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1.
《Ceramics International》2022,48(6):8155-8168
In the present study, the effect of oxy-acetylene flame angle on the erosion resistance of SiC/ZrB2–SiC/ZrB2 multilayer coatings with the gradient structure was investigated. To this aim, first, the SiC inner layer was applied by the reactive melt infiltration (RMI) technique; then ZrB2 and ZrB2–SiC layers with 10, 20 and 30%wt. SiC were applied on graphite by the plasma spraying technique. To prevent the oxidation of ZrB2 and SiC particles, the plasma spraying process was performed by a solid protective shield. To evaluate the performance of the coatings in erosive environments, the samples were exposed to oxy-acetylene flame at the angles of 30°, 60° and 90° for 360 s; the destruction mechanism of SiC/ZrB2–SiC/ZrB2 multilayer coatings appeared to be controlled mechanically and chemically. The results of the erosion test showed that at the low flame angles of about 30°, due to the shear forces of oxy-acetylene flame, mechanical erosion overcame the chemical one. With increasing the flame angle, due to raising the surface temperature, chemical erosion overcame the mechanical one; so, most chemical destruction occurred at the flame angle of 90°. Also, the results of the erosion test showed that the total chemical and mechanical destruction at the angle of 60° was greater than that in other angles. Also, among the coatings tested, SiC/ZrB2- 20% wt. SiC/ZrB2 coatings had the best erosion resistance; so, the weight changes under the oxy-acetylene flame at the angles of 30° and 60°, respectively, were about ?0.038%. and ?0.355%; meanwhile, at the angle of 90°, it was about +4.3%.  相似文献   
2.
Graphene nanoplatelets (GNPs) as reinforcement in the ceramic matrix is rising continuously due to their outstanding mechanical and lubricative properties. Herein, different compositions of GNPs (0.5–2 wt%) reinforced alumina-titania coatings were prepared using atmospheric plasma spraying. The relative density of AT coating increased from 83% to 94% with just (1.5 wt%) addition of GNP. Consequently, mechanical properties i.e. hardness and elastic modulus were improved by ~77% and ~69% respectively. Fracture toughness also increased from 2.65 ± 0.95 MPa.m1/2 to 5.85 ± 1.07 MPa.m1/2. Furthermore, the seawater wear test, using a ball-on-disc tribometer revealed that the wear rate of AT coating decreased from ~11 × 10?14 m3/Nm to ~4 × 10?14 m3/Nm, whereas the coefficient of friction reduced from 0.33 ± 0.05–0.16 ± 0.03. The mechanisms involved to improve these properties, viz. GNP sandwiching, crack bridging, crack arrest, etc. GNP’s multi-layers facilitated long-term lubricity and enhanced the wear resistance properties of the coatings.  相似文献   
3.
本文研制了2 mg/g碲化镉(CdTe)溶液中无机痕量杂质成分分析的5种标准物质,每种包含21种杂质元素,浓度分别为0、1、2、4、8 ng/g。通过辉光放电质谱(GD-MS)法对CdTe原料纯度进行测量,筛选得到纯度>99.999%的高纯原料;使用HCl-HNO3混酸将其溶解,再根据成分设计定量添加杂质元素,制备得到标准物质候选物。建立了基体匹配-内标校正-电感耦合等离子体质谱法用于标准物质定值与均匀性、稳定性检验,采用标准物质EB507验证方法可靠性。对包装容器溶出进行考察,以高密度聚乙烯(HDPE)作为包装容器可满足要求。采用建立的方法对全部元素进行检验,结果表明,标准物质均匀性以及长、短期稳定性良好,有效期12个月。通过8家实验室联合定值的方式,对标准物质中21种元素进行定值,以算数平均值作为标准值,并对不确定度进行全面、系统地评估。该系列基体标准物质填补了国内外空白,对于验证测量方法的可靠性、确保测量结果的一致性与溯源性具有重要作用。  相似文献   
4.
用机械合金化和放电等离子烧结(SPS)工艺制备名义成分为Fe-18Mn-0.6C的高锰钢,对其组织及力学性能进行分析。结果表明:SPS烧结制备的Fe-18Mn-0.6C块体为平均晶粒尺寸为1μm的超细晶单一奥氏体合金钢,晶粒内部存在较多的层错及退火孪晶,还分布着大量的纳米级弥散颗粒。Fe-18Mn-0.6C块体硬度为475HV、抗拉强度为925 MPa,较多的孔隙缺陷导致块体致密度低,仅为96.27%。孔隙与晶粒内部大尺寸颗粒在拉应力作用下易萌生裂纹发生撕裂,造成沿晶脆断,塑性较差。850℃/1 h的热处理能显著改善块体韧性,伸长率由4%升至13%,以脆断为主、韧断为辅的混合断裂模式。  相似文献   
5.
