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 21,279 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

A method for determining approximately 0.2 microg/g or more of germanium in ores, concentrates, zinc-processing products and related materials is described. The sample is decomposed by fusion with sodium peroxide and the cooled melt is dissolved in dilute sulphuric acid. Silica, if > 50 mg, is removed by volatilization with hydrofluoric acid. Germanium is separated from sodium salts by co-precipitation with hydrous ferric oxide, the precipitate is dissolved in 3M hydrochloric acid and germanium is subsequently separated from iron(III) and other co-precipitated elements by a single heptane extraction of germanium tetrachloride from approximately 9.4M hydrochloric acid. The extract is washed with 12M hydrochloric acid to remove residual iron(III), then germanium is stripped with water and determined spectrophotometrically with phenylfluorone in a 1.4M hydrochloric acid-0.002M cetyltrimethylammonium bromide medium in the presence of ascorbic acid as a reductant for co-extracted chlorine. The apparent molar absorptivity of the complex is 1.71 x 10(4) l.mole(-1).mm(-1) at 507 nm, the wavelength of maximum absorption. Up to 5 mg of tin(IV), 10 mg of antimony(V) and tungsten(VI) and approximately 50 mg of silica do not interfere. Germanium values are given for some Canadian certified reference ores, concentrates and iron-formation samples and for a metallurgical dust.
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PMID:Spectrophotometric determination of germanium in ores, concentrates, zinc-processing products and related materials with phenylfluorone and cetyltrimethylammonium bromide after separation by iron collection and heptane extraction of germanium tetrachloride. 1896 6

A simple, low pressure, low temperature vapour phase decomposition (VPD) of quartz powder has been developed for the determination of phosphorus. A platinum dish containing the quartz or silicon powder was placed inside a polypropylene vessel containing 40 ml of 1:1 mixture of HF and HNO(3). After capping the vessel, the entire assembly was heated on a water bath at approximately 90 degrees C for 8 h. The platinum dish was removed from the vessel, the sample solution was treated with 0.5 ml of H(2)SO(4) and 0.5 ml of HClO(4) and was heated on a hot plate till HClO(4) fumed out. The resultant solution was diluted to 40 ml ( approximately 0.4N), analysed for phosphorus by spectrophotometry as an ion-pair of molybdophosphate with crystal violet. Phosphorus contamination by reagents has been drastically reduced (around 250 times) compared to the conventional dissolution procedure. The optimum reaction conditions were [H(+)]=0.42N, [H(+)]/Mo=62 for the formation of molybdophosphate and its extraction into n-butyl acetate. No interferences due to fluoride, silicate (active silica) and arsenic (V) upto 6.7x10(3),2.7x10(3) and 2.0x10(3) times the content of phosphorus, respectively were observed. The LOD was found to be 0.066 mug g(-1) (+/-3 s). RSD is 0.4-2.3% and the molar absorptivity is 2.7x10(5) l mole(-1) cm(-1).
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PMID:A simple vapour phase decomposition (VPD) of quartz powder in a polypropylene vessel and determination of phosphorus by spectrophotometry. 1896 95

Pyrolysis of the silicon-containing polymer {(NP[O2C12H8])0.5[NP(OC6H4 x SiMe3)2]0.5-x [NP(OC6H5) x (OC6H4SiMe3)]x}n (1) (x = 0.13), (2) (x = 0.3), and (3) {(NP[O,2C12He])0.5[NP(OC6H4SiMe2Ph),2]0.2 [NP(OC6H5)(OC6H4SiMe2Ph)]0.3}n in air at 600 degrees C, 800 degrees C and 1000 degrees C results in the formation of nanostructured SiP,2O7, along with P4O7. The morphology as well as the size and shape of the nanostructures is observed to depend on both the mole fraction of silicon, the polymer precursor and the temperature of the pyrolysis. The first observation of nanotube formation using polyphosphazenes as a template, was noted during pyrolysis of the precursor (1) at 600 degrees C. The surface morphology of the Si or SiO2, studied by AFM, depends strongly on the crystallinity of the wafer surface used during deposition. Regular lance or point-like structures were obtained from SiP2O7 deposited on SiO2 from its precursor (2). The unique formation of micro and nanostructured SiP2O7 is discussed and a mechanism of the formation of the nanostructured materials is proposed.
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PMID:Nanostructured silicon containing materials derived from solid state pyrolysis of sililated polyphosphazene derivatives. 1943 45

