Potentiodynamic anodic polarisation and dynamic electrochemical impedance spectroscopic (DEIS) measurements were carried out
on type 316L stainless steel (SS), alloys 33 and 24 in natural sea water environment in order to assess pitting corrosion
resistance. The results revealed that the pitting corrosion resistance was higher in the case of alloys 33 and 24 than 316L
SS; due to the higher contents of nitrogen, chromium and molybdenum. DEIS measurements were performed over a wide range of
potentials covering the corrosion potential, passive region, breakdown region and dissolution region. It was shown that the
impedance measurements in potentiodynamic conditions allow simultaneous investigation of changes in passive layer structure.
The impedance spectra of various potential regions were also discussed. The Nyquist plots were fitted using non-linear least-square
(NLSS) method for different potential regions. 相似文献
HfO2–SiCN (polymer-derived silicon carbonitride) composites were prepared by two methods. In one case, equal volume fractions of HfO2 and pyrolyzed powders of SiCN were co-sintered, to create a particulate composite . The second type, called interface composites , were prepared by coating HfO2 particles with a thin film of the polymer precursor, followed by sintering so that densification and pyrolysis of the precursor occurred simultaneously; this process results in a ∼5-nm-thick grain boundary film constituted from Hf, O, and Si. The fracture properties and environmental degradation (in a humid environment at a velocity of 17.6–35.0 cm/s at 1300°C) of these two composites were measured. They were compared with the properties of a reference material made by sintering HfO2 powders without any additives, under similar conditions (1450°C for 2 h in air). The interface composite yielded the highest sintered density (0.90), exhibited negligible grain growth, and possessed the highest fracture strength (110 MPa). The strength remained immune to hydrothermal oxidation for several hundred hours. In contrast, the particulate composite suffered severe degradation in strength after hydrothermal exposure. The interface composites, with their highly refractory grain boundaries, represent a new class of ceramics for structural applications in harsh environments and at ultrahigh temperatures. 相似文献
High density polyethylene (HDPE) was reinforced with 0-40 wt% of wood flour (aspen). The effects of: stearic acid, mineral oil, maleated polyethylene wax, and sodium silicate on the tensile and impact strength of the composite were studied. The comparison of tensile properties of the composites showed that the addition of maleated polyethylene wax produced a significant increase in tensile strength, with the increase in filler concentration, while the tensile modulus remained relatively unaffected. Microscopic studies of the composites indicate a better dispersion of the fibers in the polymer matrix when stearic acid was used. 相似文献
The effect of fillers such as glass, ferrite, and carbon on the dielectric properties of epoxide resin along with conductivity has been studied as a function of frequency (1–100 kHz) and temperature (30–200°C). The glass transition temperature is not much affected by the presence of the fillers. The observed higher values of dielectric permittivity and loss in the case of filled polymers are attributed to Maxwell–Wagner–Sillars polarization. 相似文献
The kinetics and mechanism of reaction of glassy carbon with a pure silicon melt or a Si + Mo melt were investigated. The results showed that the growth of a continuous reaction-formed SiC layer followed a fourth-power rate law in the temperature range of 1430° to 1510°C. A model that could explain the fourth-power rate law was developed. In this model, an internal electric field was assumed to be set up over the reaction-formed SiC layer through a negative space charge, and then the diffusion of the carbon-ion vacancies across this layer, driven predominately by this electric field, was considered as the rate-limiting step for the SiC growth. Neither an increase in the processing temperature nor an addition of 10 wt% Mo into the silicon melt had a significant influence on the reaction kinetics. X-ray diffraction analysis revealed that the reaction products were β-SiC, and β-SiC + MoSi2 for the Si-C and Si-C-Mo reactions, respectively. 相似文献
