Stability of gamma-valerolactone under neutral,acidic, and basic conditions

Dry gamma-valerolactone (GVL) is stable for several weeks at 150 °C and its thermal decomposition only proceeds in the presence of appropriate catalysts. Since GVL does not react with water up to 60 °C for several weeks, it could be used as a green solvent at mild conditions. At higher temperatures, GVL reacts with water to form 4-hydroxyvaleric acid (4-HVA) and reaches the equilibrium in a few days at 100 °C. Aqueous solutions of acids (HCl and H₂SO₄) catalyze the ring opening of GVL even at room temperature, which leads to the establishment of an equilibrium between GVL, water, and 4-HVA. Although the 4-HVA concentration would be below 4 mol% in the presence of acids, it could be higher than the concentration of a reagent or a catalyst precursor, not to mention a catalytically active species. The latter could be especially worrisome as 4-HVA could be an excellent bi- or even a tri-dentate ligand for transition metals. Aqueous solution of bases (NaOH and NH₄OH) also catalyzes the reversible ring opening of GVL. While in the case of NaOH, the product is the sodium salt of 4-hydroxyvalerate, the reversible reaction of GVL, with NH₄OH results in the formation of 4-hydroxyvaleric amide. The reversible ring opening of (S)-GVL in the presence of HCl or NaOH has no effect on the stability of the chiral center.     

Effect of temperature on sulfate transport in two Penicillia

We studied the effects of temperature on the sulfate permease of Penicillium chrysogenum (PC) (a mesophile with a growth temperature range of 4-35°C) and Penicillium duponti (PD) (a thermophile with a growth temperature range of 27-58°C). Arrhenius plots of sulfate permease activity from mycelia grown at 50°C (PD), 30°C (PD and PC) or 8°C (PC) indicate that at temperatures below the transition point there is little difference in the activation energy of sulfate permease in mycelia from PD grown at 50°C or 30°C or PC grown at 30°C or 8°C; however, the temperature of the transition point for the permease from each set of mycelia assayed reflects the optimum growth temperature of the fungal source. Transitions occur at 15 °C for mycelia from PC and 35 ° C for PD mycelia. Kinetic measurements indicate that the K_m of sulfate permease in PC cells grown at a variety of temperatures is essentially the same at various temperatures. As an example, the K_m of 8°C or 30°C grown PC is about 55 μM at 25°C and 45 μM at 8°C. V_max measurements reflect growth conditions such as temperature and growth stage. p]Lipid composition of the mycelia dramatically reflect growth temperatures. Double bond index values vary from 1.94 for PC grown at 8°C to 0.81 for PD grown at 50°C. The percentage of total fatty acid represented by linolenic acid varies from 45% in 8°C grown PC to 4.2% or less in 30°C grown PC. No linolenic is found in mycelia from PD.     

Stereoselective nucleophilic substitution of poly(vinyl chloride) with sodium thiophenate in cyclohexanone solution: Influence of the reaction temperature on the mechanism

Nucleophilic substitution of PVC with sodium thiophenate was carried out in cyclohexanone solution at 5, 25, 40, 60, and 70°C. The initial rate obeys an Arrhenius law from 25 to 60°C, with an activation energy of 70 kJ/mol. Conversion limits are observed which strongly depend on the temperature. The stereoselectivity of the reaction with respect to the configurational triads does not depend on the temperature: the distribution of configurations is only dependent on the conversion. Assuming an S_N2 substitution mechanism governed by steric factors, the Monte Carlo simulation procedure described in a prior study is shown to give a good account for all temperatures above 40°C assuming for the mm, mr or rm, and rr triads a reactivity such as R_mm = 2 R_mr and R_rr nil at low temperature and very low at temperatures ≥ 40°C. The low conversion limits observed at 5 and 25°C cannot be explained by a limited accessibility of a part of the polymer. Finally, it is shown that the elimination reaction, which remains limited, does not interfere with the substitution process.     

