用于射频滤波器的LN单晶薄膜XBAR的性能研究

基于铌酸锂(LN)薄膜的横向激发体声波谐振器(XBAR)能够兼具大机电耦合系数(K²)和高谐振频率(f)特性，有望满足5G应用的频段要求。然而，常规LN薄膜单层XBAR结构的温度稳定性较差，频率温度系数(TCF)较低。该文提出一种具有SiO₂温度补偿层的SiO₂/LN双层结构XBAR，并建立了精确分析层状结构XBAR的有限元模型。理论分析表明，该双层结构XBAR上激励的主模式是一阶反对称(A1)兰姆波。通过合理优化结构参数配置，能够获得高谐振频率(f~4.75 GHz)和大机电耦合系数(K²~8%)，同时其温度稳定性也得到显著改善(TCF~-36.1×10^-6/℃)，相较于单层XBAR结构提高了近70×10^-6/℃，这为研制温补型高频、大带宽声学滤波器提供了理论基础。     

无黏土相盐水储层钻开液体系构建及其抗污染性能评价

采用NaCl/KCl/HCOONa复配欠饱和盐水作为钻开液的基础液相,自研的聚合物VIS-B作为流型调节剂,可酸溶的改性淀粉STA作为体系的降失水剂,Dua及Jqw作为暂堵材料,构建了一套无黏土相钻开液体系。该体系在密度1.10~1.28 g/cm^3间稳定可调,抗温可达130℃,具有较高的低剪切速率黏度和较好的润滑性能,且能有效抵抗各类储层污染物的污染,满足了Missan油田不同储层段的作业需求。     

One step from nanofiber to functional hybrid structure: Pd doped ZnO/SnO2 heterojunction nanofibers with hexagonal ZnO columns for enhanced low-temperature hydrogen gas sensing

In this paper, a novel hybrid structure of Pd doped ZnO/SnO₂ heterojunction nanofibers with hexagonal ZnO columns was one step synthesized from electrospun precursor nanofibers. Due to the synergistic effect of hexagonal ZnO, SnO₂ and Pd, the structure exhibited excellent hydrogen (H₂) gas sensing properties. At low-temperature of 120 °C, the response (R_a/R_g) to 100 ppm H₂ gas exceeded 160, the response/recovery time was only 20 s and 6 s respectively and the limit of detection was only 0.5 ppm. Meanwhile, it also had good selectivity for H₂ gas and excellent linearity. In addition, the materials were characterized by XRD, FESEM, HRTEM, XPS, and the synthesis mechanism and gas sensing mechanism were proposed.     

Ammonia production using iron nitride and water as hydrogen source under mild temperature and pressure

Ammonia generation was studied in the reaction between water and nitrogen-containing iron at 323 K and atmospheric pressure. Similar to metallic Fe, the interstitial compound Fe₃N reduced water through Fe oxidation to produce hydrogen gas, while the N combined with atomic hydrogen to produce ammonia as a byproduct. The addition of carbon dioxide to this system accelerated the reaction with concomitant consumption of carbon dioxide. The promoted ammonia production upon addition of carbon dioxide can be attributed to the generation of atomic hydrogen from the redox reaction of carbonic acid and Fe, as well as removal of used Fe from the reaction system through the formation of a soluble carbonato complex. When carbonate was added to the reaction system, the production rates of ammonia and hydrogen increased further. The results here confirmed that ammonia can be synthesized from iron nitride under mild conditions by utilizing carbon dioxide.     

Preparation of high-activity coal char-based catalysts from high metals containing coal gangue and lignite for catalytic decomposition of biomass tar

The potential of using high metals containing coal gangue and lignite to prepare high-activity coal char-based catalysts is investigated for effective biomass tar decomposition. Loose structure and rough surface are formed for these char-based catalysts with heterogeneous distribution of a large number of inorganic particles. In the biomass tar decomposition, the performance of the coal char-based catalysts is significantly influenced by the content of the metals in the raw materials and coal gangue char (GC) with the ash content as high as 50.80% exhibits the highest activity in this work. A high biomass tar conversion efficiency of 93.5% is achieved at 800 °C along with a significant increase in the fuel gas product. During the five-time consecutive tests, the catalytic performance of GC increases a little at the second or third times reuse and remains relatively stable, showing the remarkable stability of the catalyst in biomass tar decomposition applications.     

