To investigate the performance of the size measurement by asymmetric flow field-flow fractionation (AF4), the measurement results of gold nanoparticles were compared among AF4, transmission electron microscopy (TEM), and small-angle X-ray scattering (SAXS) in terms of the average size and full width at half maximum (FWHM) of the size distribution. Although the average size was almost the same for the three methods, the FWHM measured using AF4 was larger than those measured using TEM and SAXS. This is attributed to the diffusion of the gold nanoparticles inside the AF4 instruments. The broadening coefficient of AF4 analysis was determined as 2.08 by the average of FWHM ratio of AF4 to TEM measured using the several sphere-like gold nanoparticles. In addition, the effect of particle shape on the above broadening coefficient was investigated using the sphere-like and plate-like silver nanoparticles. The broadening coefficient for plate-like particles apparently became smaller than that for sphere-like particles, possibly because the Brownian motion of plate-like particles was suppressed.Furthermore, the AF4 analysis with the FWHM correction method using the broadening coefficient was applied to niobium carbide (NbC) precipitates in steels. The average size measured by AF4 was mostly consistent with the results obtained in regions observed by TEM. Moreover, an increase in the number density of nanometer-sized NbC by heat treatment was successfully detected. The effect of particle shape on FWHM should be further investigated and improved; however, AF4 with the broadening coefficient can semi-quantitatively analyze the size distribution of nanoprecipitates in steels.

No abstract

Inductively coupled plasma mass spectrometry using isotope dilution (ID-ICP-MS) with liquid-liquid extraction was used for determining ultra-trace tellurium (Te ) in steels to improve the sensitivity, accuracy, and precision of the analysis. Single quadrupole-type ICP-MS cannot be used to determine the trace amount of Te because of contribution of mass spectrometric interference by Xe. To overcome this, tandem mass-filter-type ICP-MS (ICP-MS/MS) was used for the determination of Te. Pretreatment by liquid-liquid extraction was also employed to compensate for the decrease in signal intensity due to the use of ICP-MS/MS. The relative standard deviations of the resulting abundances defined by repeated analysis from separated three steel samples were <1.3%. Furthermore, the determined values of Te in standard reference materials were close to the reference values. Thus, the developed determination method is useful for the analysis of ultra-trace Te in steels.

An asymmetric flow field-flow fractionation (AF4) combined with inductively coupled plasma mass spectrometry (ICP-MS) was applied to measure the concentration and size distribution of nanometer-sized carbides in steel sheets, such as titanium carbides (TiC) and vanadium carbides (VC). Prior to AF4-ICP-MS measurement, TiC and VC nanoparticles in steel were extracted into a solution via selective potentio-static etching by electrolytic dissolution (SPEED) method. The SPEED method enabled the selective dissolution of iron and the carbide nanoparticles were dispersed as primary particles in solution with surfactant. However, sulfur-free surfactant was required in AF4-ICP-MS carrier solutions because sulfur in SDS, generally used to disperse various nanoparticles, causes a spectral interference with titanium and vanadium in ICP-MS analysis. In this study, sulfur-free sodium cholate (SC) was applied as the dispersant of carbide nanoparticles for the SPEED method and AF4 measurements. SC provides a high absolute value of zeta potential on a particle surface and membrane of an AF4 separation channel to prevent particle adsorption on the membrane. Additionally, SC does not generate the spectral interference due to sulfur, in contrast to SDS. Thus, it enabled the sensitive detection of titanium and vanadium in carbide nanoparticles extracted from a steel sheet in AF4-ICP-MS. These results indicate that sulfur-free surfactants are useful for analyzing some precipitates in steels using AF4-ICP-MS.