Thin lead free ferroelectric fibres with oriented grain growth by tailoring inorganic-organic interface (LeaFInOrFace)

• Forschungsstelle: COST
• Projektnummer: C14.0099
• Projekttitel Englisch: Thin lead free ferroelectric fibres with oriented grain growth by tailoring inorganic-organic interface (LeaFInOrFace)

Schlüsselwörter (Englisch)

Ferroelectric fibres; melt spinning; grain oriented fibres; ethyl cellulose-KNN hybrid; polyethylene oxide-KNN hybrid

Forschungsprogramme (Englisch)

COST-Action MP1202 - Rational design of hybrid organic-inorganic interfaces: the next step towards advanced functional materials

Kurzbeschreibung (Englisch)

In the last few years Empa developed a new melt spinning method to synthesise lead-free fibres. Powder coated with a surfactant is dispersed in a polymer-solvent mixture. After extraction of the solvent the inorganic-organic hybrid material is extruded by melt spinning technology. The goal of this project is the development of a stronger interphase between the polymer and the ceramic powder to avoid inhomogeneity during the mixing process and die blocking during extrusion of fibres with a diameters below 500 µm. Special surfactants, e.g. different lengths of fatty acids or comb-polyelectrolyte can be used to optimize the interphase between the ceramic powder and the polymeric matrix. A strong interface is important to both reduce the viscosity and to achieve a high ceramic powder loading. On the other hand such an optimized interface is necessary to avoid phase separation during the spinning process where shear rates of 1'000 to 10'000 1/s can occur. The polymer chains will be oriented and the particles must have good adhesion to be able to follow the extension of the polymer to avoid die blocking. We propose the investigation of organic-inorganic interfaces using special surfactants to be able to extrude homogeneous lead-free fibres with diameters below 500 µm. Those fibres are required for the development of lead-free ultrasonic composite transducers, active fibre composites for energy harvesting or structural health monitoring of light weight structures.

Weitere Hinweise und Angaben (Englisch)

Full name of research-institution/enterprise: EMPA - Eidg. Materialprüfungs- und Forschungsanstalt Laboratorium für Hochleistungskeramik

Partner und Internationale Organisationen (Englisch)

AT; BE; BG; HR; CZ; FI; FR; DE; EL; IE; IL; IT; LT; NL; NO; PL; PT; RO; RS; SI; ES; SE; TR; UK

Abstract (Englisch)

Empa developed a new melt spinning method to synthesise lead-free fibres. Powders are coated with a surfactant and Uispersed in a polymer-solvent mixture. In a second step, solvent is removed and the composite can be extruded by melt spinning process. Solubilfty/swellability of the polymer and the bonding between ceramic and polymeric matrix are two of the main key points tor this technology. A strong bonding can be tailored by so called surfactants and is essential to avoid phase separation during high shear forces where polymer chains are onented and particles have to strongly connect to the polymer. According to the project plan, KNN powder as platelets were synthesized by molten salt technology. The platelets will act as templates for the production of textured fibres. Orientation of the platelets in the fibres will be obtained by extrusion. Additionally KNL-NTS powder was synthesized for Iead-free fibre synthesis. Later, ferroelectric powders were mixed with different polymers and surfactants. Thermoplastic polymers like paraffin, EVA, PE, PS, polyethylene oxide, ethyl cellulose, in combination with different surfactants, like Hypermer and different fafty acids were used to study the mixing process. The mixed composites fceramic-surfactant-polymer hybnd material) were investigated visually and by extrusion method. KNN and KNL-NTS fibres have been successfully produced using EVA as a bindet and stearic acid as surfactant additive. Using spectroscopy it was not possible to investigate the Interface between the ceramic powder and the polymer. Rheological characterisation to investigate the activation energy and to characterize the interface will start soon. Additional to KNN and KNL-NTS, commercial BaTIO3 was used. Using this commercial powder, a flexible hybrid fibre fBaTiO3-EVA composite) has been developed and electromechanically characterized. Large electromechanical propetties could be directly measured on those fibres. To our knowledge such a material has not been reported so far and because of this we further investigated this phenomenon. Hybrid fibres with PZT powder could be also successfully tested. For comparison, ferroelectric properties ot ferroelecffic hybrid fibres and sintered ferroelectric ceramic fibres were investigated. In comparison to sintered fibres, the fermelectric hybrid fibres reached 10% of the maximum strain and polarisation. The results of this part will be submifted for the journal, advanced functional materials.

Datenbankreferenzen (Englisch)

Swiss Database: COST-DB of the State Secretariat for Education and Research Hallwylstrasse 4 CH-3003 Berne, Switzerland Tel. [phone] Swiss Project-Number: C14.0099