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1.
Nanosized particles dispersed uniformly on Al 2O 3 particles were prepared from the decomposition of precursor Cr(CO) 6 by metal organic chemical vapor deposition (MOCVD) in a fluidized chamber. These nanosized particles consisted of Cr 2O 3, CrC 1−x, and C. A solid solution of Al 2O 3–Cr 2O 3 and an Al 2O 3–Cr 2O 3/Cr 3C 2 nanocomposite were formed when these fluidized powders were pre-sintered at 1000 and 1150 °C before hot-pressing at 1400 °C, respectively. In addition, an Al 2O 3–Cr 2O 3/Cr-carbide (Cr 3C 2 and Cr 7C 3) nanocomposite was formed when the particles were directly hot pressed at 1400 °C. The interface between Cr 3C 2 and Al 2O 3 is non-coherent, while the interface between Cr 7C 3 and Al 2O 3 is semi-coherent. 相似文献
2.
The effect of Al 2O 3 on mechanical properties of Ti 3SiC 2/Al 2O 3 composite fabricated by SPS was studied systematically. The results show that the hardness of the Ti 3SiC 2/Al 2O 3 composite can reach 10.28 GPa, 50% higher than that of pure Ti 3SiC 2. However, slight decrease in the other mechanical properties was observed with Al 2O 3 addition higher than 5–10 vol.%, which is believed to be due to the agglomeration of Al 2O 3 in the composite. 相似文献
3.
The hot corrosion behavior of the Ni-based superalloy M38G covered with a film of molten 0.9Na 2SO 4–0.1K 2SO 4 (mole fraction) has been studied by electrochemical impedance spectroscopy at 900 °C in air. For comparison, the corrosion of the alloy immersed in molten (Na,K) 2SO 4 was also examined. The electrochemical impedance spectra in deep molten salt during an initial stage consisted of a semicircle at high frequency and a line at low frequency indicating a diffusion-controlled reaction. With extended immersion the impedance spectra were composed of two capacitive loops, i.e., a small semicircle at high-frequency port, and a large one at low-frequency port. The change of the impedance spectra is related to the formation of a protective scale. Contrary to the corrosion in deep molten salt, the corrosion of the alloy in the presence of a film of fused salt presented the characteristics of two capacitive loops for all the duration of the experimental test. Equivalent circuits representing the corrosion of the alloy in both corrosion conditions are proposed to fit the impedance spectra and electrochemical parameters in the equivalent circuits are also calculated. 相似文献
4.
使用分析纯MgO、CaCO 3、SiO 2、Al 2O 3与Na 2SO 4在1350℃保温1 h合成了掺杂Na 2SO 4的含MgO铝酸钙熟料,在Na 2CO 3溶液体系下研究了其氧化铝浸出性能,通过XRD等分析手段对其晶体结构和自粉化性能进行了研究。结果表明,Na 2SO 4可以显著提升铝酸钙熟料的浸出性能,Na 2SO 4掺杂量由0%提高到4%,熟料的氧化铝浸出率由61.89%提高到92.01%,继续添加Na 2SO 4,浸出性能趋于稳定。由XRD结果可知,Na 2SO 4促使20CaO·13Al 2O 3·3MgO·3SiO 2(Q相)发生分解并使其转变为12CaO·7Al 2O 3(C 12A 7)。Na +进入C 12A 7晶格引起晶格畸变,从而提高C 12A 7的氧化铝浸出性能。Na 2SO 4的加入降低了熟料的自粉化性能,Na 2SO 4掺杂量由0%提高到6%,熟料的自粉率由97.46%下降到85.34%,当Na 2SO 4掺杂量达到10%后,熟料自粉率仅为36.3%。 相似文献
5.
高径厚比片状Al 2O 3在高端珠光颜料片状基材应用方面潜力巨大,但是其制备技术为国外所垄断,开发片状Al 2O 3商用生产技术迫在眉睫。熔盐法是制备片状Al 2O 3的理想方法,目前尚无系统研究熔盐法关键工艺参数对片状Al 2O 3影响规律的报道。本文通过片状Al 2O 3的形成机理,系统研究了TiO 2添加剂、Na 3P 3O 9添加剂、煅烧温度和熔盐用量4种关键工艺参数对制备片状Al 2O 3的影响规律,并进一步优化制备工艺,提出最优工艺参数。利用扫描电子显微镜和X射线衍射仪分析Al 2O 3的形貌、粒度和物相。结果表明:采用熔融盐(Na 2SO 4-K 2SO 4)添加NaCO 3为凝胶剂,再加入质量分数分别为3.0%的Na 3P 3O 9和2.0%的TiO 2为添加剂,在煅烧温度为1200℃、保温时间5h时,所制得的六角片状Al 2O 3粉体具有优异的品质,其平均粒径约为4μm,厚度为50~200nm,径厚比为20~80。 相似文献
6.
