J. Ding

Formation of spinel Mn-ferrite during mechanical alloying

Abstract Mechanical alloying of Mn 2 O 3 + 2Fe 2 O 3 in air resulted in formation of a mixture of MnFeO 3 and Fe 2 O 3 , while milling under an argon atmosphere resulted in the formation of the magnetite phase, MnFe 2 O 4 . The formation of MnFe 2 O 4 was accelerated by additions of metallic Mn. A nanocrystalline spinel ferrite phase, MnFe 2 O 4 , was formed after annealing at 600–700°C, and found to exhibit good soft magnetic properties.

High-coercivity ferrite magnets prepared by mechanical alloying

Abstract Nanocrystalline hexaferrite (BaFe 12 O 19 or SrFe 12 O 19 ) and mixed Fe,Co-ferrite ((Fe x Co 1− x )Fe 2 O 4 with x =0–1) materials have been prepared by mechanical alloying and subsequent annealing. High coercivities were obtained in these nanocrystalline materials, 6–7 kOe for hexaferrite and ∼3 kOe for Co-ferrite. Hexaferrite powders prepared by mechanical alloying have been used as the starting material for high-coercivity bonded magnets. Hot-pressed anisotropic hexaferrite magnets have been produced with high values of coercivity and remanence. High magnetic performance was also achieved in some mixed Fe,Co-ferrites after magnetic annealing.

Magnetic properties of mechanically alloyed CoFe2O4

Abstract Single nanocrystalline spinel phases have been formed in mechanically alloyed CoFe 2 O 4 and Co 0.8 Fe 2.2 O 4 powders after heat treatment at temperatures above 750°C. High coercivities (2.6–2.7kOe) were associated with nanocrystalline structures in CoFe 2 O 4 . In Co 0.8 Fe 2.2 O 4 a high remanence equal to 78% of the saturation magnetisation and a coercivity of 3.2kOe were obtained in magnetically annealed samples.

Ultrafine Co and Ni particles prepared by mechanochemical processing

Mechanochemical processing has been used for producing ultrafine magnetic metal powders, including Co and Ni. Uniform particle sizes of 10 - 20 nm were obtained by the chemical reduction of cobalt and nickel chlorides during mechanical milling with Na. The occurrence of combustion during milling was prevented by the addition of excess of NaCl as a diluent. The ultrafine particles were characterized by saturation magnetization values 90 - 95% of their respective bulk values and significantly increased coercivities.

Structure and magnetic properties of mechanically alloyed SmxCo1−x

Abstract A study of the phase structure and magnetic properties of mechanically alloyed and heat-treated Sm x Co 1− x with x = 0.13 to 0.24 has been carried out. Remanence enhancement above 0.5 M s ( M s = saturation) was found in samples with x = 0.12 to 0.17 after annealing at 700 °C. A maximum energy product of 16.6 M G Oe was measured for Sm 0.13 Co 0.87 . Coercive forces above 50 kOe were obtained for x = 0.17–0.20 after heat treatment at approximately 800 °C. The highest value of 57 kOe was measured for Sm 0.19 Co 0.81 .

Mechanochemical synthesis of ultrafine ZrO2 powder

Abstract The synthesis of ultrafine zirconia powders by mechanochemical reaction of ZrCl 4 with CaO has been investigated using x-ray diffraction, TEM and DSC measurements. Mechanical milling resulted in a nanoscale mixture of CaO and amorphous ZrCl 4 . with no evidence of any reaction having occurred. Subsequent heat treatment at temperatures above 300 °C resulted in the formation of separated particles of cubic ZrO 2 ,5–10 nm in diameter, within an CaCl 2 matrix. Measurements of the effect of particle size on the crystal structure of ZrO 2 are also reported.

Ultrafine Cu particles prepared by mechanochemical process

The solid-state displacement reaction of CuCl2 + 2Na = Cu + 2NaCl induced by mechanical milling has been studied. Ultrafine Cu particles have been produced after removing the by-product NaCl from the as-milled mixture in a washing process. Two different morphologies of Cu particles were observed by transmission electron microscopic examinations. Cu particles of uniform size in the range of 20–50 nm were found after a steady-state reaction during mechanical milling, whereas larger particles were observed when combustion had occurred.

High magnetic performance in isotropic α‐Fe+Sm2Fe17Nx

The structure and magnetic properties of nanocrystalline, two‐phase Sm2Fe17Nx+α‐Fe alloys prepared by mechanical alloying and heat treatment have been studied. Remanence enhancement and single‐phase magnetic behavior were observed in isotropic powders crystallized at low temperatures (about 600 °C), while crystallization at high temperatures resulted in two‐phase demagnetization curves due to increase of the grain size of the soft phase. With increasing Sm concentration the coercivity increased and the remanent magnetization decreased.

Mechanochemical synthesis of ultrafine zinc sulfide particles

Abstract The synthesis of nano-sized ZnS particles by the mechanochemical solid-state reaction of ZnCl 2 and CaS has been investigated using X-ray diffraction, TEM and DTA measurements. Mechanical milling of ZnCl 2 and CaS resulted in the formation of ∼ 500 nm ZnS particles containing aggregates of 12 nm crystallites. The addition of 71 vol% CaCl 2 as a diluent to the reactants resulted in the formation of separated 16 nm particles of ZnS. Using mechanically alloyed CaS (10–50 nm particle size) enabled the synthesis of isolated ZnS particles 7–9 nm in size. The effects of milling time and subsequent annealing on particle size have also been investigated.

Hexaferrite magnetic materials prepared by mechanical alloying

Abstract The structure and properties of hexaferrites in the form of MFe 12 O 19 with M = Ba, Sr and Pb prepared by mechanical alloying and heat treatment have been studied. Coercivities of 6–7 kOe were measured for Ba- and Sr-hexaferrite powders. The high values of coercivities have been associated with small particle sizes (∼ 0.1 μm) resulting from the mechanical alloying and subsequent heat treatment. High-coercivity anisotropic samples have been synthesized using hot-pressing, with remanences of 70–75% of the saturation magnetisation being obtained.