Some applications of thermomagnetometry to the study of chromindur alloys

Thermomagnetic experiments are shown to be a useful and rapid technique for studying phase changes involving magnetic materials. Particular examples are chosen from Chromindur II (Fe28Cr10.5Co) alloys having different thermal histories. The Curie temperature of the single phase alloy is found to be ～650°C and the metastable spinodal decomposition boundary is at essentially the same temperature. The Cr-rich near equilibrium decomposition product is less magnetic and has a lower T_c, while the Cr-deficient product is more magnetic, with a T_c ? 720°C.Comparisons are made at different heating and cooling rates between temperatures measured using magnetic standards and those measured by a thermocouple in close proximity to the sample.     

The influence of concentration of doping elements on anatase–rutile transformation at the synthesis of rutile pigments (Ti,Cr,Nb)O2 and their pigmentary properties

An analysis of the effects of dopants concentration and different starting titanium compounds on the anatase to rutile phase transformation at the synthesis of rutile pigments Ti_1?3xCr_xNb_2xO_2±δ is presented in this study. The main goal was to analyze reaction mixtures for x = 0.05 (previous study) and 0.30 by simultaneous TG–DTA analysis and to determine the temperature of anatase–rutile transition. For x = 0.05, initial temperatures 760–830 °C are needful for a formation of rutile structure. The temperature is the lowest for the hydrated Na₂Ti₄O₉ paste (760 °C) and similar for other starting compounds of titanium. But for x = 0.30, the anatase–rutile transition begins at higher temperatures 910–1,030 °C because of high-Nb content, which is the inhibitor of this modification change. In addition, we found the influence of calcination temperatures (850, 900, 950, 1000, 1050, 1100, and 1150 °C) on color properties and particle size distribution of these materials prepared from anatase TiO₂ and with x = 0.30. Selected pigments were also analyzed by X-ray powder diffraction.     

On the oxidation behaviour of monolithic TiB2 and Al2O3-TiB2 and Si3N4-TiB2 composites

In view of the susceptibility of TiB₂ to oxidation, the thermal stability of monolithic TiB₂ and of Al₂O₃-30 vol% TiB₂ and Si₃N₄-20 vol% TiB₂ composites was investigated. The temperature at which TiB₂ ceramic starts to oxidize is about 400°C, oxidation kinetics being controlled by diffusion up toT≈900°C and in the first stage of the oxidation at 1000°C and 1100°C (up to 800 min and 500 min respectively), and by a linear law at higher temperatures and for longer periods. Weight gains in the Al₂O₃-TiB₂ composite can be detected only at temperatures above ≈700°C and the rate governing step of the oxidation reaction is characterized by a one-dimensional diffusion mechanism atT=700°C andT=800°C and by two-dimensional diffusion at higher temperatures. Concerning the Si₃N₄-TiB₂ composite, three different oxidation behaviours related to the temperature were observed, i.e. up to ≈1000°C the reaction detected regards only the second phase; at ≈1000<T<≈1200°C, the diffusion of O₂ or N₂ through an oxide layer is proposed as the rate-governing step; atT〉=1200°C, a linear kinetic indicates the formation of a non protective scale.     

Impedance-based total-NOx sensor using stabilized zirconia and ZnCr2O4 sensing electrode operating at high temperature

We report here a new-type zirconia-based sensor that can detect total NO_x content at high temperatures such as 700 °C. A closed-one-end yttria-stabilized zirconia (YSZ) tube was used as a base sensor material. An oxide sensing electrode (SE) and a Pt counter electrode (CE) were formed on the outer and inner surfaces of the YSZ tube, respectively. The complex impedance of the device using a ZnCr₂O₄-sensing electrode was measured with an impedance analyzer in the frequency and the temperature ranges 0.1 Hz–100 kHz and 600–700 °C, respectively. A large semicircular arc was observed in complex impedance plots (Cole–Cole plots) in the lower frequency range examined and it seemed to correspond to the electrolyte/electrode interface. The impedance value at 1 Hz of the present device was found to vary almost linearly with the concentration of NO (or NO₂) from 50 to 400 ppm in the sample gas at 600–700 °C. Furthermore, it is noted that the sensitivity of NO is almost equal to that of NO₂. This means that the present device can detect the total NO_x at higher temperatures.     

