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1.
W. Schmid K. P. Egger V. Krivan 《Journal of Radioanalytical and Nuclear Chemistry》1988,123(2):561-571
The indicator radionuclide31Si produced in neutron and deuteron activation analysis for silicon via the reactions30Si(n,) and30Si(d,p), respectively, is specifically separated from the irradiated sample by distillation as31SiF4. In the case of aluminium, the distillation is carried out from a HF(HNO3)H2O2 medium and in the case of molybdenum, niobium, tantalum, titanium and vanadium from a HF/HNO3/HBr/H2SO4 medium. Using liquid scintillation counting, the achievable detection limits for neutron activation analysis are, depending on the type of the matrix, between 4–50 ng/g, and for the deuteron activation analysis of tantalum the detection limit is 5 ng/g. 相似文献
2.
Pierre Braunstein Chantal Charles Richard D. Adams Ralph Layland 《Journal of Cluster Science》1996,7(2):145-154
The reaction of the siloxyl containing ferrate [Fe(CO)3(
1-dppm){Si(OMe)3}]–,1 (dppm = Ph2PCH2PPh2) with Sn(OAc)2(n-Bu)2 has yielded the new dimeric complex [Fe(CO)3(
1-dppm){µ-Sn(n-Bu)2}]2, 3 in 89% yield. Compound3 was characterized crystallographically and was found to be a centrosym-etrical molecule with a rhomboidal Fe2Sn2 cluster at the center. Each iron atom contains me
1-dppm ligand. Compound3 was found to react with [Pd(dmba) (µ-Cl)]2 (dmba=dimethylbenzylamine) to yield the new complexmer-[Fe(CO)3{Sn(n-Bu)2}(µ-dppm)Pd(dmba)Cl]2, 4 by attachment of a palla-dium grouping to each of the uncoordinated phosphorus atoms in 3. Crystal data for 3: space groupP
,a=11.399(2) Å, 6=15.98(3) Å, c=10.869(3) Å, =94.10(2)°.=100.56(2)°, =69.35(1)°,Z=2, 3533 reflections,R=0.034. 相似文献
3.
The stability constants of zirconium(IV) and hafnium(IV) fluoride complexes in 1 M (H,Na)ClO4 medium were measured potentiometrically at 293 K for the first time using a fluoride ion selective electrode (F-ISE). This technique has been recommended by IUPAC as the best tool for studying fluoride complexes. A number of precautions were taken to ensure the stabilization of zirconium or hafnium in 1 M (H,Na)ClO4 medium and to prevent the formation of polynuclear hydroxo complexes. The formation of only mononuclear complexes was indicated. The average log values of the overall stability constants of zirconium(IV)-fluoride complexes, 1, 2, 3 and 4 were computed by varying the concentration of metal ion and were found to be 8.49 ± 0.11, 15.76 ± 0.15, 21.57 ± 0.10, and 26.68 ± 0.16, respectively, whereas the corresponding values for hafnium(IV)-fluoride complexes were 8.22 ± 0.06, 15.48 ± 0.15, 21.76 ± 0.14, and 27.42 ± 0.15, respectively. The thermodynamic stability constant, 1, calculated for these complexes follows the same trend as expected from the linear correlation based on the Brown Sylva Ellies (BSE) model for metal-fluoride complexes provided the effective charge on Zr is taken as +4.1 instead of the formal charge of +4. Without considering this adjustment of formal charge, an attempt has also been made to explain the trend in 1 values of group(IV) metal-fluoride complexes based on electronegativity values. A good linear correlation was obtained that could explain the ability of these group(IV) ions to form different fluoride complexes with varying number of fluoride ions. 相似文献
4.
