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1.
The effect of sample preparation, including degassing conditions and method to stop cement hydration, on the specific surface area (SSABET) of synthetic ettringite (AFt) was studied. Dehydration of AFt occurs even at moderate temperatures under N2 flow (0% RH). However, partial dehydration associated to a loss of up to 12 water molecules does not imply a change in SSABET. A mild degassing 16 h at 40 °C under N2 flow is suggested mainly to preserve the chemical composition and morphology of calcium sulfate carrier. At higher temperatures, ettringite dehydration involves a significant modification of its crystalline structure and increase of the SSABET. Typical protocols to stop cement hydration, solvent exchange and freeze-drying, lead to larger water removal from the AFt and crystallinity reduction, being significantly higher when the latter is applied. However, only freeze-drying leads to a moderate increase of the synthetic AFt SSABET. 相似文献
2.
Xiaojun He Ruchun Li Jieshan Qiu Kang Xie Pinghua Ling Moxin Yu Xiaoyong Zhang Mingdong Zheng 《Carbon》2012,50(13):4911-4921
Mesoporous carbons (MCs) for supercapacitors were prepared from coal tar pitch by a microwave-assisted one-step process coupling the potassium hydroxide (KOH) activation and magnesium oxide (MgO) template. MCs were characterized by scanning electron microscope and X-ray diffraction. The results show that the specific surface area (SBET), micropore volume and specific capacitance of MCs made by microwave heating as well as the energy density of MC capacitors pass through a maximum with increasing mass of MgO and the relative mass ratio of KOH/pitch. The SBET of MCs varies from 1003 to 1394 m2/g. The SBET and total pore volume of MC and microporous carbon made by microwave heating are bigger than that made by conventional heating. Under optimum conditions with the masses of coal tar pitch, MgO, KOH at 9 g, 12 g, 6 g, and the microwave power at 600 W, MC (MC9-12-6) made at 30 min heating time shows a high specific capacitance of 224 F/g in 6 M KOH aqueous electrolyte after 1000 cycles. The results have shown that microwave-assisted rapid KOH activation coupled with the MgO template is an efficient one-step approach to the preparation of low cost yet high performance MCs for supercapacitors. 相似文献
3.
《Applied catalysis. B, Environmental》2007,69(3-4):147-153
A mix-valenced nickel oxide, NiOx, was prepared from nickel nitrate aqueous solution through a precipitation with sodium hydroxide and an oxidation by sodium hypochlorite. Further, pure nickel oxide was obtained from the NiOx by calcination at 300, 400 and 500 °C (labeled as C300, C400 and C500, respectively). They were characterized by thermogravimetry (TG), X-ray diffraction (XRD), nitrogen adsorption at −196 °C and temperature-programmed reduction (TPR). Their catalytic activities towards the degradation of phenol were further studied under continuous bubbling of air through the liquid phase. Also, the effects of pH, temperature and kinds of nickel oxide on the efficiency of the microwave-enhance catalytic degradation (MECD) of phenol have been investigated. The results indicated that the relative activity affected significantly with the oxidation state of nickel, surface area and surface acidity of nickel oxide, i.e., NiOx (>+2 and SBET = 201 m2 g−1) ≫ C300 (+2 and SBET = 104 m2 g−1) > C400 (+2 and SBET = 52 m2 g−1) > C500 (+2 and SBET = 27 m2 g−1). The introduction of microwave irradiation could greatly shorten the time of phenol degradation. 相似文献
4.
《Diamond and Related Materials》1999,8(1):73-77
The diamond forming regions in the anhydrous MgSO4 and hydrous MgSO4·H2O–graphite systems, as well as the morphology of diamond synthesized from both of systems were investigated under the conditions of 6.5–7.7 GPa and 1600–2000 °C. The region was basically the same in both systems, although the melting point of MgSO4 is at least 600 °C higher than that of MgSO4·H2O at 7.7 GPa. In the anhydrous system, the appearance of {111} faces is favored at higher temperatures and that of {100} faces at lower temperatures, while in the hydrous system, {111} faces are predominant at all examined conditions. 相似文献
5.
