Composition and microhardness of Si–Ge solid solution precipitates in Al–Si–Ge alloys solidified during centrifugation
Abstract The chemical composition of precipitates, the Knoop microhardness of the precipitates and of the matrix of Al–Si–Ge alloys solidified during centrifugation at 7 ×  g were investigated. The initial content of (Si + Ge) was (10 + 10), (20 + 20) or (25 + 25) at.%. The Knoop microhardness of the ingots varied with height in the ingot. This variation is attributed to sedimentation of Si–Ge during solidification. Chemical analysis showed that the maximum Si:Ge ratio in the precipitates for Al–10 at.% Si–10 at.% Ge alloy was about 92:8, and decreased with increasing Si and Ge content in ingots. The Si:Ge ratio and Knoop micro hardness also varied throughout each precipitate. The composition was constant along precipitates of alloy solidified without centrifugation. A variation in Knoop microhardness along the precipitates was attributed to this composition variation. The variation of the maximum Si:Ge ratio in the precipitates in ingots of different composition solidified with centrifugation is attributed to nonequilibrium conditions of solidification induced by decreased mass transport in the melt adjacent to the growing precipitates. The variation of Si and Ge along the Si –Ge precipitates is created by convection of the melt during solidification with centrifugation.
The effect of melt refining upon inclusions in aluminum
A series of aluminum melts has been refined with respect to inclusions by use of ALCOA 469, FILD, or SNIF. The content and size distribution of inclusions in the original-and the refined melts-have been measured by use of neutron activation (oxygen content), gas chromatography (carbide content), sedimentation analysis, and dissolution of metal in hydrochloric acid and subsequent analysis of oxides by means of a Coulter Counter. All the units tested have a beneficial effect and decrease the inclusion content, but the number of analyses are too few to make general conclusions. However, for melts cleaned by use of SNIF, it was found that oxides larger than 50 μm in cross section and borides larger than 20 μm in diameter were removed, while the smaller borides were agglomerated only. The effect of FILD and ALCOA 469 upon the melt tested was removal of borides larger than 5-10 μ m and oxides larger than 15μm in diameter, respectively.
Political authority and obligation in Aristotle
1. The explanatory power of ethics in Aristotle's theory of politics and law 2. Nature and normativity 3. The concept of political authority 4. Morality and political obligation 5. The question of political obligation 6. The justification of political authority 7. The limits of political obligation Conclusion Index locorum Index nominum General index