In order to reveal the mechanism of water fog explosion suppression and research the combined effect of water fog and obstacle on hydrogen/air deflagration, multiple sets of experiments were set up. The results show that the instability of thermal diffusion under lean combustion conditions is the main influencing factor of hydrogen/air flame surface instability, and the existence of water fog will aggravate the hydrogen/air flame surface instability. When obstacle is not considered, 8 μm, 15 μm, 30 μm water fog can significantly reduce the flame velocity and explosion overpressure of hydrogen/air, 45 μm fine water fog plays the opposite role. When considering the relative position of the water fog release position and the obstacle, the 8 μm, 15 μm, 30 μm water fog has almost no suppression effect when released near the obstacle, but a significant suppression effect occur, when using the 45 μm water fog. In the field of theoretical research, the research results not only provide an experimental basis for the fine water fog to reduce the consequences of hydrogen explosion accidents, and the optimal diameter range used by the water fog, but also provide experimental reference for the numerical simulation of hydrogen/air explosion suppression in semi-open space, and promote the development of hydrogen explosion suppression theory. In terms of engineering applications, this study can provide a theoretical basis for the layout of fire fighting equipment in the engine room of nuclear power plants or hydrogen-powered ships.  相似文献   
6.
孙建恒 《分析仪器》2022,(1):149-154
对气相色谱双等离子体硫化学发光检测器(GC-DPSCD)法测定低温甲醇洗装置气体痕量硫化物的影响因素进行了探讨,包括载气种类及流量的选择、柱温的确定、双等离子体燃烧器条件的优化等。通过对上述影响因素的控制和优化,建立了良好的工作曲线,得到了较低的检出限,保证了痕量硫化物分析结果的准确度和精密度,满足了分析要求。  相似文献   
7.
According to the Food and Agriculture Organization of United Nations reports, approximately half of the total harvested fruits and vegetables vanish before they reach the end consumer due to their perishable nature. Enzymatic browning is one of the most common problems faced by fruit and vegetable processing. The perishability of fruits and vegetables is contributed by the various browning enzymes (polyphenol oxidase, peroxidase, and phenylalanine ammonia-lyase) and ripening or cell wall degrading enzyme (pectin methyl-esterase). In contrast, antioxidant enzymes (superoxide dismutase and catalase) assist in reversing the damage caused by reactive oxygen species or free radicals. The cold plasma technique has emerged as a novel, economic, and environmentally friendly approach that reduces the expression of ripening and browning enzymes while increasing the activity of antioxidant enzymes; microorganisms are significantly inhibited, therefore improving the shelf life of fruits and vegetables. This review narrates the mechanism and principle involved in the use of cold plasma technique as a nonthermal agent and its application in impeding the activity of browning and ripening enzymes and increasing the expression of antioxidant enzymes for improving the shelf life and quality of fresh fruits and vegetables and preventing spoilage and pathogenic germs from growing. An overview of hurdles and sustainability advantages of cold plasma technology is presented.  相似文献   
8.
Using spark plasma sintering (SPS), >98.5 % dense boron carbide (B4C) samples were made from commercially available and lab-synthesised powders made via a low temperature synthesis (LTS) process. The work showed that the LTS powder can be produced in batches of tens to hundreds of grams whilst maintaining a high purity material with lower levels of residual free carbon (20.6–21.3 wt.% C) than commercially available samples (22.4 wt.% C). The LTS material was seen to exhibit higher hardness values (37.8 GPa) than the commercial grade material (32.5 GPa) despite featuring a coarser average grain size (10.8 μm and 2.4 μm respectively). This is largely thought to be due to the influence of ZrO2 and AlB2 impurities introduced to the material during micronising milling of the powder after synthesis, as opposed to the influence of the materials lower carbon content.  相似文献   
9.
The plasma spray technique was well proven in producing metal oxide based gas sensors in the last two decades using different powder feedstocks. However, limited research was made to fabricate hydrogen gas sensor from tin oxide layer coated over tungsten oxide layer. This paper attempts to interpret the hydrogen gas sensing performances of plasma sprayed coating derived by depositing tin oxide layer over tungsten oxide (SnO2/WO3) layer. Plasma sprayed SnO2/WO3 sensor showed maximum response of 90% at 150 °C in contrast to stand-alone WO3 (89% at 350 °C) and stand-alone SnO2 (89% at 250 °C). The lower operating temperature of SnO2/WO3 sensor without compromising gas response was attributed to the WO3–SnO2 hetero-junction. SnO2/WO3 sensor showed selective sensing towards hydrogen with respect to carbon monoxide and methane gases. This sensor also possessed repeatable characteristics after 39 days from the initial measurement. In a nut-shell, plasma spayed SnO2/WO3 sensor showed stability of base resistance, repeatability after successive response and recovery cycles, selective sensing towards 500 ppm H2 with significant magnitude of gas response of 90%, response time of 35 s and recovery time of 269 s at a temperature of 150 °C.  相似文献   
10.
The effects of non-thermal plasma (NTP) on the physicochemical properties of wheat flour and the quality of fresh wet noodles ( FWN) were investigated. The results showed that NTP effectively decreased the total plate count (TPC), yeast and mould count (YMC) and Bacillus spp. in wheat flour. Wet gluten contents and the stability time reached the maximum when treated for 20 s. The viscosity of starch increased significantly after treatment due to the increased of damaged starch. The contents of secondary structure were altered to some extent, which was because that the ordered network structure of gluten protein broken. Furthermore, compared with the control, texture properties of FWN were enhanced significantly at 20 s, and the darkening rate of FWN was greatly inhibited due to the low polyphenol oxidase (PPO) activity. Consequently, the most suitable treatment was 500 W for 20 s, providing a basis for the application of NTP in flour products.  相似文献   
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