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1.
Neutron incoherent elastic scattering data have been collected on homologues disaccharides (trehalose, maltose, sucrose)/H 2O mixtures as a function of temperature. The results show a dynamical transition at T238 K, T235 K and T233 K for trehalose, maltose and sucrose/H 2O mixtures, respectively, marking a cross-over in molecular fluctuations between harmonic and non-harmonic dynamical regimes, proving a higher ‘rigidity’ of trehalose mixture with respect to maltose and sucrose mixtures. This finding accounts for the higher cryptobiotic effectiveness of trehalose, namely a capability to encapsulate biostructures in a more rigid environment. 相似文献
2.
The electrical conductivity of Cr 2O 3 nominally doped with 2 mol% MgO has been studied by the four point a.c. technique as a function of the oxygen activity (O 2 + Ar, CO + CO 2 and H 2 + H 2O) in the temperature range 400–1200 °C. It is concluded that Cr 2O 3 doped with MgO is an extrinsic conductor and that the dissolved Mg-dopant is compensated by the formation of electron holes at near atmospheric oxygen pressures and by oxygen vacancies (or possibly interstitial chromium ions) at highly reduced oxygen activities (in CO + CO 2 and H 2 + H 2O gas mixtures). In H 2 + H 2O mixtures Mg-doped chromia also dissolves hydrogen as protons and significantly affects the defect structure and electrical conductivity. The defect structure of the oxide under various conditions is discussed. 相似文献
4.
Atomic layer deposition of hafnium dioxide (HfO 2) on silicon substrates was studied. It was revealed that due to low adsorption probability of HfCl 4 on silicon substrates at higher temperatures (450–600 °C) the growth was non-uniform and markedly hindered in the initial stage of the HfCl 4–H 2O process. In the HfI 4–H 2O and HfI 4–O 2 processes, uniform growth with acceptable rate was obtained from the beginning of deposition. As a result, the HfI 4–H 2O and HfI 4–O 2 processes allowed deposition of smoother, more homogeneous and denser films than the HfCl 4–H 2O process did. The crystal structure developed, however, faster at the beginning of the HfCl 4–H 2O process. 相似文献
5.
Raman scattering experiments on the Γ 15− LO 1 mode in Cu 2O crystals were performed using incident light near the resonance with the 1 S exciton level of the ‘yellow serie’. The enhancement of the Raman efficiency observed in this experiment is attributed to the activation of the normally forbidden transition by stoechiometric defects in the Cu 2O crystals. 相似文献
6.
The paper presents the results of a study of the radiation-induced processes and defects in nonlinear optical crystals Li 2B 4O 7 (LTB), LiB 3O 5 (LBO), CsLiB 6O 10, KB 5O 8·4H 2O, β-BaB 2O 4. It was revealed that a pulsed electron beam irradiation at 290 K forms the radiation-induced pairs of the ‘vacancy—interstitial atom’ defects in the cation sublattice of these crystals. This gives rise to a creation of metastable electronic (interstitial atom) and hole (small-radius polaron near the cation vacancy) centers in high concentrations. Optical hole-transitions from the local level of the trapped hole centers to the valence band states are responsible for the transient optical absorptions (TOA) of borates in the visible and UV spectral ranges. A sublattice of the weakly bound mobile lithium cations in LTB and LBO favors a spatial separation of the radiation-induced pair defects ‘hole polaron near Li-vacancy—mobile interstitial Li 0 atom’. Their decay rated by the electron–hole nonradiative tunnel recombination determines a peculiar feature of the TOA decay kinetics in LTB and LBO. 相似文献
7.
Nanoparticles of NiMn 2O 4 were successfully obtained by mixing gelatin and inorganic salts NiCl 2·6H 2O and MnCl 2·4H 2O in aqueous solution. The mixture has been synthesized at different temperatures and resulted in NiMn 2O 4 nanoparticles with crystallites size in the range of 14–44 nm, as inferred from X-ray powder diffraction (XRPD) data. We have also observed that both the average crystallite size and the unit cell parameters increase with increasing synthesis temperature. Magnetic measurements confirmed the presence of a magnetic transition near 110 K. 相似文献
8.
