Atomic Processes

The use of tetramethylammonium hydroxide, tertiary amines and strongly alkaline reagents for sample treatment involving extraction and digestion procedures is discussed in this review. The preparation of slurries is also discussed. Based on literature data, alkaline media offer a good alternative for sample preparation involving an appreciable group of analytes in different types of samples. These reagents are also successfully employed in tailored speciation procedures wherein there is a critical dependence on maintenance of chemical forms. The effects of these reagents on measurements performed using spectroanalytical techniques are discussed. Several undesirable effects on transport and atomization processes necessitate use of the method of standard additions to obtain accurate results. It is also evident that alkaline media can improve the performance of techniques such as inductively coupled plasma mass spectrometry and accessories, such as autosamplers coupled to graphite furnace atomic absorption spectrometers.

Powder metals are the basis of powder metallurgy with a large variety of applications, including sintering and thermal spray coatings. The Gas atomization process has been widely employed as an effective method to produce fine spherical metal powders. New applications and emerging surface technologies demand high quality powders with a very narrow particle size distribution. A computational fluid dynamics (CFD) approach is developed to examine complex fluids during atomization from different nozzle designs, using the volume of fluid (VOF) method and the Reynolds Stress Model (RSM). The modeling results show that the swirling gas atomizer is not beneficial to the atomization process while the inner-jet atomizer can improve the powder generation processing.► Primary breakup of gas atomization is successfully modeled. ► Three different nozzle designs for closed-coupled atomizers are compared. ► I-nner jet atomizer performs better than a swirling gas atomizer.

Thermal history of droplets associated with gas atomization of melt has been investigated. A mathematical model, based on classical theory of heterogeneous nucleation and volume separation of nucleants among droplets size distribution, is described to predict undercooling of droplets. Newtonian heat flow condition coupled with velocity dependent heat transfer coefficient is used to obtain cooling rate before and after nucleation of droplets. The results indicate that temperature profile of droplets in the spray during recalescence, segregated and eutectic solidification regimes is dependent on their size and related undercooling. The interface temperature during solidification of undercooled droplets rapidly approaches the liquidus temperature of the alloy with a subsequent decrease in solid-liquid interface velocity. A comparison in cooling rates of atomized powder particles estimated from secondary dendrite arm spacing measurements are observed to be closer to those predicted from the model during segregated solidification regime of large size droplets.

The use of tetramethylammonium hydroxide, tertiary amines and strongly alkaline reagents for sample treatment involving extraction and digestion procedures is discussed in this review. The preparation of slurries is also discussed. Based on literature data, alkaline media offer a good alternative for sample preparation involving an appreciable group of analytes in different types of samples. These reagents are also successfully employed in tailored speciation procedures wherein there is a critical dependence on maintenance of chemical forms. The effects of these reagents on measurements performed using spectroanalytical techniques are discussed. Several undesirable effects on transport and atomization processes necessitate use of the method of standard additions to obtain accurate results. It is also evident that alkaline media can improve the performance of techniques such as inductively coupled plasma mass spectrometry and accessories, such as autosamplers coupled to graphite furn...

The use of tetramethylammonium hydroxide, tertiary amines and strongly alkaline reagents for sample treatment involving extraction and digestion procedures is discussed in this review. The preparation of slurries is also discussed. Based on literature data, alkaline media offer a good alternative for sample preparation involving an appreciable group of analytes in different types of samples. These reagents are also successfully employed in tailored speciation procedures wherein there is a critical dependence on maintenance of chemical forms. The effects of these reagents on measurements performed using spectroanalytical techniques are discussed. Several undesirable effects on transport and atomization processes necessitate use of the method of standard additions to obtain accurate results. It is also evident that alkaline media can improve the performance of techniques such as inductively coupled plasma mass spectrometry and accessories, such as autosamplers coupled to graphite furnace atomic absorption spectrometers.

Aims:To estimate the total contribution of the absorption processes ɛ_λ + H2+(X2Σ_g+) → H(1s) + H+ and ɛ_λ + H(1s) + H+ → H+ + H(1s) to the opacity of Solar atmosphere in UV and VUV region, and compare it with the contribution of other relevant radiative processes included in standard models. Methods: The strict quantum-mechanical method was used for the determination of the average cross-section for the photo-dissociation of the molecular ion H2+(X2Σ_g+); the previously developed quasi-static method was used for determination of the corresponding spectral coefficient which characterizes the absorption charge exchange in H(1s) + H+ collisions. Results: Spectral absorption coefficients characterizing the considered processes were calculated for the solar photosphere and lower chromosphere, within the 90 nm ≤ λ ≤ 370 nm spectral range; the total contribution of the considered processes to the solar opacity was estimated and compared to relevant radiative processes included in standard Solar models. Conclusions: In comparison with other absorption processes included in standard Solar models, the contribution of the considered processes in the UV and VUV regions is so important that they have to be taken into account in modeling the Solar photosphere and the lower chromosphere.