Chromatography using a water stationary phase and a carbon dioxide mobile phase

A novel chromatographic separation method is introduced which employs water (saturated with CO(2)) as a stationary phase and CO(2) (saturated with water) as a mobile phase. Since water and CO(2) have little miscibility, conditions can be attained that create a stationary phase of water lining the inside of an uncoated stainless steel capillary. Because altering temperature and pressure can change both the density of the mobile phase and the polarity of the stationary phase, these experimental parameters offer good flexibility for optimizing separations and allow for different gradient programmed separation options. Further, since this method is free of organic stationary and mobile phase components, it is environmentally compatible and allows the use of universal flame ionization detection. This system offers very good sample capacity, peak symmetry, and retention time reproducibility (～1% RSD run-to-run, ～4% RSD day-to-day). Analytes such as alcohols, carboxylic acids, phenols, and tocopherols are employed to investigate this relatively inexpensive and robust method. As an application, the system is used to quantify ethanol in alcoholic beverages and biofuel and to analyze caffeine levels in drinks. In all cases, quantitative results are obtained with quick throughput times and often little need for sample preparation.     

Effect of sintering temperature on the phase composition and microhardness of WC-8 wt % Co cemented carbide

The effect of sintering temperature (800–1600°C) on the phase composition, density, and microhardness of WC-8 wt % Co cemented carbide has been studied using x-ray diffraction, scanning electron microscopy, optical microscopy, and density measurements. The results indicate that, during sintering of the starting powder mixture, containing not only WC and Co but also the lower carbide W₂C and free carbon, W₂C reacts with cobalt metal to form Co₃W. At sintering temperatures from 900 to 1200°C, the reaction intermediate is the ternary carbide phase Co₆W₆C. During sintering at 1300°C, this phase reacts with carbon to form Co₃W₃C. Sintering at 1000°C and higher temperatures is accompanied by the formation of a cubic solid solution of tungsten carbide in cobalt, β-Co(WC). The density and microhardness of the sintered samples have been measured as functions of sintering temperature, and the optimal sintering temperature has been determined.     

Effect of temperature on the viscoelastic and viscoplastic behavior of polypropylene

Observations are reported on isotactic polypropylene in tensile tests with various cross-head speeds and relaxation tests in a wide interval of temperatures ranging from room temperature to 120°C. A constitutive model is derived for the viscoelastic and viscoplastic responses of a semicrystalline polymer at arbitrary deformations with small strains. The stress–strain relations involve 6 adjustable parameters that are found by fitting the experimental data. The presence of a critical temperature is demonstrated at which some parameters of the model reach their maxima. This temperature is associated with the α-relaxation temperature of polypropylene.     

Factor analysis and experiment design in high-performance liquid chromatography: III. Influence of mobile phase modifications on the selectivity of chalcones on a diol stationary phase

Walczak, B., Morin-Allory, L., Chrétien, J.R., Lafosse, M. and Dreux, M., 1986. Factor analysis and experiment design in high-performance liquid chromatography. III. Influence of mobile phase modifications on the selectivity of chalcones on a diol stationary phase. Chemometrics and Intelligent Laboratory Systems, 1: 79–90.Chromatographic data for a series of 45 chalcones were determined for eight chromatographic systems with LiChrospher 100 DIOL as the stationary phase and with heptane + 0.5% of a modifier (dichloromethane, tetrahydrofuran, ethanol, propanol, octanol, dimethylsulphoxide or dimethylformamide) as the mobile phase. Analysis of the data was carried out with the help of hierarchical ascending classification (HAC) and correspondence factor analysis (CFA). Such a strategy of data processing allows normal-phase high-performance liquid chromatography data to be treated as a source of information on the electronic and steric properties of compounds. CFA also helps to give a better insight into the chromatographic process.     

Factor analysis and experiment design in high-performance liquid chromatography: IV. Influence of mobile phase modifications on the selectivity of chalcones on an ODS stationary phase

Walczak, B., Chrétien, J.R., Dreux, M., Morin-Allory, L. and Lafosse, M., 1987. Factor analysis and experiment design in high-performance liquid chromatography. IV. Influence of mobile phase modifications on the selectivity of chalcones on an ODS stationary pase. Chemometrics and Intelligent Laboratory Systems, 1: 177–189.Chromatographic data were determined for a series of 45 chalcones (E-s-cis and Z-s-cis), separated in systems with Zorbax ODS and heptane + 0.5% of a modifier (tetrahydrofuran, dioxane, ethanol, propanol, octanol or dimethylformamide). To discuss changes in chalcone selectivity arising from mobile phase modifications data processing is carried out with the help of hierarchical ascending classification and correspondence factor analysis. The same methods of analysis are used to compare chalcone selectivity in systems with stationary phases of different polarity (Zorbax ODS and LiChrospher 100 DIOL), and with the same mobile phases. A better understanding of retention mechanism is obtained.     

