Contamination of walls, floors and surfaces of many articles that we use in day-to-day life is the main reason why a disease spreads rapidly and ensuring these surfaces to be free of microbial contamination, especially in hospitals, is an important factor in maintaining the general health of people. Silver in the form of metallic silver or silver salts is known to be toxic to micro-organism, particularly bacteria while being relatively harmless to a man. When nano scaled silver is introduced to a hybrid sol-gel matrix, it results in an antimicrobial coating due to the silver and scratch resistant due to the inorganic network of sol-gel coatings providing high degree of abrasion resistance too. This helps in retarding the growth of microbes and thus minimizes the use of autoclaving process or cleaning using harsh chemicals. Other functionalities such as easy to clean property can also be incorporated into the coatings.
- Incorporation of anti-microbial nanoparticles, controlled release mechanism
- Easy-to-clean coatings have surface properties comparable to perfluorinated polymers (hydrophobic surface)
- SS sheets in hospital wall panels
- Medicine/Pharamaceutical: Medicine bottles/containers
- Health care: Hearing aids, hospital furniture
- Food packaging
- Textile and fabric: textile walls and textile roofs, sun shades, blinds
Anti-microbial coatings For door mats
Antimicrobial Coatings on SS Kidney Trays
Metals look attractive due to their luster and texture depending on finishing process and are used in innumerable applications due to their strength, ease of formability and hardenability. Metals such as stainless steel, tarnish when used at high temperature and aluminium can even easily corrode in saline environment. Organic paints and toxic hexavalent chromium-based conversion coatings are being used to overcome corrosion related problems. Sol-gel glass like coatings offer excellent abrasion resistance and protection against corrosion while being eco-friendly, maintaining transparency and gloss. These coatings offer excellent tarnish resistance upto 500oC and can even be made coloured by introducing suitable pigments.
- Anti-fingerprint, easy-to-clean
- High scratch hardness and abrasion resistance
- High temperature tarnish protection
- Low temperature curable compositions used as replacement for chrome-free primers
- Protection against acid attack and ion leaching
- Coloured coatings possibility
- Household appliances
- Medicine and health care:medical/surgical instruments
- Automotive: exhaust parts for motor cycles, cars
Automotive, Architectural, Health-care
Transparent corrosion and scratch resistant coatings on carbon steel
Coloured tarnish resistant glass like coatings on stainless steel
Coloured scratch resistant coatings on cooking utensils
Health and Hygiene care products based industries have a huge market and their products are of primary importance because of increased awareness among population for health and hygiene. These industries have a huge demand for an efficient and economic antimicrobial material to improve the performance of their products. Since ancient times antimicrobial properties of gold, platinum, silver, copper, zinc and mercury are well known and they have been in use as anti microbials in the form of metals or as their compounds, eg. Silver or, silver sulpha hydrazine. Among the noble metals silver being affordable is used extensively as an anti microbial material in many products like wound dressing, water treatment, etc. As reported in literature, silver can effectively kill fungus, 650 families of bacteria and few viruses also. Lower concentrations of nano silver kills unicellular micro organisms whereas, it is inactive towards multi cellular human cells. Hence, silver is a safe and an effective antimicrobial material. Nano silver opens new dimensions of the well-known anti-bacterial properties of bulk silver. It also gives us the privilege of utilizing the antibacterial properties of silver at an affordable cost. With this motivation ARCI had initiated the project on nanosilver for antibacterial applications. Realizing the potential of nano silver as an antibacterial material we have made an attempt to develop nano silver coated antimicrobial water filters and textiles. Both the projects started with laboratory experiments to develop novel synthesis methods, continued with proof of concept by demonstrating the antibacterial performance and finally scaled-up for large scale synthesis. Both the technologies were successfully transferred to Indian industries.
Pulsed electrolytic deposition is a novel and economical technique for deposition of nanocrystalline coatings on variety of metallic as well as plastic substrates. The basic advantage over conventional direct current deposition includes virtually porosity free coatings, better surface finish and higher deposition rates. Apart from these, the choice over changing pulse parameters to control the coating properties results in near net shape components without post treatment. The pulsating current allows deposition of coatings with controlled mechanical properties as well as composites. At present we are looking into development of graded, layered coatings, hard chrome replacement coatings and galvanic zinc coatings using pulsed electrodeposition.
