We have used a combination laser/electrospark method for fast determination of carbon content in soil. Excitation of the spectra is carried out both directly in a laser ablation plume and when a pulsed electric discharge is applied to it. We have plotted a calibration curve that is linear for the major concentration range of practical importance for the analyte element, all the way up to 8.6%. The carbon detection limit for the combination discharge approach is 0.07%. We have analyzed the ratio of the nitrogen and carbon contents, and also the hydrogen and carbon contents as a function of the carbon concentration in the studied soils samples.Description of the Method. The laser spectral analysis method (LIBS, laser-induced breakdown spectrometry) essentially involves exposure of the analyte sample to a focused high-power laser radiation flux, ablation of the sample material and formation of a plasma plume, the luminescence spectrum of which is recorded by a detector and processed by a measurement system [1][2][3]. Generally the amount of the material entering the plasma plume is fractions of a microgram, so LIBS is actually considered a nondestructive method.Broad development and application of LIBS began as a result of technical upgrade and expansion of production of high-power laser radiation sources based on yttrium aluminum garnet operating in the frequency regime. An important role was played by development of semiconductor 2-D array optical signal detectors, systems for data accumulation and processing, and optical instruments with high spectral resolution. Expansion of the area of application of LIBS is also due to more thorough study of the laser plasma itself: methods have been refined for determining the electron concentration and temperature of the plasma plume, self-absorption of emission spectral lines, the presence of local thermodynamic equilibrium (LTE). Thus the foundations have been laid for determination of the elemental composition of analyte objects without using certified samples [4,5], although the latter have maintained their role in validation of LIBS methods and also in cases involving analysis of samples of rather complex composition. The correctness of the results obtained by LIBS in the standard-free variant can be ensured, in the absence of matrix effects, when stoichiometry is satisfied in the composition of the plasma and the test object, which is possible when the power density of the laser radiation is at a level higher than 1 GW/cm 2 .In order to improve the sensitivity of LIBS, "dual" laser pulses are used [6,7], i.e., a second laser pulse is applied to the ablation plume with a certain time delay, which excites the material vaporized by the precursor in the relatively rarefied state of the vapor/gas atmosphere; in this case, robustness of the discharge is increased, re-absorption of the spectral lines is reduced.LIBS is a very promising method for solving practical problems in many areas of science and technology: quality control for industrial production, the composition of c...
This article examines the three stages in the development of slide-gate systems. The modern slide gate is characterized by the presence of elastic elements and reliable fastening of the plates. Different methods are discussed for securing the refractory plates in the carriage of the slide gate. Reliable operation of the gate is provided by the drive and auxiliary elements designed with allowance for the specific features of the casting of metal with the use of slide gates. Hydraulic drives have proven to be the most effective drives in Russia and abroad. The article also discusses the shapes of refractory slide-gate plates that help reduce crack propagation and make the plates more reliable in service. The latest generation of slide-gate plates is now in wide use, these plates being made with carbon-based, oxygen-free, or cermet binders.A slide-gate system is a complex of production equipment, auxiliary equipment and refractory elements that allows metal to be cast through a slide gate. The system includes slide gates for steel-pouring ladles and tundishes, a drive mechanism and feed devices, and auxiliary equipment and materials (molds, mortars, fillers, etc.). The introduction of slide-gate systems has been characterized by three stages of development. First Generation of Slide-Gate Systems (1965 -1980)The refractory systems of this generation allowed the casting of just a single heat [1]. The slide gate -a massive structure weighing 500 -1000 kg -was made in auxiliary shops. The gate designs were of the "rigid" type and the plates comprising the gate were pressed against one another by bolts. The plates were installed in the gate with the use of a mortar. They were serviced in special shops, and it was necessary to maintain a large stock of reserve gates. The service life of a gate was 70 -100 heats. It took more than 2 h to replace the refractories in the casting unit. Each metallurgical plant developed its own design of drive (hydraulic, pneumatic, or electrical) without regard for the details of the casting operation itself.The characteristic features of the plates used for the first generation of slide gates were as follows:-the use of plate materials with a single-component composition based on fused or sintered periclase, mullite, corundum, zircon, or other material;-the use of unconcentrated raw materials; -the use of a ceramic binder; -partial alloying of the plate material with refractory oxides to improve certain properties (Cr 2 O 3 was used to reduce the wettability of the surface of the metal, ZrO 2 was used to improve heat resistance, etc.); -impregnation of the plates with carbon-bearing liquids (coal-tar pitch, liquid bakelite, etc.); -the use of a coarse porous structure in which 70 -75% of the pores were 20 -30 mm in size and 20 -25% were smaller than 1 mm; the presence of individual pores with a size in the range 40 -70 mm contributed to significant wear of the plates;-the absence of metal casings and the use of a system of mortars to join the refractories together.Most of the plates in the ...
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