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1.
A sample pretreatment procedure for the dry radioactive waste such as paper, cotton, vinyl, and plastic generated from nuclear power plants (NPPs) was established to determine the activity concentrations of 60Co and 137Cs. Because the volatility of cesium is temperature-dependent, the heating temperature was examined from 300 to 650 °C. Although the cesium was not volatile until 500, 450 °C was selected to save time. Cesium with a paper towel and a planchet of stainless steel were quantitatively recovered at 450 °C. The produced ash was completely dissolved with 10 mL of HNO3, 4 mL of HCl, and 0.25 mL of HF in a high-performance microwave digestion system using a nova high temperature rotor at 250 °C for 90 min until 0.2 g was reached. This procedure was applied to low and intermediate level radioactive wastes generated from NPPs.  相似文献   

2.
Batch equilibrium studies were conducted at 20 ± 0.5 °C with indigenously synthesized spherical resorcinol–formaldehyde resin beads, using radioanalytical technique, to determine their capacity for sorption of cesium ions from alkaline medium. Equilibrium isotherm studies were carried out, by varying the initial concentrations of cesium from 0.1 to 50 mM. The liquid-to-solid phase ratio of ~100 ml:1 g was maintained for all the sorption experiments. The equilibrium data were fitted to Langmuir and Freundlich isotherm models. It was observed that Freundlich isotherm explains sorption process nicely. The effect of resin size on percentage cesium ion uptake was also investigated, and 20–40 mesh size was found to be the optimum particle size. The cesium sorption capacity of the beads was determined to be ~238 mg/g. The kinetics of the sorption was studied at different initial cesium ion concentrations, and the kinetics data were fitted into various kinetics models. The kinetics of the cesium ion sorption was found to be pseudo second-order. The mechanistic steps involved were found to be complex, consisting of both film diffusion and intraparticle diffusion with film diffusion as the rate limiting step.  相似文献   

3.
Vesicles composed of N-[3-(dimethylamino) propyl]-octadecanamide (DMAPODA) and 2-(hexadecyloxy) cinnamic acid (HOCA) in an equimolar ratio were prepared by taking advantage of salt bridge formed between the amino group and the carboxylic group. The structure of vesicle was observed on a Transmission electron microscopy (TEM), and the size was determined on a dynamic light scattering equipment. The phase transition of the vesicular membrane was found to be around 35 °C on a differential scanning calorimeter. HOCA of the vesicular membrane was readily dimerized under the irradiation of a UV light (λ?=?254 nm, 6 W). The release degree of rhodamine B from vesicle suspended in distilled water (pH 6.8) was about 70 % in 1 h at 25 °C, and the UV irradiation during the release experiment had little effect on the release degree. However, it had a significant effect when the temperature of release medium was 40 °C. Upon the photodimerization, HOCA would readily change its orientation in the vesicular membrane vesicle at 40 °C, possibly because the vesicular membrane is in a liquid crystalline state at the temperature, which is higher than the phase transition temperature (around 35 °C). In addition, the vesicle released rhodamine B in a pH-dependent manner. The release degrees were the highest at pH 3.0 and the lowest at pH 9.0 among the pH values tested. The salt bridge formed between DMAPODA and HOCA is labile at a strong acidic condition so it would be responsible for the extensive release at pH 3.0.  相似文献   

4.
In this research, 24 of water-in-diesel fuel nanoemulsions were prepared using mixed nonionic surfactants of sorbitan monooleate and polyoxyethylene sorbitan trioleate (MTS). The emulsions were formed using a new modified low-energy method at hydrophilic-lipophilic balance (HLB) value of 10 and a working temperature of 20°C. Five HLB values of 9.6, 9.8, 10, 10.2, and 10.4 were prepared to identify the optimum value that gives low water droplet size at working conditions as: 5 wt% of water contents, 10 wt% of mixed surfactant concentration, and a temperature of 20°C. The effect of mixed surfactant concentration and water content on the droplet size for 0, 15, 30, 60, and 90 days has been studied. Droplet size of the prepared nanoemulsions was determined by dynamic light scattering and the nanoemulsion stability was assessed by measuring the variation of the droplet size as a function of time. Results show that the mean droplet sizes were formed between 26.23 and 277.1 nm depending on the surfactant concentrations, water contents, and storage time.  相似文献   

