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1.
The effect of catalyst pore size has been studied for the hydroliquefaction of a West Virginia coal in the presence of Co/Mo/Al 2O 3 catalyst. The alumina supports used for catalyst preparation had relatively sharp, unimodal pore size distribution with average pore diameters in the range of 100 Å to almost 1000 Å. Loading of MoO 3 and CoO on the Al 2O 3 supports was in the constant weight ratio of 5:1, but the absolute loading was in direct proportion to the surface area of the support. Two series of catalyst were studied: “High loading”, with 9.7 × 10 ?4 g MoO 3/m 2 Al 2O 3, and “low loading”, with 4.5 × 10 ?4 g MoO 3/m 2 Al 2O 3; both loadings were less than the amount necessary for monolayer distribution of MoO 3 on Al 2O 3. The weight of catalyst charged in each autoclave run was varied so that the same weight of MoO 3 and CoO was present for each experiment.The principal results were: (1) Al 2O 3 alone is not catalytic, even in large amount; (2) conversion of coal increases as catalyst pore diameter increases; from 100 Å to at least 500 Å; (3) the increased conversion with increasing pore size is manifested mainly as increased yield of asphaltenes at 400°C, so the ratio of oil to oil-plus-asphaltenes decreases as pore diameter increases; and (4) catalysts with “low loading” of MoO 3 and CoO on the Al 2O 3 surface give higher liquefactions than their counterparts with “high loading”. Most of the results are consistent with an expected low diffusion rate of large, coal-derived molecules through the catalyst pore system. The higher liquefaction with “low loading” of the Al 2O 3 surface might result from slow desorption of large product molecules (asphaltenes) exhibiting multiple-site adsorption to Mo neighbors on the surface. 相似文献
2.
Formation of porous anodic films on sputtering-deposited aluminium incorporating Al-Hf tracer layers has been examined at constant current in sulphuric and phosphoric acids. Hafnium was selected as the tracer species since the migration rates of Hf 4+ and Al 3+ ions are similar in barrier-type anodic alumina. The distribution of hafnium in the films was determined using ion beam analysis, scanning electron microscopy and transmission electron microscopy. Increases in the anodizing voltage and barrier layer thickness accompany the oxidation of hafnium and the migration of Hf 4+ ions through the barrier layer region of the porous film. Hf 4+ and Al 3+ ions that migrate to the pore bases are lost to the electrolyte. Other Hf 4+ ions are incorporated into the cell walls. For films formed in phosphoric acid, with relatively thick barrier layers, channelling of the ion current leads to accelerated outward transport of Hf 4+ ions toward the pore base, while a U-shaped inner edge of the hafnium distribution beneath the pores is associated with more slowly transported hafnium species. The tracer behaviours for films formed in both acids are consistent with the transport of Hf 4+ ions in the barrier layer regions by a combination of flow of film material and ion migration, the flow being a key factor in the development of the pores. The percentage losses of Hf 4+ and Al 3+ ions from the films to the electrolyte are relatively similar, correlating with their similar migration rates, and contrast with the retention in the film of slow migrating W 6+ ions, found previously, due to a more dominant role of flow. 相似文献
3.
Portland blast-furnace slag cement pastes were prepared with various water/cement ratios. Specific surface areas and pore structures of the hardened pastes were investigated by nitrogen adsorption. The “accessibility” of the nitrogen molecules to the pore structure is discussed in terms of degree of hydration and total porosities of the pastes. Effect of presence of CaCl 2, a typical steel reinforcement corrosive agent, was also studied, and results indicated that it alters the area and pore structure extensively, to a more “open structure,” thus facilitating its own accessibility. Lime and gypsum addition was also studied in presence and in absence of CaCl 2, and the effect of the Blaine surface area of the unhydrated cement is particularly emphasized in this investigation. 相似文献
4.
