Band 35, Heft 6 -

The present work attempts to convert bamboo into a high surface area activated carbon via microwave heating. Different chemical activating agents such as KOH, NaOH, K 2 CO 3 and Na 2 CO 3 were utilized to identify a most suitable activating agent. Among the activating agents tested KOH was found to generate carbon with the highest porosity and surface area. The effect of KOH/C ratio on the porous nature of the activated carbon has been assessed. An optimal KOH/C ratio of 4 was identified, beyond which the surface area as well as the pore volume were found to decrease. At the optimized KOH/C ratio the surface area and the pore volume were estimated to be 3,441 m 2 /g and 2.093 ml/g, respectively, with the significant proportion of which being microporous (62.3%). Activated carbon prepared under the optimum conditions was further characterized using Fourier transform infrared spectroscopy (FTIR) and scanning electron microscope (SEM). Activated carbons with so high surface area and pore volume are very rarely reported, which could be owed to the nature of the precursor and the optimal conditions of mixture ratio adopted in the present work.

The present work is focused on the development of microstructure of Ti-7Cu alloy as a function of forging temperature and forging ratio in semi-solid state and the influence of resulting microstructure on the mechanical properties. The experimental results showed that the dynamic recrystallization occurred during semi-solid forging and the grain refinement was attained which is considered to be favorable for improving the semi-solid formability. The grain size increased with forging temperature and decreased with forging ratio. Forging temperature has a significant effect on the precipitation behavior in grain boundary regions during the semi-solid processing. More acicular-Ti 2 Cu tended to precipitate in grain boundary regions with higher forging temperature and finally formed precipitates zones adjacent to grain boundaries after forged at 1,100°C. High ultimate tensile strengths and low elongation have been achieved after semi-solid forging. The strength and hardness decreased with increase of forging temperature, while the ductility increased with increase of forging ratio. The relative contributions of tensile properties were attributed to the varieties of grain size and the distribution of Ti 2 Cu precipitates obtained by semi-solid forging.

BiFeO 3 nanopowders with new morphology have been synthesized by different methods. X-ray diffraction analysis, scanning electron microscopy, Fourier transform infrared and vibrating sample magnetometer were carried out at room temperature to study the structural and magnetic properties of as-synthesized products. VSM was utilized to measure the size-dependent magnetic behaviors of the as-prepared nanoparticles. Results show that the method has strong effect on the purity of the products. BFO synthesized by third method was pure. Crystallite size has a great effect on the magnetic properties. According to these results the nanoparticle diameter is smaller than the critical single-domain diameter, avoiding the configuration of magnetic domain walls decreases the magnetization. Even though the diameter of particle becomes even smaller, the thermal stability of the magnetization orientation decreases.

PbS nanostructures were synthesized successfully via hydrothermal approach with a new precursor. The products were characterized with X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and UV–Vis diffuse reflectance spectroscopy (DRS). The effect of different sulfur sources were investigated on product size and morphology.

This paper uses finite element method and neutron diffraction measurement to study the residual stress in lattice truss sandwich structure. A comparison of residual stress and thermal deformation between X-type and pyramidal lattice truss sandwich structure has been carried out. The residual stresses are concentrated in the middle joint and then decreases gradually to both the ends. The residual stresses in the X-type lattice truss sandwich structure are smaller than those in pyramidal structure. The maximum longitudinal and transverse stresses of pyramidal structure are 220 and 202 MPa, respectively, but they decrease to 190 and 145 MPa for X-type lattice truss sandwich structure, respectively. The thermal deformation for lattice truss sandwich panel structure is of wave shape. The X-type has a better resistance to thermal deformation than pyramidal lattice truss sandwich structure. The maximum wave deformation of pyramidal structure (0.02 mm) is about twice as that of X-type (0.01 mm) at the same brazing condition.

The influence of V–N microalloying on the high-temperature mechanical behavior of high strength weathering steel is discussed through thermomechanical simulation experiment. The difference of tensile strength caused by variation of [%V][%N] appears after proeutectoid phase change, and the higher level of [%V][%N] is, the stronger the tensile strength tends to be. The ductility trough apparently becomes deeper and wider with the increase of [%V][%N]. When the level of [%V][%N] reaches to 1.7 × 10 −3 , high strength weathering steel shows almost similar reduction of area to 0.03% Nb-containing steel in the temperature range of 800–900℃, however, the ductility trough at the low-temperature stage is wider than that of Nb-containing steel. Moreover, the net crack defect of bloom is optimized through the stable control of N content in low range under the precondition of high strength weathering steel with sufficient strength.

To improve the center segregation of billet for 50CrMo structural alloy steel, a 3D numerical model of solidification and heat transfer process for continuous casting had been established. The influence law of continuous casting process parameters on the secondary dendrite arm spacing (SDAS) and equiaxed crystal ratio had been obtained. It was shown that reducing superheat and casting speed and increasing the secondary cooling intensity could decrease SDAS. Reducing any one of the three parameters could increase the equiaxed crystal ratio. Adjusting only secondary cooling intensity could not make the SDAS and equiaxed crystal ratio change in the desired direction, but regulating the other two parameters could supply this gap. After optimizing the continuous casting process parameters of 50CrMo billet, the defect of center segregation was solved basically.

