Introduction to High‐Temperature Coatings

Coatings for turbine blades possess some attractive properties like oxidation and hot corrosion resistance, maintain their strength, cohesion and etc. High temperature damages divide in three general groups: High temperature corrosion type II (600–850°C), High temperature corrosion type I (750–950°C), Oxidation (950°C and higher). There are three types of high temperature coating: 1- Diffusional coating, 2- Overlay coating, 3- Thermal Barrier coating (TBC). The third type, considered as the overlay coating widely used for critical high temperature conditions like, combustion chamber, rotating blades, etc. The advantages of TBC are: increasing the life time of part, improving the engine efficiency (by increasing TIT (Turbine Inlet Temperature)), decreasing the coolant air flow. TBC coating system contains 4 layer that they totally differs from each other. Four principal segments of TBC layers are: 1- super alloy substrate, 2- aluminum intermediate coating, 3- TGO (Thermally Grown Oxide), 4- ceramic final coating. Some advantages of thermal sprayed coatings are: 1- making thick coating with high velocity, 2- low cost recoating damaged regions, 3- covering a wide variety of materials that can be melt without decomposition, 4- mechanically joint coating particles to the substrate, 5- applicable either manually or automatically

Investigation on microstructure and oxidation behavior of Cr-modified aluminide coating on γ-TiAl alloys

Microstructure and oxidation behavior of aluminide coating has been investigated. The layers were examined by optical microscopy, scanning electron microscopy (SEM) equipped with EDS and X-ray diffraction method. The isothermal oxidation behaviors of samples were investigated at 950°C for 200 h. The results indicated that TiAl₃ were formed on substrate. In addition, aluminide coating improved the oxidation resistance of γ-TiAl alloys by forming a protective alumina scale. Moreover, during oxidation treatment the interdiffusion of TiAl₃ layer with γ-TiAl substrate results in depletion of aluminum in the TiAl₃ layer and growth of TiAl₂ layer. After oxidation treatment the coating layer maintained a microstructure with phases including TiAl₃, TiAl₂ and Al₂O₃.Досліджено мікроструктуру алюмінідного покриву та його поведінку під час високотемпературного окислення. Шари алюмінідів титану вивчали за допомогою оптичної мікроскопії, сканівної електронної мікроскопії (SЕМ) з використанням дисперсного рентгеноспектрометра (EDS) та рентгенівським дифракційним методом. Випробовування проводили при 950°C впродовж 200 h. Встановлено, що на підкладці з титанового сплаву утворився TiAl₃. Покрив з алюмініду титану покращує стійкість до окислення сплавів з γ-TiAl, утворюючи захисну плівку з оксиду алюмінію. Під час окислення дифузійна взаємодія TiAl₃ з підкладкою γ-TiAl спричиняє зменшення кількості алюмінію у шарі TiAl₃ та збільшення шару TiAl₂. Після окислення в покриві утворюється мікроструктура з фазами, що містять TiAl₃, TiAl₂ та Al₂O₃.Исследовано микроструктуру алюминидного покрытия и его поведение при высокотемпературном окислении. Слои алюминида титана изучали с помощью оптической микроскопии, сканирующей электронной микроскопии (SЕМ) с использованием дисперсного рентгеноспектрометра (EDS) и рентгеновским дифракционным методом. Испытания проводили при 950°C в течение 200 h. Установлено, что на подкладке из титанового сплава образовался TiAl₃. Покрытие из алюминида титана улучшает стойкость к окислению сплавов из γ-TiAl, образовывая защитную пленку из окисла алюминия. Во время окисления диффузионное взаимодействие TiAl₃ с подкладкой γ-TiAl влечет уменьшение количества алюминия в слое TiAl₃ и увеличение слоя TiAl₂. После окисления в покрытии образуется микроструктура с фазами, которые содержат TiAl₃, TiAl₂ и Al₂O₃

Electrocatalytic oxidation of phenol from wastewater using Ti/SnO2–Sb2O4 electrode: chemical reaction pathway study

Abstract In this study, a titanium plate was impregnated with SnO2 and Sb (Ti/SnO2–Sb2O4) for the electrocatalytic removal of phenol from wastewater, and the chemical degradation pathway was presented. The effects of various parameters such as pH, current density, supporting electrolyte, and initial phenol concentration were studied. At optimum conditions, it was found that phenol was quickly oxidized into benzoquinone because of the formation of various strong radicals during electrolysis by the Ti/SnO2–Sb2O4 anode from 100 to <1 mg/L over 1 h. The results of GC/MS analysis showed the presence of some esters of organic acid such as oxalic acid and formic acid. HPLC analysis showed only trace amounts of benzoquinone remaining in the solution. The efficiency of TOC removal at the Ti/SnO2–Sb2O4 anode surface showed a degradation rate of 49 % over 2 h. Results showed that the molecular oxygen potential at the electrode was 1.7 V. The phenol removal mechanism at the surface of the Ti/SnO2– Sb2O4 anode was influenced by the pH. Under acidic conditions, the mechanism of electron transfer occurred directly, whereas under alkaline conditions, the mechanism can be indirect. This research shows that the proposed electrolyte can significantly influence the efficiency of phenol removal. It can be concluded that the treatment using an appropriate Ti/SnO2– Sb2O4 electrode surface can result in the rapid oxidation of organic pollutants

Nanocoatings: size effect in nanostructured films

Size effect in structures has been taken into consideration over the last years. In comparison with coatings with micrometer-ranged thickness, nanostructured coatings usually enjoy better and appropriate properties, such as strength and resistance. These coatings enjoy unique magnetic properties and are used with the aim of producing surfaces resistant against erosion, lubricant system, cutting tools, manufacturing hardened sporadic alloys, being resistant against oxidation and corrosion. This book reviews researches on fabrication and classification of nanostructured coatings with focus on size effect in nanometric scale. Size effect on electrochemical, mechanical and physical properties of nanocoatings are presented

Magnesium Alloys

Magnesium alloys usually have desirable properties including high chemical stability, easy processing and manufacturing, and also lightweight. Magnesium alloys weigh about 70% of aluminum alloy weight and 30% of iron and steel weight. Most of these alloys are used for fabrication of structures in aerospace industries. Magnesium belongs to the second main group of the periodic table of elements (alkaline earth metal) and therefore can't be found in pure state in nature and only exists as a chemical composition. This book collects new developments about magnesium alloys and their use in different industries

Wetting and Wettability

On the liquid 's surface, the molecules have fewer neighbors in comparison with the bulk volume. As a result, the energy interaction shows itself in the surface tension. Traditionally, the surface tension can be assumed as a force in the unit of the length which can be counted by the unit of Newton on squared meter, or energy on the units of the surface. The surface tension, implies the interface between liquid and vapor, which is an example of the surface tensions. The equilibrium between these surface tensions, decides that a droplet on a solid surface, would have a droplet form or will change to layer form. This book collects new developments in wetting and wettability science