Tantalum is widely used in hip joint replacement and knee joint repair, but its clinical application is limited due to its poor biological activity and weak ability to promote new bone formation. Ca and Mg ions are thought to be involved in bone metabolism and play an important physiological role in the angiogenesis, growth, and mineralization of bone tissue. In this work, NaTaO3 films doped with Ca2+ and Mg2+ were prepared by hydrothermal synthesis and molten salt method. The doping amounts of Ca2+ doped at 450, 550, 650 and 750 °C were 0.59, 3.44, 32.75 and 29.88 at%, and that of Mg2+ doped at 300, 350, 400, 450, 500, 550 and 650 °C were 0.62, 1.03, 1.54, 20.12, 21.38, 14.37 and 0.74 at%, respectively. Ca2+ and Mg2+ are evenly incorporated into NaTaO3 and cause the change of crystal plane spacing without any significant changes of morphologies below 550 and 400 °C respectively. XPS shows that the cations are the A-site substitution of perovskite structure (ABO3). According to the morphology and composition analysis of Ca-incorporated samples and Mg-incorporated samples, the optimal preparation temperature of them is 550?°C and 400?°C, respectively. The results show that for “550?°C-Ca” and “400?°C-Mg” the hydrophilicity is 13.9° and 96.1°, the roughness is 114.3 and 54.3?nm, the doping ion concentration of Ca and Mg is 3.44 and 1.54 at%, and the 7-day ICP results is 69.8 and 1.4?ppm, respectively. In addition, cell proliferation experiments and cell morphology related to biological activity and osteogenic properties are discussed, and it is found that the performance of “550?°C-Ca” is better than “400?°C-Mg”. Ca2+–NaTaO3 is a promising implantable material that will be extensive used in bone implants, joint replacements and dental implants. 相似文献
5.
Structural and electrical behavior of Al 2O 3 doped ZnO-based ceramics were investigated as function of the aluminum doping ratios under reducing sintering atmosphere (N 2+CO). With Al 2O 3 doping from 0.1 mol% to 0.55 mol%, the electrical conductivity increases firstly to a maximum (1.52 × 10 5 S·m −1) at 0.25 mol%, and then decreases gradually. The increased conductivity is explained by the formation of shallow donors as Al Zn-Zn i complexes with doping to 0.25 mol%. As Al 2O 3 doping further increasing to 0.55 mol%, ZnAl 2O 4 spinel phase and more ZnO-ZnO grain boundaries are formed, hindering charge carriers transport, to decrease charge carrier mobility, thus to decrease the conductivity of ZnO ceramics. Therefore, the Al Zn-Zn i complexes, grain boundaries and ZnAl 2O 4 spinel can be adjusted by doping different Al 2O 3 amount, thus the carriers’ concentration and their mobility are optimized to increase the conductivity. Our work, as a fundamental research, is of great significance to control conductivity by regulating Al 2O 3 doping. 相似文献
6.
Impedance spectra and potentiodynamic curves of oxidation and reduction reactions in the quinone/hydroquinone and Ce 3+/4+ systems were measured in a 0.5M H 2SO 4 solution on amorphous carbon thin-film electrodes grown by magnetron sputtering or ion source techniques. The electrode equivalent circuit contains a constant phase element. Only narrow-bandgap (“graphitelike”) amorphous carbon is electrochemically active; however, the wider bandgap (“diamondlike”) material also acquires the activity on “doping” it with platinum (ca 10%) in the course of film growth. The admixture of platinum does not effect film conductivity; its action probably is of catalytic character. In its electrochemical activity, the platinum-containing amorphous diamondlike carbon films resemble boron-doped polycrystalline diamond. 相似文献
7.
Despite the transformative role in society, information storage materials remain vulnerable to the corrosion by water, oxygen and heat, while topological engineering of glass provides an attractive solution to this tricky problem. Here, a considerable discovery is reported that the doping of Pb 2+ ions could greatly affect the luminescence behavior of SrAl 2O 4:Eu 2+, Dy 3+ borate glass, resulting in a controllable property between long persistent luminescence and photostimulated luminescence. Specifically, high concentration Pb doped samples featuring the deeper continuously distributed trap levels with 0.97–1.47 eV performed highly efficient photostimulated luminescence. In other words, the ultraviolet-visible photons could be “written” in the deeper traps and then “read out” under the stimulation of a 980 nm near-infrared laser. From the combined structural and luminescence characterizations, it was speculated that the deeper trap originated from the increase of oxygen vacancies at defect levels. The practical anti-counterfeiting application was successfully realized based on this material with superior photostimulated luminescence phenomenon, which rendered the SrAl 2O 4:Eu 2+, Dy 3+ borate glass shine in a new field such as anti-counterfeiting, yet as a promising candidate for information storage application. 相似文献
8.
