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1.
The thermal transformations of the products of hydrous aluminium nitrate hydrolysis in ammonia medium were studied by thermal analysis, mass spectrometry, infrared spectrophotometry, X-ray phase analysis, and sorption methods. Experiments have shown that the hydrolysis of hydrous aluminium nitrate in ammonia medium at pH=6-7 leads to the formation of boehmite. The degree of crystallinity of this product increases, if the hydrolysis is carried out for 264 h at 100°C, with respect the samples separated from the mother liquor just after completing the dosage of the reagents. It has also been found that aluminium oxide, obtained by thermal decomposition of the products of hydrolysis carried out for 264 h at an increased temperature, is characterized by a well developed specific surface, stable at high temperatures, amounting to about 100 m2 g-1, after calcination for 2 h at 1200°C. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

2.
Aluminium hydroxide was precipitated during a hydrolysis of aluminium perchlorate in ammonia medium. The materials were studied with the following methods: thermal analysis, IR spectroscopy, X-ray diffraction, low-temperature nitrogen adsorption and adsorption–desorption of benzene vapours. Freshly precipitated boehmite had a high value of SBET=211 m2 g–1 determined from nitrogen adsorption, good sorption capacity for benzene vapours, developed mesoporous structure and hydrophobic character. After prolonged refluxing at elevated temperature its crystallinity increased which was accompanied by an increase of specific surface determined from nitrogen adsorption up to 262m2g–1 , decrease of sorption capacity for benzene vapours and stronger hydrophobic character. The calcinations of all boehmites at temperature up to 1200°C resulted in formation of à-Al2O3 via transition form of γ-, δ- and θ-Al2O3. The samples of aluminium oxides obtained after calcination at 550 and 900°C were characterised with high values of specific surface area of 205–220 and 138–153 m2 g–1 , respectively. The SBET values calculated for the oxide samples derived from aged hydroxides and calcined at 1200°C are higher than for the analogous sample prepared without the ageing step. It was concluded that the process of ageing at elevated temperature developed thermal stability of aluminium oxides.  相似文献   

3.
The differential enthalpies of solution of sodium nitrate in water have been measured calorimetrically at 25°C, from 0.5 to 10.4 mol (kg H2O)–1. The concentration dependence is described by the equation H=20.4537+1.0562m1/2-7.0568m+2.8659m3/2-0.3382m2 From the calorimetric measurements, the enthalpy of crystallization of sodium nitrate was calculated as Hc=9.98±0.16 kL-mol-1. The literature data on the solubility, activity and osmotic coefficients of NaNO3 at 25°C yielded a value of –9.98±0.38 kJ-mol–1. The good agreement between the experimental and calculated Hc values indicate the reliability of the input data.  相似文献   

4.
A co-precipitation method was adopted for the immobilization of yttrium radioactive waste over crystalline titania. A high uptake of91Y was observed over the preformed hydrous titania. Weighable quantity of Y was coprecipitated with Ti(IV) hydroxide and a maximum of 38 wt% was found to be adsorbed. Mixed masses were calcined separately at 800 and 1000°C for 20 hours, and soxhlet leach tests at 97°C, repeated 7 times at an interval of 24 hours, showed the release of yttrium in the order of 10–1 and 10–2 g·m–2·d–1, respectively. X-ray powder diffraction analysis revealed that the yttrium was immobilized in the titania crystal lattice which suffered some structural changes with the formation of new mineral phase Y2Ti2O7 which is accompanied by rutile and little quantity of anatase form of titania at 800°C, and only rutile form of titania at 1000°C.  相似文献   

5.
Summary Measurements of the corrosion rate of aluminium in 2N HCl at 27°C with and without addition of phenyl semicarbazide derivatives (10–3–10–5 mol/l) were performed. The adsorption of these compounds was elucidated. Results show that phenyl semicarbazide derivatives are adsorbed on the aluminium surface according to the Frumkin isotherm. From the adsorption isotherm some thermodynamic data for the adsorption process (G° ads . andf) are calculated and discussed.
Phenylsemicarbazide als Korrosionsinhibitoren für Aluminium in salzsauren Lösungen
Zusammenfassung Es wurden Messungen der Korrosionsgeschwindigkeit von Aluminium in 2N HCl bei 27°C mit und ohne Zusatz von Phenylsemicarbaziden (10–3–10–5 mol/l) durchgeführt. Es wurde die Adsorption dieser Verbindungen untersucht, wobei sich zeigte, daß die Adsorption der Phenylsemicarbazidderivate der Frumkin-Isotherme gehorcht. Aus der Isotherme wurden einige thermodynamische Parameter des Adsorptionsprozesses (G° ads. ,f) berechnet.
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6.
An attempt to obtain aluminium hydroxide that could give aluminium oxides of increased thermal stability was made. Aluminium hydroxide was precipitated during a hydrolysis of aluminium chloride in ammonia medium. The influence of preparative conditions, such as a dosing rate of aluminium precursor, pH, duration of the precipitate refluxing and temperature of calcination, on the properties of obtained hydroxides and oxides was investigated. The materials were studied with the following methods: thermal analysis, IR spectroscopy, low-temperature nitrogen adsorption and adsorption–desorption of benzene vapours. Precipitated boehmites had high values of S BET determined from nitrogen adsorption (220–300 m2g–1), good sorption capacity for benzene vapours, developed mesoporous structure and hydrophilic character. It has been proved that a high pH value during the precipitation of aluminium hydroxide favoured better crystallisation of boehmite structure, higher temperature of its dehydroxylation into γ-Al2O3, and delayed transformation of γ phase into α-Al2O3. Aluminium oxides derived from the hydroxides precipitated at a high pH were the most stable at high temperatures, and were characterised with the best surface properties. The online version of the original article can be found at  相似文献   

7.
Hollow fibers formed from water glass and metal salts of IIA(Ca), VIIB(Fe, Co, Ni) and IB(Cu) groups were characterised in this study. Fragile fibres obtained herein broke down into small pieces during isolation and drying. Quantitative information about morphology, chemical composition and surface structure of the fibres were obtained. The diameter and wall thickness of the fibers were around 50 and 3 . respectively. They had particulate inner and smooth outer surfaces. Fibers had variable composition with metal (II) oxide/SiO2 ratio in the range 0.31 to 1.02. While group VIIB metal (II) fibres were amorphous, group IIA and IB metal (II) fibres were partially crystalline All the fibres had pores both in micro pore and meso pore region. The B.E.T surface area from N2 adsorption data was in the range of 10–249 m3 g–1 and 8–176 m2 g–1 from Langmuir and B.E.T models respectively.  相似文献   

8.
The removal behavior of hydrous titanium oxide and sodium titanate for Cs(I) from aqueous solutions by radiotracers was studied. Batch experiments revealed that an increase in Cs concentration (10–8 to 10–2 mol·dm–3), temperature (298 to 328 K) and pH (2.50 to 10.20) apparently enhanced the uptake of Cs(I) on hydrous titanium oxide whereas a high degree of uptake of Cs(I) on sodium titanate was almost unaffected by a change in adsorption temperature (298 to 328 K) and pH (2.50 to 10.20). Both systems follow Freundlich adsorption isotherm. Uptake of Cs(I) on hydrous titanium oxide obeys first order rate law. According to thermodynamic data the uptake is endothermic and apparently irreversible in nature.This revised version was published online in November 2005 with corrections to the Cover Date.  相似文献   

