ISSN (Print): 2328-3491, ISSN (Online): 2328-3580, ISSN (CD-ROM): 2328-3629 American International Journal of Research in Science, Technology, Engineering & Mathematics AIJRSTEM 19-226; © 2019, AIJRSTEM All Rights Reserved Page 134 Available online at http://www.iasir.net AIJRSTEM is a refereed, indexed, peer-reviewed, multidisciplinary and open access journal published by International Association of Scientific Innovation and Research (IASIR), USA (An Association Unifying the Sciences, Engineering, and Applied Research) Study of Size Dependent Thermal Conductivity of Gold FCC Nanomaterial Atul Kumar and Mahipal Singh * Department of Physics, R.H. Govt. P.G. College, Kashipur-244713, Uttarakhand, India I. Introduction The physical properties of nanomaterials have been investigated extensively both theoretically and experimentally due to their scientific and industrial importance [1]. It has been reported that the nanomaterials exhibit interesting physical, chemical, electrical and thermal properties that are significantly different from the corresponding properties of bulk materials [2-4]. Because of the enormous surface area to volume ratio of nanomaterials, the energy associated with the atoms of these nanomaterials will be different in comparision of conventional bulk materials, leading to the size dependent properties of nanomaterials[5]. The energy of the free surface atoms is entirely different as compared to the energy related to the atom of the bulk. The surplus energy associated with the surface atom is known as the free surface energy. In bulk materials, this free surface energy is neglected because it has associated with only top most layers of the atoms on the surface. Also the ratio of the resided volume of surface atoms and the total volume of the material is extremely small. As the size of the low dimensional materials decreases to the nanometer size range, the electronic, magnetic, optic, catalytic, electrical and thermal properties of these materials are significantly altered from those of either the bulk or a single molecule [1]. Among these properties, the thermal conductivity of nanomaterials have received considerable attention because thermal conductivity is a fundamental property of nanosolids that directly affects its applications. However, few efforts have been focused on studying thermal conductivity of these materials. Some experimental studies have been carried out to investigate the effect of nanoparticles on the thermal conductivity of various materials. Katika and Pilon [6] have studied the effect of size of nanoparticles on the thermal conductivity of crystalline thin films at low temperatures and reported that the thermal conductivity decreases with decreasing particle radius. There are some theoretical studies on the size effect on thermal conductivity of nanomaterials. Singh et al. [7] have studied the grain-size effect on the thermal conductivity of nanosolids and found that the thermal conductivity of nanosolids decreases as the grain size decreases. Very recently, Bhatt et al. [8]have proposed a theoretical model to study the size effects on thermal conductivityof nanomaterials and found a significant reduction in the thermal conductivity of nanomaterials by decreasing the size. Li et al. [9] have reported the decrease in thermal conductivity of nickel nanoparticles with decrease in their size. It is found that very few experimental and theoretical works have been done in this field while sufficient work is required in this direction. In all these studies, the crystal order of the materials has not been taken into account as it plays a vital role in the study of thermal conductivity of various nanomaterials. When the concentration of building blocks (atoms or ions) of a solid becomes enough high, they accumulate into small clusters through homogeneous nucleation. With continuous supply of the building blocks, these clusters tend to coalesce and grow to form a large cluster assembly. The cluster may be considered as an onion-like structure formed by many concentric shells around the central site. All surface site, which may belong to various shells, are defined as crusts, the number of crusts, n, defines the order of the cluster [9, 10]. It is, therefore, interesting to study and analyze the size effect on thermal conductivity of nanomaterial by considering the effect of cluster order. In the present work, we have modified available theoretical model by including cluster order for the study of thermal conductivity of Gold FCC nanomaterials. Abstract: A theoretical model for the study of size dependent thermal conductivity of Gold FCC nanomaterial has been developed by considering the cluster order with particle size of Gold (Au) FCC nanomaterial. Using this model, the thermal conductivity of Gold FCC nanomaterial has been calculated and compared with other theoretical models and existing experimental data. It is found that the thermal conductivity of Gold FCC nanomaterial decreases as the size of the nanoparticle decreases. The comparision of theoretical findings of thepresent work indicates that the developed theoretical model is in good agreement with available experimental data which shows the validity of the present work. Keywords: size, thermal conductivity, gold, nanomaterial