Optimization of UV/H2O2 process for integration with biological waste treatment unit was done by Taguchi's orthogonal design. Four factors were considered for optimization: Dosage of H2O2, pH, circulation rate and number of doses of oxidant. For each of the four factors, experiments were run at four levels. For reduction in TOC, single dosage of hydrogen peroxide was observed to be more effective than dosing the same quantity in 2, 4 or 6 equal parts. The effect of circulation rate was found to be insignificant. If AOP were to be designed as a pretreatment step before biological oxidation, 1 mole H2O2/mole TOC is the optimum level of dosage. This level of addition increased biodegradability. If AOP were to be designed as a post-treatment step after biological oxidation, then 4 mole H2O2/mole TOC would be the optimum level of dosage. At this level, decrease in TOC was high. Higher pH of the waste liquor generally favoured reduction in TOC. 相似文献
The first-matrix cracking stress and fiber-matrix interfacial shear stress were measured in zircon-matrix composites uniaxially reinforced with either uncoated or BN-coated silicon carbide filaments to study the role of intentional changes in interfacial shear stress on first-matrix cracking stress. The first-matrix cracking stress was measured by mechanical tests performed in either tension or flexure, and the filament-matrix interfacial shear stress was measured by a fiber pushout test. The first-matrix cracking stress was independent of the measured interfacial shear stress and did not conform to the predictions of a number of energy-based micromechanics models. In contrast, the first-matrix cracking stress showed a good correlation with the first-matrix cracking strain, which is hypothesized to be a more realistic criterion for first-matrix cracking in this class of filament-reinforced ceramic-matrix composites. 相似文献
In this paper, small printed flower-shape triple notch ultra-wideband (UWB) monopole antenna with high band rejection is presented. Notch bands include WiMAX (IEEE802.16 3.30–3.80 GHz), WLAN IEEE802.11a/h/j/n (5.15–5.35, 5.25–5.35, 5.47–5.725, 5.725–5.825 GHz), and X-band downlink satellite system (7.1–7.9 GHz). By including inverted T-shape stub and etching two C-shaped slots on the radiating patch, triple band-notch function is obtained with measured high band rejection (VSWR = 14.52 at 3.58 GHz, VSWR = 15.88 at 5.69 GHz and VSWR = 6.95 at 7.61 GHz) and covers a UWB useable fractional bandwidth of 114.30% (2.74–10.57 GHz = 7.83 GHz). In short the antenna offers triple band-notch UWB systems as a compact multifunctional antenna to reduce the number of antennas installed in wireless devices for accessing multiple wireless networks with wide radiation pattern. The proposed antenna has a small size of about 0.25λ × 0.30λ at 4.2 GHz (first resonance frequency), which has a size reduction of 30% with respect to the earlier published antenna. Both the experimental and simulated results of the proposed antenna are presented, indicating that the antenna is a good candidate for various UWB applications.
A novel multifunctional amide additive N-phenyl-p-phenylenediamine-dodecenylsuccinic anhydride (PPA-DDSA) was synthesized by the reaction of DDSA and N-phenyl-p-phenylenediamine. The successful synthesis of amide additive was confirmed by various analytical techniques like Fourier Transform infrared spectroscopy, nuclear magnetic resonance spectroscopy, and thermogravimetric analysis. Performance of prepared additive was evaluated as multifunctional additive for anti-oxidant, detergent dispersant, anti-corrosion, and lubricity properties. The MAK-500® mineral base oil and synthetic polyol base oil were used as a reference. The antioxidant property was evaluated by using the 2,2-diphenyl-1-picrylhydrazyl method, which revealed that PPA-DDSA was better antioxidant than PPA and gallic acid but less effective than butylated hydroxytoluene. PPA-DDSA was found to be excellent detergent dispersant in polyol in comparison to the MAK-500. At 4000 ppm additive concentration, the coking value is reduced to 0.0205 g from the value of 0.0840 g for blank polyol while the % dispersancy increased to 40.67 from 20.00 for polyol base oil. The anti-wear property was observed to be better in the MAK-500 while the antifriction potential was found to be better in polyol base oil. The average wear scar is reduced from 881 to 550 μM at 2000 ppm concentration in MAK-500 base oil, while at 3000 ppm PPA-DDSA concentration, the average friction coefficient reduces to 0.0826 from 0.1276 for blank polyol. 相似文献