《Ceramics International》2017,43(16):13254-13263
Carbon-coated LiFePO4/C composite as cathode materials is synthesized by solid-state method using anhydrous FePO4 and hydrous FePO4·2H2O as precursors.The effects of sintering temperature and carbon content on the properties of LiFePO4/C composite are compared by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and charging–discharging test. The crystallinity, morphology, and particle size distribution of these two precursors are compared to investigate their effect on the electrochemical performances of LiFePO4/C composite. Compared with hydrous FePO4·2H2O, anhydrous FePO4 has good crystallinity, uniform particle morphology and symmetrical size distribution, contributing to LiFePO4/C composite have excellent electrochemical performances. Due to the dehydration of hydrous FePO4·2H2O during synthesis, uneven distribution of carbon content and carbon layer is coated on LiFePO4 surface, deteriorating the electrochemical performance of LiFePO4/C composite. When anhydrous FePO4 was used as the precursor, the LiFePO4/C composite sintered at 700 °C with carbon content of 0.4 by molar ratio show high discharge capacity and stable cycling performance, with discharge capacity of 106.3 mA h g−1 at 10 C, and a capacity retention rate of 99.2% after 200 cycles at 1 C. 相似文献
6.
Shashank Mishra Liliane G. Hubert-Pfalzgraf Stéphane Daniele Marc Rolland Erwann Jeanneau Bernadette Jouguet 《Inorganic chemistry communications》2009,12(2):97-100
In order to obtain a better anhydrous precursor for various applications in materials science and catalysis, thermal dehydration reactions of Y(TFA)3(H2O)3 (TFA = trifluoroacetate) (A) were investigated. Thermal treatment of A at different temperatures under vacuum (5 × 10?2 mm) for several hours failed to give totally anhydrous yttrium trifluoroacetate (as indicated by IR). Two different complexes, a partially dehydrated [Y(μ,η1:η1-TFA)3(THF)(H2O)]1∞·THF (1) and a partially hydrolyzed [Y4(μ3-OH)4(μ,η1:η1-TFA)6(η1-TFA)(η2-TFA)(THF)3(DMSO)(H2O)] · 6THF (2), were obtained with good and moderate yield, respectively, by crystallization of two different thermally treated batches of A from THF (or THF + DMSO) at room temperature. More efficient dehydration of A could be achieved at 200 °C in a furnace, the obtained anhydrous yttrium tris-trifluoroacetate giving Y(TFA)3(THF)2 (3) on crystallization from THF. All the products were characterized by elemental analyses, FT-IR and 1H NMR spectroscopy as well as thermo-gravimetric analysis. In addition, single crystal X-ray structures are reported for 1 and 2, which show either a terminal (η1 and η2) or bridging (μ,η1:η1) bonding behavior of the TFA ligand. 相似文献
7.
The effect of fineness of fly ash on mechanical properties and alkali–silica reaction resistance of cement mortar mixtures incorporating fly ash has been investigated within the scope of this study. Blaine fineness of fly ash has been increased to 907 m2/kg from its original 290 m2/kg value by a ball mill. Test samples were prepared by replacing cement 20, 40 and 60%, with finer and coarser fly ashes and kept under standard and steam curing conditions until testing. Test results showed that grinding process improved the mechanical properties of all samples significantly. The beneficial effect of grinding fly ash, may increase utilization of this by-product in precast and ready-mix concrete industries. Incorporation of fly ash with different fineness values and ratios also decreased the expansions to harmless levels of cement mortars due to alkali–silica reaction. 相似文献
8.
《Carbon》2015
Highly microporous carbons with narrow pore size distribution have been prepared by simultaneous carbonization and self-activation of tobacco wastes at temperatures ranging from 600 to 1000 °C. The efficiency of porosity development, without pores broadening, is attributed to well-distributed alkalis at the molecular level in the tobacco precursor. With Burley tobacco, the BET specific surface area and average micropore size L0 increased up to 800 °C (Burley 800), where the values reached maxima of 1749 m2 g−1 and 1.2 nm, respectively. At temperatures higher than 800 °C, annealing of the materials dominates and provokes a decrease of SBET and L0. Burley carbons were implemented in supercapacitors using 1 mol L−1 aqueous Li2SO4 or 1 mol L−1 TEABF4 in acetonitrile. In both electrolytes, the capacitance of Burley carbons followed the same trend as SBET and L0. Burley 800 demonstrated outstanding capacitance values of 167 F g−1 (at 0.8 V limit) and 141 F g−1 (at 2.3 V limit) in 1 mol L−1 aqueous Li2SO4 and 1 mol L−1 TEABF4, respectively. Such values, about 50% higher as compared to commercially available carbons, are attributed to the narrow pore size distribution of this carbon with a maximum of pores around 1.2 nm close to the size of solvated ions in these electrolytes. 相似文献
9.
