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排序方式: 共有4269条查询结果,搜索用时 46 毫秒
41.
Gamal A. M. Hussein 《Powder Technology》1994,80(3):265-270
The thermal decomposition up to 400 °C of ammonium ferric citrate hydrate, of unknown structure and formula weight, was studied by thermogravimetry, differential thermal analysis, infrared (IR) spectroscopy and X-ray diffractometry. The possible identities of the formula weight and the intermediate products of calcination are discussed. The results revealed that the parent material is amorphous and contains two moles of water and two moles of ammonia. Decomposition takes place via six weight-loss processes, three endothermic (90–230 °C) and three exothermic (240–298 °C), leading eventually to the formation of Fe2O3. The intermediate solid products are mainly unstable amorphous oxycarbonates, as indicated by X-ray and IR spectroscopies. The gas-phase decomposition products identified by IR spectroscopy are NH3, CO2, CO, CH3COCH3, CH4 and NH4OH. Surface area measurement and scanning electron microscopy showed that Fe2O3, the final product at 400 °C, hada surface area of 40 m2/g and good crystalline and porous character. 相似文献
42.
George M. Campbell 《Chemical Engineering Communications》1990,98(1):223-230
The room temperature adsorption of PuF6(g) on a solid substrate was compared to the adsorption of UF6(g) on the same surface. Significantly more PuF6(g) was adsorbed at pressures in the range of 1.2 to 0.2torr, accompanied by the evolution of molecular fluorine. The adsorbed UF6 was easily desorbed by reducing the pressure. Most of the adsorbed PuF6 remained on the surface when subjected to the same treatment. 相似文献
43.
《Expert systems with applications》2014,41(3):886-892
This work presents a comparative analysis of specific, rather than general, mathematical programming implementation techniques of the quadratic optimization problem (QP) based on Support Vector Machines (SVM) learning process. Considering the Karush–Kuhn–Tucker (KKT) optimality conditions, we present a strategy of implementation of the SVM-QP following three classical approaches: (i) active set, also divided in primal and dual spaces, methods, (ii) interior point methods and (iii) linearization strategies. We also present the general extension to treat large-scale applications consisting in a general decomposition of the QP problem into smaller ones, conserving the exact solution approach. In the same manner, we propose a set of heuristics to take into account for a better than a random selection process for the initialization of the decomposition strategy. We compare the performances of the optimization strategies using some well-known benchmark databases. 相似文献
44.
A deterministic model for multipurpose, multiperiod batch plants was presented in a linearized form to predict the future
design according to the change of demand by using a modified Benders’ Decomposition. The OSL code offered by the IBM corporation
as optimizer was employed for solving several example problems. The decomposition method was successful, showing remarkable
reduction in the computing times as compared with those of the direct solution method. Also the heuristic used as a solution
approach for the multiperiod model provided an efficient methodology to the block-structured problem by dividing the large
overall problem into the manageable single period blocks. 相似文献
45.
46.
The decomposition of hexachlorobenzene (HCB) has been investigated over ultrafine Ca–Fe composite oxide catalyst (Ca/Fe atomic
ratio was 3.4), CaO and α-Fe2O3 by using in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). Adsorption experiments on the surface
of oxides monitored by in situ DRIFTS showed that partial oxidation products, i.e., phenolate and acetate species were formed
on the surface of Ca–Fe composite oxide. The further studies indicated that Ca–Fe composite oxide catalyst was easier to induce
the rupture of C–Cl bond and C–C bond of aromatic rings. The best catalytic activity of Ca–Fe composite oxide may be related
to the acidity, which was determined by NH3–TPD. The products after reaction have been analyzed by XRD and chloride selective electrode. Ca–Fe composite oxide exhibited
the highest extent of mineralization for organic chlorine among the different oxides tested. The combined results of current
and previous experiments demonstrated that two competitive reactions took place during the decomposition process of HCB: (1)
hydrodechlorination resulting in the formation of lower chlorinated benzenes and (2) oxidation of aromatic rings leading to
the rupture of aromaticity and the formation of oxidation products. The latter is the major process in the coexisted competitive
reaction. A possible decomposition pathway was discussed. 相似文献
47.
Cobalt sulphide catalyst prepared via a new method involving the precipitation reaction between cobaltous acetate and ammonium sulphide solutions has been shown to be favourably active for the catalytic decomposition of H2S when compared with data for other transition metal sulphides.
