The science of coating surfaces to increase their ability to withstand wear and tear and, sometimes, impart lubrication has immensely helped industry. The newly launched Advanced Conformal-Coating Technology (AdCoaTech) lab at IIT-Madras is developing technologies to give Indian defence capabilities an ‘atmanirbhar coat’.

The AdCoaTech lab was set up jointly by DRDO-CVRDE lab and IIT in August. “This is the first-of-its-kind set-up in any academic institute in India for physical vapour deposition technique for conformal coatings on the inner surface of long cylinders and tubes,” says Dr N Arunachalam, Associate Professor, Manufacturing Engineering Section, IIT-M.

As India aims for self-reliance (atmanirbharta) in defence production, it would manufacture more weapons such as guns and tanks. As bullets and shells shoot through barrels, the friction generates tremendous heat. If a machine gun fires 100 rounds rapidly, the barrel can glow red hot — that’s why they have ‘barrel shrouds’ for the gunner to grip it safely. There is the same problem in the barrels of tanks and artillery guns.

It would greatly help if the insides of the barrels were ultra-smooth to reduce friction (and hence heat).

This calls for a suitable coating material for the insides of the barrels that can give both hardness and lubrication properties. Such coats find use in several other areas too. For example, the insides of the cylinders that house the pistons attached to a tank’s wheels — the up-down motion creates tremendous heat and wear-and-tear.

There are many methods for coating surfaces. Coating materials are deposited onto surfaces physically, chemically, in the form of plasma, or by cold spray — all of which are extensively used in industry — but coating the insides of surfaces is a challenge. The research in this area is for developing ‘recipes’ and the equipment that will do the coating. AdCoaTech lab has developed such coating equipment in collaboration with Excel Instruments, Mumbai.

As for the recipe, Dr Arunachalam’s team uses what is called ‘diamond-like carbon’. Diamond is the hardest material in the world, but how do you get it to stick to surfaces. Besides, aren’t they expensive? Well, no. In science, diamond is not necessarily a shining stone; it just refers to a particular structure of arrangement of carbon atoms.

Carbon atoms make three types of bonds — sp1, sp2 and sp3. “The bonding arrangements between carbon atoms produce different types of carbon allotropes such as graphite or diamond,” notes Prof Abdul Wasy Zia, of the City University of Hong Kong, in a 2020 scientific paper. In graphite, the carbon atoms form sp2 bonds with neighbouring carbon atoms to form a honeycomb-like structure. But if the bonds are of sp3 type (formed under extreme pressure and temperature), carbon exists as diamond. Diamond is very hard — around 100 giga pascals, as compared with graphite’s 3 GPa.

‘Diamond-like carbon’ coatings are a mixture of sp1, sp2, and sp3 carbon. The more the sp3, the better the tribological characteristics. ‘Diamond-like carbon’ coatings have been used in industry for long. However, IIT-M is perfecting the technology for defence applications — the collaboration with DRDO will develop complex coatings for the special needs of the defence forces. “The aim of this project is to develop diamond-based coating technologies, which are essential for DRDO’s immediate and future needs for defence components,” says Dr Arunachalam.

Prof MS Ramachandra Rao of the Department of Physics at IIT-M says the AdCoaTech lab has “produced innovative technology to develop diamond-based coatings on inner surfaces of industrial-scale cylinders, which conventional coating technology cannot achieve”. He said the coating dissipates heat and can withstand tremendous loads. “Pneumatic and hydraulic systems, aerospace parts, and defence vehicles are a few of the applications for these coatings,” Prof Rao said.

A new material that possesses high transparency in the visible and near infra-red (NIR) range and is also highly conducting could have promising application as transparent electrodes (TEs) in optoelectronic devices.

TEs are one of the critical components of optoelectronic devices and are based on materials that can be tuned to become simultaneously optically transparent and electrically conductive. These fundamentally contrasting attributes make it applicable in areas extending from energy generation and emission devices to gas sensors, low-emissivity windows, thermoelectric generators, and flat panel displays.

The most widely used TEs are based on metal oxide thin films like tin-doped indium oxide (ITO), fluorine-doped tin oxide (FTO), and aluminium-doped zinc oxide (AZO), with ITO extensively used for its high optical transparency in the visible range and low electrical resistivity.

Alongside the relatively low NIR transparency of the metal-oxide TEs, the scarcity, high cost and cytotoxicity of tin, toxicity of fluorine, and poor chemical stability of zinc oxide necessitate the development of new high-NIR transmittance TE with high visible transparency.

The development of infrared (IR) transparent electrodes (specifically in the near-infrared range) is crucial for improving the efficiency of certain optoelectronic devices and opening up applications in emerging areas like IR photodetectors, IR switching devices, sensors, and modulators for telecommunication.

Researchers at IIT-Gandhinagar, have developed a material with high transparency in the visible and NIR range that is highly conducting. Moreover, its abundance (hence cost-effectiveness), non-cytotoxicity, and chemical inertness make it a promising alternative, says a press release.

Low-cost stroke diagnosis

Researchers at the Indian Institute of Technology, Mandi, in collaboration with PGIMER Chandigarh have developed a simple, portable and cost-effective device to detect and diagnose stroke caused by impaired blood flow to the brain.

Ischemic stroke caused by insufficient or interrupted blood supply to parts of the brain affects one in 500 Indians each year.

Surveys have shown that 10-15 per cent of all strokes affect people below 40 years of age. The efficient management and treatment of stroke depends upon early identification and diagnosis.

Currently, magnetic resonance imaging (MRI) and computer tomography (CT) techniques are considered the gold standard for ischemic stroke detection. While these are indeed reliable methods, they require considerable infrastructure and high cost, and are inaccessible to many in India — there is only one MRI service for every one million people in the country.

“We are working towards finding a low-cost diagnostic technique to precisely detect ischemic stroke at the point of care so that such tests can be used in rural, poor and remote areas.

“Our team has designed and developed a small wearable device that makes use of near-infrared spectroscopy to detect ischemic stroke.

“In this device, a near-infrared light emitting diode (NIRS LED) emits light in the range of 650 nm to 950 nm. This light interacts with the coloured components of the blood like haemoglobin and provides information on blood characteristics such as regional oxygen saturation, regional oxygen consumption, and regional blood volume index,” says Dr Shubhajit Roy Chowdhury, Associate Professor, IIT-Mandi.