首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献,搜索用时 921 毫秒
1.
A barium‐containing three‐way automotive emission catalyst was submitted to a NOx storage step in flowing lean gas mixture containing 340 ppm NO and 8 vol% O2 in helium. NOx release was carried out in the 250–550°C temperature range, either in pure helium or in the presence of a 10 vol% CO2 in helium mixture. It was shown that at 450–550°C all of the stored NOx on the barium trap can be released fastly in the CO2‐containing gas mixture or, after a longer time, in pure helium: these data show that NOx release can occur in the absence of a reducing agent. The NOx release was not complete at 350°C and did not occur at 250°C. The assisting effect of CO2 as regards to NOx release was interpreted in terms of the existence of the CO2,gas + *NO2,stored ⇌ *CO2,stored + NO2,gas equilibrium, suggesting the competitive storage of CO2 and NO2 for a unique type of barium storage sites (*). This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

2.
The effect of electric fused ZrO2,m-ZrO2 and zirconite on the sintering properties of MgO-CaO bricks was studied and the effect of the ZrO2 content and temperature on BD (bulk density), AP(apparent porosity)and CCS (Cold Crushing strength) of MgO-CaO bricks was investigated.The microstructure of burned specimens was analyzed by SEM. The result shows that the sintering property is best while 5% m-ZrO2 was added at 1 600 ℃.  相似文献   

3.
Electrodeposition of PbO2 and Bi–PbO2 on Ebonex was carried out under various conditions, and the surfaces and coating/substrate interfaces examined by SEM, XPS and SIMS. Excellent adhesion to Ebonex was obtained with both crystalline and amorphous surfaces. Low plating temperatures resulted in dark grey, bright PbO2 and black, mirror-like Bi–PbO2 surfaces. Extrapolation of electrode lifetime test data indicated corrosion rates of 716 m yr–1 for PbO2 and 158 m yr–1 for Bi–PbO2.  相似文献   

4.
Parameters which affect the electrosynthesis of 4,4-dinitroazobenzene from p-nitroaniline on platinum and PbO2 electrodes were investigated and optimum conditions were determined. Maximum conversion efficiency for electrosynthesis was 95% with a pure -PbO2 electrode. It was found that the electrocatalytic activity of a PbO2 electrode depends upon its / ratio and its degree of crystallinity. The effects of the added base and water on the conversion efficiency were also elucidated.  相似文献   

5.
6.
The catalytic reduction of N2O by H2, NH3, CO, propene and n-decane, in the presence of O2, has been studied on two Fe-zeolite-β (Fe-BEA) catalysts. In the following experimental conditions (GHSV=35 000 h−1, 2000 ppm N2O, 3% O2), CO starts to reduce N2O from 473 K and is the most efficient reductant in the low temperature domain. The absence of strong adsorption and the ability to reduce FeIII oxo-cations can be put forward to explain this behaviour. At medium temperature range n-decane become very reactive to reduce N2O. Finally, in the absence of NH3 slip, this reductant can be considered as an excellent candidate owing to the harmless of its reduction products.  相似文献   

7.
A chemical treatment to remove residual CeO2 phase on CeO2–ZrO2 (CZ) solid solution was carried out. A CZ was treated by H2O2 for the reduction of Ce4+ to Ce3+ and then HNO3 for the dissolution of Ce3+ compounds (H–CZ). H2-TPR, TEM-EDX and XPS analyses revealed the removal of CeO2 phase and the homogeneous distribution of Ce species. About 20% improvement in oxygen storage capacity (OSC) of H–CZ was confirmed at 773 K by the weight measurements under H2/N2 and air atmospheres, indicating that the HNO3/H2O2 treatment was effective to avoid the deterioration of the OSC by segregated CeO2 on the CZ binary oxides.  相似文献   

8.
Three different spinel compositions with MgO:Al2O3 molar ratios 2:1, 1:1 and 1:2 were studied using TiO2 as an additive up to 2 wt.%. Solid state reaction sintering technique was employed for all the compositions in the temperature range of 1550–1650°C. Attrition milling was done for the reduction of particle size. Sintered products were characterised in terms of densification and shrinkage studies, phase analysis, strength evaluation both at ambient temperature and at elevated temperature, strength retention after different number of thermal cycles at 1000°C, quantitative elemental analysis and microstructural studies.  相似文献   

