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1.
The effect of SiC used as antioxidant in carbon-containing CaO–ZrO 2 refractories and the behaviour of SiC in CO gas were studied. SiC was found to react initially with CO to form SiO 2(s) and C(s) at 1200 °C, and then the formed SiO 2 reacted with CaO in the refractories to form belite (2CaO·SiO 2). The refractory microstructure was modified by addition of SiC. Due to the deposition of SiO 2 in the large (2–10 μm) pores of the refractory through the reaction of SiO(g) with CO, the percentage of large pores decreased and a dense layer, mainly consisting of belite, was formed near the surface of the refractory after it was heated at high temperature (1500 °C). The oxidation resistance of CaO–ZrO 2–C refractories was improved by reaction of SiC with CO to deposit C(s) and decrease the size of the large pores. The oxidation resistance of such refractories can be improved significantly when such a dense layer is formed near their surfaces. 相似文献
2.
In this study, three different industrial frits BaO–Al 2O 3–SiO 2 (BAS), CaO–MgO–Al 2O 3–SiO 2 (CMAS), CaO–ZrO 2–Al 2O 3–SiO 2 (CZAS) have been deposited on porcelainized stoneware tiles by plasma spraying. In the as-sprayed conditions, the microstructure of the coatings is defective because of pores, microcracks and low intersplat cohesion. Hot stage microscope and differential thermal analysis measurements made on the glass powders allowed to characterize the frits thermal behaviour. Post process thermal treatments have been arranged, following these indications as well as preliminary tests, in order to achieve the lowest porosity and the highest resistance to abrasion. At the chosen temperatures, a microstructural improvement has been induced, but in the BAS specimens, an optimal sintering has not been accomplished because of the unavoidable full overlapping of the sintering and crystallization processes. 相似文献
3.
Bioactive glasses and particles reinforced composites were used to coat alumina substrates, in order to combine the mechanical properties of the high-strength alumina with the bioactivity of the coatings. The coatings were either monolithic glass or glass-matrix/zirconia particle composite and were prepared by a low-cost firing method. A multilayer approach was applied to minimize crack propagation at the interface between the coating and the substrate. Functionally graded structures were developed to achieve a compliant material to withstand the stresses due to the expansion coefficient mismatch between the substrate and the coatings. The sequential coating of the alumina with glass-matrix/zirconia particle composite layers produced a structurally stable composite structure. A systematic study revealed that multiple layers were necessary to provide a gradual compliance of the thermal expansion coefficient. The glass-matrix/zirconia particles composites layers were also essential for the control of the Al 3+ diffusion from the substrate through the glass. This is in accordance with the experimental results of previous works. Thus, the alumina content in the coating should be maintained as low as possible in order to preserve its bioactivity. The composite layers were further coated by a glass belonging to the system SiO 2–CaO–P 2O 5–Na 2O–MgO–F −, known for its bioactivity. The experimental results were substantiated by optical and scanning electron microscopy (SEM) with compositional analysis (EDS) and by a mechanical characterization. The in vitro behavior of the coated samples was investigated by means of soaking in simulated body fluid (SBF) followed by SEM observation and XRD analysis. 相似文献
4.
Since the electromechanical devices move towards enhanced power density, high mechanical quality factor ( Qm) and electromechanical coupling factor ( kp) are commonly needed for the high powered piezoelectric transformer with Qm≥2000 and kp=0.60. Although Pb(Mn 1/3Nb 2/3)O 3–PbZrO 3–PbTiO 3 (PMnN–PZ–PT) ceramic system has potential for piezoelectric transformer application, further improvements of Qm and kp are needed. Addition of 2CaO–Fe 2O 3 has been proved to have many beneficial effects on Pb(Zr,Ti)O 3 ceramics. Therefore, 2CaO–Fe 2O 3 is used as additive in order to improve the piezoelectric properties in this study. The piezoelectric properties, density and microstructures of 0.07Pb(Mn 1/3Nb 2/3)O 3–0.468PbZrO 3–0.462PbTiO 3 (PMnN–PZ–PT) piezoelectric ceramics with 2CaO–Fe 2O 3 additive sintered at 1100 and 1250 °C have been studied. When sintering temperature is 1250 °C, Qm has the maximum 2150 with 0.3 wt.% 2CaO–Fe 2O 3 addition. The kp more than 0.6 is observed for samples sintered at 1100 °C. The addition of 2CaO–Fe 2O 3 can significantly enhance the densification of PMnN–PZ–PT ceramics when the sintering temperature is 1250 °C. The grain growth occurred with the amount of 2CaO–Fe 2O 3 at both sintering temperatures. 相似文献
5.
