Plasma processing of fibre materials for enhanced impact protection

The performance of lightweight impact protective clothing depends on the constituting materials, their assembly in a system and interaction under various dynamic impact conditions. In this paper an overview of options for improved impact protective clothing systems based on a new plasma technology is presented. Plasma is an ionized gas providing a very active environment which can be used to implement functional chemical groups at the top layer of fibers so as to improve their surface energy or – when adding a coating precursor gas – to deposit thin functional coatings. One type of plasma technology, known as corona, is used in the textile finishing industry because of its ability to improve adhesion properties of various types of substrates such as polyethylene and polyester fabrics. TNO is developing a new type of cold atmospheric pressure plasma treatment, the surface dielectric barrier discharge (SDBD), which performs better with respect to spatial homogeneity, coating efficiency, temperature conditioning and stability of operation. As a result, unprecedented progress in terms of fibre surface properties can be achieved. The conference contribution will present examples in the area of improved adhesion and multifunctional coatings (e.g. impact and antimicrobial protection) applied to existing high performance fibre materials.Following practical examples will be discussed: (i) High flexural strength high density polyethylene fibers with poor adhesion properties have been plasma treated in various gas environments resulting in significant adhesion improvement (up to 400%) in a binder material with negligible tensile strength reduction. Surface analysis (SEM, surface tension measurements) shows that some increased roughness and mainly interfacial chemical bonding is responsible. (ii) The deposition of plasma-polymerized functional coatings on textile yarns has been shown feasible, maintaining the original comfort properties such as flexibility, breathability and feel. The benefits of the plasma-assisted deposition process can be directly related to the observation that coatings are deposited as very thin layers on the individual fibres of yarns. As an example, results of deposited antimicrobial quaternary ammonium chemicals are presented. Plasma assisted grafting is used to deposit AM coatings on both cotton and polyester substrates. The AM compound is non-leaching and AM efficiencies of more than log 5 against Escherichia coli are demonstrated. (iii) Finally, the concept of plasma deposition of a stab resistant layer on aramide type fabrics is presented. There is a significant need for extending ballistic protective body armour with knife, needle and spike protection without significant weight increase. The deposition of polymer bonded hard (metal/ceramic) particles in the micrometer-millimeter range on existing high performance fabrics should enhance their performance in stab protection. The development is directed to the deposition of a fully flexible composite layer containing hard and refractory materials for effective prevention against penetration of knives and other sharp objects. The main process features, the product development road map and preliminary results are discussed

Particle coating – a novel trend in energetic materials engineering

The development of new energetic materials with enhanced blast properties requires better understanding of factors as particle type, size and particle/matrix distribution. The ability of growing a coating on particles opens new possibilities in energetic materials engineering. Functionalities as ingredient compatibility, increased burning rates and accelerated or delayed ignition become possible upon applying versatile coatings. TNO Defence, Security and Safety investigates the required technologies for the development and production of a new class of shock insensitive, blast enhanced explosives based on modified/functionalized (energetic) materials. The contours of the underlying research program are briefly presented. This program includes e.g. the development of coated materials like Al powder. Using plasma enhanced chemical vapour deposition (PECVD) technology, test powder is coated with SiOx containing layers (with HMDSO as a precursor) and fluorinated layers (with C2F6 as a precursor). The results are presented and discussed

New fluidized bed reactor for coating of energetic materials

The process of altering and changing the properties of the energetic materials by coating has been studied extensively by several scientific groups. According to the desired application different coating techniques have been developed and applied to achieve satisfactory results. Among the already developed and used techniques are: ALD (atomic layer deposition), CVD (chemical vapor deposition), FEM (fluid energy mill), crystallization, aerosol-spray pyrolysis, Ziegler-Natta reaction and others. In TNO Defence, Security and Safety in The Netherlands, a facility for coating of energetic materials has been constructed. We propose a new plasma coating technique for energetic materials where a new type of Dielectric Barrier Discharge (DBD) is used with sufficiently improved production rates. Our facility aims to treat powders in the low micron range and at ambient temperature. The range of materials that can be treated is not restricted by their temperature sensitivity. Our facility is based on circulating solid-gas fluidized bed. The coating capacity is approximately 40g of energetic powder material per minute. This is possible because of the re-circulation nature of the fluidized bed. The precursors are introduced in the system in gas phase. The energy efficiency of the coating process is determined by the input plasma power, flow rate and molecular weight of the reaction gas and the treatment time. The research field, in which the facility is primarily used, is the reduction of sensitivity of several MIC’s (metastable intermolecular composites) and possibilities for prolonged shelf-life. This paper describes the design of the new fluidized bed plasma reactor as well as the research program on reduction of energetic materials sensitivity and manufacturing of novel energetic materials

