PLASMA PROCESSING UPDATE

A newsletter from the

Facilitation Centre for Industrial Plasma Technologies,

Institute for Plasma Research

Issue 46 May - August 2004

Contents

Editor's Note

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Rock Fracturing by Plasma Blasting Technology

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Plasma Processing in PV Device Fabrication

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Demonstration of Plasma Pyrolysis System for Plastic Waste Disposal

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Plasma Nitriding System Installed at SINP

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Influence of Alloying Elements on the Corrosion Properties of Various Plasma Nitrided Steels

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DAE-BRNS Workshop on Plasma Surface Engineering

Editor's note

Conventional rock blasting causes many negative environmental impacts including ground vibration, flyrock, air blast and the emission of noise, dust and gases. An unconventional alternative process is the application of Plasma Blasting Technology. This process is able to fracture and rupture rocks almost instantly. A high current impulse generator produces the energy to fracture the rocks without the above environmental impacts caused by the conventional explosives. Dr. Shashank Chaturvedi tells us about the advantages of this techniques over the other conventional methods.

Fabrication of solar cells with very high efficiencies currently requires extremely complex processing. In order to make photovoltaics an economical large-scale source of energy, very high efficiencies have to be achieved by low cost processing. One of the most simple and environmentally safe innovative approach for cost effective production is deposition of silicon nitride by plasma -enhanced chemical vapour deposition process. A meeting was organised to assess the plasma processing existing technologies for materials used in photovoltaics application. An overview of the contents of the meeting is

discussed by Prof. P. I. John.

Plastics have become an indispensable part of modern life. Unfortunately, those very desirable attributes, which have created an ever-expanding demand for plastic products, have created an environmental nuisance. Several techniques are available for disposal of plastic waste. One of the most eco-friendly method for all types of waste disposal is plasma pyolysis. Facilitation Centre for Industrial Plasma technologies have developed this eco-friendly technology. The central government through DST has invested to install four-plasma pyrolysis system for plastic waste disposal in India. This article reports on the two systems that have been successfully installed at Goa medical college hospital's premise at Goa and Port Blair, Andaman & Nicobar.

Plasma nitriding has potential as an industrial process to improve the wear, fatigue and corrosion resistance of steels. It is well known that the corrosion properties of stainless steel deteriorate when treated with temperatures above 450 ^oC. This is because the chromium-alloying element, which is responsible for protection against corrosion, gets converted to chromium nitrides at these temperatures. Whereas low alloy steels and high alloy steels exhibit better corrosion resistance. This article indicates the influence of alloying elements on the corrosion properties of EN 8 (AISI 1045), En 24 (AISI 4340), AISI H13 and AISI 304 steels after plasma nitriding.

Dr. K. S. Ganesh Prasad

Editorial Assistance: Alphonsa Joseph

Facilitation Centre for Industrial Plasma Technologies

The Institute for Plasma Research (IPR) is exclusively devoted to research in plasma science, technology and applications. India’s  first high temperature plasma device `Aditya Tokamak’, built at IPR, produces plasmas at 5 million degrees temperature - comparable to that of the sun.  An advanced fusion device with superconducting magnets, capable of steady state operation is under fabrication. IPR is also active on a broad front of fundamental studies. It has engineering groups skilled in technologies of Superconducting Magnetics, Ultra High Vacuum, Pulsed Power, Microwave and RF, Computer-based Control and Data Acquisition, theory and computer simulation complement experimental programmes.

The Facilitation Centre for Industrial Plasma Technologies (FCIPT) links the Institute with the Indian industries and commercially exploits the IPR knowledgebase. FCIPT interacts closely with entrepreneurs through the phases of development, incubation, demonstration and delivery of technologies. Complete package of a broad spectrum of plasma-based industrial technologies and facilitation services is offered.

Some of the recent FCIPT achievements are: plasma nitriding of industrial components to increase wear resistance and hardness, coating of quartz-like films on brassware to inhibit oxidation and tarnishing, ceramic synthesis and processing, plasma ion implantation and ion plating for surface engineering, thermal plasma technologies for smelting of minerals and waste treatment etc.

