RICERCA ITALIANA     

Ceramic nanocomposites from preceramic precursors and carbon nanotubes

Università degli Studi di Trieste

Abstract

This research project deals with the preparation and the structural, physical and mechanical characterizazion of novel ceramic nanocomposites made of a silicon oxycarbide matrix and carbon nanotubes (CNTs).
Silicon oxycarbide glasses (SiCO) belong to the family of Polymer Derived Ceramics (PDCs). PDCs have shown excellent properties: they resist crystallization up to extremely high temperatures (up to 1800°C) and they are creep and oxidation resistant.
The PDCs are processed by a novel, low-cost polymer-based process which consists of two essential steps. First, the organic precursor is polymerized into a rigid plastic form, for example fiber or film. These forms are then pyrolyzed under controlled conditions at about 1000°C to convert them into the ceramic.
The introduction of CNTs into the PDC matrix will allow to improve the excellent properties of these materials, in particular their mechanical, thermal and electrical properties. Indeed, CNTs may be the strongest materials known and they also have very high thermal and electrical conductivity.
The project will be developed in the following steps:
1) The research unit of Bologna (henceforth, UOBO) will study the optimal procedure for the dispersion of the CNTs in preceramic precursors obtained by (i) the sol-gel method (research unit of Trento, UOTN) or (ii) from silicone resins (UOBO);
2) Characterization of the structural evolution during pyrolysis by means of: DTA/TG >>>

Principal Investigator

Valter SERGO Università degli Studi di TRIESTE

Research Objectives

The goal of the research project is the development, for the first time, of a new class of ceramic nanocomposites from preceramic precursors (PDCs) and carbon nanotubes (CNTs). In particular we will develop CNTs/SiCO nanocomposites.
We also propose to develop specific components (such as fibers, films, foams and bulk samples) which might increase even more the expected properties of the PDCs/CNTs nanocomposites. These components will also be used to measure the physical/mechanical properties of these novel materials.
Achieving the following intermediate objectives will pursue the goal:
1. Study of the optimal conditions for the insertion of CNTs in preceramic precursors (either sol-gel solutions and siloxane polymers). We will study the role of chemical additives (surfactants) on the CNTs dispersion in the liquid preceramic. We will evaluate the possibility of functionalize the CNTs surface with suitable bonding agents to promote either their dispersion and the maximum amount of CNTs that can be introduced in the PDCs. For this objective we will benefit from the long experience of UOPD in the field of functionalizing fullerenes to help their insertion in sol-gel matrices. We will also study the role of the type of silicon polymers and the different silicon alkoxides on the CNTs dispersion. To characterize the CNTs dispersion in the preceramic polymers, SEM and HRTEM analysis will be performed before and after pyrolysis.
2. Study of the influence >>>

Timescale

24 months

National and international background

Polymer Derived Ceramics (PDCs) are a new a new class of nano-materials which display very interesting properties [1]. Actually, even if they are mainly amorphous they display the same creep [2] and oxidation resistance [3] as crystalline SiC and thermal stability up to 2000°C [4]. From a chemical point of view, PDCs belong to two families: silicon carbonitrides (SiCN) and silicon oxycarbides (SiCO). From a structural point of view, both materials are formed by an amorphous network built up by covalent Si-C, Si-O and Si-N bonds. Usually, an excess of C (compared to the stoichiometric amount necessary to saturate all the valences of Si atoms), is present and forms a graphite-like phase. In the scientific literature references can be found which attribute to the presence of this C phase and its distribution in the amorphous matrix many of the exceptional properties of these materials, such as the high chemical durability in strongly aggressive media or the resistance to crystallization [5]. These materials are processed through an innovative method based on the polymer technology. The starting material is a metallorganic polymer that is first shaped into a plastic form, then crosslinked into a thermosetting polymer and finally it is converted into the ceramic with a pyrolysis process in controlled atmosphere. The first commercial products made with this technology are the SiC-based Nicalon [6] and the SiTiCO-based Tyranno fibers [7]. Then, many other ceramic systems have been >>>