9.
Specific heats and apparent molar heat capacities of aqueous 1,1,1,3,3,3-hexafluoroiso- proanol (HFIP) have been determined at temperatures from 20.0 to 45.0°C using micro differential scanning calorimetry in the molality range of 0.06741 to 1.24053 mol-kg– 1. Densities and apparent molar volumes have also been determined for aqueous HFIP at temperatures from 10.3 to 30.0°C using digital densimetry in the molality range of 0.04009 to 0.67427 mol-kg– 1. The results of these measurements have been used to calculate the following partial molar quantities and temperature derivatives for aqueous HFIP as a function of temperature: Cp,2,m°, (Cp,2,m°/T)p, (2Cp,2,m°/T2)p, V2,m° and (V2,m°/T)p. The contribution of the — F atom to the partial molar heat capacity and volume has been calculated. The results have been explained in terms of structural changes in water in aqueous HFIP solution. The results obtained in this work contain essential information needed for the development of an equation of state for this system, when used in combination with other thermodynamic properties of aqueous HFIP.  相似文献   

10.
During precipitation and calcination at 200°C nanocrystalline Co3O4 was obtained with average size crystallites of 13 nm and a well developed specific surface area of 44 m2 g?1. A small addition of a structural promoter, e.g. Al2O3, increases the specific surface area of the cobalt oxide (54 m2 g?1) and decreases the average size of crystallites (7 nm). Al2O3 inhibits the reduction process of Co3O4 by hydrogen. Reduction of cobalt oxide with aluminium oxide addition runs by equilibrium state at all the respective temperatures. The apparent activation energy of the recrystallization process of the nanocrystalline cobalt promoted by the aluminium oxide is 85 kJ mol?1. Aluminium oxide improves the thermostability of both cobalt oxide and the cobalt obtained as a result of oxide phase reduction.   相似文献   

11.
Heats of dilution of concentrated aqueous solutions (4.43 moles-kg–1) of FeCl2 were measured at 15, 25, and 35°C. The heat capacities of these concentrated solutions were also measured at the same temperatures. From these data the partial molal heat capacity, C p2 0 (FeCl2, aq, 298.15°K)=–2.56±30 J–°K–1–mole–1, was calculated. The partial molal heat capacity of Fe2+(aq), –2±30 J-°K–1-mole–1, was correlated with the correspondence principle equations of Criss and Cobble.  相似文献   

12.
Investigation of the aqueous lithium and magnesium halide systems   总被引:1,自引:0,他引:1  
The solubilities of the system LiBr–MgBr2–H2O have been investigated at 25°C and 50°C. It is established that the system is of a simple eutonic type. Pitzer's model is used for calculating the thermodynamic functions needed for plotting the solubility isotherms of the systems LiX–MgX2–H2O (X=Cl, Br) at 25°C. According to calculations made, the Gibbs energy of formation of LiCl·MgCl2·7H2O from simple salts is rm=–2.01 kJ-mol–1, while the value fm=–2748 kJ-mol–1 corresponds to formation from the elements.  相似文献   

13.
Very fine nickel hydroxide and oxide xerogel powders were prepared using a new sol-gel synthesis procedure in which nickel ethoxide was produced through the reaction of nickel chloride, as a precursor, with sodium ethoxide in dehydrated ethanol, followed by the hydrolysis of nickel ethoxide with ammonia and drying the resulting hydrogel under subcritical pressures to form the xerogel. The effects of thermal treatment on the surface area, pore volume, crystallinity and particle structure of the resulting xerogels were investigated and found to have significant effects on all of these properties. Overall, the xerogel remained amorphous as Ni(OH)2 space up to 200°C, with little change in the surface area and pore volume. At 250°C, the Ni(OH)2 began to decompose and form crystalline NiO with the uniformity of the crystals increasing with an increase in temperature. The surface area and pore volume decreased sharply when increasingthe temperature beyond 250°C; this was the temperature where maximums of about 270 m2/g and 0.33 cm3/g were exhibited by this composite amorphous Ni(OH)2 and crystalline NiO xerogel powders. At the higher calcination temperatures, very uniform NiO crystals with average crystallite sizes of 1.7 nm and 14.5 nm were obtained at 400 and 600°C, respectively.  相似文献   