5.
Electrochemical characteristics of single cell performances at various humidity conditions and constant temperatures of 40?100 °C using membrane electrode assemblies (MEAs) were studied. The MEAs consist of alternative proton-conducting hybrid membrane electrolyte and noble Pt/C catalyst for the H2/O2 proton exchange membrane fuel cells (PEMFCs). The function of humidity on the cell performances was investigated at larger current density values of 501 mA cm?2 and constant cell temperatures of 80 and 90 °C and the relative humidity of 100 %. The power density value of 400 mW cm?2 was obtained when the same MEA at similar operating conditions was used. The effects of temperature on the single cell performances were investigated at various temperature ranges of 40–100 °C and constant relative humidity of 50, 70, and 100 %. The maximum current density and power density values of about 600 mA cm?2 and 160 mW cm?2, respectively, were obtained at 90 °C with 100 % RH. The results were compared with the reported results of Nafion membrane and similar hybrid membranes operating at low temperatures for H2/O2 fuel cells. Finally, the results provided an alternative proton-conducting electrolyte as promising candidate for low/intermediate temperature operating H2/O2 fuel cells.  相似文献   

6.
In this paper, novel low-cost oxygen carriers containing Fe2O3 are evaluated for use in chemical looping combustion. Sewage sludge ashes and reference samples were prepared and used in cyclic reduction and oxidation experiments in a thermogravimetric analyzer (TG). A gaseous (3 % H2) fuel and a solid fuel (hard coal) were tested. Three-cycle CLC tests were carried out in the 600–800 °C temperature range and long-term testing was performed at 950 °C. A reactivity study showed that the natural sewage sludge ash sample was stable during the cycling TG tests when hydrogen was used as a fuel at all of the temperatures investigated. Strong temperature effects on the oxygen transport capacity were observed. An one-cycle test at 900 °C showed also that the sewage sludge ash successfully reacted with coal. The oxygen released was fully used for coal combustion, with appreciable reaction rate at temperature of ~750–800 °C, that is significantly lower than that obtained for pure Fe2O3-based oxygen carrier. The oxidation reaction was much faster than the reduction reaction. Moreover, the sewage sludge ash showed a low tendency toward agglomeration in the cyclic test, which was superior to the behavior of synthetic materials. The sewage sludge ash exhibited also high mechanical strength, an attrition index of 1 % and a high-temperature resistance of 1,170 °C in a reducing atmosphere. We conclude that sewage sludge ash can be effectively used as a low-cost, valuable oxygen carrier in practical application in chemical looping combustion technology for power generation.  相似文献   

7.
Novel reprocessing schemes and techniques are the focus of the Euratom FP7 project “Actinide Recycling for Separation and Transmutation” (ACSEPT), where the Paul Scherrer Institute (PSI) is represented in the pyrochemical domain. The subject of investigation is the selective separation of fission products (FPs) from spent nuclear fuel as a head-end step to either classical hydro based or pyro processes which are not yet applied on a large scale. The selective removal of FPs that are major contributors to the overall radiation dose or bear great potentials in terms of radiotoxicity (i.e. cesium or iodine), is advantageous for further processes. At PSI a device was developed to release volatile FPs by means of inductive heating. The heating up to 2,300 °C promotes the release of material that is further transported by a carrier gas stream into an inductively coupled plasma mass spectrometer for online detection. The carrier gas can be either inert (Ar) or can contain reducing or oxidizing components like hydrogen or oxygen, respectively. The development of the device by computer aided engineering approaches, the commissioning and evaluation of the device and data from first release experiments on a simulated fuel matrix are discussed.  相似文献   

