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Silicon carbide fiber-reinforced silicon carbide ceramic matrix composites（SiCf/SiC） used in aero-engines are damaged or even failed due to the oxidation and corrosion by high-temperature and high-speed combustion gases. In this work，the gas generation device was used to simulate the complex gas environment in the aircraft engine，and the aviation kerosene mixed with liquid oxygen fuel in a certain proportion was ignited to form a high-temperature and high-speed combustion gas to assess the material. The oxidation test for 10 h and thermal shock test for 1000 cycles in combustion gas environment at 1200 ℃ were conducted on SiCf/SiC composites respectively. And the protective effect of environmental barrier coating（EBC）on SiCf/SiC composites was investigated. Uniaxial tensile tests were conducted on SiCf/SiC composites and SiCf/SiC-EBC composites after combustion gas environment assessment，and their fracture and cross-section micro-morphologies were observed by scanning electron microscopy. The results show that no significant oxidation of fibers and interphases is found in SiCf/SiC composites and SiCf/SiC-EBC composites after oxidation for 10 h in combustion gas environment，and their uniaxial tensile strength decreases by less than 2%. After 1000 thermal shock cycles in combustion gas environment，multiple micro-cracks are formed and oxidative corrosion of the interfacial layer occurs inside the SiCf/SiC composites，and the uniaxial tensile strength decreases by 41.3%. The EBC coating can effectively protect the SiCf/SiC composites from oxidation and corrosion of high-temperature gas，and the uniaxial tensile strength of SiCf/SiC-EBC composites decreases by 16.6% after 1000 thermal shock cycles.

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Compared with wall emission, gas thermal radiation is much more complicated because of its nongray and volumetric property. In this paper, a numerical method is established to calculate 3D radiative heat transfer in combustor by modelling radiative transfer as well as nongray radiative properties of combustion gases. Energy exchanges caused by thermal radiation and conduction are calculated and compared in a rectangular combustor, which shows the significant role of thermal radiation in heating fuel-air mixtures and prompting internal combustion reactions. Besides, radiative heat flux on the wall is also quite obvious although a non-contacting flow case, revealing the special challenges for thermal protections brought by radiant energy. Lastly, increasing the working pressure means much more participating species in radiative transfer process and the radiative effects will be also magnified. The numerical method in this paper provides a direct technique to analyze the role of thermal radiation in complex thermochemical reactions while the application case proves the necessity of coupling a high-accuracy radiation model when simulating combustion and flame propagation. [ABSTRACT FROM AUTHOR]

Introduction: Global warming and the need to reduce greenhouse gas emissions from various emission sectors are not hidden from anyone. The aim of this study was to determine Carbon dioxide (CO2)capture from combustion gases of methane for cultivation of microalgae spirulina platensis. Materials and methods: Microalgae culture medium was added in two photobioreactor. Air and combustion gas was injected into control and test reactors respectively. Artificial light with 10 Klux intensity was used and operated in continuous and intermittent (14 h ON and 8 h OFF) modes. Inlet concentration of carbon dioxide in to the test photobiorector was set in the range of 2000 to 6000 ppm and was measured in the inlet and outlet of photo-bioreactor by ND-IR CO2 analyzer. Results: In the control photo-bioreactor, the average removal of CO2 from the air was 42%. In the test reactor with an inlet CO2 concentration of 4100 ppm, the average removal of CO2 from the combustion gas was 23%. After 9 days of cultivation, the amount of carbon dioxide stabilized by microalgae was 0.528 and 1.14 g/L (dry weight) in the control and experimental photobioreactors respectively. The CO2 bio-fixation rate was in the range of 2.2% and 4.0% at different runs. After 9.0 days of cultivation concentration of microalgae was 0.25 and 1.0 g/L in the control and test reactors respectively. Algae productivity with intermittent light was 35% less than continuous light exposure. Conclusion: It is possible to use CO2 capture from combustion gases of commercial heater for cultivation of microalgae spirulina.

