کد مقاله کد نشریه سال انتشار مقاله انگلیسی نسخه تمام متن
1331376 1500118 2013 12 صفحه PDF دانلود رایگان
عنوان انگلیسی مقاله ISI
Phase relations and structural features in the system Ni–Zn–B
موضوعات مرتبط
مهندسی و علوم پایه شیمی شیمی معدنی
پیش نمایش صفحه اول مقاله
Phase relations and structural features in the system Ni–Zn–B
چکیده انگلیسی

Phase relations for the system Ni–Zn–B have been established in the isothermal section at 800 °C based on X-ray powder diffraction and electron microprobe analyses of about 60 samples, which have been prepared by hot pressing of pre-annealed powder compacts of arc-melted master alloys NixBy and Zn-filings. Six ternary compounds (labeled τ1 to τ6) were found to exist, which in some cases exhibit considerable mutual solid solubilities mostly as an exchange of Ni–Zn at constant B-content, but in the case of the so-called τ-phase τ1-(Ni1−xZnx)21[Zn1−y−z□y(B4)z]2B6 (0.07≤x≤0.11, 0.07≤y≤0.53, 0≤z≤0.3) also with Zn/B substitution. Single crystal X-ray data analysis for the composition x=0.07, y=0.125, z=0.30, and a=1.05800(3) nm confirmed the Cr23C6 type with space group Fm3¯m, but revealed partial replacement of Zn-atoms by B4-tetrahedra (RF=0.014). Whereas Ni/Zn exchange (at constant B-content) ranges at about 4–5 at% for τ4-Ni3ZnB2 and τ5-Ni48Zn32B20, it is below 3 at% for τ2-Ni12ZnB8−x (x=0.43), τ3-Ni21Zn2B20 and τ6-Ni47Zn23B30. The crystal structures of τ2-Ni12ZnB8−x (x=0.43; Ni12AlB8 type), τ3-Ni21Zn2B20 (own type) and τ4-Ni3ZnB2 (own type) have been determined in our foregoing paper [8]. Due to the non-availability of suitable single crystals, the crystal structures of τ5-Ni48Zn32B20 (body-centered orthorhombic; a=1.6(2) nm, b=0.63(7) nm, and c=0.27(0) nm, determined from TEM) and of τ6-Ni47Zn23B30 have not been elucidated yet. Phase equilibria at 800 °C are dominated by a large three-phase field (βB)+Ni2Zn11+τ3, as practically all ternary compounds form at compositions with less than about 50 at% Ni. Furthermore, precise data on atom site distribution and positional parameters have been provided from X-ray single crystal refinements for Ni-borides, for which crystal structures hitherto have only been derived from X-ray diffraction photographs: o-Ni4B3−x (x=0.19; Pnma, a=1.9665(4) nm, b=0.29852(1) nm, c=0.65750(2) nm; RF=0.015) and m-Ni4B3 (C2/c, a=0.64356(3) nm, b=0.48867(3) nm, c=0.78267(3) nm, β=103.288(3)°, RF=0.021).

Ni–Zn–B isothermal section at 800 °C.Figure optionsDownload as PowerPoint slideHighlights
► Phase relations were determined for the system Ni–Zn–B at 800 °C.
► Existence of six ternary compounds (τ1–τ6) has been confirmed at 800 °C.
► Homogeneity range for τ1 with respect to Ni/Zn and Zn/B at 800 °C has been determined.
► The crystal structures of τ5-Ni48Zn32B20 from TEM (oI, a=1.6(2) nm, b=0.63(7) nm, and c=0.27(0) nm).
► Precise data on τ1-(Ni1−xZnx)21[Zn1−y−z□y(B4)z]2B6 (0.07≤x≤0.11, 0.07≤y≤0.53, 0≤z≤0.3), o-Ni4B3−x and m-Ni4B3 have been presented.

ناشر
Database: Elsevier - ScienceDirect (ساینس دایرکت)
Journal: Journal of Solid State Chemistry - Volume 198, February 2013, Pages 150–161
نویسندگان
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