A.Pulsed Electrodeposition (PED) of nanocrystalline coatings
The process parameters have been fine tuned to control the grain size within 10-200 nm range for pure nickel coatings. This economical process can deposit bulk coatings with desired mechanical properties. The compositional analysis and mechanical properties obtained led to understand the mechanism of coating formation. The novel process can also be applied to variety of coatings such as Cr, Zn and Cd deposited using pulsed current deposition. Common applications involving PED coatings are automobile, communications, space etc.
B.Pulsed Electrodeposition of layered and graded coatings
The graded and layered coatings have been reported to exhibit excellent improvement in corrosion and tribological properties over their monolithic counterparts. These coatings have found numerous applications in magnetic storage media, dental implants, articulated surfaces in hip and knee prosthesis etc. The precise control over deposition parameters is the key issue towards development of these coatings which ultimately determines their service life. Given the advantages of pulsed electrodeposition (PED), we have reported for the first time the control over the microstructure by electrodeposition of graded as well as layered structure from a single electrolytic bath without alloying and utilizing least possible quantity of additives and grain refiners.
C.Pulsed Electrodeposition of galvanic Zinc coatings
Zinc (Zn) is widely accepted as a sacrificial coating on ferrous components in automobile, construction, marine industries. The fact that Zn not only corrodes slowly during atmospheric exposure as compared to the bare steel but also provides an adequate corrosion protection in or near water, soils and marine environment, makes it most widely available metal utilized for cathodic protection of steel. It offers barrier protection by providing a layer between the underlying ferrous substrate and the corrosive elements of environment. Given the advantages of PED, ARCI has recently initiated a research activity on Zn coatings, utilizing pulsed electrodeposition. The present work investigates the influence of direct current (DC), pulsed current (PC) and pulsed reverse current (PRC) deposition modes employed for Zn coatings on the corrosion resistance of mild steel. Amongst the electrodeposited coatings pulse reverse electrodeposited Zn provides best sacrificial effect i.e. the slower the corrosion, and therefore protects the underlying mild steel substrate.
D. Development of Hard chrome replacement Nickel Alloy coatings
(DST-SERB Sponsored Project)
During last 6 decades, hard chrome layers have gained wide acceptance as durable and high performance coatings on structural as well as engineering parts for wear and corrosion resistance. The hard chrome process utilizes chromium in hexavalent state in the plating bath (Cr6+) is a known carcinogen that evolves in the form of fumes during the process. Any methodology aimed at reducing emission level in turn increases the effective coating cost. Several countries especially in Europe have imposed a ban on use of Cr6+ in the bath. This led to interest in finding suitable replacement globally using either thermal spray or electroplating. Electroplated Ni-W coatings have the potential to be a promising alternative for hard chrome replacement due to its hardness and high temperature thermal stability. The present work focuses on the development of Ni-W alloy coating employing a novel pulsed electrodeposition technique that has already yielded emerging preliminary results.
E. Copper-Graphene Composite Foils with High Hardness by Pulse Reverse Electrodeposition
Metal matrix nanocomposites have witnessed an enormous attention during the past decade, due to the feasibility of controlling the mechanical, electrical and thermal properties which lead to numerous industrial applications. Since the emergence of carbon nanotubes (CNTs), the use of composites has taken a new turn for the industrial applications due to their superior features compared to the oxide and carbide nanopowders. Discovery of graphene gave a possibility to replace the CNTs in the composites. Graphene exhibits extremely superior physical, mechanical (Young's modulus of ~2 TPa and tensile strength of ~130 GPa), electrical (Electrical conductivity~106 O-1cm-1) and thermal properties (K~ 5000 W m-1 K-1) when compared with to CNTs. In addition, its open structure/sheet like structure, high surface area and available contact area inhibit the entanglement of graphene unlike CNTs, when it is reinforced into the matrix making graphene as an ideal filler compared to CNT reinforcement. Metal matrix graphene reinforced composites have been studied very recently with Al, Mg, Cu and Ni by several methods. Electrodeposition is an economical and suitable process for electronic applications. Pulse reverse electrodeposition (PRED) technique exhibits enhanced properties of the foils in terms of density, roughness, porosity etc., due to minimal residual stresses, grain refinement etc.
