Synthesis, characterization and dielectric properties of a novel temperature stable (1-x)CoTiNb2O8-xZnNb(2)O(6) ceramic

(1-x)CoTiNb2O8-xZnNb(2)O(6) microwave dielectric ceramics were prepared via the conventional solid-state reaction route with the aim of reducing the (f) value and improving the thermal stability. The phase composition and the microstructure were investigated using X-ray diffraction, Raman spectra, and scanning electron microscopy. A set of phase transitions which were induced by composition had been confirmed via the sequence: rutile structurecoexistence of rutile and columbite phasecolumbite phase. For (1-x)CoTiNb2O8-xZnNb(2)O(6) microwave dielectric ceramics, the addition of ZnNb2O6 content (x = 0-1) led to the decrease of epsilon(r) from 62.98 to 23.94. As a result of the high Q x f of ZnNb2O6 ceramics, the increase of ZnNb2O6 content also led to the lower sintering temperatures and the higher Q x f values. The (f) value was reduced from +108.04 (x = 0) to - 49.31 ppm/degrees C (x = 1). Among them, high density 0.5CoTiNb(2)O(8)-0.5ZnNb(2)O(6) ceramics were obtained at 1175 degrees C with excellent microwave dielectric properties of epsilon(r) 39.2, Q x f 40013 GHz, and (f)+3.57 ppm/degrees C

Structural, Raman spectroscopic and microwave dielectric studies on (1-x) NiZrNb2O8 - x ZnTa2O6

(1 - x) NiZrNb2O8 - x ZnTa2O6 microwave dielectric ceramics were prepared via the conventional solid-state reaction route. Structural and lattice parameters of the (1 - x) NiZrNb2O8 - x ZnTa2O6 ceramics were analyzed through X-ray diffraction, Raman spectra, and scanning electron microscopy. The results showed that there were serious ionic diffusion and solid solution reaction in the composite ceramics. The substitution of Ni2+, Zr4+, and Zn2+ at A-sites and the substitution of Nb5+ and Ta5+ at B-sites led to the change of the lattice parameters. There was a gradual transformation in crystal structure from monoclinic phase into Tri-alpha PbO2 phase with the increasing ZnTa2O6 content. With the increase of x value from 0 to 1, the epsilon (r) value increased from 23.76 to 35.71 and the Q x AE' value increased from 32107 to 46709 GHz. The temperature frequency resonance coefficient near zero could be obtained at x = 0.8. The 0.2NiZrNb(2)O(8) - 0.8ZnTa(2)O(6) ceramics were obtained at 1275 A degrees C with excellent microwave dielectric properties: epsilon (r) similar to 33.69, Q x AE' similar to 37,529 GHz and tau(AE') similar to + 2.56 ppm/A degrees C

synthesischaracterizationanddielectricpropertiesofanoveltemperaturestable1xcotinb2o8xznnb2o6ceramic

(1–x)CoTiNb_2O_8 –xZnNb_2O_6 microwave dielectric ceramics were prepared via the conventional solid-state reaction route with the aim of reducing the τ_f value and improving the thermal stability. The phase composition and the microstructure were investigated using X-ray diffraction, Raman spectra, and scanning electron microscopy. A set of phase transitions which were induced by composition had been confirmed via the sequence: rutile structure→coexistence of rutile and columbite phase→columbite phase. For (1–x)CoTiNb_2O_8 –xZnNb_2O_6 microwave dielectric ceramics, the addition of ZnNb_2O_6 content (x =0–1) led to the decrease of ε_r from 62.98 to 23.94. As a result of the high Q ×? of ZnNb_2O_6 ceramics, the increase of ZnNb_2O_6 content also led to the lower sintering temperatures and the higher Q ×? values. The τ_f value was reduced from+108.04 (x =0) to – 49.31 ppm/℃ (x = 1). Among them, high density 0.5CoTiNb_2O_8 -0.5ZnNb_2O_6 ceramics were obtained at 1175 ℃ with excellent microwave dielectric properties of ε_r 39.2, Q ×? 40013 GHz, and τ_f+ 3.57 ppm/℃

