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81.
Summary Two methods of instrumental neutron activation analysis for the determination of selenium in steels, based on respectively77mSe (t
1/2
= 17.5 s) and75Se (t
1/2 = 120 d) are presented. Good agreement is obtained by application of both methods on a series of steels containing selenium at the 0.1% level. Interferences and advantages associated with either method are discussed.
Bestimmung von Selen in Stahl durch Neutronenaktivierung und Ge(Li)--Spektrometrie
Zusammenfassung Zwei Methoden werden beschrieben, die auf der Messung von77mSe (t 1/2 = 17,5 s) bzw.75Se (t 1/2 = 120 d) beruhen. Bei der Anwendung auf Stähle mit Selengehalten in der Größenordnung von 0,1 % wurden gut übereinstimmende Werte erhalten. Störungen und Vorteile der Methoden werden diskutiert.相似文献
82.
Takeuchi Y Nishikawa M Hachiya H Yamamoto H 《Magnetic resonance in chemistry : MRC》2005,43(8):662-664
High-resolution solid-state magic angle spinning (73)Ge NMR spectra of some organogermanium compounds were measured. Most tetrasubstituted germanes with identical substituents exhibited signals except for one case. Tetrasubstituted germanes with two kinds of different but somewhat similar substituents exhibited broad peaks. Trisubstituted germanes failed to show signals, indicating the importance of symmetry around germanium. 相似文献
83.
Keggin结构杂多酸的有机衍生物[SiW_(11)(RSiOSiR)O_(39)]~(4-)(R=C_2H_5、C_6H_5、NC(CH_2)_3、C_3H_7)已有报道,根据其红外光谱中出现1040cm~(-1)(Si-O-Si的振动峰),Knoth提出了图1的结构。从中可以看出RSiOSiR基占据了Keggin结构杂多酸[SiW_(11)O_(39)]~(8-)的空缺齿顶位置。当然处于齿顶位置的硅原子和中心位置的硅原子的化学环境显然是不同的,所以可用~(29)Si NMR来鉴定这两种硅原子,并推测其结构。 相似文献
84.
B. Saha T. K. Mukherjee A. K. Das P. K. Mukherjee 《International journal of quantum chemistry》2003,91(5):626-632
Dipole‐allowed transitions have been studied for the first few members of the Si isoelectronic sequence. Transition energies, oscillator strengths, transition probabilities and quantum defect values have been estimated for the low‐ and high‐lying excited states of s and d symmetries up to the principal quantum number n=7 for these 3p open shell ions from P+ to Cr10+. Time‐dependent coupled Hartree–Fock (TDCHF) theory has been utilized to calculate such transition properties. Most of the results for transition energies, oscillator strengths, and transition probabilities for higher excited states are new. The transition energies for low‐lying excited states agree well with experimental data wherever available. © 2001 John Wiley & Sons, Inc. Int J Quantum Chem, 2001 相似文献
85.
High-resolution solid-state 29Si NMR has been applied to the study of partially exchanged Li, K, and Cs NaY zeolites. The order of the 29Si chemical shifts of dehydrated samples is Li, Na-Y < Na-Y < K, Na-Y. The correlation between the 29Si chemical shift and the Li or K loading on Li, Na-Y or K, Na-Y was rationalized in terms of the interaction between the framework and the cations inside the small cages. Because of the restrictive migration of large Cs+ ions from the supercages to the small cages, the 29Si chemical shift of Cs, Na-Y was found to be similar to that of Na-Y. 相似文献
86.
A natural CXN zeolite (stilbite, type code-STI) discovered in China was modified with NH4^ exchange by using ammonium salt and calcinations (procedure Ⅰ), or with NH4 exchange followed by treatment with acid (procedure Ⅱ). The coordination state of Si and A1 atoms in the framework, the property of ion exchange, and the adsorption of the H-STI zeolite samples prepared by different modification procedure were investigated with XRD,EDX,^29Si and ^27Al MAS NMR, Ag^ ion exchange and Ne adsorption. The results of the investigations indicate that different procedure of the modification made variety on the distribution of the framework Si atoms and A1 atoms,the content of non-framework aluminum, and the blocking channels and the shielding effect to the positions of the exchangeable cations. The H-STI zeolite prepared by the procedure Ⅱ possesses high ion exchange capacity, open and perfect pore system, and high thermal stability. 相似文献
87.
