Helium atmospheric

Transparent vitreous sihca cmcibles can be produced by firing shp-cast pieces in a vacuum or a helium atmosphere (48,49), or in helium followed by argon (50). The cmcible is usually supported on a graphite form to minimi2e distortion. 

Carbon soot from resistive heating of a carbon rod in a partial helium atmosphere (0.3bar) under specified conditions is extracted with boiling C H or toluene, filtered and the red-brown soln evapd to give crystalline material in 14% yield which is mainly a mixture of fullerenes C q and C70. Chromatographic filtration of the crude mixture with allows no separation of components, but some separation was observed on silica gel... 

The CNTs were prepared by the group at EPF in Lausanne [10] following the method of Ebbesen et al. [ll]. A 100 A, 20 V dc arc between a 6.5 mm diameter graphite anode and a 20 mm graphite cathode is sustained in a 6.7x10 Pa helium atmosphere for about twenty min. Nanotubes were found on the cathode, where they were encapsulated in a cylindrical 1 cm long shell. The shell was cracked and the powdery soot-like deposit extracted. The powder was then... 

In these gas-flow proportional counters, the windows are exceedingly thin, fragile,. and unavoidably leaky. Such a window is satisfactory only if a steady flow of. the filling gas is maintained at minimum pressure differential against the helium atmosphere in the optical path. The purging of impurities from the counter is an incidental benefit derived from the gas flow. Hendee, Fine, and Brown20 look upon the gas-flow proportional counter as a steppingstone on the road toward a windowless counter. 

Preparation of Reactants. Reagent-grade, thiophene free benzene was stored over 4A molecular sieves and sodium ribbon in a helium atmosphere. Styrene was distilled to remove dissolved oxygen and moisture and stored under a helium atmosphere. Prior to use, styrene was injected into a copious quantity of methanol to determine if any polymerization had occurred. If there was... 

MOCVD of Titania. Ti02 is often produced by the pyrolysis of a titanium alkoxide, such as titanium ethoxide, Ti(OC2H5)4, in an oxygen and helium atmosphere at 450°C. Another reaction is based on titanium tetraisopropoxide, Ti(OC3H-7)4, with oxygen at 300°C and at low pressure (< 1 Torr).P ]P ] These precursors have low boiling point (ca. 120°C). 

MOCVD of Zirconia. Yttria-stabilized zirconia is also deposited by MOCVD.Deposition can be accomplished by the codecomposition of the tetramethyl heptadiones of zirconium and yttrium, Zr(CjjHj902)3 and Y(CjjHj902)3, at 735°C. Deposition is also achieved by the decomposition of the trifluoro-acetylacetonates in a helium atmosphere above 300°C.P 1 Other potential MOCVD precursors are bis(cyclopentadienyl)zirconium dichloride, (C5H5)2ZrCl2, and zirconium (IV) trifluoroacetylacetonate,... 

Fig. 6.17. The intensity of emission of singlet oxygen as a function of temperature in freshly ground quartz 1 — grinding in helium atmosphere, chemisorption of O2 at 20 C 2 - same as above + treatment at 280"C 3 sample obtained as stage 2 followed by oxidation at 20 C.

Aniline and 1-hexanol were left over a reduced catalyst at 383 K in a helium atmosphere. After 0.3 h N-hexylenebenzenamine (HBA) was detected, no N-hexylaniline (HA) was observed. 

Fig. 15. Evolution of molecular oxygen, detected right after dissolution of 1 jjlmol of 19 into 10 ml of various solutions at various pHs at room temperature under a helium atmosphere (HEPES = A/r -2-hydroxyethylpiperazine-Af-2-ethanesulfonic acid). All the measurements were performed under a helium atmosphere in glove box equipped with a gas chromatograph. Reproduce under permission from Ref. (115). 

Ti content in the polymer films was measured with a Princeton Gamma Tech System 4 x-ray Fluorescence Spectrometer. The conditions employed were Cr target, 50 keV source operating at 3 mA, 0.75 mm aperture, 4.8 mm beam stop, helium atmosphere and 100 sec. counting time. A calibration curve was constructed by plotting the fluorescence counts versus the amount of Ti in HB-HPR 206 films determined by Rutherford Backscattering Spectroscopic (RBS) analysis. 

