The effect of dolomite addition on the properties of sinters produced from a high aluminous iron ore

This study provides a systematic approach to an evaluation of the sinter properties with increased MgO addition for superfluxed sinters produced from a high aluminous ore. The investigation revealed that part or full replacement of limestone by dolomite in the sinter mix leads to a drop in sinter cold strength, reducibility and production rate, but has a favourable influence on low-temperature reduction strength and probably better softening and meltdown properties. The change in sinter mineralogy due to the MgO addition has a paramount influence on the sinter properties. The Gua iron ore having a high alumina content, is easily amenable to sintering and the sinters produced can constitute a good burden material because of their high reducibility, good cold and hot-strength characteristics. Improved production rates can be expected by choosing dolomites having a smaller crystal size or choosing other suitable MgO-bearing materials. A high circulating load should be expected while producing MgO-bearing sinters.     

A study of the interaction of mechanically generated polypropylene radicals with phenolic antioxidant in the presence of oxygen by EPR spectroscopy

Isotactic polypropylene (iPP) was mechanically degraded in the absence and presence of a phenolic antioxidant at liquid nitrogen temperature in the presence of oxygen. The interaction of the primarily formed iPP macroradicals with oxygen and phenol was studied by EPR spectroscopy in the temperature region between 77 and 303 K at antioxidant concentrations of 0.1, 0.5, and 3.0 wt%. It was found that iPP macroradicals react at low temperature with oxygen, yielding peroxy radicals, and with antioxidant, with a simultaneous formation of phenoxy radicals. The development and decay of all kinds of radicals was studied. The rate constants for peroxy radical decay were determined and the apparent activation energies for the regions of slow and fast decay were calculated. © 1993 John Wiley & Sons, Inc.     

Ausscheidungsvorgänge während der Wärmebehandlung kupferhaltiger Stähle

Kupferzusätze in Stahl können in bezug auf Korrosionswiderstand und Festigkeit vorteilhaft sein. Es wurde der Einfluß von Kupfer auf die Korngröße, mechanische Eigenschaften und Mikrostruktur von quasi-binären Fe-Cu-Legierungen ermittelt. Der Verfestigungseffekt von Kupfer im abgeschreckten Stahl entsteht durch Kornverfeinerung, Mischkristallverfestigung (46 N/mm²/(% Cu)) und eventuell durch Ausscheidung von Kupfer während des Abkühlens. Es gilt einen linearen Zusammenhang zwischen Korngröße und Kupfergehalt. Zwischen einigen mechanischen Eigenschaften (Härte, Zugfestigkeit und Streckgrenze) und dem Kupfergehalt gilt aber nur ein linearer Zusammenhang, wenn keine Cu-Ausscheidung während des Abkühlens nach dem Lösungsglühen stattgefunden hat. Die eventuell auftretende Ausscheidungshärtung während der Abkühlung kann eine Erhöhung der Streckgrenze mit bis zu 130 N/mm² bewirken. Das Auftreten einer Ausscheidung während des Abkühlens wurde elektronenmikroskopisch nachgewiesen. Der theoretische Verfestigungsbeitrag wurde mit Hilfe dieser Messungen berechnet und stimmt gut mit den Ergebnissen überein. Mittels Jominy-Versuchen wurde die notwendige Abkühlungsgeschwindigkeit zur Vermeidung einer Ausscheidung wie folgt bestimmt: ln(Abk. Geschw.) [°C/s] = 1,98 · (% Cu) ? 0,08.     

Czech Republic 20 years after Chernobyl accident

The territory of the Czech Republic was contaminated as a result of the breakdown in the Chernobyl nuclear power plant in 1986. The Czech population received low doses of ionising radiation which, though it could not cause a deterministic impact, could have had stochastic effects expressed in the years following the accident. Twenty years after the accident is a long enough time to assess its stochastic effects, primarily tumours and genetic impairment. The moderate amount of radioactive fallout received by the Czech population in 1986 increased thyroid cancer in the following years; on the other hand, no obvious genetic impact was found.     

