1.2.4 Conclusions

The efficient plasma-detonation device (PDD) is offered to provide an integrated impact on the surface being modified by the electric, magnetic, thermal, mechanical, acoustic pulses. Pulsed plasma jets generated by PDD have power density of 103 to 107 W cm-2, temperature of 4􀀃103 to 20􀀃104 K, and velocity of 2000 to 8000 m/s. Surface treatment is accompanied by a set of effects providing accelerated transfer of alloying elements in the liquid and solid phases, and crystallisation with formation of a submicrocrystalline layer up to 60 m thick. This layer contains alloying elements, which are introduced into the plasma jet. The plasma-detonation technology allows formation of a modified coating layer on the working surface of parts. Combination and quantity of alloying elements introduced into plasma are selected on the basis of application of a part and type of a metal alloy. Alloying elements can be introduced to the plasma in the form of products of erosion of a special electrode, in the form of gas (propane, nitrogen), and in the form of a powder. Addition of vapour-droplet Mo phase (from the fractured electrode) to the plasma leads to a change in phase composition of the surface layer and formation of intermetallic compounds Fe7Mo6 and FeMo. Treatment of the coating surface by the pulsed plasma jet provides formation of intermetallic compounds, and melting with the electron beam provides mixing of the coating and substrate components. The plasma-detonation technology allows a short-time heating of the surface layer (20-40 m) up to its melting. Introduction of metals into the molten layer and simultaneous effect by a combination of physical fields provide stirring

and formation of new alloys containing intermetallic compounds. The time of interaction of the metal-containing plasma with the work piece surface is no longer that 10-3 s, which allows the surface of parts to be modified without heating. The technology offered provides formation on the work piece surface of a thin layer, which contains different alloying elements, such as nitrogen, carbon and metals. Crystallisation of the layer of the melt on the work piece surface takes place in a set of different physical fields (acoustic, electromagnetic) at high temperature gradients, which provides formation of its dispersed crystalline state. The layers formed on the surface are characterised by high hardness and adhesion to the work piece surface. This allows the plasma-detonation technology to be recommended to harden surfaces of heavy-loaded parts without their heating and loss in strength. Experience of commercial application of the technology showed that performance, e.g. of metal-working tools at steel-rolling mills, increases 3-6 times after the plasmadetonation treatment .

2.Summary of the arrticles.

2.1 Plasma technology.

Lower cost of operation, improved durability and wear and development of new attributes for textiles are the key benefits that plasma based manufacturing of textile can bring, affirm Anita A Desai. That drove the need for sizing added to the yarn. Electric lighting enabled the mills to work through the night. As many do today. new chemical treatment for bleaching, dyeing and mercerising provided better strength, less shrinkage, bright colours and whiter cottons. At higher production rate and longer production hours, mills could produce more finished fabric than ever before and with greater consumer appeal. The changing technology, from hand power, to water power to steam and then to electricity, fundamentally changed the textile industry, its product marketability and its profitability. Now its time for yet another change! Plasma technology is poised to change the concept of textile wet processing.

These cost factors vary by location. If the technology is same everywhere, then the region with lowest cost factor will have the lowest cost of production and can therefore under-price everyone else. But what if the technology is not the same? What if a new technology changes the cost structure of textile industries by reducing the energy consumption, environmental waste and using fewer chemicals? This is the cost benefit that plasma based technology can offer the textile industry. History has also shown that consumer will pay more for clothing with a defining and desirable attribute. The development of wash and wear clothing, laterfollowed by permanent press finishes demonstrated this. The second significant benefit that plasma based textile manufacturing offer is development of new fabric treatment with a desired attribute that can not be achieved by other means.

Over the past decade there has been rapid exploration and commercialisation of plasma technology to improve the surface properties of textile material without changing the bulk properties. Modification of textile surface by plasma treatment offers a lot of benefits and overcomes the draw back of the classical wet chemical finishing. A major advantage of plasma surface treatment is the lack of harmful by product from the treatment process Plasma, as a very reactive material, can be used to modify the surface of a certain substrate (typically known as plasma activation or plasma modification), depositing chemical materials (plasma polymerisation or plasma grafting) to impart some desired properties, removing substances (plasma cleaning or plasma etching), which were previously deposited on the substrate (Pane, et al 2001).

Plasma is any substance (usually a gas) whose atoms have one or more electrons detached and therefore become ionised. The detached electrons remain, however, in the gas volume that in an overall sense remains electrically neutral. Thus, any ionised gas that is composed of nearly equal numbers of negative and positive ions is called plasma. The ionisation can be effected by the introduction of large concentrations of energy, such as bombardment with fast external electrons, irradiation with laser light, or by heating the gas to very high temperatures.

Plasma treatments have been used to induce both surface modifications and bulk property enhancements of textile materials, resulting in improvements to textile products ranging from conventional fabrics to advanced composites. These treatments have been shown to enhance dyeing rates of polymers, to improve colourfastness and wash resistance of fabrics, to increase adhesion of coatings, and to modify the wet-ability of fibres and fabrics. Research has shown that improvements in toughness, tenacity, and shrink resistance can be achieved by subjecting various thermoplastic fibres to a plasma atmosphere.

