• Transactions of the Korean hydrogen and new energy society
• /
• v.17 no.4
• /
• pp.418-424
• /
• 2006

In order to improve the activation properties of the $AB_2$ type hydrogen storage alloys for Ni-MH battery, the alloy surface was modified by employing high energy ball milling. The $Zr_{0.54}Ti_{0.45}V_{0.54}Ni_{0.87}Cr_{0.15}Co_{0.21}Mn_{0.24}$ alloy powder was ball milled for various period by using the high energy ball mill. As the ball milling time increased, activation of the $AB_2$ type composite powder electrodes were enhanced regardless of additives. When the ball milling time was small discharge capacities of the $AB_2$ type composite powder electrodes increased with the milling time. On the other hand for large milling time it decreased with increasing milling time. The maximum discharge capacity was obtained by ball milling for 3-4 min.

• Transactions of the Korean hydrogen and new energy society
• /
• v.17 no.3
• /
• pp.309-316
• /
• 2006

Co-ferrite was synthesized by HEBM (High Energy Ball Milling) with a stoichiometric (Co/Fe=0.5/2.5) mixture of CoO and $Fe_2O_3$ powders. The effect of milling time on the phase transformation of the mixture was investigated by XRD. Mono-phase solid solution of Co-ferrite, which was milled for 4 h and then calcined at $900^{\circ}C$ in the Ar atmosphere, was confirmed by XRD analysis. The composition and thermal reduction behavior of Co-ferrite were analyzed by TGA and XRF. As a result, oxygen deficient Co-ferrite was synthesized by HEBM and the weight decrease of the Co-ferrite, which was oxidized at $600^{\circ}C$ for 10h by $H_2O$ vapor, was 2.41 wt% during thermal reduction at $1300^{\circ}C$.

• Transactions of the Korean hydrogen and new energy society
• /
• v.28 no.2
• /
• pp.137-143
• /
• 2017

In the present study, Ni and $TaF_5$ were chosen as additives to enhance the hydriding and dehydriding rates of Mg. A sample with a composition of 80 wt% Mg + 14 wt% Ni + 6 wt% $TaF_5$ (named $80Mg+14Ni+6TaF_5$) was prepared by high-energy ball milling in hydrogen. Its hydriding and dehydriding properties were then examined. At the fourth cycle, the activated sample absorbed 3.88 wt% H for 2.5 min, 4.74 wt% H for 5 min, and 5.75 wt% H for 60 min at 593 K under 12 bar $H_2$. $80Mg+14Ni+6TaF_5$ had an effective hydrogen-storage capacity (the quantity of hydrogen absorbed for 60 min) of about 5.8 wt%. The sample desorbed 1.42 wt% H for 5 min, 3.42 wt% H for 15 min, and 5.09 wt% H for 60 min at 593 K under 1.0 bar $H_2$. Line scanning results by EDS for $80Mg+14Ni+6TaF_5$ before and after cycling showed that the peaks of Ta and F appeared at different positions, indicating that the $TaF_5$ in $80Mg+14Ni+6TaF_5$ was decomposed.

• Transactions of the Korean hydrogen and new energy society
• /
• v.8 no.1
• /
• pp.43-47
• /
• 1997

A new type of anode materials in form of nanocrystalline composite powders has been developed that offers the potential for dramatically improved discharge capacity and initial activation rate. The composites are synthesized by ball milling of two components - a major component (basic component) having high hydrogen capacity and a minor component (surface activator) with good electrocatalytic activity. The capacity increase observed by ball milling with surface activator. The ball-milled composite materials are easier to activate than the non ball-milled basic component.

• Transactions of the Korean hydrogen and new energy society
• /
• v.10 no.1
• /
• pp.49-57
• /
• 1999

In order to study the effect of high energy ball milling on the $Mg_2Ni+Ni$, $Mg_2Ni+0.5Ni+0.5Al$ powders, we have investigated on the discharge properties, microstructures. The powder size of samples decreased as ball milling time. From the XRD results, the crystal structure of $Mg_2Ni+Ni$ mixed powders were changed to amorphous or nano-structure after 60hr ball milling. The discharge capacities of both $Mg_2Ni+Ni$ and $Mg_2Ni+0.5Ni+0.5Al$ powders increased, with increasing ballmilling time, the maximum capacity(342mAh/g) was shown for the 60 hrs ballmilled $Mg_2Ni+Ni$ sample. The capacity decreased drastically after a few charge-discharge cycles.