8.
The availability of stable polymeric membranes with good proton conductivity at medium temperatures is very important for the development of methanol PEM fuel cells. In view of this application, a systematic investigation of the conductivity of Nafion 117 and sulfonated polyether ether ketone (S-PEEK) membranes was performed as a function of relative humidity (r.h.) in a wide range of temperature (80–160°C). The occurrence of swelling/softening phenomena at high r.h. values prevented conductivity determinations above certain temperatures. Nevertheless, when r.h. was maintained at values lower than 80%, measurements were possible up to 160°C. The results showed that Nafion is a better proton conductor than S-PEEK at low r.h. values, especially at temperatures lower than 120°C. The differences in conductivity were, however, leveled out with the increasing r.h. and temperature. While at 100°C and 35% r.h. the conductivity of S-PEEK 2.48 was about 30 times lower than the conductivity of Nafion, both membranes reached a comparable conductivity (4×10−2 S cm−1) at 160°C and 75% r.h. The effect of superacidity and crystallization of the polymers on the conductivity, as well as the possibility of using Nafion and S-PEEK membranes in medium temperature fuel cells, are discussed.  相似文献   

9.
The present study deals with PEM fuel cells, namely with the optimization of the hot pressing process for membrane electrode assembly (MEA) fabrication. Designs of experiments (DoE) have been used for evaluating the effect of hot pressing parameters (pressure, temperature, and time) on the MEA electrical performances. Full factorial 23 DoE showed that the most important parameter is the pressing temperature. Surface response methodology indicated a non-monotonous behavior of the MEA electrical performances with respect to the pressing temperature. The MEA electrical performances increased with the pressing temperature in the temperature range from 100 to 115 °C, and decreased significantly in the temperature range from 115 to 130 °C. This behavior was attributed to drastic changes of the Nafion® 112 membrane properties and membrane/electrode interface over this temperature range. Observations of the MEA cross-section structure by scanning electron microscopy confirmed such hypotheses. Thermo-mechanical properties of Nafion® as determined by dynamic scanning calorimetry allowed estimating the glass transition temperature at ca. T g?≈?117 °C in the conditions of the present study. The higher H2/air fuel cell performance of ca. 0.8 W cm?2 was obtained with the optimized pressing temperature for MEA fabrication of ca. 115 °C close to the T g temperature of Nafion® 112, whereas for higher temperature the structure of the Nafion® membrane and of the membrane–electrode interface is damaged.  相似文献   

10.
Thermal cracking of waste cooking oil (WCO) for production of liquid fuel has gained special interest due to the growing demand of renewable fuel, depleting fossil fuel reserves and environmental issues. In the present work, thermal cracking of WCO to produce liquid hydrocarbon fuels without any preprocessing has been studied. Moreover, non-isothermal kinetics of WCO using thermogravimetric analysis (TGA) has been studied under an inert atmosphere at various heating rates. According to TGA result, active thermal decomposition of WCO was found to be between 318 and 500 °C. Furthermore, the temperature at which the maximum mass loss rate attained was shifted to higher values as the heating rates increased from 10 to 50 °C min?1 and the values were found to be approximately similar to that of R 50. Besides, model-free iso-conversion kinetic methods such as Friedman (FM), Kissinger–Akahira–Sunose (KAS) and Flynn–Wall–Ozawa (FWO) were used to determine the activation energies of WCO degradation. The average activation energy for the thermal degradation of WCO was found to be 243.7, 211.23 and 222 kJ mol?1 for FM, KAS and FWO kinetic methods, respectively. Additionally, the cracking of WCO was studied in a semi-batch reactor under an inert atmosphere and the influences of cracking temperature, time and heating rates on product distribution were investigated. From the reaction, an optimum yield of 72 mass% was obtained at a temperature of 475 °C, time of 180 min and a heating rate of 10 °C min?1. The physicochemical properties studied were in accordance with ASTM standards.  相似文献   

