High-temperature Liquid State Research Articles

Molecular aggregation by hydrogen bonding in cold-crystallization behavior of mixed nucleobases analyzed by temperature-controlled infrared spectroscopy.

The cold-crystallization behaviors of dodecyl-substituted nucleobases (adenine, uracil, and thymine) were analyzed. The dodecyl derivative from uracil alone did not exhibit cold crystallization; however, a mixture of adenine and uracil derivatives at a molar ratio of 1 : 1 exhibited cold crystallization. These results are similar to the thermal behavior of dodecyl derivatives of adenine and thymine alone and in mixtures reported in a previous study. Temperature-controlled infrared spectroscopy was used to observe the molecular assembly states of the liquid, supercooled state, and cold-crystallized compounds. Hydrogen-bonded molecular pairs in the high-temperature liquid state, multiple hydrogen-bonded networks in the supercooled state, and reverse Hoogsteen-type complementary hydrogen bonds in cold-crystallized compounds were observed using infrared spectroscopy. The heterogeneity of the system, due to multiple types of hydrogen bonding, retarded the crystallization rate, resulting in supercooling and cold crystallization. Infrared spectroscopy, which can be used to measure the aggregation state of molecules, including the liquid and supercooled states, is an effective analytical method for clarifying the process of cold crystallization.

Investigation of Dynamic Behavior of Confined Ionic Liquid [BMIM]+[TCM]- in Silica Material SBA-15 Using NMR.

The molecular dynamics of 1-butyl-3-methyl imidazolium tricyanomethanide ionic liquid [BMIM]+[TCM]- confined in SBA-15 mesoporous silica were examined using 1H NMR spin-lattice (T1) relaxation and diffusion measurements. An extensive temperature range (100 K-400 K) was considered in order to study both the liquid and glassy states. The hydrogen dynamics in the two states and the self-diffusion coefficients of the cation [BMIM]+ above the glass transition temperature were extracted from the experimental data. The results were then compared to the corresponding bulk substance. The effects of confinement on the dynamic properties of the ionic liquid clearly manifest themselves in both temperature regimes. In the high-temperature liquid state, the mobility of the confined cations reduces significantly compared to the bulk; interestingly, confinement drives the ionic liquid to the glassy state at a higher temperature Tg than the bulk ionic liquid, whereas an unusual T1 temperature dependence is observed in the high-temperature regime, assigned to the interaction of the ionic liquid with the silica-OH species.

Flux melting of metal-organic frameworks.

Recent demonstrations of melting in the metal-organic framework (MOF) family have created interest in the interfacial domain between inorganic glasses and amorphous organic polymers. The chemical and physical behaviour of porous hybrid liquids and glasses is of particular interest, though opportunities are limited by the inaccessible melting temperatures of many MOFs. Here, we show that the processing technique of flux melting, 'borrowed' from the inorganic domain, may be applied in order to melt ZIF-8, a material which does not possess an accessible liquid state in the pure form. Effectively, we employ the high-temperature liquid state of one MOF as a solvent for a secondary, non-melting MOF component. Differential scanning calorimetry, small- and wide-angle X-ray scattering, electron microscopy and X-ray total scattering techniques are used to show the flux melting of the crystalline component within the liquid. Gas adsorption and positron annihilation lifetime spectroscopy measurements show that this results in enhanced, accessible porosity to a range of guest molecules in the resultant flux melted MOF glass.

Experimental Study on Utilization of Low-Grade Complex Ore through Direct Reduction-Melting and Separation

The direct reduction-melting and separation combined process was the metallurgical processing route, where the iron oxide was reduced with pulverized coal at the solid state. Then, the metallic Fe and the slag were melted and separated at high temperature liquid state. The experiments of this direct reduction-melting and separation combined process were conducted with vanadic titanomagnetite, nickel-laterite ores and copper tailings as raw materials. The experimental results demonstrated that the process could contribute to the comprehensive utilization of the low grade complex iron ore, which is suitable for commercialization.

Orientational order of liquids and glasses via fluctuation diffraction.

Liquids, glasses and other amorphous matter lack long-range order, which makes them notoriously difficult to study. Local atomic order is partially revealed by measuring the distribution of pairwise atomic distances, but this measurement is insensitive to orientational order and unable to provide a complete picture of diverse amorphous phenomena, such as supercooling and the glass transition. Fluctuation scattering with electrons and X-rays is able provide this orientational sensitivity, but it is difficult to obtain clear structural interpretations of fluctuation data. Here we show that the interpretation of fluctuation diffraction data can be simplified by converting it into a real-space angular distribution function. We calculate this function from simulated diffraction of amorphous nickel, generated with a classical molecular dynamics simulation of the quenching of a high temperature liquid state. We compare the results of the amorphous case to the initial liquid state and to the ideal f.c.c. lattice structure of nickel. We show that the extracted angular distributions are rich in information about orientational order and bond angles. The diffraction fluctuations are potentially measurable with electron sources and also with the brightest X-ray sources, like X-ray free-electron lasers.

