Fast crystallization of alumino- and silicoaluminophosphates with a VFI framework topology

A fast crystallization method for VPI-5-like products is reported. The method allows, for the first time, the full crystallization in less than 1 h of pure aluminophosphates and silicoaluminophosphates. This method requires a high rate of temperature increase of the hydrogel. Products are characterized by X-ray diffraction patterns, scanning electron microscopy, electronic microprobe analysis, ²⁷Al MAS n.m.r., ²⁹Si MAS n.m.r., and ³¹P MAS and CPMAS n.m.r.. N.m.r. spectra are unique and this is due to the high crystallinity of the products. These spectra are compared to the literature and are briefly commented on.     

Thermal expansion of alumino-alkalisilicate and alumino- borosilicate glasses -- comparison of empirical models

Abstracts are not published in this journal This revised version was published online in November 2006 with corrections to the Cover Date.     

Crystalline transformation of Ti-B-O,Al-Ti-B-O,Si-Ti-B-O and Al-Si-Ti-B-O by thermal treatments

The thermal transformations of Ti-B-O, Al-Ti-B-O, Si-Ti-B-O and Al-Si-Ti-B-O have been investigated using the methods of thermal analysis and X-ray powder diffraction. The materials are a crystalline series of TiO₂ with partial replacement of titanium by the elements, aluminium, boron and silicon. The anatase form of the materials was transformed to the rutile form at 520680 °C for Ti-B-O, 880950 °C for Al-Ti-B-O, 10801280 °C for Si-Ti-B-O and 11801330 °C for Al-Si-Ti-B-O. The rate constant for the anatase-rutile transformation of Ti-B-O was 6.908×10^–3 min^–1 under isothermal conditions at 680 °C. Analysis of the kinetic data obtained by differential thermal analysis (DTA) gave the activation energy for transformation of anatase into rutile as 663.7 Kcal mol^–1 for Al-Ti-B-O. The lattice parameters for the compounds studied at various temperatures were calculated by least-squares fitting of the X-ray powder diffraction data.     

Liquid Crystalline Elastomers

Today, material science is directed towards the development of multifunctional and oriented structures. One example of such supramolecular systems are liquid crystalline (LC) elastomers which combine the properties of LC phases (the combination of order and mobility) with rubber elasticity, one of the most typical polymer properties. Their most outstanding characteristic is their mechanical orientability; strains as small as 20% are enough to obtain a perfectly oriented LC monodomain. This orientability, if LC elastomers with chiral phases are used, leads, for example, to elastomers with chiral smectic C* phases which are likely to show piezo-electric behavior.     

Ultrastiff,Strong, and Highly Thermally Conductive Crystalline Graphitic Films with Mixed Stacking Order

A macroscopic film (2.5 cm × 2.5 cm) made by layer‐by‐layer assembly of 100 single‐layer polycrystalline graphene films is reported. The graphene layers are transferred and stacked one by one using a wet process that leads to layer defects and interstitial contamination. Heat‐treatment of the sample up to 2800 °C results in the removal of interstitial contaminants and the healing of graphene layer defects. The resulting stacked graphene sample is a freestanding film with near‐perfect in‐plane crystallinity but a mixed stacking order through the thickness, which separates it from all existing carbon materials. Macroscale tensile tests yields maximum values of 62 GPa for the Young's modulus and 0.70 GPa for the fracture strength, significantly higher than has been reported for any other macroscale carbon films; microscale tensile tests yield maximum values of 290 GPa for the Young's modulus and 5.8 GPa for the fracture strength. The measured in‐plane thermal conductivity is exceptionally high, 2292 ± 159 W m^?1 K^?1 while in‐plane electrical conductivity is 2.2 × 10⁵ S m^?1. The high performance of these films is attributed to the combination of the high in‐plane crystalline order and unique stacking configuration through the thickness.     

Heats of Solution,Transition, and Formation of Three Crystalline Forms of Metaboric Acid

The three crystalline forms of metaboric acid HBO₂ were prepared, purified, and analyzed. Heats of solution in water or of reaction with sodium hydroxide solution were compared with those of orthoboric acid H₃BO₃(c). The best values for the heats of transition at 25 °C are: (c,I) to (c,II), 2.33±0.23 kcal/mole; (c,II) to (c,III), 1.30±0.05 kcal/mole; (c,I) to (c,III), 3.63±0.24 kcal/mole. The following heats of formation at 25 °C were derived: −192.77 ± 0.35 kcal/mole for the cubic HBO₂(c,I), −190.43 ±0.34 kcal/mole for the monoclinic HBO₂ (c,II), and −189.13 ± 0.34 kcal/mole for the orthorhombic HBO₂(c,III).     

