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1.
The transformation of the crystal structure by isomorphous K+-Cs+ substitutions in the non-tetrahedral positions leading to the phase transition has been studied in the series of K1 − x Cs x BSi2O6 solid solutions. The samples have been crystallized from the glass at 850°C for 10 h. According to the data on the crystal structures refined by the Rietveld method, the compositions with 0 ≤ x ≤ 0.35 crystallize in space group I[`4]3dI\bar 43d, structural type KBSi2O6, and those with 0.37 ≤ x ≤ 1.0, crystallize in Ia[`3]dIa\bar 3d, structural type CsBSi2O6. The reversible cubic-cubic phase transition I[`4]3d \rightleftarrows Ia[`3]dI\bar 43d \rightleftarrows Ia\bar 3d occurs in the composition range x = 0.35–0.37.  相似文献   

2.
Hydrate effects on the conformations of ethylene oxide oligomers (EO-x, x = 1–8 mers) were examined using quantum chemical calculations (QCC). Conformational analyses were carried out by RHF/6-31G. The models were constructed by locating a water molecule to each ether–oxygen in the structures optimized for non-hydrate oligomers. Hydrate ratio, h (h = H2Omol/Omol in oligomer), was set from 0 to 1.0. The six type conformations with repeated units of O–C, C–C and C–O bonds were examined. Conformational energy, E c (HF), was calculated as difference between the energy of oligomer with water molecules and that of non-hydrogen and/or hydrogen bonding water molecules. Hydrate energies for each conformer, ∆μ h (kcal/m.u., based on E c in non-hydrate state), were negative and linearly decreased with the increase of h values, and such effects with the increase of h values were weaken with increasing x values. These results were consistent with our previous results calculated using the permittivity, ε (ε = 0–80.1), by QCC. In non-hydrate (h = 0), the (ttt) x conformers were the most stable independent of x. However, in hydrate states (h = 0.44–0.67), the (tg+t) x conformers were the most stable independent of x values, and in h = 1, the (tg+t)8 conformer (8-mer) was most stable [∆E c(g) = −1.3 kcal/m.u., ∆E c(g): energy difference between a given oligomer and the (ttt) x oligomer]. These results supported the experimental those based on NMR analyses using dimethoxyethane and triglyme solutions. Molecular lengths (l) of (tg+t) x , (tg+g) x and (g+g+g+) x conformers having higher x values significantly decreased with increasing h values. Such contraction with hydration, however, was independent of ΔE c(g) values of each conformer.  相似文献   

3.
ETS-10 was ion exchanged by various alkali cations (Li+, Na+, K+, Rb+ and Cs+) and the BET surface area and pore volume was exactly consistent with cationic size; that is, in the order of Li+ > Na+ > K+ > Rb+ > Cs+. It was observed that a single point adsorption capacity was inversely proportional to cationic size. The largest CO2 capacity was observed for Li+-ETS-10 and it is attributed to greater cation–quadrupole interactions with CO2 than larger cation. The results also suggests that as the CO2 loading is increased, the accessibility of adsorbing CO2 to framework basic O sites should have become difficult with the increase in cationic size due to the blocking effect by extra-framework CO2-M+. The slight decrease in the slope of adsorption capacity with temperature, especially beyond 373 K for Li+-ETS-10 and K+-ETS-10 suggests that the adsorption of CO2 on small alkali cation exchanged-ETS-10 at high temperature is somewhat associated with basic oxygen anion sites in framework due to the existence of large pore. The CO2-TPD results show that the amount of desorbed CO2 at higher temperature was proportionally increased due to the increased basicity of oxygen anions in framework. It also shows that the desorption temperature associated with alkali cations in extra-framework (corresponding to low temperature desorption peak) has been lowered with the increase in cationic size, indicating weak cation–quadrupole interactions with CO2 for larger cations.  相似文献   

4.
In this work, we have investigated the influence of some alkali metal ions on the Krafft temperature (TK) and critical micelle concentration (CMC) of a classical ionic surfactant, sodium dodecyl sulfate (SDS), over a wide range of temperature. The alkali metal cations such as Li+, Na+, Cs+, and K+ are found to affect the solubility and hence the TK of the surfactant. It was observed that kosmotropic Li+ lowers the TK of the surfactant. Due to the common ion effect, the solubility of SDS decreases in the presence of Na+, resulting in an increase in the TK. On the other hand, chaotropic K+ and Cs+, capable of forming contact ion pairs with the chaotropic dodecyl sulfate ion, lower the solubility and hence elevate the TK. In terms of decreasing the TK, the ions follow the trend: Li+ > Na+ > Cs+ > K+ except for 0.0025 M CsCl. The added cations screen the charge of the micelle surface and facilitate closer packing of the surfactant with a consequent decrease in the CMC. In terms of the effectiveness in lowering the CMC, the ions follow the order: Cs+ > K+ > Na+ > Li+. In the presence of added electrolytes, the γCMC values are found to be lower than the corresponding values in pure water. The thermodynamic parameters (Gibbs free energy, enthalpy, and entropy changes) of micellization were calculated to gain insights into the mechanism of the process.  相似文献   

