Key Engineering Materials Vol. 616

Abstract: In this paper, using ZrO₂ and Ca (NO₃)•4H₂O as raw materials, we prepared a series of calica stabilized zirconia (CSZ) ceramics by pressureless sintering method. The results show that the relative densities of all sintered samples are above 90%, and the sintered samples are composed of cubic, tetragonal and monoclinic ZrO₂, and the main phase is cubic ZrO₂ and tetragonal ZrO₂. The content of cubic phase increases with the increase of sintering temperature and adding CaO content. The grain size of the sintered samples is relatively uniform and some pores exist. Increasing the additive amount of CaO, the conductivity first rises and then decreases, and the conductivity value of the sample containing 5wt% CaO is the maximum. When the sintering temperature is up to 1600 ^oC, the conductivity of the sample containing 5wt% CaO is up to 0.016S•cm^-1 at 800 ^oC. Furthermore, the conductivity of sintered samples is increasing with the increase of test temperature according to the Arrhenius equation.

Abstract: In this work, the microwave dielectric ceramic (1-m)(Mg_0.8Zn_0.2)TiO₃·m{Ba₄Nd_28/3Ti₁₈O₅₄·0.18Bi₂O₃}(m=0.1~0.4)(MZT-BNT) was studied to improve dielectric properties. The results of the dielectric properties, density, XRD and SEM show that the value of m and the sintering temperature affected the structure and properties of the ceramics. MZT-BNT composite system is a two-phase composite system. With the adding of BNT, the dielectric properties of MZT increase significantly. As m value increases, the bulk density and the dielectric constant of the composite system increase, while the quality factor reduces and the temperature coefficient of resonant frequency is close to zero. The dielectric properties of MZT-BNT sintered at 1200 °C (m = 0.3) are ε_r = 34.03, Q_f = 7177 GHz,τ_f = -3.39 ppm/°C, respectively.

Abstract: The single phase of Bi-doped Mg₂Si_0.3Sn_0.7 compounds have been successfully fabricated by solid state reaction and spark plasma sintering (SPS). The effect of Bi doping concentration on the thermoelectric properties of Mg₂Si_0.3Sn_0.7 is investigated. The doping of Bi atom results in the increase of carrier concentrations and ensures the increase of electrical conductivity. Although the thermal conductivity and Seebeck coefficient shows a slight increase, the figure of merit of Mg₂Si_0.3Sn_0.7 compounds still increases with the increasing contents of Bi-doping. When Bi-doping content is 1.5at%, the Mg₂Si_0.3Sn_0.7 compound obtained the maximum value, ZT, is 1.03 at 640 K.

Abstract: Transparent conducting antimony doped tin oxide (ATO) films were sputtered on quartz glass substrates by RF magnetron sputtering at an oxygen flow rate ranging from 0 to 15 sccm. The films were prepared at room temperature and annealed for 15 min in air atmospheres at a temperature of 450 °C. The effect of oxygen flow rate has been investigated by comparing eletrical and optical properties of ATO films. The results suggest that, oxygen flow rate has a great impact on Sb⁵⁺/Sb³⁺ ratio and lattice structure integrity, which finally affects the transmittance and electrical resistivity. With the increase of oxygen flow rate, the grain size is enlarged, which leads to a higher average optical transmittance. On the other hand, with oxygen flow rate increasing, the Sb⁵⁺/Sb³⁺ ratio first increases and then decreases sharply when the oxygen flow rate exceeds 5 sccm. The increase of Sb⁵⁺/Sb³⁺ ratio results in the increase of carrier concentration and finally contributes to a decrease of electrical resistivity. The optimal resistivity is 8.9×10^-2 Ω·cm and the average transmittance is about 95% at an oxygen flow rate of 5 sccm.

