High vacuum definition

The first definite production of plutonium metal was made in November, 1943 by Baumbach and coworkers (1958). Approximately 35 micrograms of PuFi in a small thoria crucible in a high vacuum was reacted with barium metal at 1400 C to yield plutonium metal. The metal was found to have a silvery lustre, a density of about 16 grams j>er cubic centimeter and it rapidly absorbed hydrogen at about 210 C to form a black powder subsequently identified as PUH3 (a proof that metal had been produced). 

InSb is a direct semiconductor, and quantum dots of InSb, made under ultra-high vacuum conditions, have already been successfully studied for laser appHcations [32]. Quantum dots are widely under investigation nowadays and this is a rapidly growing research field. Definite electrodeposition from ionic Hquids would be an important contribution. 

A very convenient way of detecting and measuring leaks is to use a tracer gas (such as He) and a selective tracer gas detector, such as a helium leak detector. In addition to the mass spectrometer, MSLD include a high vacuum pumping system of definite pumping speed. 

Metal films condensed in a high vacuum have, usually, a much lower catalytic activity than films condensed in a low pressure of an inert gas.3 The films condensed in the gas had an oriented structure, with the (110) face parallel to the backing in the case of nickel, the (111) face in the case of iron. There was little, if any, definite orientation in the films condensed in vacuo. It has been suggested that the increased catalytic activity is, in part at least, due to the special spacing on the exposed crystal faces but there may be other reasons, perhaps the presence of linear interfaces between the bare metal and the parts covered by adsorbed gas, or a larger real surface. The suggestion is interesting, however, and now that it is possible to make faces in selected crystal planes, to the practical exclusion of others, the study of the catalytic activity of special crystal faces does not seem beyond the bounds of possibility. 

James Wei Not product driven, it s process driven. You ve got something you want to get done, you want to put it in the kitchen and cook it until it s done, that is chemical reaction engineering, my definition of it. The second issue you raised concerned the relationship of studies at high vacuum... 

It has been recognized for several years from ultra-high-vacuum investigations that alkali metals can lower the work function of metal surfaces [for review, see Ref. 75]. In its simplest form, the work function is defined as the minimum energy required to extract one electron from a metal. Although this definition is correct, it does not lend itself to description of how an adsorbate can alter the work function of a metal. 

Thus, to obtain definitive results on the influence of parameters such as lattice defects, electronic and geometric factors, and contaminants, it is essential to develop and apply techniques which permit the study of simple systems under conditions such that the several contributing factors can be separated and investigated individually. Since chemisorbed gases are included in the class of objectionable contaminants, it is necessary to employ the most effective means available of cleaning the catalyst in high vacuum. This requirement places severe limitations on the construction of the reaction chamber, the size of the catalyst, the pressures of the reactants, and the means of detecting the reaction constant. 

The method uses speeial effusion cameras with holes of a definite form, maintaining high vacuum in the system. The method is widely applied to the measurements of a vapor pressure of low volatile substances. 

A form of EGA involves heating the sample at a constant rate in the probe of a mass spectrometer and the resulting TA technique is known as programmed probe analysis or more simply as analytical pyrolysis . By such a process, samples are pyrolyzed in high vacuum since the sample environment is equivalent to the operating pressure of the mass spectrometer. This technique has been used by Bratspies et al. to determine thermal decomposition mechanisms of metal complexes, particularly tin dithiocarba-mate complexes and this definitive study has been reviewed. 

The second point that should be made is that the situation of isolated particles in the high vacuum—in particular the ill-definition of temperature and the non-Boltzmann distribution of internal energies—may appear to be somewhat uncommon for many chemists who are used to do chemistry in solution. Nevertheless, if one considers the great new insights into, for example, the intramolecular reactivity of supermolecules, it is certainly worthwhile even for solution-phase supramolecular chemists to invest effort and time into mass spectrometric analyses of their supermolecules. 

Outer space (lx 10 -<3 x 10 Torr) is generally much more empty than any artificial vacuum. It may or may not meet the definition of high vacuum or ultrahigh vacuum, depending on what region of space and astronomical bodies are being considered. For example, the mean free path of interplanetary space is smaller than the size of the solar system but larger than small planets. As a result, solar winds exhibit continuum flow on the scale of the solar system but must be considered as a bombardment of particles with respect to the Earth and Moon. 

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