5.
Keggin-type heteropoly compounds (HPCs) H3.2−x Cs x Cu0.25As0.1PMo11VO40 (x, 0–2.5) were used as catalysts for coupling reaction of methylmethacrylate (MMA) from methacrolein (MAL) in this study. And the catalytic performance of the HPCs was investigated in the oxidation-esterification coupling reaction. Moreover, the HPCs were characterized by NH3-TPD, TG-pyridine-adsorption/desorption, N2-adsorption/desorption, ICP, TG-DSC, FT-IR, XRD and TPR. These reactive results have been correlated to the acidity, surface area and reducibility. With the increasing of Cs content, surface area of the HPCs increased, while the acidity and reducibility decreased. Difference of the quantity of acid sites originated from the hydration protons being substituted by Cs+. Effects of Cs+ content on the reducibility of the HPCs indicated that Cs+ changed the structural stability of V as coordinating atoms and the proportion of the different reducible states of Mo6+.  相似文献   

6.
The structures of endohedral complexes of the polyhedral oligomeric silsesquioxane (POSS) cage molecule (HSiO3/2)12, with both D 2d and D 6h starting cage symmetries, containing the atomic or ionic species: Li0, Li+, Li, Na0, Na+, Na, K0, K+, K, F, Cl, Br, He, Ne, Ar were optimized by density functional theory using B3LYP and the 6-311G(d,p) and 6-311 ++G(2d,2p) basis sets. The exohedral Li+, Na+, K+, K, F, Cl, Br, He, Ne, Ar complexes, were also optimized. The properties of these complexes depend on the nature of the species encapsulated in, or bound to, the (HSiO3/2)12 cage. Noble gas (He, Ne and Ar) encapsulation in (HSiO3/2)12 has almost no effect on the cage geometry. Alkali metal cation encapsulation, in contrast, exhibits attractive interactions with cage oxygen atoms, leading to cage shrinkage. Halide ion encapsulation expands the cage. The endohedral X@(HSiO3/2)12 (X = Li+, Na+, K+, F, Cl, Br, He and Ne) complexes form exothermically from the isolated species. The very low ionization potentials of endohedral Li0, Na0, K0 complexes suggest that they behave like “superalkalis”. Several endohedral complexes with small guests appear to be viable synthetic targets. The D 2d symmetry of the empty cage was the minimum energy structure in accord with experiment. An exohedral fluoride penetrates the D 6h cage to form the endohedral complex without a barrier.  相似文献   

7.
Fourier transform infrared (FTIR) spectroscopy provides a simple and rapid means of detecting lard blended with chicken, lamb, and cow body fats. The spectral bands associated with chicken, lamb, and cow body fats and their lard blends were recorded, interpreted, and identified. Qualitative differences between the spectra are proposed as a basis for differentiating between the pure animal fats and their blends. A semiquantitative approach is proposed to measure the percent of lard in blends with lamb body fat (LBF) on the basis of the frequency shift of the band in the region 3009–3000 cm−1, using the equation y=0.1616x+3002.10. The coefficient of determination (R 2) was 0.9457 with a standard error (SE) of 1.23. The percentage of lard in lard/LBF blends was also correlated to the absorbance at 1417.89 and 966.39 cm−1 by the equations y=0.0061x+0.1404 (R 2=0.9388, SE=0.018) and y=0.004x+0.1117 (R 2=0.9715, SE=0.009), respectively. For the qualitative determination of lard blended with chicken body fat (CF), the FTIR spectral bands in the frequency ranges of 3008–3000, 1418–1417, 1385–1370, and 1126–1085 cm−1 were employed. Semiquantitative determination by measurement of the absorbance at 3005.6 cm−1 is proposed, using the equation y=0.0071x+0.1301 (R 2=0.983, SE=0.012). The percentage of lard in lard/GF blends was also correlated to the absorbance at 1417.85 cm−1 (y=0.0053x+0.0821, with R 2=0.9233, SE=0.019) and at 1377.58 cm−1 (y=0.0069x+0.1327, with R 2=0.9426, SE=0.022). For blends of lard with cow body fat (CBF) bands in the range 3008–3006 cm−1 and at 1417.8 and 966 cm−1 were used for qualitative detection. The equation y=−0.005x+0.3188 with R 2=0.9831 and SE=0.0086 was obtained for semiquantitative determination at 966.22 cm−1.  相似文献   

