فهرست مطالب

Iranian Journal of Materials science and Engineering
Volume:2 Issue: 4, Dec 2005

  • تاریخ انتشار: 1384/10/11
  • تعداد عناوین: 8
|
  • IN SITU REFRACTORIES USED IN THE CONTAINMENT OF MOLTEN IRON AND STEEL; STRATEGIES FOR THEIR DEVELOPMENT
    Moore R.E., Karakus M Page 1
    In situ refractories are defined as brick or unshaped products, which react internally or with furnace atmospheres and/or slag components so as to be enhanced in their performance. Examples of such products are discussed with emphasis on those that are currently employed and are being developed for the melting of iron and steel. Some strategies for the development of future in situ products are outlined.
  • STRENGTH AND FRACTURE TOUGHNESS OF WHISKER REINFORCED DENTAL RESIN-BASED COMPOSITES
    Hadian A.M., Abu Fanas S.H. Page 2
    Enhancing the properties of dental resin composites is of interest to researchers. The objective of the present investigation was to improve the strength and fracture toughness of dental composites via addition of silicon carbide whiskers and substitution of commonly used filler materials with stabilized zirconia ceramic powder. It was also intended to study the effect of powder- to- whisker ratio on mechanical properties of the resultant composites. The flexural strength and fracture toughness of composite samples with different whiskers loadings were measured. It was found that addition of whiskers to the composites enhances the mechanical properties of the composites. The strength and fracture toughness increased by increasing the amount of whiskers. The flexural strength of a composite having 60wt% whisker and 10wt% zirconia powder was about 210 MPa while that of the composite having only 60wt% ceramic powder was about 110 MPa. The microstructural examinations revealed that reinforcing mechanism was whiskers pull-out as well as crack deflection.
  • MODELING OF NEW PROCESS IN MIDREX SYNGAS SYSTEM
    Homayonifar P., Saboohi Y., Firouz Abadi B Page 3
    Iron and steel is an energy intensive industry and its contribution to the pollution of environment is considerable. Direct reduction iron (DRI) is a major element of an iron and steel production plant. Its share in natural gas and electricity consumption of total plant is estimated to be 70% and 15% respectively. Reduction gases are produced in natural gas reforming unit and its elements are CO and H2. A major consequence of using this technology is high level of CO2 emission, which pollutes the environment. An alternative to the existing technology is utilization of H2 as reducing agent. A comparison of various hydrogen production processes indicate that thermal decomposition of methane provides an attractive option from economical and technical point of view. Therefore, a system for producing hydrogen, based on thermal decomposition technique, has been designed in the framework of the present paper
  • SYNTHESIS OF ULTRA-FINE PARTICLES OF BAFE12O19 BY CO- PRECIPITATION ROUTE USING CHLORIDE/NITRATE PRECURSORS
    Sheikhi Moghaddam K., Ataie A Page 4
    Ultra-fine particles of barium hexaferrite have been synthesized by co-precipitation method using barium nitride and iron chloride precursors with a Fe/Ba molar ratio of 11. Co-precipitation was carried out at 25 and 80°C using NaOH as a precipitant. Effect of coprecipitation and annealing temperatures on the phase composition and morphology of the products have been investigated using XRD and SEM, respectively. XRD results indicated existence of BaFeO3-x as a major phase in co-precipitated samples. Analysis of the XRD results also revealed that barium hexaferrite starts to form at a relatively low temperature of 700°C for sample synthesized at 80°C. SEM micrographs exhibit plate-like hexagonal particles of barium hexaferrite for calcined samples. The SEM results showed that the mean particle size of co-precipitated sample at 25°C is smaller than that of 80°C after calcining.