The study included testing the effect of different concentrations methanol and hexane extracts and mixture for both extract of Chlorococcum humicola algae against pathological fungi affecting the gramineae family, particularly wheat crops such as Fusarium graminearum, Aspergillus niger and Alternaria triticina. The study included the collection of nondiatomic dietumal algae samples from different areas within Baghdad, screening and diagnosis, and preparing pure insulation of algae most present in some samples. The study identified 186 species of 67 genera non-diatomic algae in which Chlorophyta prevailed 53%, followed by Cyanophyta 35%, Euglenophyta, Pyrrophyta 4% and the lowest percentages 2% Chrysophyta, Cryptophyta. Some sampling areas were found containing large numbers of species C. humicola so it was isolated, purified and growen in the Chu.13 medium to get a mass of 1.5g of it which extracted by two types of organic solvents using Soxhlet. The results of the study showed that the mixing extract (methanol + hexane) of C. humicola algae showed a more efficient inhibition effect than ketoconazole fungal pesticide (control agent) and other extracts on all species of fungi tested with the highest inhibition zone of 13.67 mm for F. graminearum fungus at the concentration of 32 mg / ml. While ketoconazole's fungal effect for the same fungus was less than 13.0 mm, and showed less inhibition zone than A. niger at 8 mg / ml concentration. Followed by methanol extract, which showed the highest inhibition zone of 11.0 mm for the A. triticina fungus at the concentration of 32 mg/ml, which was higher than the ketoconazole fungal pesticide effect of the same fungus, which recorded a inhibition zone of 8.0 mm. As for hexane extract, it showed less antifungal activity than fungicide and previous extracts, with the highest inhibition zone of 8.0 mm for A. niger at a concentration of 32 mg / ml, which was found to be the same inhibition zone as ketoconazole on A. triticina fungus, while the lowest inhibition zone was 4.67 mm at the concentration of 16 mg / ml on A. niger fungus. [ABSTRACT FROM AUTHOR]

HBPP uses hot dense bubbles as heat and mass carriers to evaporate the solution with improved evaporation efficiency, compared with the traditional thermal method. To develop an energy efficient water treatment process, we applied combustion gas as inlet gas within HBPP, for the first time to evaporate synthetic seawater. The advantage of using combustion gas is that the hot waste combustion gas from factories can be used at almost no energy cost, thereby reducing energy consumption. In this paper, the evaporation efficiency was determined by measuring the weight loss of column solution of HBPP in a 60 min run. Firstly, the ability of the HBPP to treat different types of wastewater, including 0.5 m NaCl solution or synthetic sewage, was tested by pumping air at the temperature of 80, 120 and 160 °C, respectively. The observed amount of evaporated water vapour was higher for the 0.5 m NaCl solution than for the synthetic sewage at inlet air temperatures of 80 °C and 120 °C but the same at a temperature of 160 °C. The HBPP shows the potential for water treatment regardless of wastewater type. Then, the evaporation efficiency was calculated for both combustion gas and air, at the inlet temperature of 120 °C to evaporate 0.5 m NaCl solution. The result showed an increment of 37% of evaporation efficiency achieved by sparging combustion gas. That is because the contained water vapour has a high capacity for efficient heat transfer to evaporate the solution. As a result, applying combustion gas within HBPP can provide an energy conservative method with improved evaporation efficiency for water treatment.

This article analysed the opportunity to implement the recovery of secondary energy resources in an industrial enterprise for the production of special building materials. The inventory of secondary energy resources and the establishment of their characteristics and energy potential is an important step in the energy balance sheet. The use of secondary energy resources, and in this case of flue gas, is one of the most effective ways to increase the use of energy consumed in industrial processes of this type. In this paper, the internal recovery solution of the secondary energy resource identified in the flue gas is analysed for the regenerative preheating of the combustion air. [ABSTRACT FROM AUTHOR]

A CO2 bubble column (CBC) has been developed as a body-temperature lab-scale water sterilization process for the inactivation of pathogens. Both CO2 and combustion gas bubbles inactivated Escherichia coli C-3000 (ATCC15597) with extraordinary efficiency in solutions with low alkalinity. The mechanisms of inactivation were not known. To characterise the phenomena a new first-order kinetic equation that correlates E.coli inactivation rates with a total alkalinity of the solutions has been developed as a first step towards understanding. This leads us to propose a new mechanism of inactivation.

