On the importance of dimension variation in determining the limiting steps in adsorption kinetics

Information about the limiting processes in adsorption kinetics can be obtained by an analysis of the shape of the uptake curves (first and second statistical moments M₁ and M₂) as well as by an analysis of the dependence of the adsorption time constants on the radii (R) of the adsorbing particles. The sensitivity of these dependences on the various models of adsorption has been investigated by introducing the factors M₁²/M₂ and d ln M₁/d ln R. d ln M₁/d ln R-2 is shown to be a reliable criterion for diffusion-limited adsorption. From the shape of M₁²/M₂ no corresponding criterion can be derived.     

4-Methylimidazol in Caramel und caramelgef?rbten Lebensmitteln

Zusammenfassung Es wird eine spezifische und kochempfindliche Methode zur Bestimmung von 4-Methylimidazol (4-MeI) in Caramel und caramelgefärbten Lebensmitteln beschrieben. Nach der Extraktion wird 4-MeI gaschromatographisch mit einem stickstoffspezifischen elektrochemischen Detektor (Hall) bestimmt. Als weniger spezifische Alternative kann ein thermoionischer Detektor eingesetzt werden. Bei Zusätzen von 5–200 mg 4-MeI/kg Karamel beträgt die Wiederfindungsrate 90–94%.Die Nachweisgrenze der Methode liegt unterhalb 0,1 mg 4-MeI/kg Caramel; in karamelgefärbten Lebensmitteln können weniger als 0,01 mg/kg nachgewiesen werden.

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4-methylimidazole in caramel and caramel-colored foodsDetermination by gas-liquid-chromatography with nitrogen-specific detectors

Summary A specific and highly sensitive method for the determination of 4-methylimidazole (4-MeI) in caramel and caramel-colored foods is described. After extraction the amount of 4-MeI is determined by gas-liquid chromatography with a nitrogen-specific electrochemical detector (Hall). As a less specific alternative a thermoionic detector can be used. With additions in the range of 5–200 mg 4-MeI/kg caramel, recoveries of 90–94% are obtained.The limit of detection is <0.1 mg 4-Mel/kg caramel; in caramel-colored foods less than 0.01 mg/kg can be detected.

     

Crosslinking of polypropylene in the presence of polyfunctional monomers

The crosslinking of atactic and isotactic polypropylene initiated by organic peroxides in presence of diallyl maleate or pentaerythrityl tetramethacrylate was studied. The influence of concentration of the components of the crosslinking system as well as the effect of temperature and reaction time was followed. For high yield of gel, a high rate of initiation is necessary. Also the rate of reaction of double bonds must be similar to the rate of peroxide decomposition.     

Crystal Chemistry of Iron in Non-Metamict Chevkinite-（Ce） ：Valence State and Site Occupation Proportions

Chevkiniteis one of the commonrare earth acces-sory minerals found in a wide occurrence of paragene-sis . About80analyses of samples in the chevkinitegroup have beenreportedto contain FeO(assuming∑Fe as FeO) rangingfrom7.11%to16·88%[1].How-ever ,in mine…     

Preparation and characterization of zinc-exchanged montmorillonite and its effectiveness as aflatoxin B1 adsorbent

A zinc-exchanged montmorillonite (Zn-MONT) was prepared from a natural montmorillonite (MONT) and the adsorption of aflatoxin B₁ (AFB₁) was investigated at pH 3 and 7. Characterization of Zn-MONT was done by determination of chemical composition, the point of the zero charge (pH_pzc), thermal (DTA/TGA/DTG) and X-ray powder diffraction (XRPD) analysis.     

Evaluation of stability and functionality of BaCe1–x Inx O3–δelectrolyte in a wider range of indium concentration

The properties of BaCe_1–xIn_xO_3–δ(x=0.05,0.10,0.15,0.20,0.25,0.30,0.35,and 0.40) as proton conducting electrolyte are examined.The dense electrolyte is formed after sintering at 1300℃for 5 h in air.The samples with In content≥25 mol%contain In₂O₃ as a secondary phase.The highest total conductivity is around 5×10^–3 S/cm for BaCe_0.75In_0.25O_3–δ in the wet hydrogen atmosphere at 700℃.After exposure to p...     

Effect of glass fibers on rheology,thermal and mechanical properties of recycled PET

PET‐glass fiber composites were prepared by melt mixing of recycled PET with chopped glass fibers (15, 20, and 30 wt%) and their degree of dispersion was assessed by scanning electron microscopy. Rotational rheometry was employed to analyze the interfacial shear strength between the fibers and polymer matrix in the molten state. The composite containing 30 wt% of glass fibers revealed a moderate G′ secondary plateau; hence strong fiber‐matrix interactions were confirmed. Results of mechanical testing were in a good accordance with structural and rheological measurements. The higher rate of mixing under production‐scale conditions resulted in lower fiber‐matrix adhesion and in a similar level of fiber dispersion as compared to the same mixture compounded on pilot‐plant scale. Thermal characterization of the composites was performed by differential scanning calorimetry and total crystalline fraction was analyzed. POLYM. COMPOS., 2008. © 2008 Society of Plastics Engineers