Filament emission

Volatiles isolated by the purge-and-trap method were analyzed by GC-MS using a Varian 3400 gas chromatograph coupled to a Finnigan MAT 8230 high resolution mass spectrometer equipped with an open split interface. Mass spectra were obtained by electron ionization at 70 eV and an ion source temperature of 250°C. The filament emission current was 1 milliampere and spectra were recorded on a Finnigan MAT SS 300 Data system. 

For MS work, the electron impact (El) mode with automatic gain control (AGC) was used. The electron multiplier voltage for MS/MS was 1450 V, AGC target was 10,000 counts, and filament emission current was 60 pA with the axial modulation amplitude at 4.0 V. The ion trap was held at 200°C and the transfer line at 250°C. The manifold temperature was set at 60°C and the mass spectral scan time across 50-450 m/z was 1.0 s (using 3 microscans). Nonresonant, collision-induced dissociation (CID) was used for MS/MS. The associated parameters for this method were optimized for each individual compound (Table 7.3). The method was divided into ten acquisition time segments so that different ion preparation files could be used to optimize the conditions for the TMS derivatives of the chemically distinct internal standard, phenolic acids, and DIMBOA. Standard samples of both p-coumaric and ferulic acids consisted of trans and cis isomers so that four segments were required to characterize these two acids. The first time segment was a 9 min solvent delay used to protect the electron multiplier from the solvent peak. 

N-C Hj-morphine as internal standard. The internal standard was added to 10 ml urine, the urine buffered to pH 8.5 and extracted with chloroform isopropanol (4 1). The extraction residue was trimethylsilylated by adding 25 ul of N,0-bis(trimethylsilylJacetamide and heating at 60°C for about 1 h. About 2 ul was analyzed on a 3 % 0V-17 column at 230°C coupled direct to a Finnegan 1015 quadrupole mass spectrometer equipped with a chemical ionization source, which was operated at an ionizing energy of 100 eV, an ion repeller voltage of 0 V and a filament emission of 300 uA. The mass spectrometer was interfaced with a System Indus-... 

Only a few specific operating parameters have a major Impact on the spectra obtained. These include the excitation level (the power of the RF pulse), the filament emission current, the electron beam voltage, the trapping voltage, (which is applied to the cell trapping plates), and the signal attenuation. Each of these has to be tuned specifically to maximize response for any peak(s) of interest, and this is particularly Important for the lower field strength analyses. 

All mass spectra were recorded using a Hewlett-Packard 5985B mass spectrometer equipped with a dual electron impact/chemical ionization source including negative ion capability. The source temperature was 125QC, filament emission current was 300 uA, and electron energy was 230 ev. The interface between the GC and MS was a glass-lined stainless steel transfer line. Methane was used both for carrier gas and as the chemical ionization reactant gas. A methane flow of 11.5 mL/min. resulted in an ion source pressure of 0.5 torr. 

We have verified experimentally, that the ring emission is a surface radiation and occurs at the boimdary of self-trapped filaments, confirming that it is a Cherenkov type radiation. To this end, we examined the special coherence of the ring emission. The laser radiation was focused into the sodium cell by a cylindrical lens and the produced pattern is shown in Fig. 1. The off-axis ring emission preserves its symmetry around the laser axis, while the laser beam spot has an ellipse form. Should the ring emission be produced in the interior of the saturated filaments, where n=l, the interference between different filament emissions would result in a pattern representing the spatial distribution of the filaments, i.e. ellipse. We thus conclude, that the ring emission is produced mainly at the interior of the filaments. 

The particle size distribution of South Afriea Coneentrate was measured using the laser diffractometer MS 2000 which is produced by Malvern Instruments. The moisture eapacity of raw material was measured in the self-made instrument in the laboratory. [5-6]The morphology of the particle surface were performed using scanning electron microscope (SEM) equipped with a tungsten filament emission source. 

Almost all emission that we usually encounter, such as that from a sodium vapour or tungsten filament lamp, is of the spontaneous type. 