Effluent and water management, in particular inactivating pathogens, have become more critical for the livestock farming industry, from both public health and business efficiency perspectives. The new hot bubble pilot plant (HBPP) uses hot air and hot combustion gases to produce hot bubbles that successfully inactivated Escherichia coli C-3000 (ATCC15597) in the lab, in different synthetic effluents and later at the farm using naturally occurring bacteria such as Salmonella, E.coli, Thermotolerant coliforms, and Cyanophyta and protozoa spores (oocysts and cysts) from Giardia and Cryptosporidium from piggery effluent.Many industries, such as pig farms, landfills, biogas power plants, and coal power plants, emit large amounts of hot combustion gases. The potential use of these hot combustion gases (waste) to produce hot bubbles in a bubble column reactor offers a new energy-efficient water sterilization process that fits within the circular economy principals by using waste gases as an input for the system. This new technology would then be able to compete with other water-disinfection technologies, such as UV irradiation, ozonation, and even chlorination, due to its low operating costs and high energy efficiency.

Radiative heat transfer plays an important role in the chemical reactions in the combustor. The widely used WSGG model proposed by Smith is established for normal pressure, which shows inevitable computational errors when dealing with radiative heat transfer problems at reduced or elevated pressures. In this paper, an improved global model is established to calculate the radiant energy exchanges between combustion gases and combustor chamber walls. Compared with the Smith model, the new model shows better performance in a wide range of pressure regions. The model accuracy is examined by computing the emissivity, radiative heat flux as well as the radiative source of H2O–CO2 gas mixtures at different pressure values. Finally, the radiative heat transfer inside a 3D TBCC(turbine-based combined cycle) engine exhaust system where strong gradients of pressure and temperature exist, is also addressed. The computational results show that the developed model provides approximate results at much less computational costs than the high-precision MSMGFSK-c8 model, which makes it competitive in complicated combustion systems. [ABSTRACT FROM AUTHOR]

The aim of this work was to investigate the carbonation kinetics of lithium orthosilicate (Li4SiO4) by thermogravimetry and via thermodynamic simulations, using CO2 concentrations of 15 vol.% (typical of combustion gases) and 100 vol.%. Tests were performed in a thermogravimetric analyzer, in two sequential steps: (1) pre-treatment at 750 ºC with N2 and (2) thermal analysis, non-isothermal (at 10 ºC min-1 up to 1000 ºC) or isothermal (at 550 ºC, 600 ºC and 650 ºC). According to the non-isothermal results, the carbonation of Li4SiO4 occurs in the range of 450-746 ºC and the decarbonation above it. Also, it was possible to capture up to 24.9 wt.%CO2. The isothermal kinetics showed that an increase in temperature promotes an increase in the reaction rate. Yet, the adsorption capacity is limited by the thermodynamics at higher temperatures and the kinetics is slow at low CO2 concentrations.

Thermometry using two-band near-infrared (NIR) emissions less than 1.1 μm has been implemented for combustion gases formed on a flat flame burner. The gas temperature was calibrated using a SiC thin filament pyrometry (TFP) above 1500 K for H 2 /air and CH 4 /air mixtures. The emission spectra were measured with a spectrometer and a monochrome CMOS sensor with an image doubler and two bandpass filters. Two pairs of bandpass filters (850 nm/925 nm and 975 nm/925 nm) were tested to measure temperature. Results indicated that strong H 2 O emissions existed in the NIR region, and they became stronger with an increase in the temperature. The CO 2 emission spectra in the NIR region were negligible compared to that of H 2 O. Calibration temperature lines were obtained as a function of the intensity ratio of the two-band emissions in the NIR region. Using a CMOS camera, the uncertainties of temperature were 59 K for 850 nm/925 nm and 145 K for 975 nm/925 nm. The resolutions were 0.7 K for 850 nm/925 nm and 1 K for 975 nm/925 nm. Using the calibration line, two-dimensional temperature measurements were performed for H 2 /air flames, CH 4 /air flames and Bunsen flames of 13A city gas. For the high temperature region above 1500 K, a quantitative two-dimensional temperature field was measured for lean and rich combustion. In addition, temperature measurement at high pressure was conducted for combustion gas of propane/air mixture with the equivalence ratio of 0.7 using a rapid compression machine. Temperature could be estimated using the calibration line obtained for the flat flame burner. We have demonstrated the performance and the possibility of thermometry two-band H 2 O emissions in the NIR region. [ABSTRACT FROM AUTHOR]