纳米晶、亚微米微晶2009铝合金塑性形变的波动特性

纳米晶、亚微米微晶2009铝合金塑性形变试样上各点的应变量是不相同的,并且呈波动性变化,随着外加载荷的增加而波动的幅度增加,表明在拉伸过程中,其应力传播和剪切变形传播在三维方向都具有波动特性。形成峰值与材料缺陷造成应力集中有关,实验结果表明纳米晶、亚微米微晶2009铝合金材料的塑性变形的流动行为的波动特性和非均匀特性,证明了介观力学提出的观点。即材料进入塑性变形后,晶粒群将进入平移-转动涡流,将材料的初始结构层次（包括晶粒、晶界、晶群以及试样整体）全部纳入变形范畴。     

A Crystalline, 2D Polyarylimide Cathode for Ultrastable and Ultrafast Li Storage

Organic electrode materials are of long‐standing interest for next‐generation sustainable lithium‐ion batteries (LIBs). As a promising cathode candidate, imide compounds have attracted extensive attention due to their low cost, high theoretical capacity, high working voltage, and fast redox reaction. However, the redox active site utilization of imide electrodes remains challenging for them to fulfill their potential applications. Herein, the synthesis of a highly stable, crystalline 2D polyarylimide (2D‐PAI) integrated with carbon nanotube (CNT) is demonstrated for the use as cathode material in LIBs. The synthesized polyarylimide hybrid (2D‐PAI@CNT) is featured with abundant π‐conjugated redox‐active naphthalene diimide units, a robust cyclic imide linkage, high surface area, and well‐defined accessible pores, which render the efficient utilization of redox active sites (82.9%), excellent structural stability, and fast ion diffusion. As a consequence, high rate capability and ultrastable cycle stability (100% capacity retention after 8000 cycles) are achieved in the 2D‐PAI@CNT cathode, which far exceeds the state‐of‐the‐art polyimide electrodes. This work may inspire the development of novel organic electrodes for sustainable and durable rechargeable batteries.     

Crystalline Host Phases for Actinides,Obtained by Self-Propagating High-Temperature Synthesis

Host matrices for actinides prepared by self-propagating high-temperature synthesis are studied. The matrices consist of a pyrochlore or fluorite phase and metallic molybdenum. The factor determining the structural type of the crystal lattice of the target phase is the ionic radius ratio. When the difference in the ionic radii is insignificant, as in the case of Y^{3 +} (r 0.102 nm) and Zr^{4 +} (r 0.084 nm), the oxide Zr_{1 - x}Y_xO_{2 - 0 . 5 x} with a fluorite structure is formed, in which the cations occupy the eight-coordinate sites. This structure permits incorporation of heavy lanthanides and tetravalent actinides: U^{4 +} (r 0.10 nm), Np^{4 +} (r 0.098 nm), and Pu^{4 +} (r 0.096 nm). When the difference in the ionic radii is more considerable, as in the case of Y^{3 +} and Ti^{4 +} (r 0.061 nm), a pyrochlore-related structure is realized. In this case the cations occupy different (eight- or six-coordinate) sites. The pyrochlore structure is preserved if the radii of ions occupying different structural sites change in parallel. This structure is typical of zirconates of trivalent actinides and light REEs. The decision on the major host phase for actinides is determined by the waste composition. At low content of light REEs and americium an oxide with a fluorite-related structure shows promise. At high content of these elements, zirconates and titanates with the pyrochlore structure are more stable.     

Switching the Proton Conduction in Nanoporous,Crystalline Materials by Light

Proton conducting nanoporous materials attract substantial attention with respect to applications in fuel cells, supercapacitors, chemical sensors, and information processing devices inspired by biological systems. Here, a crystalline, nanoporous material which offers dynamic remote‐control over the proton conduction is presented. This is realized by using surface‐mounted metal–organic frameworks (SURMOFs) with azobenzene side groups that can undergo light‐induced reversible isomerization between the stable trans and cis states. The trans–cis photoisomerization results in the modulation of the interaction between MOF and guest molecules, 1,4‐butanediol and 1,2,3‐triazole; enabling the switching between the states with significantly increased (trans) and reduced (cis) conductivity. Quantum chemical calculations show that the trans‐to‐cis isomerization results in the formation of stronger hydrogen bridges of the guest molecules with the azo groups, causing stronger bonding of the guest molecules and, as a result, smaller proton conductivity. It is foreseen that photoswitchable proton‐conducting materials may find its application in advanced, remote‐controllable chemical sensors, and a variety of devices based on the conductivity of protons or other charged molecules, which can be interfaced with biological systems.     

Synthesis and Conductivity of Nano Crystalline Ceria

Nanoparticles of cerium oxide were synthesized by the co-precipitation method. Synthesis conditions were optimized for phase purity, particularly the effect of pH (=14,13,11) of solutions during reaction, was studied. The phase analysis and structural properties of the prepared particles were determined by X-ray diffraction analysis. The average crystallite size decreased with the increase in pH of solution. The temperature-dependent DC conductivity was measured in the temperature range 300 °C to 700 °C and was found to be increasing with the increase in measurement temperature. AC conductivity and dielectric constants were measured in the frequency range of 1 kHz to 3 MHz and also at different temperatures.