高岭土与针铁矿胶结样中27Al、29Si NMR谱与其原子电荷关系

由NMR谱实验得高岭土与针铁矿胶结样中²⁷Al、²⁹Si的化学位移较单一高岭土分别正移了2.7ppm和2.33ppm.由CNDO/2方法计算得到胶结样中Al、Si原子电行比高岭土分别减少了0.0787和0.0286.胶结样中Al、Si原子电荷的减少与²⁷Al、²⁹Si NMR谱化学位移相吻合,可以认为在高岭土与外铁矿的界面上形成了氢键而呈现胶结态.     

丝光沸石催化剂的固体高分辨核磁共振研究

利用²⁹Si MAS NMR及²⁷Al MAS NMR技术研究了丝光沸石催化剂制备过程中的结构变化,并利用Al的四极作用大小来区分重叠在一起的不同的Al物种.     

Y型沸石脱铝机制和铝状态的NMR研究

对Y型沸石原粉及几种不同脱铝样品进行了几种不同NMR方法的测量,确定了不同处理过程的脱铝机制和骨架内外铝状态的变化,²⁹Si MAS NMR谱给出了骨架Si、Al分布的信息,反映了不同方法处理样品其脱铝机制的差异,据此可以控制Y沸石脱铝过程获得更高的硅铝比,²⁷Al MAS NMR谱、二维章动NMR及¹H-²⁷Al CP/MAS NMR测量表明:水热处理的Y沸石中存在4种不同的铝状态。综合²⁹Si和²⁷Al MAS NMR观测,可相当程度地推断Y型沸石分子筛脱铝改性所发生的内部过程。     

由29Si NMR谱看高岭土与针铁矿的胶结本质

通过对高岭土与针铁矿的人工胶结样的²⁹Si NMR谱的分析,认为氢键生成是胶结本质.     

固体NMR考察有机硅聚合物的热解过程

应用²⁹Si和¹³C固体NMR方法考察了几种有机硅聚合物前驱体热解制备SiC陶瓷的过程,通过²⁹Si和¹³C NMR谱分析了热解产物的结构.结果表明聚碳硅烷及其氧化交联聚合物前驱体在高温下的热解可以获得SiC陶瓷相.     

焙烧对HL沸石结构的影响

运用MAS NMR研究了焙烧对HL沸石结构的影响. 结果表明,高温焙烧将引起HL沸石骨架的脱铝,当焙烧温度高于650 ℃后,沸石骨架脱铝明显;²⁷Al MAS NMR谱表明,从沸石上脱下来的铝,部分形成了NMR不可测的无定形态,且随焙烧温度的升高,NMR不可测铝增多.     

丙硅乳液的核磁共振研究

单介绍了²⁹Si NMR实验技术;用²⁹Si NMR测定了丙硅乳液原料羟基硅氧烷的平均聚合度、平均分子量、平均羟基含量;用¹³C NMR分析了丙硅乳液的结构组成。     

笼形倍半硅氧烷NMR的研究

笼形倍半硅氧烷是一类典型的多面体有机-无机分子复合物. ²⁹Si NMR是测定这类含硅化合物结构的有效方法. 利用²⁹Si NMR对6种笼形八聚倍半硅氧烷的结构进行了研究,结合所得数据探讨了这类化合物中取代基电负性对²⁹Si NMR化学位移的影响.根据¹H,¹³C NMR数据及各峰归属可以进一步判断笼形倍半硅氧烷取代基R的类型和结构.     

NASICON型化合物结构的NMR研究

在水热晶化合成一系列NASICON型化合物的基础上,应用固体高分辨³¹P和²⁹Si MAS NMR,研究了几种NASICON化合物的结构,观察其骨架原子P和Si在结构中的状态及分布,并解释了由于在结构中发生取代作用而引起,Si或P的化学位移的变化.     

用固体核磁方法研究MCM-22分子筛中的Al状态

用固体NMR技术研究了新型分子筛MCM-22在不同水合状态下的²⁷Al谱和¹H谱.并用新的¹H/²⁷Al双共振方法TRAPDOR对MCM-22分子筛的各种铝状态进行了研究,得到了样品脱水后B酸位(Bronsted)、L酸位(Lewis)以及非骨架Al(OH)的四极耦合常数.     

Tetrahedral cation ordering in layer silicates by 29Si NMR spectroscopy

²⁹Si NMR spectra of layer silicates with a wide range of tetrahedral composition (Si/Al ratios from 7.7 to 2.7) indicate that Si, Al distribution is mainly controlled by the electrostatic requirement of homogeneous dispersion of Al, confirming our earlier conclusions derived from the analysis of natural samples of micas with Si/Al ratios near to 3. This requirement includes, as a partial aspect, the Loewenstein's rule which forbids the presence of Al in neighbouring tetrahedra.     

On the mechanism of the 27Al(α, d)29Si reaction

The ²⁷Al(α, d)²⁷Si reaction has been studied at three bombarding energies: 26.2, 26.45 and 26.7 MeV. The energy-averaged angular distributions for states populated in ²⁹Si have been compared with the microscopic and macroscopic DWBA calculations and Hauser-Feshbach theory. Spectroscopic amplitudes were calculated using the available shell-model wave functions.     

Incomplete fusion of the 16O + 27Al reaction

Velocity spectra of fusion-like residues produced in the reactions of 90 MeV and 150 MeV ¹⁶O with ²⁷Al were measured. At 90 MeV the velocity spectra were well reproduced by a statistical model calculation. At 150 MeV the observed centroids of the velocity spectra deviate from the statistical model predictions. The centroid shifts as a function of the atomic and mass numbers of evaporation residues were analyzed by two different model calculations based on the assumption that incomplete fusion is (a) a peripheral process, or (b) independent on the angular momentum of the entrance channel, respectively. The later assumption is in better agreement with the presented data.     