Heated Slurry Sampling for the Determination of Cadmium in Food by Electrothermal Atomic Absorption Spectrometry

A heating procedure is reported with slurry sampling electrothermal atomic absorption spectrometry to improve the accuracy of cadmium determination in food. In comparison to conventional slurry sampling, the heating significantly increased cadmium recovery and improved the precision. For the optimized procedure, 25–250 mg of food were treated with 2% HNO₃ and 1% H₂O₂ with heating at 120°C for 20 min, followed by the addition of 50 µL of 10% Triton X-100, and homogenization in an ultrasonic bath prior to analysis. Tungsten and rhodium were employed as a permanent modifier with optimum pyrolysis and atomization temperatures of 500°C and 1500°C. Calibration with aqueous standards resulted in good agreement between certified or information values and measured results at the 95% confidence level. A characteristic mass of 0.8 ± 0.1 pg and a detection limit of 0.7 ng g^?1 for a 2% slurry were obtained. The method was employed for the direct determination of cadmium in food certified reference materials.     

Neutron diffraction study of dehydrogenation of titanium carbohydrides TiC<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>H<Subscript><Emphasis Type="Italic">y</Emphasis></Subscript>

The possibility of the synthesis of hydrogen-nonstoichiometric cubic titanium carbide ТiС _х of high purity from powdery nonstoichiometric cubic titanium carbohydride ТiС _х H _y or nonstoichiometric titanium carbide with admixture hydrogen by annealing in a continuously maintained vacuum of no worse than 1.33 × 10^–3 Pa at temperatures of 600–750°C for several hours has been shown. Similar annealing at higher temperatures (T ≥ 800°C) does not lead to the complete removal of hydrogen from a sample due to intensive sintering. In this case, it seems that pores between sintered particles are hydrogen traps, and the release of hydrogen through the surface of sintered particles is hindered.     

Phase equilibria in the ZnGeAs2-CdGeAs2 system

The phase diagram of the ZnGeAs₂-CdGeAs₂ system was constructed using a set of physicochemical analysis methods (X-ray powder diffraction, differential thermal, and microstructural analyses). It was shown that there is a continuous series of solid solutions Zn _x Cd_{1 ? x} GeAs₂ in the system at temperatures above 600°C. At temperatures below 600°C, there is a significant phase separation region. The solubility at room temperature on the side of ZnGeAs₂ does not exceed 12 mol % CdGeAs₂, and that on the side of CdGeAs₂ is no more than 16 mol % ZnGeAs₂. The change in the crystal lattice parameters of the solid solutions within these concentration ranges obeys Vegard’s law, which is indicative of the mutual replacement of Zn and Cd in the cation sublattice of the compounds ZnGeAs₂ and CdGeAs₂.     

Colorimetric determination of osmium (VI) with 1-naphthylamine-3,5,7-trisulfonic acid

An investigation has been made of the organic compound, 1-naphthylamine-3,5,7-trisulfonic acid, for use as a colorimetric reagent for the determination of trace quantities of osniiun(Vl). When this compound is added to an osmium (OsO₄^-2) solution, a violet colored organo-osmium complex is formed which has highest sensitivity at wavelength 560 mμ. The complex reaches maximum color intensity after four hours. The solution should be brought to pH 1.5 and maintained at tins pH with a buffer, after maximum color development. The colored complex conforms to Beer's law over an osmium concentration range of 0 to 6 p.p.m. Its absorbance is not affected by either excess reagent (up to a 7 : 1 ratio) or by temperature variation over the range 15° to 35° C. Many metallic ions interfere with the color reaction and hence require a separation, of osmium from these ions.The nature of the complex in solution was studied by the following three methods: (1) mole ratio, (2) continuous variations and (3) slope ratio. All three methods indicate a ratio of reagent to osmium of 2 to 1.A procedure for the colorimetric determination of osmium(VI) has been developed; it has a sensitivity of 1 part osmium in 15,000,000 parts of solution, with good precision.     

