Physikingenieurwesen (PHY)
The potential use of an EMG-20 mass-spectrometric gas analyzer for process control and safe operation and environmental monitoring in metallurgy (oxygen converter process) is considered. The EMG-20 parameters are adequate for rapid, automatic on-line analysis of metallurgical waste gases. A multichannel system of sampling. sample preparation, and transportation of sampled gases for analysis is proposed.
Self-sustained current oscillations in a Townsend discharge that is excited in a short plane discharge gap and is uniform along the electrode surface are investigated experimentally. A thin semiconductor plane serves as a discharge cathode, a ballast resistor, and an additional capacitor in the dc power supply circuit. The domain of existence and the frequency and waveform, of oscillations are determined over a wide pressure range.
Current self-sustained oscillations in a Townsend discharge are studied analytically. The proposed method for solving simple equations is applicable even when the Townsend coefficient of electron reproduction g (the main factor governing the oscillations) cannot be determined theoretically. The coefficient g is related to the discharge current-voltage characteristic, which can be obtained experimentally or from numerical simulations. Self-oscillating solutions (limit cycles) are found under various conditions. The mechanisms governing the excitation and stabilization of the solutions obtained are interpreted. It is shown that the waveform of the undamped oscillations may change significantly (the current peaks are smoothed, and the oscillation period decreases) when a weak constant cathode current, which is presumably related to the emission caused by slowly diffusing metastable molecules, is included in the equations.
In this paper a novel concept of ablation cell for laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) is presented. Suppression of the turbulence in the flush gas flow in the ablation region reduces the wash-out time of the ablation cell considerably. An ablation chamber which enables ICP-MS pulse duration down to several ten milliseconds has been designed. Dependence of the ICP-MS peak amplitude, width, and shape on the gas flow parameters is studied experimentally for aerosol ablated under laminar and turbulent conditions. Experiments demonstrate that the ICP-MS peak becomes sharper and the amplitude of the signal grows as the turbulence in the ablation cell is suppressed. Furthermore, the possibility of the LA-ICP-MS analysis with a sampling rate of more than 10 Hz has been demonstrated. Express in-depth profiling in the new ablation cell is demonstrated on examples of an Al -Zn multilayer structure and an industrial Mg -Zn coating.