Effect of composition on friction coefficient of Cu–graphite composites

Cu–graphite composites were prepared by hot isostatic pressing from the copper and graphite powders in the range of 0–50 vol.% of graphite. The same graphite powder was copper coated and used for the preparation of coated composites with 30 and 50 vol.% of graphite. It was confirmed that with increasing concentration of graphite the coefficient of friction and wear rate of coated and uncoated composites at first decreases. When critical concentration threshold of graphite is reached the coefficient of friction of composites becomes independent on the composition while the wear rate decreases further. This threshold is not simply 20 vol.% of graphite as stated [P.K. Rohatgi, S. Ray, Y. Liu, Tribological properties of metal matrix graphite particle composites, Int. Mater. Rev. 37 (1992) 129–149.] for metal matrix composites, but it significantly depends on the composite structure: for uncoated composites, it is 12 vol.% of graphite for fine graphite powder (16 μm), while for coarse powder (25–40 μm, [S.F. Moustafa, S.A. El-Badry, A.M. Sanad, B. Kieback, Friction and wear of copper–graphite composites made with Cu-coated and uncoated graphite powders, Wear 253 (2002) 699–710.]) it is 23 vol.% of graphite. For coated composites the concentration threshold was found above 25 vol.% of graphite. The reason is that the increased number of fine copper debris within graphite rich tribolayer occurs homogeneously also at high graphite composition.     

Complexes of carbon nanotubes with selected carotenoids

As proven by the UV-VIS, micro-Raman spectroscopies, differential scanning calorimetry, beta-carotene, lycopene, retinoic acid, and retinol adsorbed on the surface of single-walled carbon nanotubes (SWCNT) form electron donor-acceptor (EDA) complexes. The rate of the adsorption of carotenoids is estimated as the rate of decrease in their concentration in solution followed the exponential curve equation. The rate of the adsorption decreased with the chain length of the guest capable sorption on the surface and steric effect of the terminals in the beta-carotene was also essential. Also, increase in the polarity of the functional groups expressed, for instance, in Taft sigma* substituent constants had its impact. The HyperChem 7 followed by Gaussian 03 computations revealed that the inclusion SWCNT-carotenoid complexes were more stable than corresponding surface complexes. In the surface complexes carotenoids acted as donors in respect to SWCNT whereas in the inclusion complexes they were acceptors.     

Modelling of simultaneous two-sided migration into water and olive oil from nylon food packaging

Nylon 6 and nylon 12 food packaging materials used as sausage casings are typically exposed to fatty food on one side and boiling water on the other during the cooking process. To simulate the migration behaviour under these conditions, a special migration cell was constructed and filled with olive oil on one side of the polymer and water on the other to find out what amounts of the migrants will transfer to either side and phase at 100 °C. Results show that when a nylon 6 film is exposed to the conditions as described above, total mass transfer of the monomer—caprolactam—into the water phase occurs after 2 h at 100 °C. Nylon 12 sausage casings release similar amounts of their monomer—laurolactam—into both the aqueous and oil phase. An existing computer migration model was adapted to simulate the situation of simultaneous two-sided migration applying previously determined diffusion and partitioning coefficients. The suitability of the model was confirmed by experimental data.     

ARVO: A Fortran package for computing the solvent accessible surface area and the excluded volume of overlapping spheres via analytic equations

In calculating the solvation energy of proteins, the hydration effects, drug binding, molecular docking, etc., it is important to have an efficient and exact algorithms for computing the solvent accessible surface area and the excluded volume of macromolecules. Here we present a Fortran package based on the new exact analytical methods for computing volume and surface area of overlapping spheres. In the considered procedure the surface area and volume are expressed as surface integrals of the second kind over the closed region. Using the stereographic projection the surface integrals are transformed to a sum of double integrals which are reduced to the curve integrals. MPI Fortran version is described as well. The package is also useful for computing the percolation probability of continuum percolation models.

Program summary

Title of program: ARVOCatalogue identifier: ADULProgram summary URL:http://cpc.cs.qub.ac.uk/summaries/ADULProgram obtainable from: CPC Program Library, Queen's University of Belfast, N. IrelandOperating system under which the program has been tested: LINUX system and Windows systemProgramming language used: FORTRANComputer: PC Pentium; SPP'2000;Number of bytes in distributed program, including test data, etc.: 322 633Number of lines in distributed program, including test data, etc.: 5051Distribution format: tar.gzCard punching code: ASCIINature of physical problem: Molecular mechanics computations, continuum percolations.Method of solution: Numerical algorithm based on the analytical formulas, after using the stereographic transformation.Restriction on the complexity of the problem: The program does not account explicitly for cavities inside the molecule.Typical running time: Depends on the size of the molecule under consideration.Unusual features of the program: No     

Thermal degradation of cellulose model compounds in inert atmosphere

Thermal degradation of cellulose model compounds was studied using thermogravimetry (TG), electric spin resonance (ESR) spectroscopy, and gas chromatography–mass spectrometry (GS–MS). The molecular weight of samples did not influence the activation energy of gasification. In the case of catalytic influence of NaOH on cellulose thermolysis formation of gaseous products in the temperature range 250–350°C increased and a greater amount of residue was formed at 350–400°C compared to noncatalytic thermolysis. Residues of compounds with hemiacetal groups showed higher concentration of unpaired electrons than residues obtained from models with the blocked hemiacetal group.