The Role of Carbene Complexes in the Phillips Olefin Polymerization (Surface Compounds of Transition Metals, Part XXXI (1))

1987 ◽  
pp. 353-362
Author(s):  
Hans L. Krauss ◽  
Erich Hums ◽  
Karin Weiss
Keyword(s):  
Transition Metals ◽  
Olefin Polymerization ◽  
Carbene Complexes ◽  
Surface Compounds

Oberflächenverbindungen von Übergangsmetallen, XXV [1]: Redoxreaktionen von Oberfläehen-Chrom(II) auf Silicagel mit Olefinen / Surface Compounds of Transition Metals, XXV [1]: Redox Reactions of Surface Chromium(II) on Silicagel with Olefins

1983 ◽  
Vol 38 (11) ◽  
pp. 1412-1418 ◽  
Author(s):  
Hans-Ludwig Krauss ◽  
Erich Hums
Keyword(s):  
Transition Metals ◽  
Redox Reactions ◽  
Olefin Polymerization ◽  
Partial Reduction ◽  
Surface Compounds ◽  
Catalytic Sites

AbstractOlefins may react with chromium(II)/silicagel catalysts at temperatures from 100 to 600 °C under formation of C1-C4 n-alkanes and organometallic species; the chromium is oxidized simultaneously. By this reaction the catalytic sites loose the ability for olefin polymerization and 〈CH2〉 transfer. A following treatment of the catalyst with hydrogen at 400 °C produces a second crop of alkanes from former organometallic species under partial reduction of the chromium back to CrII ; the polymerization activity is restorted correspondingly.

scholarly journals Using of Microsilica for Strength Improvement of Fiber Reinforced Cementitious Surface Compounds

2013 ◽  
Vol 2013 ◽  
pp. 1-7
Author(s):  
S. S. Shebl ◽  
Ibrahim S. Khalil ◽  
H. Shoukry
Keyword(s):  
Date Palm ◽  
Fine Sand ◽  
Structural Performance ◽  
Polypropylene Fibers ◽  
Hydration Products ◽  
Fiber Reinforced ◽  
Surface Compounds ◽  
Extension Work ◽  
Strength Improvement

This study represents an extension work to investigate the role of ultra fine sand (UFS) in enhancing the mechanical properties of fiber reinforced cementitious compounds. The micro-structural origins were identified by scanning electron microscope (SEM). About 50% of UFS had a diameter of less than 20 μm. Ordinary Portland Cement (OPC) was partially substituted by UFS at 3, 5, 7 and 10% by weight of binder. It was found that as UFS loadings increase, the flexural, compressive, and tensile strengths increased up to about 5% UFS loading by 12.9, 15.7 and 30.1%, respectively, thereafter, a decrease in these properties was observed. This can be attributed to the pozzolanic effect besides the filling effect of UFS resulting in enhancing the interfacial bonds between the sand grains and hydration products that makes the paste more homogeneous and dense. The effect of both short natural and artificial fiber loadings on the structural performance of compounds was also studied. Loadings of 2%, by weight, of short natural date palm leaves’ midribs fibers (DP) and artificial polypropylene fibers (PP) were added to the 5% UFS blended mix. An increase in both flexural and tensile strength was achieved, while a decrease in the compressive strength was observed.

Ion chemistry of transition metals in hydrocarbon flames. II. Cations of Sc, Ti, V, Cr, and Mn

1988 ◽  
Vol 66 (9) ◽  
pp. 2219-2228 ◽  
Author(s):  
John M. Goodings ◽  
Quang Tran ◽  
Nicholas S. Karellas
Keyword(s):  
Transition Metals ◽  
Metal Atom ◽  
Chemical Ionization ◽  
Metallic Ions ◽  
Ion Chemistry ◽  
Hydrocarbon Flames ◽  
Basic Series ◽  
First Time ◽  
Isomeric Structures

The same fuel-rich, premixed, conical, methane–oxygen flame at 2200 K and atmospheric pressure used for studies of Fe, Co, Ni, Cu, and Zn in Part I (1) is doped with the same concentration (~1 ppm) of Sc, Ti, V, Cr, and Mn to complete the first row of ten transition metals. Metallic ions of these metals and their compounds formed by chemical ionization reactions with H3O+ are observed by sampling the flame through a nozzle into a quadrupole mass spectrometer. Concentration profiles of individual and total cations are measured as a function of distance along the flame axis, and also mass spectra at a fixed point in the burnt gas. If A is the metal atom, the observed ions can be represented by four hydrate series including (a) A+•nH2O, (b) AOH+•nH2O, (c) AO+•nH2O, and (d) AO2H+•nH2O with n = 0–3 or 4, giving a maximum of four ligands around the metal atom. However, alternative isomeric structures are possible for each of the four basic series (e.g. AO+•2H2O ~ A(OH)2+•H2O ~ A(OH)3H+). The ions observed with Cr and Mn, in common with those of Fe, Co, Ni, and Cu, strongly favour series (a). On the other hand, Sc is completely different; the ions of series (c) are dominant. All four series are observed with each of Ti and V. Series (b) dominates for Ti and series (c) for V; ions from series (d) were observed for the first time. The ion chemistry of these metals is discussed in detail with emphasis on the probable chemical ionization reactions responsible for metallic ion formation. The pre-eminent role of proton transfer processes is apparent.

Room temperature p-orbital magnetism in carbon chains and the role of group IV, V, VI, and VII dopants

Nanoscale ◽  
2018 ◽  
Vol 10 (23) ◽  
pp. 11186-11195 ◽  
Author(s):  
C. H. Wong ◽  
E. A. Buntov ◽  
A. F. Zatsepin ◽  
J. Lyu ◽  
R. Lortz ◽  
...  
Keyword(s):  
Rare Earth ◽  
Transition Metals ◽  
Room Temperature ◽  
Group Iv ◽  
Rare Earth Ions ◽  
Next Generation ◽  
Spintronic Devices ◽  
Carbon Chains ◽  
Orbital Magnetism

The study of magnetism without the involvement of transition metals or rare earth ions is considered the key to the fabrication of next-generation spintronic devices.

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