CNR-INFM Protective Space coatings for Ti, Al and Mg alloys: Nanoscale materials based on organically modified ceramics A. R. Phani and S. Santucci

CNR-INFM CASTI Regional Laboratory at Department of Physics - University of L’Aquila, via Vetoio, 67010 Coppito, L’Aquila, ITALY Tel: 0039-0862-433037 Fax: 0039-0862-433033 e-mail: [email protected] or [email protected]

Motivation – Objectives

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The main objective of this proposal is to protect space materials from corrosion such as Ti and Mg alloys with nanostructured multifunctional coatings.

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In the proposed system, deposition of nanolayering of inorganic and organic nanocomposite materials embedded with nanoparticles (corrosion inhibitors) with additional functional groups on the surface will be developed.

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These nanocomposite materials will be prepared by simple, wet chemical processing system (sol-gel process) at relatively low temperatures (> 150 °C).

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The basic structure consists of inorganic network with organic cross-linking or network modifying structural units. A main advantage of this system is the combination of hardness (coming from the high amount of inorganic network structures) and flexibility (coming from the nature and amount of cross linking structures).

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This could be possible by covalently bonding the networks leading to stable functionalisation and incorporating the corrosion inhibitor nanoparticles with in these networks to have corrosion resistance properties.

Background

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Magnesium alloy has a light weight, high thermal conductivity, high dimensional high damping characteristics, good machineability and as well as recyclability stability, good electromagnetic shielding,

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These properties make it valuable in a number of applications including automobile, aerospace components, mobile phones, sporting goods, handheld tools, and household equipment

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The use of magnesium alloys can significantly decrease the weight of automobiles without sacrificing structural strength

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Unfortunately, magnesium alloys have a number of undesirable properties including poor corrosion and wear resistance, poor creep resistance, and high chemical reactivity that have hindered its widespread use in many applications

Metal Alkoxide (M-O-R)

Hydrolysis and Condensation Solution Polymerisation Coating

Xerogel film

substrate Heating substrate Dense Film

Sol-gel Process

Sol-gel Process

Wet gel Extraction of solvent Evaporation Xero gel Heating Aero gel Dense ceramics Uniform particles Sol s Fiber

ADVANTAGES

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Uniformity High purity Easy Operation Cost Effective Low temperature Controlled structure Coating on irregular shapes Selective doping

FACTORS EFFECTING

      pH (acid / base) Temperature Water and Solvent Reagent concentration Catalyst Dipping (spinning) speed

Mg and its Space Applications

Applications

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Magnesium has a number of unique physical and mechanical properties which, depending on strength, safety and weight aspects can be used by automotive, aerospace and electronic goods designers AUTOMOTIVE

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Fuel consumtion Emission Safety Braking Dynamic WEIGHT SAVING AEROSPACE Aerospace Value of a pound in segnment weight saved (Euro) Commercial -------------------- 357 Space ----------------------------- 35.4

Automobile -------------------- 1.78 – 3.2

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Properties

Light wieght (36% lower than Al) High strength to weight ratio High stiffness to weight ratio Excellent damping capacity Castability, mechanibility, recyclibility

100 nm 1500 nm

Innovative approach

Light-alloy substrate

Radical Innovative Approach:

Silica based fluoropolymer for scratch and hydro-oleophobic Slicon/metal-oxo clusters for nanoscale reinforcement hybrid coatings

Fig 1: Schematic diagram of the nanoscale hybrid structure for multifunctional properties for light-weight alloys applied for space applications

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This type of system will be applied on different types of Titanium, Magnesium and Aluminium alloys applicable to aerospace applications.

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It has been recognised by the aerospace industries that the degradation of carbon-based materials (organic coatings) in low earth orbit (LEO) is due to the presence of ground state atomic oxygen, ultra-violet radiation and vehicle’s extreme velocity.

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The UV radiation that is present in low earth orbit is of adequate energy to cleave organic bonds, which can bring about chain scission and cross-linking reactions in organic polymeric materials. In addition to this, thermal cycling, particulate radiation, vacuum, and micrometeoroids and debris affect organic materials.

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In this respect, materials consisting of inorganic/organic (polymer) can offer protection from atomic oxygen as well as UV radiation and high energy particles via the in situ fabrication of nanophase silicon / metal-oxo clusters.

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Siloxane polymers, which have rates of erosion one to two orders of magnitude slower than organic polymers in low earth orbit, have been chosen in the present investigation.

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In addition, to slower erosion rates, when exposed to atomic oxygen siloxane polymers form protective silicon oxide barrier.

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This provides enhanced atomic oxygen resistance, and will offer a self-healing property if the coating is scratched or etched from the debris.

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The silica layer on the surface prevents further degradation of the polymer underneath with increased exposure to atomic oxygen.

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The proposed mechanism explains where a space debris erode a part of coating which is self healed by consuming the atomic oxygen present in the space, there by forming a new protective layer which can withstand both atomic oxygen degradation, high energy UV radiation and atomic particles.

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Once the coating is exposed to atomic oxygen a protective layer of silicon oxide is formed and with the incorporation of silicon-metal-oxy-clusters the coating should protect against atomic oxygen erosion, high energy particles, and deep UV radiation.

        Smart windows Sun roofs Capacitors Semiconductors Heat insulating Memory devices Dispalys Wave guides      Energy storage Fuel cells Solar cells Laser diodes Decorative

Sol-gel Nanotechnology Applications Project Goals

Sol-gel Coatings Applications Scientific and Technological Objectives that CASTI might pursue in this project:

Optical Coatings Chemical Industry Aviation Engineering Building – construction Technology Functional Thin Films Aeroneutic Industry Thin films Sol-gel Technology Applications Composites Nanostructures Solar Technology Automotive Coatings Bio-medical Engineering

        Corrosion Abrasion Erosion Scratch Anti-adhesion Anti-finger print Anti-fouling Antibacterial      Biosensors Implant coatings Gas sensors Hydrophobic Photocatalytic

To optimize the developed pretreatment process for light weight alloys prior to the deposition of the nanostructured coatings for better adhesion strength To deposit organic-inorganic hybrid nanocomposites embedded with functional corrosion inhibitor nanoparticles (CeO2, La2O3) To deposit low friction, wear, scratch, abrasion resistant inorganic-polymer hybrid nanostructured coatings as top layer with additional hydro-oleophobic properties to fulfill the objective of the multifunctional coatings.

To characterize the deposit or thermally treated coatings for their structural, mechanical, tribological and corrosion (salt spray) and humidity resistance (intermittent, prohesion, and condensation humidity tests) measurements.

To optimize the developed nanocomposites embedded with nanoparticles for scale up process upon dealing with the industrial partners in the respective countries in the field of automobile, aeronautic, construction and microelectronic industries.

Services offered by CASTI in the project:

CASTI will analyze the coated samples as well as corrosion resistance tested (salt spray test) samples by employing full length scale characterization techniques available in the laboratory.