Oxygen tracer diffusion ( D*) and surface exchange rate constant ( k*) have been measured, using isotopic exchange and depth profiling by secondary ion mass spectrometry (SIMS), in La 1−xSr xFe 0.8Cr 0.2O 3−δ ( x=0.2, 0.4 and 0.6). Measurements were made as a function of temperature (700–1000 °C) and oxygen partial pressure (0.21–10 −21 atm) in dry oxygen, water vapour and water vapour/hydrogen/nitrogen mixtures. At high oxygen activity, D* was found to increase with increasing temperature and Sr content. The activation energies for D* in air are 2.13 eV ( x=0.2), 1.53 eV ( x=0.4) and 1.21 eV ( x=0.6). As the oxygen activity decreases, D* increases as expected qualitatively from the increase in oxygen vacancy concentration. Under strongly reducing conditions, the measured values of D* at 1000 °C range from 10 −8 cm 2 s −1 for x=0.2 to 10 −7 cm 2 s −1 for x=0.4 and 0.6. The activation energies determined at constant H 2O/H 2 ratio are 1.21 eV ( x=0.2), 1.59 eV ( x=0.4) and 0.82 eV ( x=0.6). The surface exchange rate constant of oxygen for the H2O molecule is similar in magnitude to that for the O2 molecule and both increase with increasing Sr concentration. 相似文献
9.
Ion desorption induced by a resonant excitation of O 1s of condensed amorphous H 2O has been studied by total ion and total electron yield spectroscopy, nonderivative Auger electron spectroscopy (AES) and Auger electron photo-ion coincidence (AEPICO) spectroscopy. The spectrum of total ion yield divided by total electron yield exhibits a characteristic threshold peak at hν = 533.4 eV, which is assigned to the 4a 1 ← O 1s resonant transition. The AES at the 4a 1 ← O 1s resonance is interpreted as being composed of the spectator-AES of the surface H 2O, and the normal-AES of the bulk H 2O, where the 4a 1 electron is delocalized before Auger transitions. H + is found to be the only ion species in AEPICO spectra measured at the 4a 1 ← O 1s resonance and at the O 1s ionization ( hν = 560 eV). The electron kinetic energy dependence of the AEPICO yield (AEPICO yield spectrum) at the 4a 1 ← O 1s resonance is found to be greatly different from that at the O 1s ionization. The peak positions of the AEPICO yield spectrum at the 4a 1 ← O 1s resonance are found to correspond to those of the spectator-AES of the surface H 2O, which is extracted from the AES at the 4a 1 ← O 1s resonance. Furthermore, the AEPICO yield is greatly enhanced at the 4a 1 ← O 1s resonance as compared with that at the O 1s ionization. On the basis of these results, a spectator-Auger-stimulated ion desorption mechanism and/or ultra-fast ion desorption mechanism are concluded to be responsible for the H + desorption at the 4a 1 ← O 1s resonance. The enhancement of the H + yield is ascribed to the O---H anti-bonding character of the 4a 1 orbital. 相似文献
10.
采用密度泛函理论中的广义梯度近似研究C 6Li吸附H 2O分子并将之进行分解的催化过程. 几何优化发现:Li原子最稳定的吸附位置是位于C 原子顶位上方. 研究表明,第一个H 2O 分子吸附在C 6Li上需要克服1.77 eV的能量势垒,然后分解为H和OH且与Li原子成键. 当吸附第二个H 2O分子时,第二个H 2O分子需要克服1.2 eV的能量势垒分解为H和OH,其中H与Li原子上的H原子结合成H 2,OH则替代Li 原子上的H结合在Li原子上. 因此C 6Li 可以作为催化剂将H 2O分子进行分解得到H 2. 分析可知:C 6Li主要是通过Li原子与H 2O之间形成的偶极矩作用来吸附H 2O 分子,与C 60Li 12 的储氢机制类似. 研究结果可为储氢材料的制备提供一个新的思路.
关键词:
6')" href="#">C 6
Li
2O')" href="#">H 2O
密度泛函理论 相似文献
11.
A detailed electrochemical study of Li insertion in the -form of VOPO 4 and the optimization of the cycling performance are presented. The redox process occurs in one step close to 3.76 V, along with a phase transition. In order to improve the intercalation kinetics, the electronic conductivity was optimized by introducing a mixed valency, and the ionic conductivity was favored by introducing ‘pillaring’ molecules or ions in the interlayer space. In this way, the electrochemical behaviors of -VOPO 4·2H 2O, -Na xVOPO 4, -K xVOPO 4 and -Mg xVOPO 4 (0≤ x≤1) have been studied: the hydrate compound shows a good specific capacity (100 mA h/g at a C/5 regime), but a poor cyclability was mainly because of water oxidation. The inserted large alkaline ions improved the cyclability up to 80 cycles (Na +) or over 100 cycles (K +). Enhancements of the VOPO 4 specific capacity have been obtained as well by mechanical ball-millings. 相似文献
12.
