Effect of composition and annealing on the dielectric properties of ZnO/mullite composite coatings

ZnO/mullite composite coatings were fabricated by atmosphere plasma spraying technology (APS). Scanning electron microscopy (SEM) and X-ray diffraction (XRD) were employed to investigate the microstructures and compositions of the feedstock and coatings. The permittivity-frequency properties were determined in the microwave frequency range of 8.2-12.4 GHz by network analysis. Our results show that both the real and imaginary part of permittivity increase greatly with increasing ZnO content over the frequency range of 8.2-12.4 GHz, which can be ascribed to interfacial polarization and orientation polarization. However, the composite coatings after 900 °C annealing for 5 h show much lower permittivity, due to the decrease of ZnO content resulting from the further reactions between the ZnO and mullite. Results indicate that the composite coating has excellent permittivity in room temperature, while for high temperature application, more investigation should be done.     

山西省某资源整合矿井副井井架与井口房联合构筑物设计

本文结合建设场地的实际情况提出了钢框架井架这一切实可行的井架形式,文中详细介绍了井架与井口房联合构筑物的结构方案、荷载计算与截面设计、基础设计、构造措施等。本工程为提升能力较小的新建、改扩建矿井快速建成投产提供了实例,可为今后类似工程设计提供参考。     

Air plasma-sprayed Y2O3 coatings for Al2O3/Al2O3 ceramic matrix composites

Al₂O₃/Al₂O₃ ceramic matrix composites (CMC) are candidate materials for hot-gas leading components of gas turbines. Since Al₂O₃/Al₂O₃ CMC are prone to hot-corrosion in combustion environments, the development of environmental barrier coatings (EBC) is mandatory. Owing to its favorable chemical stability and thermal properties, Y₂O₃ is considered a candidate EBC material for Al₂O₃/Al₂O₃ CMC. Up to 1 mm thick Y₂O₃ coatings were deposited by means of air plasma spraying (APS) on Al₂O₃/Al₂O₃ CMC with a reaction-bonded Al₂O₃ bond-coat (RBAO). APS Y₂O₃ coatings exhibit a good adherence in the as-deposited state as well as upon isothermal annealing up to 1400 °C. Moreover, furnace cyclic testing performed at 1200 °C revealed an excellent durability. This is explained by the formation of a continuous, approximately 1 μm thick reaction zone at the APS Y₂O₃/RBAO interface. The reaction zone between Y₂O₃ and Al₂O₃ comprises three layers of thermodynamically stable yttrium-aluminates exhibiting strong bonding, respectively.     

Structure of the hydroxyapatite plasma-sprayed coatings deposited on pre-heated titanium substrates

Plasma spraying is the most commonly used thermal spray method for the application of hydroxyapatite (HA, Ca₁₀(PO₄)₆(OH)₂) coatings. In the present study, the HA coatings were plasma spraying deposited onto plates of titanium pre-heated to 20 °C, 300 °C and 550 °C. The obtained HA coatings were investigated by means of X-ray diffraction and scanning electron microscopy. It is found that the coatings, in addition to HA, contain the tetracalcium phosphate (TTCP, (Ca₄(PO₄)₂O) phase (~10%) and a small amount of CaO (<2%). Crystal structure of HA in the coatings is revealed to be distorted. The PO4 tetrahedrons are deformed (Baur distortion coefficient D1(TO) ~0.2). The distances Ca1-O1 and Ca1-O2 are changed as compared to these in stoichiometric hydroxyapatite. These distortions are considered as a result of internal stresses, which are demonstrated in the broadening of peaks on X-ray diffraction pattern of HA. Microstructure of coatings consisting of flattened splats was formed by fully molten particles. The axial base texture was developed in the coatings. Ultrastructure is columnar with a preferred orientation of c-axes of the crystals parallel to the normal of plane coating n. The heating of substrate has a marked effect on the ultrastructure of coatings: the domain size increases from 790 to 1100 Å, the strain Δ decreases from 1.6·10^-3 to 1,2·10^–3, TTCP content diminishes from 12% to 7%. These results show that the effects due to heating of the substrate may be associated with partial recovery of HA microstructure.     