Aluminate with the magnetoplumbite-type (LaZnAl 11O 19) represents a big family technology important compound. Crystallographic sites for transition metal and rare earth ion in the magnetoplumbite structure have always been a hot topic. Here, manganese-based magnetoplumbite-type La(Zn,Mn)Al 11O 19 phosphors were successfully synthesized via the traditional solid-state reaction and all the samples crystallized into the hexagonal structure. A narrow green emission band at approximately 518 nm with quantum efficiency (~unit one) is demonstrated in LaZnAl 11O 19 host with Mn 2+ doping equal 0.3. Temperature dependent photo-luminescence indicate that LaZn 0.7Mn 0.3Al 11O 19 sample keep excellent thermal stability. Meanwhile, the thermal ionization process was elaborated in detail. At last, a high-power w-LED with a high color rendering index and low associated color temperature is produced by inserting the microcrystals into the glass host using a “phosphor-in-glass (PiG)” technique. 相似文献
9.
采用Al 2O 3和MgO同时掺杂改性的方法制备了CaO-Ca 3Al 2O 6-MgO复合钙基高温吸附CO 2材料。复合钙基材料孔隙发达,活性物相为CaO,惰性骨架物相为Ca 3Al 2O 6和MgO。Ca 3Al 2O 6/MgO质量比偏小的材料,表面微粒粒径较小。在10%(体积分数,下同)CO 2和90% N 2的混合气气氛下,采用热重分析仪测量了复合钙基材料吸附CO 2容量、碳化反应速率以及循环碳化(670℃)/煅烧(900℃)过程的稳定性。结果发现,复合钙基材料CaO-Ca 3Al 2O 6-MgO具有较好的吸附CO 2性能,提高Ca 3Al 2O 6/MgO质量比,合成材料的循环稳定性较好;降低Ca 3Al 2O 6/MgO质量比,合成材料的碳化反应速率加快,CaO转化率提高。最后,通过对不同循环次数下复合钙材料的比表面积、孔径分布、微观形貌、表面元素分布,晶相、晶粒大小进行研究分析,对合成材料的失活以及掺杂物质对烧结的抑制机理进行了讨论。 相似文献
10.
LiCoO 2 nano-particles precursor was synthesized through a mixed-alkalis (LiOH-NaOH) hydrothermal reaction, and finally sintered into LiCoO 2 nanobricks with a sickness of ~300?nm. This LiCoO 2 nanobrick cathode delivered a specific capacity of 131.8 mAh g ?1 at 1?C between 3.0 and 4.2?V and 90% capacity retention after 100 cycles. Those synthesized LiCoO 2 nanobricks were further treated by surface Al 3+ doping to achieve much enhanced 4.5?V lithium storage capability and cycling stability. EIS results showed the surface Al 3+ doping operation can signification decrease the charge-transfer resistances of the LiCoO 2 cathodes for both before and after cyclings. 相似文献
11.
This paper presents studies on the immobilization of the polyoxometalate [PV 2Mo 10O 40] −5 (referred to as “POM”) on modified mesoporous MCM-41. The MCM-41 host material was made cationic by functionalization of the surface with [(MeO) 3Si(CH 2) 3N +(CH 3) 3]Cl. In polar solvents, POM is deprotonated and could be easily immobilized by wet impregnation of the modified silica using MeOH as the solvent. The physical properties of the samples were examined using XRD, FTIR, DR UV–Vis spectroscopy, 31P MAS-NMR, N 2 physisorption, and TEM. These techniques indicated that the POM is intact on the surface after impregnation. High loadings of POM caused a decrease in the surface area and pore volume of the solid, presumably due to both pore blockage and restructuring of the silica during wet impregnation. The texture and structure of the MCM-41 was studied as a function of POM loading. 相似文献
12.
