Multi-Property Design of HV Dielectrics Michel F. Fréchette Hydro-Québec’s research institute (IREQ) Varennes, Québec, Canada Dielectrics 2011, Institute of Physics, University of Kent, 13-15 April, UK

WHY THIS PRESENTATION? It has been more than 10 years that the concept of NANODIELECTRICS (2001) have been introduced What is the status?

WHY THIS PRESENTATION? There was hope for NOVELTY in terms of properties What is falsely expected ?

WHY THIS PRESENTATION? In the concept there was the allusion to designing the material properties … Where has it gone ?

content Concept Achievements Other than interface Multi-properties

Understanding and using False effervescence OR Effervescing pot All is nano, nano is all and all you need is love New or not New look at New interpretation Gain in knowledge Design at nanoscale

The definition A “Nanodielectric” consists of a multi-component dielectric possessing nanostructures, the presence of which resulting into the change of one or several of its dielectric properties. Nanodielectrics would be found in two material categories of interest: ceramics and polymers.

Included in the definition Dielectrics at first Presence of nanostructures Nano scale processes Intregration producing a macroscopic observable Dependent on the dimension of the stress NANODIELECTRICS

TOLERANCE .. slight changes in one property We have been tolerant in regards of the results obtained .. slight changes in one property .. large improvement or change .. still awaiting confirmed novelty

Elementals (nanocomposite) + + + Stress dimensions Integrable

It depends .. Less nano Large nanometer sizes Agglomerated micron-size Interface controlled More nano Less than 2 nanometers Nano structuring Relation BB – B Less molecules Improvement .. Novelty/Design

Recipe ● The recipe is often different, dependent on case ● And various factors will affect the end results Nanostructured microcomposite: Epoxy + micrometric quartz + nanoclay PE-SiO2 sol-gel: Penetration of the deposit

Case 1 a - additives Schema listing some property roles of additives These compounds added to polymers are essentially chemical in nature and one characteristic that stands out is their adjunct may reach very small quantities, e.g. 0.2w% Santonox as antioxidant

Case 1 b - polydispersity Being chemical, the additive corresponds to a composite situation where polydispersity is very low. It is of molecular dimension, see for instance Fig. 1 where some Azo-compounds are depicted and were used to modify the conduction in PE.

Self-assembly Generation of order in systems of components The example shows an extremely thin layer of molecules (alkanethiols) self-assembled onto a metal surface to impart a water beading effect.

Case 2 a

Case 2 b - agglomeration 5% wt. SiO2 in HD PE

Case 3 - Influence of Chemical Structure and Solubility of Bisamide Additives on the Nucleation of Isotactic Polypropylene and the Improvement of Its Charge Storage Properties A comparative study on the influence of chemical structure and solubility of a series of low-molecular-weight 1,4-phenylene−bisamides in isotactic polypropylene (i-PP) was conducted to explore their performance as nucleating agents and electret additives. The best β-nucleating efficiency was observed for the symmetrically substituted compounds, whereas the nucleation efficiency was substantially reduced in the presence of n-alkyl-substituents. The charge storage behavior of i-PP was improved only for the three dicyclohexyl-substituted 1,4-phenylene bisamides at concentrations of 100 ppm and even below. For example, a film comprising 10 ppm additive displayed charge retention of 90% after an accelerated aging (annealing for 24 h at 90 °C). Nils Mohmeyer et al. (2006)

Case 4 a A situation involving polyhedral oligomeric silsesquioxane (POSS) cage structures chemically reacted into the polymeric network. These cage structures with a particle diameter in the range of 1–3 nm can be functionalized to provide chemical reactivity with various polymer systems. Examples include octavinyl (R = vinyl group) incorporation for copolymerization with PMMA, amine groups for incorporation into polyamides and polyimides. Hybrid- Plastics

Case 4 b The basic POSS® structure can be thought of as a cage of molecular silica comprised of 8 silicon atoms linked together with oxygen atoms. At each of the 8 corners is a substituent which can be just about any chemical group known in organic chemistry. Hybrid-Plastics

Case 4 c 50nm POSS® molecularly dissolved in PP, each black dot is a 1.5nm POSS® cage Hybrid-Plastics

Case 4 d Hybrid-Plastics

Case 4 b IBM Research at Almaden

Scaling Sol-Gel POSS

Achievements to change morphology and related properties Partial nanostructuration of polymer nanocomposites were found: to change morphology and related properties to improve partial-discharge resistance, to suppress space charge formation and affect charge relaxation, and to prolong the treeing lifetime to open a way to tailoring/design

What’s lacking ? The possibility to link (clearly and easily) the nano intervention to the macroscopic property To make the materials with reproducibility and with successful quality control To establish the stability and ageing of the nanocomposites

MORPHOLOGY ● Morphology ●

MORPHOLOGY – classi 1 Barium titanate is an oxide of barium and titanium with the chemical formula BaTiO3. It is a ferroelectric ceramic material, with a photorefractive effect and piezoelectric properties. It has five phases as a solid, listing from high temperature to low temperature: hexagonal, cubic, tetragonal, orthorhombic, and rhombohedral crystal structure. All of the structures exhibit the ferroelectric effect except cubic. Barioperovskite is a very rare natural analogue of BaTiO3, found as microinclusions in benitoite.