I. Kovacs V. Balema A. Bassowa E. Matern E. Sattler G. Fritz H. Borrmann R. Bauernschmitt R. Ahlrichs 《无机化学与普通化学杂志》1994,620(12):2033-2040
Synthesis and Structure of Phosphinophosphinidene-phosphoranes tBu2P? P?P(Me)tBu2 1, tBu(Me3Si)P? P?P(Me)tBu2 2, and tBu2P? P?P(Br)tBu2 3 A new method for the synthesis of 1 and 2 (Formulae see ?Inhaltsübersicht”?) is reported based on the reaction of 5 with substitution reagents (Me2SO4 or CH3Cl). The results of the X-ray structure determination of 1 and 2 are given and compared with those of 3 . While in 3 one P? P distance corresponds to a double bond and the other P? P distance to a single bond (difference 12.5 pm) the differences of the P? P distances in 1 and 2 are much smaller: 5.28 pm in 1 , 4.68 pm in 2 . Both 1 and 2 crystallize monoclinic in the space group P21/n (Z = 4). 2 additionally contains two disordered molecules of the solvent pentane in the unit cell. Parameters of 1 : a = 884.32(8) pm, b = 1 924.67(25) pm, c = 1 277.07(13) pm, β = 100.816(8)°, and of 2 : a = 1 101.93(12) pm, b = 1 712.46(18) pm, c = 1 395.81(12) pm, β = 111.159(7)°, all data collected at 143 K. The skeleton of the three P atoms is bent (PPP angle 100.95° for 1 , 100.29° for 2 and 105.77° for 3 ). Ab initio SCF calculations are used to discuss the bonding situation in the molecular skeleton of the three P atoms of 1 and 3 . The results show a significant contribution of the ionic structure R2P? P(?)? P(+)(X)R2. The structure with (partially) charged P atoms is stabilized by bulky polarizable groups R (as tBu) as compared to the fully covalent structure R2P? P(X)? PR2. 相似文献
88.
镓在裸Si系和SiO2/Si系掺杂效应 总被引:3,自引:0,他引:3
Based on the diffusion action of gallium in silicon and SiO2 ,a diffusion model of gallium doping in bare silicon system and SiO_2/Si system is first presented in this paper ,the gallium doping effect in the two systems is analyzed theoretically. Experiments and applications have proved that the use of the open-tube gallium deffusion in SiO2/Si system can substantially improve diffusion quality and device characteristics . 相似文献
89.
A. A. Dadykin A. G. Naumovets Yu. N. Kozyrev M. Yu. Rubezhanska P. M. Lytvyn Yu. M. Litvin 《Progress in Surface Science》2003,74(1-8):305-318
Monolayer and multilayer Ge nanocluster structures were prepared on Si(1 0 0) using molecular beam epitaxy. The cluster size was 10 nm and cluster density was 1010 cm−2. A stable field electron emission was obtained from these structures, showing current peaks in the current–voltage characteristics, which may be attributed to the resonant electron tunneling via the energy levels of the nanocluster potential well. For cluster multilayers, the current–voltage curves also showed current peaks with a complex shape. The cluster multilayer structures had a considerable temperature sensitivity, as well as photosensitivity, in the wavelength range from 0.4 to 10 μm. 相似文献
90.
The new oxonitridosilicates Ba4?xCaxSi6N10O have been synthesized by means of high‐temperature synthesis in a radio‐frequency furnace, starting from calcium, barium, silicon diimide and amorphous silicon dioxide. The maximum reaction temperature was at about 1450 °C. The solid solution series Ba4?xCaxSi6N10O with a phase width 1.81 ≤ x ≤ 2.95 was obtained. The crystal structure of Ba1.8Ca2.2Si6N10O was determined by X‐ray single‐crystal structure determination (P213, no. 198), a = 1040.2(1) pm, Z = 4, wR2 = 0.082). It can be described as a highly condensed network of corner‐sharing SiN4 and SiON3 tetrahedra, the voids of which are occupied by the alkaline earth ions. The structure is isotypic with that of BaEu(Ba0.5Eu0.5)YbSi6N11. In the 29Si solid‐state MAS‐NMR spectrum two isotropic resonances at ?50.0 and ?53.6 ppm were observed. 相似文献