Calcium compounds have been known to be important for enhancing aggregation and dewaterability of activated sludge. In this study, the effect of calcium compounds (CaO, Ca(OH)2, CaCl2, CaSO4 and CaCO3, respectively) on sludge dewaterability and calorific value was investigated. Upon addition of CaO, Ca(OH)2, CaCl2, CaSO4 and CaCO3 (112 mg/g dry sludge) into activated sludge, after compressed filtration the moisture content of sludge was found to be 49.7%, 55.7%, 57.1%, 65.3% and 56.5%, respectively. The addition of calcium compounds altered the structure of sludge by CaCO3 and Ca(OH) 2 production, which improved sludge filterability and provided frameworks and water passages during compression. Furthermore, sludge conditioned by CaO addition had better dewaterability than other calcium compounds. The heat generated from the CaO hydration and high pH might damage flocs' structure and improve dewaterability of sludge. Moreover, it was found that excess addition of calcium compounds led to low calorific value in combustion process. The study concluded that CaO is the optimal additive for sludge further dewatering by compressed filtration. [ABSTRACT FROM AUTHOR]

In the context of the optimization of stationary gas turbines, the surface temperatures of the turbine blades have to be measured by a non-contact technique using radiation thermometers during operation of the turbine. Nowadays turbine blades are protected by thermal barrier coatings. The infrared-optical properties of these coatings require the usage of the MIR or LWIR region for non-contact measurement of the surface temperatures. For performing such measurements and for properly analyzing the derived data, the transmission and absorption spectra of the combustion gas mixture within the turbine were determined at the local conditions during operation of the turbine. Therefore, subject of this work is the measurement of the transmission spectra of carbon dioxide and water vapor at high temperatures and high pressures to identify a wavelength range, which is almost free of absorption and emission effects. In order to perform these measurements a Fouriertransform infrared spectrometer in combination with a high temperature and high pressure gas cell was used. The obtained results showed that the wavelength region around 10 μm is nearly free of influence of the combustion gas, even at high temperatures and high pressures. The received data was compared with equivalent HITRANsimulations that matched the measurement results well. Therefore, this wavelength region is available for non-contact temperature measurement. [ABSTRACT FROM AUTHOR]

Fires involving electric vehicles have attracted considerable attention in the media. In particular, the toxic gases released upon combustion of electric vehicles and lithium-ion batteries has been a major concern. In this study, the results of six large-scale vehicle fire tests are presented including three electric vehicles, two internal combustion engine vehicles, and one electric vehicle with the battery pack removed. Additionally, separate battery component tests were performed. In two of the vehicle fire tests a sprinkler system was used to assess the effect of water application on the combustion gases. Furthermore, calculations of the heat release rate, peak heat release rate and total heat release were performed, as well as chemical analysis of gas and soot. Peak heat release rate and total heat release were affected by the fire scenario and vehicle model, but not significantly by the type of powertrain. Regarding the combustion gases, hydrogen fluoride represented the largest difference between electric vehicles and internal combustion engine vehicles. Additionally, battery specific metals such as manganese, nickel, cobalt and lithium were found in higher concentrations in the electric vehicle tests than in the internal combustion vehicle tests, in which larger quantities of lead were found. • Large-scale fire tests of battery electric vehicles and internal combustion engine vehicles. • The total heat release was not affected by the type of traction energy. • A higher concentration of lead was found for the conventional vehicles. • HF, Ni, Co, Li and Mn, constituted the largest difference in the combustion gases between EVs and ICEVs. • Water application inhibited the quantification of HF. [ABSTRACT FROM AUTHOR]

