Preparation and practical application of spinel pigment Co0.46Zn0.55(Ti0.064Cr0.91)2O4

Synthesis of the green spinel pigment Co_0.46Zn_0.55(Ti_0.064Cr_0.91)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.     

Yellow pigments based on Fe2TiO5 and TiO2

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 Li_0.05Fe_0.07Ti_2.44O₅. 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.     

Single-longitudinal-mode optical parametric oscillator for spectroscopic applications

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.     

Iterative tandem catalysis of secondary diols and diesters to chiral polyesters

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.     

Characterization of high molecular weight polyethylenes using high temperature asymmetrical flow field-flow fractionation with on-line infrared, light scattering, and viscometry detection

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.     

Evaluation of the sweep co-distillation cleanup technique for the determination of environmental contaminants in human adipose tissue

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.     

Structure and Bonding in CE5− (E=Al–Tl) Clusters: Planar Tetracoordinate Carbon versus Pentacoordinate Carbon

The structure, bonding, and stability of clusters with the empirical formula CE₅^? (E=Al–Tl) have been analyzed by means of high‐level computations. The results indicate that, whereas aluminum and gallium clusters have C_2v structures with a planar tetracoordinate carbon (ptC), their heavier homologues prefer three‐dimensional C_4v forms with a pentacoordinate carbon center over the ptC one. The reason for such a preference is a delicate balance between the interaction energy of the fifth E atom with CE₄ and the distortion energy. Moreover, bonding analysis shows that the ptC systems can be better described as CE₄^?, with 17‐valence electrons interacting with E. The ptC core in these systems exhibits double aromatic (both σ and π) behavior, but the σ contribution is dominating.