Homogeneous-eutectic microstructure of Y 3Al 5O 12–Al 2O 3 system without coarse primary crystals was formed at an off-eutectic composition. This method utilizes a low migration rate in an amorphous phase. A mixture of Y 2O 3 and Al 2O 3 having the off-eutectic composition was melted and quenched rapidly to form an amorphous phase. A heat-treatment of the amorphous phase at 1000 °C and 1300 °C for 30 min formed Y 3Al 5O 12 and Al 2O 3 phases. SEM observation of this material, which was formed from the amorphous phase at 1300 °C for 30 min, showed homogeneous eutectic-like microstructure. The formation of the primary crystals (coarse Al 2O 3), which are always observed in the off-eutectic compositions by ordinary method, was completely suppressed. 相似文献
7.
Mixed oxides of alumina and zirconia having a relative composition of 50, 80 and 100% Zr 2O were synthesized by means of sol–gel methods. The catalysts were sulfated with H 2SO 4 1N, and were loaded with 0.3% Pt metal using the incipient wetness technique. The characterization of the physicochemical properties was carried out using XRD, N 2-adsorption at 78 K, and SEM. The catalytic properties of the Al 2O 3–ZrO 2 series were studied by means of dehydration of 2-propanol at 180°C and isomerization of n-hexane at 250°C, 1 atm. The sulfated solids presented a high surface acidity and a limited crystallinity, together with high activity for alcohol dehydration (i.e. 2-propanol). On the other hand, the Al 2O 3–ZrO 2 solid solutions (i.e. those having a 20–80% composition) turned out to be the most active ones for the isomerization of n-hexane. 相似文献
8.
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
9.
以平均孔径为20 nm的Al 2O 3管式超滤膜为载体,经多巴胺改性后,利用压力驱动沉积法成功制备出能在水溶液中长期稳定的GO/Al 2O 3复合纳滤膜,并通过改变负载量实现了对GO层厚的调控。结果表明,随错流时间的延长,不同GO负载量下GO/Al 2O 3复合纳滤膜的纯水渗透系数均呈现先降低后稳定的趋势。且随着GO负载量的增加,稳态纯水渗透系数逐渐降低;当GO负载量增加到90 mg/m 2后,GO/Al 2O 3复合纳滤膜对一二价盐的渗透系数与截留率均无显著变化。同时,由于盐测试过程中残余的盐离子在GO片层间产生了交联作用,从而导致随着在纯水中存放时间的延长,不同GO负载量的GO/Al 2O 3复合纳滤膜对一二价盐的截留率均呈上升趋势。GO负载量为140 mg/m 2的GO/Al 2O 3复合纳滤膜在水中浸泡680 h后对1 mmol/L Na 2SO 4的截留率可达到91.0%。GO/Al 2O 3复合纳滤膜对四种一二价盐的截留率满足: R(Na 2SO 4) > R(MgSO 4) > R(NaCl) > R(MgCl 2)。 相似文献
10.
The mechanism and kinetics of molten salt corrosion of reaction-sintered Si 3N 4---SiC-based ceramics, as well as the effect of these salts on its strength and fracture toughness at 20°C and 1200°C, were investigated. It was found that this material is highly resistant to corrosion in NaCl and sea salt up to 1100°C but degrades easily in Na 2SO 4 being a strong oxidant. Molten salt corrosion and salt-assisted oxidation cause mechanical properties' deterioration. Thus, NaCl effects involve up to 25% and 30% strength decrease at room temperature and at 1200°C, respectively. The results are explained by the etching of grain boundaries and by the formation of sodium silicate glassy layer during oxidation with it further cracking after cooling. 相似文献
11.
