共查询到20条相似文献,搜索用时 31 毫秒
1.
以淀粉为原料,使用水热法将其碳化后用活化剂KOH对其活化,制备了淀粉基多孔碳材料,并对其进行结构表征和CO2/CH4的吸附性能测试,计算吸附热以及材料对CO2/CH4的吸附选择性,讨论了碳材料结构对其吸附性能的影响。结果表明:在制备过程中,随着活化剂KOH用量比例的增大,所制得的材料其比表面积和孔容增大,其孔径分布也就越宽。所制得的碳材料其比表面积可达2972 m2·g-1。这些淀粉基多孔碳材料对水蒸气的吸附等温线呈现出Ⅳ类等温线。所制备材料对CO2吸附容量主要取决于其孔径小于0.8 nm的累积孔容(Vd < 0.8 nm)。材料的超微孔的孔容越大,其对CO2吸附容量也越大。所制备的C-KOH-1材料在101325 Pa和298 K条件下,对CO2的吸附量达到4.2 mmol·g-1,其对CO2的吸附热明显高于其对CH4吸附热,其对CO2/CH4吸附选择性为3.7~4.26,同时本文通过对材料的水蒸气吸附等温线进行测试,结果表明所得材料主要表现为中等憎水性,这对材料在实际工况的应用奠定了基础。 相似文献
2.
D. R. LARSON J. A. COPPOLA D. P. H. HASSELMAN R. C. BRADT 《Journal of the American Ceramic Society》1974,57(10):417-421
The fracture energies and spalling resistance of high-Al2 O3 refractories were studied. The fracture energies, γ WOF and γ NBT , were measured by the work-of-fracture and the notched-beam-test methods, respectively. Spalling resistance, as measured by the relative strength retained in a water quench, correlated well with the thermal-stress resistance parameter applicable to stable crack propagation under conditions of thermal shock, (γ WOF /α2 E 0 ). Many of the refractories exhibited high ratios of γWOF to γNBT ; such high ratios were shown analytically to maximize the parameter ( R 1111 = E 0γWOF /S1 2 ) which describes the resistance to catastrophic spalling. The increase of crack length with increasing quenching temperature difference (Δ T ) was somewhat less than that predicted theoretically; the discrepancy was attributed to an increase of crack density with Δ T . In general, the results show that fracture energy is important in establishing the spalling resistance of high-Al2 O3 refractories. 相似文献
3.
The enthalpies of transformation of pure, well-characterized samples of brookite and anatase to rutile were determined by solution calorimetry in a 3Na2 O·4MoO3 melt at 971 ±2 K. The experiments gave the following results: brookite→rutile, ΔH°971 = -0.17±0.09 kcal mol−1 ; anatase → rutile, ΔH°971 = -0.78±0.20 kcal mol−1 . 相似文献
4.
Koichiro Fukuda Iwao Maki Suketoshi Ito 《Journal of the American Ceramic Society》1997,80(6):1595-1598
Crystals of β-Ca2 SiO4 (space group P 121 / n 1) were examined by high-temperature powder X-ray diffractometry to determine the change in unit-cell dimensions with temperature up to 645°C. The temperature dependence of the principal expansion coefficients (αi ) found from the matrix algebra analysis was as follows: α1 = 20.492 × 10−6 + 16.490 × 10−9 ( T - 25)°C−1 , α2 = 7.494 × 10−6 + 5.168 × 10−9 ( T - 25)°C−1 , α3 =−0.842 × 10−6 − 1.497 × 10−9 ( T - 25)°C−1 . The expansion coefficient α1 , nearly along [302] was approximately 3 times α2 along the b -axis. Very small contraction (α3 ) occurred nearly along [ 01]. The volume changes upon martensitic transformations of β↔αL ' were very small, and the strain accommodation would be almost complete. This is consistent with the thermoelasticity. 相似文献
5.
Jon-Paul Maria Joseph F. Shepard Jr. Susan Trolier-McKinstry T. R. Watkins A. E. Payzant 《International Journal of Applied Ceramic Technology》2005,2(1):51-58
Pb(Mg1/3 Nb2/3 )O3 –PbTiO3 (PMN–PT) (70/30) thin films were deposited by pulsed laser deposition using two growth strategies: adsorption controlled deposition from lead-rich targets (∼25–30 mass%) and lower-temperature deposition ( T d ≤600°C) from targets containing a small amount of excess lead oxide (≤3 mass %). The substrates used were (001) SrRuO3 /LaAlO3 . Typical remanent polarization values ranged between 12 and 14 μC/cm2 for these films. The longitudinal piezoelectric coefficient ( d 33,f ) was measured using in situ four-circle X-ray diffraction, and the transverse coefficient ( d 31,f or e 31,f ) was measured using the wafer flexure method. d 33,f and e 31,f coefficients of ∼300–350 pm/V and ∼−11 C/m2 were calculated, respectively. In general, the piezoelectric coefficients and aging rates were strongly asymmetric, suggesting the presence of a polarization bias. The large, extremely stable piezoelectric response that results from poling parallel to the preferred polarization direction is attractive for miniaturized sensors and actuators. 相似文献
6.
