Platinum filament

Similar results have been derived in generating free radicals through pyrolysis of acetone on a platinum filament [50]. Adsorption of more complex radicals such as C2H5, C3H7, CH2C6, etc. has been studied using the same methods. The above relationship asserts satisfactorily in these cases, too. This provides the evidence for versatility of the found relationship (3.22) which can be successfully applied in the methods involving the use of sensors. 

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.

Hinshelwood and Burk [J. Chem. Soc., 127 (1105), 1925] have studied the decomposition of ammonia over a heated platinum filament at 1138° C. The reaction stoichiometry is... 

Thermocouple gauges work on a similar principle but have a thermocouple as sensor connected to a heated platinum filament. The e.m.f. of the thermocouple is measured with a galvanometer or potentiometer. Such gauges have a normal working range from 10 to 10" Torr, but otherwise have characteristics similar to Pirani gauges. 

Immeasurable ions are formed when hydrocarbons in an air stream are oxidized in the presence of a heated platinum filament (3,10). The experimental evidence suggests that these ions are produced by the chemical oxidation reactions catalyzed by the platinum surface (10). That this process is one of chemionization is supported by the fact that the extent of ionization observed depended greatly on the molecular structure of the particular hydrocarbon being oxidized. This is in contrast to the ionization measured in flames, where the extent of ionization for saturated hydrocarbons, for example, does not appear to depend in any way on the molecular structure but only on the number of carbon atoms (9). 

All of the data reported in this paper were obtained using a platinum filament as the catalyst. Under the experimental conditions used, a maximum of about 35 to 60% of the hydrocarbon in each case was oxidized. Although the ion yields can be expressed in several ways, for the most part they are presented as coulombs per mole of hydrocarbon oxidized. 

Effect of Hydrocarbon Molecular Structure on Ionization from Catalytic Oxidation in Air. Figure 1 shows the data for the ion yields obtained for several hydrocarbons during oxidation in air over a platinum filament in the approximate temperature range of 400° to 900°C. The hydrocarbons fall into two broad categories those which produced about 0.04 coulomb per mole of hydrocarbon oxidized, and those which produced about 1.0 coulomb or more per mole. The latter yield is similar to that obtained during combustion of hydrocarbons in a hydrogen flame... 

Halogenated Hydrocarbons. A few halogenated hydrocarbons were studied by the usual procedure, using mixtures in air over the platinum filament. Neither dichlorodifluoromethane (CC12F2) nor 1,1-dichloro-ethene yielded a measurable ion current at temperatures up to 900°C. 1,1,1-Trichloroethane yielded a modest ion current, but the results were erratic and not reproducible. There was some indication that the halogen compounds changed the behavior of the filament. Consequently, no further experiments with halogenated compounds were conducted. This erratic behavior was in contrast with the very reproducible results with hydrocarbons. 

Contact with a heated platinum filament also promotes the cteConn position.1... 

He was the first to observe the very stable adsorbed monatomic hints on tungsten and platinum filaments, and was able, alter experiments with oil films on water, lo formulaic a general theory ol adsorbed films. He also studied the catalytic properties of such films. 

The method determines the partial pressure of methane in the gas phase above the solution (Henry s law). Methane catalytically oxidizes on a heated platinum filament, that is part of a Wheatstone bridge. The heat generated increases the electrical resistance of the filament which is measured and compared against calibrated standards. 

De La Rive invented a new -> electroplating method to deposit gold onto brass and silver, and designed one of the first incandescent lamps using a platinum filament in a partially evacuated glass tube. He also designed an electrochemical - capacitor (condenser), 1843. 

Platinum—Kelley 259 j s used the experimental data given by Jones, Langmuir, and Mackay2 54 on the rate of evaporation of platinum filaments to deduce 124 4 kcal for A//25 c The data are not very concordant and the N.B.S. deduces 121 6 kcal -29,... 

This type of pyrolyser commonly uses a platinum filament that has a precisely determined electrical resistance R1. This filament is incorporated in a Wheatstone electrical bridge. This bridge is balanced (V1 = V2) when the values of the electrical resistances in the bridge fulfill the relation ... 

The decomposition of ammonia on the surface of a glowing platinum filament follows approximately the equation... 

The high molecular weight DOC samples were analyzed by Py-MS using the in-source platinum filament pyrolysis technique. The filament, bearing a 1- to 20-(tg sample, was heated at 15°C/sec to a final temperature of 800°C. The mass spectrometer collected one scan/sec over the m/z range of 20 to 800 amu for 1.5 nun. 

When a resistively heated filament pyrolyzer (e.g., the Pyroprobe from CDS Analytical, Inc., Oxford, PA) is used, the sample may be placed directly on a platinum filament or in a quartz tube or boat inside a platinum coil. In either case, the placement of sample with respect to the sampling tube or the ribbon should be the same for all samples. For liquid sample suspensions placed on a ribbon or in a coil, the solvent is evaporated prior to pyrolysis. Solid microbial samples can be sandwiched between quartz wool plugs inside the quartz sampling tube so as to reduce extraneous nonvolatile material from leaving the sampling tube during pyrolysis. With quartz, the sample never comes into direct contact with the pyrolyzer filament, as it does when sample is coated directly on a thin ribbon filament. Ribbon filaments sometimes exhibit a memory effect (particularly with polar components), are harder to clean, and typically have a shorter lifetime. Quartz tubes may be reused after cleaning. 

Figure 6 Heated interface for Py-GC. Sample material is placed directly onto the platinum filament, which is inserted into the glass cell of the interface. The injection needle passes through the injection port of the GC to the column inlet. (Diagram kindly supplied by Dr I. Ericsson, Pyrolab, Lund, Sweden.)...

Since negative thermal ion mass spectrometry (N-TIMS) for rhenium/osmium dating (see O Sect. 17.18) was developed about 1990, not too much work has been published. This is probably due to the high rhenium blanks from the current generation of clean platinum filaments and to problems in achieving isotopic exchange and equilibrium between sample and spike for osmium. Another drawback is the non-homogeneity of samples. Because of this, rhenium and osmium concentrations may vary hy up to 40% in the same sample. 

The similar chemical effects of frictional and voltaic electricity led him to conclude that they were identical, long before such a view became commonplace. Later, after perfecting the process of drawing extremely fine platinum wires, Wollaston constructed his "thimble battery", which was a very small galvanic cell capable of bringing a platinum filament to incandescence upon iimiersion in dilute vitriolic acid. Both demonstrations illustrate Wollaston s talent for eadiibiting natural phenomena by means of inexpensive "shirt-pocket" devices. 

When the beam enters the pyrolysis cell, it is focused directly above the platinum filament of the pyrolyser. An IBM PS2 computer was used to collect the data obtained. The spectra were baseline corrected using a polynomial baseline correction routine. Sample sizes ranged from 100 to 500 pm. 

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