Buffers for the Physiological pH Range: Studies of 4-(N-Morpholino)butanesulfonic Acid (MOBS) from 5 to 55 °C

In this study, we report the pH values of two buffer solutions without chloride ion and eight buffer solutions with NaCl with an ionic strength I=0.16 mol?kg^?1. Electromotive force (emf) techniques have been used to get the cell potentials at 12 temperatures from 5 to 55?°C, including 37?°C. An extended form of the Bates-Guggenheim convention is used in the entire ionic strength range, 0.04 to 0.16?mol?kg^?1. The residual liquid junction potentials (??E _j ) of the buffer solutions of MOBS have been estimated from previous measurements with a flowing junction cell. These values of ??E _j have been used for correction in order to ascertain the operational pH values of four buffer solutions of MOBS at 25 and 37?°C. These solutions are recommended as pH standards for physiological application in the pH range 7.4 to 7.7.     

Effect of Temperature on the Variation of Retention Time of Unretained Compound and Retention Indices of Some Explosives and Related Compounds Calculated Using a Multiparametric Method in RP-LC

In reversed phase liquid chromatography (RP-LC), a multiparametric non-linear least-squares regression iterative method has been evaluated at different column temperatures (ranging from 30 to 60 °C in 5 °C steps) for calculating the retention time of the unretained compound t _M and the regression parameter (slope b), based on the use of alkan-2-ones, alkyl aryl ketones and 1-nitroalkanes homologous series on two different columns: Spherisorb-ODS2 C₁₈ and Nucleosil C₈. The calculated parameters t _M and b by the multiparametric method (MP) were compared with those obtained by using the iterative method of Guardino’s. The influence of the number of subsets of homologues used for the calculation of t _M and b values was investigated. The retention indices (RI) of some neutral and acidic explosives and related compounds (nitramines, nitroaromatics, aminonitroaromatics and nitrophenols) based on the alkan-2-ones retention index standards have been determined and compared at various temperatures by the MP method. Good agreement was observed between retention data calculated by the MP and GU methods.     

Urea and CaCl2 as inhibitors of coal low-temperature oxidation

Thermal analysis was used to study the influence of CaCl₂ and urea as possible chemical additives inhibiting coal oxidation process at temperatures 100?C300?°C. Weight increase due to oxygen chemisorption and corresponding amount of evolved heat were evaluated as main indicative parameters. TA experiments with different heating rates enabled determination of effective activation energy E _a as a dependence of conversion. In the studied range of temperatures, the interaction of oxygen with (untreated) coal was confirmed rather as a complex process giving effective activation energies changing continuously from 70?kJ?mol^?1 (at about 100?°C) to ca. 180?kJ?mol^?1 at temperatures about 250?°C. The similar trend in E _a was found when chemical agents were added to the coal. However, while the presence of CaCl₂ leads to higher values of the effective activation energies during the whole temperature range, urea causes increase in E _a only at temperatures below 200?°C. Exceeding the temperature 200?°C, the presence of urea in the coal induces decrease in activation energy of the oxidation process indicating rather catalysing than inhibiting action on coal oxidation. Thus, CaCl₂ can only be recommended as a ??real?? inhibitor affecting interaction of coal with oxygen at temperatures up to 300?°C.     