《Carbon》2014
Nanoporous S-doped carbon and its composites with graphite oxide were tested as adsorbents of CO2 (1 MPa at 0 °C) after degassing either at 120 °C or 350 °C. The adsorption capacities were over 4 mmol/g at ambient pressure and 8 mmol/g at 0.9 MPa in spite of a low volume of micropores. The nitrogen adsorption experiments showed an increase in porosity upon an increase in the degassing temperature. The extent of this effect depends on the stability of surface groups. Interestingly, the CO2 adsorption, especially at low pressure, was not affected. The good performance is due to the presence of ultramicropores similar in sizes to CO2 molecule and to sulfur in various functionalities. Sulfur incorporated to aromatic rings enhances CO2 adsorption via acid–base interactions in micropores. Moreover, sulfonic acids, sulfoxides and sulfones attract CO2 via polar interactions. Hydrogen bonding of CO2 with acidic groups on the surface can also play an important role in the CO2 retention. These carbons have high potential for application as CO2 removal media owing to their high degree of pore space utilization. The results obtained also show that high degassing temperatures might result in the decomposition of surface groups and thus in changes in surface interactions. 相似文献
10.
Mesoporous silicon oxycarbide ceramics without free carbon were prepared by pyrolysis of cross-linked polysiloxane at different temperatures (1300–1450 °C) followed by post treatments. The post treatments comprised two steps (HF etching and oxidation at 650 °C in air). The sample pyrolyzed at 1300 °C after post treatments exhibits the largest specific surface area (SSA) reaching up to 204 m2/g and the biggest total pore volume (0.58 cm3/g) with an average pore size of 11.4 nm. Increasing pyrolysis temperature will lead a quick decline of SSA and total pore volume. The thermal stability of pore structure of the sample pyrolyzed at 1300 °C with post treatments was investigated in air. The SSA and total pore volume almost keeps the same up to 750 °C, and subsequently decreases with a high speed. The most possible reason is the pores are severely closed by viscous flow of SiO2 produced from SiC nanocrystallites. 相似文献
11.
A. Kusior J. Klich-Kafel A. Trenczek-Zajac K. Swierczek M. Radecka K. Zakrzewska 《Journal of the European Ceramic Society》2013,33(12):2285-2290
Nanopowders of TiO2–SnO2 over a full composition range extending from 100 mol% TiO2 to 100 mol% SnO2 are obtained by the sol–gel method from TTIP and SnCl2·5H2O precursors of Ti and Sn, respectively followed by calcination at 400 °C. The samples are characterized by means of BET, XRD and TEM. Optical properties of the prepared nanomaterials are studied as well. TEM images indicate that the nanoparticles are regular in shape. The specific surface area, SSA of TiO2 is 95 m2/g while that of SnO2 amounts to 129 m2/g. The highest SSA of 156 m2/g is achieved at 20 mol% of TiO2. Occurrence of rutile, anatase and brookite polymorphic forms depends on the chemical composition of nanopowders. Formation of rutile-type solid solution of TiO2–SnO2 over the range of 0–80 mol% TiO2 is confirmed by Vegard rule applied to lattice constants. Electronic band gap decreases with Ti content from 3.84 eV (100 mol% SnO2) to 3.18 eV (100 mol% TiO2). 相似文献
12.
《Journal of the European Ceramic Society》2014,34(5):1365-1373
In this work, Al2O3 self-flowing castables (SFCs) were produced based on various cement contents. The SFCs were sintered at 1273 K, 1573 K and 1773 K and the exhibited properties were experimentally determined. Among the properties determined in this work are bulk density (BD), apparent porosity (AP), water absorption (WA), cold crushing strength (CCS), modulus of rupture (MOR) and fracture toughness (KIC). It is found that additions of 5% cement lead to SFCs with maximum MOR and KIC values after firing at 1773 K. Firing at 1573 K leads to a reduction in both, MOR and KIC. In SFC containing 3% cement, maximum KIC values of 3.53 MPa m1/2 were achieved after firing at 1573 K. In the low cement SFCs (1 wt%) after firing at 1773 K the exhibited KIC values were below those obtained in either the SFC-3 or SFC-5, but they were significantly high (3.43 MPa m1/2). 相似文献
13.
