Papers by Author: Young Jin Yum

Abstract: Carbon black (CB) filled rubber is microscopically heterogeneous although homogeneous on a macroscopic scale. CB particles are generally in the form of aggregates, which form the CB network in the rubber matrix. In this work, the junction width between CB aggregates is modeled as a contact resistor and the tunneling conduction mechanism is taken into account, and then an infinite circuit consisting of numerous contact resistors, interconnected with each other, is proposed to simulate the CB network in filled rubber. Prior to determination of the junction width distribution, CB spheres equivalent to CB aggregates in volume is assumed in a specifically random arrangement. Thus, the effect of CB aggregate distribution on the electrical resistivity is discussed. It is found that, for CB (N330) filled natural rubber with volume fraction of 27.5%, the simulated electrical resistivity at a standard deviation of 0.1 mean junction width is in good agreement with the experimental data available in the literature.

Abstract: Preparation of titanium diboride reinforced copper matrix composites with high conductivity and mechanical strength was developed based on in situ produced powders. The effect of the titanium diboride content on the mechanical properties of the bulk material produced from the powders by Spark Plasma Sintering technique was studied. Increasing titanium diboride content from 2.5 up to 7.5 wt.% resulted in a 1.5-fold increase in yield strength, tensile strength and hardness and 5-fold increase in wear resistance with only 10% decrease in conductivity.

Abstract: Cu-TiB2 nanocomposite powders were in situ synthesized by combining high-energy ball milling of Cu-Ti-B elemental powder mixtures as precursors and subsequent self-propagating high temperature synthesis (SHS). Cu-40wt.% TiB2 was produced after SHS reaction and then diluted by copper to obtain desired homogeneous composites with 2.5, 5 and 10wt.%TiB2. Spark plasma sintering (SPS) was used to inhibit grain growth and thereby obtain fully Cu-TiB2 sintered bodies with nanocomposite structure. After SHS reaction, only Cu and TiB2 phases were detected in the SHS-product. Spheroidal TiB2 particles smaller than 250nm were formed in the copper matrix after SHS-reaction. Mechanical and electrical properties were investigated after SPS at 650°C for 30min under 50MPa. The electrical conductivity decreased from 75 to 54% IACS with increasing of TiB2 contents from 2.5 to 10wt.%. However, hardness increased from 56 to 97HRB. In addition, the tensile strength increased with increasing the TiB2 content.