  • EFFECT OF NOZZLE DIAMETER AND ATOMIZING AIR PRESSURE ON CHARACTERISTICS OF IN-FLIGHT PARTICLES IN WIRE ARC SPRAYING
    Nouroozi S., Vardelle A. Page 5
    Compositions of Al2O3+Si, SiO2+Al and Al+Si systems were prepared to study the effect of reaction bonding process on the mullite formation. The composition of each system was adopted according to mullite stoichiometery and sintered in 700-1600°C range. Results showed that the formation of reaction bonded mullite starting from Al2O3+Si mixtures, proceeded in two partially overlapping steps, the oxidation of Si to SiO2, and the reaction of SiO2 and Al2O3 to form mullite. In this system, up to 1400°C, conversion of Si to SiO2 was taken place and cristobalite formed, but mullite formation was not observed. Mullite phase started to form at 1450°C. Results indicated that complete reaction was not occurred up to 1600°C and 2 hours soaking time. XRD patterns of samples in Al+ SiO2 system showed that the reaction through sequences: (a) reduction of SiO2 by Al, (b) formation of a- Al2O3 and SiO2-rderived Si oxidation, and (c) mullite formation. X-ray diffraction patterns of heat-treated Al+Si system showed that reaction between Al and oxygen at 900°C was occurred with the reaction product being a- Al2O3 Oxidation of Si and formation of mullite were not detected in this system. SEM micrographs showed that both Al2O3+Si and SiO2+Al systems have similar microstructures, which consisted of a- Al2O3, mullite and free Si. The microstructures of the samples in Al+Si system consisted of a- Al2O3 free Al and Si with intermetallic Al-Si compound.
  • EFFECT OF COMPOSITION ON PHASE EVOLUTION AND MICROSTRUCTURE OF REACTION BONDED MULLITE (RBM)
    Salahi E., Ebadzadeh T., Moztar Zadeh F., Solati Hashjin M. Page 6
    Compositions of Al2O3+Si, SiO2+Al and Al+Si systems were prepared to study the effect of reaction bonding process on the mullite formation. The composition of each system was adopted according to mullite stoichiometery and sintered in 700-1600°C range. Results showed that the formation of reaction bonded mullite starting from Al2O3+Si mixtures, proceeded in two partially overlapping steps, the oxidation of Si to SiO2, and the reaction of SiO2 and Al2O3 to form mullite. In this system, up to 1400°C, conversion of Si to SiO2 was taken place and cristobalite formed, but mullite formation was not observed. Mullite phase started to form at 1450°C. Results indicated that complete reaction was not occurred up to 1600°C and 2 hours soaking time. XRD patterns of samples in Al+ SiO2 system showed that the reaction through sequences: (a) reduction of SiO2 by Al, (b) formation of a- Al2O3 and SiO2-rderived Si oxidation, and (c) mullite formation. X-ray diffraction patterns of heat-treated Al+Si system showed that reaction between Al and oxygen at 900°C was occurred with the reaction product being a- Al2O3 Oxidation of Si and formation of mullite were not detected in this system. SEM micrographs showed that both Al2O3+Si and SiO2+Al systems have similar microstructures, which consisted of a- Al2O3, mullite and free Si. The microstructures of the samples in Al+Si system consisted of a- Al2O3 free Al and Si with intermetallic Al-Si compound.
  • ELECTROCHEMICAL NOISE ANALYSIS OF 70-30 BRASS DURING STRESS CORROSION CRACKING TEST IN MATTSON S SOLUTION
    Saremi M., Nouri Delavar A., Kazemi M. Page 7
    An investigation of the electrochemical noise generation during Stress Corrosion Cracking (SCC) of 70-30 Brass in Mattson''s solution was conducted. The fluctuations of potential and current were monitored. The relationship between potential and current fluctuations has been evaluated in time domain and the obtained data has been analyzed in the frequency domain using Power Spectral Density (PSD). It is shown that 70-30 Brass has characteristic noise behavior during SCC that is step-by-step change in current and potential up to the final stage of fracture, and this may be used for SCC monitoring.
  • NEW METHOD FOR LIFE ASSESSMENT OF 1%CR-0.5% MO LOW ALLOY STEEL ON THE BASE OF GRAIN BOUNDARY CREEP CAVITATIONS
    Arabi H., Seyedein S.H., Satari M., Tabatabaie N. Page 8
    Life assessment on the base of grain boundary creep cavitation of 1%Cr - 0.5%Mo low alloy steel has been discussed in this paper. Since microstructural degradation is one of the most important mechanisms that affects creep life, it is necessary to assess microstructural damage in order to estimate the life. Microstructural damage within the grain boundaries is a continuous phenomena starting from about the beginning of secondary stage of creep process. In this research, the amounts of damage accumulation in the form of grain boundary cavitations for various creep times up to the ends of secondary creep stage for each creep condition was found by using quantitative metallography technique, i.e. image analyser. Then from the data obtained for grain boundary area cavitated and number of cavities per unit area, which was about linear as a function of time for each of creep conditions, the amount of damage in the tertiary stage was estimated for various times. Then a creep damage parameter was proposed for the creep process. Finally, having this damage parameter (?) and using continuum damage mechanics (CDM), a new version of Rabotnov-Kachanov equation for tertiary creep rate was established.