Catalytic dehydration of glycerol to acrolein over sulfuric acid-activated montmorillonite catalysts
For the development of efficient solid acid catalysts for the catalytic dehydration of glycerol to acrolein, catalysts made from montmorillonitic clay activated by sulfuric acid were investigated. Montmorillonite was activated in diluted sulfuric acid in the concentration range of 5–40 wt.%. The effects of sulfuric acid treatment on the structure of the montmorillonite were characterized by X-ray diffraction, measurements of acidity, N2 adsorption–desorption isotherms, and Fourier transform infrared spectroscopy. The catalytic behavior of sulfuric acid-activated montmorillonite catalysts in the gas-phase dehydration of glycerol were investigated under varying conditions, including the reaction temperature, the feed rate, and the concentration of glycerol. After montmorillonitic clay was activated by sulfuric acid, the layered structural features of montmorillonite remained nearly intact. Ca2 +-montmorillonite was changed to H+-montmorillonite by ion exchange reaction during activation. The optimal catalytic glycerol dehydration reaction conditions were found to be: temperature at 320 °C, liquid hourly space velocity (LHSV) = 18.5 h− 1, concentration of glycerol solution = 10 wt.%, and the flow rate of N2 carrier gas = 10 mL/min. A conversion of 54.2% of glycerol and a yield of 44.9 wt.% acrolein were achieved over the montmorillonite catalyst activated by an aqueous 10 wt.% sulfuric acid solution. The H+ in the interlayer space of acid-activated montmorillonite catalysts played a critical role in the catalytic dehydration of glycerol. The temperature, the LHSV, and the concentration of glycerol affected the performance of the catalysts through their influence on the reaction mechanism, the contact time, and the reaction equilibrium. 相似文献
14.
《Microporous and mesoporous materials》2007,98(1-3):29-40
Zeolite Li-BEA and Na-BEA with Si/Al = 3–4 were synthesized by alumination and ion exchange, then characterized by XRD, TG–DSC and NMR. The enthalpies of formation and dehydration of Li and Na ion exchanged zeolite beta are investigated by high temperature oxide melt solution calorimetry. For Li-BEA, the formation enthalpies of formation from oxides at 25 °C are 25.6 ± 1.7 kJ/mol TO2 for the dehydrated zeolite and −8.45 ± 0.94 kJ/mol TO2 for the fully hydrated zeolite; for Na-BEA they are −2.4 ± 0.6 kJ/mol TO2 for the dehydrated and −17.8 ± 1.0 kJ/mol TO2 for the fully hydrated zeolite. The integral dehydration enthalpy at 25 °C is 33.2 ± 1.8 kJ/mol H2O for Li-BEA and 16.5 ± 1.1 kJ/mol H2O for Na-BEA. The partial molar dehydration enthalpies of both Li-BEA and Na-BEA are a linear function of water content. Molecular mechanics simulations explore the cation and water molecule positions in the framework at several water contents. 相似文献
15.
Aluminosilicate nanorolls were prepared using a method of one-step delamination of kaolinite. In this method, cetyltrimethylammonium chloride (CTMACl) was intercalated into the interlayer space of methoxy-modified kaolinite, which resulted in the delamination and rolling of kaolinite layers. The reaction conditions of CTMACl intercalation significantly influenced the formation of nanorolls, as shown by characterizations using X-ray diffraction, electron microscopy, infrared spectroscopy, thermal analysis, and nitrogen adsorption. Overall, increasing the CTMACl-intercalation temperature helps to promote the transformation from platy kaolinite to nanorolls. The initial kaolinite particles were mostly transformed to nanorolls in the product prepared at 80 °C, whereas considerable kaolinite particles remained untransformed in the product prepared at 30 °C. At 80 °C, the obtained specific surface area (SSA) and the porous volume (Vpor) values of the nanoroll product are nearly twice the values obtained at 30 °C and the tubular structure exhibits higher thermal persistence. The tubular morphology and the porosity of these nanorolls obtained at 80 °C, were largely retained after calcination at 600–800 °C. However, a calcination at 900 °C led to an obvious distortion of the nanorolls and a decrease in SSA and Vpor values. The observed structural changes of the nanorolls under calcination generally resembled that of natural halloysite but occurred at lower temperatures because the prepared nanorolls were of lower structural order with thinner tube walls. 相似文献
16.
Kinga Łuczka Barbara Grzmil Joanna Sreńscek-Nazzal Krzysztof Kowalczyk 《Journal of Industrial and Engineering Chemistry》2013,19(3):1000-1007
Aluminium ammonium calcium phosphates were prepared with the use of AlCl3, CaCO3, H3PO4. The influence of the process parameters (pH 5 ± 3, the molar ratios of Ca2+:Al+3:PO4?3 in the substrates, respectively 0.31:0.62:1; 0.5:0.5:1; 0.72:0.36:1, temperature 40 ± 20 °C) on the phase composition and the product properties was determined. The process parameters that enable to obtain the material with expected physicochemical properties were determined based on the statistical evaluation of the experiments (fractional factorial design at three levels 3(k?p)27). The phase composition of the obtained samples was studied with the use of XRD analysis. The specific surface area was calculated with the use of SBET method and the particle size was determined by the laser scanning microscopy. The materials with the molar ratio of Al3+/NH4+ and Al3+/Ca2+ in the range of 0.70–27.93 and 0.47–24.48, respectively, with an absorption oil number of 95–157 g/100 g paraffin oil, the SBET within 25–118 m2/g, the pore volume within 0.14–0.74 cm3/g and the particle size in the range of 168–285 nm were obtained. 相似文献
17.