Sensitivity to change in laminar burning velocity and Markstein length resulting from variable hydrogen fraction in blast furnace gas for changing ambient conditions

The sensitivity to changes in fuel characteristics has been investigated for combustion of Blast Furnace Gas resulting from small volumetric increases in H₂ concentration. A nonlinear methodology has been employed to quantify unstretched flame speeds and the effect of flame stretch from outwardly propagating spherical flames. Following benchmarking work with CH₄, results were obtained under ambient conditions of 303 K and 0.1 MPa, with small absolute change in hydrogen concentration shown to at least triple the laminar burning velocity for all tested mixtures. Fuel composition and equivalence ratio were shown to independently influence mixture diffusivity and Lewis number, quantified by change in the obtained values of Markstein length. Temperature and pressure were increased to respective values of 393 K and 0.2 MPa to investigate influence of ambient conditions, with a power law correlation presented. Finally the performance of several published chemical reaction mechanisms has been evaluated through comparison of 1-D flame models.     

Lewis number effect on the propagation of premixed flames in narrow adiabatic channels: Symmetric and non-symmetric flames and their linear stability analysis

The propagation of premixed flames with different Lewis numbers in a planar channel subject to a Poiseuille flow is considered within the diffusive-thermal model for steady and time-dependent cases. It was found that, depending on the Lewis number and the flow rate, symmetric and non-symmetric flames are possible. The existence of multiple steady solutions in cases of the low Lewis number is demonstrated. The time-dependent simulations carried out for high Lewis number flames also showed the symmetric and non-symmetric oscillatory solutions.Linear stability analysis of two-dimensional steady-states was performed using a practical method developed in the paper and applied to calculate the main eigenvalue. It was shown that for symmetric flames with a low Lewis number the increase in the flow rate leads to a loss of stability with subsequent formation of non-symmetric solutions. For flames with a high Lewis number the Poiseuille flow produces a stabilization effect. The results of the stability analysis were successfully compared with the results of direct numerical simulations.     

我国纺织品阻燃检测标准概况

纺织品阻燃材料的研究，特别是纺织品阻燃检测技术对于减少火灾造成的损失具有十分重要的意义。本文重点介绍国内纺织品阻燃检测方法标准，主要包括垂直法、45°法、氧指数、减光系数法、水平法、可点燃性试验方法、辐射热源法。     

鼓风预混式大面积红外火焰钎焊设备及工艺

研究了鼓风预混式大面积红外火焰钎焊设备的设计，红外火焰温度的分布和铜的管－管板的钎焊工艺，该设备的关键器件为红外火焰燃烧器，它是由红外辐射材料经混合，压挤，焙烧而自然形成的多孔陶瓷燃烧器，这种燃烧器具有燃烧面积大，温度高的特点，非常适合大面积密束式管－管板的钎焊。     

Combustion properties and transference behavior of ultrafine microencapsulated ammonium polyphosphate in ramie fabric‐reinforced poly(L‐lactic acid) biocomposites

Flame‐retardant biocomposites have attracted much attention in past decades. They can provide many advantages, such as total biodegradability and their abundant renewable sources. In the work reported, biocomposites based on poly(L ‐lactic acid) (PLLA), ramie fabric (FAB) and microencapsulated ammonium polyphosphate (MCAPP) were synthesized via hot press molding using the powder‐stacking procedure. The effects of transference behavior of the flame retardant on sustaining flame retardancy of the biocomposites were investigated. Thermogravimetric analysis shows that the improved flame retardancy is due to an increased char residue at high temperature. Field emission scanning electron microscopy images and wide‐angle X‐ray diffraction data were used to investigate the hydrolysis reaction and transference behavior of ammonium polyphosphate in the biocomposites. UL‐94 testing and limiting oxygen index measurements show that the PLLA/FAB/MCAPP biocomposites retain their flame retardancy even after 21 days in UV‐irradiation hydrothermal aging tests. The good sustained flame retardancy of the PLLA/FAB/MCAPP biocomposites is attributed to the docking interactions and good distribution of MCAPP in the biocomposites. Copyright © 2010 Society of Chemical Industry     

导管架腿内热喷铝施工工艺

金属喷涂是通过喷涂熔化金属来达到防腐保护的一种措施。热喷铝是金属热喷涂的一种形式．利用某种热源（例如电弧、等离子孤、火焰等）将丝状或粉末状的金属铝加热至熔融或者半熔融状态，再借助热源的焰流或者外加的高速气流，将熔融或半熔融状的铝喷射到经过合理处理过的金属底材表面上，在表面形成一层具有防腐保护作用的金属铝涂层。某项目导管架的4个导管腿（A1．A4．B1，B4）内设计储存贫乙二醇的罐体内壁以及内部的所有附件就采用了这种电弧热喷铝的施工工艺，这是在海油系统内首次大范围地采用热喷铝施工工艺，具有施工面积大（3500m^2）、施工难度大（封闭空间内施工）、施工质量控制难的特点。