Piezoresistive sensors based on conductive films based on micro graphite

• Grant number: 20/09502-2
• Support Opportunities: Research Grants - Innovative Research in Small Business - PIPE
• Start date: April 01, 2021
• End date: December 31, 2021
• Field of knowledge: Physical Sciences and Mathematics - Chemistry - Physical-Chemistry
• Principal Investigator: Osvaldo Correa
• Grantee: Osvaldo Correa
• Company: Flex IC Indústria Microeletrônica Ltda
• CNAE: Fabricação de equipamentos e aparelhos elétricos não especificados anteriormente
• City: Sorocaba
• Pesquisadores principais: Pompeu Pereira de Abreu Filho
• Associated scholarship(s): 21/06717-0 - Piezoresistive sensors based on micro graphite conductive film, BP.PIPE

Abstract

Technologies involving conductive pastes and films have applications in piezoresistive sensors, electrical devices, flexible or rigid conductive films formed on different substrates (paper, ceramics, plastics, glass, leather, etc.) and thermoelectric films applied to footwear, clothing and heated seats for vehicles. The most important applications are in the automotive and aeronautical sectors where piezoresistive conductive films are used in particular in pressure sensors. Such films consist of a conductive phase based on ruthenium oxides. These oxides are derived from metallic ruthenium (Ru0), which is a metal that is not very abundant in the earth's crust and has a low extraction percentage. Such situations of scarcity and high prices have been discouraging investments in industrial R&D in the search for new technologies dependent on Ru0. Given this scenario, this project is based on replacement of the conductive phase in piezoresistive systems by micro-structured graphite. The use of graphite is justified by its highly competitive price in relation to metals, as Brazil is the first placed in mineable graphite reserves and the urgent need to add value to its derivatives. In addition to the price and abundance, graphite has other advantages, such as: thermal resistance, high conductivity, inert (does not oxidize up to 6000C) and absence of electro migration even at high temperatures. The methodology to be used is based on a new use of carboxymethylcellulose (CMC) resulting from its interactions with graphite particles, changing their physical and chemical characteristics. Such interactions result in hydrophilic particles composed of micro crystals, graphite and CMC that can be dispersed in aqueous media and used in an innovative production of conductive pastes and films. Such particles, resulting from this new use of CMC, have already enabled the production of micro graphite dispersions (paints) and conductive pastes stable in aqueous media and in the absence of toxic solvents. The results have shown that CMC has a decisive role in the formation of hydrophilic micro particles composed of graphite and CMC. Such particles are responsible for the wettability of the glass matrix particles, homogeneity and control of electrical conductivity. The physico-chemical characterizations of the conductive films and piezoresistive sensors will be made using some instrumental techniques, such as: Raman spectroscopy, scanning electron microscopy, 3D X-ray computed tomography, X-ray dispersive energy spectrometry (EDS) for acquisition of elementary maps, rheometry to study the rheology of pastes, four and two-point methods for determining electrical resistances, and laser scattering for determining particle size distributions. The expected results are: i) sustainable and profitable industrial and service production; ii) replacement of RuO2 in conductive films by natural graphite and iii) ecologically friendly industrial processes. The expected impacts are innovations in the industrial processes for the production of conductive pastes, new market opportunities for the devices built and the reduction of costs with the replacement of RuO2 by natural graphite. (AU)