Average pore sizes and effective porosity of microporous polysulfone hollow fibers were determined by the gas permeability method. Surface structure and porosity were determined by scanning electron microscopy. The values of effective porosity ε/ q2 (porosity/tortuosity factor) are approximately one order of magnitude lower than those reported previously for flat sheet porous membrane. These lower values are a direct outcome of a higher polymer concentration in the spinning dope. Correlations between the wall void volume, equivalent pore size, and hydraulic permeabilities of the hollow fibers have been determined. Rather low values of ε/ q2 have been calculated compared to those of the void volume; these effective porosity values indicate either a very high tortuosity factor or a large number of “dead end” pores. Exposure of the fibers to elevated temperature (110°C) for a short period of time drastically reduces the surface pore size and narrows the pore size distributions, whereas overall fiber dimensions are reduced only by 1%, and 85% of the fiber's hydraulic permeability is retained. The scanning electron microscopy study reveals the formation of a relatively dense skin in some spun fibers. For such “skinned” fibers, kinetic (permeability) evaluation of static structure such as mean pore size is not realistic and is further generalized to the term “equivalent pore size.” 相似文献
13.
Aluminum doped silica aerogel (ASA) exhibiting improved high-temperature resistance is usually prepared via supercritical drying from organic silicon and/or aluminum precursors, which propels the production cost significantly. Herein we demonstrate a simple and effective method to prepare highly thermal resistant ASA via the sol-gel and ambient pressure drying route by using water glass and aluminum chloride as precursors. Effects of the Al/Si molar ratio in precursor, the calcination temperature and the modifier type on the crystallinity, morphology, pore structure of ASA are investigated. Results show that the Al/Si molar ratio and the calcination temperature have significant effects on the structure and heat resistance performance of ASA at temperature of 600–1000 °C. The sample with Al/Si molar ratio of 0.15 shows the highest specific surface area of 805.9 m 2/g and pore volume of 5.038 cm 3/g after heated to 600 °C, and retains 179.5 m 2/g and 1.295 cm 3/g respectively after heated to 1000 °C. Mechanism analysis indicates that, though the actual aluminum content is extremely low (0.18%, wt%), the high-temperature resistance of ASA is greatly improved owing to the effective doping of aluminum in the lattice of SiO 2 and the corresponding electrostatic repulsion between neighboring nanoparticles induced by the replacement of Si 4+ by Al 3+ ions. 相似文献
14.
Perovskite ceramics with a formula of Ca 0.7Ti 0.7La 0.3Al 0.3O 3 (CTLA) were produced through a conventional solid-state reaction procedure following three different La 3+-doping methods using powders of La 2O 3, or La 2O 3/Al 2O 3 powder mixture, or LaAlO 3. La 3+ doping favored grain growth and densification, affected the grain size distribution, and improved the dielectric properties of the produced sintered CTLA ceramics. The doping methods had a strong influence on these properties. More specifically, doping with La 2O 3 and La 2O 3/Al 2O 3 resulted in formation of solid solution, while a secondary phase formed in the CTLA ceramics doped with LaAlO 3, which caused a coarsening of the microstructure and lowered the La 3+ doping effects on the dielectric properties. The experimental results suggest that La 3+ doping improves the dielectric properties of the sintered CTLA perovskite ceramics, which are further enhanced by doping with Al 3+ ions in small amounts. However, further increase of Al 3+ ions content jeopardizes them. 相似文献
15.
In present study, we report a V doping fabrication method for obtaining rod-like MgO crystals decorated with a nanoflake layer. This novel structure has only been minimally reported in literature. Pure MgO and Mg 2V 2O 7–MgO composite materials were obtained by precipitation and impregnation methods, with vanadium added concentrations of 0–9%. The influence of V doping on crystal structure and particle morphology of MgO was investigated by scanning electron microscopy (SEM). X-ray diffraction (XRD) analysis demonstrated that MgO has a cubic structure, while X-ray photoelectron spectroscopy (XPS) revealed that V 5+ exists on the surface of MgO. The specific surface areas and pore sizes of MgO composites were calculated by BET and BJH analysis. These techniques revealed that specific surface area and pore size of MgO increased due to vanadium doping. The antibacterial effects of Mg 2V 2O 7–MgO composite materials against Escherichia coli ( E. coli) and Staphylococcus aureus ( S. aureus) were assessed using a bacterial killing/colony-forming unit (CFU) assay and bacteriostatic ring method. Our results demonstrate that V doping dramatically improved antimicrobial properties of MgO, with 7 mol% doping inducing the best antibacterial activity. The antibacterial mechanisms of Mg 2V 2O 7–MgO composite material were also proposed. 相似文献
16.