Initially in this review the sodalite framework [T12O24]6– (T=Al, Si] is modeled with regular tetrahedra and disordered T atoms. Equations are given for calculating atomic coordinates from the unit cell parameter a and the T—O distancet; the expansion or contraction of the sodalite-cage is related quantitatively to changes ina through the cooperative twists of TO4 tetrahedra about 4 axes and changes in < TOT bridge angles. The fully expanded cage has=0° and the maximum value ofa. The equations are general for any framework formed by isomorphous substitution of T by atoms other than Al, Si and for any SiAl ratio. The model and equations are extended to the zeolite A framework, which can be built from fully expanded sodalite cages. With the cooperative tilt of the TO4 tetrahedra of zeolite A, described by Depmeier, the major variable features of the zeolite A framework are explained quantitatively. The faujasite framework has twisted-cages (>0), as in sodalite examples, and is quantitatively modeled most conveniently from sodalite examples with similar-cage contents. The review is extended to structures with T-ordering and distorted tetrahedra. Methods are given for estimating a for sodalites from a knowledge of the cavity contents, especially the sizes of cations and anions, and so on, present. Ways of predicting cavity sites in zeolite A as a function of cation size are presented, and the principal cavity sites in the faujasite-cage region are discussed. Finally the review considers isomorphous replacement of T atoms (Si or Al) by B, Be, Fe, Ga, Ge, and P; many of these substituted frameworks are stabilized by templates, or guest molecules, which reside in the cavities. Templates also stabilize Si, Al frameworks with high SiAl ratios. The modeling approach reviewed here is tested on a range of isomorphously substituted frameworks isotypic with sodalite; observed and calculated values of twist and 12O24]12– with distorted tetrahedra; these are structures with Al-O-Al bridges, which violate Loewenstein's Rule. 相似文献
5.
The non-destructive methods of thermal and epithermal neutron activation analysis have been employed to determine the aluminum concentration of seven National Institute of Standards and Technology certified biological reference materials. Through the judicious use of both thermal and epithermal neutron activation analysis using bare and boron-lined irradiation carriers, the major and minor contributions of the31P/n, /28Al and of the28Si/n, p/28Al reactions, respectively, to the27Al/n, /28Al reaction could be corrected for explicitly. Based on replicate determinations precision of the analysis ranged from 2.5% for citrus leaves determined at the 75 ppm level to 18% for bovine liver measured at the 1 ppm level. Accuracy was demonstrated whenever possible by comparison to existing published data. 相似文献
6.
V. D. Maiorov I. S. Kislina S. G. Sysoeva V. M. Zakoshanskii M. I. Vinnik 《Russian Chemical Bulletin》1991,40(5):887-892
Complexation in the acetone-phenol system and the effect of water on the ionic-molecular interaction in the acetone-phenol-H2SO4 system at 30C were investigated by MFTIR (multifrustrated total internal reflection) IR spectroscopy. Acetone and phenol form a 11 complex (PAC-l). In an excess of acetone, all of the phenol is bound with this complex, and a 21 complex (PAC-2) is formed in an excess of phenol. Relatively small amounts of H2O virtually do not decompose PAC-1. A broad continuous absorption band due to the formation of complexes with a strong quasisymmetric H bond is observed in the IR spectra of solutions with H2SO4. Quasi-ion pairs HOSO2O...H...OC-(CH3)2, are formed in an anhydrous system. The acid-solvent complexes decompose and (H2O...H...OH2)+ ions are formed on addition of water. The continuous absorption coefficients, 2000, of (H2O...H...OH2)+ ions and quasi-ion pairs were determined.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 5, pp. 1001–1006, May, 1991. 相似文献
7.