Recently, plasma treatments have produced increased moisture absorption in fibres, altered degradation rates of biomedical materials (such as sutures), and deposition of low friction coatings. Unlike wet processes, which penetrate deep into the fibres, plasma produces no more than a surface reaction, the properties it gives the material being limited to a surface layer of around hundred angstroms. . The plasma is formed by applying a DC, low frequency (50 Hz) or radio frequency (40 kHz, 13.56 MHz) voltage over a pair or a series of electrodes. (Figure A, B, C) Alternatively, a vacuum glow discharge can be made by using microwave (GHz) power supply.:

Corona Discharge formed at atmospheric pressure by applying a low frequency or pulsed high voltage over an electrode pair, the configuration of which can be one of many types. Typically, both electrodes have a large difference in size (Figure shown below). The corona consists of a series of small lightning-type discharges; their in homogeneity and the high local energy levels make the classical corona treatment of textiles problematic in many cases.

Atmospheric pressure plasma technique:

As discussed earlier, there are various forms of plasma depending on the range of temperature and electron density. Generally, high plasma densities are desirable, because electrons impact gas molecules and create the excited-state species used for textile treatment. Having more electrons generally equates to faster treatment time. This is due to the fact that the energy of the plasma is mainly confined to the energy of low mass electrons. Non-thermal plasma or cold plasma is characterised by a large difference in the temperature of the electrons relative to the ions and neutrals. Thus, Te >> Ti � Tn. As the electrons are extremely light, they move quickly and have almost no heat capacity. Ionisation is maintained by the impact of electrons with neutral species. These plasmas are maintained by passing electrical current through a gas. Despite all the significant benefits, plasma processing has failed to make an impact in the textile sector because of a particular constraint, which is incompatible with industrial mass production. All the technologies developed to date are based on the properties of low-pressure plasmas.

The process must take place in an expensive, closed-perimeter vacuum system and cannot be used for continuous production lines operating at room temperature, with machines processing fabric 2 metres wide at high speed. The Atmospheric Pressure Plasma is a unique, non-thermal, glow-discharge plasma operating at atmospheric pressure. The discharge uses a high-flow feed-gas consisting primarily of an inert carrier gas, like He, and small amount of additive to be activated, such as O2, H2O or CF4.

Corona Discharge is non-arcing, non-uniform plasma that ignites the region of the high electric field generated by the sharp points of the electrodes. To prevent arcing, no grounded surface is near these field emission points. Thus the discharge is non-uniform and the plasma density drops off rapidly with increasing distance from the electrode. Atmospheric Pressure Plasma Jet is the most promising technique among all Atmospheric Pressure Plasma Techniques and is widely used for textile processing. Here, helium feed-gas (about 99 %) mixed with a small amount of reactive gas (typically 1-3 % oxygen) enters the annular volume formed between RF powered electrode and the outer, grounded metal tube. One novel aspect of APPJ is that the discharge is formed in this small volume, which has insufficient room for the immersion of the substrate. However, the active chemical species formed by the plasma, rapidly exit the source and impinge downstream on the work-piece. In this way, the substrate is mostly exposed to active neutrals and radicals, rather than ions. The absence of ion chemistry in the downstream flow increases chemical selectivity and reduces surface damage

Experimental set-up in schematic diagram of the plasma configuration can be seen in figure (a). Two circular copper electrodes (diameter = 7 cm) are placed within a cylindrical enclosure. Both electrodes are covered with a glass plate (thickness = 2 mm) and the inter electrode distance is 8 mm. The upper electrode is connected to an ac power source (frequency 50 kHz). The lower electrode is fixed and connected to the earth. The discharge current is obtained by measuring the voltage over a small resistor R (100_), inserted into the current loop. The voltage is measured using a high voltage probe (Tektronix P6015A). The current and voltage waveforms are recorded using an oscilloscope (Tektronix TDS210-60 MHz) connected to a computer.

Plasma may be used for removing the contaminants, finishing and sizing agents from the fabric. Desizing of polyester fabric that used polyvinyl alcohol as the sizing agents can be removed by plasma treatment. The wet-ability of polyester fabric also increases significantly. Polyester fibre can be effectively modified by low pressure plasma treatment. Treatment of polyester fibre by glow discharge in air or oxygen causes a partial degradation of the fibre surface together with an increase in the capillary sorption of Iodine or cation in aqueous solution. Wetting out properties of polyester can be achieved by treatment of polyester with plasma and corona discharge. The fabric can be processed without the use of wetting out agents. A small scale matched for the preparation of liner fabric is described, which practically eliminates the use of chemical reagents. The grey fabric is treated in a glow discharge plasma in air and then the process maintains the strength of the fabric. Maintaining the strength of the fabric does not affect the natural colour of liner and does give fabric a high degree of hydrophilicity. Plasma treatment of wool has already been examined by several research institutes. In general similar results are reported although the intensity of the obtained effect might differ from case to case. For our trials a knitted wool fabric, without special pre treatment was used. Plasma treatment was performed in a plasma chamber of ± 1mі, using secondary plasma generated with a 40 kHz plasma generator with a plasma power between 2,000 and 3,500 watt. Treatment times were varied between 1 and 7 minutes. The most important effects observed during our evaluations are: No significant change in mechanical properties of individual fibres. Plasma treatment modifies the fibre surface rather than its interior, which allows the fabric to retain strength over time.

Plasma process is applicable for all types of fibres making the modifications simpler even for inert materials. Also some special textile properties can only be obtained via plasma processing. Consumption of chemicals is very low and this being dry process, less energy and time are required.