Synthesis, characterization and dielectric properties of a novel temperature stable (1-x)CoTiNb2O8-xZnNb(2)O(6) ceramic

(1-x)CoTiNb2O8-xZnNb(2)O(6) microwave dielectric ceramics were prepared via the conventional solid-state reaction route with the aim of reducing the (f) value and improving the thermal stability. The phase composition and the microstructure were investigated using X-ray diffraction, Raman spectra, and scanning electron microscopy. A set of phase transitions which were induced by composition had been confirmed via the sequence: rutile structurecoexistence of rutile and columbite phasecolumbite phase. For (1-x)CoTiNb2O8-xZnNb(2)O(6) microwave dielectric ceramics, the addition of ZnNb2O6 content (x = 0-1) led to the decrease of epsilon(r) from 62.98 to 23.94. As a result of the high Q x f of ZnNb2O6 ceramics, the increase of ZnNb2O6 content also led to the lower sintering temperatures and the higher Q x f values. The (f) value was reduced from +108.04 (x = 0) to - 49.31 ppm/degrees C (x = 1). Among them, high density 0.5CoTiNb(2)O(8)-0.5ZnNb(2)O(6) ceramics were obtained at 1175 degrees C with excellent microwave dielectric properties of epsilon(r) 39.2, Q x f 40013 GHz, and (f)+3.57 ppm/degrees C

Microwave dielectric properties of sol-gel derived NiZrNb2O8 ceramics

NiZrNb2O8 microwave dielectric ceramics were prepared by an optimized sol-gel method using Nb2O5 center dot nH(2)O as a precursor. The thermal decomposition behavior of the Nb2O5 center dot nH(2)O was characterized by different thermal analysis and thermogravimetry (DTA/TG). Nanoscale NiZrNb2O8 particles with wolframite structure were obtained at about 950 degrees C. Regarding the microwave dielectric properties of NiZrNb2O8 ceramics, significant dependence has been verified with the sintering conditions, microstructure and compositions. The correlation between NiZrNb2O8 crystal structure and microwave dielectric properties was investigated from the analysis result of crystal structure refinement, chemical bonding ionicity and lattice energy based on the theory of valence. The relative density, dielectric constants, quality factors and temperature coefficients of the resonant frequency of NiZrNb2O8 ceramics sintered at 1100 degrees C reached 5.585 g/cm(3), 29.31, 22985 GHz and -24.96 ppm/degrees C, respectively. (C) 2018 Elsevier B.V. All rights reserved.</p

Synthesis of nano-sized TiC powders by designing chemical vapor deposition system in a fluidized bed reactor

Chemical vapor deposition (CVD) process is an effective way to fabricate highly pure ultra-fine powders; however commercial fabrication of high quality TiC powders through conventional CVD (TiCl4-H-2-CH4) system remains a great challenge. The main obstacle is that the conversion of chemically stable TiCl4 to TiC is too low (theoretically 133% at 1000 degrees C) to provide sufficient supersaturation to form powders but only coating. To tackle this problem, relatively unstable TiCl3 was proposed as a novel precursor, which is easier to achieve homogeneous nucleation due to the higher conversion of TiCl3 to TiC in the TiCl3-CH4-H-2 system (theoretically 37.7% at 1000 degrees C). In addition, a fluidized bed reactor (FBR) with fluidized TiC seeds providing local turbulence was employed to boost the homogeneous nucleation. Based on the novel idea, for the first time, high purity nanosized TIC powders (about 77.1 nm, purity 99.46 at.%) were successfully fabricated by a fluidized bed chemical vapor deposition (FBCVD) process. More importantly, an advanced simple and effective process was successfully developed to activate the common TiCl4 raw material to synthesize nano-sized TiC powders by designing the reactor. (C) 2020 Elsevier B.V. All rights reserved

Study on the Chemical Compatibility Study Between Li2TiO3 Pebbles and 14Cr-ODS Steel