9.
Effect of Additives on Sintering of Cr2O3 in Reductive Atmosphere   总被引:2,自引:0,他引:2  
The influence of additives TiO2,Y2O3 and composite rare earth on sintering of Cr2O3 in reductive atmosphere was studied.Results show that TiO2 can effectively increase the sinteed density at low temperature,As the increase of sintering temperature,such kind of effect becomes more and more unobvious and finaly disappear at 1550℃.Moreover,Y2O3 and composite rare earth have negative effect on sintering.  相似文献   

10.
《Ceramics International》2020,46(6):7403-7412
The impact of various volume percentages of TiB2 additive (0, 10, 20, and 30) on the microstructure, relative density (RD), Vickers hardness, flexural strength, and thermal conductivity of as-sintered TiC-10 vol% SiCw-based composite samples were scrutinized. All four samples were sintered using the SPS method under the following circumstances; sintering temperature of 1900 °C, dwell time of 7 min, and external pressure of 40 MPa. The best relative density of 98.73% was achieved for the sample with no TiB2 additive, indicating the negative effect of TiB2 additive on the RD and formation of porosity. The microstructural observations and XRD results confirmed the chemical interaction of TiO2 and B2O3 oxide layers and SiCw and in-situ formation of the TiSi brittle phase and TiC. The most significant values of flexural strength (511 MPa) and hardness (27.67 GPa) were related to TiC-10 vol% SiCw and TiC-10 vol% SiCw-30 vol% TiB2 samples, respectively. On the contrary, the specimens with 30 vol% and 10 vol% TiB2 as additive presented the poorest qualities of flexural strength (234 MPa) and Vickers hardness (22.12 GPa). Finally, the influence of the TiB2 content on the thermal conductivity was evaluated, indicating the positive impact of this secondary phase on this characteristic, so with adding 30 vol% TiB2 to TiC-10 vol% SiCw, a thermal conductivity of 30.7 W/m.K was obtained.  相似文献   

11.
The paper describes the effect of additives Al,Si,SiC and A4C on the expanson of MgO-ZrO2-C material after being coked.Theresults indicate that Al and Si were oxi-dized to form Al2O3 and SiO2 respectively,and then re-acted with CaZrO3 or stabilizer in c-ZrO2 to form calcium aluminate,spinel(MA),dicalcium silicate(C2S) and forsterite (M2S) ,Meznwhile,α-C2S ras transformed to γ-C2S and c-ZrO2 to m-ZrO2 when temperature changed.All the above reactions resulted in the decrease of the amount of Al4C3 and SiC and the increase in bulk volume,which caused the stucture of MgO-ZrO2-C material de-stroyed.Hence,contrary to the MgO-C material,when adding Al,and Si,the MgO-ZrO2-C material would be structurally deteriorated after heat-treatment and its strength and corrosion resistance decreased.  相似文献   

12.
《应用陶瓷进展》2013,112(6):352-357
Abstract

MgO–Al2O3–SiO2 (MAS) cordierite based glass ceramics were prepared by volume crystallisation. X-ray diffraction, Scanning electron microscopy and Energy diffraction scanning were used to investigate crystallisation behaviour and the influence of P2O5 on microstructure MAS based glass ceramics. The results showed that P5+ could promote the phase separation of MAS glass and that the glass was divided into two areas, such as Mg4Al2Ti9O25 and the containing P5+ area at <900°C. Mg4Al2Ti9O25 and Mg3(PO4)2 in the area were both advantageous to the precipitation of μ cordierite, which further transformed to α cordierite due to P5+ in the residual glassy phase. However, P5+ inhibited the presence of cordierite when the heat treatment temperature was >900°C.  相似文献   