The above w was measured118, for instance, for polycrystalline surfaces of U02 kept for various times in a helium atmosphere at various high temperatures. The slope of the curve In w = /(/ t) was between 0.33 and 0.37 so that the exponent 1/3 in Eq. (58) seemed to be confirmed. When an approximate value for D was selected, the 7S of U02 appeared to vary irregularly between 385 and 806 erg/cm2 the annealing temperature ranged from 1660 °C to 1940 °C. 

Chemical/Physical. Diuron decomposes at 180 to 190 °C releasing dimethylamine and 3,4-dichlorophenyl isocyanate. Dimethylamine and 3,4-dichloroaniline are produced when hydrolyzed or when acids or bases are added at elevated temperatures (Sittig, 1985). The hydrolysis half-life of diuron in a 0.5 N NaOH solution at 20 °C is 150 d (El-Dib and Aly, 1976). When diuron was pyrolyzed in a helium atmosphere between 400 and 1,000 °C, the following products were identified dimethylamine, chlorobenzene, 1,2-dichlorobenzene, benzonitrile, a trichlorobenzene, aniline, 4-chloroaniline, 3,4-dichlorophenyl isocyanate, bis(l,3-(3,4-dichlorophenyl)urea), 3,4-dichloroaniline, and monuron [3-(4-chlorophenyl)-l,l-dimethylurea] (Gomez et al., 1982). Products reported from the combustion of diuron at 900 °C include carbon monoxide, carbon dioxide, chlorine, nitrogen oxides, and HCl (Kennedy et al., 1972a). 

An interesting method for obtaining a pure sample of terbium is to place one of the terbium halides (fluorine or chlorine) in a crucible and heat it in a helium atmosphere. The two elements will separate as a result of different densities. When the sample cools, the terbium can be separated from the halide. 

The use of appropriate ligands for a given metal can permit one to obtain high purity deposits. The Tjballyl and T -cyclopentadienyl ligands coordinated to palladium seem to be especially attractive for the deposition of pure palladium on silica surfaces. It has been proposed that [Pd(T hC3H5)(T -C5H5)] under a helium atmosphere could easily react with a silica surface to produce a surface allyl palladium species and cyclopentadiene [57] (9.9) ... 

IR spectrometric data reveal that the thermolysis of octa(methylsilsesquioxane) is a heterogeneous reaction involving the formation of a non-volatile solid phase similar to SiOj In a helium atmosphere at 150-300 °C (CHjSiO j)g almost completely evaporates without marked decomposition. When heat i in the air, however, this compound begins to decompose slowly at 270 °C, and at 450 °C an exo-effect attributed to the oxidation by air oxygen is observed When the temperature is raised to 500 °C, 66% of (CH3SiOi,5)g are oxidized to SiOj. 

To make sure of identical background and other conditions all sampling were done at the same time in the greenhouse. Twelve pots, four with plants of the barley cultivar Etu, four with barley cultivar Tellus, and four with soil only, were placed on a table with holes for the pots. The bottom of the pot was then easily accessible for all the necessary connections. Two samples from each pot and in all twenty-four samples in each set were obtained. After sampling, all tubes were stored in screw-capped glass tubes under inert conditions (low temperature and helium atmosphere) until gas chromatographic analysis. 

Fullerenes can also be produced by direct inductive heating of a carbon sample held in a boron nitride support [43]. Evaporation at 2700 °C in a helium atmosphere affords fullerene-containing soot that is collected on the cold Pyrex glass of the reaction tube. This method allows a continuous operation by keeping the graphite... 

The Kroll process involves heating molten magnesium and zirconium tetrachloride vapor in a sealed furnace in the absence of air under a helium atmosphere. The reaction forms zirconium sponge and magnesium chloride ... 

The >>Na NMR experiments were performed on static samples and on a Bruker MSL—200 spectrometer. Dehydrated samples were evacuated at 350 C under shallow bed condition, cooled under vacuum (lO torr), stored in helium atmosphere and introduced into a sample cell in a glove-bag under helium atmosphere. 

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