Tai Qiu

Electromagnetic and absorption properties of carbonyl iron/rubber radar absorbing materials

We measured the effective complex magnetic permeability /spl mu//sub eff//sup */ and dielectric permittivity /spl epsiv//sub eff//sup */ spectra in rubber radar absorbing material (RAM) with various carbonyl iron volume fractions by using the transmission/reflection method with a vector network analyzer. We studied the effects of carbonyl iron content and rubber thickness on the microwave absorption properties in the frequency range of 2.6 to 18 GHz. Our mathematical analysis is based on electromagnetic theory. The results indicate that the effective complex magnetic permeability and dielectric permittivity values of the RAM increase as the carbonyl iron volume fraction increases. For sample thickness of 3.0 mm, an increase in carbonyl iron content reduces the minimum reflection loss from -1.3 to -23.9 dB and shifts the frequency of the minimum reflection loss from 15.5 to 3.5 GHz. For an equal volume fraction of carbonyl iron, the frequency of the minimum reflection loss decreases as the thickness is increased. However, the dip in the reflection loss plot (in decibels) initially decreases to a minimum value before it increases with a further increase in thickness. We determined the value of the reflection loss for the samples by the impedance matching degree (reflection coefficient), which depends on the thickness and composition of the RAM.

Effect of manganese addition on the microstructure and electromagnetic properties of YIG

Abstract Y 3 Mn x Fe 4.85- x O 12 ( x =0, 0.02, 0.04, 0.06, 0.08 and 0.1) garnet ferrites (YMnIG) were prepared by conventional solid-state reaction method in air atmosphere. The effect of Mn addition on the microstructure and electromagnetic properties of YIG were investigated by means of techniques such as X-ray diffraction, scanning electron microscopey, network analyzer, hysteresigraph, magnetic balance and electron paramagnetic resonance spectrometry. Pure garnet phase of Y 3 Fe 5 O 12 was identified for all the samples, except for minor YFeO 3 phase appearing in the sample with x =0.06. The addition of Mn showed little influence on the dielectric constant of YIG, which varied between 14.2 and 14.5. Substituting Mn n + for Fe n + in YIG decreased the total amount of Fe ions, inhibited the reduction of Fe 3+ and promoted the grain growth of garnet phase, which led to the decrease in dielectric loss and coercivity. Because the amount of Mn 3+ ions in octahedral sites increased with Mn concentration, the saturation magnetization showed a slight decrease firstly and then increased notably. The addition of Mn could also increase the remanence ratio of YIG ferrites by decreasing the magnetostriction constant γ 111 . Therefore, doping Mn into YIG ferrites with proper quantity could improve electromagnetic properties of YIG significantly. The YMnIG ferrite with x =0.08, i.e., Y 3 Mn 0.08 Fe 4.77 O 12 , showed the optimum electromagnetic properties: ɛ r =14.2, tan δ e =1.5×10 −4 , H c =36 A/m, 4π M S =192 mT, B r / B s =0.84, Δ H =6.8 KA/m.

A novel catalyst of silicon cerium complex oxides for selective catalytic reduction of NO by NH3

Abstract A series of CeO 2 /SiO 2 and Si x Ce 1- x O 2 complex oxides supported on an activated Al 2 TiO 5 -TiO 2 -SiO 2 complex phase (ATS) ceramics were prepared by step impregnation and co-impregnation methods, and characterized by N 2 -BET, XRD, SEM and NH 3 -TPD techniques. The effects of reaction temperature, CeO 2 /SiO 2 loadings and Si/Ce molar ratio on the granular catalysts for NO selective catalytic reduction with ammonia (NH 3 -SCR) were studied. Results indicated that both CeO 2 /SiO 2 /ATS and CeO 2 /ATS catalysts showed the same active temperature window of 250–300 °C, mainly depending on the chemical composition of ceria. Moreover, the Si x Ce 1- x O 2 /ATS catalysts exhibited higher activity and stability than those of CeO 2 /SiO 2 /ATS, and the Si 0.75 Ce 0.25 O 2 represented the highest activity of 88.70% at 300 °C and the broadest active temperature window of 250–400 °C. Furthermore, the NH 3 -SCR of NO over the Si x Ce 1- x O 2 complex oxide catalysts was a result from synergetic catalysis between the acid catalysis and the redox catalysis.