Recent interest in the suitability of Australian bituminous coals for use in integrated gasification-combined cycle (IGCC) technologies has provided the opportunity to determine viscosity data for a range of coal ashes slags fluxed with limestone at the tapping temperatures of entrained flow gasifiers. Experimental viscosity measurements have been made over a range of slag compositions covering the anorthite region at the 0–2.5, 2.5–5, 5–7.5 and 7.5–10 wt% FeO levels of the quaternary SiO 2–Al 2O 3–CaO–FeO system. Contour plots of viscosities at 1450°C for the four FeO ranges are presented as an example for predicting slag behaviour in entrained flow gasifiers. The viscosity measurements have also been fitted empirically using a modified Urbain treatment to give separate models for the four FeO levels. Polynomial expressions are given for the evaluation of viscosities covering the temperature range 1400–1550°C for slags within the compositional range used in the derivation. 相似文献
6.
In order to assess the role of carbon with respect to the grain boundary chemistry of Si 3N 4-based ceramics model experiments were performed. Y 2O 3–SiO 2 glass systems with various amount of carbon (from 1 to 30 wt.%) were prepared by high-temperature treatment in a graphite furnace. High carbon activity of the furnace atmosphere was observed. EDX analysis proved the formation of SiC by the carbothermal reduction of SiO 2 either in the melt or in the solid state. The melting temperature of the Y 2O 3–SiO 2 system is strongly dependent on the amount of reduced SiO 2. XRD analysis of the products documented the presence of Y 2Si 2O 7, Y 2SiO 5 and Y 2O 3 crystalline phases in that order with an increasing amount of free C in the starting mixture. The reduction of Y 2O 3 was not confirmed. 相似文献
7.
The hydrogenation of CO over an Rh vanadate (RhVO 4) catalyst supported on SiO 2 (RhVO 4/SiO 2) has been investigated after H 2 reduction at 500°C, and the results are compared with those of vanadia-promoted (V 2O 5–Rh/SiO 2) and unpromoted Rh/SiO 2 catalysts. The mean size of Rh particles, which were dispersed by the decomposition of RhVO 4 after the H 2 reduction, was smaller (41 Å) than those (91–101 Å) of V 2O 5–Rh/SiO 2 and Rh/SiO 2 catalysts. The RhVO 4/SiO 2 catalyst showed higher activity and selectivity to C 2 oxygenates than the unpromoted Rh/SiO 2 catalyst after the H 2 pretreatment. The CO conversion of the RhVO 4/SiO 2 catalyst was much higher than that of V 2O 5–Rh/SiO 2 catalyst, and the yield of C 2 oxygenates increased. We also found that the RhVO 4/SiO 2 catalyst can be regenerated by calcination or O 2 treatment at high temperature after the reaction. 相似文献
8.
Monolithic structures made of cordierite, γ-Al 2O 3 and steel have been prepared as catalysts and tested for Fischer–Tropsch activity. The monoliths made of cordierite and steel were washcoated with a 20 wt.% Co–1 wt.% Re/γ-Al 2O 3 Fischer–Tropsch catalyst whereas the γ-Al 2O 3 monoliths were made by direct impregnation with an aqueous solution of the Co and Re salts resulting in a loading of 12 wt.% Co and 0.5 wt.% Re. The activity and selectivity of the different monoliths were compared with the corresponding powder catalysts. Higher washcoat loadings resulted in decreased C5+ selectivity and olefin/paraffin ratios due to increased transport limitations. The impregnated γ-Al2O3 monoliths also showed similar C5+ selectivities as powder catalysts of small particle size (38–53 μm). Lower activities were observed with the steel monoliths probably due to experimental problems. 相似文献
9.
Supported nickel phosphides were prepared by treating an amorphous Ni–B alloy on silica–alumina support with phosphine (15 vol.% PH 3/H 2) at relatively low temperature. The amorphous Ni–B/SiO 2–Al 2O 3 precursors were synthesized by silver-induced electroless plating. The amorphous precursors and catalysts were characterized by X-ray diffraction, high-resolution transmission electron microscopy, selected area electron diffraction, BET surface area and inductively coupled plasma measurements. The transmission electron micrographs of the Ni 2P/SiO 2–Al 2O 3 particles with their size ranging from 60 to 80 nm showed that they were homogeneously dispersed over the SiO 2–Al 2O 3 support. The as-prepared catalysts exhibited an excellent catalytic activity in the hydrodesulfurization (HDS) of dibenzothiophene. 相似文献
10.