Abstract: Synthesis of monolithic A-type zeolite (LTA) was attempted by hydrothermal processing from recycling flat glass. Crashed flat glass were pretreated and subsequently hydrothermally treated at 95°C for 24 h. As a result, monolithic A-type zeolite without another phase was successfully synthesized by the hydrothermal treatments. The synthetic condition was clarified during the pretreatment and hydrothermal treatments. The development of hydrothermal process for recycle of flat glass was carried out since the monolithic A-type zeolite was obtained under the optimum synthetic conditions (reaction temperatures, reaction time and pretreatment conditions etc).

Abstract: The effect of high magnetic field on diamagnetic fluid flow has been studied by in-situ optical observation. The Schlieren optics utilizable under high magnetic fields was developed to carry out in-situ observation of the behavior of feeble magnetic fluids. Using a crystal of the diamagnetic aluminum potassium sulfate dodecahydrate, the behavior of the downward flow of high concentration solution in the sample dissolution process was observed. It was found that the direction of diamagnetic fluid flow was changed under spatially varied magnetic field. This phenomenon was understood qualitatively by considering the magnetic force acting on the high concentration solution and the surrounding solution.

Abstract: WC-Co-cBN composites were consolidated by SPS at 1373 to 1673 K under a moderate pressure of 100 MPa. The addition of cBN increased the starting and finishing temperature of shrinkage and decreased the relative density of WC-Co. The relative density of WC-(10-20 vol%) cBN composites was about 97-100% at 1573 K and decreased with increasing the sintering temperature to 1673 K due to the phase transformation of cBN to hBN. The highest hardness and fracture toughness of WC-Co-20 vol% cBN composite sintered at 1573 K were 23.2 GPa and 8.0 MP m^1/2, respectively.

Abstract: Porous Al with controlled pore size was prepared by the spacer method including spark plasma sintering and the dissolution of space-holding NaCl particles. The NaCl of the controlled pore size (particle diameter control range of 5˰ڌm~20˰ڌm) were prepared by precipitation method. The effects of sintering condition such as the sintering electric current intensity, voltage and the size, morphology and content of NaCl powder on the porosity and size of porous Al are investigated. The porous Al with higher porosity of 69.41% and smaller pore size of 5 ڌm was obtained.

Abstract: The technique of combustion reaction and quick pressing was adopted to prepare dense nanocrystalline ceramics. The densification process of magnesia compact with a particle size of 100 nm was investigated, under the applied pressure of up to 170 MPa, and the temperature of 1740–2080 K with ultra-high heating rate of above 1700 K/min. As a result, pure magnesia ceramics with a relative density of 98.8% and an average grain size of 120 nm was obtained at 1740 K and 170 MPa, while the ones with decreased relative density and increased grain size were produced under the increasing temperature and the identical pressure conditions. The results indicated that grain growth of the nanocrystalline magnesia was effectively restrained by the combined effect of the ultra-high heating rate and the high pressure. Moreover, under the particular sintering conditions, there existed an appropriate temperature range for the preparation of dense nanocrystalline magnesia, and the excessive temperature would not only exaggerate grain growth but also impede densification.

Abstract: Aluminum (Al) and Copper (Cu) have been used in graded density impactors. Al-Cu composites with different compositions have been prepared by hot pressing sintering. Intermetallic compounds were produced when the temperature was above 723 K, while they can’t be found at the temperature of 723 K. The relative density of Al-Cu composites from pure Al to pure Cu consolidated at 723K all exceeded 98.5%. The optimum sintering conditions were then determined to sintering temperature of 723 K, uniaxial pressure of 100 MPa, and duration time of 2 h. Al and Cu were mixed homogeneously and well compacted, and no obvious pores were found. The thickness of diffusion layer between Al and Cu was very thin, only about 0.6 μm. The wave impedance values increased almost linearly from 16.98×10⁶ to 40.66×10⁶ kg/m²·s with increasing Cu content in Al-Cu composite from 0 to 100 vol.%, which was well consistence with the values calculated according to the rule of mixtures. The elastic modulus of different compositions matched well with the theoretical model of Voigt and Reuss. Highly densified Al-Cu composites without intermetallic compounds were successfully prepared using hot-pressure sintering, which was the basis of fabricating Al-Cu system graded density impactors.