Effect of Tb2O3 additive on structure of anatase and photocatalytic activity of TiO2/(O′ +β′)-Sialon multi-phase ceramics

Effect of rare earth oxide Tb2O3 additive on transformation behavior and grain growth of anatase and photocatalytic activity for TiO2/(O′ +β′)-Sialon multi-phase ceramic was investigated and the mechanism was discussed. X-ray diffractometer (XRD) was employed for the analysis of phase composition, grain size and lattice parameters of anatase. Photocatalytic activity of the composites was investigated through its photocatalytic degradation to methylene blue (MB) solution. The results showed that Tb2O3 significantly inhibited the transformation process, which displayed an appreciably intensified effect with increasing Tb2O3 content. It could be attributed to the coaction of the active and passive influence mechanisms. For Tb3+ entering TiO2 lattice, replacing Ti4+ accelerated the transformation, whereas the lattice distortion caused by it was unfavorable for the process. On the other hand, the redox reaction between Tb3+ and TiO2 as well as the Tb2O3 deposited on the surface of TiO2 inhibited the transformation. The addition of Tb2O3 effectively restrained the grain growth of TiO2 and the effect became significant with the increase of its content. With the increase of Tb2O3 addition, the photocatalytic activity of the catalysts increased and then dropped after reaching the maximum at about 2%. The action mechanism of Tb2O3 could be attributed to its optical properties and its effect on phase transformation, grain growth and crystal structure of TiO2.

Preparation and Performance of Ceria Doped Two-Component deNOx Monolithic Catalysts at Low Temperature

Abstract The (V-W-Ti-O)x (Cu-Al-O)1-x (Ce-O)0.03, (x = 0.9, 0.8) deNOx monolithic catalysts were prepared by low temperature co-sintering (LTC) within the sintering temperature range of 650–850°C. The effects of sintering temperature on the mechanical strength, porosity and water absorption of the monolithic catalysts and the effect of reaction temperature on catalytic activity were investigated. The microscopic structure of the catalysts was analyzed by X-ray diffraction (XRD), scanning electron microscopy (SEM) and fourier infrared spectroscopic analysis (FT-IR). Results show that catalysts are porous in micro-structure and grains are distributed uniformly. The crystallographic forms are mainly TiO2 (rutile), TiVO4, WV2O6, CeVO4, Cu2V2O7, AlV2O4, CuAlMnO4 and Cu1.9V12O29. For the reforming monolithic catalysts sintered at 700°C for 2 h, the two-component catalysts exhibit high catalytic activities in the low temperature range of 100-200°C and their bending strength reaches to 45.5 MPa. The NO conversion of (V-W-Ti-O)0.8 (Cu-Al-O)0.2 (Ce-O)0.03 monolithic catalyst corresponds to 75.9% at reactor temperature of 150°C.

Microwave dielectric properties of Ba6–3xLa8+2x(Ti1–zZrz)18O54 (x=2/3) ceramics

Abstract Zr substitution for Ti was investigated to modify the dielectric properties of Ba 6–3 x La 8+2 x Ti 18 O 54 ( x =2/3) ceramics. A single-phase solid solution with tungstenbronze-like structure was formed in the range of 0 z 6–3 x La 8+2 x (Ti 1– z Zr z ) 18 O 54 ceramics. As Zr content exceeded this range, a secondary phase of Ba 2 ZrO 4 was detected. This is correlated with the decrease of tolerance factor. As Zr content increased, there was an expansion of the b-axis and c-axis, and increase in the cell volume. Incorporation of small levels of Zr into the structure led to a significant increase in Q · f values, from 2053 to 6665 GHz, a decrease in dielectric constant (ɛ r ) from 107.4 to 79.6 and the temperature coefficient of resonant frequency ( τ f ) slightly improved. The maximum value of Q · f (6665 GHz, f =4.83 GHz) was achieved while ɛ r was 79.6 and τ f was 109.83×10 −6 °C −1 for z =0.1. Microstructure studies with SEM indicated that the ceramics with larger and homogenous columnar grains had high Q · f value.

Studies on the (1- x )(Mg 0.7 Zn 0.3 )TiO 3 - x Ca 0.61 La 0.26 TiO 3 Microwave Dielectric Ceramics System: Studies on the (1- x )(Mg 0.7 Zn 0.3 )TiO 3 - x Ca 0.61 La 0.26 TiO 3 Microwave Dielectric Ceramics System