Thin films of LaO were deposited onto glass substrates by ultrasonic spray pyrolysis. Their structural and morphological properties were characterized by X-ray diffraction, Fourier transform Raman spectroscopy, scanning electron microscopy, transmission electron microscopy, X-ray photo-electron spectroscopy, Brunauer-Emmett-Teller and optical absorption techniques. The sensor displays superior CO gas sensing performance at a low operating temperature of 498 K. The signal change on exposure to 300 ppm of CO is about 75%, and the signal only drops to 91% after 30 days of operation. [ABSTRACT FROM AUTHOR]

Torrefaction is a mild thermochemical treatment of biomass between 473-573 K in inert atmosphere. The poor economic feasibility of torrefaction due to continuous supply of inert gas hinders the commercialization of this technology. The present study investigates torrefaction of oil palm empty fruit bunch (EFB) in a vertical tubular reactor under the presence of gas from charcoal combustion. The combustion gas consisted of nitrogen, carbon dioxide, oxygen, carbon monoxide and hydrogen at percentages of 75.5, 16.4, 4.0, 3.5 and 0.3 vol%, respectively. In the present study, the thermal energy generated through charcoal combustion was directly utilized for torrefaction of EFB. Torrefaction experiment was carried out at 461 – 494 K for 30 min. The mass and energy yields and properties of torrefied biomass were investigated. Torrefaction in the presence of combustion gas resulted in an increase in the energy density and carbon content of torrefied EFB. The SEM cross-sectional observation of EFB torrefied in combustion gas showed presence of hollow porous structure like honeycomb. The result of torrefaction in combustion gas was compared with torrefaction carried out at 493 K for 30 min in a mixture of CO 2 (12.0 vol%), O 2 (9.0 vol%) and N 2 (balance) from gas cylinder. [ABSTRACT FROM AUTHOR]

One of the basic methods to improve both the thermal efficiency and power output of a gas turbine is to increase the firing temperature. However, gas turbine blades are easily damaged in harsh high-temperature and high-pressure environments. Therefore, ensuring that the blade temperature remains within the design limits is very important. There are unsolved problems in blade temperature measurement, relating to the emissivity of the blade surface, influences of the combustion gases, and reflections of radiant energy from the surroundings. In this study, the emissivity of blade surfaces has been measured, with errors reduced by a fitting method, influences of the combustion gases have been calculated for different operational conditions, and a reflection model has been built. An iterative computing method is proposed for calculating blade temperatures, and the experimental results show that this method has high precision. [ABSTRACT FROM AUTHOR]

An optical-fiber-based sensor suitable for the detection of combustion gases was designed and experimentally implemented with state-of-the-art sensitivity and capabilities. The system can not only provide imaging capability, but also provide spectral capability of the field of view (FOV) center guided by the imaging. The sensor employs a Fourier transform infrared (FT-IR) spectrometer, coupled with chalcogenide glass optical fiber, and a specially designed infrared optic lens. A special kit provided by Bruker Optics is connected on the spectrometer to focus the infrared beam from the lens at the entry of the fiber. It was tested in situ, in real time, under real-world conditions. Since each gas shows a characteristic optical emission spectrum, it is possible to detect selectively and quantitatively the presence of gases in combustion environment by analyzing mid-IR spectra. Spectral investigation techniques based on spectral shape band intensities and areas are tested to find the most effective tool for monitoring combustion gases. A comparison with experimental data has demonstrated that this sensor is well designed to study gases coming from combustion processes. [ABSTRACT FROM AUTHOR]