SDBD plasma jet for skin disinfection

A consortium consisting of the research institute TNO, the medical university and hospital St Radboud and two industrial enterprises is working on a non-thermal plasma treatment method for skin and wound disinfection. The group is seeking for cooperation, in particular in the field of validation methods and potential standardization for plasma based disinfection procedures. The present paper briefly presents the technical progress in plasma source development together with initial microbiological data obtained

Modification and characterization of (energetic) nanomaterials

Nanomaterials are a topic of increased interest, since they have properties which differ from their macroscopic counterparts. Many applications nowadays take advantage of the new functionalities which natural and manufactured nanoparticles possess. Based on these developments, also the research on energetic nanomaterials is receiving more and more attention. Apart from the synthesis of energetic nanomaterials, another area of interest is the coating of energetic (nano)powders, in order to be able to modify their properties or to add new functionalities to these particles. (Modified) energetic materials find applications in explosives, gun and rocket propellants and pyrotechnic devices. The modified energetic materials are expected to yield enhanced properties, e.g. a lower vulnerability towards shock initiation, enhanced blast, enhanced shelf-life and environmentally friendly replacements of currently used materials. An experimental set-up for the coating of existing powders has been designed and constructed. The experimental technique is based on a special plasma application which, contrary to more general plasmas, can be operated at relatively low temperatures and ambient pressure. This allows the handling of heat-sensitive materials, which would otherwise readily decompose or react at higher temperatures. The facility used for the coating of energetic powders in the lower micron range is based on a fluidized bed reactor in which the powder circulates. In this paper, the experimental technique will be described and experimental results will be shown of CuO powders that have been coated with a very thin, nanoscale deposit of a SiO-containing layer. © 2009 Elsevier Ltd. All rights reserved

A Spatial ALD oxide passivation module in an all-spatial etch-passivation cluster concept

Traditional plasma etching in silicon is often based on the socalled 'Bosch' etch with alternating half-cycles of a directional Sietch and a fluorocarbon polymer passivation, respectively. Also shallow feature etching is often performed as a cycled process. Similarly, ALD is cyclic with the additional benefit of being composed of half-reactions that are self-limiting, thus enabling a layer-by-layer growth mode. To accelerate growth rate, spatial ALD has been commercialized as a large-scale, high-throughput, atmospheric-pressure method. In this paper we describe a related concept for high-rate spatiallydivided etching which eventually may be further developed towards Atomic Layer Etching. The process is converted from the timeseparated into the spatially-separated regime by inserting N2-gas 'curtains' confining the reactive gases to individual injection slots in a gas injector head, and also serving as gas-bearing. By moving substrates back and forth under such gas injector one can perform alternate etching/passivation-deposition cycles at optimized local pressures, thus eliminating the idle times for switching pressure or purging. An extra improvement towards an all-spatial approach is the use of ALD-based oxide (Al2O3, SiO2, etc.) as passivation during, or as gap-fill after etching. This disruptive concept, named spatial ALDenabled RIE, has industrial potential for cost-effective front-end-ofline and back-end-of-line processing, especially in patterning structures requiring minimum interface, line edge and fin sidewall roughness (atomic-scale fidelity with selective removal of atoms and retention of sharp corners). Besides in CMOS scaling this etch concept may also become an interesting option for fast die dicing of silicon (or III/V) in TSV and MEMS processing

Electrospray crystallization for high-quality submicron-sized crystals

Nano- and submicron-sized crystals are too small to contain inclusions and are, therefore, expected to have a higher internal quality compared to conventionally sized particles (several tens to hundreds of microns). Using electrospray crystallization, nano- and submicron-sized crystals can be easily produced. With the aid of electrospray crystallization, a mist of ultrafine solution droplets is generated and subsequent solvent evaporation leads to crystallization of submicron-sized crystals. Using cyclotrimethylene trinitramine (RDX) solutions in acetone, the conditions for a stable and continuous jet were established. At relatively small nozzle diameters and relatively low potential differences, hollow spheres of RDX crystals were observed. At a higher nozzle diameter and potential difference and in the region of a continuous jet, RDX crystals with an average size of around 400nm could be produced. In order to test the quality of the submicron-sized energetic material, impact and friction sensitivity tests were carried out. The test results indicate that the submicron-sized product had reduced friction sensitivity, indicating a higher internal quality of the crystalline product. Electrospray crystallization is proposed as a method for creating high-quality submicron-sized crystals of the energetic material cyclotrimethylene trinitramine (RDX). The friction sensitivity of the obtained unagglomerated submicron-sized crystals was lower than that of conventional RDX, indicating that they have a better internal quality. © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim