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Concise Dictionary of Materials Science Part 9

Tham khảo tài liệu 'concise dictionary of materials science part 9', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | silica Silicon dioxide SiO2. Interatomic bond in silica is partially covalent and partially ionic see electronegativity . It has three polymorphic modifications . cristobalite tridymite and quartz with the transformation temperatures 1470 cristobalite tridymite and 867 C tridymite quartz . In all of the modifications Si atoms are arranged at the centers of tetra-hedra formed by O atoms. simple lattice See primitive lattice. single crystal Body consisting of one crystal only. There are no grain boundaries in single crystals although subboundaries and sometimes twin boundaries can be found. single-domain particle Magnetic particle whose minimum linear size is smaller than the domain wall thickness because of this it consists of one magnetic domain. If several domains were present in such a particle the particle s free energy would be increased. In the particle the energy of the magnetic poles at its surface is the lowest in the case of the largest pole spacing. Thus in a single-domain particle of an elongated shape the orientation of its magnetization vector is determined not only by its magnetic crystalline anisotropy but also by its shape anisotropy. If elongated singledomain particles are oriented predominately along the same direction in a body the latter possesses a magnetic texture and excellent hard-magnetic properties. single slip Dislocation glide motion over a single slip system characterized by the maximum Schmid factor. sintering Procedure for manufacturing dense articles from porous particulate compacts porosity in green compacts usually is between 25 and 50 vol resulting from spontaneous bonding of adjacent particles. The main driving force for sintering is a decrease of an excess free energy associated with the phase boundaries. Sintering is fulfilled by firing the compacts at high temperatures up to 0.9 Tm and is always accompanied by their shrinkage and densification i.e. a decrease in porosity . Shrinkage evolves primarily through coalescence of .