The Centre has process development laboratories, jobshops and material characterisation facilities. The process development laboratory exploits the areas of expertise in plasma and other allied fields of the institute in developing new plasma based technologies for the industry. The jobshop executes job work for surface and material treatment on an industrial scale to promote the acceptance of plasma based technologies and to generate techno-commercial data relevant to entrepreneurs. The advanced instruments in the material characterisation facility are open to users from industry, research establishments and universities.

This newsletter is designed to help you keep abreast with the developments in the important field of plasma assisted manufacturing and  to look for new industrial opportunities. We would be  very happy to have you write to us on ways of improving this service or visit us for further discussions.

Please visit our website: http://www.plasmaindia.com

Rock Fracturing by Plasma Blasting Technology

There is a great deal of interest in fragmentation of rocks in such areas as tunneling, quarrying and mining. Conventionally, blasting by explosives is the usually employed method in excavation work. Due to problems of vibration, noise, and scattering of stones, this method is prohibited of use near important buildings and residential areas. The alternatives to this method are breakage by such crushing machines as large breakers and by chemical substances. However, such breakage methods are high in cost and the problems of decrease in breaking performance were observed.

Plasma Blasting Technology (PBT) involves the production of a pulsed electrical discharge by inserting a blasting probe in a water-filled cavity drilled in a rock, which produces shocks or pressure waves in the water. These pulses then propagate into the rock, leading to fracture.

Compared with conventional blasting method such as rock drilling machines, the PBT technology is friendlier to the earth, because it causes less vibration, noise, and dust, and uses no chemical substances. In the blasting procedure, a reusable blasting electrode and a power supply main body incorporating capacitors and other devices that are connected by a cable are used.

Newly developed compact blasting equipment is suitable for blasting of platy structures and boulder stones. Holes for blasting can be opened by hand-held tools. Therefore, the blasting procedure is easy and simple. By creating more than one hole in linear orientation and discharge at the same time, the object can be blasted as if it were cut.

This compact blasting equipment is suited for following applications.

· Blasting of thin, platy object (structures such as buildings and furnaces).

· Blasting of boulder stones. Digging of riverbed.

· Use in places where transportation of heavy load is difficult (such as mountains, slopes, and high places).

· Flexible and imprompt blasting under various situations (such as recovery work in a time of disaster).

· In the case where blasting like cutting is required, such as finishing of the blasted surface after main excavation work.

The main features of the PBT technology are as follows.

· Low vibration, low noise.

· No scattering of stones.

· No chemical reaction.

· Discharge portion is reusable.

· Blasting in the sea is possible.

· No heavy machinery is required.

Fig.1: Blasting probe in water filled cavity drilled in a rock

Fig.2: Fractured rock

At the Institute for Plasma Research, rock fracturing using underwater electrical discharges has been demonstrated on rocks upto 500 kg in weight as illustrated in Fig. 1 and 2.

Plasma Processing in PV Device Fabrication

A two-day meeting on ‘Plasma Processing in Photo-Voltaic Device Fabrication’ was organized at the Institute for Plasma Research on 21-22 June, 2004. The principal aim of the meeting was to assess the existing know-how in plasma processing for materials used in photovoltaic applications and to promote inter-institutional activity. The theme was chosen in the context of the significant on-going activity by various groups in the country and the role of IPR in basic and applied research on plasmas for semiconductor applications, starting with photovoltaic devices. Sixteen scientists attended the meeting. In addition to research and academic institutions, two major industries manufacturing photovoltaic modules (BHEL and TATA-BP) were invited to participate in the meeting so as to integrate the on-going and future research activity with development of industrially viable plasma processing. Prof. V. Dalal, Director, Materials Research Centre, Iowa State University, and an expert on plasma processing for photovoltaic applications was invited to give the plenary talk of the meeting. The meeting consisted of presentations from several active researchers in the field, representing the national activity at various institutes as well as talks on the plasma processing efforts at Institute for Plasma Research.

The programme also included a visit to the RF power laboratory at IPR and to the FCIPT laboratories. The FCIPT Lab visit was followed by a discussion of the FCIPT technology base. The participants expressed keen interest regarding participation of FCIPT in plasma processing for semiconductor applications. In particular, the role of FCIPT as an indigenous source of plasma processing equipment, starting from Langmuir probes to complete plasma deposition systems was voiced by several participants. There was a general consensus that it is important to set up a demo PECVD system at FCIPT and a market survey be conducted to know how many groups in the country have a requirement of such a system manufactured indigenously.