The reaction of CO 2 and H 2O to form bicarbonate (HCO −3) was examined on the nearly perfect and vacuum annealed surfaces of TiO 2(110) with temperature programmed desorption (TPD), static secondary ion mass spectrometry (SSIMS) and high resolution electron energy loss spectrometry (HREELS). The vacuum annealed TiO 2(110) surface possesses oxygen vacancy sites that are manifested in electronic EELS by a loss feature at 0.75 V. These oxygen vacancy sites bind CO 2 only slightly more strongly (TPD peak at 166 K) than do the five-coordinated Ti 4+ sites (TPD peak at 137 K) typical of the nearly perfect TiO 2(110) surface. Vibrational HREELS indicates that CO 2 is linearly bound at the latter sites with a νa(OCO) frequency similar to the gas phase value. In contrast, oxygen vacancies dissociate H 2O to bridging OH groups which recombine to liberate H 2O in TPD at 490 K. No evidence for a reaction between CO 2 and H 2O is detected on the nearly perfect surface. In sequentially dosed experiments on the vacuum annealed surface at 110 K, CO 2 adsorption is blocked by the presence of preadsorbed H 2O, adsorbed CO 2 is displaced by postdosed H 2O, and there is little or no evidence for bicarbonate formation in either case. However, when CO 2 and H 2O are simultaneously dosed, a new CO 2 TPD state is observed at 213 K, and the 166 K state associated with CO 2 at the vacancies is absent. SSIMS was used to tentatively assign the 213 K CO 2 TPD state to a bicarbonate species. The 213 K CO 2 TPD state is not formed if the vacancy sites are filled with OH groups prior to simultaneous CO 2+H 2O exposure. Sticking coefficient measurements suggest that CO 2 adsorption at 110 K is precursor-mediated, as is known to be the case for H 2O adsorption on TiO 2(110). A model explaining the circumstances under which the proposed bicarbonate species is formed involves the surface catalyzed conversion of a precursor-bound H 2O–CO 2 van der Waals complex to carbonic acid, which then reacts at unoccupied oxygen vacancies to generate bicarbonate, but falls apart to CO 2 and H 2O in the absence of these sites. This model is consistent with the conditions under which bicarbonate is formed on powdered TiO 2, and is similar to the mechanism by which water catalyzes carbonic acid formation in aqueous solution. 相似文献
13.
The far infrared transmittance of H 2O has been measured in the laboratory. A gas correlation radiometric technique was adopted for comparison with atmospheric H 2O measurements made by the Stratospheric and Mesospheric Sounder on Nimbus 7. Atmospheric paths were simulated in a multipass cell containing pure H 2O and H 2O + N 2 mixtures at various pressures and temperatures. A spectral transmittance model was developed using the simple Lorentz line shape and the HITRAN molecular line database and was compared with the transmittance measurements. The self-broadened continuum absorption, spectrally averaged over a passband centred at 7.85 THz (262 cm -1), was determined and confirmed the continuum model of Clough et al. The foreign-broadened continuum was smaller by a factor of at least 19. 相似文献
14.
The stability of SiC coating in helium with a low concentration of O 2, CO 2, and H 2O is a key factor for their application in improvement of oxidation resistance of graphite for high temperature gas-cooled reactors (HTGRs). Through thermodynamic analysis, it is found that the influence factor controlling the critical temperature of passive oxidation for SiC is partial pressure of active gas in helium; the critical temperature of passive oxidation for SiC increases with the partial pressure of O 2, CO 2, and H 2O, SiC is prone to undergo active oxidation in He–CO 2 and He–H 2O system. SiO 2/SiC multilayer coating can improve the oxidation resistance of graphite at higher temperature than SiC coating does under normal operation condition for HTGRs. 相似文献
15.
