Clathrate formation in binary aqueous systems with CH2Cl2, CHCl3 and CCl4 at high pressures

P,T,X phase diagrams of the CH₂Cl₂-H₂O, the CHCl₃-H₂O and the CCl₄-H₂) systems have been studied by DTA in the pressure range 10^–3 to 5.0 kbar. Under pressure the cubic structure II (CS-II) hydrates forming in all the systems are replaced by hydrates with the composition M·7.3 H₂O whose stoichiometry and positive dT/dP values of melting lead us to believe that they are CS-I hydrates.In the CH₂Cl₂ and CHCl₃ systems the nonvariant point coordinates of the hydrate transformationQ ₂ ^h (l₁h17h7l₂, where l₁ and l₂ are liquid phases abundant in water and hydrate former, respectively, h₁₇ and h₇ are hydrates with hydrate numbers 17 and 7, respectively) areP = 0.6 kbar, T = –1.5°C andP =2.65 kbar,T = –10.5°C, respectively. In the CCl₄ system the 4-phaseQ ₃ ^h point (l₁h₁₇h₇s, where s is crystalline CCl₄) has coordinatesP = 0.75 kbar and T = 0.4°C.The main obstacle of the present study, the very slow achievement of equilibrium, has been eliminated by adding small amounts (0.25% by mass) of surfactants followed by ultrasonic mixing. We have shown that this accelerates the achievement of equilibrium without changing its position.     

Dielectric study on pure and KOH-doped tetrahydrofuran clathrate hydrates

Complex dielectric permittivities of pure and KOH-doped (x = 1.8 x 10^–4) tetrahydrofuran clathrate hydrates were measured in the temperature range 20–260 K and in the frequency range 20 Hz-1 MHz. The relaxation time of the water reorientational motion was found to decrease drastically as a result of the doping; e.g., the relaxation time of the doped sample was 10^–9 times shorter than that of the pure sample at 70 K. The activation enthalpy of the motion was reduced to 7.4 kJ mol^–1. On cooling the crystal, the value of decreased suddenly at the 62 K phase transition to the ₂ value of the pure sample and at the same time disappeared. No dispersion effect due to the guest reorientation was observed below the transition. These data indicate that both the host and guest molecules become ordered or, at least, change their mobility drastically. In the pure sample, a relaxation phenomenon of ₀₂ was found around the glass transition region. The relaxation times agreed well with those derived from the enthalpy of relaxation in a calorimetric study.Dedicated to Dr D. W. Davidson in honor of his great contributions to the sciences of inclusion phenomena.     

The Inclusion Mode of tert-Butylbenzene in the 1-D Channel of Microporous β-Bis(1,1,1-trifluoro-5, 5-dimethyl-5-methoxy-acetylacetonato) copper(II)

Inclusion of tert-butylbenzeneinto the l-D channel of the titlehost matrix results in a-[CuL₂]1/3(tert-butylbenzene)inclusion compound(trigonal, space groupR =3;a = 24.495(3),c = 10.510(2) Å,V = 5461(1) ų,Z = 9;R = 0.049). The observed guest–host mole ratio of 1/3 was confirmed by X-ray diffraction and arises from the stoichiometric filling of the larger wide segments of the channel. This contrasts with the benzene inclusion compound studied previously, where both the larger and smaller wide segments were occupied to give a 2/3 guest–host stoichiometry. A comparison of these two structures explains the experimental fact that the guest–host mole ratios for inclusions of the title host lie between values of 1/3 and 2/3for 20 different benzene derivatives.     