8.
Cesium-exchanged Cs x H3.0−x PW12O40 (X=2.0–3.0) heteropolyacid catalysts were prepared and applied to the decomposition of benzyl phenyl ether to aromatics. Benzyl phenyl ether was chosen as a lignin model compound for representing α-O-4 bond in lignin. Phenol, benzene, and toluene were mainly produced by the decomposition of benzyl phenyl ether. Conversion of benzyl phenyl ether and total yield for main products (phenol, benzene, and toluene) were closely related to the surface acidity of Cs x H3.0−x PW12O40 (X=2.0–3.0) heteropolyacid catalyst. Conversion of benzyl phenyl ether and total yield for main products increased with increasing surface acidity of the catalyst. Among the catalysts tested, Cs2.5H0.5PW12O40 with the largest surface acidity showed the highest conversion of benzyl phenyl ether and total yield for main products.  相似文献   

9.
By doping the core of a triplex quartz optical fibre with P2O5, GeO2, and B2O3, it is possible to reduce its temperature sensitivity (TS) from 7·10−6K−1 to (4–5)·10−6K−1. The same decrease in TS can be obtained by doping the third layer with TiO2. The doping level in both cases should be 30–40 mole%. The TS of an optical fibre greater than 80 μm in diameter is almost not a function of random changes in the diameter. For a liquid-crystalline polymer cladding above a fixed value, the TS of the fibre is weakly dependent on the change in the thickness. Moscow State Textile University. Translated fromKhimicheskie Volokna, No. 5, pp. 48–49, Setember–October, 1999.  相似文献   

10.
As part of a series of studies, effects of Na+ substitution on the thermal evolution of cesium‐based geopolymers on heating were studied. A series of sodium‐substituted cesium‐based geopolymers, Cs(1?x)NaxGPs (where x=0, 0.1, 0.2, 0.3, and 0.4), were prepared and treated at 1300°C for 2 hours to obtain the corresponding ceramic products. The thermal evolution process was disclosed by virtue of a variety of technical, including TG‐DTA, thermal shrinkage, XRD analysis, SEM, and TEM investigation. The results indicated that unheated Cs(1?x)NaxGPs was not completely amorphous after the substitution of Na+ and the crystallinity of Cs(1?x)NaxGPs gradually increased with the rise of sodium content. Meanwhile, the average particle sizes of Cs(1?x)NaxGPs also increased evidently with increases in sodium substitution. The final product after heat treatment mainly consisted of pollucite (CsAlSi2O6) and amorphous glass phase. The particle size of pollucite grain gradually decreased as more Cs+ were replaced maybe owing to the role of Na+ in the nucleation process of pollucite. Two forms of Na+ present in the final products: A small portion was present in the pollucite grains due to Na+ partial occupied the crystallographic sites of Cs+; and the rest were present in the amorphous glass phase among the pollucite grains. The average coefficient of thermal expansion (CTE) of resulting Cs(1?x)NaxGPs ceramics increased from 4.80×10‐6 K?1 (x=0) to 7.26×10?6 K?1 (x=0.4) with increases in sodium substitution, which could be due to the amorphous glass phase had a relatively higher CTE than that of pollucite.  相似文献   

11.
Simple inorganic salts of the ions K+, NH 4 + , Cs+, NO 3 , and Cl are strongly repellent to infective second-stage larvae of the root knot nematode,Meloidogyne incognita. Some of these salts are known to be beneficial to plant growth. The results suggest a new means of plant protection.  相似文献   