Beta decays of 25Na, 25Al and 29Al

The radioactivities ²⁵Na, ²⁵Al, and ²⁹Al were produced in the ²³Na(t, p)²⁵Na, ²⁴Mg(d, n)²⁵Al, and ²⁷Al(t, p)²⁹Al reactions using a 3.5 MV Van de Graaff. γ-radiations were measured by means of a target-transfer system and a Ge(Li) detector with or without Compton suppression. Decay schemes derived for ²⁵Na and ²⁹Al are in general agreement with earlier results, but with improved accuracy of branching ratios and much sharper limits on the intensities of certain unobserved β- and γ-ray transitions. Precision measurements of the energies of principal γ-rays gave results in keV for the listed decaying bodies as follows: ²⁵Na ? 1611.716(11); ²⁵Al ? 1611.708(11); and ²⁹Al ? 1273.361(9). The energy determinations of the ²⁵Mg 1612 keV γ-transition measured in the decays of ²⁵Na and ²⁵Al differ by 8 ± 9 eV.     

Multinuclear MAS NMR study of the microporous aluminophosphate AlPO4-17 and the related silicoaluminophosphate SAPO-17.

AlPO4-17 and SAPO-17 in their as-synthesized, calcined, and calcined and subsequently rehydrated forms have been studied by 27Al and 31P MAS NMR. Pronounced structural changes caused by template removal and rehydration can unambiguously be attributed to a change in the coordination number (on calcination: 5-->4, on rehydration/dehydration: 4<-->6) of part of the framework aluminium atoms. The different resonance lines can be assigned to crystallographically inequivalent sites present in the modified ERI framework. 27Al quadrupolar coupling parameters of the two aluminium sites in the calcined AlPO4-17 (CQ = 4.4 MHz and 2.1 MHz) were determined by recording spectra at different field strengths. The isotropic chemical shifts were obtained from rotation sidebands of the (+/- 3/2, +/- 1/2) satellite transitions. 2D 27Al nutation MAS NMR was used to corroborate the line assignment for the as-synthesized and the rehydrated AlPO4-17. By using 13C MAS NMR it was shown that the occluded template (cyclohexylamine) is present as ions. For the first time, a splitting of the 29Si NMR line caused by crystallographically inequivalent sites in a SAPO-type material is reported. The line splitting of 4.3 ppm is comparable with that observed for isostructural aluminosilicate erionite.     

The transfer reactions induced by 38 MeV 19F ions on 27Al

The reactions induced by 38 MeV ¹⁹F on ²⁷Al have been studied using the Tandem Van de Graaff accelerator at Harwell together with a mass identification system based on a combination of a Buechner magnetic spectrograph and position sensitive silicon detectors in the focal plane of the magnet. Comparison of the elastic scattering measurements with Coulomb cross sections provided an absolute normalisation to the measured reaction yields. Transfer reactions were measured as a function of emitted particle energy and angle for single nucleon pick-up and stripping and for 2, 3 and 4 particle stripping. Essential features of the experimental technique are outlined and the experimental results are presented. The significance of the energy spectra and angular distributions are discussed. The results of DWBA analyses of one-nucleon transfer reactions yield spectroscopic factors for levels in ²⁸Si, ²⁸Al and ²⁶Al which are in fair agreement with those obtained in other studies.     

Fast 29Si magic-angle-spinning NMR acquisitions by RAPT-CP 27Al --> 29Si polarization transfer

Using enhancement of the 27Al central-transition magnetization by applying RAPT prior to 27Al --> 29Si cross-polarization, we demonstrate fast acquisition of 29Si one-dimensional MAS and two-dimensional 27Al-29Si HETCOR spectra on a new sialon phase Ba2Al3Si9N13O5.     

Lifetime measurements in 29 Al

The lifetimes of the first six excited states of ²⁹Al have been measured by the DSA method with two different reactions,²⁶Mg(α, p)²⁹Al and²⁷Al(t, p)²⁹Al. The recoil distance method was also used to remeasure the mean lifetime of the first excited state, leading to a value τ_m = 6.5 ± 0.5 ps. Experimental results are compared with shell model calculations.     

Unambiguously distinguishing Si[3Si,1Al] and Si[3Si,1OH] stuctural units in zeolite by 1H/29Si/27Al triple resonance solid state NMR spectroscopy

We present an experimentally feasible triple-resonance NMR method that establishes the correlation among three different nuclei, avoiding the difficulty to directly explore the weak coupling between two NMR nuclei, such as (29)Si and (27)Al. Using this method, we are able to give an unambiguous assignment to the various peaks in (29)Si CP NMR spectrum of MCM-22 zeolite and discriminate (29)Si signals from SiOHAl and SiOH groups. In addition, in combination with (1)H/(27)Al double-resonance technique, the (1)H/(27)Al/(29)Si triple-resonance experiment suggests the presence of two different kinds of Br?nsted acid sites in H-MCM-22 zeolite.     

The total cross section for the reaction 24Mg(α, n)27Si up to 13.1 MeV

The total cross section for the ²⁴Mg(α, n)²⁷Si reaction was determined in 10 keV energy steps from threshold to 13.1 MeV incident energy using the activation method. Variations observed in the cross section were interpreted using fluctuation theory with two notable results; firstly, that Γ, the average width of the observed fluctuations, does not vary at the rate expected over the energy range measured, and secondly that the majority of this reaction goes by a direct mechanism. This latter result was also found for the ²⁷Al(p, n)²⁷Si reaction after a reanalysis of published data.