熔体旋甩工艺对Zn掺杂Ⅰ-型Ba8Ga12Zn2Ge32笼合物微结构及热电性能的影响

采用新颖的熔体旋甩(MS)结合放电等离子烧结(SPS)技术制备了单相Zn掺杂的Ⅰ-型Ba₈Ga₁₂Zn₂Ge₃₂笼合物,研究了熔体旋甩工艺对其微结构以及热电性能的影响. 结果表明,MS得到的薄带自由面主要由300nm—1μm的小立方体单晶组成,薄带经SPS烧结后得到了具有大量层状精细结构的致密块体. 与熔融+SPS工艺制备的试样相比,熔融+MS+SPS制备的Ba₈Ga₁₂Zn 关键词： 熔体旋甩 Ⅰ-型笼合物 热电性能     

通过量子噪声信道之后Werner态的纠缠特性研究

利用并发度作为纠缠的度量研究了Werner态通过量子噪声信道(包括振幅和相位阻尼信道)之后的纠缠动力学性质,给出了Werner态通过量子噪声信道之后并发度的解析表达式,获得了纠缠突然死亡的参数条件。     

Thin-film formation of Si clathrates on Si wafers

In this study, we prepared Si clathrate films (Na₈Si₄₆ and Na_xSi₁₃₆) using a single-crystalline Si substrate. Highly oriented film growth of Zintl-phase sodium silicide, which is a precursor of Si clathrate, was achieved by exposing Na vapour to Si substrates under an Ar atmosphere. Subsequent heat treatment of the NaSi film at 400 °C (3 h) under vacuum (<10⁻² Pa) resulted in a film of Si clathrates having a thickness of several micrometres. Furthermore, this technique enabled the selective growth of Na₈Si₄₆ and Na_xSi₁₃₆ using the appropriate crystalline orientation of Si substrates.     

Some less usual properties of tetracyano complexes

The structure and reactivity of one unique molecule may be understood only in relation to its molecular surroundings. The non-stoichiometric forms of the tetracyano complexes M(B) _mM (CN)₄·nG (B=nitrogen or oxygen containing base; G=aromatic compound or H₂O,m0,n>0) are understood in this respect. Their stoichiometric or non-stoichiometric forms, with voids either completely or more often partially occupied, are responsible for their observed sorptive and resorptive abilities. The effects of the surroundings are correlated with the results of thermal analysis, magnetic measurements and their sorptive abilities.Dedicated to Professor H. M. Powell.     

The Synthesis and Characterization of Mononuclear and Binuclear Iron(II) Clathrochelate Complexes Derived from 2,3-Butanedione Oxime Hydrazone

The synthesis and characterization of a new series of iron(II) clathrochelate complexes, including the first example of a binuclear covalently linked c1athrochelate complex, is reported. The ligand system is based on the bifunctional chelate 2,3-butanedione oxime hydrazone which forms a tris-complex with iron(II). The c1athrochelate is completed by capping the complex with both a boronic acid/oxime capping reaction and a formaldehyde/hydrazone capping reaction. Electrochemical and spectroscopic characterizations of the complexes are discussed.     

Kinetic hydrate inhibitor performance of new copolymer poly(N-vinyl-2-pyrrolidone-co-2-vinyl pyridine)s with TBAB

In oil and gas field, the application of kinetic hydrate inhibitors (KHIs) independently has remained problematic in high subcooling and high water-cut situation. One feasible method to resolve this problem is the combined use of KHIs and some synergists, which would enhance KHIs’ inhibitory effect on both hydrate nucleation and hydrate crystal growth. In this study, a novel kind of KHI copolymer poly(N-vinyl-2-pyrrolidone-co-2-vinyl pyridine)s (HGs) is used in conjunction with TBAB to show its high performance on hydrate inhibition. The performance of HGs with different monomer ratios in structure II tetrahydrofuran (THF) hydrate is investigated using kinetic hydrate inhibitor evaluation apparatus by step-cooling method and isothermal cooling method. With the combined gas hydrate inhibitor at the concentration of 1.0 wt%, the induction time of 19 wt% THF solution could be prolonged to 8.5 h at a high subcooling of 6℃. Finally, the mechanism of HGs inhibiting the formation of gas hydrate is proposed.