Graphene reinforced copper (Cu-Gr) composite foils were prepared by PRED technique in order to enhance the mechanical properties of copper. The presence of graphene was confirmed by TEM (Fig 1). Hardness and elastic modulus of the copper and Cu-Gr foils weare studied by nanoindentation technique. Hardness and elastic modulus calculated from the load-displacement curves for the copper and PR electrodeposited composite foils show that there is a significant enhancement in the values of hardness for the composite foils compared to that of pure copper foil. Graphene reinforced copper composite foils exhibit a higher hardness in the range of 2.2 - 2.5 GPa for different set of foils prepared by PRED compared to 1.5 - 1.6 GPa observed for pure PR deposited copper foils. Although a small increment in the hardness is observed for copper foils after annealing, probably due to the formation twins, the values are much lower than those obtained for both as-deposited and annealed Cu-Gr foils. Decrement in the hardness upon annealing of Cu-Gr composite films is very less and can be attributed to the effective inhibition of grain growth by graphene which is uniformly distributed throughout grain boundaries, inhibiting the dislocation motion.
TEM micrograph illustrating grains in PED Ni coating
Magnesium aluminate spinel based scaffolds are processed and being evaluated for the biocompatibility with INMAS (DRDO). Initial results are found encouraging.
A process suitable for generation of transparent, antireflective and scratch resistant coating on transparent plastics, especially polycarbonate.
Plastics especially transparent plastics are used to replace mineral glass in both industrial and domestic environment due to their low density and shock resistance. But they are easily prone to scratches and abrasion as they are soft in nature. They reflect about 10-12% of the visible light thereby decreasing transmission. Sol-gel antireflective cum scratch resistant coatings can enhance their visible light transmission, maintaining the scratch resistance.
Salient features of the coating:
- Visible light transmission -97%
- Haze change after 1000 cycles of crockmeter testing using fibre: <2%
- Can be applied on window glass also
Patent application filed, if any:"An improved composition for antireflective coating with improved mechanical properties and a process of coating the same" patent application number 2330/DEL/ 2013 on 05/08/13.
Self-cleaning coatings can be divided into two categories: hydrophobic and hydrophilic. The former class of coatings is based on the lotus effect and the later is based on photocatalysis. TiO2 is well known photocatalyst that is used for self-cleaning applications. Due to the versatility of sol-gel coating technique, self cleaning TiO2 coatings generated by sol-gel process are expected to be viable for commercial exploitation.
Dip, spray and flow coating process can be used to get transparent wet gel TiO2 thin film on soda lime glass (SLG), fused silica glass (FSG) and glazed ceramic wall tiles (GCWT). The final dense TiO2 thin film can be obtained by firing the wet gel film at temperatures higher than 450oC in a continuous belt furnace at the production rate of 3.5 m2/h. The coating thickness, refractive index and microstructure properties were analyzed using variable angle spectroscopic ellipsometry (VASE) and validate the proposed model using transmission electron microscopy (TEM). The self-cleaning stain removal ability of the TiO2 coated glazed tiles was demonstrated using a permanent marker stain. Figure shows the degradation activity of stain made using permanent marker ink on spray and flow coated ceramic glazed tiles. Figure shows two zone TiO2 coated (bottom) and uncoated (top) area. The permanent marker stain made on uncoated area is clearly visible after 55 h exposure to sun light, whereas, the stain made on TiO2 coated zone is rarely visible because of photocatalytic degradation.
- Self- cleaning and self sterilizing surfaces
- Hydrophilic surface formation facilitating easy cleaning by rain or rinsing with water (self-cleaning effect)
- Self-cleaning coatings activated by sunlight/artificial UV light
- Long life, strongly enhanced UV protection by TiO2
- Architectural glass and tiles
- Medical/Pharmaceutical: Medicine bottles/containers
- Textiles and fabric: textile walls, textile roofs, sun shades and blinds