本实验研究了(1- x )(Mg 0.7 Zn 0.3 )TiO 3 – x (Ca 0.61 La 0.26 )TiO 3 (MZT-CLT)系陶瓷的微观结构和微波介电性能, 通过(Ca 0.61 La 0.26 )TiO 3 来协调(Mg 0.7 Zn 0.3 )TiO 3 陶 瓷 的谐振频率温度系数. MZT-CLT陶瓷的主晶相为(Mg 0.7 Zn 0.3 )TiO 3 , 第二相为Ca 0.61 La 0.26 TiO 3 和(Mg 0.7 Zn 0.3 )Ti 2 O 5 . 烧结温度和陶瓷组成对微波介电性能影响显著, 当烧结温度为 1275℃ 时, 可以获得良好的致密度, 当烧结温度超过 1300℃ 时, Zn的蒸发导致陶瓷致密度和介电性能下降. 随着(Ca 0.61 La 0.26 )TiO 3 含量的增大, 材料的介电常数增大, 品质因数减小. 当 x =0.13, 烧结温度为 1275℃ 保温4h, (MZT-CLT)陶瓷具有优良微波介电性能, e r =26, Q·f =86000 GHz, τ f = -6×10 - 6 /℃.本实验研究了(1- x )(Mg 0.7 Zn 0.3 )TiO 3 – x (Ca 0.61 La 0.26 )TiO 3 (MZT-CLT)系陶瓷的微观结构和微波介电性能, 通过(Ca 0.61 La 0.26 )TiO 3 来协调(Mg 0.7 Zn 0.3 )TiO 3 陶 瓷 的谐振频率温度系数. MZT-CLT陶瓷的主晶相为(Mg 0.7 Zn 0.3 )TiO 3 , 第二相为Ca 0.61 La 0.26 TiO 3 和(Mg 0.7 Zn 0.3 )Ti 2 O 5 . 烧结温度和陶瓷组成对微波介电性能影响显著, 当烧结温度为 1275℃ 时, 可以获得良好的致密度, 当烧结温度超过 1300℃ 时, Zn的蒸发导致陶瓷致密度和介电性能下降. 随着(Ca 0.61 La 0.26 )TiO 3 含量的增大, 材料的介电常数增大, 品质因数减小. 当 x =0.13, 烧结温度为 1275℃ 保温4h, (MZT-CLT)陶瓷具有优良微波介电性能, e r =26, Q·f =86000 GHz, τ f = -6×10 - 6 /℃.

The Influence of Conditions on Synthesis Hydroxyapatite By Chemical Precipitation Method

Particles of Hydroxyapatite (HAp) were synthesized by means of chemical precipitation method, under atmosphere pressure. The starting solution with the Ca/P ratio of 1.67 was prepared by mixing 0.167 mol?dm?3 Ca(NO3)2?4H2O, 0.100 mol?dm?3 (NH4)2HPO4, 0.500 mol?dm?3 (NH2)2CO and 0.10 mol?dm?3 HNO3 aqueous solutions. The hydroxyapatite were prepared by heating the solution at 80 ?C for 24 hour and then at 90?C for 72 hour. Then followed, the dry powers were heat treatment at 660?C temperatures for 8 hour. The obtained powder was analyzed using XRD, XRF, FT-IR, SEM, TG-DTA. The results showed that obtained HAp powers were greatly influenced by synthetic conditions. HAp powders with various morphologies, such as sphere, rod, layered, dumbbell, fibre, scaly, were obtained by controlling the synthetic conditions.

Synthesis of Nanocrystalline Ag-Cu Supersaturated Solid Solution by Mechanical Alloying

Nanocrystalline Ag-28Cu supersaturated solid solution is prepared by mechanical alloying (MA) using a planetary ball mill. The mechanical alloyed powders are characterized by x-ray diffraction (XRD), scanning electron microscopy (SEM), high resolution transmission electron microscopy (HRTEM) and differential scanning calorimeter (DSC). XRD patterns show that the main peak of Ag-28Cu supersaturated solid solution exists at about 2θ=39° when the milling time is 30h. HRTEM images show that the grain sizes of as-prepared solid solutions have distributions from 10nm to 15nm. The interplanar spacing of (111) plane for fcc Ag-28Cu supersaturated solid solution is about 2.24Å. DSC measurement result indicates that the melting temperature of Ag-28Cu supersaturated solid solution is 783.8°C. The Ag(Cu) supersaturated solid solutions are in metastable state and they will be transformed into Ag-rich phase and Cu-rich phase simultaneously by annealing at 215°C- 415°C.

Synthesis of Ag-Cu-Sn Nanocrystalline Alloys as Intermediate Temperature Solder by High Energy Ball Milling

To obtain intermediate temperature alloy solders with melting temperature of 400~600°C, (Ag-Cu28)-25Sn and (Ag-Cu28)-30Sn alloys were prepared by high energy ball milling. Ag-Cu-Sn nanocrystalline alloys have been obtained after milling for 40h. XRD results show that the (Ag-Cu28)-25Sn alloy consists of Ag4Sn and Cu3Sn, and the (Ag-Cu28)-30Sn alloy contains Ag4Sn, Cu3Sn and Cu6Sn5. The small polydispersed particles with size ranging from 1μm to about 25μm are observed from the (Ag-Cu28)-30Sn alloys milled for 40h by SEM. A large amount of small particles comprised of two or three grains are commonly observed by HRTEM, and average grain size is about 17.50nm. DSC results indicate that the melting points of the (Ag-Cu28)-25Sn and (Ag-Cu28)-30Sn alloys milled for 40h are 548.5°C and 539.3°C, respectively.