Pressure-induced transparency of MgO,Al2O3, AlN,and cBN ceramics at room temperature

The in situ axial X-ray diffraction patterns of four ceramic powder samples (MgO, Al₂O₃, AlN, and cBN) that were compressed in a diamond anvil cell under uniaxial non-hydrostatic conditions were recorded. The microscopic deviatoric stress as a function of the pressure was determined from the X-ray diffraction peak broadening analysis: the curves increased approximately linearly with the pressure at the initial compression stage and then levelled off under further compression. Pressure-induced transparency was observed in all of the samples under compression, and the pressure at the turning point on the curves of the microscopic deviatoric stress versus pressure corresponded to the pressure at which the samples became transparent. Analysis of the microstructural features of the pressure-induced transparent samples indicated that the compression caused the grains to fracture, and the broken grains bonded with each other. We demonstrated that the ceramics’ pressure-induced transparency was a process during which the grains were squeezed and broken, the pores were close between the grains, and the broken grains were re-bonded under compression.     

浸渍剂和压紧系数对全膜电容器端部电场分布的影响研究

全膜电容器边缘处的电场畸变是影响电容器元件击穿的重要因素之一.为研究浸渍情况和压紧系数对全膜电容器电场分布的影响,对电容器端部进行建模,通过改变浸渍情况和压紧系数,计算不同参数下电容器端部的电场分布情况,结果表明:未浸渍情况下电场最大值集中在折边处两侧,浸渍情况下场强在折边圆弧处分布较为均匀.同时发现,在浸渍情况下增大压紧系数K可以明显改善全膜电容器端部电场的分布情况.     

Preparation and electrochemical characterization of Ti-based amorphous metallic glass with high strength

Ti-based amorphous metallic glasses have excellent mechanical, physical, and chemical properties, which is an important development direction and research hotspot of metal composite reinforcement. As a stable, simple, efficient, and large-scale preparation technology of metallic powders, the gas atomization process provides an effective way of preparing amorphous metallic glasses. In this study, the controllable fabrication of a Ti-based amorphous powder, with high efficiency, has been realized by using gas atomization. The scanning electron microscope, energy-dispersive spectrometer, and X-ray diffraction are used to analyze surface morphology, element distribution, and phase structure, respectively. A microhardness tester is used to measure the mechanical property. An electrochemical workstation is used to characterize corrosion behavior. The results show that as-prepared microparticles are more uniform and exhibit good amorphous characteristics. The mechanical test shows that the hardness of amorphous powder is significantly increased as compared with that before preparation, which has the prospect of being an important part of engineering reinforced materials. Further electrochemical measurement shows that the corrosion resistance of the as-prepared sample is also significantly improved. This study has laid a solid foundation for expanding applications of Ti-based metallic glasses, especially in heavy-duty and corrosive domains.     

Tempering–preservation treatment inactivated lipase in wheat bran and retained phenolic compounds

Wheat bran is rich in functional ingredients, but the high level of lipase limits its applications. Tempering–preservation treatment (at 70–90 °C with moisture of 20%–40% for 1–4 h) was exploited for stabilising wheat bran and its effect on polyphenols was investigated. The results showed that more lipase was inactivated at higher tempering moisture, temperature and longer time. The optimum condition for inactivation of wheat bran lipase was 30% moisture and 90 °C for 4 h. The inactivation rate reached 93.8% with a residual enzyme activity of 0.264 U g⁻¹. Under the optimum condition, the sum of free phenolic acids rose from 25.4 to 55.8 µg g⁻¹. As for bound phenolic acids, there was a slight increase of hydroxybenzoic acid derivatives but a slight decrease of hydroxycinnamic acid derivatives. The total contents of phenolic acids before and after stabilisation were not significantly different. This study showed the possibility of using tempering–preservation as an efficient method for inactivation of wheat bran lipase while maintaining its phenolic compounds, which could be used in the production of whole wheat flour.