Corrosion Resistant Fiber-Reinforced Plastic (FRP). Fiber glass reinforcement bonded with furfuryl alcohol thermosetting resias provides plastics with unique properties. Excellent resistance to corrosion and heat distortion coupled with low flame spread and low smoke emission are characteristics that make them valuable as laminating resins with fiber glass (75,76). Another valuable property of furan FRP is its strength at elevated temperature. Hand-layup, spray-up, and filament-win ding techniques are employed to produce an array of corrosion-resistant equipment, pipes, tanks, vats, ducts, scmbbers, stacks, and reaction vessels for industrial appHcations throughout the world. 

The source requited for aes is an electron gun similar to that described above for electron microscopy. The most common electron source is thermionic in nature with a W filament which is heated to cause electrons to overcome its work function. The electron flux in these sources is generally proportional to the square of the temperature. Thermionic electron guns are routinely used, because they ate robust and tehable. An alternative choice of electron gun is the field emission source which uses a large electric field to overcome the work function barrier. Field emission sources ate typically of higher brightness than the thermionic sources, because the electron emission is concentrated to the small area of the field emission tip. Focusing in both of these sources is done by electrostatic lenses. Today s thermionic sources typically produce spot sizes on the order of 0.2—0.5 p.m with beam currents of 10 A at 10 keV. If field emission sources ate used, spot sizes down to ca 10—50 nm can be achieved. 

Hafnium nitride s high, emissivity in the visible spectmm at high temperature has led to a proposed use (52) as a coating on incandescent light filaments to improve visible light output. 

Tungsten with the addition of as much as 5% thoria is used for thermionic emission cathode wires and as filaments for vibration-resistant incandescent lamps. Tungsten—rhenium alloys are employed as heating elements and thermocouples. Tantalum and niobium form continuous soHd solutions with tungsten. Iron and nickel are used as ahoy agents for specialized appHcations. 

Real or gray bodies deviate from these ideal blackbody values by the A-dependent emissivity, but the color sequence remains essentially the same. This mechanism explains the color of incandescent light sources such as flames in a candle, tungsten filament light bulb, flash bulb, carbon arc, limelight, lightning in part, and the incandescent part of pyrotechnics (qv). 

There are three major types of electron sources thermionic tungsten, LaBg, and hot and cold field emission. In the first case, a tungsten filament is heated to allow... 

The most likely cause of problems in any MS is associated with the ion source. When a MS problem is discovered, a good rule is to clean the source and check for shorts or a burned-out filament. For most instruments, it is relatively simple to determine that a filament has burned out because the emission current will be zero. Sometimes, the filament will short to the block. In this case, the emission current will read high when in the Cl mode where emission current is read between the filament and the ion source block. In either case, the source should be cleaned and the filament inspected. If the filament is sagging, it is a good idea to replace it. 

The tube-current stabilizer is usually put in the grounded return output circuit of the high-voltage transformer. The stabilizer functions by properly adjusting the a-c heating current through the filament (x-ray tube cathode), and in this way regulating the electron emission. 

From Fig. 6.14 it becomes clear why one must heat filaments to very high temperatures to see electron emission in electron guns. Only the part of the electron distribution that has obtained energies above 0 can be utilized. The occupation number at the vacuum level can be approximated by e hT leading to the well known Richardson-Dushman formula, which describes the fluxj of electrons evaporating from a surface with work function 0 at temperature T ... 

Fig. 6.1. Experimental set-up to study emission of active particles i, 2 - chambers 3 - evaporating tray 4 - platinum filament 5 - target 6 - mobile sensor 7 - shatter 8 - contacts 9 - thermocouple 10 - weight to move sensor.

Fig. 6.11. The schematics of experimental set-up to study emission of atomic oxygen. 1 — sensor of oxygen atoms 2 samples of reduced silver 3 shutter 4 weights to brake membranes 5 platinum filament to calibrate sensor against the concentration of oxygen atoms.

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