11.
Hydrothermal reaction experiments of silicate minerals (actinolite, pyroxene, etc.) were carried out using flow-through reactors in the temperature range from 25 to 400 °C at 23 MPa. The dissolution in water of a multi-oxide silicate mineral, for example actinolite or pyroxene may require the breaking of more than one type of metal?Coxygen bond. Differences between the rates at which these bonds break are often sufficiently large for dissolution to be non-stoichiometric. Dissolution rates (of Si) for actinolite and pyroxene in water were found to increase with increasing T from 25 to 300 °C, and then decrease with increasing T from 300 to 400 °C. The maximum release rates of Si are reached at 300 °C. The different metals in the minerals often have different release rates at a fixed temperature. At T < 300 °C the release rates of Na, Ca, Mg, Fe, and Al from minerals are usually higher than that of Si. In contrast, release rates of Si are higher than those of the others at T ?? 300 °C. The hydrolysis of Si?CO?CSi bonds and metal ion-H+ exchange reactions at T < 300 °C are different from reactions at T ?? 300 °C, at 23 MPa, because the solvent properties of water (decreasing density and dielectric constant in the region from sub-critical to supercritical state) affect reaction rates. log r (dissolution rates of Si) increases with 1/dielectric constant, as the temperature rises to close to 300 °C (or up to 374 °C) and at the critical pressure.  相似文献   

12.
An in situ pyrolysis process of high moisture content lignite in an autogenerated steam agent was proposed. The aim is to utilize steam autogenerated from lignite moisture as a reactant to produce fuel gas and additional hydrogen. Thermogravimetric analysis revealed that mass loss and maximum mass loss rate increased with the rise of heating rates. The in situ pyrolysis process was performed in a screw kiln reactor to investigate the effects of moisture content and reactor temperature on product yields, gas compositions, and pyrolysis performance. The results demonstrated that inherent moisture in lignite had a significant influence on the product yield. The pyrolysis of L R (raw lignite with a moisture content of 36.9 %, wet basis) at 900 °C exhibited higher dry yield of 33.67 mL g?1 and H2 content of 50.3 vol% than those from the pyrolysis of the predried lignite. It was also shown that increasing reaction temperature led to a rising dry gas yield and H2 yield. The pyrolysis of L R showed the maximum dry yield of 33.7 mL g?1 and H2 content of 53.2 vol% at 1,000 °C. The LHV of fuel gas ranged from 18.45 to 14.38 MJ Nm?3 when the reactor temperature increased from 600 to 1,000 °C.  相似文献   

13.
The fire that occurred at ALA nightclub was the deadliest nightclub fire in Taiwan. This study used the ALA nightclub fire as a case study and conducted a burning test based on the official fire investigation report. Fireworks that had been used during the performance were the cause of fire. Their heat release rate is approximately 180 kW, and the flame temperature is 300 °C. Soundproof foam collected from the fire debris was used to conduct a thermal analysis experiment under two different heating rates. In addition, related studies were referenced. It was found that when the sample was heated to between 45 and 55 °C, pyrolysis reaction started and the sample started to release harmful substances. The burning behavior of soundproof foam is considered ultrafast. When the heating temperature reaches between 225 and 370 °C, the sample releases 1,819.09–2,894.59 J g?1 of heat. It is evident that it poses a serious degree of thermal hazard. Finally, it is recommended that the emergency egress time in entertainment establishments such as nightclubs should be kept between 60 and 90 s or less as a reference for fire safety strategies for nightclubs.  相似文献   

