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81.
82.
Field experiments were conducted at Al-Qatif area in the eastern region of Saudi Arabia to study the status and availability of B under B fertilization regime in three types of calcareous soils and to evaluate the response of two alfalfa varieties, Hassawi (local variety) and Hyden (american variety), to increasing levels of added B.Boron was applied at 7 rates as Na2B4O7.10H2O. Four cuttings were taken from each site at different intervals. Data showed that extractable B by hot-water and NH4HCO3-DTPA (8 days after borax application) was significantly (p <0.001) affected by soil type and B applications. The amount of B recovered by hot-water from the three soils, 200 days after borax application, was in the following order: sandy loam > sandy clay loam > clay loam.Total dry matter of alfalfa (4 cuttings) was significantly (p <0.05) affected by soil type, borax application rates and alfalfa variety.The critical level of B in plant as determined by Cate and Nelson analysis, ranged from 148 to 652 mg kg–1 dry matter for Hassawi cultivar and 138 to 521 mg kg–1 for Hyden cultivar in the first harvest. However, the upper critical levels for the 2nd, 3rd and 4th harvests were 800, 875 and 935 mg B kg–1 dry matter for Hassawi and 603, 723 and 812 mg B kg–1 for Hyden varieties, respectively. Nevertheless, the lower critical levels for 2nd, 3rd and 4th harvests ranged from 148 to 153 mg B kg–1 dry matter for Hassawi and 138 to 142 mg B kg–1 for Hyden. 相似文献
83.
制备了含10vol%,20vol%及30vol%SiC晶须的Si_3N_4基复合材料,对其室温及高温机械强度的测试研究表明,SiC晶须对基体的高温机械性能有明显的增强作用。含20vol%SiC晶须的复合材料1200℃下强度达780MPa,比基体材料提高50%。通过SEM和TEM研究,讨论了SiC晶须增强的原因。 相似文献
84.
The influence has been studied of the partial pressure of hydrogen (0–30 kPa) upon the coking rate of a Cr2O3/Al2O3 commercial catalyst during 1-butene dehydrogenation. Coke deposition has been analysed using a monolayer-multilayer reversible coke growth model (MMRC model). This model provides good fits to the experimental data, within the range of partial pressure of H2 studied, and allows us to estimate the main kinetic parameters involved in the coking-deactivation process. The results obtained reveal a dual effect of hydrogen: competition against 1-butene for the active sites and the removal of coke precursors from the catalyst surface. Bom effects diminish the coking rate as the H2 partial pressure is increased. 相似文献
85.
A kinetic study for the one-step conversion of synthesis gas to gasoline on a ZnO–Cr2O3–ZSM-5 catalyst is described. On this catalyst, three reactions are involved in the overall transformation of synthesis gas: the methanol synthesis, the conversion of methanol to hydrocarbons and the water–gas shift reaction. Under the operating conditions selected for the study, it was found that the water–gas shift was at equilibrium and the methanol was completely converted to hydrocarbons. Consequently, it was postulated that the kinetics of the limiting reaction step, the methanol synthesis on the ZnO–Cr2O3 component, was the one that controls the overall reaction rate. Three kinetic model equations describing the rate of synthesis gas conversion on the bifunctional catalyst, were considered to fit the data of the experimental runs performed in a Berty well-mixed reactor. Those equations were derived under very special conditions where the methanol decomposition term could be neglected. It was also observed that in the kinetic equations a term involving the fugacity of CO2 was required to predict the rate properly. The catalyst deactivation was also taken into account in the analysis. 相似文献
86.
Ragnar Larsson 《Catalysis Letters》1991,10(3-4):317-324
Kinetic data on the exchange reaction betwee hexane and deuterium have recently been reported by Maier and coworkers [1]. The reaction was catalysed by a series of platinum or rhodium systems, some of which had the property that the upper surface was shielded by a silica overlayer. The data are reinterpreted to indicate an isokinetic temperature of 580 K. This observation indicates that all the catalysts behave in a similar manner, which means that the exchange reaction does not require a free metal surface. 相似文献
87.
A novel sol–gel method based on V2O5·nH2O hydro-gel was developed to synthesize nanocrystalline Li3V2(PO4)3/carbon composite material. In this route, V2O5·nH2O hydro-gel, NH4H2PO4, Li2CO3 and high-surface-area carbon were used as starting materials to prepare precursor, and the Li3V2(PO4)3/carbon was obtained by sintering precursor at 750 °C for 4 h in flowing argon. The sol–gel synthesis ensures homogeneity of the precursors and improved reactivity. The sample was characterized by XRD, SEM and TEM. X-ray diffraction results show Li3V2(PO4)3 sample is monoclinic structure with the space group of P21/n. The TEM image indicates that the Li3V2(PO4)3 particles modified by conductive carbon are about 70 nm in diameter. The Li3V2(PO4)3/carbon system showed that the discharge capacities in the first and 50th cycle are about 155.3 and 143.6 mAh/g, respectively, in the range of 3.0–4.8 V. The sol–gel method is fit for the preparation of Li3V2(PO4)3/carbon composite material which may offer some favorable properties for commercial application. 相似文献
88.
Gas hold-up structure was studied in a three phase sparged reactor of 200 mm diameter. Air and aqueous solutions of carboxymethyl cellulose were used as gas and liquid phases. Spherical glass beads formed the solid phase. The superficial gas velocity, rheological properties, particle size and solid loading were varied over a wide range and their effects on gas hold-up structure were studied. A correlation for the estimation of the gas hold-up as a function of superficial gas velocity, apparent liquid viscosity, particle settling velocity and solid loading was established. 相似文献
89.
90.