12.
Uptake of cesium and strontium cations by potassium-depleted phlogopite   总被引:2,自引:1,他引:1  
Phlogopite mica was equilibrated with 1.0 N sodium chloride (NaCl)–0.2 N sodium tetraphenylborate (NaTPB)–0.01 M disodium ethylenediaminetetraacetic acid (EDTA) solution at room temperature resulting in an almost complete removal (92%) of the mica's interlayer K. X-ray powder diffraction analysis provides additional evidence that hydrated Na+ ions had almost completely replaced the interlayer K+. Following equilibration, the c-axis spacing of the mica increased from 10.0 Å to approximately 12.2 Å. Cesium and Sr ion exchange isotherms indicate that K-depleted phlogopite is highly selective for both elements, the Cs+ exchange capacity is 1.26 meq/g or 65% of the theoretical cation exchange capacity and the Sr2+ exchange capacity is 1.94 meq/g or 100% of the theoretical exchange capacity of the mica. Kielland plots indicated that the mica was selective for Cs+ when the equivalent exchange capacity of Cs+ in the exchanger phase (Cs) was < 0.66 and selective for Sr2+ when Sr < 0.41. At equivalent fractions greater than these levels, layer collapse and/or steric effects limit the diffusion of these ions into the interlayers of the mica. Analysis of the Cs+ equilibrated mica utilizing XRD indicated that a collapse of the c-axis spacing had occurred. Based on the high selectivity of < 45-μm K-depleted phlogopite for Sr2+ and Cs+, this material may prove useful as an inorganic ion exchanger for these radioactive isotopes.  相似文献   

13.
In south-east Queensland, Australia, extensive areas of sandy soils (Podosols) with shallow (<1 m) watertables are used for exotic pine tree production. Despite concerns that surface-applied fertilisers (di-ammonium phosphate (DAP) and potassium chloride (KCl)) may be contributing to a decline in local groundwater quality, published information on nutrient leaching in these Podosols is scarce. Large (0.3 m i.d. ×0.85 m long) undisturbed soil cores were intermittently leached with deionised water following a single surface application of KCl in combination with DAP. Potassium was applied at rates (equivalent on a surface area basis) of 0 (K0), 50 (K50), 100 (K100) and 300 (K300) kg K+/ha, and DAP was applied at a rate equivalent to 50 kg P ha−1. Applied ions appeared in the leachate very quickly after surface application, and reactive ions leached at the same rate as non-reactive ions. This behaviour was attributed to preferential soil–water flow, and limited ion sorption. About 30, 35, 100 and 25 percent of the applied K+, phosphorus (P), chloride (Cl) and ammonium (NH4+) was leached from the soil cores. Cation exchange was the major mechanism responsible for K+ and NH4+ retention, although nitrification may have also contributed to NH4+ losses. Findings indicate that significant amounts of surface-applied fertiliser ions can potentially be rapidly leached below the tree root-zone, and into the underlying groundwater. Immobile water regions were estimated to comprise nearly 50% of the soil–water. Intermittent leaching resulted in secondary concentration peaks along the trailing edge of the ion breakthrough curves (BTCs). This was attributed to diffusion of solute from immobile water regions into mobile water regions during periods of no-flow.  相似文献   

14.
The reverse osmosis separations of some ethers, ketones, aldehydes, monocarboxylic acids, and inorganic salts in single-solute (55–454 ppm) aqueous solution systems using aromatic polyamide membranes have been studied at 250 psig. It was found that reverse osmosis separation was essentially a function of steric parameter for ethers, and of both polar and steric parameters for ketones, aldehydes, and alcohols. Solute separations for monocarboxylic acids passed through a minimum at a pKa value of ~4.8. The values for the free-energy parameter for Li+, Na+, K+, Rb+, Cs+, and F?, Cl?, Br?, I?, and IO3? ions have been calculated for the polyamide membranes used. The above values for cations are negative and those for anions are positive, suggesting that the polyamide membrane surface behaves as if it is positively charged. Further, the data show that the polyamide membrane material is only about 40% as polar as that of the cellulose acetate membrane material studied earlier.  相似文献   

15.
Compositions are developed, technological parameters are determined, and the main properties are investigated for devitrified glass composite heat-resistant coatings of the R x O - Al2O3 - SiO2 - TiO2 system (R is Na+, K+, Mg2+, Ca2+, Ba2+) for Nichrome alloys. Translated from Steklo i Keramika, No. 1, pp. 29–31, January, 2000.  相似文献   

