Vol. 5 No. 6 December 1997
Optical Window Grade Zinc Sulphide
Zinc sulphide is an important material for the fabrication of infrared transmitting windows/domes used in areas like remote sensing. This is because of its excellent thermo-mechanical properties coupled with its very good transmission in 2-12 micron range of infrared.
The known processes for the preparation of zinc sulphide have the drawback that either the yield of optical window grade zinc sulphide is low or the process leads to irregular-sized particles with irregular physical properties or has impurities like zinc oxide.
DRDO has developed a process for the preparation of zinc sulphide which leads to high yield of the order of 70 to 80 per cent of optical window grade zinc sulphide. The grain size of the optical window grade zinc sulphide is relatively larger which reduces IR transmission losses and therefore accounts for its improved IR transmission capability.
Organo-Nickel Coordinated Compounds
The organo-nickel coordinated compounds having applications in some laser and laser-based systems are prepared by multistep processes wherein before each step, the intermeDIATe has to be transferred to a different reaction vessel. These processes result in lower yield and low purity of the product.
DRDO has developed an improved process for the synthesis of organo-nickel coordinate compounds. The process involves only two steps and is convenient as it does not require transfer of intermeDIATes to a different reaction vessel at each step. The process leads to higher yield and higher purity of product and is cost-effective.
Inorganic High Temperature Resistant Sealant
The high temperature resistant sealants are required in laser and electronic fields wherein the temperature encountered may vary from 800 to 1400 oC. The known organic sealants loose their property of adhesion or sealing at temperatures over 300 oC.
DRDO has developed a process for preparation of high temperature sealant which can withstand temperatures up to 1600 oC and high pressure of 4 to 6 atm. The process leads to higher yield and uses non-toxic oxides and water as solvent making it free from fire hazards. The sealant is capable of joining metal to ceramic as well as ceramic to ceramic.
Epoxy Non-Skid Paint
The non-skid paint is used to provide rough texture with requisite coefficient of friction to prevent slippage of personnel and VTOL aircraft while taking off and landing on the ship. The paint is also required to possess adequate thermal resistance to withstand stresses generated by hot fuel gases from the aircraft. The known non-skid paints have relatively short life and inadequate thermal resistance due to which the decks of ships necessitate frequent repainting.
DRDO has developed a process for the preparation of a non-skid paint which is abrasion and impact resistant to a fairly high degree. The paint has thermal resistance to withstand hot fuel gas emanating from the aircraft operating from the ship deck. The paint is resistant to sea water and kerosene and also has weathering resistance under ultraviolet raDIATions.
Rubber-based Passive Acoustic Materials
Acoustic baffles are used in large high performance transducer arrays for isolating ship noise as well as for improving directivity and sensitivity of transducer elements. The materials used for construction of baffles are required to possess specific acoustic and dynamic mechanical properties and have to be compatible with hostile marine conditions, such as salinity, sub-ambient temperature, hydrostatic pressure etc.
DRDO has developed a process for preparation of rubber-based passive acoustic material for construction of acoustic baffles. The material has a flat acoustic velocity in the operational frequency of 1-10 Hz, which has been possible because of the specific compounding materials used in the process for preparation of the material. The material obtained has the requisite mechanical properties for operations in deep sea conditions and has sea water resistance for conditions deployment around five years.
Rapid Estimation of Deterioration in Foods
Food materials deteriorate during storage as a result of chemical and bio-chemical reactions forming chemicals, such as acids, peroxides, aldehydes, ketones, hydrocarbons etc. These chemicals are responsible for off-tastes, off-flavour and deterioration in quality. The known kits for estimation of the deterioration are based on estimation of acidity, peroxide concentration, aldehyde level etc in the spoiled food material. The tests based on the known formulations used for testing the deterioration in foods are lengthy and time consuming. These tests require laboratory facilities for measuring deterioration in foods and therefore cannot be used for on-the-spot assessment of deterioration in foods.
DRDO has developed a formulation which is capable of testing the storage deterioration in food materials within 3 to 4 min. The testing with this formulation does not require any laboratory facilities. The formulation is stable with shelf-life of around eight months at ambient conditions.