Raman spectroscopic measurements were performed at ambient temperature onaqueous silica-bearing solutions (0.005 < m
Si < 0.02; 0 < pH < 14). The spectraare consistent with the formation of monomeric Si(OH)o
4, SiO(OH)–
3 andSiO2(OH)2–
2 species at acid to neutral, basic, and strongly basic pH, respectively.Raman spectra of aqueous Al-bearing solutions at basic pH confirm thepredominance of the Al(OH)–
4 species in a wide concentration range (0.01 < m
Al < 0.1).Raman spectra of basic solutions (12.4 < pH < 14.3), containing both Al andSi, exhibit a strong decrease in intensities of SiO(OH)–
3, SiO2(OH)2–
2, andAl(OH)–
4 bands in comparison with Al-free Si-bearing and Si-free Al-bearingsolutions of the same metal concentration and pH, suggesting the formation ofsoluble Al—Si complexes. The amounts of complexed Al and Si derived fromthe measurements of the Al and Si band intensities in strongly basic solutions(pH 14) are consistent with the formation, between Al(OH)–
4 andSiO2(OH)2–
2, of the single Al—Si dimer SiAlO3(OH)3–
4 according to the reactionSiO2(OH)2–
2 + Al(OH)–
4 SiAlO3(OH)3–
4 + H2OAt lower pH ( 12.5) the changes in band intensities are consistent with theformation of several, likely more polymerized, Al—Si complexes. 相似文献
8.
Richard M. Farmer P. -H. C. Heubel Alexander I. Popov 《Journal of solution chemistry》1981,10(8):523-532
The concentration formation constants of phosphonoacetic acid (PAA) complexes with the Ca2+ and Mg2+ ions were determined in aqueous solution at 25°C by potentiometric and coulometric titrations at different ionic strengths and were extrapolated to I=0 in order to obtain thermodynamic values of the formation constants. Complexes were formed by the completely deprotonated K
f
(ML) and monoprotonated K
f
(MHL) forms of the PAA anion. The respective values for the complexes are: log K
f
(CaL)=4.68±0.03, log K
f
(CaHL)=2.61±0.08; log K
f
(MgL)=5.58±0.09, log K
f
(MgHL)=3.0±0.3. The enthalpy and entropy of complexation for the deprotonated Ca2+ and Mg2+ PAA species, determined from the temperature dependence of the log K
f
(ML), are: H0(Ca) =0.6±0.2 kcal-mol–1, S0(Ca)=21.4±0.6 cal-mol–1-K–1, H0(Mg)=3.0±0.7 kcal-mol–1, and S0(Mg)=35±2 cal-mol–1-K–1. It is seen there-fore, that the complexes are entropy stabilized but enthalpy destabilized. Formation constants were also determined for Ca2+ and Mg2+ complexes with PAA analogs, phosphonoformic and 3-phosphonopropionic acids and the complexation of PAA was also studied at a single ionic strength, with Na+, Ag+, Tl+, Sr2+, Ba2+, Cd2+, Cu2+, and Pb2+ ions. 相似文献
9.
The self-assembly of the CdII ion, hexamethylenetetramine (hmt) and malonate ligand yields a three-dimensional (3D) coordination polymer [Cd2(C3H2O4)2(H2O)2(
2-hmt)]
n
with channels. The CdII ion is located in a octahedral coordination environment, composed of four oxygen atoms from three malonates, one oxygen atom of water and one nitrogen atom of hmt. Two oxygen atoms of each malonate coordinate to the same CdII ion and the other two oxygen atoms connect to adjacent two CdII ions respectively to form a two-dimensional infinite network, these networks are bridged by
2-hmt coordinated to CdII ions to product a 3D architecture. 相似文献
10.
Kathryn R. Williams 《Journal of Radioanalytical and Nuclear Chemistry》1996,212(5):361-371
A new method for the determination of aluminum and silicon has been developed for zeolite catalysts. In contrast to previous methods, thermal neutrons are used for the analysis of both elements, and cadmium absorbers are not needed. The silicon determination utilizes a one-hour irradiation to observe the31Si produced by the (n, ) reaction of30Si. A 15-second irradiation is used for the27Al(n, )28Al reaction. The28Al activity is corrected for the contribution from the28Si(n,p)28Al reaction by using the analyzed weight of silicon in the sample and the data for a silicon standard irradiated simultaneously with the zeolite and the aluminum standard. The quantitation limits are 0.012 g for silicon and 3.3×10–5 g for aluminum. Sodium presents a significant interference, but this element can be removed by taking advantage of the ion exchange properties of these materials. 相似文献
11.