• Journal of Powder Materials
• /
• v.10 no.4
• /
• pp.270-274
• /
• 2003

Recently, the fabrication process of W-Cu nanocomposite powders has been researched to improve the sinterability by mechanochemical process (MCP), which consists of ball milling and hydrogen-reduction with W- and Cu-oxide mixture. However, there are many control variables in this process because the W oxides are hydrogen-reduced via several reduction stages at high temperature over 80$0^{\circ}C$ with susceptive reduction conditions. In this experiment, the W-15 wt%Cu nanocomposite powder was fabricated with the ball-milling and hydrogen-reduction process using W and CuO powder. The microstructure of the fabricated W-Cu nanocomposite powder was homogeneously composed of the fine W particles embedded in the Cu matrix. In the sintering process, the solid state sintering was certainly observed around 85$0^{\circ}C$ at the heating rate of 1$0^{\circ}C$/min. It is considered that the solid state sintering at low temperature range should occur as a result of the sintering of Cu phase between aggregates. The specimen was fully densified over 98% for theoretical density at 120$0^{\circ}C$ for 1 h with the heating rate of 1$0^{\circ}C$/min.

• Transactions of the Korean hydrogen and new energy society
• /
• v.12 no.1
• /
• pp.39-50
• /
• 2001

Vanadium based solid solution alloys have been studied as a potential negative electrode of Ni/MH battery due to their high hydrogen storage capacity. In order to improve the kinetic property of V-Ti alloy in KOH electrolyte, the ball-milling process with Ni, which has a catalytic effect of hydrogen absorption/desorption, was carried out to modify the surface properties of V-Ti-Cr alloys with high hydrogen storage capacity. Moreover, to overcome the problem of poor cycle life, V-Ti alloy substituted by Cr, V0.68 Ti0.20 Cr0.12, has been developed showing a good cycle performance (keeping about 80 % of initial discharge capacity after 200 cycles). The cycle life of surface-modified V0.68 Ti0.20 Cr0.12 alloy was improved by suppressing the formation of TiO2 layer on the alloy surface while decreasing the amount of dissolved vanadium in the KOH electrolyte. In order to promote the effect of Ni coating on the surface property of V0.68 Ti 0.20 Cr 0.12 alloy by ball-milling, filamentary-typed Ni, which has higher surface coverage area than sphere-typed Ni was used as a surface modifier. Consequently, the surface-modified V0.68 Ti0.20 Cr0.12 alloy electrode showed a improved discharge capacity of 460 mAh/g.

• Transactions of the Korean hydrogen and new energy society
• /
• v.15 no.2
• /
• pp.98-107
• /
• 2004

Modified Ni/YSZ cermets for high temperature electrolysis were synthesized by dry or wet mechanical alloying methods. The Ni/YSZ composit particle was directly fabricated from the ball milling of Ni and YSZ powder or obtained from the reduction of NiO/YSZ particle after the ball milling of NiO and YSZ. In the case of the NiO/YSZ composite particle, the dry milling increased the average particle size whereas the wet milling decreased the size. The dry milling showed that fine YSZ particles were distributed over large Ni surfaces while Ni and YSZ particles similar in size were well mixed in the wet milling method. These features were the same in the Ni/YSZ composite particle prepared from Ni and YSZ powders. The electrical conductivity of the wet-milled Ni/YSZ cermet showed the highest value of $2{\times}10^2S/cm$ among the specimens and this value was increased to $1.4\times10^4S/cm$ after the sintering at $900^\circ{C}$ for 1 h.

• Journal of Powder Materials
• /
• v.25 no.3
• /
• pp.240-245
• /
• 2018

This study focuses on the fabrication of a WC/Co composite powder from the oxide of WC/Co hardmetal scrap using solid carbon in a hydrogen gas atmosphere for the recycling of WC/Co hardmetal. Mixed powders are manufactured by mechanically milling the oxide powder of WC-13 wt% Co hardmetal scrap and carbon black with varying powder/ball weight ratios. The oxide powder of WC-13 wt% Co hardmetal scrap consists of $WO_3$ and $CoWO_4$. The mixed powder mechanically milled at a lower powder/ball weight ratio (high mechanical milling energy) has a more rapid carbothermal reduction reaction in the formation of WC and Co phases compared with that mechanically milled at a higher powder/ball weight ratio (lower mechanical milling energy). The WC/Co composite powder is fabricated at $900^{\circ}C$ for 6 h from the oxide of WC/Co hardmetal scrap using solid carbon in a hydrogen gas atmosphere. The fabricated WC/Co composite powder has a particle size of approximately $0.25-0.5{\mu}m$.

• Transactions of the Korean hydrogen and new energy society
• /
• v.18 no.3
• /
• pp.238-243
• /
• 2007

The composite powder of Cu and YSZ was synthesized for a high temperature electrolysis cathode by mechanical milling. The average Cu particle size was reduced to 5 micro-meter from 48 micro-meter after the mechanical ball milling. The composite powder showed that Cu particles were uniformly covered with finer YSZ particles. Sub-micron sized pores were uniformly dispersed in the Cu/YSZ composit. Homogeneously-dispersed fine YSZ in the composite is expected to the increase in triple phase boundaries, thereby leading the enhanced performance of cathode.