16.
Poly(vinyl chloride) (PVC) membrane electrodes to determine monomer concentrations of tetradecyltrimethylammonium ion (TTA+) and hexadecylpyridinium ion (HPy+) based on neutral ion-pair carrier complexes of tetradecyltrimethylammonium dodecyl sulfate (TTA+-DS) and hexadecylpyridinium dodecyl sulfate (HPy+-DS), respectively, are reported here. The electrodes exhibit a Nernstian slope of 59 mV per decade for TTA+ and a sub-Nernstian slope of 34.5 mV per decade for HPy+ ions. The TTA+ ion-selective electrode (ISE) and the HPy+-ISE can determine the monomer units down to concentrations as low as 4.0×10−4M and 1.66×10−5 M, respectively. The effect of various additives, such as the anionic polyelectrolyte sodium dextran sulfate and macrocyclic β-cyclodextrin, on the surface activity exhibited by the cationic surfactants TTA+-DS and HPy+-DS, in the presence of background concentrations of NaCl was also examined with surfactant-selective sensors. The Gibbs free energy of micelle formation (ΔG m ) of both surfactants in the presence of various additives was calculated and found to be less favorable with respect to an increase in the amount of additives due to less availability of cationic surfactant monomer units. The ion-pair complexes TTA+-DS and HPy+-DS were found to behave as selective carrier compounds in PVC membranes in determining the concentration of monomer units of both TTA+ and HPy+, respectively. The proposed sensors worked well at a fairly acidic pH of 1–6.5 with response time of 60 s. The sensors responded well to the surfactant ions even in the presence of additives at lower concentration. The lifetime of the sensors is 3 mon.  相似文献   

17.
Zirconium umbite, K2ZrSi3O9·H2O, is a microporous framework ion exchanger whose potential as a carrier for Zn2+ ions in antimicrobial formulations has not yet been investigated. Accordingly, batch Zn2+-exchange kinetics of synthetic zirconium umbite (K-UM) and the subsequent antimicrobial action of the zinc-bearing phase (Zn-UM) against Staphylococcus aureus and Escherichia coli are reported. Nonstoicheiometric over-exchange of Zn2+ for K+ was observed and attributed to hydrolysis and complexation reactions of Zn2+ within the umbite framework. The exchange process, which was described by a simple pseudo-first-order model (k 1 = 2.69 × 10−4 min−1, R 2 = 0.992), did not achieve equilibrium within 120 h at 25 °C, by which time the uptake of zinc was found to be 1.04 mmol g−1. The minimal bactericidal concentrations of Zn-UM for E. coli and S. aureus were found to be >10 g cm3 and <1.0 g cm3, respectively.  相似文献   

18.
Ion exchange equilibria of alkali metal ions (Li+, Na+, K+,, Rb+, and Cs+)H+, systems have been studied in MNO-j-HNOj media with ionic strength of 0.1 at 30, 45 and 60 °C on tin(IV) antimonate as a cation exchanger. The ion exchange isotherms have been measured for both forward and backward reactions by the batch technique. The isotherms showed S-shaped curves for all exchange systems studied. The selectivity coefficients (logarithmic scale) vary with the equivalent fraction XM of alkali metal ions in the exchanger and give two linear functions of XM with a break point (XM= 0.14, except 0.04 for Li+, /H+) indicating two different exchanging sites. The selectivity sequence, Na+, ? K+, ? Rb+, ? Cs+, ? ? Li, holds in the range of Xu= (0 - 0.04) and the sequence, Cs < Rb +, ? K +, ? Na +, < Li +, applies when XM is higher than 0.14.

Hypothetical thermodynamic data on “zero loading” of the ion exchange reaction was evaluated.  相似文献   

19.
Manganese oxide catalysts were synthesized by direct reaction between manganese acetate and permanganate ions, under acidic and reflux conditions. Parameters such as pH (2.0–4.5) and template cation (Na+, K+ and Cs+) were studied. A pure cryptomelane-type manganese oxide was synthesized under specific conditions, and it was found that the template cation plays an important role on the formation of this kind of structure. Cryptomelane was found to be a very active oxidation catalyst, converting ethyl acetate into CO2 at low temperatures (220 °C). This catalyst is very stable at least during 90 h of reaction and its performance is not significantly affected by the presence of water vapour or CO2 in the feed stream. The catalyst performance can be improved by the presence of small amounts of Mn3O4.  相似文献   

20.
The electrochemical properties of amorphous vanadium pentoxide (V2O5) thin films deposited by reactive r.f.-sputtering were investigated using galvanostatic charge/discharge cycling and galvanostatic intermittent titration technique (GITT). As x in Li x V2O5−y increased (x = 0–2.0), the electromotive force of the lithium (Li)∣1 M LiClO4–propylene carbonate∣Li x V2O5−y cell decreased gradually without a potential plateau or an abrupt potential reduction, demonstrating that an irreversible structural change did not occur in the entire Li content. Chemical diffusivity of the Li ion in the Li x V2O5−y thin film measured using GITT was determined to be 4 × 10−13–7 × 10−14 cm2 s−1 in the Li content range investigated.  相似文献   

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