13.
The effects Cr2O3 on properties of alumina-spinel castable has been discussed in this paper,The results show that modulus of rupture(MOR) and cold crushing strength(CCS) of the alumina-spinel castable can be improved when Cr2O is added to this material.At higher temperature,Cr2O3 moves into the melt and raises its viscosity,forming high creep resistance bonding phase,so the thermal shock resistance and slag corrosion resistance are improved.  相似文献   

14.
《Carbon》1987,25(4):495-502
IR spectroscopic studies were carried out on the character of interactions between adsorbed molecules of SO2 and O2, H2O or H2S on the surface of carbons. The character of bonding between adsorbed molecules and the carbon films depends on the chemical structure of the surface functional groups. Weakly adsorbed SO2 gives rise to the bands at 1330 and 1140 cm−1. Strongly held SO2 is indicated by the band around 1045 cm−1. Catalytic activity of carbon films in the oxidation of aqueous sulfur dioxide solution has been studied. The results suggest that Superoxide ions take part in the adsortion of acids on the surface of carbon as well as in the catalytic oxidation of aqueous SO2 solution by O2.  相似文献   

15.
Reaction of hydrogen with CCl2F2 has been studied on a -Al2O3 catalyst at 300°C. Pure -Al2O3 appears to be unselective in the catalytic conversion of CCl2F2, however, halogenated alumina showed high activity in a reaction leading to the formation of disproportionation products.  相似文献   

16.
《Carbon》1987,25(3):431-436
IR spectroscopic studies were carried out on the bond character of SO2 molecules adsorbed on the surface of carbons. No spectroscopic evidence was found for the formation of any stable surface carbon-sulfur complexes after interaction of SO2 with a carbon surface in the temperature range 25–600 Simultaneous adsorption of SO2 and O2 occurs with the participation of π electrons of condensed aromatic systems. It can be concluded from IR investigations that SO2 retards the oxidation of carbon by O2.  相似文献   

17.
Guest-host complex formation of three drug derivatives of anthranilic acid, mefenamic acid, niflumic acid, and flufenamic acid with 2-hydroxypropyl-β-cyclodextrin (2HP-β-CD) in aqueous solutions was investigated using "Phase solubility study" with UV-vis spectrophotometry. Solubility of sparingly soluble drugs has been improved by addition of 2HP-β-CD at two temperatures 298.15 K and 310.15 K and two pH values 2 and 7. The influence of different 2HP-β-CD concentration on solubility of drugs at different pH and temperatures has been investigated. The 2HP-β-CD-drug complex stability constants (K(s)), and dissociations constants (K(d)), as well as the thermodynamic parameters of reaction, i.e., the free energy change (ΔG), the enthalpy change (ΔH) and the entropy change (ΔS), were determined. The experimental data indicated formation of 1:1 inclusion complexes, which were found effective binders increasing the solubility of drugs.  相似文献   

18.
Nanopowders with cubic fluorite-type structure as well as uniform distribution in particle size were synthesized by hydrothermal method in the ternary oxide zirconia–yttria–ceria system with ceria content of 0–25 mol%. X-ray diffraction (XRD), thermogravimetric analysis/differential scanning calorimeter (TG/DSC), Fourier transform infrared spectroscopy (FT-IR), Raman spectroscopy (Raman), specific surface area (SBET) and high resolution transmission electron microscopy (HRTEM) were applied to characterize the structure, thermal decomposition, morphological characteristic and crystal growth of the produced powders. Qualitative analyses indicate that the as-synthesized nanoparticles are single-phase crystallites with an average particle size of 4–9 nm. The specific surface area, lattice parameter and microstrain are closely related to Ce4+ concentration. Moreover, activation energy of crystal growth is significantly dependent on the dopant (CeO2) concentration. It firstly increased and then decreased with increasing dopant concentration, and the maximum value was observed at the dopant concentration of 5 mol%.  相似文献   

19.
20.
The influences of four kinds of additives added into the matrix of MgO-Al2O3 unbuned products were investigated,The results show that samples with proper MgO/Al2O3 ration and proper addition of Cr2O3(2%- 4%) have good thermal shock resistance and slag corrosion resistance as well,XRD and SEM determination results indicate that a kind of compound spinel(Mg,Al, Cr) O4 was formed and the microstucture of the samples are denser.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号