利用电喷雾质谱(ESI-MS)和紫外-可见吸收光谱(UV-Vis)分析,研究了CrCl 3·6H 2O 浓度为0.1~0.6 mol·L-1的水溶液和[1ChCl∶2EG]/CrCl 3·6H 2O ILs中,Cr(Ⅲ)配合物的存在形式。研究结果表明,在含有CrCl 3·6H 2O的溶液中,Cr(Ⅲ)与Cl-和H 2O形成[Cr(H 2O) nCl 6-n] n-3配合物,其配合物的优势物种受CrCl 3·6H 2O浓度的影响。水溶液中Cr(Ⅲ) 的优势配合物为[Cr(H 2O) 6]3+与[Cr(H 2O) 5Cl]2+,并随CrCl 3·6H 2O浓度增加,水溶液的UV-Vis吸收光谱峰红移,[Cr(H 2O) 5Cl]2+的相对含量增加。而[1ChCl∶2EG]/CrCl 3·6H 2O ILs中的优势配合物为[Cr(H 2O) 2Cl 4]-和[Cr(H 2O) 3Cl 3],且随CrCl 3·6H 2O 浓度增加,溶液的颜色从浅橙红色逐渐变为深绿色,溶液的UV-Vis吸收光谱峰蓝移,[Cr(H 2O) 3Cl 3]的相对量增加。说明CrCl 3·6H 2O的浓度变化,将影响配体Cl-和H 2O与Cr(Ⅲ)配位结合的配位数,从而影响配合物优势物种的相对量。 相似文献
16.
A new procedure for the preparation of Tl 2Ba 2CaCu 2O 8-δ is presented. In the first step stoichiometric amounts of Cu(NO 3) 2·3H 2O, Ba(OH) 2·H 2O, CaO and Tl 2O 3 are reacted in a closed alumina crucible at 760°C to form a mixture of Tl- 2212, CuO, CaO and other oxide phases. In the second step this material is milled, pelletized and fired in a gold-sealed alumina crucible at 860–900°C for three to eight hours. Three batches of Tl-2212 prepared by this method were investigated showing less than 1% loss of thallium while Tc was close to 110 K. Rietveld refinements using time-of-flight neutron-diffraction data demonstrate that the method produces pure material in a reproducible way and that the materials are substoichiometric with respect to oxygen (δ=0.3). Investigations using electron diffraction and high-resolution electron microscopy indicate the absence of stacking faults. 相似文献
17.
The reactions of H 2S with predosed surface oxygen on Ni(110) surfaces were studied for a variety of coverage conditions. The primary reaction product is H 2O, but the details of the water formation and desorption depends on the coverage of both O and H 2S. For high coverages of oxygen (p(2 × 1)−O; 0.5 ML), the reaction to form water is quantitative. The loss of oxygen from the surface (as measured by AES) is equal to the increase in sulfur coverage. XPS and HREELS measurements indicate the presence of chemisorbed H2O immediately following large exposures of H2S on the oxygen predosed surface at 110 K. Deuterium incorporation results suggest that the primary mechanism for these coverage conditions involves direct transfer of hydrogen from SH or H2S moieties to the oxygen. A second mechanism involving reaction of surface hydroxyl groups with surface hydrogen was also identified. This mechanism is particularly important for high coverages of oxygen (0.5 ML) and low coverages of H2S (0.15 ML), where water desorption was observed at 235 K, but was not observed spectroscopically at 110 K. The sequential addition of two surface hydrogen atoms to surface oxygen is not an important mechanism in this system. These reactions were modeled using a bond-order conservation method, and the model successfully reproduced the important mechanistic conclusions. 相似文献
18.
H 2O和CH 4在气候变化过程中起着关键作用,实时在线测量H 2O和CH 4浓度一直都是国内外学者研究的热点问题之一。利用1.653 μm可调谐半导体激光器作光源,结合反射率为99.997 6%的两片高反射镜组成离轴腔增强吸收光谱装置,开展了H 2O和CH 4的高灵敏度测量研究。离轴腔增强系统的有效吸收光程通过吸收面积-浓度关系法来标定,吸收面积-浓度关系法的可行性首先通过已知光程的光学吸收池进行验证,确定有效后用于标定离轴腔增强系统的有效光程。结果表明,基长为21 cm的离轴腔增强系统的有效吸收光程达到了8 626.3 m。当谐振腔内压力为5.06 kPa时,利用7组不同浓度的CH 4标准气体(0.2~1.4 μmol·mol-1)对系统进行了线性响应标定测试,得到了CH 4吸收的积分面积与浓度拟合关系曲线。系统的稳定性、可实现的最小探测灵敏度等信息通过Allan方差进行分析,结果表明系统对探测CH 4的最佳平均时间为100 s,最小可探测浓度极限为7.5 nmol·mol-1;系统对探测H 2O的最佳平均时间为200 s,最小可探测浓度极限为55 μmol·mol-1。对提高系统测量精度的数据处理方法也进行了分析研究,结果表明相比于多次平均方法,Kalman滤波能显著的提高测量精度,而且缩短了系统的响应时间。最后,利用搭建的离轴腔增强实验系统结合Kalman滤波数据处理方法对实际大气中CH 4和H 2O浓度进行了连续两天的测量,CH 4每天平均的浓度分别为2.1和2.08 μmol·mol-1,H 2O每天平均的浓度分别为11 515.6和11 628.6 μmol·mol-1,由此可知建立的离轴腔增强吸收光谱装置能够用于大气CH 4和H 2O的测量,另外建立的系统也可用于相关工业领域的高灵敏度CH 4和H 2O监测。 相似文献
19.