THEODORE M. BESMANN TERRENCE B. LINDEMER 《Journal of the American Ceramic Society》1983,66(11):782-785
Thermodynamic values for PUO1.5 were assessed using an improved method for estimating fef ° 1.5 and new data for S°298 1.5 . Based on the assessment, a value of ΔH°298 , 1.5 =–828 kJ/mol is recommended. Measurements of (CO) pressure over the nominal equilibrium 1.5 + 1.5 + C were performed between 1348 and 1923 K, yielding pressures between 0.644 and 11600 Pa. Second- and third-law analyses were used to obtain a value for ΔH°298 1.5 =–93.3°3.3 kJ/mol. 相似文献
7.
The changes in surface area and mesoporosity in aggregates of ∼0.01 μm cross-section CaO particles when heated in CO2 at 686°C were determined from N2 adsorption isotherms. Initially, the surface area decreases rapidly with little change in porosity. When the surface area has decreased below ∼90 m2 /g, surface area and porosity variations become consistent with expectations for coarsening by grain-boundary or bulk diffusion. The initial rapid decrease in surface area must result from CO2 -catalyzed surface diffusion, but the data suggest that surface diffusion is not rate-limiting. The rate-limiting step may be reaction of CO2 to form surface CO3 2- ions or decomposition of these ions to O2- ions and CO2 gas. 相似文献
8.
B. N. ROY 《Journal of the American Ceramic Society》1980,63(1-2):10-13
Using an ordinary Arrhenius equation kDl = k0 e−EIRT , energy ( E ), enthalpy (Δ H a ), entropy (Δ Sa ), and free energy (δ G a ) of activation and the preexponential factor ( K 0 ) were estimated for diffusion-controlled crystal growth of calcium tungstate from solutions in lithium chloride and sodium tungstate melts. Although E was small and increased slightly with increased cooling rates ( RT ), there was no direct correlation. The Δ H a , Δ S a , and Δ Ga were unaffected by the changes in RT and crystallization temperature ( T 0 ). The distance ( d 12 ) between a diffusing particle and its host crystal, necessary for a successful diffusion, was estimated. Such distances increased with T0 and RT for the system CaWO4 -Na2 WO4 but, for the system CaWO4 -LiCl, they decreased with RT and increased with T 0 . 相似文献
9.
Noriyuki Wada Takashi Tsuneoka Kazuo Kojima 《Journal of the American Ceramic Society》2002,85(6):1396-1402
Chloride glasses of the ZnCl2 and 20KCl-20BaCl2 -60ZnCl2 -0.5ErCl3 systems were prepared using NH4 Cl as a dehydrating and chlorinating agent, under the melt-quenching method. Water- and ammonium-chloride-related residues in ZnCl2 glasses were investigated by infrared and near-infrared absorption spectra. Water, Zn—OH, ClO, ClO2 − , Zn2+ -coordinated water, free NH3 , NH4 + , and Zn2+ -coordinated NH3 were identified in ZnCl2 glasses. 20KCl-20BaCl2 -60ZnCl2 -0.5ErCl3 glasses prepared by melting at 500°C for 20 min, under reduced pressure, contained the smallest amounts of water, Zn—OH, and Zn2+ -coordinated NH3 and showed strong Er3+ upconversion fluorescence. 相似文献
10.
Porous glass-ceramics with a skeleton of the fast-lithium-conducting crystal Li1+ x Ti2− x Al x (PO4 )3 (where x = 0.3–0.5) were prepared by crystallization of glasses in the Li2 O─CaO─TiO2 ─Al2 O3 –P2 O5 system and subsequent acid leaching of the resulting dense glass-ceramics composed of the interlocking of Li1+ x Ti2− x Al x (PO4 )3 and β-Ca3 (PO4 )2 phases. The median pore diameter and surface area of the resulting porous Li1+ x Ti2− x Al x (PO4 )3 glass-ceramics were approximately 0.2 μm and 50 m2 /g, respectively. The electrical conductivity of the porous glass-ceramics after heating in LiNO3 aqueous solution was 8 × 10−5 S/cm at 300 K or 2 × 10−2 S/cm at 600 K. 相似文献
11.
