Xenon arc systems

Reactive system Azo chromogen Perspiration (acid)/light ATTS test Light Xenon arc... 

In a Rapra study both natural PP and HDPE were tested together with similar materials containing carbon black as a stabiliser. The carbon black containing materials showed essentially no change in tensile strength after 1,035 days exposure in the UK, 510 days in Australia and 200 days in various accelerated exposures using QUVA lamps (fluorescent tubes which stimulate the UV sector (<400 nm wavelength)) and Xenon arc equipment (which stimulates the solar system). 

Polymerization of methyl methacrylate (MMA) was initiated with methylalumi-num tetraphenylporphyrin (1, X=Me) under irradiation with visible light. At a monomer conversion less than 10%, Lewis acids such as methylaluminum diphenolates 3a-i and methylaluminum dialcoholates 4a,b were added to the system in order to examine whether they could accelerate the polymerization (Scheme 2) (Table 1). For example, a CH2CI2 solution (10 ml) of a mixture of MMA and 1 (X=Me) with a mole ratio of 217 was irradiated at 35 °C with xenon arc light (k>420 nm) to initiate the polymerization. During 2.5-h irradiation, all the molecules of the initiator 1 (X=Me) were transformed into the growing enolate species 2 (R=Me), where the conversionof the monomer was 6.1%, as estimated by NMR. 

Fig. 2.17. Schematic layout of a microscope spectrophotometer system used to measure polarized absorption spectra of very small mineral crystals. The computer-operated, single-beam instrument shown here comprises a polarizing microscope equipped with a stabilized light source (xenon arc lamp or tungsten lamp cover the range 250-2000 nm), a modulator that chops the light beam with a frequency of 50 Hz (the amplifier for the photodetector signals is modulated with the same phase and frequency), and a Zeiss prism double monochromator. Single crystals as small as 10 ji.m diameter may be measured with this system. A diamond-windowed high-pressure cell can be readily mounted on the microscope scanning table for spectral measurements at very high pressures (after Burns, 1985, reproduced with the publisher s permission).

A discussion of photostability is not as straightforward as that of thermal stability due to the complexity of photoexposure. Correlation between devices of the same type, either in the same laboratory or at different locations, can be very good if they are operated under the same test conditions. Test results between devices with different sources of radiation (e.g., xenon arc and fluorescent tube) will vary according to the spectral absorption characteristics of the product being tested. Thus it is possible that some products may decompose at an equal rate in systems having different types of irradiation sources however, other products may react quite differently. Although the proposed test is reasonably simple to conduct, there are some practical problems not definitively resolved (e.g., selection of adequate irradiation source and calibration). This chapter will focus on practical problems related to the use of the current guideline. 

Hydrogen and deuterium arcs, and high pressure xenon arcs are convenient, near-continuous, light sources for absorption studies. Kaufman and Del Greco have, however, used a rather special light source in experiments on hydroxyl radicals prep u ed in a low pressure flow system by the reaction... 

Coherent forward scattering (CFS) atomic spectrometry is a multielement method. The instrumentation required is simple and consists of the same components as a Zeeman AAS system. As the spectra contain only some resonance lines, a spectrometer with just a low spectral resolution is required. The detection limits depend considerably on the primary source and on the atom reservoir used. When using a xenon lamp as the primary source, multielement determinations can be performed but the power of detection will be low as the spectral radiances are low as compared with those of a hollow cathode lamp. By using high-intensity laser sources the intensities of the signals and accordingly the power of detection can be considerably improved. Indeed, both Ip(k) and Iy(k) are proportional to Io(k). When furnaces are used as the atomizers typical detection limits in the case of a xenon arc are Cd 4, Pb 0.9, T11.5, Fe 2.5 and Zn 50 ng [309]. They are considerably higher than in furnace AAS. 

If it can be assumed that the photon source is uniform in its output, this would not affect the result unfortunately, that is not the case because xenon arc lamps may vary by as much as 20% over a period of 5 to 6 hours. Fundamentally, the ferrioxalate system remains the actinometer of choice when a narrow range of wavelength is used for the irradiation. A possible approach to extend the range of application is... 

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