The NiSO 4 supported on Fe 2O 3-promoted ZrO 2 catalysts were prepared by the impregnation method. Fe 2O 3-promoted ZrO 2 was prepared by the coprecipitation method using a mixed aqueous solution of zirconium oxychloride and iron nitrate solution followed by adding an aqueous ammonia solution. No diffraction line of nickel sulfate was observed up to 20 wt.%, indicating good dispersion of nickel sulfate on the surface of Fe 2O 3–ZrO 2. The addition of nickel sulfate (or Fe 2O 3) to ZrO 2 shifted the phase transition of ZrO 2 (from amorphous to tetragonal) to higher temperatures because of the interaction between nickel sulfate (or Fe 2O 3) and ZrO 2. 15-NiSO 4/5-Fe 2O 3–ZrO 2 containing 15 wt.% NiSO 4 and 5 mol% Fe 2O 3, and calcined at 500 °C exhibited a maximum catalytic activity for ethylene dimerization. NiSO 4/Fe 2O 3–ZrO 2 catalysts was very effective for ethylene dimerization even at room temperature, but Fe 2O 3–ZrO 2 without NiSO 4 did not exhibit any catalytic activity at all. The catalytic activities were correlated with the acidity of catalysts measured by the ammonia chemisorption method. The addition of Fe 2O 3 up to 5 mol% enhanced the acidity, surface area, thermal property, and catalytic activities of catalysts gradually, due to the interaction between Fe 2O 3 and ZrO 2 and due to consequent formation of Fe–O–Zr bond. 相似文献
11.
Effect of additives, In 2O 3, SnO 2, CoO, CuO and Ag, on the catalytic performance of Ga 2O 3–Al 2O 3 prepared by sol–gel method for the selective reduction of NO with propene in the presence of oxygen was studied. As for the reaction in the absence of H 2O, CoO, CuO and Ag showed good additive effect. When H 2O was added to the reaction gas, the activity of CoO-, CuO- and Ag-doped Ga 2O 3–Al 2O 3 was depressed considerably, while an intensifying effect of H 2O was observed for In 2O 3- and SnO 2-doped Ga 2O 3–Al 2O 3. Of several metal oxide additives, In 2O 3-doped Ga 2O 3–Al 2O 3 showed the highest activity for NO reduction by propene in the presence of H 2O. Kinetic studies on NO reduction over In 2O 3–Ga 2O 3–Al 2O 3 revealed that the rate-determining step in the absence of H 2O is the reaction of NO 2 formed on Ga 2O 3–Al 2O 3 with C 3H 6-derived species, whereas that in the presence of H 2O is the formation of C 3H 6-derived species. We presumed the reason for the promotional effect of H 2O as follows: the rate for the formation of C 3H 6-derived species in the presence of H 2O is sufficiently fast compared with that for the reaction of NO 2 with C 3H 6-derived species in the absence of H 2O. Although the retarding effect of SO 2 on the activity was observed for all of the catalysts, SnO 2–Ga 2O 3–Al 2O 3 showed still relatively high activity in the lower temperature region. 相似文献
12.
NiMo/( X)SiO 2–Al 2O 3 catalysts were synthesized with various SiO 2 contents ( X = 0, 10, 25 and 50 wt%) using the pH-swing method. In order to find the optimum SiO 2 content, the catalysts were evaluated in the hydrodesulfurization of 4,6-DMDBT, hydrogenation of naphthalene and hydrodenitrogenation of carbazole. Kinetic parameters of Langmuir–Hinshelwood type equations for all the reaction systems were estimated. FTIR analysis of CO adsorption for the sulfided catalysts shows that the amount of coordinatively unsaturated Mo sites promoted by nickel (CUS-NiMoS) follows the order NiMo/10ASA > NiMo/25ASA > NiMo/0ASA. This tendency agrees with the results obtained in catalytic activity. 相似文献
13.