At the end of all the presentations, a discussion on ‘Promoting inter-institutional activity and future work’ in the field was co-coordinated by Professor P.I. John. An organizing committee consisting of Dr. P.N. Dixit, Prof. K. Narasimhan and Prof. Swati Ray will explore the possibility of NPL organizing the next meeting in 2005.

Demonstration of Plasma Pyrolysis System for Plastic Waste Disposal

At FCIPT, Institute for Plasma Research, Gandhinagar plasma pyrolysis technology has been developed and demonstrated for medical and plastic waste. Department of Science and Technology has given funds to install prototype four-plasma pyrolysis system for plastic waste disposal. Out of four plasma pyrolysis systems, two systems have been successfully installed at Goa medical college hospital's premise at Goa and Port Blair, Andaman & Nicobar. Pyrolysis process has an edge over conventional techniques in terms of low dioxin level and low gas requirements. In this process, pyrolysis is done at very high temperatures of plasma arc in an oxygen starved environment that completely decompose waste material into very simple molecules. High energy density and temperatures associated with thermal plasmas generate highly reactive environment in the reactor. High volume reduction of organic waste (99%) is another advantage of plasma pyrolysis process. Rapid start up and shut down and good controls over chemistry make the plasma pyrolysis technology a potential candidate for handling and safe destruction of toxic chemicals. The system include (Figure 1) primary chamber with feeder which helps in batch feeding without disturbing the pyrolysis process going on in the primary chamber. Pyrolysed gases will be combusted in secondary chamber. The gases coming out were later scrubbed and exhausted using induced draft fan. The emission measured was within the permissible limits of pollution control board. These systems are demonstration models and no commercial sale has been made.

Figure 1: Demonstration Model of Plasma Pyrolysis system

The system at Goa was installed at the end of March 2004. It was inaugurated by Chief Minister of Goa Mr. Manohar Parikar on 18th June 04 (see Figure 2). Similarly the system at Andaman was inaugurated by honorable Lt. Governor Prof. Kapse on 13th June 04 (see Figure 3).

Figure 2: Goa Chief Minister Mr. Manohar Prikhar Inaugurating

Demonstration model of Plasma Pyrolysis system at GMC, Goa

Figure 3: Prof. Kapse, Lt. General Andaman & Nicobar Island

Inaugurating Demonstration Model of Plasma Pyrolysis system

at Brookshabad, Andaman.

Plasma Nitriding System Installed at SINP

FCIPT has successfully installed and commissioned a plasma nitriding system at Saha Institute for Nuclear Physics (SINP), Kolkatta. SINP has the recognition of the University of Calcutta as a Center for conducting research for doctoral degrees and providing facilities for teaching and research in Physical and Biological Sciences. Basic research is carried out in frontline areas of Physical, Electronic and Biophysical sciences. Such activity is co-ordinated by six research groups in the academia like Biophysical Sciences, Condensed matter Physics, High Energy Physics, Microelectronics, Material Physics and Nuclear Science.

The Plasma nitriding system consists of a 300mm diameter and 300mm height bell shaped vacuum chamber connected to a 10KW, 30 kHz DC pulsed power supply as shown in Figure 1. The DC pulsed system consisted of a DC Power unit and a Switching unit. Sophisticated measurement instruments like absolute pressure gauges, mass flow controller and precision gas dosing valves were supplied along with the system. The system has safety and process interlocks along with process automation using microcomputer. An user-friendly, menu driven process software was provided for smooth uninterrupted operation. The system was supplied for carrying out basic research in glow discharge plasma nitriding.

Fig. 1: Plasma nitriding system supplied to SINP

Influence of Alloying Elements on the Corrosion Properties of Various Plasma Nitrided Steels

Plasma nitriding is one of the surface hardening processes widely used for improving wear, fatigue and corrosion properties of steel due to its beneficial features such as good reproducibility and low distortion of the treated parts. It is known that depending on the type of metals and corrosion environment, nitriding can either increase or decrease the corrosion resistance [1]. In general, the corrosion resistance of stainless steels is usually adversely affected by nitriding, whereas, beneficial effect can be obtained for low alloy steels [2]. It is reported that the improvement in corrosion resistance is related to the presence of the g' - nitride and the predominance of CrN precipitation is responsible for the deterioration in corrosion. Ibendorf and Schroter measured the surface corrosion potential of ferrous metals and indicated that the e- phase exerted a strong passivation tendency. The present study investigates the effect of alloying elements on the corrosion behaviour of steels after plasma nitriding.