通过对粘度、自旋-自旋弛豫时间以及1H NMR谱的测定,研究了PVP在不同体积配比的水/丙酮溶液中的特性粘数变化和分子运动规律,并讨论了引起这些变化的原因.结果表明:随着丙酮的不断加入,PVP的特性粘数[η]先增加后减小,而T2H先减小后增大.[η]出现最大值也是T2H出现最小值的时候,丙酮的体积百分数为40%.丙酮的加入破坏了水分子间自身氢键相互作用形成的网状结构,解离出来的水分子被PVP优先吸附到大分子链上,部分与羰基形成氢键,另一部分以自由水的形式被包裹在大分子线团内.水分子的不断进入以及与水形成新的氢键使PVP链逐渐伸展,引起特性粘数的增大,分子运动受阻.当丙酮含量增加到一定程度时,水的含量不足以使大分子链继续膨胀,故链呈卷缩状态,使大分子运动逐渐恢复自由.1H NMR谱中各质子的化学位移变化也证实了此过程中的氢键变化规律. 相似文献
20.
四丁基溴化铵(TBAB)半笼型水合物在二氧化碳(CO 2)捕集和封存技术中具有巨大的发展与应用潜力。由于晶体结构的复杂性,TBAB半笼型水合物的动力学过程尚未得到充分的研究。为了解TBAB半笼型水合物在储气方面的动力学特性,实验采用原位激光拉曼技术和多晶粉末X射线衍射仪(PXRD)对 nCO 2·TBAB·26H 2O和 nCO 2·TBAB·38H 2O水合物的光谱特征进行了鉴别与分析,利用原位激光拉曼技术考察了CO 2分子分别进入2种晶体结构的动力学过程。研究结果表明,2种晶体结构的拉曼光谱具有较高的相似性,值得注意的是 nCO 2·TBAB·26H 2O中位于1 309.5和1 326.9 cm-1的拉曼峰为TBA+阳离子中C-C键的变形振动峰,在 nCO 2·TBAB·38H 2O水合物中峰基本不发生改变,但半峰宽降低,峰形也变得相对清晰;同时, nCO 2·TBAB·26H 2O中位于1 446.6和1 458 cm-1的拉曼峰为TBA+阳离子中C-H键的剪切振动峰,在 nCO 2·TBAB·38H 2O水合物中分别向左、右两边发生了位移,峰形的重叠度也随之下降。依据上述2处拉曼光谱特征可以对2种晶体结构进行辨别。通过PXRD图谱可以发现2种晶体结构的衍射图谱存在着比较明显的差距。 nCO 2·TBAB·26H 2O晶体属于四方晶系,空间群( P4/ m),而 nCO 2·TBAB·38H 2O属于正交晶系,空间群( Pmma)。图谱中2 θ=8.406°和10.941°分别为 nCO 2·TBAB·38H 2O的(200)和(220)晶面的特征峰,而2 θ=5.976°和6.969°分别为nCO 2·TBAB·26H 2O的(012)和(003)晶面特征峰,可以用来判别样品中水合物的晶体结构。在原位拉曼测量过程中, nCO 2·TBAB·26H 2O和 nCO 2·TBAB·38H 2O分别在已经合成好的TBAB·26H 2O和TBAB·38H 2O水合物表面形成。在276 K,2 MPa条件下,气相中的CO 2分子分别进入2种晶体结构中用于储气的512笼形结构,在1 275.4和1 379.3 cm-1处形成特征峰并逐渐增长。实验以2种TBAB水合物位于1 110.3 cm-1的拉曼峰作为参考,比较了CO 2在水合物中的增长速率。研究发现在反应初期的75 min内CO 2在2种水合物中的含量基本保持线性增长且上升速率的差别不大。由于测量点位于水合物表面,受气体在水合物中扩散的阻力较小同时2种TBAB水合物均采用512笼形结构储气导致了储气速率相近。以上的微观晶体结构研究结果对TBAB水合物法捕集和封存CO 2技术应用具有重要的意义。 相似文献
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