Amorphous graphene: a realization of Zachariasen’s glass

Amorphous graphene is a realization of a two-dimensional Zachariasen glass as first proposed 80 years ago. Planar continuous random networks of this archetypal two-dimensional network are generated by two complementary simulation methods. In the first, a Monte Carlo bond switching algorithm is employed to systematically amorphize a crystalline graphene sheet. In the second, molecular dynamics simulations are utilized to quench from the high temperature liquid state. The two approaches lead to similar results as detailed here, through the pair distribution function and the associated diffraction pattern. Details of the structure, including ring statistics and angular distortions, are shown to be sensitive to preparation conditions, and await experimental confirmation.

Retrograde Melting and Internal Liquid Gettering in Silicon

Retrograde Melting and Internal Liquid Gettering in Silicon

Quantitative analysis of recycled polyolefines by means of high temperature liquid state 1H and 13C NMR

Poly(ethylene) (PE)/poly(propylene) (PP) post-consumer blends were analyzed by novel 1H and 13C “high temperature liquid state” NMR spectroscopy. Quantitative data about the PE/PP ratio and a qualitative identification of brominated flame-retardant compounds were obtained.

Amorphous Fe-based metal foam

A foam synthesis method that takes advantage of the viscous high-temperature liquid state of Fe-based bulk glass-forming alloys to produce amorphous steel foam is introduced. Zirconium hydride is utilized as a foaming agent taking advantage of the low hydrogen solubility of these glass-forming alloys. Amorphous foams with porosities up to 65% were produced having homogenous cellular morphologies that exhibit cell-size uniformity. Even though intracellular solid regions as thin as a few micrometers are detected, on a global scale the cellular structure is determined to be incapable of alleviating the foam from the brittle nature of the monolithic glass.

Crystallisation of spray-dried amorphous precursors in the SrO–Al2O3 system: a DSC study

Abstract The crystallisation of amorphous precursors in the SrO–Al 2 O 3 system has been studied by DSC and XRD. Amorphous precursors were obtained for compositions ranging from 12SrO.7Al 2 O 3 to Al 2 O 3 by spray-drying aqueous solutions of strontium and aluminium nitrates followed by heating the powders to decompose the nitrates. Of the stable compounds SrA, SrA 2 and SrA 6 , only SrA crystallises directly at a usual heating rate of 5 °C/min (in this notation Sr=SrO and A=Al 2 O 3 ). All the alumina-richer compositions are characterised by the first and strong crystallisation of metastable solid solutions of SrA in its hexagonal form, stabilised by excess aluminium cations, or γ-Al 2 O 3 stabilised by strontium cations, or even the two solid solutions, depending on the composition. The hexaaluminate SrA 6 is formed as single phase by an exothermic transformation of the γ-Al 2 O 3 solid solution at 1183 °C. The formation of SrA 2 is complicated by the easy and competitive formation of Sr 4 A 7 , of close composition. The latter compound is stable only up to 1500 °C and is decomposed at higher temperatures. However SrA 2 , which is characterised by a slow kinetics of formation from the amorphous state as well as from the high temperature liquid state, may be obtained pure by slow heating or annealing at 900–1000 °C.

Ultrasonic and hypersonic properties of molten KNO3–Ca(NO3)2 mixture

A picosecond time-domain light scattering technique is used to study the viscoelastic KNO3–Ca(NO3)2 60:40 glass-forming liquid mixture. By using scattering angles between 1.92° and 85.67°, acoustic frequencies from 50 MHz to 4 GHz are sampled. Together with existing ultrasonic and Brillouin scattering data, a temperature-dependent distribution of relaxation times is found to be well fit with a Cole–Cole distribution whose width changes from several decades in the glassy state to nearly single relaxation time in the high-temperature liquid state. The characteristic relaxation time is found to obey the Vogel–Tammann–Fulcher law with T0=338 K.

Molecular dynamics study of boron trioxide glass

Boron trioxide (B2O3) glass has been simulated here by molecular dynamics using an interionic force law. The parameters for the force law were varied until the results of the simulated system agreed with the experimental findings. The simulation was performed for two systems, one with 64 molecules (128 B and 190 O atoms) and the other with 640 molecules, by slowly cooling the systems from a very high-temperature liquid state at constant volume. The characteristic curves of energy versus temperature and pressure versus temperature show change in slopes around 600K indicating a glass transition in the system. The mean square displacement with temperature also shows a sudden change around this temperature. These properties and the glass transition temperature of small and large systems are very close to each other. The structural analysis of the simulated glass reveals that almost all the boron and oxygen atoms form planar BO3 triangles.