14.
The standard molar enthalpies of formation f H m ° (l) at the temperature T = 298.15 K were determined using combustion calorimetry for N-methylpiperidine (A), N-ethylpiperidine (B), N-propylpiperidine (C), N-butylpiperidine (D), N-cyclopentylpiperidine (E), N-cyclohexylpiperidine (F), and N-phenylpiperidine (G). The standard molar enthalpies of vaporization l g H m ° of these compounds were obtained from the temperature variation of the vapor pressure measured in a flow system. From these data the following standard molar enthalpies of formation in gaseous phase f H m ° (g) were derived for: A –(61.39 ± 0.88); B –(88.1 ± 1.3); C –(105.81 ± 0.66); D –(126.2 ± 1.3); E ( –88.21 ± 0.75); F –(135.21 ± 0.94); G (70.3 ± 1.4) kJ · mol–1. They are used to determine the strain enthalpies of the cyclic amines A–G. The N-alkylated piperidine rings have been found to be about strainless.  相似文献   

15.
The sorption of hafnium on hydrous titanium oxide (TiO2·1.94 H2O) has been studied in detail. Maximum sorption of hafnium can be achieved from a pH 7 buffer solution containing boric acid and sodium hydroxide using 50 mg of the oxide after 30 minutes shaking. The value ofk d, the rate constant of intraparticle transport for hafnium sorption, from 0.01M hydrochloric and perchloric acid and pH 7 buffer solutions has been found to be 17 mmole·g–1·min–2. The kinetics of hafnium sorption follows Lagergren equation in 0.01M HCl solution only. The values of the overall rate constantK=6.33·10–2 min–1 and of the rate constant for sorptionk 1=6.32·10–2 min–1 and desorptionk 2=2.28·10–5 min–1 have been evaluated using linear regression analysis. The value of correlation factor() is 0.9824. The influence of hafnium concentration on its sorption has been examined from 4.55·10–5 to 9.01·10–4 M from pH 7 buffer solution. The sorption data followed only the Langmuir sorption isotherm. The saturation capacity of 9.52 mmole·g–1 and of a constant related to sorption energy have been estimated to be 2917 dm3·mole–1. Among all the additional anions and cations tested only citrate ions reduce the sorption significantly. Under optimal experimental conditions selected for hafnium sorption, As(III), Sn(V), Co(II), Se(IV) and Eu(III) have shown higher sorption whereas Mn(II), Ag(I) and Sc(III) are sorbed to a lesser extent. It can be concluded that a titanium oxide bed can be used for the preconcentration and removal of hafnium and other metal ions showing higher sorption from their very dilute solutions. The oxide can also be employed for the decontamination of radioactive liquid waste and for pollution abatement studies.  相似文献   

16.
The reaction product of uranyl nitrate with whole-protein Bushmaster snake venom in nitrate buffer at pH 3.5 has been studied. The maximum uptake of uranium was 291 mol U·g–1 of venom. The infrared spectrum of the product showed an asymmetric O–U–O vibration at 921 cm–1 typical of complex formation with the uranyl ion. Stability measurements with the UO 2 2+ -protein complex in neutral medium indicated moderate hydrolytic stability, with 14% dissociation after 16 hours at 0°C. Neutron irradiation and desorption studies with a235U-labelled complex showed that generated fission products such as lanthanides and barium were readily lixiviated at pH 7, whereas Ru and Zr were highly retained by the protein substrate.  相似文献   

17.
A study of fixation of cobalt on the crystalline matrix of titania by co-precipitation was carried out. The tracer level solid-liquid distribution of60Co over preformed hydrous titania showed an appreciable uptake of 71%. Macro amounts of Co2+ ions were precipitated along with Ti(IV) hydroxide (pH 8–9) and a maximum loading of 29 wt% was observed. The Soxhlet leachabilities of the calcined mixed mass, heated at 1000 °C, were found to be in the order of 10–1 g·m–2·d–1 and the observation of structural changes of the original host matrix of titania revealed the fixation of cobalt in the mineral assemblage of CoTiO3 (rhombohedral) and the rutile form of titania.  相似文献   

