and Repair of Concrete Components of the German Committee on Reinforced Concrete (DAfStb) are among others a possibility to meet this requirement. On the market available crack-bridging coating systems with a general technical approval are not usefull on concrete surfaces with high water contents (water saturation values of 90 %) as they may occur in floor slabs of watertight concrete constructions. Experiences with practical damage cases show, that with approved SPS 11-systems osmotic induced bubbles may occur preferably on backside saturated floor slabs of watertight concrete constructions. In consequence the physical stresses of a coating (osmotic processes, capillarity reactions, hydraulic pressures as well as gas pressures) will be quantitatively estimated and compared with the capability of market systems. Alternative coating systems are presented and practical recommendations in order to avoid damages are given. [source] | ||||||||||||||||||||||