The purpose of this study is to develop the compact auxiliary water heater using tubular flame for home CHP (combined heat and power). The tubular-flame water-heater consists of the tubular flame burner, the coiled tube heat exchanger and the inserted tube installed at the center of the coiled tube as an additional heat exchanger. The tubular flame is formed in a rotating flow field by injecting the air-fuel mixture tangentially into the cylindrical chamber. The swirling flow of the combustion gas flows through the gap between the coiled tube and inserted tube. The high heat transfer performance can be achieved on these heat exchangers without the expanded heat transfer surface due to the swirling flow. Thus, the compact water heater can be constructed by using the tubular flame burner. At the first stage of the development, the maximum thermal efficiency achieves 81 % at the combustion rate of 15 kW. The heat transfer characteristics on the coiled tube and the inserted tube is investigated under the combustion and non-combustion conditions. Heat transfer coefficient on the coiled tube has about 5.6 times higher than that under the no-swirling flow condition at the same flow rate. Nusselt number on the coiled tube heat exchanger and the inserted tube can be estimated by Dhir's correlation equation for the swirling flow, which was provided as a function of the ratio between tangential momentum and axial momentum. The heat transfer characteristics on not only the coiled tube but the inserted tube was dominated by the swirling convection flow.

Four kinds of gas generant compositions comprised of 5-aminotetrazole nitrate(5-ATN) as the oxidizing component are provided. The combustion gases are determined through qualitative and quantitative analysis by gas chromatograph, ultraviolet spectrophotometer and a comprehensive system of flue gas analyses. The main components of the combustion gas are N 2 , CO 2 and H 2 as well as a small amount of CO, NO x and NH 3 . Hopcalite is selected as purifying agent, and the results of experiments show that the agent can remove all of the CO and reduce the content of NO x to 100 mg·m -3 , NH 3 to 10 mg·m -3 . [ABSTRACT FROM AUTHOR]

A general correlation has been proposed for the first time for accurate prediction of the acidic combustion gases dew points to mitigate the corrosion potential in pollution control and energy recovery equipments. Acidic combustion gases can cause rapid corrosion when they condense on the surfaces of the heat recovery and flue gas treatment equipments. The most important acidic gases, namely, SO3, SO2, NO2, HCl, and HBr, are considered in this investigation. The presented correlation can be used for accurate prediction of the flue gas acid dew point temperatures over wide ranges of acid and water vapor concentrations in oil and gas industries. [ABSTRACT FROM AUTHOR]

C/SiC composites prepared by chemical vapor infiltration (CVI) were subjected to a stationary loading of 160 MPa in a combustion gas environment with flame temperature of 1300 °C. Lifetime of C/SiC composites in such environment was measured. Microstructures of the composites after the testing were also characterized by SEM. The experimental results indicate the lifetime of C/SiC composites is average 2.3 hours in combustion gas environments. The combustion gas flow accelerates the damage of carbon fibers and the failure of the composites by speeding up the diffusion of gas reactants and products, destroying the layer of SiO on the surface of SiC coating and bringing fused SiO inside the composites. The fracture face of C/SiC is uneven, i e, a flat area close to the windward side and a pulling-out of long fibers near the leeward side, which results from the directionality effect of the combustion gas flow. [ABSTRACT FROM AUTHOR]

The combustion characteristics of wallpaper and the toxicity of gas produced from wallpaper fires were analyzed to evaluate the fire risk of wallpaper used in living spaces. Ash content was measured with a high-temperature electric furnace, and thermal analysis was carried out with thermogravimetric analysis (TGA). Combustion time and smoke concentration were measured with a cone heater and a combustion gas analyzer. The smoke density of samples was measured using the smoke chamber ASTM E 662. Pyrolysis in silk wallpaper began at a lower temperature than the other samples. This means that silk wallpaper can be ignited at a low heat flux and will have a greater fire risk than other kinds of wallpaper. Heat by radiation flux caused silk wallpaper to ignite in the shortest time compared to the other samples, so the time for evacuation in this situation may also be reduced. Silk wallpaper also released the highest carbon monoxide concentration, so the toxicity and harmful effects to consciousness were stronger than any other wallpaper. The smoke densities of silk wallpaper and fire retardant-treated silk wallpaper were very high due to their vinyl coatings. [ABSTRACT FROM AUTHOR]