Specific Detection of Vibrio Parahaemolyticus by Fluorescence Quenching Immunoassay Based on Quantum Dots

In this study, anti-Vibrio parahaemolyticus polyclonal and monoclonal antibodies were prepared through intradermal injection immune and lymphocyte hybridoma technique respectively. CdTe quantum dots (QDs) were synthesized at pH 9.3, 98 °C for 1 h with stabilizer of 2.7:1. The fluorescence intensity was 586.499, and the yield was 62.43 %. QD probes were successfully prepared under the optimized conditions of pH 7.4, 37 °C for 1 h, 250 μL of 50 mg/mL EDC?·?HCl, 150 μL of 4 mg/mL NHS, buffer system of Na₂HPO₄-citric acid, and 8 μL of 2.48 mg/mL polyclonal antibodies. As gold nanoparticles could quench fluorescence of quantum dots, the concentration of V. parahaemolyticus could be detected through measuring the reduction of fluorescence intensity in immune sandwich reaction composed of quantum dot probe, gold-labeled antibody, and the sample. For pure culture, fluorescence intensity of the system was proportional with logarithm concentration of antigen, and the correlation coefficient was 99.764 %. The fluorescence quenching immunoassay based on quantum dots is established for the first time to detect Vibrio parahaemolyticus. This method may be used as rapid testing procedure due to its high simplicity and sensitivity.     

Synthesis of ultra-high-molecular-weight polyacrylonitrile by anionic polymerization

The anionic polymerization of acrylonitrile in DMF initiated by lithium 1,2-bis(diethylamino)-2-oxoethanolate in the range ?60 to 0°C has been studied. The initiator efficiency at low temperatures (?60 to ?40°C) is 2–6%; it remains nearly invariable with conversion owing to the associated state of the initiator. The low concentration of growing active centers is constant throughout the process; as a result, polymers with M > 3 × 10⁵ are produced. The polymers are characterized by a narrow molecular-mass distribution, M _w/M _n = 1.3–1.6, and contain insignificant amounts of low-molecular-mass fractions. It has been shown that controlled polymerization processes can be carried outat moderately low temperatures (?30 to 0°C), and experimental conditions for freezing of polymerization and its recommencement have been ascertained. Optimum conditions for the synthesis of a high-molecular-mass polyacrylonitrile with M > 3 × 10⁵ have been established, and the method for preparing polymers with M = (6.50–8.5) × 10⁵ on an enlarged scale using high concentrations of the monomer has been developed.     

Dyed polyvinyl chloride films for use as high-dose routine dosimeters in radiation processing

Characteristics of the polyvinyl chloride (PVC) films containing 0.11 wt% of malachite green oxalate or 6GX-setoglausine and about 100 μm in thickness were studied for use as routine dosimeters in radiation processing. These films show basically color bleaching under irradiation with ⁶⁰Co γ-rays in a dose range of 5–50 kGy. The sensitivity of the dosimeters and the linearity of dose-response curves are improved by adding 2.5% of chloral hydrate [CCl₃CH(OH)₂] and 0.15% hydroquinone [HOC₆H₄OH]. These additions extend the minimum dose limit to 1 kGy covering dosimetry requirements of the quality assurance in radiation processing of food and healthcare products. The dose responses of both dyed PVC films at irradiation temperatures from 20°C to 35°C are constant relative to those at 25°C, and the temperature coefficients for irradiation temperatures from 35°C to 55°C were estimated to be (0.43±0.01)%/°C. The dosimeter characteristics are stable within 1% at 25°C before and 60 days after the end of irradiation.     

