Band 32, Heft 5

The thermodynamic quantities such as the thermal expansion (α p ), isothermal compressibility (K T ) and the specific heat (C P  − C V ), are predicted at various pressures up to 26 GPa (T = 540 K) in the solid phase II of benzene using volume data from the literature. The Pippard relations are examined using the pressure dependence of α p , K T and C P  − C V and the value of the slope dP/dT is deduced for the solid phase II of benzene. The thermodynamic quantities studied here decrease with increasing pressure, as expected, which can be compared with the experimental measurements for the solid phase II of benzene. We find that the Pippard relations are validated within the pressure range considered, in particular, at high pressures for the solid phase II of this molecular crystal.

Conductive concrete is a construction material that can be utilized for a number of applications: in particular, electromagnetic shielding. In this research, the microwave shielding effectiveness of a carbon containing electrically conductive concrete was determined from both the real and the imaginary permittivities. Also, the permittivities and the shielding effectiveness of a normal concrete were determined for comparison purposes. It was shown that the permittivities of the conductive concrete were significantly higher than those of the normal concrete. The shielding abilities of both of the concretes were determined as a function of concrete thickness and temperature, and the conductive concrete had a superior shielding effectiveness. For the normal concrete, at room temperature and a frequency of 912 MHz, a shielding effectiveness of 30 dB was achieved for a thickness of about 400 cm. For the conductive concrete, under the same conditions, a thickness of only about 3 cm was required to achieve the same shielding effectiveness.

Two copper based composites: an experimental Cu-Al 2 O 3 and commercial GlidCop AL-60 grade (with 1.1 wt.% Al 2 O 3 ) with grains size approximately 1–2 µm were treated by Equal Channel Angular Pressure (ECAP) technique in order to induce severe plastic deformation and to reduce the grain size by about an order of magnitude. Microstructure of the as-received and ECAPed states of both systems were observed. Hardness of the experimental materials was measured by instrumented indentation. Tribological properties were studied by pin-on-disk technique in dry sliding against a steel ball at a various temperatures from room temperature up to 873 K. For all systems the coefficient of friction and specific wear rates were evaluated. Worn surfaces were studied by scanning electron microscopy and level of oxidation was measured using EDX spectrometry. It was found that between 473 K and 673 K the coefficient of friction decreased significantly. At lower temperatures the finer grained systems were more wear resistant than the as-received ones. The wear rate of all systems decreased down to zero at 673 K due to formation of hard oxide rich layers. Damage mechanisms were identified and their relationship with structural characteristics was inferred.

The dissolution of the NiO cathodes and the corrosion of bipolar plates are great obstacles to the commercialization of molten carbonate fuel cells (MCFC). Rare earth element dysprosium is effective in inhibiting the corrosion of Ni in molten carbonates. In this presentation, electrochemical impedance spectroscopy was employed to study the corrosion behavior of two-phase Ni-Dy alloys containing 1 and 3 wt.% Dy, respectively, in molten (0.62Li,0.38K) 2 CO 3 at 650 °C in air. The experimental results indicate that the Nyquist plots for the corrosion of both Ni-1Dy and Ni-3Dy are all composed of a small capacitive loop at high frequencies and a line at low frequencies, but with larger impedance values for Ni-3Dy. The emergence of Warburg impedance at low frequencies suggests that the corrosion of alloys is controlled by the diffusion of oxidants in molten carbonates, as observed for pure nickel. The addition of dysprosium to nickel can decrease its corrosion rate, with a better effectiveness for the 3% Dy addition. Based on the diffusion impedance, the oxidants involved in corrosion are also discussed.

A series of high temperature and organosoluble poly(amide-imide)s 8a–g were prepared by direct polycondensation from 1,4-bis[4-aminophenoxy]butane 4 and various aromatic diacids 7a–g in a medium consisting of N-methyl-2-pyrrolidone (NMP)/triphenyl phosphite (TPP)/calcium chloride (CaCl 2 )/pyridine system. Aromatic diacids 7a–g were synthesized by reaction of 3,3′,4,4′-benzophenone tetra carboxylic dianhydride 5 and various amino acids 6a–g . All of the above polymers were fully characterized by 1 H-NMR and FT-IR spectroscopy, inherent viscosity, solubility test and thermogravimetric analysis (TGA). The resulted polyamides (PAs) 8a–g have showed admirable good inherent viscosities, thermal stability and solubility.

The effect of ultrasonic treatment on the solidification structure of Fe-36Ni invar alloy was investigated. The experiment results showed that the ultrasonic treatment before its solidification had no significant effect on the solidification structure. However, when ultrasonic was inputted into the molten alloy during its solidification process, the primary dendrites were broken up into lots of fragments and solidification structure was refined significantly. When ultrasonic treatment was applied in the melt doped with yttrium before its solidification, ultrasonic cavitation could break up precipitates into many small ones, which could refine its solidification structure as nucleation cores. In samples containing yttrium treated by ultrasonic at 1753 K, the number of the precipitates was 623/mm 2 and its average size was 2.18 µm; while at 1803 K, they were 604/mm 2 and 2.34 µm respectively. The ultrasonic cavitation had a similar effect at two different temperatures. The solidification structure refined greatly at 1753 K was due to its low pouring temperature.