18.
Summary Base hydrolysis of methyl ethylenediaminemonoacetate has been studied at I=0.1 mol dm–3 (NaClO4) over the pH range 7.4–8.8 at 25 °C. The proton equilibria of the ligand can be represented by the equations, where E is the free unprotonated ester species. Values of pK1 and pK2 are 4.69 andca. 7.5 at 25° (I=0.1 mol dm–3). For base hydrolysis of EH+, kOH=1.1×103 dm3 mol–1 s–1 at 25 °C. The species E is shown to undergo lactamisation to give 2-oxopiperazine (klact ca. 1×10–3 s–1) at 25 °C. Formation of the lactam is indicated both by u.v. measurements and by isolation and characterisation of the compound.Base hydrolysis of the ester ligand in the complex [CuE]2+ has been studied over a range of pH and temperature, k OH 25 =9.3×104 dm3 mol–1 s–1 with H=107 kJ mol–1 and S 298 =209 JK–1 mol–1. Base hydrolysis of [CuE]2+ is estimated to be some 1055 fold faster than that of the free ester ligand. The results suggest that base hydrolysis occursvia a chelate ester species in which the methoxycarbonyl group of the ligand is bonded to copper(II).  相似文献   

19.
(n)MnOx–(1–n)CeO2 binary oxides have been studied for the sorptive NO removal and subsequent reduction of NOx sorbed to N2 at low temperatures (150 °C). The solid solution with a fluorite-type structure was found to be effective for oxidative NO adsorption, which yielded nitrate (NO 3) and/or nitrite (NO 2) species on the surface depending on temperature, O2 concentration in the gas feed, and composition of the binary oxide (n). A surface reaction model was derived on the basis of XPS, TPD, and DRIFTS analyses. Redox of Mn accompanied by simultaneous oxygen equilibration between the surface and the gas phase promoted the oxidative NO adsorption. The reactivity of the adsorbed NOx toward H2 was examined for MnOx–CeO2 impregnated with Pd, which is known as a nonselective catalyst toward NO–H2 reaction in the presence of excess oxygen. The Pd/MnOx–CeO2 catalyst after saturated by the NO uptake could be regenerated by micropulse injections of H2 at 150 °C. Evidence was presented to show that the role of Pd is to generate reactive hydrogen atoms, which spillover onto the MnOx–CeO2 surface and reduce nitrite/nitrate adsorbing thereon. Because of the lower reducibility of nitrate and the competitive H2–O2 combustion, H2–NO reaction was suppressed to a certain extent in the presence of O2. Nevertheless, Pd/MnOx–CeO2 attained 65% NO-conversion in a steady stream of 0.08% NO, 2% H2, and 6% O2 in He at as low as 150 °C, compared to ca. 30% conversion for Pd/–Al2O3 at the same temperature. The combination of NOx-sorbing materials and H2-activation catalysts is expected to pave the way to development of novel NOx-sorbing catalysts for selective deNOx at very low temperatures.  相似文献   

20.
The hydrolysis equilibrum of gallium (III) solutions in aqueous 1 mol-kg–1 NaCl over a range of low pH was measured potentiometrically with a hydrogen ion concentration cell at temperatures from 25 to 100°C at 25°C intervals. Potentials at temperatures above 100°C increased gradually because of further hydrolysis of the gallium(III) ion, followed by precipitation. The results were treated with a nonlinear least-squares computer program to determine the equilibrium constants for gallium(III)–hydroxo complexes using the Debye–Hückel equation. The log K (mol-kg–1) values of the first hydrolysis constant for the reaction, Ga3+ + H2O GaOH2+ + H+ were –2.85 ± 0.03 at 25°C, –2.36 ± 0.03 at 50°C, –1.98 ± 0.01 at 75°C, and –1.45 ± 0.02 at 100°C. The computed standard enthalpy and entropy changes for the hydrolysis reaction are presented over the range of experimental temperatures.  相似文献   

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