排序方式: 共有54条查询结果,搜索用时 15 毫秒
1.
Žaneta Mesíková Petra Šulcová M. Trojan 《Journal of Thermal Analysis and Calorimetry》2006,84(3):733-736
Synthesis of the green
spinel pigment Co0.46Zn0.55(Ti0.064Cr0.91)2O4 by a novel two-step method of preparation have
been investigated. Inorganic pigments are almost always prepared by a solid
state reaction. It is classical ceramic method which used oxides, hydroxides
or carbonates as precursors. The reaction is performed at temperature higher
than 1300°C and an agent of mineralization is usually present. The presented
novel method of preparation decreases the calcining temperature necessary
for reaching of bright and clear hue of the pigments prepared. Main attention
was focused on the influence of two types of titanium raw materials on the
temperature region of the spinel structure formation and on the colour properties
of the pigments. The mixture of precursors with TiO2
gives a one-phase system when calcining at 1100°C but the colour properties
are more interesting at 1150°C. Thermal stability of this pigment is limited
by temperature 1300°C. This temperature is connected with partial oxidation
of Cr(III) to Cr(VI). Thermal analysis provided the first information about
the temperature region of the pigment formation and determined the thermal
stability of pigment. 相似文献
2.
The
aim of our research was to prepare yellow pigments based on structure of pseudobrookite
Fe2TiO5. Part of Fe was substituted
with Li and Ti from Fe2TiO5
to Li0.05Fe0.07Ti2.44O5.
Synthesis and pigmentary-application properties in the Li2O–Fe2O3–TiO2 system were studied for 800 and 900°C using classical ceramic
method of preparation. The main attention was aimed to usage of four different
sources of titanium compounds as raw materials. We studied the influence of
different sources of titanium compounds on the structural and the colour properties
of the prepared pigments. The thermal analysis was used for characterization
of titanium compounds and determination of their thermal stability. 相似文献
3.
Single-longitudinal-mode optical parametric oscillator for spectroscopic applications 总被引:1,自引:0,他引:1
We have developed a tunable, narrow-bandwidth nanosecond optical parametric oscillator system and applied it to spectroscopic studies. The system consists of a narrow-bandwidth grazing-incidence oscillator and a seeded power oscillator, generating Fourier-transform-limited 1.5-ns pulses (bandwidth <500 MHz) in the wavelength range 435 to 2000 nm with energy of 3.5 mJ at a pump energy of 22 mJ. Continuous scanning over 30 to 100 GHz (depending on wavelength) is demonstrated by recording of the resonance line of the Hg atom at 253.7 nm and a vibrational transition of the CO (2) molecule at 1528 nm. 相似文献
4.
Moldovan L Melinte S Bayot V Papadakis SJ De Poortere EP Shayegan M 《Physical review letters》2000,85(20):4369-4372
We report very low temperature ( T) thermopower and resistivity ( rho) measurements on variable-density, two-dimensional hole systems confined to GaAs quantum wells. As the hole density is lowered from 1.49x10(11) cm(-2) to 0.14x10(11) cm(-2), the system crosses from an insulating ( drho / dT less, similar0) to a metallic regime ( drho / dT>0) and finally displays insulating behavior ( drho / dT<0). Diffusion thermopower shows a striking sign reversal in a narrow range of density in the metallic regime, suggesting a qualitative change in the conduction or the scattering mechanism. 相似文献
5.
6.
7.
van As BA van Buijtenen J Mes T Palmans AR Meijer EW 《Chemistry (Weinheim an der Bergstrasse, Germany)》2007,13(29):8325-8332
The well-known dynamic kinetic resolution of secondary alcohols and esters was extended to secondary diols and diesters to afford chiral polyesters. This process is an example of iterative tandem catalysis (ITC), a polymerization method where the concurrent action of two fundamentally different catalysts is required to achieve chain growth. In order to procure chiral polyesters of high enantiomeric excess value (ee) and good molecular weight, the catalysts employed need to be complementary and compatible during the polymerization reaction. We here show that Shvo's catalyst and Novozym 435 fulfil these requirements. The optimal polymerization conditions of 1,1'-(1,3-phenylene) diethanol (1,3-diol) and diisopropyl adipate required 2 mol% Shvo's catalyst and 12 mg Novozym 435 per mmol alcohol group in the presence of 0.5 M 2,4-dimethyl-3-pentanol as the hydrogen donor. With these conditions, chiral polyesters were obtained with peak molecular weights up to 15 kDa, an ee value up to 99% and with 1-3 % ketone end groups. Also with the structural isomer, 1,4-diol, a chiral polyester was obtained, albeit with lower molecular weight (8.3 kDa) and slightly lower ee (94%). Aliphatic secondary diols also resulted in enantio-enriched polymers but at most an ee of 46 % was obtained with molecular weights in the range of 3.3-3.7 kDa. This low ee originates from the intrinsic low enantioselectivity of Novozym 435 for this type of secondary aliphatic diols. The results presented here show that ITC can be applied to procure chiral polyesters with good molecular weight and high ee from optically inactive AA-BB type monomers. 相似文献
8.