The effect of CaO substitution by different amounts of MgO on crystallization and various properties of CaF 2–CaO–Al 2O 3–SiO 2 glass system were investigated. It was shown that the properties of obtained glass–ceramics are greatly influenced by MgO contents. The Avrami exponent and activation energy for crystallization of the most promising and the MgO-free specimens were determined. Results suggested that surface crystallization was the main precipitation mechanism of both samples and while the activation energy for crystallization of MgO containing sample was less than MgO-free one, its ability to crystallize was diminished. SEM results confirm occurrence of surface crystallization of samples and depicts the phenomenon of microstructure coarsening by increasing MgO content and also reduced densification of specimen with magnesium oxide more than 9 wt.%. 相似文献
14.
The development of a catalytically active filter element for combined particle separation and NO x removal or VOC total oxidation, respectively, is presented. For NO x removal by selective catalytic reduction (SCR) a catalytic coating based on a TiO 2–V 2O 5–WO 3 catalyst system was developed on a ceramic filter element. Different TiO 2 sols of tailor-made mean particle size between 40 and 190 nm were prepared by the sol–gel process and used for the impregnation of filter element cylinders by the incipient wetness technique. The obtained TiO 2-impregnated sintered filter element cylinders exhibit BET surface areas in the range between 0.5 and 1.3 m 2/g. Selected TiO 2-impregnated filter element cylinders of high BET surface area were catalytically activated by impregnation with a V 2O 5 and WO 3 precursor solution. The obtained catalytic filter element cylinders show high SCR activity leading to 96% NO conversion at 300 °C, a filtration velocity of 2 cm/s and an NO inlet concentration of 500 vol.-ppm. The corresponding differential pressures fulfill the requirements for typical hot gas filtration applications. For VOC total oxidation, a TiO 2-impregnated filter element support was catalytically activated with a Pt/V 2O 5 system. Complete oxidation of propene with 100% selectivity to CO 2 was achieved at 300 °C, a filtration velocity of 2 cm/s and a propene inlet concentration of 300 vol.-ppm. 相似文献
15.
Co–Nb 2O 5–SiO 2 catalysts were prepared using three different sol–gel procedures: (i) the colloidal sol–gel method using NbCl 5 and SiCl 4 as precursors; (ii) the polymeric sol–gel method using niobium ethoxide and tetraethyl-orthosilicate (TEOS); (iii) an intermediate procedure between the colloidal and polymeric sol–gel method in which the precursors were those utilized in the CSG but dissolved in a mixture of anhydrous ethanol and CCl 4. In all procedures, the elimination of the solvent carried out between 80 and 110°C was followed by a reduction in hydrogen flow (30 ml min −1) at 773 K. Following these procedures, samples containing 10 wt.% Co and 15 wt.% niobium oxide (expressed as Nb 2O 5) were obtained. The characterization of the catalysts was performed using various techniques: N 2 adsorption and desorption curves at 77 K, NH 3- and H 2-chemisorption, TPO, XPS, XRD, and solid state 1H MAS-NMR. Hydrogenolysis of butane was evaluated. The low reaction rates are assigned to the effect of the metal size, whereas the isobutane selectivity as well as the relatively high stability is due to the acidity of the support. 相似文献
16.
The local structure and the photoactivity of B 2O 3–SiO 2/TiO 2 ternary mixed oxides (SiO 2 content was fixed as 30 at.% with respect to TiO 2) was investigated by using XRD, FT-IR, BET, UV-vis spectra, and electron paramagnetic resonance (EPR) measurement. In FT-IR analysis, boron was incorporated into the framework of titania matrix with replacing Ti---O---Si with Si---O---B or Ti---O---B bonds. Also, paramagnetic species such as O − and Ti 3+ defects were formed by the boron incorporation. In SiO 2/TiO 2 mixed oxides, a blue shift in the light absorption band was observed due to the quantization of band structure. All B 2O 3–SiO 2/TiO 2 samples had pure anatase phase and no rutile phase was formed even though the calcination temperature was over 900 °C. Incorporating boron oxides of more than 10% enlarges the grain size of anatase phase and causes a red shift of the light absorption spectrum. The surface area was monotonically decreased with increasing the content of boron content. As a result, the photoactivity of B 2O 3–SiO 2/TiO 2 ternary mixed oxides was greatly influenced by the content of boron oxide. The highest photoactivity (g moles/min l) was obtained when the boron content was 5% and seven times higher than that of silica/titania binary mixed oxide. In addition, the specific photoactivity (g moles/m 2 l) was maximum still at 5%. It was concluded that the large reduction of surface area, the change of band structure, and more formation of bulk Ti 3+ sites are responsible for the deterioration in the photoactivity of B 2O 3–SiO 2/TiO 2 ternary mixed oxides when the content of boron is over 10%, although their crystallinity was enhanced by increasing the calcination temperature with keeping anatase phase. 相似文献
17.
