Silicides

  The structures of the metal silicides (prepared by direct combination of the elements at high temperatures) are diverse, and a full discussion of the structures is beyond the scope of this book.† Some examples of their solid state structural types are:

• isolated Si atoms (e.g. Mg₂Si, Ca₂Si);
• Si₂-units (e.g. U₃Si₂);
• Si₄-units (e.g. NaSi, KSi, CsSi)
• Sin-chains (e.g. CaSi);
• planar or puckered hexagonal networks of Si atoms (e.g. b-USi₂, CaSi₂);
• three-dimensional network of Si atoms (e.g. SrSi₂, a-USi₂).

  The Si₄-units present in the alkali metal silicides are noteworthy. The [Si₄]^4- anion is isoelectronic with P₄ and the solid state structures of several group 1 metal silicides contain tetrahedral Si₄-units, but these are not isolated anions. The structure of Cs₄Si₄ comes close to featuring discrete, tetrahedral [Si₄]^4- ions, but significant cation–anion interactions exist. The silicide K₃LiSi₄ possesses tetrahedral Si₄-units linked by Li‏ ions to give infinite chains, and in K₇LiSi₈, pairs of Si₄-units are connected as shown in below structure with additional interactions involving K‏ ions.

     Silicides are hard materials, but their melting points are generally lower than those of the metal carbides. Treatment of Mg₂Si with dilute acids gives mixtures of silanes. The properties of some silicides make them  useful as refractory materials (e.g. Fe₃Si and CrSi₂); Fe₃Si is used in magnetic tapes and disks to increase their thermal stability.

مواضيع ذات صلة

كيمياء القصدير

تطبيقات الطبقات الثنائية الهيدروكسيد

تطبيقات عملية التبادل الأيوني

مواد التبادل الأيوني Ion exchanger

ظاهرة التبادل الايوني Ion Exchange

تاريخ التبادل الايوني Ion Exchange History

كيمياء البلاتين ومعقداته

كيمياء البلاديوم ومعقداته

طرائق تقدير النحاس

كيمياء النحاس ومعقداته

طرائق تقدير النيكل

كيمياء النيكل ومعقداته