Distillation is a ubiquitous method of separating liquid mixtures based on differences in volatility. Performing such separations in microfluidic systems is difficult because interfacial forces dominate over gravitational forces. We describe distillation in microchemical systems and present an integrated silicon device capable of separating liquid mixtures based on boiling point differences. Microfluidic distillation is realized by establishing vapor-liquid equilibrium during segmented flow. Enriched vapor in equilibrium with liquid is then separated using capillary forces, and thus enabling a single-stage distillation operation. Design criteria for operation of on-chip distillation is set forth, and the working principle demonstrated by separation of binary mixtures of 50 : 50 mol% MeOH-toluene and 50 : 50 mol% DCM-toluene at 70.0 degrees C. Analysis of vapor condensate and liquid exiting a single-stage device gave MeOH mole fractions of 0.22 +/- 0.03 (liquid) and 0.79 +/- 0.06 (vapor). Similarly, DCM mole fractions were estimated to be 0.16 +/- 0.07 (liquid) and 0.63 +/- 0.05 (vapor). These experimental results were consistent with phase equilibrium predictions.
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PMID:Distillation in microchemical systems using capillary forces and segmented flow. 1953 58

The relative reactivities of alkynes to alkenes on hydrogen-terminated silicon (100) surfaces, under conditions where a monolayer will be produced via hydrosilylation, were measured using two different approaches. The first approach was to form monolayers from a series of solutions containing different mole fractions of an alkyne, with a trifluorothioacetate distal moiety and an alkene with a terminal carboxylic acid functional. X-ray photoelectron spectroscopic analysis of the resultant surfaces showed that the mole fraction of alkyne on the surface was larger than that in the respective alkyne/alkene mixture. By fitting the XPS data, we estimated that the reactivity ratio of alkyne to alkene was approximately 1.7 +/- 0.2 when monolayers were formed at 120 degrees C. The second approach was using a molecule containing both an alkyne at one end and an alkene at the other, non-1-yne-8-ene, as the hydrosilylation reagent such that either end could attach to the silicon surface. The relative orientation of this molecule, once reacted with a hydrogen-terminated Si(100) surface, was determined by coupling an additional reagent to the distal end of the monolayer. The reagent used was azidoferrocene, which could attach onto free alkyne moieties on the surface only via the 1,3-Huisgen cycloaddition "click" reaction. Electrochemical analysis was then used to determine how many ferrocene moieties were attached to the SAM surface. In this way, it was shown that the alkyne end reacted preferentially with the silicon surface compared with the alkene end. The reactivity ratio of the alkyne end to the alkene end was increased from 2.0 +/- 0.2 to 9 +/- 1 when the temperature was decreased from 120 to 65 degrees C.
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PMID:Comparing the reactivity of alkynes and alkenes on silicon (100) surfaces. 1958 53

The boundary film formation and lubrication effects of low molecular weight silicone lubricant molecules with cationic side groups were studied. Poly(N,N,N-trimethylamine-3-propylmethylsiloxane-co-dimethylsiloxane) iodide was synthesized and deposited on silicon oxide surfaces to form a bound-and-mobile lubricant film. The bound nature was investigated with ellipsometry, water contact angle, and X-ray photoelectron spectroscopy for the polymers with cationic mole percent of 6, 15, and 30 mol % (monomer based). The bound layer thickness decreased as the cationic content increased. The quaternary ammonium cations in this layer were electrostatically bound to the substrate surface. The mobile nature of the multilayers was explored with scanning polarization force microscopy. The multilayer films exhibited characteristic topographic features due to ionic interactions within the polymer film. Contact scratching of these films altered the multilayer topography within the contact scanned area. Even after high load contact scanning, the bound layer was not removed from the scanned region. These results implied that the molecules in the first layer are strongly bound and the molecules in the multilayers are mobile. Both nanoscale and macroscale tribological tests of these films revealed that the polymer with 15 mol % cationic groups gives lower friction and adhesion than the 6 and 30 mol % cationic polymers as well as the polydimethylsiloxane control sample. This seems to be due to a synergistic effect between the bound and the mobile layers.
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PMID:Effects of ionic side groups attached to polydimethylsiloxanes on lubrication of silicon oxide surfaces. 1970 84

