Microstructural evolution during unsteady-state horizontal solidification of Al-Si-Mg(356) alloy

The increasing demand for reducing vehicle weight in the automotive and aerospace industries has raised the need to develop improved structural aluminum-based alloys. Thus, horizontal solidification experiment with the Al-7%Si-0.3%Mg（mass fraction） alloy was carried out. A water-cooled horizontal directional solidification device was developed and used. Microstructural characterization was carried out using traditional techniques of metallography, optical microscopy and SEM microscopy. The Thermo-Calc software was used to generate the solidification path of the investigated alloy with addition of 0.17% Fe（mass fraction）. The effects of the thermal parameters such as the growth rate（VL）, cooling rate（TC） and solidification local time（tSL） on the formation of the macrostructure and on the dendritic microstructure evolution were evaluated. A columnar to equiaxed transition（CET） was found for VL and TC values from 0.82 to 0.98 mm/s and from 1.71 to 2.55 ℃/s, respectively. The microstructure was characterized by the measurement of the primary and secondary dendrite arm spacings（λ1 and λ2, respectively）. Experimental laws of λ1 =f（VL, TC） and λ2 =f（tSL） were proposed. It is observed that the interdendritic region is composed of the following eutectic mixture： a（Al）＋Si＋p-Al8 Mg3 Fe Si6＋q-Mg2 Si.

Structural effects induced by dialysis-based purification of carbon nanomaterials

Dialysis plays a crucial role in the purification of nanomaterials but its impact on the structural properties of carbon nanomaterials was never investigated.Herein,a carbon-based nanomaterial generated electrochemically in potassium phosphate buffer,was characterized before and after dialysis against pure water.It is shown that dialysis affects the size of the carbon domains,structural organization,surface functionalization,oxidation degree of carbon,and grade of amorphicity.Accordingly,dialysis drives the nanomaterial organization from discrete roundish carbon domains,with sizes ranging from 70 to 160 nm,towards linear stacking structures of small nanoparticles(<15 nm).In parallel,alcohol and ether(epoxide)surface groups evolve into more oxidized carbon groups(e.g.,ketone and ester groups).Investigation of the as-prepared nanomaterial by electron paramagnetic resonance(EPR)revealed a resonance signal consistent with carbon-oxygen centred radicals.Additionally,this study brings to light the selective affinity of the carbon nanomaterial under study to capture Na^(+)ions,a property greatly enhanced by the dialysis process,and its high ability to trap oxygen,particularly before dialysis.These findings open new perspectives for the application of carbon-based nanomaterials and raise awareness of the importance of structural changes that can occur during the purification of carbon-based nanomaterials.