The present paper deals with the evaluation of different vacuum heat treatments on the fracture surfaces of a low alloyed sintered steel in correlation with the mechanical and plastic properties achieved. The heat treatment conditions consist of the sintering process in vacuum furnace at 1393 K for 1800 s with an integrated final tempering at 473 K for 3600 s. The average cooling rates were calculated in the range of 1393 K to 673 K and were 0.1 K/s, 0.235 K/s, 3 K/s and 6 K/s, respectively. Vacuum heat treatment performed is supporting bainite/martensitic microstructure with increasing cooling rates; it provides a marked increase in strength coupled to a decrease in ductility. The typical microstructure appearances on the fracture surfaces show that microstructure-fracture developments are closely associated with strength/plastic properties. The fracture surface mode at higher magnification revealing two main micromechanisms of fracture: brittle (transgranular cleavage fracture) and ductile (dimples and plastic deformation by slip). Finally, the cooling rate of the vacuum furnace in order of 3 K/s is sufficient to obtain suitable properties of strength and plasticity which can however be accepted for several applications.

Ratcheting experiments were carried out on type 316LN stainless steel (SS) at different temperatures in the range, 300–923 K using different mean stress ( σ m ) – stress amplitude ( σ a ) combinations. Occurrence of dynamic strain aging (DSA) in the intermediate temperature range led to an anomalous temperature dependence of ratcheting strain accumulation. While the peak DSA temperature was found to be 823 K for all mean stress-stress amplitude combinations, the temperature regime of occurrence of DSA was found to depend on the σ m – σ a combinations used.

The kinetics of carbothermic reduction of ZnFe 2 O 4 in the temperature range 823–1223 K, was investigated in a microwave reactor. The mechanism of formation of ZnO and Fe 3 O 4 /FeO by decomposition of ZnFe 2 O 4 was explained using the equilibrium calculations and thermodynamics analysis using HSC chemistry software 6.0. In addition the effect of parameters such as the decomposition temperature, C/ZnFe 2 O 4 ratio, particle size and microwave power were assessed on the decomposition kinetics. Zn recovery as high as 98.83% could be achieved at a decomposition temperature of 1023 K, C/ZnFe 2 O 4 ratio of 1:3, particle size of +74–61 µm and microwave power of 1200 W. The kinetics of decomposition was found to be carbon gasification reaction controlled, with the activation energy of 39.21 kJ/mol.

To understand the hot corrosion mechanism of materials it is of significance to establish electrochemical measurements under a thin film of fused salts. In this paper, the hot corrosion behavior of Fe-Cr alloys containing 5, 10 and 25wt% Cr, respectively, in the presence of a fused film of 0.9Na 2 SO 4 -0.1K 2 SO 4 (mole fraction) at 1173 K in air has been investigated by electrochemical impedance spectroscopy using a two-electrode system. The Nyquist plots for the corrosion of both Fe-5Cr and Fe-10Cr are composed of a very small semicircle at high frequencies and a line at low frequencies indicating that the corrosion is controlled by the diffusion of oxidants in the fused salt film. The alloys were severely corroded, forming a thick porous corrosion layer containing large amounts of non-protective precipitated Fe oxide particles. Conversely, the Nyquist plots for the corrosion of Fe-25Cr are composed of double capacitive loops, with significantly larger impedance values, which are associated with the formation of a protective Cr 2 O 3 scale. Based on the experimental diffusion impedance results and the theoretic solubility and diffusion coefficient of oxygen in molten salts, respectively, a theoretical value of the diffusion flux of molecular O 2 has been calculated.

To develop a new method of refining silicon for use in solar cell materials, liquation refining with Al-Si alloying was proposed for purification of metallurgical grade silicon (MG-Si). The morphologies of impurities, especially for phosphorus and iron, before and after purification were analyzed. By alloying MG-Si with Al, phosphorus in MG-Si formed Al-Si-Ca-P impurity phase and iron formed skeletal-shaped α-Al 8 SiFe 2 phase into the Al-Si eutectic phase from MG-Si with the presence of Al. It can be concluded that removal mechanism of phosphorus and iron was not only a segregating process, but also a recombining process within certain elements to form specified impurity phases. By centrifugal separation, average separation ratio was 75.73% and average recovery ratio was 82.52% for Al-45%Si system, which is better than traditional separation methods and avoids considerable loss of Al and acid. After refining for four times, mass fractions of phosphorus and boron were reduced to 0.46 × 10 −6 and 0.21 × 10 −6 respectively. For transition metal impurities, Fe, Ti and Mn, removal fractions of those all were more than 95%.

Yb:YAG transparent ceramic nano-powder was prepared by chemical co-precipitation method, with ammonium bicarbonate as the precipitant and polyethylene glycol as surfactant. The addition of polyethylene glycol can reduce the agglomeration and particle size of the prepared Yb:YAG powder. The morphology, thermal stability and phase structure of Yb:YAG nano-powder were charactered by scanning electron microscopy (SEM), thermogravimetry and differential thermal analysis (TG-DTA), X-ray diffraction (XRD), and Fourier transform infrared spectroscopy. The results show that well-crystallized nano-powder was obtained by calcining the precursors at 900 °C for 3 h. The average particle size of Yb:YAG powder is about 100–200 nm. When the volume amount of polyethylene glycol is 2.0%, well-dispersed Yb:YAG powder with spherical particles of 100 nm diameter was obtained.