Ethylene's cycloadditions to unsaturated hydrocarbons occupy well-established ground in classical organic chemistry. In contrast, its reactivity toward alkene and alkyne analogs of carbon's heavier-element congeners silicon, germanium, tin, or lead has been little explored. We show here that treatment of the distannynes Ar(iPr4)SnSnAr(iPr4) [Ar(iPr4) = C6H3-2,6(C6H3-2,6-iPr2)2, 1] or Ar(iPr8)SnSnAr(iPr8) [Ar(iPr8) = C6H-2,6(C6H2-2,4,6-iPr3)2-3,5-iPr2, 2] with ethylene under ambient conditions affords the cycloadducts Ar(iPr4) Sn(mu2:nu1:n1-C2H4)2Sn Ar(iPr4 (3) or Ar(iPrs) Sn(mu2:nu1:nu1-C2H4)2Sn AriPrs (4) that were structurally and spectroscopically characterized. Ethylene incorporation in 3 and 4 involves tin-carbon sigma bonding and is shown to be fully reversible under ambient conditions; hydrocarbon solutions of 3 or 4 revert to the distannynes 1 or 2 with ethylene elimination under reduced pressure or upon standing at approximately 25 degrees C. Variable-temperature proton nuclear magnetic resonance studies showed that the enthalpies of reaction were near -48 (3) and -27 (4) kilojoules per mole.
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PMID:Reversible reactions of ethylene with distannynes under ambient conditions. 1977 79

Iron oxides catalyze the conversion of hydrogen peroxide (H(2)O(2)) into oxidants capable of transforming recalcitrant contaminants. Unfortunately, the process is relatively inefficient at circumneutral pH values because of competing reactions that decompose H(2)O(2) without producing oxidants. Silica- and alumina-containing iron oxides prepared by sol-gel processing of aqueous solutions containing Fe(ClO(4))(3), AlCl(3), and tetraethyl orthosilicate efficiently catalyzed the decomposition of H(2)O(2) into oxidants capable of transforming phenol at circumneutral pH values. Relative to hematite, goethite, and amorphous FeOOH, the silica-iron oxide catalyst exhibited a stoichiometric efficiency, defined as the number of moles of phenol transformed per mole of H(2)O(2) consumed, which was 10-40 times higher than that of the iron oxides. The silica-alumina-iron oxide catalyst had a stoichiometric efficiency that was 50-80 times higher than that of the iron oxides. The significant enhancement in oxidant production is attributable to the interaction of Fe with Al and Si in the mixed oxides, which alters the surface redox processes, favoring the production of strong oxidants during H(2)O(2) decomposition.
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PMID:A silica-supported iron oxide catalyst capable of activating hydrogen peroxide at neutral pH values. 1994 68

We utilize a vapor deposition setup and cross-diffusion of functionalized chlorosilanes under dynamic vacuum to generate a nearly linear gradient in surface energy and composition on a silicon substrate. The gradient can be tuned by manipulating chlorosilane reservoir sizes and positions, and the gradient profile is independent of time as long as maximum coverage of the substrate is achieved. Our method is readily amenable to the creation of gradients on other substrate surfaces, due to the use of vapor deposition, and with other functionalities, due to our use of functionalized chlorosilanes. Our gradients were characterized using contact angle measurements and X-ray photoelectron spectroscopy. From these measurements, we were able to correlate composition, contact angle, and surface energy. We generated a nearly linear gradient with a range in mole fraction of one component from 0.15 to 0.85 (34 to 40 mJ/m(2) in surface energy) to demonstrate its utility in a block copolymer thin film morphology study. Examination of the copolymer thin film surface morphology with optical and atomic force microscopy revealed the expected morphological transitions across the gradient.
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PMID:Generation of monolayer gradients in surface energy and surface chemistry for block copolymer thin film studies. 1995 Sep 10

Silicon nanomaterials are encouraging candidates for application to photonic, electronic, or biosensing devices, due to their size-quantization effects. Two-dimensional silicon nanosheets could help to realize a widespread quantum field, because of their nanoscale thickness and microscale area. However, there has been no example of a successful synthesis of two-dimensional silicon nanomaterials with large lateral size and oxygen-free surfaces. Here we report that oxygen-free silicon nanosheets covered with organic groups can be obtained by exfoliation of layered polysilane as a result of reaction with n-decylamine and dissolution in an organic solvent. The amine residues are covalently bound to the Si(111) planes. It is estimated that there is ca. 0.7 mol of residue per mole of Si atoms in the reaction product. The amine-modified layered polysilane can dissolve in chloroform and exfoliate into nanosheets that are 1-2 microm wide in the lateral direction and with thicknesses on the order of nanometers. The nanosheets have very flat and smooth surfaces due to dense coverage of n-decylamine, and they are easily self-assembled in a concentrated state to form a regularly stacked structure. The nanosheets could be useful as building blocks to create various composite materials.
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PMID:Silicon nanosheets and their self-assembled regular stacking structure. 2012 Dec 77


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