The BET surface area of this unsupported catalyst is about an order of magnitude higher than cobalt sulphide formed by direct sulphidation of cobalt oxide with H2S gas. XRD, SEM and TEM analyses were used to obtain bulk composition and morphological characteristics. Catalyst specimen calcined at 823 K showed the best activity.
The kinetics of the decomposition reaction has been studied over this new preparation. Experiments conducted at atmospheric pressure between 933-983 K using about 11 feed compositions showed that below 40% H2S/Ar the reaction was essentially 1st order with respect to H2S partial pressure. Beyond this point, rate remained invariant with feed composition. A mechanism involving catalysis via co-ordinative unsaturation sites on the CoS was proposed and kinetic model based on the cleavage of the surface H-S bond as the rate-determining step appeared to be the most adequate representation of the rate data. Hydrogen production rates at all temperatures also paralleled the behaviour seen for H2S decomposition. Activation energy for H2S decomposition and H2 production rates were estimated as 111 kJ mol-1 and 88 kJ mol-1 respectively 相似文献
The BET surface area of this unsupported catalyst is about an order of magnitude higher than cobalt sulphide formed by direct sulphidation of cobalt oxide with H2S gas. XRD, SEM and TEM analyses were used to obtain bulk composition and morphological characteristics. Catalyst specimen calcined at 823 K showed the best activity.
The kinetics of the decomposition reaction has been studied over this new preparation. Experiments conducted at atmospheric pressure between 933-983 K using about 11 feed compositions showed that below 40% H2S/Ar the reaction was essentially 1st order with respect to H2S partial pressure. Beyond this point, rate remained invariant with feed composition. A mechanism involving catalysis via co-ordinative unsaturation sites on the CoS was proposed and kinetic model based on the cleavage of the surface H-S bond as the rate-determining step appeared to be the most adequate representation of the rate data. Hydrogen production rates at all temperatures also paralleled the behaviour seen for H2S decomposition. Activation energy for H2S decomposition and H2 production rates were estimated as 111 kJ mol-1 and 88 kJ mol-1 respectively 相似文献
48.
The effects of reaction temperature, pressure and residence time were investigated with a flow apparatus. Cellobiose decomposition
kinetics and products in suband supercritical water were examined at temperatures from 320 to 420 °C at pressures from 25
to 40 MPa, and at residence times within 3 sec. Cellobiose was found to decompose via hydrolysis and pyrolysis. The yield
of desired hydrolysis product, glucose, was the maximum value of 36.8% at 320 °C, 35 MPa, but the amount of 5-(hydroxymethyl)furfural
(HMF), fermentation inhibitor increased too because residence time increased in the subcritical region owing to decrease of
reaction rate. Meanwhile, though the yield of glucose is low in the supercritical region, the yield of HMF decreased compared
with the subcritical region; and at the minimum yield of HMF (380 °C, 25 MPa), the yield of glucose was 21.4%. The decomposition
of cellobiose followed first-order kinetics and the activation energy for the decomposition of cellobiose was 51.05 kJ/mol
at 40MPa. 相似文献
49.
A fully continuous lab scale supercritical fluid extraction system has been designed, built and tested. The system continuously pumps carbon dioxide under supercritical conditions and soil slurry into a counter‐current contacting column. Delhi Loamy Sand, spiked with approximately 10 mg/g of naphthalene, was used as the testing soil. The soil slurry ranged from 0.0028 g dry soil per g slurry to 0.072 g/g. The operating temperature was 43°C and the operating pressure was 7.7 MPa. Near steady state, fully continuous flow was achieved with runs lasting as long as 2 h. All carbon dioxide samples contained measurable quantities of naphthalene and the measured mass transfer coefficients were as high as 4.6×10?4 s?1. 相似文献
50.
In this paper, a simple technique is proposed for face recognition among many human faces. It is based on the polynomial coefficients, covariance matrix and algorithm on common eigenvalues. The main advantage of the proposed approach is that the identification of similarity between human faces is carried out without computing actual eigenvalues and eigenvectors. A symmetric matrix is calculated using the polynomial coefficients-based companion matrices of two compared images. The nullity of a calculated symmetric matrix is used as similarity measure for face recognition. The value of nullity is very small for dissimilar images and distinctly large for similar face images. The feasibility of the propose approach is demonstrated on three face databases, i.e., the ORL database, the Yale database B and the FERET database. Experimental results have shown the effectiveness of the proposed approach for feature extraction and classification of the face images having large variation in pose and illumination. 相似文献