Al 2O 3–SiO 2 mixed oxide has been investigated as a support for hydrotreating catalyst with variation of its composition [Si/(Si + Al) = 0.06, 0.12, 0.31, 0.56, 0.78] and its interaction with the surface active metals (NiMo). The composition of support and surface species (NiMo) of catalysts were characterized by specific surface area, atomic absorption, SEM-EDX, XRD, temperature programmed reduction (TPR), Raman analysis, scanning electron microscopy (STEM) and transmission electron microscopy (TEM). Incorporation of SiO 2 in Al 2O 3 promotes a weak interaction between the active phases and particularly catalyst that predominated with SiO 2 content. The oxide and sulfided catalysts characterization indicated that the effect of support is responsible to form different catalytic sites. Crystallization of MoO 3 phases and a relatively longer crystal of MoS 2 in the sulfided catalyst were attributed to an increasing SiO 2 content in the support. The catalytic behavior of the NiMo supported catalysts is explained in terms of structural changes on the surface due to the support and active metal interactions. The activity of the different catalysts evaluated in the thiophene hydrodesulfurization reaction was higher for the catalyst having lower SiO 2 content in the support. 相似文献
18.
Four series of cobalt-based catalysts, such as bare Co 3O 4 and CoO, CoO x–CeO 2 mixed oxides, CoO x supported over alumina and alumina–baria and CoMgAl and CoNiAl hydrotalcites have been synthesized and investigated for the oxidative degradation of phenol in the presence of ozone. Characterizations were obtained by several techniques in order to investigate the nature of cobalt species and their morphological properties, depending on the system. Analyses by XRD, BET, TPR, UV–visible diffuse reflectance spectroscopy and TG/DT were performed. The CoNiAl hydrotalcite exhibits, after 4 h of reaction, the highest phenol ozonation activity followed by Co(3 wt%)/Al2O3–BaO and CoMgAl. The samples Co(1 wt%)/Al2O3–BaO and Co(1 and 3 wt%)/Al2O3 show a comparable medium activity, while the oxidation properties of bare oxides Co3O4, CoO and CoOx–CeO2 are really low. Leaching of cobalt ions in the water solution was detected during the reaction, the amount varied depending on the nature of catalysts. A massive release was observed for the CoMgAl and CoNiAl hydrotalcites, while cobalt catalysts over alumina and alumina–baria look much more stable. The recycle of CoOx/Al2O3 and CoOx/Al2O3–BaO was studied by performing three consecutive cycles in the phenol oxidation. Because of the potential interest of the cobalt-supported catalysts in the ozonation process, the oxidative degradation of naphtol blue black was also investigated. On the basis of TPR and UV–visible results it appears that highly dispersed Co2+ ions especially present over Co(3 wt%)/Al2O3–BaO are the main active sites for phenol and naphtol blue black oxidative degradation by ozone. 相似文献
19.
Ni catalysts supported on various solid solutions of ZrO 2 with alkaline earth oxide and/or rare earth oxide were synthesized. The catalytic activities were compared for partial oxidation of methane and autothermal reforming of methane. For partial oxidation of methane, the Ni catalyst supported on a CaO–ZrO 2 solid solution showed a high activity. Incorporation of CaO in the ZrO 2 matrix was effective for increasing the reduction rate of the NiO particles and for decreasing the coke formation. On the other hand, the Ni particles supported on the CaO–CeO 2–ZrO 2 solid solution had a strong interaction with the support, and the Ni particles showed high activity and stability for autothermal reforming of methane. 相似文献
20.
The phase diagram of the Al 2O 3–ZrO 2–Nd 2O 3 system was constructed in the temperature range 1250–2800 °C. The liquidus surface of the phase diagram reflects the preferentially eutectic interaction in the system. Two new ternary and one new binary eutectics were found. The minimum melting temperature is 1675 °C and it corresponds to the ternary eutectic Nd 2O 3·11Al 2O 3 + F-ZrO 2 + NdAlO 3. The solidus surface projection and the schematic of the alloy crystallization path confirm the preferentially congruent character of phase interaction in the ternary system. The polythermal sections present the complete phase diagram of the Al 2O 3–ZrO 2–Nd 2O 3 system. No ternary compounds or regions of remarkable solid solution were found in the components or binaries in this ternary system. 相似文献
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