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  • Polymer and Materials Science  (229)
  • Chemical Engineering  (77)
  • 1990-1994  (306)
  • 1991  (306)
  • 1
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 42 (1991), S. 225-232 
    ISSN: 0021-8995
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The micelle-forming monomers of sodium 6-acrylamidocaproate (Na 6-AAC), sodium 11-acrylamidoundecanoate (Na 11-AAU), sodium 11-(N-methylacrylamido) undecanoate (Na 11-MAAU), and sodium 11-(N-ethylacrylamido) undecanoate (Na 11-EAAU) have been synthesized and polymerized. Except poly(Na 6-AAC), the molecular weights of the other three poly(sodium acrylamidoalkanoate) s were over 106. They behave as strong anionic polyelectrolytes in aqueous solutions. Their solution properties, such as viscosity, charge density, and radius of gyration, were investigated. The performance of these anionic polyelectrolytes as coagulant aids in water treatment were assessed by jar test. Poly(Na 6-AAC) and poly (Na 11-AAU) were superior to poly (Na 11-MAAU) and poly (Na 11-EAAU) in terms of flocs settling. All these four anionic polyelectrolytes tested in water treatment are as effective as a commercially available cationic polyamine organic coagulant (Hyperfloc CP 753).
    Additional Material: 6 Ill.
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  • 2
    Electronic Resource
    Electronic Resource
    New York : Wiley-Blackwell
    Die Makromolekulare Chemie 192 (1991), S. 1993-2008 
    ISSN: 0025-116X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The stirring speed n influences the emulsion polymerization of butadiene, (1) by reducing the effective emulsifier concentration [E]eff available for particle nucleation and stabilization at high n, and (2) by limiting diffusion of monomer to the latex particles at low n. The large density difference between butadiene and water promotes the breaking up of droplets at high n, while the same condition constitutes a large driving force for (partial) phase separation at low n. Increasing the monomer/water ratio at constant [E] decreases [E]eff, and thus the final particle number. At monomer volume fractions 〉0,6 mixed emulsions are likely to be formed initially, reducing [E]eff even further. In the presence of mixed emulsions, polymerization in the monomer phase may no longer be neglected, giving rise to a complex kinetic behaviour.
    Additional Material: 13 Ill.
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  • 3
    ISSN: 0025-116X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The role of thiols of low water solubility, commonly used in the emulsion polymerization of butadiene, has been considered. The following effects have become apparent: (1) dodecanethiols act as efficient chain transfer agents in limiting the formation of heavily cross-linked polymer networks; (2) the monomer concentration within the particles is not influenced by such thiols; (3) C12-thiol radicals do not desorb because of their extremely low water solubility. The ‘promoting effect’ of thiols in emulsion polymerizations of diene-hydrocarbons is still poorly understood, but it appears to be related to impurities present in the emulsifier, as it was found completely absent in emulsifier-free polymerizations.
    Additional Material: 3 Ill.
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  • 4
    Electronic Resource
    Electronic Resource
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 29 (1991), S. 599-602 
    ISSN: 0887-624X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Additional Material: 1 Ill.
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  • 5
    Electronic Resource
    Electronic Resource
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 37 (1991), S. 1895-1899 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Additional Material: 4 Ill.
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  • 6
    Electronic Resource
    Electronic Resource
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 37 (1991), S. 1900-1903 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Additional Material: 5 Ill.
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  • 7
    Electronic Resource
    Electronic Resource
    Weinheim [u.a.] : Wiley-Blackwell
    Materials and Corrosion/Werkstoffe und Korrosion 42 (1991), S. 403-409 
    ISSN: 0947-5117
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Description / Table of Contents: Korrosionsmechanismen von gesintertem nichtrostendem Stahl (AISI 316L) in NatriumchloridlösungDas elektrochemische Verhalten eines gesinterten nichtrostenden Stahls wurde mit dem von Schmiedematerial derselben Zusammensetzung verglichen. Die elektrochemischen Messungen umfaßten die Änderung des Korrosionspotentials mit der Zeit, die anodische und kathodische Polarisation und die Strom/Zeit-Transienten. Ein weiterer Vergleich erstreckte sich auf die Sinterlegierung vor und nach Stabilisierung des Korrosionspotentials. Die geringe Korrosionsbeständigkeit des gesinterten nichtrostenden Stahls ist bedingt durch die Bildung eines Elements zwischen der freien Oberfläche und der inneren Oberfläche der untereinander verbundenen Poren. Die freie (äußere) Oberfläche wird demnach durch die Poren kathodisch geschützt, während innerhalb der Poren, wegen der Größe der reaktionsfähigen Oberfläche, die Korrosion verstärkt wird.