Abstract. We investigate the estimation of parameters in the random coefficient autoregressive (RCA) model X k = ( φ + b k ) X k −1 + e k , where ( φ , ω 2 , σ 2 ) is the parameter of the process, , . We consider a nonstationary RCA process satisfying E log | φ + b 0 | ≥ 0 and show that σ 2 cannot be estimated by the quasi-maximum likelihood method. The asymptotic normality of the quasi-maximum likelihood estimator for ( φ , ω 2 ) is proven so that the unit root problem does not exist in the RCA model. 相似文献
12.
The effects of substituting Nb5+ with Ta5+ on the microwave dielectric properties of the ZnNb2 O6 ceramics were investigated in this study. The forming of Zn(Nb1− x Ta x )2 O6 ( x =0–0.09) solid solution was confirmed by the measured lattice parameters and the EDX analysis. By increasing x , not only could the Q × f of the Zn(Nb1− x Ta x )2 O6 ( x =0–0.09) solid solution be tremendously boosted from 83 600 GHz at x =0 to a maximum 152 000 GHz at x =0.05, the highest ɛr ∼24.6 could also be achieved simultaneously. It was mainly due to the uniform grain morphology and the highest relative density of the specimen. A fine combination of microwave dielectric properties (ɛr ∼24.6, Q × f ∼152 000 GHz at 8.83 GHz, τf ∼–71.1 ppm/°C) was achieved for Zn(Nb0.95 Ta0.05 )2 O6 solid solution sintered at 1175°C for 2 h. 相似文献
13.
The thermodynamic properties of the α and β polymorphs of NiMoO4 were directly investigated by calorimetry. The standard entropies of formation, Δf S ° T , of α and β were determined from measuring the molar heat capacity, C p,m , from near absolute zero (2 K) to high temperature (1380 K) by a relaxation method and differential scanning calorimetry. The standard enthalpies of formation, Δf H ° T , of α and β were determined by combining C p,m with the standard enthalpy of formation, Δf H °298 , at 298 K obtained from drop solution calorimetry in molten sodium molybdate at 973 K. The standard Gibbs energies of formation, Δf G ° T , of α and β were determined from their Δ f S ° T and Δ f H ° T values. The Δ f G ° T values indicate that the polymorphic transformation from α to β occurs at 1000 K, consistent with the observed phase transformation at 1000 K. 相似文献
14.
Spectra of divalent transition metal ions in ZnCl2 , KOAc-Ca(OAc)2 , KNO3 -Ca(NO3 )2 , and K2 SO4 -ZnSO4 glasses are presented. Ions with low octahedral site preference energies (e.g. CO2+ ) can be used as "probes" for divalent cations in glass and can indicate the presence or absence of network structures. Thus ZnCl2 glass has a tetrahedral network structure, analogous to vitreous BeF2 , but KOAc-Ca(OAc)2 and KNO3 -Ca(NO3 )2 glasses contain potassium ions and discrete acetatocalcate(II) and nitratocalcate(II) "complex ions." The structure of acetate and nitrate glasses is discussed in terms of the ideal glass concept. 相似文献
15.
Calcium silicate hydrate (C-S-H) can be viewed as a solid solution, 0.833Ca(OH)2 .SiO2 .0.917H2 O-xCa(OH)2 , at equilibrium at 30°C. On this basis, the change in Gibbsfree energy (ΔGr ) in the solid-solution reaction was calculated from solubility duta for C-S-H in water. The change in ΔGr with real ratio decreased notably for the higher calcium contents (CaO/Si02 1.7; ×0.867). Thermochemical values for C-S-H (CaO/SiO2 =1.7) were estimated to be ΔH°=-2890 kJ/mol, ΔG°=-2630 kJ/mol, and S°=200 J1/mol.K at 298 K . 相似文献
16.
A. Cuneyt Tas 《Journal of the American Ceramic Society》2007,90(8):2358-2362
A novel, one-pot technique of synthesizing calcium phosphate whiskers was developed. Commercially available β-tricalcium phosphate (β-Ca3 (PO4 )2 ) powders were aged in unstirred 30% H2 O2 solutions at 90°C for 48 h in ordinary glass media bottles. Resultant samples consisted of whiskers (200 nm wide and 5 μm-long) of a biphasic mixture of octacalcium phosphate (OCP: Ca8 H2 (PO4 )6 ·5H2 O) and carbonated apatitic (apatite-like) calcium phosphate (Ap-CaP). As-formed whiskers possessed a Ca/P molar ratio of 1.46 and a BET surface area of 8 m2 /g. Upon soaking these whiskers in a Tris-HCl-buffered SBF solution of 27 mM HCO3 − for 6 days, Ca/P molar ratio and surface area values were increased to 1.60 and 52 m2 /g, respectively. The technique, owing to its simplicity, may prove useful in providing large amounts of biocompatible short whiskers for numerous technology sectors. 相似文献
17.
