Time-resolved laser-induced plasma spectrometry for determination of minor elements in steelmaking process samples

A pulsed Nd:YAG laser operating on the fourth (266 nm) and second (532 nm) harmonics has been used to generate plasmas on the target surface in air at atmospheric pressure. The influence of wavelength on quantitative analysis of 4 minor elements in stainless steel samples (Si, Ti, Nb and Mo) was investigated. Stainless steel samples with different elemental concentrations were prepared and analyzed by laser-induced plasma spectrometry (LIPS). The effect of laser wavelength on analytical figures of merit (calibration curves, correlation coefficients, linear dynamic ranges, analytical precision, and accuracy values) was found to be negligible when internal standardization (an Fe line) and time-resolved laser-induced plasma are employed. For both wavelengths, the calibration curves presented a good linearity and an acceptable linear dynamic range in the concentration interval investigated. For the four elements studied, limits of detection lower than 150 microg g(-1) were achieved. To evaluate the influence of wavelength on precision and accuracy, a set of fifteen high-alloyed steel samples from different stages of steelmaking process have been analyzed. Finally, the long-term stability of the analytical measurements for Mo with 532 nm wavelength has been discussed. RSD values were lower than 5.3% for the elements studied.     

Direct determination of nickel in gas oil by atomic absorption spectrometry with electrothermal atomization

A rapid graphite-furnace atomic absorption procedure with simple dilution of samples was tested for the direct determination of sub-ppm levels of nickel in gas oils. The selection of appropriate graphite-furnace parameters, the type of solvent and organometallic standard, the effect of gas oil concentration in diluted samples, precision, accuracy and detection limit were investigated. Sample dilution was necessary because of high viscosity. Results obtained by standard addition for heavy gas oils were confirmed by a wet-ashing flame atomic absorption procedure. The relative standard deviation (r.s.d.) for consecutive determinations of nickel in gas oil solution containing 19 μg Ni l^?1 was 3.1%, and day-to-day r.s.d. for a reference gas oil sample was 5.3%. Accuracy was determined with an NBS standard reference oil GM-5 (4.6 ± 4.7% relative error in four determinations). Recovery experiments gas 104 ± 12% of the added nickel.     

Conservative methods for the Toda lattice equations

We are concerned with the numerical integration of the Todalattice equations by using different conservative methods. Numericalexperiments suggest that the global error for isospectral schemesdecreases exponentially with time but it is almost constantfor either symplectic or more general integrators. We providea theoretical explanation for these experimental findings.     

Saturation effects in the laser ablation of stainless steel in air at atmospheric pressure

A pulsed Nd?:?YAG laser was used to generate a plasma from stainless steel targets in air at atmospheric pressure. Laser focusing was found to be an important factor in the ablation process. The influence of focal conditions on spatial profiles of plasma, emission intensity and averaged ablation rate (AAR, μm pulse^–1) of stainless steel samples as a function of laser energy are discussed. At high energies and depending on laser beam focusing, ablation efficiency tends to decrease compared to that at lower energies. This effect can be due to plasma shielding and air breakdown. The averaged ablation rate was found to be dependent on the thickness of the sample. This effect results in shielding of the incoming laser beam and redeposition of removed material in the crater. By focusing the beam inside the material free expansion of plasma is allowed, resulting in more efficient erosion of the sample at larger energies. For comparative purposes, data on ablated mass per pulse are presented.