    Notes: The electrochemical behaviour of a sintered stainless steel and of a wrought AISI type stainless steel of the same composition were compared. The electrochemical measurements used were the evolution of the corrosion potential vs time, the anodic and cathodic polarizations and the current-time transients. Comparisons were also performed for the sintered alloy before and after stabilization of the corrosion potential. The low corrosion resistance of the sintered stainless steel is due to the formation of a galvanic couple between the free surface and the inside of the interconnected pores. Hence the free surface is cathodically protected by the pores, but reciprocally the corrosion increases inside the pores where the reactive area is very large.
    Additional Material: 12 Ill.
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  • 8
    Electronic Resource
    Electronic Resource
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 31 (1991), S. 592-595 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Reinforced plastics based on poly(cyclohexanedimethylene terephthalate) (PCT) are excellent for electrical and electronic applications, particularly in the manufacture of electrical connectors. PCT offers a high heat deflection temperature, low cost, and relative ease of processing. For the injection molding process, stability of the melt is an important consideration, especially for materials with high melting points such as PCT. The combination of the polyester resin with flame retardant additives, processing aids, and thermal stabilizers results in a number of competing reactions which can change the molecular weight and molecular-weight distribution (MWD) of the base polymer in the composite. Typical analytical techniques such as melt or dilute solution viscosity do not give adequate means of monitoring these changes so as to allow the polymer chemist to determine the effects of various additives on MWD. Size-exclusion chromatography (SEC), by virtue of providing information on the entire MWD, was found suitable to study molecular-weight changes in the melt due to both branching and chain cleavage, even when both phenomena occur simultaneously. Changes in the MWD over time at processing temperatures can be used to determine kinetic parameters and have been used to optimize PCT additive formulations for best processability and mechanical property retention.
    Additional Material: 4 Ill.
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  • 9
    Electronic Resource
    Electronic Resource
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 31 (1991), S. 1665-1669 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The Differential Scanning Calorimetry (DSC) trace for a commercial phenolic resole resin shows two distinct peaks. Assuming that these represent two independent cure reactions results in a kinetic model of the form: \documentclass{article}\pagestyle{empty}\begin{document}$$ \frac{{dx}}{{dt}} = p\kappa _1 \left({1 - x_1} \right)^{n_1} + \left({1 - p} \right)\kappa _2 \left({1 - x_2} \right)^{n_2} $$\end{document} with κi = κio exp(-Bi/T).The Arrhenius parameters were estimated from a plot of ln(β/Tp2) versus 1/Tp. The parameters, p, n1, and n2 were obtained by writing the DSC response predicted by the equation above in terms of a function which contains temperature as the only variable. \documentclass{article}\pagestyle{empty}\begin{document}$$ \dot q = q_{tot} \left[{p\kappa _1 \left({1 - \theta _1 /r_1} \right)^{r_1 - 1} + \left({1 - p} \right)\kappa _2 \left({1 - \theta _2 /2} \right)^{r_2 - 1}} \right] $$\end{document} with \documentclass{article}\pagestyle{empty}\begin{document}$ \theta _i = \left({1/\beta} \right)\int_{T_0}^T {\kappa _i dT \le r_i} $\end{document} dT ≤ ri and ri = 1/(1-ni).Fitting this equation to the DSC response measured at a scan rate of 4°C/min obtains p ≈ 0.66; n1 ≈ 0.55; n2 ≈ 2.2; B1 ≈ 8285; B2 ≈ 7480; κ1 ≈ 1. 12 × 108 s-1; κ2 ≈ 0.99 × 106 S-1.
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  • 10
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The conductance of the gramicidin A single channels in glycerolmonooleate membranes is strongly reduced in the presence of Mn2+ cations. The nmr experiments were performed for N-terminal to N-terminal gramicidin A dimer formed by two right-handed single-stranded helixes incorporated into the sodium dodecyl sulfate micelles in the presence of Mn2+ ions. Dependence of the nonselective spin-lattice relaxation rates of the gramicidin A protons on Mn2+ concentration was analyzed to determine coordinates of the divalent cation binding sites. It is inferred that Mn2+ ions are bound at the channel mouths at distances of 6.4, 8.6, and 8.8 Å (±2 Å) from the oxygen atoms of exposed carbonyl groups of D-Leu 12, 14, and 10, respectively. The bounded Mn2+ retains its hydrate shell, the size of which (≈ 6 Å) exceeds the inner pore diameter (≈ 4 Å). That makes the gramicidin A channel impermeable for divalent cations.
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