ASIAN JOURNAL OF CHEMISTRY ASIAN JOURNAL OF CHEMISTRY https://doi.org/10.14233/ajchem.2018.21162 INTRODUCTION As the modern technology pursues the lighter, smaller, thinner products, the heat dissipating technology becomes more important. The need for faster and broader communi- cation tends core devices to consume more powers, therefore more heat generation. Fast heat spreading and dissipation is a key technology of preventing the core devices from default operation and life-shortening [1,2]. Many kinds of thermal sheets have been used for heat spreading out from core power devices. Indium, aluminum, copper are well known materials for its high thermal performance, but have been suffered from its limited fabricable thickness and cost effectiveness. Graphite has been used in fields of mobile communication and flat panel display industries due to its excellent thermal managing property [3-5]. There have been several kinds of graphite sheets according to its fabrication process and source material treat- ment. Many graphite sheet providers adduce the proofs of thermal properties such as comparison of thermal flux gradient images and their experimental data. However, the accurate physical values are difficult to get due to complicated measurement instrument and many environmental factors should be con- sidered in application. Some researchers suggested thermal impedance of their products rather than intrinsic physical property values. Sometimes, thermal impedance reflecting many environmental factors during fabrication and application can be more practical and valuable to both of provider and consumer. Empirical Two Step Approximation for Characterizing Thermal Properties of Ultrathin Graphite Sheet JU YONG CHO 1 , SEUNG HOON LEE 2 and WON KWEON JANG 1,* 1 Department of Electronic Engineering, Hanseo University, Seosan-si, Chungcheongnam-do 31962, Republic of Korea 2 Department of Satellite Payload Technology, Korea Aerospace Research Institute, Daejeon 34133, Republic of Korea *Corresponding author: Fax: +82 41 6883448; Tel: +82 41 6601324; E-mail: jwk@hanseo.ac.kr; wonkjang@naver.com Received: 2 December 2017; Accepted: 20 December 2017; Published online: 31 January 2018; AJC-18767 The estimation method for unknown thermal properties of ultrathin graphite sheet is suggested in this work. Based on the well known thermal properties of a few materials, the estimation was done by two step approximation algorism. The experimental measurement for four materials of copper, aluminum, indium and graphite was performed at the restricted laboratory environment to get the mutual relation indicating special regularity between those materials. The estimated value of thermal conductivity for a graphite ultrathin thermal sheet was 646 W/m·K that was reasonable comparing to its functional capacity. Keywords: Two step approximation algorism, Ultrathin, Graphite, Thermal conductivity. Asian Journal of Chemistry; Vol. 30, No. 3 (2018), 689-692 In this paper, we suggest a practical method of evaluating thermal properties for the ultrathin graphite sheet that is becoming popular heat spreading part for power system mana- ging. We designed and built the experimental measurement system to get the one dimensional heat spreading data under the vacuum environment to exclude the effect of convection and postulated the two-step approximation algorism. The experiments were performed with four samples of indium, alu- minum, copper and graphite to get the positional temperature variation from the heat source. The experimental data of four samples were analyzed with two-step approximation algorism that we built. Two-step approximation algorism is composed of two- step data fitting processes. The first step is to get the exponential decay fitting formula for four samples of indium, aluminum, cooper and graphite. The empirical data points of positional temperature for four samples could be inspected with experi- mental equipment. Then secondary fitting process was done for each coefficient to get the extrapolated values about unknown thermal property of ultrathin graphite thermal sheet. EXPERIMENTAL The experimental setup was designed and fabricated as shown in Fig. 1. The temporal positional temperatures were collected by thermistors and recorded by data acquisition unit. The sample was placed inside vacuum chamber to exclude the effect of convection. The chamber was shielded to exclude