《Ceramics International》2017,43(14):10799-10804
Silica aerogel is deemed as a kind of high-performance thermal insulation materials. However, the existence of macropores in the structure is always ignored in the research and application of aerogels. Thus the thermal insulation performance of silica aerogels could be further improved if the macropores are reduced. In this work, nano-sized Al2O3 powders are explored as nano fillers to reduce the macropore volume fraction in silica aerogels by filling the big voids among the silica aggregates, and further lower the thermal conductivity. The experimental results showed that the macropore volume fraction () was dramatically reduced from 63.05% to 23.12% with the addition of Al2O3 powders ranging from 0.0 g to 1.0 g. This trend was also verified by the variation of (VT*-VBET) and (VBET/VT*). Accordingly, the thermal insulation performance was improved due to the reduction of macropores in aerogels. The lowest thermal conductivity of Al2O3-doped aerogels reached 7.41 mW/(m K) in contrast with that of pure silica aerogels (9.00 mW/(m K)), which was a significant decline for aerogel-based materials due to the gaseous heat transfer being further weakened. Moreover, the increment of thermal conductivity from 7.41 to 9.71 mW/(m K) with the Al2O3 powders increasing could be attributed to the enhancement of solid heat transfer in the system. The variation of experimental thermal conductivity was in good agreement with the result of theoretical calculation. This study proposed an innovative idea to improve the thermal insulation of aerogel under ambient conditions. 相似文献
18.
《Journal of Industrial and Engineering Chemistry》2014,20(3):759-766
Liquid phase dehydration of glycerol to acrolein catalyzed by Brønsted acidic ionic liquids (BAILs) using semi-batch reaction technique was investigated. For the BAILs catalysts, the acrolein yields were in an order of [Bmim]H2PO4 > [Bmim]HSO4 > [BPy]HSO4 > [PSPy]HSO4 > [N2224]HSO4 > [PSPy]H2PO4 > [BPy]H2PO4 > [N2224]H2PO4. When [Bmim]H2PO4 and [Bmim]HSO4 were used as the catalysts at 270 °C with the molar ratio of catalyst to glycerol of 1:100, the acrolein yields were 57.4% and 50.8%, respectively, at complete conversion of glycerol. The BAILs with [Bmim] cation and moderate acidity favored the formation of acrolein in liquid phase glycerol dehydration. 相似文献
19.
Jaturong Jitputti Thitima Rattanavoravipa Surawut Chuangchote Sorapong Pavasupree Yoshikazu Suzuki Susumu Yoshikawa 《Catalysis communications》2009,10(4):378-382
Monodispersed flower-like titanate superstructure was successfully prepared by simple hydrothermal process without any surfactant or template. N2-sorption analysis, scanning electron microscopy (SEM), and X-ray diffraction (XRD) observation of as-synthesized product revealed the formation of flower-like titanate with diameter of about 250–450 nm and BET surface area (SBET) of 350.7 m2 g?1. Upon thermal treatment at 500 °C, the titanate nanosheets were converted into anatase TiO2 with moderate deformation of their structures. The as-prepared flower-like titanate showed high photocatalytic activity for H2 evolution from water splitting reaction. Moreover, the sample heat treated at 500 °C exhibited higher photocatalytic activity than that of commercial TiO2 anatase powder (ST-01). 相似文献
20.
《Catalysis communications》2011,16(1):41-45
Mesoporous CuO/TixZr1 − xO2 catalysts were prepared by a surfactant-assisted method, and characterized by N2 adsorption/desorption, TEM, XPS, in-situ FTIR and H2-TPR. The catalysts exhibited high specific surface area (SBET = 241 m2/g) and uniform pore size distribution. XPS and in-situ FTIR displayed that Cu+ and Cu2+ species coexisted in the catalysts. The CuO/TixZr1 − xO2 catalysts presented obviously higher activity in CO oxidation reaction than the CuO/TiO2 and CuO/ZrO2 catalysts. Effect of molar ratios of Ti to Zr and calcination temperature on catalytic activity was investigated. The CuO/Ti0.6Zr0.4O2 catalyst calcined at 400 °C exhibited excellent activity with 100% CO conversion at 140 °C. 相似文献