Papers by Keyword: Adiabatic Temperature

Abstract: Ni-Al-WC ternary system during self-propagating high-temperature synthesis (SHS) was analyzed and calculated based on thermodynamic principle, and the curves of adiabatic temperature (T_ad) and preheating temperature (T₀) and WC content (wt.%) were drawn. The results showed that adiabatic temperature of the system decreased with the increase of WC content and the maximum of WC content was about 34 wt.% for preheating temperature of 933K. Adiabatic temperature increased with increasing preheating temperature and properly increasing preheating temperature could promote the reaction self-sustaining when WC content was excessive and adiabatic temperature was less than 1912K.

Abstract: According to the different reaction mode, the combustion synthesis sintering can be divided into two kinds of mode: the self-propagating by heating ignition such as laser (SHS, Self-propagating High-temperature Synthesis) and whole explosion in the vacuum furnace (TE, Thermal Explosion). In this experiment, the Ni-Al powder compact is synthesized completely to nickel aluminides by SHS and TE. The experimental parameters controlling the ignition step such as material parameter and adiabatic temperature were calculated as a function of initial stoichiometry. Al mole ratio in initial powder mixture was varied from Ni: Al=3:1 to Ni: Al=1:1 for controlling adiabatic temperature.

Abstract: The preparation of AlB₁₂ powder by SHS has been investigated. Mg, Al₂O₃ and B₂O₃ powders were mixed as staring materials. SHS products were treated by acid pickling. Adiabatic temperatures were calculated by HSC software. XRD, SEM, TEM analyses were used products after acid picking treatment. The reason caused AlB₁₂ low purity is the formation of Mg_0.4Al_2.4O₄ and insoluble matter

Abstract: As increasing hydrogen demand for fuel cell application is expected in the near future, the efficient production of hydrogen is vital enabling technology for commercialization of fuel cell for residences and automobiles. Among different technologies of hydrogen production, autothermal reforming is considered to be thermally self-sustaining that the external heat source is not required. In this work, a steady state modeling of autothermal reforming of ethanol for hydrogen production has been performed. Because the operating condition at adiabatic temperature is designed for autothermal reformer, the estimated function of adiabatic temperature as function of steam-to-carbon (S:C) and air-to-carbon (A:C) molar ratios can be determined. At autothermal condition, the effect of S:C and A:C ratios on the product distributions of hydrogen rich stream is thermodynamically investigated. At fixed reactor pressure of 1 bar and preheat temperature of 200 °C, the favorable operating condition for the autothermal reforming of ethanol is found to be a S:C ratio of 2.0 and an A:C ratio of 1.75 at adiabatic temperature of 639 °C.

Abstract: SHS technique and conventional melting and casting technology were combined and used for the preparation of Al-Ti-C grain refiner alloy. Experimental results show that when SHS reaction occurs to the Al, Ti and C powder reactant in Al melt and the composition proportion factor, n , is between 4 and 10, the effect of composition on the initial temperature of SHS reaction is small and its initial temperature ranges from 810 to 815°C. However, the highest temperature of the melt increases with increasing n values and increases gradually from 845 to 1370°C. In the meantime, when the composition proportion factor for Al, Ti and C powder reactant, n, is greater than 5.95, its adiabatic temperature Td>1800K which conforms to the empirical criterion proposed by Merzhanov et al. The SHS reaction of reactant can accomplish by self-maintenance.

Abstract: Abstract. The present study concerns a development of cement-free concrete using finely grained ground granulated blast furnace slag (GGBS) rather than ordinary Portland cement (OPC) as a binder in concrete mix. The GGBS was very finely ground to the level of 10,000 cm2/g, prior to casting concrete, compared to OPC of which the Blaine value accounts for about 3,200 cm2/g. In concrete casting, the NaOH activator was added to mixing water to enhance the hydration rate for cement-free concrete. To ensure the compatibility of GGBS in concrete, a development of concrete strength, ionic penetrability and pore structure were examined. As a result, it was found that cement-free concrete using the GGBS has a higher concrete strength at all ages from 7 to 56 days. In turn, the ionic penetrability, in terms of chloride diffusivity, was slightly lower in cement-free concrete than OPC concrete, presumably due to the dense pore structure, which was confirmed by the mercury intrusion porosimetry. Simultaneously, the adiabatic temperature for cement-free concrete initially rose more rapidly, leading to an accelerated hydration process. This suggests that the cement-free concrete containing GGBS can be used for structural concrete structures, imposing an economical benefit and structural stability.

Abstract: ZrC fine powder has been prepared by self-propagating high-temperature synthesis (SHS) using exothermic reaction of ZrO2-C-Mg system. By theoretical calculating, the adiabatic temperature (Tad) for the system is about 2235K enough to react as SHS process. The Tad observed during experiment is 1850K. The results show that high pure ZrC powder is obtained with appropriate Mg contents. The scanning electron micrograph shows that the average size of ZrC particles is about 2μm.

Abstract: The combustion process of Mg-TiO2 system was preliminarily investigated from three aspects of thermodynamics, reaction kinetics and the technological parameters. The result indicates that the adiabatic temperature of Mg-TiO2 system is between 2060K and 2140K because the major existent modalities of TiO2 is the rutile and anatase, this meets the empirical criterion that the SHS reaction will be self-sustaining; The solid-solid reaction occurs at about 767K; Ti powders can be produced only when the ratio between Mg and TiO2 arrives at 2.9:1; The higher the vacuum, the more complete the reaction; The combustion temperature arrives at its peak when the pressure of green compact arrives at 250MPa; the velocity of the combustion wave increases with the augmentation of the pressure of green compact. So the proper control of the technological parameters can change the reaction temperature, reaction rate and the components of reaction products.

Abstract: It is favorable to disperse fine strengthening particles under 1μm to expect the effective dispersion strengthening mechanism of metal matrix composites. In this research, TiB2 particle was synthesized in Al matrix by a combustion reaction and the influence of the powder blending ratio was examined in detail. The mole mixture ratio of Ti and B powder was fixed to B/Ti=2, and the blending ratio of Al powder was varied from 40 to 70vol%. The compacted blended powder was heated under an Ar atmosphere in an induction furnace, and heating was stopped immediately after the combustion reaction took place. The synthesized TiB2 particle became finer by increasing the blending ratio of Al, and the dispersion of particles about 0.3μm was achieved. However, large quantity of Al-Ti intermetallic compounds remained when 70vol% Al was blended, indicating that the combustion reaction was not completed in this specimen.