TiP 2O 7 carbon composite photocatalyst was successfully prepared by using ion-exchanged resin (C467) containing amino phosphate by metal ion-exchanged carbothermal reduction (MIER-CTR) method using TiCl 3 and TiCl 4. During the carbonization process in nitrogen, the pre-oxidation (300–350 °C) in air is essential for producing homogeneously dispersed TiP 2O 7 on the carbon matrix. In the absence of pre-oxidation, the resin was melted. The carbonization temperature 500 °C was found to be suitable for producing single phase TiP 2O 7 with higher yields. Powder X-ray diffraction (XRD) and Raman spectroscopic results suggest the formation of TiP 2O 7, while X-ray diffraction results reveal that the crystallite size was less than 35 nm. UV-Vis studies show that the band gap of TiP 2O 7 was 3.32 eV. The TiP 2O 7 carbon composite catalyst was applied for the photocatalytic decomposition of 2-propanol at 30 °C using a mercury lamp (365 nm). 相似文献
12.
Surface-phase ZrO 2 on SiO 2 (SZrOs) and surface-phase La 2O 3 on Al 2O 3 (SLaOs) were prepared with various loadings of ZrO 2 and La 2O 3, characterized and used as supports for preparing Pt/SZrOs and Pt/SLaOs catalysts. CH 4/CO 2 reforming over the Pt/SZrOs and Pt/SLaOs catalysts was examined and compared with Pt/Al 2O 3 and Pt/SiO 2 catalysts. CO 2 or CH 4 pulse reaction/adsorption analysis was employed to elucidate the effects of these surface-phase oxides. The zirconia can be homogeneously dispersed on SiO2 to form a stable surface-phase oxide. The lanthana cannot be spread well on Al2O3, but it forms a stable amorphous oxide with Al2O3. The Pt/SZrOs and Pt/SLaOs catalysts showed higher steady activity than did Pt/SiO2 and Pt/Al2O3 by a factor of three to four. The Pt/SZrOs and Pt/SLaOs catalysts were also much more stable than the Pt/SiO2 and Pt/Al2O3 catalysts for long stream time and for reforming temperatures above 700 °C. These findings were attributed to the activation of CO2 adsorbed on the basic sites of SZrOs and SLaOs. 相似文献
13.
Well crystallised aluminium borate Al 18B 4O 33 has been synthesised from alumina and boric acid with a BET area of 18 m 2/g after calcination at 1100 °C. Afterwards, 2 wt.% Pd/Al 18B 4O 33 was prepared by conventional impregnation of Pd(NO 3) 2 aqueous solution and calcination in air at 500 °C. The catalytic activity of Pd/Al 18B 4O 33 in the complete oxidation of methane was measured between 300 and 900 °C and compared with that of Pd/Al 2O 3. Pd/Al 18B 4O 33 exhibited a much lower activity than Pd/Al 2O 3 when treated in hydrogen at 500 °C or aged in O 2/H 2O (90:10) at 800 °C prior to catalytic testing. Surprisingly, a catalytic reaction run up to 900 °C in the reaction mixture induced a steep increase of the catalytic activity of Pd/Al 18B 4O 33 which became as active as Pd/Al 2O 3. Moreover, the decrease of the catalytic activity observed around 750 °C for Pd/Al 2O 3 and attributed to PdO decomposition into metallic Pd was significantly shifted to higher temperatures (820 °C) in the case of Pd/Al 18B 4O 33. The existence of two distinct types of PdO species formed on Al 18B 4O 33 and being, respectively, responsible for the improvement of the activity at low and high temperature was proposed on the basis of diffuse reflectance spectroscopy and temperature-programmed desorption of O 2. 相似文献
14.
Sulfidation of trimetallic CoNiMo/Al 2O 3 catalysts was studied by thermogravimetry at 400 °C under flow and pressure conditions. Results were compared with those obtained on prepared and industrial CoMo/Al 2O 3 and NiMo/Al 2O 3 catalysts. The amount of sorbed H 2S on the sulfided solids was measured at 300 °C in the H 2S pressure range 0–3.5 MPa at constant H 2 pressure (3.8 MPa). The adsorption isotherms were simulated using a model featuring dissociated adsorption of H 2S on supported metal sulfides and bare alumina. The amount of sulfur-vacancy sites could thus be determined under conditions close to industrial practice. A relationship with activity results for thiophene HDS and benzene hydrogenation was sought for. 相似文献
15.