14.
Low temperature lithium titanate compounds (i.e., Li4Ti5O12 and Li2TiO3) with nanocrystalline and mesoporous structure were prepared by a straightforward aqueous particulate sol–gel route. The effect of Li:Ti molar ratio was studied on crystallisation behaviour of lithium titanates. X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR) revealed that the powders were crystallised at the low temperature of 500 °C and the short annealing time of 1 h. Moreover, it was found that Li:Ti molar ratio and annealing temperature influence the preferable orientation growth of the lithium titanate compounds. Transmission electron microscope (TEM) images showed that the average crystallite size of the powders annealed at 400 °C was in the range 2–4 nm and a gradual increase occurred up to 10 nm by heat treatment at 800 °C. Field emission scanning electron microscope (FE-SEM) analysis revealed that the deposited thin films had mesoporous and nanocrystalline structure with the average grain size of 21–28 nm at 600 °C and 49–62 nm at 800 °C depending upon the Li:Ti molar ratio. Moreover, atomic force microscope (AFM) images confirmed that the lithium titanate films had columnar like morphology at 600 °C, whereas they showed hill-valley like morphology at 800 °C. Based on Brunauer–Emmett–Taylor (BET) analysis, the synthesized powders showed mesoporous structure containing pores with needle and plate shapes. The surface area of the powders was enhanced by increasing Li:Ti molar ratio and reached as high as 77 m2/g for the ratio of Li:Ti = 75:25 at 500 °C. This is one of the smallest crystallite size and the highest surface areas reported in the literature, and the materials could be used in many applications such as rechargeable lithium batteries and tritium breeding materials.  相似文献   

15.
Mutations at codons 248 and 249 of p53 gene showed a relatively high incidence in gastric cancer patients. Development of novel methods for the detection of codon mutations is of great importance for gastric cancer research. Studies have showed that the separation matrix can significantly influence the separation efficiency and resolution of small DNA fragments in CE. In order to achieve baseline separation of PCR-amplified products of small DNA fragments from gastric cancer tissue, linear polyacrylamides (LPA I and LPAII) were designed and synthesized in the current study. LPAI and LPAII were used as separation matrixes to separate small size fragments (less than 70 bp) of pBR322/BsuRI DNA Marker and the separation conditions were optimized. Optimum separations were performed at 25 kV in reversed-polarity mode with capillary temperature set at 15 °C. The signal of DNA fragments was detected using laser-induced fluorescence detector, with an argon ion laser as the excitation source that emits at 488 nm. A 520 nm bandpass filter was used as an emission cut-off filter. The resolution of small DNA fragments was higher when LPAI was used as separation matrix compared to LPAII, accompanied with longer migration time. The results indicated that LPAI as separation matrix was more efficient for the separation of small DNA fragments (less than 70 bp) than other LPAs. A rapid and sensitive analysis method for the separation and detection of small DNA fragments (less than 70 bp) was established in this study. The method was successfully applied to detect the mutations at codons 248 and 249 in p53 gene from gastric cancer tissues.  相似文献   

16.
Pechini method is a materials synthesis method based on the preparation of a polymeric matrix. The advantage of this method is the ability to obtain materials with different particle sizes depending on the synthesis condition with a homogeneous distribution. In this work, carbonated hydroxyapatite (c-OHAp) nanoparticles were obtained by a modified Pechini method. To obtain the polymeric precursor of the c-OHAp, the polymeric matrix was prepared through a polyesterification reaction between citric acid and ethylene-glycol. Adding calcium hydroxide and ortophosphoric acid in aqueous solutions, raising the temperature up to 140 °C/2 h and keeping constant the pH at 8. The polymeric matrix was calcinated at different ranges of temperature from 200 to 600 °C in order to obtain the c-OHAp powder. The results show the presence of c-OHAp a as unique phase. The thermal analysis indicates that the c-OHAp phase was obtained at 600 °C. The particle size of the obtained material was <50 nm.  相似文献   

17.
A series of thermoresponsive sodium alginate-g-poly(vinyl caprolactam) (NaAlg-g-PNVCL) beads were prepared as drug delivery matrices of 5-flurouracil (5-FU) crosslinked by glutaraldehyde (GA) in the hydrochloric acid catalyst. Graft copolymers of sodium alginate with vinyl caprolactam were synthesized using azobisisobutyronitrile as an initiator, and characterized by Fourier infrared spectroscopy, differential scanning calrimetry and X-ray diffraction for analysis of the amorphous nature drug in the beads, and by scanning electron microscopy for the spherical nature of the beads. Preparation condition of the beads was optimized by considering the percentage of encapsulation efficiency, swelling behavior of beads and their release data. Effects of variables such as GA concentration, drug/polymer ratio and catalyst concentration on the release of 5-FU were carried out at two different temperatures (25 and 37 °C) in simulated intestinal fluid for 12 h. It was observed that, drug release from the beads decreased with increasing drug/polymer (d/p) ratio, extent of crosslinking agent and catalyst concentration. The swelling degree of graft copolymer beads was found to be increased with decreasing of environmental temperature. In vitro release studies were performed at 25 and 37 °C for 12 h, and showed that thermoresponsive graft copolymer beads had higher drug release behavior at 25 °C than that at 37 °C, following Fickian diffusion transport mechanism with slight deviation.  相似文献   