A CP-MAS NMR study of some deactivation methods in capillary gas chromatography

The effect of temperature, water content, and the type of reagent on the silylation of fused silica capillaries was studied by ²⁹Si and ¹³C CP-MAS NMR. Fumed silica (Cab-O-Sil M5), which is essentially a highly dispersed vitreous quartz with a surface comparable to that of fused silica capillary columns, was selected as a model material. Hexamethyldisilazane (HMDS) and 1,2-diphenyl-1,1,3,3-tetraphenyldisilazane (DPTMDS), which were used as silylation reagents, yielded trimethyl- and dimethylphenylsilyl surface groups respectively at lower temperatures (< 350°C and <250°C respectively). At higher temperatures, increasingly more dimethylsilyl groups are formed, with the silicon bound to two oxygen atoms. This process occurs for DPTMDS at a considerably lower temperature than for HMDS. The formation of silyl groups on the surface and the disappearance of hydroxyl groups are followed independently. The ¹³C NMR and GC-MS of the reaction products showed that with DPTMDS, the formation of two Si-O-Si links is accompanied by a loss of phenyl groups rather than of methyl groups. After the Cab-O-Sil had been dried over P₂O₅, the formation of these double links occurred for HMDS only at temperatures above 460°C and for DPTMDS at 400°C. Thus we concluded that water supplies oxygen atoms for double Si-O-Si links (possibly crosslinks) necessary for efficient deactivation. This may explain the less successful silanization of fused silica capillaries because their water content is lower than that of glass capillaries.     

Water splitting as a tool for obtaining insight into metal–support interactions in catalysis

This review is focused on the use of the water splitting reaction for characterizing oxygen vacancies in supported metal catalysts and more generally to get insight into the high-temperature modifications of metal–support interactions. Three supports widely used in catalysis are considered, namely alumina, silica and ceria. The catalysts were reduced at temperatures T_R ranging from 200 to 1000 °C. The reaction with water was carried out at temperatures T_OX ranging from 100 to 1000 °C. In every case, the metal (Rh or Pt) was chosen among those which are not oxidizable by water. Extensive investigations of the reactivity of water with unsupported metals and films confirmed this choice. The reaction is then selective for the titration of O vacancies, generally associated with reduced cations of the support. On alumina-supported catalysts, reduction at T_R > 600 °C leads to the formation of oxygen vacancies strictly confined to the periphery of metal particles. The amount of hydrogen produced Q_H is coherent with the peripheral oxygen density. Reduction of silica-supported catalysts at T_R > 600 °C generates metal silicides that can be selectively destroyed by water with reformation of silica and metal nanoparticles. Oxygen vacancies are formed on ceria catalysts at 200 °C. These oxygen vacancies are confined to the surface up to 600 °C. At higher temperatures, oxygen vacancies are formed in the bulk: about 50% of CeO₂ would be reduced at 900 °C. The amount of H₂ produced by reaction with water is thus very high on metal-ceria catalysts. At T_R > 900 °C, metal cerides start to form. Remarkably, a significant reactivity of H₂O on a Rh/CeO₂ catalyst reduced at 850 °C is recorded as of 100 °C. However, the quantitative titration of oxygen vacancies required temperatures T_OX > 500 °C. As a rule, the technique of water splitting allows the detection of 1 μmol g⁻¹ of oxygen vacancies, i.e. a few 0.1% of the surface in the case of reducible oxides of 10–20 m² g⁻¹.     

Spectrophotometric investigation of the mechanism of polymerization of isobutylene with vanadium tetrachloride and visible light

The spectra of n-heptane solution of VCl₄, isobutylene, and their mixture at temperatures ranging from +25 to ?80°C in the range of wavelengths from 200 to 2000 nm were investigated. In the region of wavelengths of visible light (400–700 nm) in which the absorption of isobutylene alone and of VCl₄ (concentration lower than 2.2 × 10^?4 mole/l.) is practically zero, their mixtures exhibit an absorption which depends on the concentration of both components and on temperature. A colored complex of VCl₄ and isobutylene is thus obtained, the concentration of which increases with decreasing temperature and is in equilibrium with that of the starting components. The polymerization of isobutylene under the experimental conditions investigated here probably is initiated with the isobutylene–VCl₄ complex after its excitation with light or heat. At low temperatures (t < ?20°C), when the polymerization of isobutylene with VCl₄ virtually does not take place at all in the dark, only excitation with light is operative in the initiation, while at higher temperatures (t > +10°C) thermal excitation plays the predominant role.