High temperature asymmetrical flow field-flow fractionation (HTAF4) coupled to infrared (IR), multi-angle light scattering (MALS), and viscometry (Visc) detection is introduced as a tool for the characterization of high molecular weight polyethylenes. The high molecular weight fraction strongly affects the rheological behaviour and processability of polyethylene materials and can often not be accurately resolved by current technology such as high temperature size-exclusion chromatography (HTSEC). Molecular weight (M), radius of gyration (Rg), and intrinsic viscosity [eta] of linear high density polyethylene (HDPE) and branched low density polyethylene (LDPE) samples are studied in detail by HTAF4 and are compared to HTSEC. HTAF4 showed a better separation and mass recovery than HTSEC for very high molecular weight fractions in HDPE and LDPE samples. As no stationary phase is present in an HTAF4 channel, the technique does not show the typical drawbacks associated with HTSEC analysis of high molecular weight polyethylenes, such as, exclusion effects, shear degradation, and anomalous late elution of highly branched material. HTAF4 is applied to study the relation between the molecular weight and the zero shear viscosity eta0 for high molecular weight HDPE. It was found that the zero shear viscosity values predicted from HTAF4 results are in good qualitative agreement with measured values obtained from dynamic mechanical spectroscopy (DMS) experiments, whereas eta0 values predicted from HTSEC do not show a strong correlation. The low molecular weight cutoff of HTAF4 is approximately 5x10(4) as a result of relatively large pores in the HTAF4 channel membrane. HTAF4 is, therefore, currently not suited to analyze low molecular weight materials. 相似文献
9.
EP Sheretov VS Gurov MV Dubkov OV Korneeva 《Rapid communications in mass spectrometry : RCM》1999,13(16):1699-1702
In this article we compare the classical monopole mass filter of von Zahn and the monopole mass filter with a hyperbolic V-shaped electrode. The experimental results and those of computer simulation for both mass spectrometers are presented. We show that the replacement of a conventional 90 degrees V-shaped electrode by an electrode with a hyperbolic profile substantially improves the peak shape of any given mass, and increases the mass resolution by a factor of 3-4 and the abundance sensitivity by a factor of 100. The potential of high analytical performance combined with electroforming techniques for electrode manufacture indicate future practical uses of such instruments. Copyright 1999 John Wiley & Sons, Ltd. 相似文献
10.
Evaluation of the sweep co-distillation cleanup technique for the determination of environmental contaminants in human adipose tissue 总被引:2,自引:0,他引:2
Beef and pork fat, corn, peanut, rapeseed and paraffin oils, as well as vegetable shortening were used to investigate their suitability as fortification media for environmental chemicals in the evaluation of the sweep co-distillation technique. The animal fats produced considerable gas chromatographic background interference, while the oils were partly carried over during the sweep co-distillation process, except for rapeseed and peanut oil. Residue free rapeseed oil was fortified with 26 environmental chemicals in several groups at 20 and 200 ng/g of oil. Recoveries for most compounds were greater than 80% with a coefficient of variation of less than or equal to 10. At the 20 ppb fortification level, recoveries for Aroclor 1260, Mirex and pentachlorobenzene were only 70-80%. A similar low recovery was observed for p,p'-DDT, Mirex, hexachloro-1,3-butadiene, while at the 200 ppb level, 1,2,4-trichlorobenzene was only 33% recovered. The sweep co-distillation technique was further evaluated by using rendered human fat and the same fat diluted with residue free peanut oil. Residue levels in diluted and non-diluted fat were in good agreement, except for hexachlorobenzene. These residue levels were further compared with those obtained by two other cleanup procedures: Florisil-silicic acid column chromatography and low temperature precipitation. In general the sweep co-distillation technique compared favourably with these other cleanup procedures. There was evidence, however, that p,p'-DDT broke down into p,p'-TDE and varying operating procedures did not completely remedy this situation. 相似文献