Influence of Porosity on the Electrical Sensing Zone and Laser Diffraction Sizing of Silicas. A collaborative study

The objective of a continuing study by the Belgian Particle Technology Group involves difficulties in practical size determinations. This part describes the behaviour of silicas with different porosities during sizing by electrical sensing zone and laser diffraction methods. Anisotropy and porosity were identified to be important particle characteristics in understanding the differences between the two methods. Especially large pore diameters and pore volumes were found to be responsible for shifts in size distribution of 50 to 100%. The use of optical values and optical models was shown to influence these shifts considerably. In the case of spherical silica particles with moderate porosity, no significant differences could be found between the two sizing methods.     

Seismic response of a set of blocks partially imbedded in soft soilRéponse sismique d'un ensemble de blocs partiellement encastrés dans un terrain mou

The seismic response of a set of ten non-equally spaced, non-equally sized, homogeneous blocks partially imbedded in a soft soil layer overlying a hard halfspace is studied numerically and shown to be generally larger, in terms of amplitude, duration and spatial variability than that of the ground in the presence of one block or in the absence of blocks. This is qualitatively similar to observed seismic response in the past at sites such as Mexico City and suggests that the built portion of cities may, under certain conditions, play a significant role in the global seismic response of a city. To cite this article: C. Tsogka, A. Wirgin, C. R. Mecanique 331 (2003).     

Lithium intercalation in polyacetylene

The coulometric titration curve for lithium intercalation in polyacetylene has been determined using poly(ethylene oxide) based solid electrolyte. The plateaus observed suggest the existence of stages, comparable to graphite. This interpretation seems also supported by the cyclic voltammetry scans on polyacetylene. Lithium intercalation appears as a very slow process with

estimated at ? 10^-13cm².s^-1.     

Etude par Spectrométrie de Masse du Di-O-isopropylidene-1,2;5,6-α-D-ribo-hexofurannosul-3-ose

The electron impact mass spectrum of 1, 2:5, 6-di-O-isopropylidene-α-D -ribo-hexofuranos-3-ulose has been studied. Fragmentation modes based upon deuterium and ¹⁸O labelling are proposed.     

Spectrographie de masse en série du bornane I: Bornanes monosubstitués

A study has been made of the fragmentation of 2- and 3-monosubstituted bornanes. Ketones, oximes, alcohols, amines and their N-methyl derivatives were examined. Different fragmentations were compared according to the 2- or 3-position of the substituents. The results show the importance of cleavage α to the substituent bearing the charge. The α bond cleaved is that bond directed to the carbon atom with the greater degree of substitution. These results allow one to differentiate, by mass spectroscopy, the 2- and the 3-positions in the bornane skeleton.     

Polysulfonylamine. LXXII [1]. Triphenylcarbenium- und Triphenylphosphonium-di(fluorsulfonyl)amid: Zwei Kristallstrukturen mit geordneten (FSO2)2N⊖-Lagen

Polysulfonyl Amines. LXXII. Triphenylcarbenium and Triphenylphosphonium Di(fluorosulfonyl)amides: Two Crystal Structures with Ordered (FSO₂)₂N^? Sites Treatment of HN(SO₂F)₂ in CH₂Cl₂ with Ph₃P, Ph₃PO or collidine (=B) affords the compounds Ph₃PH^⊕[(FSO₂)₂N]^? ( 3 ), Ph₃PO · HN(SO₂F)₂, and BH^⊕[(FSO₂)₂N]^? ( 7 ). The carbenium salt Ph₃C^⊕[(FSO₂)₂N]^? ( 5 ), obtained by metathesis of Ph₃CBr with [(C₆H₆)AgN(SO₂F)₂] in CH₂Cl₂, crystallizes from chloroform/petroleum ether as a monosolvate Ph₃C^⊕[(FSO₂)₂N]^? · CHCl₃ ( 6 ). In presence of a sterically hindered base, viz. collidine, 5 is a suitable reagent for the tritylation of molecules containing weakly activated H atoms (e. g.: MeCN → Ph₃CCH₂CN, acetone → tritylacetone; co-product: 7 ). The crystal structures of the ionic solids 3 (monoclinic, space group P2₁/n) and 6 (monoclinic, P2₁/c) were determined by X-ray diffraction at ?130°C; the structure refinements were not impaired by the notorious tendency of the (FSO₂)₂N moiety towards crystallographic disorder. As in the known structure of the tetraphenylarsonium salt, the anion of 3 and 6 adopts a staggered conformation of approximately C₂ symmetry (averages of all values: S? N? S 121.4°, N? S 156.2, S? O 141.6, S? F 156.6 pm). The crystal packing of 6 displays a three-centre C? H(…?O)₂ hydrogen bond between the CHCl₃ molecule and two oxygen atoms of a single anion, resulting in a six-membered ring [R₁²(6) pattern; H …? O 234 and 262 pm]. The crystal of 3 contains one-dimensional arrays of alternating cations and anions connected by a three-centre P? H(…?O)₂ bond [C(6) pattern; H …? O 237 and 254 pm]. The Ph₃C^⊕ cation of 6 is propeller-shaped, with three coplanar central bonds (mean C? C 144.5 pm) and interplanar angles of 52.7, 56.4 and 60.1° between the phenyl groups.     

Aziridines—XVI: Etude des conformations privilegiees cycle aromatique-petit cycle dans les C-aryl aziridines N-non-substituees

The preferred conformation of phenyl-2 aziridine involves the phenyl ring nearly bisecting the plane of the small ring (maximum conjugation). As the steric hindrance due to substituents on the aromatic ring is more substantial, the aromatic ring moves towards a perpendical plane. Good agreement between experimental (IR and NMR) and theoretical studies of the syn-anti configurational equilibrium of NH in these compounds is demonstrated. The analysis of the total electronic populations clarifies an understanding of the variation of the charge transfer small ring?aromatic cycle as a function of the aromatic nucleus.     

Characterization of chlorins within a natural chlorin mixture using electrospray/ion trap mass spectrometry

Chlorins in a sedimentary mixture were characterized, without prior isolation of individual components, using electrospray ionization combined with ion trap mass spectrometry. Collision-induced dissociation in the atmospheric sampling interface and multi-step mass spectrometry (i.e. MSⁿ where n ? 2) were used in order to obtain structural information about the macrocycle. Fragmentation pathways are proposed for different macrocycle types based on data from model chlorins. Three unknown chlorins (RMM = 888, 844 and 790) are assigned as having bacteriochlorophyll macrocycle types esterifled to unusual side-chains (i.e. dihydrophytol for the unknown with a bacteriopheophorbide a structure, phytol and an alcohol with a molecular mass of 242 u for the two unknowns with a proposed bacteriopyropheophorbide d structure).     

Neue Chlorsilyl- und Alkoxysilyl-alkyl-peroxide

The alkyl-chlorosilyl-peroxides1 and2, the alkoxysilylalkyl-peroxides3 to7 (Table 1) as well as the hitherto unknown chlorosilanes (n-PrO)Me ₂SiCl and (t-BuO)Me ₂SiCl were prepared, isolated and characterized by analytical and¹H-NMR data. Attempts to isolate the unstable peroxides (i-PrO)₃SiOOCMe ₃ and (Me ₃CO)Me ₂SiOOCMe ₂ Ph failed.