Laminating two-layer sensing thick films sensors for the application to a portable gas alarm device was fabricated by screen-printing technique. For miniaturization, a sensor’s construction of two-side substrate was adopted. The first layer was SnO2-based film covered directly with alumina-supported Pd catalyst as second layer promoting the selectivity and stability of C4H10 gas determination and at low operation temperature. The maximum sensitivity was obtained using 15–20 μm thickness of the first layer and the second layer for C4H10. The sensor cross-sensitivity effect (selectivity) and the humidity effect were effectively restrained using laminating two-layer thick films at low operation temperature (250 °C). The sensor is composed of 15–20 μm thickness first layer and 30–40 μm thickness second layer was chosen as the optimal sensor structure for testing the basic sensor characteristics. The sensor had fast response (less 30 s), good repeatability, good linearity (Y=−0.513X+5.05R2=0.9990) for C4H10 gas with concentrations from 50 to 1000 ppm and good long-term stability (at least 78 days) at operation temperature of 250 °C. [Copyright &y& Elsevier]

The thermal formation of dioxins is typical of recent environmental issues relating to metallurgy. To analyze the behavior of these toxic species, computer assisted thermodynamic assessments were extensively carried out. In the homogeneous gas phase equilibria of the C−O−H−Cl system, the formation of dioxins is usually observed below 300–350°C, but is observed at higher temperature under the condition of oxygen deficiency. It has become clear that the presence of enough oxygen and hydrogen, as well as a decrease in chlorine content, would be desirable to prevent dioxin formation. From a strict thermodynamic standpoint, dioxins are meta-stable products observed under the retardation of the carbon deposition reaction which must be very slow at low temperature. The effects of some inhibitors or accelerators on the formation of dioxins are also discussed. [ABSTRACT FROM AUTHOR]

The corrosion behavior of a Nb-modified TiAl intermetallic compound containing 11 at.% Nb in a simulated combustion gas with and without deposits of a NaSO−NaCl mixture was examined at 600-800°C for times up to four days. In the absence of salt deposits the corrosion rates were rather low and increased only slightly with temperature, producing very thin scales of mixed oxides of Ti, Al, and Nb without sulfides. The presence of the salt deposits produced higher weight gains during an initial stage of one to two days at 600 and 700°C, after which the reaction stopped. A more important and longlasting effect was observed instead at 800°C, when the kinetics of hot corrosion became nearly linear. The scales formed by hot corrosion were complex mixtures of various corrosion products at all temperatures and showed a porous outer region containing a mixture of unreacted salts with oxides (mainly TiO), an intermediate region of a mixture of variable composition of oxides of the three metals, and a TiO-rich layer beneath it. At 800°C the scales tended to form a thin, discontinuous AlO-rich layer in the middle and contained an additional innermost region presenting a large concentration of sulfur, very likely as Nb and Ti sulfides. The high rate of hot corrosion at 800°C is attributed to the appearance of sulfides in the inner region of the scale and to a more efficient scale fluxing. [ABSTRACT FROM AUTHOR]

The corrosion behavior of NiAl containing small additions of Ti, Zr, and B in combustion gases both with and without NaSO−NaCl deposits at 600-800°C has been studied for times up to four days. The corrosion of the saltfree NiAl leads to the formation of very thin alumina scales at 600°C but of mixed NiO−AlO scales containing also some sulfur compounds at higher temperatures, while the rate increases with temperature up to 800°C. The presence of the salt deposits considerably accelerates the corrosion rate, especially at 600 and 800°C. The duplex scales formed at 600°C are composed mostly of a mixture of NiO and unreacted salt in the outer layer and of alumina and aluminum sulfide with some nickel compounds in the inner layer. The scales grown at 700°C contain only one layer of complex composition, while those grown at 800°C are similar but have an additional outer layer containing similar amounts of nickel and aluminum. At 600 and 700°C NiSO can be detected also in the salt layer. The samples corroded at 700°C and 800°C also show an Al-depleted zone containing titanium sulfide precipitates at the surface of the alloy. The hot corrosion of NiAl involves a combination of various mechanisms, including fluxing of the oxide scale as well as mixed oxidation-sulfidation attack. At all temperatures NiAl shows poor resistance to hotcorrosion attack as a result of the formation of large amounts of Ni compounds in the scales. [ABSTRACT FROM AUTHOR]