## 3 Materials and Methods  
Six commercial powders from the subsieve range, i.e., with particle sizes less than 45 \(\upmu\)m, were selected for characterization. Their main attributes, provided by powder suppliers, are listed in Table 1.  
As demonstrated in Figures 3 and 4, the powders were deliberately chosen to cover a relatively broad range of particle shapes, sizes, size distributions, specific surface areas, and tendencies to agglomeration. The Hoganas iron powders were provided with particle sizes up to around 150 \(\upmu\)m. Therefore, prior to testing, they were screened to \(-\)38 \(\upmu\)m (\(-\)400 mesh) in order to suit the SAS application requirements. Both powders have similar morphology (compare Figure 3c,d), but their internal structure is different. The NC100.24 grade has a spongy (porous) structure that originates from the fabrication process. The ABC100.30 grade, like the other atomized and carbonyl powders, is solid and may contain only microporosity that is hardly detectable by light microscopy (LM). \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Powder Designation** & **Producer/Supplier** & **Density g/cm\({}^{3}\)** & **Nominal Chemical Composition wt.\%** & **Production Method** \\ \hline \multirow{3}{*}{316L-A} & \begin{tabular}{c} Oerlikon Metco \\ (Pfaeffikon, Switzerland) \\ \end{tabular} & \multirow{3}{*}{8.00} & \multirow{3}{*}{Fe-18 Cr-12 Ni-2 Mo} & \multirow{3}{*}{Gas atomization} \\  & & & & \\ \hline \multirow{3}{*}{316L} & \begin{tabular}{c} Dynamet Anval \\ (Torshälla, Sweden) \\ \end{tabular} & \multirow{3}{*}{8.00} & \multirow{3}{*}{Fe-18 Cr-12 Ni-2 Mo} & \multirow{3}{*}{Gas atomization} \\  & & & & \\ \hline \multirow{2}{*}{NC100.24} & \begin{tabular}{c} Hoganás AB \\ (Hoganás, Sweden) \\ \end{tabular} & \multirow{2}{*}{7.87} & \multirow{2}{*}{Fe} & \multirow{2}{*}{\begin{tabular}{c} Reduction by carbon \\ (\(-\)400 mesh fraction) \\ \end{tabular} } \\  & & & & \\ \hline \multirow{2}{*}{ABC100.30} & \multirow{2}{*}{Hoganás AB} & \multirow{2}{*}{7.87} & \multirow{2}{*}{Fe} & \multirow{2}{*}{\begin{tabular}{c} Water atomization \\ (\(-\)400 mesh fraction) \\ \end{tabular} } \\ \cline{1-1} \cline{3-5}  & \begin{tabular}{c} Yuelong \\ (Foshan, China) \\ \end{tabular} & \multirow{2}{*}{7.87} & \multirow{2}{*}{Fe} & \multirow{2}{*}{\begin{tabular}{c} Carbonyl \\ decomposition \\ \end{tabular} } \\ \hline \begin{tabular}{c} Cobalite \\ CNF \\ \end{tabular} & \begin{tabular}{c} Umicore CEP \\ (Olen, Belgium) \\ \end{tabular} & \multirow{2}{*}{8.19} & \multirow{2}{*}{\
\begin{tabular}{c} Fe-26 Cu-3 Sn-2W- \\ 0.6Y\({}_{2}\)O\({}_{3}\) \\ \end{tabular} } & \multirow{2}{*}{
\begin{tabular}{c} Reduction in \\ hydrogen \\ \end{tabular} } \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Main characteristic of experimental powders. Figure 3: _Cont._The internal structure of the Hoganas iron powders is shown in Figure 5.  
Two common techniques based on laser light scattering and air permeability were compared with respect to how they respond to changes in particle size, shape, internal porosity, and tendency to agglomeration of the experimental powders. Figure 4: SEM-magnified views of the finest powders: YTF-HY2 (**a**); Cobalite CNF (**b**). Figure 3: SEM micrographs of powders used in this study: 316L-A (**a**); 316L (**b**); NC100.24 (**c**); ABC100.30 (**d**); YTF-HY2 (**e**); Cobalite CNF (**f**). The Winner 2000B Laser Particle Size Analyzer (LPSA) manufactured by Jinan Winner Particle Instruments Stock Co., Ltd. (Jinan, China), equipped with the He-Ne light source (>2 mW; \(\lambda\) = 632.8 nm), was used to determine the particle size distribution. Distilled water was selected as the carrier fluid. Vigorous water stirring and ultrasonically vibrating the suspension by a 70 W/40 kHz sound generator were applied simultaneously to separate loosely agglomerated particles throughout the test. The values reported in this study are the average of five readings taken at 15 s intervals.