Hideo Hosono Zhibo Zhang Yoshihiro Abe 《Journal of the American Ceramic Society》1989,72(9):1587-1590
A porous glass-ceramic in the CaO–TiO2 —P2 O5 system has been prepared by crystallization and subsequent chemical leaching of the corresponding glass. By applying a two-step heat treatment to 45CaO · 25TiO2 · 30P2 O5 glasses containing a few mol% of Na2 O, volume crystallization results in the formation of dense glass-ceramics composed of CaTi4 (PO4 )6 and β-Ca3 (PO4 )2 phases. By leaching the resultant glass ceramics with HCI, β-Ca3 (PO4 )2 is selectively dissolved out, leaving a crystalline CaTi4 (PO4 )6 skeleton. The surface area and mean pore radius of the porous glass-ceramics were approximately 40 m2 /g and 13 nm, respectively. 相似文献
18.
Jeanette Persson Per-Olov Käll Mats Nygren 《Journal of the American Ceramic Society》1992,75(12):3377-3384
The oxidation process of Si2 N2 O, prepared by a hot isostatic pressing technique, has been studied by the thermogravimetric method. The oxidation has been performed in oxygen for 20 h in the temperature range 1300° to 1600°C, producing oxide scales of amorphous SiO2 and α-cristobalite. The weight gain for T 1350°C does not begin to follow a parabolic rate law, until a certain time, t 0 . The A 0 parameter in the parabolic rate law, (Δ w / A 0 )2 = K p t + B , represents the cross section area, A , through which the oxygen diffuses; in the derivation of this law A is assumed to be constant during the experiment. If crystallization occurs during the oxidation process, A will decrease with time. A function, A ( t ), describing the time dependence, has been developed and incorporated into the parabolic rate law, yielding a new rate law, which reads Δ W/A 0 = a arctan √ bt + c √ t . This new rate law is valid in the time interval t < t 0 , whereas, for t > t 0 , the oxidation process follows the equation (Δ w/A 0 )2 = K °p t + B 0 . The relation of the latter equation to the common parabolic rate law is described. All of the oxidation curves are described by these equations. The activation energy of the oxygen diffusion (and of the oxidation ( K p )) is found to be 245 ± 25 kJ/mol, which is consistent with literature values reported for oxygen diffusion. 相似文献
19.
Gaofei Chen Yaxiong An Yuanhui Shen Yayan Wang Zhongli Tang Bo Lu Donghui Zhang 《中国化学工程学报》2020,28(4):1062-1068
In this paper, a model of activated carbon was established by molecular simulation and the separation performance of N_2 and CH_4 on activated carbon was studied. In order to evaluate the adsorption selectivity and diffusion selectivity of N_2 and CH_4, Grand Canonical Monte Carlo and molecular dynamic methods were used to obtain equilibrium adsorption isotherms and mean square displacements of N_2 and CH_4 on activated carbon with different pore sizes. Research results showed that the difference in adsorption isosteric heat of N_2 and CH_4 at the pore size of 0.46 nm is the largest, which is 5.759 and 7.03 kcal·mol~(-1)(1 cal=4.184 J), respectively. Activated carbon with pore size of 0.46 nm has the best N_2 and CH_4 adsorption selectivity, while its diffusion selectivity is not obvious. 相似文献
20.
Adsorption of Remazol Red B on activated carbon prepared from olive stone and commercial activated carbon from aqueous solutions was compared. Different activating agent (ZnCl2) amounts and adsorbent particle size were studied to optimize adsorbent surface area. The adsorptive property of commercial activated carbon and activated carbon prepared from olive stone were investigated in terms of adsorbent dose, temperature, equilibrium time and pH. Then the obtained results were compared for all parameters, According to the results, the equilibrium time, optimum pH, adsorbent dosage were found 60 min, pH < 3–4 and 1.0 g/50 ml respectively. Lower adsorption capacity for RRB on activated carbon prepared from olive stone was found. The kinetic data for both adsorbents supports pseudo-second order model (r2 > 0.99) and intra-particle model (r2 > 0.95) but the first order kinetic model did not adequately fit to the experimental values (r2 < 0.76). The equilibrium adsorption data were interpreted using Langmuir and Freundlich models. The adsorption of Remazol Red B was better represented by the Langmuir equation. In addition, the thermodynamic parameters, standard free energy (ΔG°), standard enthalpy (ΔH°), standard entropy (ΔS°) of the adsorption process were calculated for both adsorbents. To reveal the adsorptive characteristics of the produced active carbon, surface area measurements were carried out and structural analysis was performed using SEM-EDS. 相似文献