A multi-component NO x-trap catalyst consisting of Pt and K supported on γ-Al 2O 3 was studied at 250 °C to determine the roles of the individual catalyst components, to identify the adsorbing species during the lean capture cycle, and to assess the effects of H 2O and CO 2 on NO x storage. The Al 2O 3 support was shown to have NO x trapping capability with and without Pt present (at 250 °C Pt/Al 2O 3 adsorbs 2.3 μmols NO x/m 2). NO x is primarily trapped on Al 2O 3 in the form of nitrates with monodentate, chelating and bridged forms apparent in Diffuse Reflectance mid-Infrared Fourier Transform Spectroscopy (DRIFTS) analysis. The addition of K to the catalyst increases the adsorption capacity to 6.2 μmols NO x/m 2, and the primary storage form on K is a free nitrate ion. Quantitative DRIFTS analysis shows that 12% of the nitrates on a Pt/K/Al 2O 3 catalyst are coordinated on the Al 2O 3 support at saturation. When 5% CO2 was included in a feed stream with 300 ppm NO and 12% O2, the amount of K-based nitrate storage decreased by 45% after 1 h on stream due to the competition of adsorbed free nitrates with carboxylates for adsorption sites. When 5% H2O was included in a feed stream with 300 ppm NO and 12% O2, the amount of K-based nitrate storage decreased by only 16% after 1 h, but the Al2O3-based nitrates decreased by 92%. Interestingly, with both 5% CO2 and 5% H2O in the feed, the total storage only decreased by 11%, as the hydroxyl groups generated on Al2O3 destabilized the K–CO2 bond; specifically, H2O mitigates the NOx storage capacity losses associated with carboxylate competition. 相似文献
16.
The effect of Al 2O 3 levels on the properties of NiO in coprecipitated NiO–Al 2O 3 samples were investigated, using samples with up to 60.7 wt.% Al 2O 3 that had been calcined in the range 300–700°C. Characterization techniques included BET surface area of fresh and reduced catalysts, X-ray diffraction analysis of structure and crystallite size, magnetic susceptibility measurements, oxidizing power, and reducibility in H 2. Only NiO was detected in samples with up to 4.1 wt.% Al 2O 3 for all sample calcination temperatures. Surface areas were similar for all fresh samples but decreased rapidly after calcination at high temperatures. The surface area loss was less for the higher Al 2O 3-containing samples. Nickel oxide crystallite sizes increased at higher calcination temperatures, but remained approximately the same for each Al 2O 3 level. The NiO was nonstoichiometric (NiO1+x), with x decreasing at higher calcination temperatures and increasing with small amounts of added Al2O3 through a maximum at about 3 wt.% Al2O3. However, this did not correlate well with microstrain in the NiO crystallites nor with reducibility, which decreased with Al2O3 addition. At higher levels of Al2O3 (13.6 wt.% and above), surface areas increased with higher Al2O3 loadings, but NiO crystallite sizes remained approximately the same, independent of both Al2O3 content and calcination temperature. X-ray diffraction patterns were very diffuse, and it was not possible to rule out the presence of pseudo-spinel combinations of NiO and Al2O3. Reducibility was more difficult than with low Al2O3 levels, and nonstoichiometry was low and independent of Al2O3 content. Reducibilities of all samples calcined at 300°C correlated well with the final BET surface area of the reduced samples, indicating that more dispersed NiO crystallites are more difficult to reduce, a conclusion that supports a model for reduction proposed previously. 相似文献
17.
The reduction of NO x by hydrogen under lean burn conditions over Pt/Al 2O 3 is strongly poisoned by carbon monoxide. This is due to the strong adsorption and subsequent high coverage of CO, which significantly increases the temperature required to initiate the reaction. Even relatively small concentrations of CO dramatically reduce the maximum NO x conversions achievable. In contrast, the presence of CO has a pronounced promoting influence in the case of Pd/Al 2O 3. In this case, although pure H 2 and pure CO are ineffective for NO x reduction under lean burn conditions, H 2/CO mixtures are very effective. With a realistic (1:3) H 2:CO ratio, typical of actual exhaust gas, Pd/Al 2O 3 is significantly more active than Pt/Al 2O 3, delivering 45% NO x conversion at 160 °C, compared to >15% for Pt/Al 2O 3 under identical conditions. The nature of the support is also critically important, with Pd/Al 2O 3 being much more active than Pd/SiO 2. Possible mechanisms for the improved performance of Pd/Al 2O 3 in the presence of H 2+CO are discussed. 相似文献
18.