Lattice parameters of BaTiO3 as a function of temperature Fraction of nano The internal electric dipoles of a ferroelectric material are coupled to the material lattice so anything that changes the lattice will change the strength of the dipoles (in other words, a change in the spontaneous polarization). The change in the spontaneous polarization results in a change in the surface charge. This can cause current flow in the case of a ferroelectric capacitor even without the presence of an external voltage across the capacitor. Two stimuli that will change the lattice dimensions of a material are force and temperature. The generation of a surface charge in response to the application of an external stress to a material is called piezoelectricity.

MORPHOLOGY – classi 2 Dielectric strength as a function of film thickness for polyethylene, using the two types of electrodes. The solid lines represent the linear regressions.

Morphology – classi 2

HPN-20E-nucleated polyethylene resins display the highest crystallization temperature and the lowest isothermal crystallization half time achievable EX1. Nucleation Nucleation technologies fall into three categories: conventional, advanced, and hyper nucleation.

EX1. Crystal size and crystallinity

EX1. Nano and crystallinity

EX1. Crystallinity and conduction A simple model for hole conduction may be proposed in which lamella regions of high conductance are inter-posed by amorphous regions of low conductance Hole transport Within the lamellae the chains will be largely free of disorder and holes may be expected to be mobile in individual chains along the c-axis. Lewis and Llewyllin (2010)

EX2. Nanoclay in polymers

Nanostructured epoxy microcomposite The two-step compatibilization creates a diffused ionic layer around the clay platelet, with additional ion clusters dispersed in the matrix. The high energy clay surface causes solidification of the organic phase up to 6 nm thick At about 3.6 wt% of clay the stacks with solidified polymer layer around them will occupy the full space and additional organoclay will remain non-dispersed.

PP+NanoClay Fuse et al. (2009) Relative dielectric constant (a) and loss factor (b) as a function of temperature observed at 10-2 and 104 Hz.

PP+NanoClay Relation between PD charge and surface degradation depth induced by the PDs. Fuse et al. (2009)

EX. 2 INTERPHASE  As concentration increases S.Raetzke, J.Kindersberger – Role of Interphase on the Resistance to HV Arching, … IEEE DEIS Transactions, 2010

EX3. INTERPHASE It is estimated that for a mere 1% volume fraction of 2 nm particles dispersed in a matrix, as much as 63% of the volume could be occupied by the interphase material. Winey and Vaia (2007)

Interphase again A three component material with the third component being a region around each nanoparticle which we call the interphase Illustrations of the interphase region surrounding the filler particles in a composite system.

Interphase Epoxy-nanosilica Measured (a) real and (b) imaginary parts of the complex permittivity of pure epoxy, nanocomposite (HN) for p v = 0.01, and numerically determined (a) real and (b) imaginary parts of the complex permittivity of pure epoxy, nanocomposite (HN) for p v = 0.01 interphase with i h = 5.5d. Maity et al. 2010

Schematic representation of the interphase in iPP/SiO2 composites Rui-Juan Zhou • Thomas Burkhart 2011

Effect on Breakdown Weibull scale parameters η for DC breakdown strength for BN-ER as function of filler size with 0 representing neat ER. Andritsch et al. (2010)

Multi-properties MULTI-PROPERTIES

EX 2-p Thermal conductivity scaled for several polymer cases. Mesogen content Thermal conductivity scaled for several polymer cases. EPAN: a matrix of epoxy with a high load (about 76% wt.) of aluminum nitride

Okasaki (2010) EX 2-p Relationship of thermal conductivity and filler content Breakdown strength

Micro performance Micro-alumina 60 vol% filled epoxy composites of 0.2 mm thick was obtainable, and it was elucidated that its thermal conductivity is 4.3 W/m/K, its relative permittivity is 6.0, and its dielectric strength is 16 kV/mm. Increased Vb by nano Kozako (2010)

Multiphase extra-ordinary Conductivity in unit of W/m K Carbon nanotubes, metallic nanofibers, etc

Milling B4C Polyvinyl alcohol (PVA) coated nano-B4C powder TEM morphologies of the nano-B4C/PVA composites milled at 700 rpm for 50min Young Rang Uhm et al. (2010)

Functions separation Nanostructured epoxy Doped for electrical conductivity Cold spray or bonding Multi-phases Nano, sub-micro, micro Breakdown and thermal

FUTURE Extra-ordinary additive or fillers (mastering) 34/36 FUTURE Extra-ordinary additive or fillers (mastering) Tailoring 2 or more properties at the same time (multi-filler and separation of functions) Higher-degree self-assembly nanodielectrics (BB and B)

CONCLUSION

CONCLUSION Morphology is called to play a key role in designing nanodielectrics Often nanometric … if so mesoscopic physics in essence

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