Dual-pulse laser-induced breakdown spectrometry of bronze alloys and coatings

Abstract

The possibilities of using dual-pulse laser atomic-emission spectroscopy for both the estimation of elemental concentrations in bronzes and layer-by-layer analysis of a bronze coating on steel bead wire have been examined. Two methods have been proposed to lower the radiation flux density q in studies of thin metallic layers. These were based respectively on using optical filters and defocusing the radiation with respect to a sample surface. It has been found that the decrease of q results in reducing the influence of tin on copper evaporation under dual-pulse laser irradiation.Introduction. Laser-induced breakdown spectroscopy (LIBS) is a method of qualitative and quantitative analysis that is based on recording emission spectra of laser-induced plasma. It depends fundamentally on the interaction of powerful optical radiation with a sample surface that produces heat, melting, vaporization, and atomization of a substance and formation of ablation plasma. One of the most rapidly developing areas of LIBS that can increase significantly the intensity of the spectral lines and, therefore, the analytical sensitivity is the use of dual laser pulses (DLP) that are phase-shifted relative to each other as the excitation source for the spectra [1, 2]. The principal reason for the increase of optical emission is the formation of a region near the surface with increased temperature and particle density. Furthermore, heating of the sample by the first pulse and the additional excitation of atoms in the initial plasma by the second pulse are also responsible for the strengthening of the analytical signal.The advantages of LIBS are the highly localized sampling area; the small amounts of substance vaporized by the radiation; the weak dependence of the ablation process on the sample physicochemical properties; and ability to use untreated surfaces. Because of these advantages, LIBS is used to analyze various objects such as industrial raw materials and finished products, minerals and soils, and biological objects [3][4][5].LIBS of bronzes has been the subject of several theoretical and experimental studies [6][7][8]. However, the attention in most of these was focused on quantitative analysis of works of art [6] or objects located under water [7]. Yet bronzes are rather common construction materials that are used to fabricate massive items and as coatings on steel wire in order to protect it and improve the adhesion of the surface to resin. LIBS studies of thin metal layers involved primarily single-component coatings such as galvanized iron [9] and copper deposited on steel boiler pipes [10]. The requirements imposed on the excitation source of the spectrum are different for analyzing works of art and industrial products made of bronze. In the first instance, it is very important to minimize surface damage by the laser radiation; in the second, to minimize the determination error of element concentrations to the corresponding GOST level. This is usually achieved by using multiple surface excitations.The goal of our work was to ...

Double Pulse LIBS of Titanium-Based PVD-Coatings with Submicron Resolution

“…A lowered density of the radiant flux with a defocused radiation leads to the decreased quantity of a substance ingressed into the ablation plasma and hence to the decreased line intensities [11][12][13][14]. Because of this, for analytical applications it is expedient to select the lines with the highest intensity for all the components in the spectral range of interest: Ti = 390.2 nm, Zr = 360.1 nm, Si = 390.6 nm, Al = 396.2 nm, and Fe = 382.0 nm.…”

“…As this takes place, a decrease of the radiant flux density occurs simultaneously with a decrease in the effective area eff of the erosion spot associated with evaporation. Based on the optical scheme of a LSS-1 spectrometer, it is possible to record a signal from the plasma evaporated from a greater (∼1-3 mm 2 ) surface area [13]. In this case an analytical signal exceeds a background level severalfold even at ℎ 0 = 0.1 m. As demonstrated by the conducted experiment elucidating the effect of a defocused laser radiation on silicon and titanium plates (sample 1 and sample 3), with a minor change in Δ the spectral line intensities of Ti and Zr are changed stepwise (Figure 2).…”

“…The thickness ℎ 0 of the layer evaporated by a defocused radiation was determined by an abrupt, during 1-2 pulses, intensity drop for the spectral line of Ti when the blank sample 1 had a marked interface between the titanium coating and steel base. Table 2 gives the values of the radiant flux density and of the thickness ℎ 0 at different distances Δ in the case of a negative defocusing [13,14].…”

Continuum removal and self-absorption correction incalibration-free laser-induced breakdownspectroscopy for efficient elemental analysis

“…'Nowadays, LIBS has been widely used for the analysis of alloys, especially for alloy classification, production control and quality assurance' [2]. In industry, Bronze alloys are used for the construction of massive instruments as well as the thin-layer coating over steel wire for protection of surface and improvement of adhesion to resin [3]. Exact quantification of bronze is needed in most cases since the material properties of bronze is mainly depend on the amount of copper in the alloy.Thisstudy used specific spectral pre-processing techniques for the abundance estimation of binary bronze alloy sample while using a low-resolution portable spectrometer.…”

Enhancement effects of flat-mirror reflection on plasma radiation

“…However, one of its drawbacks is the low sensitivity, which hinders further lowering of the limit of detection (LOD) and limits the detection ability of micro amounts of components in soil [9]. Hence, several different methods have achieved good results, such as dual-pulse laser excitation [10,11], which uses magnetic fields to confine the laser-induced plasma [12]. Although the dual-pulse laser excitation technique can improve the detection limit and the ability of spectrum analysis technology, it complicates the instrument and operation sequence.…”