A comparison study was carried out on non-thermal plasma (NTP)-assisted selective catalytic reduction (SCR) of NO x by propene over Ag/USY and Ag/Al 2O 3 catalysts. Ag/USY was almost inactive in thermal SCR while it showed obvious activities in NTP-assisted SCR at 100 °C–200 °C. Although the NO x conversion over Ag/Al 2O 3 was also enhanced at 300 °C–400 °C by the assistance of NTP, it was ineffective below 250 °C. The intermediates over Ag/USY and Ag/Al 2O 3 were investigated using in situ DRIFTS method. It was found that key intermediates in HC-SCR, such as NCO, CN, oxygenates and some N-containing organic species were enriched after the assistance of NTP. The differences in the behaviors of above intermediates were not found between these two kinds of catalysts. However, some evidences suggested that different properties of the absorbed NO x species resulted in the distinction of SCR reactions over Ag/USY and Ag/Al 2O 3. TPD profiles of Ag/Al 2O 3 showed that nitrates formed over the catalyst were quite stable at low temperatures, which might occupy the active sites and were unfavorable to SCR reactions. The nitrates over Ag/USY were unstable, among which the unidentate nitrate species is probably contributed to the SCR reactions at low temperatures. 相似文献
19.
采用熔融-淬冷法制备了不同(Al 2O 3+P 2O 5)含量的碱铝硅酸盐玻璃,通过拉曼光谱、X射线衍射光谱、扫描电镜研究了其结构特征和析晶性能。发现随着(Al 2O 3+P 2O 5)含量减少,玻璃中Na 2O含量增加,玻璃化转变温度从685 ℃降低到622 ℃,当减少至摩尔分数为22%时,出现析晶峰且起始析晶温度降低。拉曼光谱表明Q 4P对应的拉曼峰强度变低且逐渐向低波数方向移动,说明Na 2O作为网络修饰体使硅酸盐玻璃结构逐步解聚,玻璃的析晶能力逐渐增强。结果表明:当(Al 2O 3+P 2O 5)摩尔分数为22%时热处理后的样品存在晶型转变,700 ℃热处理时以NaAlSiO 4霞石晶体为主,900 ℃时转变为以Na 6.8Al 6.3Si 9.7O 32霞石晶体为主。当(Al 2O 3+P 2O 5)的摩尔分数为21%和20%时,热处理后的样品能稳定析出Na 3PO 4和Na 6.8Al 6.3Si 9.7O 32晶体。热处理后的样品析出了耐酸侵蚀性较差的富磷相和Na 3PO 4晶体,导致化学稳定性变差。 相似文献
20.
The role of La 2O 3 loading in Pd/Al 2O 3-La 2O 3 prepared by sol–gel on the catalytic properties in the NO reduction with H 2 was studied. The catalysts were characterized by N 2 physisorption, temperature-programmed reduction, differential thermal analysis, temperature-programmed oxidation and temperature-programmed desorption of NO. The physicochemical properties of Pd catalysts as well as the catalytic activity and selectivity are modified by La2O3 inclusion. The selectivity depends on the NO/H2 molar ratio (GHSV = 72,000 h−1) and the extent of interaction between Pd and La2O3. At NO/H2 = 0.5, the catalysts show high N2 selectivity (60–75%) at temperatures lower than 250 °C. For NO/H2 = 1, the N2 selectivity is almost 100% mainly for high temperatures, and even in the presence of 10% H2O vapor. The high N2 selectivity indicates a high capability of the catalysts to dissociate NO upon adsorption. This property is attributed to the creation of new adsorption sites through the formation of a surface PdOx phase interacting with La2O3. The formation of this phase is favored by the spreading of PdO promoted by La2O3. DTA shows that the phase transformation takes place at temperatures of 280–350 °C, while TPO indicates that this phase transformation is related to the oxidation process of PdO: in the case of Pd/Al2O3 the O2 uptake is consistent with the oxidation of PdO to PdO2, and when La2O3 is present the O2 uptake exceeds that amount (1.5 times). La2O3 in Pd catalysts promotes also the oxidation of Pd and dissociative adsorption of NO mainly at low temperatures (<250 °C) favoring the formation of N2. 相似文献
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