Effect of mechanical activation procedure on the phase composition of gypsum

This paper examines the effect of mechanical activation by impact and attrition milling in planetary and ball ring mills on the phase composition of gypsum. Partially dehydrated powders obtained without heat treatment contain up to 60–70% β-CaSO₄ · 0.5H₂O (impact milling) and up to 40–47% α-CaSO₄ · 0.5H₂O (attrition milling). On the addition of a set retarder (maleic acid + poly(vinyl alcohol)), such materials acquire high strength during hardening: up to 11–17 MPa in compression and 7–12 MPa in bending.     

Effect of metal content on the structure and phase composition of Fullerite-Sn films

This paper reports a study of fullerite-Sn films containing 4, 6, 8, 10, 12, or 20 at % Sn grown by thermal evaporation in vacuum using a combined atomic-molecular flow. The influence of metal content and thermal annealing on the surface topography, structure, and elemental and phase compositions of the fullerite-Sn films has been studied by atomic force microscopy, X-ray and electron diffraction, scanning electron microscopy, and X-ray microanalysis. The results demonstrate that films grown by codeposition of Sn atoms and fullerene molecules on oxidized single-crystal silicon substrates have a granular structure. The phase composition of the fullerite-Sn films varies widely, depending on the percentage of Sn: from an intercalated structure to a mixed-phase composite containing a hexagonal fullerite phase, tetragonal Sn, and fullerite-like structures containing Sn nanoparticles. Thermal annealing of the fullerite-Sn films leads to the formation of a new phase.     

Effect of phase composition and microstructure on the thermal diffusivity of silicon nitride

The effects of compositional and microstructural variables and processing conditions on the room temperature thermal diffusivity of hot-pressed and reaction-sintered silicon nitride were determined. The thermal diffusivity for hot-pressed silicon nitride increases with-content. Maximum thermal diffusivity is reached at about 3 wt % MgO. The higher thermal diffusivity of the -phase is attributed to its higher purity level and the less distorted crystal structure compared to the-phase. In reaction-sintered nitride the thermal diffusivity is strongly influenced by the relative amount and needle-like morphology of the-phase. Correlations of the thermal diffusivity with mechanical properties are discussed.     

Effects of composition on the phase transformation behavior of anatase TiO2 in photocatalytic ceramics

The present work focuses on the phase transformation mechanism of TiO₂ nanoparticles in photocatalytic ceramics. TiO₂ nanoparticles were mixed with fused quartz, glaze No.1, and glaze No.2 respectively and heat-treated. The phase transformation behavior of anatase TiO₂ was analyzed by XRD. The results show that the phase transformation behavior of anatase TiO₂ in photocatalytic ceramics is highly dependent on the glaze compositions rather than the crystal size effect, which is significantly different with TiO₂ alone. The phase transformation from anatase to rutile always starts near the softening temperature and finishes below the sphere temperature of the glaze. The higher flux contents in glaze the lower phase transformation temperature. The significant retarding effects of silica and phosphate on the anatase-to-rutile phase transformation appear negligible when modified TiO₂ are applied in glaze. The eutectic liquid is essential for the phase transformation behavior of anatase TiO₂ in photocatalytic ceramics.     

Effect of the surface heterogeneity of the stationary phase on the range of concentrations for linear chromatography

The range of sample sizes within which linear chromatographic behavior is achieved in a column depends on the surface heterogeneity of the RPLC adsorbents. Two widely different commercial adsorbents were tested, the end-capped XTerra-C18 and the non-end-capped Resolve-C18. Adsorption isotherm data of caffeine were acquired by frontal analysis. These data were modeled and used to calculate the adsorption energy distribution (AED). This double analysis informs on the degree of surface heterogeneity. The best adsorption isotherm models are the bi-Langmuir and the tetra-Langmuir isotherms for XTerra and Resolve, respectively. Their respective AEDs are bimodal and quadrimodal distributions. This interpretation of the results and the actual presence of a low density of high-energy adsorption sites on Resolve-C18 were validated by measuring the dependence of the peak retention times on the size of caffeine samples (20-microL volume, concentrations 10, 1, 0.1, 1 x 10(-2), 1 x 10(-3), 1 x 10(-4), and 1 x 10(-5) g/L). The experimental chromatograms agree closely with the band profiles calculated from the best isotherms. On Resolve-C18, the retention time decreases by 40% when the sample concentration is increased from 1 x 10(-5) to 10 g/L. The decrease is only 10% for Xterra-C18 under the same conditions. The upper limit for linear behavior is 1 x 10(-4) g/L for the former adsorbent and 0.01 g/L for the latter. The presence of a few high-energy adsorption sites on Resolve-C18, with an adsorption energy 20 kJ/mol larger than that of the low-energy sites while the same difference on Xterra is only 5 kJ/mol, explains this difference. The existence of adsorption sites with a very high energy for certain compounds affects the reproducibility of their retention times and a rapid loss of efficiency in a sample size range within which linear behavior is incorrectly anticipated.     

