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Hydrogen cryostat

Although cryogenic liquid hydrogen has been stored in spacecraft to power fuel cells and for other uses (as will be described later in this chapter), liquid hydrogen Dewars/cryostats have not been used for cooling sensors or other devices [77-79]. However, solid hydrogen cryostats have been used on two past space missions [89] and are intended for a future NASA/ESA mission being planned for a launch around 2011. [Pg.392]

The simplest way to hold constant temps is to use a bath medium which either melts or boils at the desired temp. Ice-salt mixts are used for temps ca 0°. Egly (Ref) presents a table of selected materials, readily available inexpensive, which are recommended for use in a wide temp range. If a cryostat is to be held at the same temp for extended periods of time, a bath liq should be chosen which freezes well below the desired temp, and the bath temp should be controlled. A large number of liq -hydrogen liq-helium generators and cryostats are described in recent literature Refs l)Kirk Othmer 8, (1952), 488 2)A. [Pg.350]

Fresh rat brain tissue is immediately immersed in 2-methyl butane at -15 to -25°C for several minutes and stored at -70°C. Sections (10 p,m) are cut in the parasagittal plane on a cryostat, which are thaw-mounted onto poly-L-lysine-coated glass slides and stored at -70°C. The sections are dried on a slide warmer at the lowest setting to avoid excessive drying. They are fixed with 4% formaldehyde in PBS (pH 7.5) for 30 min and then rinsed three times for 10 min each in PBS to remove excess fixative. This is followed by treatment with 0.3% hydrogen peroxide in PBS for 30-40 min to quench endogenous peroxidase activity. [Pg.199]

Fia. 5. Arrangement of cryostat for studying reactions with hydrogen atoms (a) General principle (b) Schematic cross-section. [Pg.11]

The reaction of toluene is of interest as toluene has been used extensively in the toluene-carrier gas technique as a means of removing radicals from a reacting system (Szwarc, 1950). The results from the rotating cryostat show that n-heptyl radicals react with toluene at 77°K by abstracting a methyl hydrogen to give the benzyl radical. As expected, addition to the aromatic ring does not occur. [Pg.48]

Experiments have been carried out with the rotating cryostat to study the reaction of 2,6-di-t-butyl-4-methyl phenol (lonol) with n-heptyl and n-heptylperoxy radicals. When lonol was deposited on n-heptyl radicals the e.s.r. spectrum showed that some reaction had occurred at 77°K. When the deposit was warmed slowly the spectrum of the residual n-heptyl radicals disappeared and was replaced by that of the substituted phenoxy-radical, (4), formed by loss of the hydroxyl hydrogen. [Pg.51]

Although it is known that free radicals add predominantly to the least substituted end of an olefinic double bond there is very little quantitative information on the relative rate of addition at the two positions in asymmetric olefins (Cadogan and Hey, 1954 Cvetanovid, 1963). The rotating cryostat has been used to examine this aspect for the case of the addition of hydrogen atoms to a variety of olefins deposited in a matrix of adamantane. The ratios of the rates of addition are given in Table 7, and for illustration the reaction with propylene is considered below. [Pg.55]

Using the rotating cryostat we have obtained direct evidence for the occuri ence of such an intramolecular hydrogen abstraction in a series of substituted vinyl radicals. The vinyl radical, RCH=CH, has been prepared in an inert matrix (water or benzene) by the reaction of sodium with the appropriate vinyl halide. [Pg.63]

It was thus of interest to determine whether a transannular addition could occur for the cyclo-octenyl radical. The cyclo-octenyl radical has been prepared from its parent halohydrocarbon in several matrices in the rotating cryostat. At 77°K the radical was stabilized in all of the matrices but when the samples were warmed reaction took place. The e.s.r. spectra showed that the main reaction in matrices of water, benzene or camphane was hydrogen abstraction adjacent to the double bond to give a cyclic allyl radical (9) rather than the bicyclic radical. However, in a matrix of bicyclopentadiene dimer cyclization occurs to give the bicyclic radical and in a matrix of adamantane both allylic and bicyclic radicals were formed. [Pg.66]

Although work below liquid nitrogen temperature necessitates a precision-engineered vacuum cryostat, it is quite easy to work between 78 K and 300 K without a vacuum by using styrofoam insulation. Standard coolants are liquid nitrogen (b.p. 77-3 K), liquid hydrogen (b.p. 20-4 K), and liquid helium... [Pg.38]

The samples were grown by MBE at 700 C (for details see [4]). The samples had 10 layers containing quantum dots. For the irradiation with 2.4 MeV protons at RT, a Van de Graaff accelerator was used. The passivation with atomic hydrogen at 250"C for 30 min was undertaken in a CVD reactor. The PL measurements were performed at a Bruker IFS 66v FTIR spectrometer equipped with a Ge detector. The samples were placed in a helium gas flow cryostat at temperatures from 5-300K. For the excitation in a wide power range we used the 488 nm line of an Ar laser. [Pg.144]


See other pages where Hydrogen cryostat is mentioned: [Pg.394]    [Pg.394]    [Pg.230]    [Pg.394]    [Pg.394]    [Pg.230]    [Pg.3]    [Pg.122]    [Pg.1787]    [Pg.89]    [Pg.302]    [Pg.132]    [Pg.562]    [Pg.1870]    [Pg.1787]    [Pg.358]    [Pg.361]    [Pg.22]    [Pg.905]    [Pg.129]    [Pg.10]    [Pg.54]    [Pg.361]    [Pg.121]    [Pg.159]    [Pg.20]    [Pg.350]    [Pg.32]    [Pg.1787]    [Pg.125]    [Pg.3]    [Pg.262]    [Pg.173]    [Pg.562]    [Pg.31]    [Pg.160]    [Pg.246]    [Pg.515]   
See also in sourсe #XX -- [ Pg.392 ]




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