In order to investigate the chemical compatibility between tritium breeder Li2TiO3 pebbles and tritium breeder blanket material oxide dispersion strengthened (ODS) steel, the contact interface between Li2TiO3 pebbles and ODS steel heated in argon atmosphere at 500, 600 and 700 degrees C for 300 h was studied. It was found that the ions of pebbles could diffuse and corrode with the cladding material after a long-time reaction at high temperature. The corrosion area formed on the surface of Li2TiO3 pebbles was small. With the increase of temperature, a zone with enriched iron was found on the surface of the pebble. This part of the surface was the direct contact surface between the pebble and the steel. At the same time, the relative density of the pebbles increased and the crush load was decreased to 30 N. In addition, a slight corrosion phenomenon was found on the surface of ODS steel. It has been proved that the main components of the corrosion products were the complex oxide containing Fe and Cr and the complex oxide containing Li and Fe.</p

A novel method to synthesize pure-phase Si2N2O powders in a fluidized bed reactor

Si2N2O ceramic, an emerging functional and structural material, has a wide range of applications. However, the preparation of pure-phase Si2N2O powder remains challenging due to the mass transfer resistance and unde-sirable side reactions in the conventional methods. Herein, a novel molecular approach combined with the decomposition process has been developed to synthesize pure-phase Si2N2O powders. The hydrated Si(NH)2 precursors were synthesized through the chemical vapor deposition (CVD) of SiCl4, NH3, and humidified N2 in a fluidized bed reactor (FBR) in two steps. Then, the hydrated Si(NH)2 precursors were decomposed into amor-phous and subsequently transformed into crystalline powders under different temperatures and time. It was found that the molar ratio of N/O of the hydrolyzed Si(NH)2 can be controlled by N2 ventilation time and played an important role in synthesizing high pure Si2N2O powder. When it varied from 2.5:1 to 2:1, pure-phase Si2N2O powder was obtained after heat treatment at 1300-1500 degrees C, which features a big tolerance for N/O ratios. This newly developed method offered a chance for the preparation of high-quality Si2N2O powder with high efficiency and low cost

Decomposition-carbonization of ammonium paratungstate in a fluidized bed

In this study, the reduction-carbonization property of WO3 obtained by thermal decomposition of ammonium paratungstate (APT) under N-2 and air atmosphere in a fluidized bed was investigated. The decomposition property of APT in N-2 and air was analyzed by TG analyzer. Phase, morphology, deoxidation rate and carbonization rate of the decomposed products in the reduction-carbonization process were investigated. It was found that APT could be rapidly decomposed into monoclinic WO3 in a fluidized bed in Ny or air atmosphere. Compared with N-2 atmosphere, air was more favorable for the rapid decomposition of APT and the crystal transition of WO3. Under the same conditions, the products obtained in N-2 atmosphere had smaller grain size, larger porosity, faster deoxidation rate and carbonization rate. Both WO3 obtained in the N-2 and air could be reduced and carbonized to nano-sized WC with SBET particle sizes of 63.70 nm and 73.49 nm in a fluidized bed, respectively.</p

The role of hydrogen coverage and location in 1,3-butadiene hydrogenation over Pt/SiO2

Hydrogenation of 1,3-butadiene over supported Pt particles has long been known as a structure sensitive reaction, yet the nature of this phenomenon has not been well understood. We have previously addressed the reaction pathway for 1,3-butadiene hydrogenation over similar to 22 nm Pt particles. In this study, the behaviors of SiO2 supported similar to 2.9 nm Pt particles towards 1,3-butadiene hydrogenation have been investigated with the aim of providing a fundamental explanation for the structure sensitivity of this reaction. Interestingly, it was found that the product distribution for the present catalyst towards 1,3-butadiene hydrogenation was sensitive to temperature. However, the evolution of 1,3-butadiene hydrogenation over the catalyst with temperature was not captured by in situ diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy. The detected carbonaceous species on the Pt surface are more likely to be spectators rather than reaction intermediates for the formation of butenes and n-butane. To understand the behaviors of the catalyst, density functional theory (DFT) calculations were employed to explore the pathways for the formation of the products with low activation barriers. The results show that the coverage and the location of the hydrogen atom are the two key factors for the interpretation of the behavior of Pt particles towards 1,3-butadiene hydrogenation