Munish Kumar

NANOMATERIALS UNDER HIGH TEMPERATURE AND HIGH PRESSURE

Two different approaches to study thermal expansion and compression of nanosystems are unified, which have been treated quite independently by earlier workers. We provide the simple theoretical analysis, which demonstrates that these two approaches may be unified into a single theory, viz. one can be derived from other. It is concluded that there is a single theory in the place of two different approaches. To show the real connection with the nanomaterials, we study the effect of temperature (at constant pressure), the effect of pressure (at constant temperature) as well as the combined effect of pressure and temperature. We have considered different nanomaterials viz. carbon nanotube, AlN, Ni, 80Ni–20Fe, Fe–Cu, MgO, CeO2, CuO and TiO2. The results obtained are compared with the available experimental data. A good agreement between theory and experiment demonstrates the validity of the present approach.

SIZE AND TEMPERATURE EFFECT ON THERMAL EXPANSION COEFFICIENT AND LATTICE PARAMETER OF NANOMATERIALS

A simple theoretical model is developed to study the effect of size and temperature on the coefficient of thermal expansion and lattice parameter of nanomaterials. We have studied the size dependence of thermal expansion coefficient of Pb, Ag and Zn in different shape viz. spherical, nanowire and nanofilm. A good agreement between theory and available experimental data confirmed the model predictions. We have used these results to study the temperature dependence of lattice parameter for different size and also included the results of bulk materials. The temperature dependence of lattice parameter of Zn nanowire and Ag nanowire are found to present a good agreement with the experimental data. We have also computed the temperature and size dependence of lattice parameter of Se and Pb for different shape viz. spherical, nanowire and nanofilm. The results are discussed in the light of recent research on nanomaterials.

Size and orientation dependence of elasticity of nanowire and nanofilm

A simple theoretical method is proposed to study the size and orientation dependence of elasticity of nanowires and nanofilms. We have studied the Young modulus of nanowires Ag, Cu and nanofilms Ag, Ni, Cu and Si. The results obtained are compared with the available experimental data and computer simulation studies. A good agreement between the theory and experiments supports the validity of the formulation developed in the present work.

THEORETICAL FORMULATION FOR THE EFFECT OF TEMPERATURE ON NANOMATERIALS

A simple theoretical formulation is developed to study the effect of temperature on nanomaterials. An alternative method is also discussed using thermodynamic analysis. The formulation discussed in the earlier literature may also be obtained from the present theory. To show the real connection with the nanomaterials, we have studied the effect of temperature. We have considered different nanomaterials viz. Zirconia, Ag, ZnO, NiO and Al composites. The results obtained are compared with the experimental data. A good agreement between theory and experiment demonstrates the validity of the present work.

Specific heat and thermal conductivity of nanomaterials

A model is proposed to study the size and shape effects on specific heat and thermal conductivity of nanomaterials. The formulation developed for specific heat is based on the basic concept of cohesive energy and melting temperature. The specific heat of Ag and Au nanoparticles is reported and the effect of size and shape has been studied. We observed that specific heat increases with the reduction of particle size having maximum shape effect for spherical nanoparticle. To provide a more critical test, we extended our model to study the thermal conductivity and used it for the study of Si, diamond, Cu, Ni, Ar, ZrO2, BaTiO3 and SrTiO3 nanomaterials. A significant reduction is found in the thermal conductivity for nanomaterials by decreasing the size. The model predictions are consistent with the available experimental and simulation results. This demonstrates the suitability of the model proposed in this paper.

Thermal properties of fullerites under high pressure and high temperature

A simple theoretical model is developed to study the properties of fullerites under varying conditions of pressure and temperature. The model is initially applied to study the compression behavior of C70 and C84 solids in the light of other relations as well as experimental data. The model performed in a better way as compared with the other relations. The results obtained are found to be encouraging. The model is therefore extended for the study of C70 and C84 solids under varying conditions of pressure and temperature. We have computed the pressure and temperature dependence of V/V0, the coefficient of volume thermal expansion and the bulk modulus. The results are compared with the available experimental data. There is a good agreement between theory and experiment, which supports the validity of the model developed for fullerites.

Size and shape dependence of Debye temperature and Raman frequency of nanomaterials

A simple theoretical model is developed to study the size and shape dependence of Debye temperature and Raman frequency of nanomaterial. We have studied the effect of size and shape on Debye temperature of nanocrystalline Fe, Co, Al and Ag. The model is extended to study the effect of size and shape on the Raman frequency of nanocrystalline SnO2, CeO2 and CdSe. The results obtained are compared with the available experimental data. A good agreement between the theory and experimental data supports the validity of the model developed. We also report the results for nanowire and nanofilm in the absence of experimental data, which may help the researchers engaged in the experimental studies.

SIZE-DEPENDENT EQUATION OF STATE FOR NANOMATERIALS

Simple theoretical method is developed to study the size dependence of equation of state of nanomaterials. The isothermal compression of Ni and e-Fe has been computed for different particle sizes. A shift in compression curve is obtained by increasing the particle size. This demonstrates the softening of the material by increasing the particle size. For larger particle size (~100 nm) the compression curve resembles with that of the bulk. This demonstrates that the nanomaterial becomes bulk for larger particle size. The results have been compared with the available experimental data. A good agreement between theory and experiment demonstrates the validity of the method proposed in the present paper.