Four different steels with varying amount of alloying elements were selected for plasma nitriding process. They are AISI 1045, 4340, H13 and 304 steels. Plasma nitriding was carried out in a plasma nitriding system described elsewhere [3]. The plasma nitriding process was performed with 35% of nitrogen and 65% of hydrogen gas mixture at 520 deg. C for 10 hours.

A typical microhardness depth profile for all steel samples are shown in Figure 1. Apparently the hardness increased after plasma nitriding. Plasma nitrided AISI 304 had a much higher hardness followed by AISI H13, AISI 4340 and AISI 1045. The profile shows that the hardness decreases gradually as a function of distance from the surface producing a diffused interface between case and core of the plasma nitrided steel in case of AISI 1045, AISI 4340 and AISI H13 steel.

Figure 2 shows the microstructure of the cross-sectioned plasma nitrided samples. A white layer of 8.8 microns and 6 microns in case of AISI 1045 and AISI 4340 steel was observed respectively with no evidence of diffusion layer. There was no white layer formation in case of AISI H13 and AISI 304 steel.

The electrochemical corrosion behaviour of AISI 1045, AISI 4340, H13 and AISI 304 without nitriding and after nitriding are shown in Figures 3 and 4. The excellent corrosion resistance of stainless steel has been attributed to the presence of native passive layer of Cr₂O₃. In the present work the plasma nitriding of SS led to CrN precipitation. The separation of Cr as a result of CrN precipitation led to the loss of its passivating property. The protection rates were highest in AISI 4340, followed by AISI 1045, AISI H13 and AISI 304 steel. Also, AISI 4340 and AISI H13 show the same trend of passivation after plasma nitriding process. This is due to the presence of
alloying elements like Mo, Ni and V.

b

a

c

d

Fig. 2 : Micrographs of cross-sectioned plasma nitrided (a) AISI 1045 (b) AISI 4340 (c) H13 and (d) AISI 304

Fig. 1: Microhardness depth profile of plasma nitrided steels

Fig. 3: Potentiodynmamic curves of untreated 1. AISI 1045, 2. AISI 4340, 3. AISI H13, AISI 304 steels

Fig. 3: Potentiodynmamic curves of treated 1. AISI 1045, 2.AISI 4340, 3. AISI H13, AISI 304 steels

It can be concluded that the low alloy steels had better corrosion resistance properties. The presence of thin white layer comprising of iron nitrides in case of low alloy steels AISI 1045 and AISI 4340 created a protective layer against corrosion. However potentiodynamic studies also indicated a better protection rate of AISI H13 steel compared to AISI 304. This increment could be due to the presence of alloying elements like Mo, Ni, and V, which extend the pre-passive potential to the noble direction.

Reference:

[1] Z. L. Zhang and T. Bell, Surf. Eng., 1 (1985) 131

[2] C. K. Lee and H.C. Shih, Corrosion, Vol. 50, 11(1995) 848

[3] I. Alphonsa, A. Chainani, P. M. Raole, B. Ganguli and P.I. John, Surface and Coating Technology, Vol. 150, 2-3 (2002) 263

DAE-BRNS Workshop on Plasma Surface Engineering

DAE-BRNS workshop on plasma Surface Engineering was organized on September 23-25, 2005 at BARC, Anushaktinagar, Mumbai. This workshop provided opportunities for active researchers, scientists and industries to review the current scenario, to report recent results, to share the available expertise and to consider future development directions in Plasma Surface Engineering. Eminent engineers and scientists shared their practical experiences in this field. Several lectures were conducted on topics that covered a wide spectrum of issues including plasma sources, deposition processes, coating characterization, performance assessment and applications.

Many scientists and engineers from FCIPT participated in this workshop. Dr. S. Mukherjee gave an invited talk on ‘Plasma Based ion Implantation’. He talked on the basic fundamentals of this process, elaborating more on the reactor design aspects. There were several papers presented by our engineers and scientist at the Poster session. Most of the current research activities were exhibited at this session. Every poster was reviewed by Prof. P.I John, IPR and Prof. S. V. Bhorasker, Pune at the poster rapporteur session.