[en] Full text: The processing of nanosized silver particles can be briefly divided into several regimes: (1) the classical Turkevich preparation of metal colloids, (2) the reversed micelle processes, (3) photoreduction, (4) ultrasonic radiation, and (5) ⁶⁰Co g-irradiation. In the above-mentioned processes, nanosized metal silver particles are synthesized with different morphologies (nanoparticulate, nanowire, and nanoprism) and sizes but only in low concentrations of silver colloids (a few millimoles per liter or less) and in the presence of surfactants as stabilizers. Microwave (MW) dielectric heating is fast emerging as a widely accepted new processing technology for variety of inorganic syntheses due to its penetration and rapid heating. In the MW-assisted syntheses of nanosized nickel and CdS particles, we found that MW heating can effectively control the size distribution of the nanosized nickel and CdS in a narrower range than the conventional heating by thermal convection, and that the effects of MW heating on the morphological structures of the nickel and CdS nanocrystallites are remarkable and attractive. Therefore, we used MW irradiation as a heating source to take advantages of the rapid, selective, and homogeneous, i.e., molecular level, heating in the reaction system for rapid and size-controlled preparation of nanosized metal silver in high concentrations. The as-prepared metal silver was indexed as cubic Ag (JCPDS card, No. 4 - 783) under MW irradiation or by conventional heating. SEM images of samples Al - A6 show that nanosized metal silver particles were formed. Figure 1 graphically expresses the detailed particle size distributions of samples Al - A6. The data of the particle size distributions and average particle sizes of samples A1 - A6 are also listed. When trisodium citrate (1.5 M) and silver nitrate (0.002 or 0.1 M) (A1 - A3) were mixed together, precipitated silver citrate (Ag₃C₆H₅O₇) was immediately formed, which was identified by powder XRD analysis (JCPDS card No. 1-30). The precipitated silver citrate was dissolved after stirring for ca. 10 min, and the reaction solution became clear and colorless even after the addition of formaldehyde (1.0 M), suggesting that citrate anions at a high concentration stabilized silver cations to form solvated complexes. The yields of silver nanocrystallites in the preparation of samples Al and A3 were 53% and 74%, respectively. On the other hand, only trace amount of metal silver was formed after MW irradiation of a silver nitrate -trisodium citrate (A7) or a silver nitrate - formaldehyde (A8) reaction solution for 1 min, respectively, showing the necessity of the coexistence of both sodium citrate and formaldehyde for the reduction of silver cations to form metal silver colloids. MW heating (A1) resulted in the formation of silver nanoparticles with a narrow size distribution and a quite large average particle size when compared to conventional heating (A3) with the same reactant composition. In general, crystal size and size distribution are determined by the both processes of nucleation and crystal growth, which are greatly affected by reaction temperature. MW irradiation can cause a homogeneous (i.e., molecular level) temperature distribution in the reaction solution due to its penetration characteristics, giving uniform nucleation and rapid crystal growth to form narrow size distributed crystallites. It can be concluded that MW irradiation results in the formation of a quite plenty of nuclei by homogeneous and rapid heating of the silver citrate colloids via reduction with formaldehyde to produce small-sized silver crystallites in the successive process of crystal growth by epitaxy