Using process of solid oxygen-ion conducting membrane (SOM), titanium metal and its alloy can be prepared directly from Ti-bearing dust slag by immersing it in the molten CaCl 2 at 1,100℃, which has been proposed by constant voltage of 3.5 V for 2–6 h. The dust slag was ball-milled and pressed into pellets, then employed as the cathode, while the liquid copper, which was saturated with graphite powder and encased in yttria-stabilized zirconia (YSZ) tube, acted as the anode. The effect of forming pressure and electrolytic time on products was analyzed. The results show that the content of titanium increased with electrolytic time and the characteristic morphology presents as granule. Ti–Fe alloy can be obtained from Ti–Fe residue by 6 h electrolysis. For titanium-rich residue, when the forming pressure of pellets decreased from 6 to 3 MPa, only electrolysis for more than 4 h can completely remove the oxygen, and pure titanium is obtained by 6 h electrolysis. Besides, there is an unprecedented finding that the porous cathode is conducive to the removal of impurity elements.

The flow behavior of 3104 aluminum alloy was investigated at temperatures ranging from 250°C to 500°C, and strain rates from 0.01 to 10 s −1 by isothermal compression tests. The true stress–strain curves were obtained from the measured load–stroke data and then modified by friction and temperature correction. The effects of temperature and strain rate on hot deformation behavior were represented by Zener–Hollomon parameter including Arrhenius term. Additionally, the influence of strain was incorporated considering the effect of strain on material constants. The derived constitution equation was applied to the finite element analysis of hot compression. The results show that the simulated force is consistent with the measured one. Consequently, the developed constitution equation is valid and feasible for numerical simulation in hot deformation process of 3104 alloy.

With the help of a four-point-bend of fatigue rig, high-cycle fatigue tests were carried out on an Ti–6.5Al–2Zr-1Mo-1V titanium alloy at room temperature, 20 Hz and R = 0.1 in ambient air. The test results indicated that the fatigue strength of base metal, 888 MPa, is about 120% of yield strength. The fatigue strength of joints is 814 MPa. It is about 110% of yield strength of base metal. When the loading stress is higher, the fatigue failure region is located in middle weld zone of weld face, which the cracks are propagated along coarse β phase’s grain boundary. When the loading stress is lower, the fatigue failure region is located between the incomplete recrystallization zone and base metal. The crack nucleation resistance gradually increases from the WN to HAZ with the variable of loading stress and β phase (little α′ phases)→ α + β phase→ α phase.

Oxidized pellets, consisting of Brazilian specularite fines and coke fines, were prepared by disc pelletizer using bentonite as binder. The roasting process of pellets includes preheating stage and firing stage. The compressive strength of preheated pellets and fired pellets reached the peak value at 1.5% coke fines dosage. During the initial stage of preheating, some original Fe 2 O 3 was reduced to Fe 3 O 4 because of partial reduction atmosphere in pellet. During the later stage of preheating and firing stage, coke fines were burnt out, and the secondary Fe 2 O 3 (new generation Fe 2 O 3 ) was generated due to the re-oxidization of Fe 3 O 4 , which improved the recrystallization of Fe 2 O 3 . Compared with the fired pellets without adding coke fines, fired pellets with 1.5% coke fines exhibited the comparable RSI (reduction swelling index) and RDI +3.15 mm (reduction degradation index), and slightly lower RI (reducibility index).

Pure niobium metal, produced by alumino-thermic reduction of niobium oxide, contains various impurities which need to be reduced to acceptable levels to obtain aerospace grade purity. In the present work, an attempt has been made to refine niobium metals by electron beam drip melting technique to achieve purity confirming to the ASTM standard. Input power to the electron gun and melt rate were varied to observe their combined effect on extend of refining and loss of niobium. Electron beam (EB) melting is shown to reduce alkali metals, trace elements and interstitial impurities well below the specified limits. The reduction in the impurities during EB melting is attributed to evaporation and degassing due to the combined effect of high vacuum and high melt surface temperature. The % removal of interstitial impurities is essentially a function of melt rate and input power. As the melt rate decreases or input power increases, the impurity levels in the solidified niobium ingot decrease. The EB refining process is also accompanied by considerable amount of niobium loss, which is attributed to evaporation of pure niobium and niobium sub-oxide. Like other impurities, Nb loss increases with decreasing melt rate or increase in input power.

The final set of equations defining the interdiffusion process in solid state is presented. The model is supplemented by vacancy evolution equation. The competition between the Kirkendall shift, backstress effect and vacancy migration is considered. The proper diffusion flux based on the Nernst–Planck formula is proposed. As a result, the comparison of the experimental and calculated evolution of the void formation in the Fe-Pd diffusion couple is shown.