Max Ziegler und Horst Winkler 《Fresenius' Journal of Analytical Chemistry》1959,166(4):241-242
Zusammenfassung Durch die Anwendung eines H2S-haltigen Laufmittels werden die Ionen Cu2+, Pb2+, Bi3+ und Hg2+ am Startpunkt des Chromatogramms als Sulfide fixiert, während Cd2+ nach kurzer Laufzeit in scharf begrenzter Zone als Sulfid im Chromatogramm nachgewiesen wird. Als Arbeitsgefäße dienen Reagensgläser. Die Spezifitäten liegen für 5 g Cd bei Cd2+Cu2+=12000, Cd2+Pb2+=12000, Cd2+Bi3+=12000, Cd2+Hg2+=1100.Herrn Prof. Dr. O. Glemser, Direktor des Anorganisch-chemischen Insituts der Universität Göttingen, danken wir für Unterstützung der Arbeit. 相似文献
12.
E. Asmus und G. Schulze 《Fresenius' Journal of Analytical Chemistry》1966,217(3):176-181
Zusammenfassung Es wird über die dünnschichtchromatographische Trennung und Reinheitsprüfung von 12 Naphthylaminmonosulfonsäuren berichtet. Für das Laufmittel n-Butanol-n-Propanol-Wasser-konz. Ammoniak (10541) werden die Rf-Werte ermittelt und ihre Standardabweichungen berechnet. Für die rechnerische Bestimmung der Rf-Werte aus den Dipolmomenten der Säuren wird eine quadratische Gleichung angegeben.
Für die Durchführung dieser Arbeit wurden dankenswerterweise Forschungsmittel aus dem ERP-Sondervermögen bereitgestellt.Dem Verbande der Chemischen Industrie und der Deutschen Forschungsgemeinschaft, die diese Arbeit unterstützt haben, danken wir bestens. 相似文献
Summary A report is presented on the thin-layer chromatographic separation and purity control of 12 naphthylaminemonosulphonic acids. Rf-values and standard deviations are determined for the solvent-mixture n-butanol-n-propanol-waterconc. ammonia (10541). A quadratic equation is given for the calculation of the Rf-values from the dipole moments of the acids.
Für die Durchführung dieser Arbeit wurden dankenswerterweise Forschungsmittel aus dem ERP-Sondervermögen bereitgestellt.Dem Verbande der Chemischen Industrie und der Deutschen Forschungsgemeinschaft, die diese Arbeit unterstützt haben, danken wir bestens. 相似文献
13.
Cline Schneider Frdric Doucet Stanislav Strekopytov Christopher Exley 《Polyhedron》2004,23(18):3185-3191
Hydroxyaluminosilicates (HAS) are critical secondary mineral phases in the biogeochemical cycle of aluminium. They are formed from the reaction of silicic acid (Si(OH)4) with an aluminium hydroxide template and act as a geochemical control of the biological availability of Al. There are two main forms of HAS which we have called HASA and HASB and which of these will predominate will depend upon the Si(OH)4 to Al ratio in any one environment. In all but the most heavily weathered environments or those undergoing a progressive acidification Si(OH)4 will be present in significant excess to Al and HASB will be the dominant secondary mineral phase. We have tried to determine the solubility of HASB(s) so that its contribution to Al solubility control might be compared with other secondary minerals such as Al(OH)3(gibbsite). In preliminary experiments, the dissolution of HASB(s) was found to be non-congruent with almost no Al being released during 18 months ageing. We then demonstrated that HASB(s) was significantly less soluble than Al(OH)3(s) prepared under identical experimental conditions. We have used this information to describe a solubility expression for HASB(s) at a predefined quasi-equibrium and to calculate a solubility constant.
K*Al2Si2O5(OH)4=[Al2O4+][SiO2]2[OH-]4