Magnetically separable Ni embedded on graphitic mesoporous carbon (NMC) material was fabricated through a facile “sol–gel” route using glucose, nickle nitrate, poly(ethylene glycol)–poly(propylene glycol)–poly(ethylene glycol) (P123) and tetraethyl orthosilicate as carbon source, catalyst and magnetic precursor, soft template and porogen. The obtained NMC material exhibited highly graphitic degree with high surface area of 790 m 2 g ?1, large pore size at 3.9 nm and pore volume of 0.69 cm 3 g ?1. The saturation magnetization was enhanced to 6.82 emu g ?1 because of aggregation of magnetic Ni particles to clusters. NMC material showed excellent removal to Rhodamine B and the adsorption capacity reached to 168.1 mg g ?1 within 120 min. NMC material could be easily separated by an external magnet and reused after ethanol extraction. 相似文献
17.
To enable the comprehensive application of Al 2O 3-Cr 2O 3 solid solutions, the crystal structures and properties of Al 2O 3-Cr 2O 3 solid solutions with different Cr 2O 3 contents were studied. It was observed that Al 2O 3 and Cr 2O 3 form a complete substitutional solid solution over the entire composition range at 1650 °C, with no compounds being formed. Lattice parameters “a” and “c” both increase linearly with an increase in the Cr 2O 3 content. The doping of the Cr 3+ ions causes a more severe lattice strain in the c-axis direction. The diffraction angles of the diffraction peaks decrease in a linear manner with the increase in the Cr 2O 3 content. The relationship between the theoretical density of the solid solution and the Cr 2O 3 content could be fitted using a second-order polynomial. It was also observed that the linear expansion coefficient of the solid solutions decreases with an increase in the Cr 2O 3 content. 相似文献
18.
The surface properties of a stannic oxide gel and its thermal dehydration products obtained both in vacuo and in the presence of air in the temperature range 100–600°C have been examined by N 2 adsorption. Phase and structural changes have been followed by differential thermal analysis and X-ray diffractometry. Complete pore structure analysis showed that samples dehydrated at or below 250°C were microporous. Above 250°C the pores were found to widen with increase of temperature, the widening occurring concurrently with the crystallisation process. Doping with cations of lower valency (Li + and Al 3+) than the host cation (Sn 4+) had little effect on the pore structure and specific surface area for the low temperature samples (≤250°), whereas at higher temperatures, e.g. 600°C, it increased the specific area remarkably. The dope ions produce oxygen vacancies and hinder or retard sintering in SnO 2. 相似文献
19.
ZrO 2/yttria-stabilized zirconia (YSZ) doping Al 2O 3 ceramic coating was fabricated via cathodic plasma electrolytic deposition (CPED) technique. The microstructures and the chemical and phase compositions of the doped coating were characterized, the mechanical properties and the high temperature oxidation resistance were evaluated, and the doping mechanism was also discussed in detail. The results showed that, doped Zr 4+ and Y 3+ ions could effectively reduce the working voltage during CPED process and increase the content of metastable γ-Al 2O 3 in the coating. Accordingly, the doped ZrO 2/YSZ significantly refined the grain size of Al 2O 3, as well as remarkably improved the high temperature oxidation resistance, the micro-structural compactness and hardness of the Al 2O 3 CPED coating. This study displayed here constructed an efficiently method for the fabrication of multifunctional coating on the surface of TiAl alloy. 相似文献
20.
The surface properties of a stannic oxide gel and its thermal dehydration products obtained both in vacuo and in the presence of air in the temperature range 100–600°C have been examined by N 2 adsorption. Phase and structural changes have been followed by differential thermal analysis and X-ray diffractometry. Complete pore structure analysis showed that samples dehydrated at or below 250°C were microporous. Above 250°C the pores were found to widen with increase of temperature, the widening occurring concurrently with the crystallisation process. Doping with cations of lower valency (Li + and Al 3+) than the host cation (Sn 4+) had little effect on the pore structure and specific surface area for the low temperature samples (≥250°), whereas at higher temperatures, e.g. 600°C, it increased the specific area remarkably. The dope ions produce oxygen vacancies and hinder or retard sintering in SnO 2. 相似文献
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