18.
Efficiency in HPLC can be enhanced by increasing the column length and/or decreasing the particle size. The use of high temperature in HPLC has emerged as a valuable tool to overcome the increase in column backpressure when using small packing particles, as it allows for reduction in mobile phase viscosity. In this study, high plate count was obtained by coupling sub-2 ??m columns at elevated temperature to reduce the viscosity of the mobile phase, thus reducing the column backpressure. At 80 °C, up to three columns of 15 cm × 4.6 mm I.D. packed with 1.8 ??m particles could be coupled generating ~84,000 theoretical plates for the last eluting compound. The number of theoretical plates was increased on average by a factor of ~3.6 when three columns were coupled at 80 °C compared with one column at 30 °C. The relationships between separation efficiency and column length were examined using Van Deemter plots constructed at 30 °C and 80 °C for different column lengths. The advantages of using coupled columns in combination with elevated temperature for the environmental analysis were illustrated using test mixtures comprised of eight sulfonamides separated on one column at 30 °C and three coupled columns at 80 °C by isocratic elution. Sample clean up was carried out by employing solid-phase extraction (SPE) using Oasis HLB cartridges. The method developed was validated based on parameters such as linearity, precision, accuracy, detection and quantification limits. Recoveries generally ranged from 71.7 to 99% (with the exception of sulfanilamide), with standard deviations not higher than 4.7%. The detection limits of the method ranged from 0.6?C2 ??g L?1, while limits of quantification were in the range 2?C6.7 ??g L?1 with UV detection.  相似文献   

19.
Phase equilibria and critical phenomena in the cesium nitrate-water-diethylamine ternary system were studied by the visual-polythermal method over the temperature range 60–150 °C, where the boundary binary liquid system was characterized by stratification with a lower critical solution temperature (LCST). The introduction of cesium nitrate into the water-diethylamine system decreased the LCST of this system from 146.1 to 69.3°C and lowered the mutual solubility of the components. The diethylamine distribution coefficients between the aqueous and organic phases were calculated for monotectic equilibria at various temperatures. The salting out of diethylamine with cesium nitrate grew stronger as the temperature increased. The conclusion was drawn that the isotherms of the phase states of the system substantiated the generalized scheme of topological transformations of phase diagrams for salt-binary solvent ternary systems with salting out. The salting out effects of cesium and potassium nitrates on the water-diethylamine binary system were compared.  相似文献   

20.
《Analytical letters》2012,45(2):393-408
Abstract

In this research, new electrodes were prepared by incorporating zeolite KY into sol-gel matrix. Calibration plot with Nernstian slope (58.6 ± 0.5 mV/decade) for cesium ion was observed over a linear range of about four decades of concentration (1.0 × 10?5 to 1.0 × 10?1 M, at 25°C). The sol-gel electrode shows detection limit of 7.3 × 10?6 M. The influences of membrane composition, the pH of the test solution, and the interfering ions on the electrode performance were investigated. The effect of temperature on the electrode response showed that the temperature higher than 60°C deteriorates the electrode performance. The proposed electrode has high mechanical and thermal stability with a low isothermal temperature coefficient, and it is 0.00018 V/°C. It has a short response time (10 s) and can be used for more than 6 months without any considerable divergence in the potentials. The selectivity coefficients for Cs+ ion with respect to alkali, alkaline earth, ammonium, and some heavy-metal ions were investigated. The results of application show that the electrode can be used successfully in determination of Cs+ ions in various water samples.  相似文献   

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