真空退火温度对VO2粉末相变性能的影响

用化学方法配合适当的真空退火工艺制备了具有较好电、光相变性能的VO2粉末.分析了经过不同真空退火工艺处理所得试样的XRD、XPS谱图、相变性能,得到了真空退火温度与VO2粉末相变性能之间的关系.     

退火温度对Gd2(Co,Al)17合金相组成和热磁特性的影响

用X射线衍射、金相观察、电子探针、透射电镜和磁性测量研究了Gd2Co17-χAlχ（χ≤5）合金的微结构、相组成、相成分和热磁特性。结果表明，在1173和1323K退火的χ≤3的样品和在1323K退火的χ=4的样品近似为单相，2：17主相仅含Gd、Co、Al 3种元素，具有菱方Th2Zn17型结构，少量ζ杂质相是富Gd氧化物、富Co相或ζ-CoAl相；在1173K退火的χ=4的样品含有较多的第二相，它是具有六方CaCu5型结构的1：5相；χ=5的退火样品是三相，主相是1：5相，第二相和第三相分别是2：17相和具有CsCl结构的ζ-CoAl相，提高退火温度，样品的2：17相含量增多，1：5相相应减少；在室温以下，样品（χ≤4）的自发磁化强度随温度降低而减小，在74和65K附近，χ=4的两相样品和单相样品的自发磁化强度M0先后降为零，但χ=5的样品磁距随温度降低而增大。     

Retention of ionizable compounds in reversed-phase liquid chromatography. Effect of the ionic strength of the mobile phase and the nature of the salts used on the overloading behavior

The retention mechanism of the protonated cation in propranolol chloride on C18-Xterra was investigated using mobile phases of various compositions. Accurate adsorption data were measured by frontal analysis, with a mixture of methanol and water (25% methanol), with no salt, as the mobile phase. The experimental isotherm has at least two inflection points, at concentrations of about 0.2 and 6.0 g/L, respectively. This precludes the modeling of these data with a simple convex-upward isotherm (e.g., Langmuir). The adsorption energy distribution or relationship between the number of sites on the adsorbent surface and the energy of adsorption on these sites was calculated by assuming Moreau isotherm behavior (S-shaped isotherm). This model has never been applied to describe the surface heterogeneity of any RPLC adsorbent. The calculation converged toward a bimodal energy distribution. Accordingly, the bi-Moreau model is the simplest theoretical model accounting for the adsorption data of propranolol from a mobile phase without salt. The complex-overloaded band profiles of propranolol measured in the presence of increasing concentrations of a supporting salt (KCl) in the mobile phase demonstrate that the same isotherm model applies also under these conditions, as was merely assumed in a previous work. The elution band profiles of propranolol calculated with the bi-Moreau isotherm model for solutions of salts of different natures (CaCl2, CsCl, Na2SO4) in the same mobile phase agree very well with the experimental band profiles.     

相分离Gd5Ge4合金的低温磁化行为及温度依赖性研究

系统研究了Gd_5Ge_4合金的晶体结构和低温磁化行为.结果表明,Gd_5Ge_4具有相分离特征,低温下出现反铁磁(AFM)和铁磁(FM)共存现象.由于相分离的存在导致127K时发生奈尔反铁磁转变.在外磁场诱导下,在4.2K以下发生AFM-FM磁转变,并导致台阶式磁化现象发生,但仅发生在第一次外加磁场增加过程中,表现出磁不可逆性.随磁场升高,在10K以下体系存在类台阶式响应和不可逆的磁滞行为,并在5572kA/m下均达到饱和磁化.在温度50～60K温区,磁循环所出现的台阶式磁化转变则是完全可逆的,更高温区域则表现为部分铁磁直至室温下的顺磁特性.     

Effect of phase transformations during synthesis on the chemical composition and structure of calcium-deficient hydroxyapatite

The chemical and phase changes during the precipitation of calcium-deficient hydroxyapatite from a solution of natural chalk in a mixture of phosphoric and nitric acids, with the use of aqueous ammonia as the precipitant, have been studied by potentiometric titration and physicochemical analysis. The initial solution concentration and precipitation time are shown to have a significant effect on the composition and structure of the precipitate. The processes in the solution and precipitate are interpreted in terms of thedegree of protonation of phosphate ions under various conditions.     

Chemical treatments of coir pith: Morphology,chemical composition,thermal and water retention behavior

Coir pith is one of the most abundant agro waste found in the southern coastal regions of India, where the economy and livehood of people are largely dependent on the coconut industry. Many technologies have been developed successfully for the alternate use of coir pith. However the application of coir pith as fillers in polymer composite is limited. The major drawback of coir pith as filler in polymer is its low adhesion with the matrix and high water sorption and retention behavior. The present work is a part of research work carried out in our laboratory to modify the morphology and chemical properties of pith to make it better filler in the processing of polymer composites. Coir pith was subjected to mercerization followed by different types of chemical treatment. The products were analyzed in detail using FTIR, XRD, optical microscope, AFM and SEM. The chemical treatment resulted in increased density, thermal stability and reduced water retention behavior.