Tanu Srivastava’s research while affiliated with Defence Research and Development Organisation and other places

Liner materials have extensive applications in automobile industry, packaging, and aeronautics. One of the specific uses of such materials is in thermal barrier, coating rockets, missile, and other systems used in space and defense. Each liner material exhibits different properties according to their chemical structure and composition. In this study, accelerated thermal aging of the liner material, silicone‐hollow glass microsphere composite (SHGC) has been studied along with the determination of its life span. The effect of such aging on the thermal properties of SHGC has been studied using thermogravimetry. Activation energy of the process has been determined to be in the range of 45–55 KJmol⁻¹. The results have been compared with already reported silicon polymers. Shelf‐life of SHGC composite has also been determined using Arrhenius model. Stochastic model has been applied to determine the lower and upper limits of shelf‐life. Shelf‐life of SHGC is found to be 24 years with 28 and 18 years of upper and lower error limits.

In the present studies, silicon based low-density ablative material has been studied for its ablative performance to protect flight hardware from temperature raises due to aerodynamic forces for a longer duration. The oxyacetylene flame test estimates ablative properties at 100–120 W/m² heat flux. The time duration for the flame test is taken 200 s. The material shows low mass and linear ablation rate with high ablative effectiveness. The degradation kinetics of silicon ablator is studied by Thermo Gravimetric Analysis (TGA) method. Non-isothermal TGA is performed in the temperature range of 30 °C to 900 °C at various heating rates, viz. 5, 10, 15, and 20 °C/ min. Knowledge of the kinetic parameters of thermal decomposition is used to predict the degradation kinetics of the material at high heating rates, which the ablator faces during aerospace applications. During ablation, the silicone ablative material consists of a virgin zone, reaction zone, and char zone. These are explained by kinetic parameters determined with the help of free software called Kinetic Calculation.

Thermo-physical properties of hollow glass microsphere (HGM) filled silicone resin are analyzed by various mathematical models to optimize the formulation for a low-density high-temperature resistant composite. The study involves analyzing effective thermal conductivity, specific heat, and density for a two-phase particulate composite system by using the most popular expressions available in the literature at various volume fractions of HGM in the silicone resin matrix. Experiments are performed to compare theoretical results with the experimental data and identified the preferred composition with a density as low as 0.39 g/cc and thermal conductivity 0.116 W/m-K. The microstructural studies by SEM are done to explain the deviation in experimental and theoretical results. FEM analysis is done to understand the heat flow phenomenon in HGM filled silicone composites.

The high-temperature stability and thermal life of silicone resin-based potting compound (SC-3), used in the aerospace application for electrical insulation, is investigated Thermo-Gravimetry Analysis (TGA) in an inert environment. Nonisothermal TGA is performed in the temperature range of 30 °C to 900 °C at 10, 20, and 30 °C / min heating rates. The kinetic parameters such as activation energy and pre-exponential factor are obtained by the model-free method proposed by Kissinger-Akahira-Sunose (KAS) and Flynn Wall Ozawa (FWO) at various degree of conversion. The thermal degradation of the SC-3 compound is observed in the temperature range of 350 °C to 580 °C, and thermal endurance or time of failure of potting compound SC-3 is estimated as per ASTM E1877 standard. The results reveal that the potting compound SC-3 can be safely used continuously at 100 °C and for ~3.6 min at 350 °C. Experimental results are also useful to understand the degradation mechanism of the SC-3 compound.

A low density material coating based on silicone polymer matrix reinforced with hollow glass microspheres is developed for thermal insulation. An organo-platinum compound is added to the resin matrix to make it a fast room temperature curing coating. It has a low density in the order of 0.39–0.34 g/cc with medium Shore A hardness in the order of 60–65. The thermal stability in an inert and oxidative environment was analyzed by the TGA method. The insulative properties are investigated using an infra-red heaters test set up, which showed almost 50 % temperature reduction on the substrate compared to the non-coated substrate. The coating properties, like adhesion, impact resistance, corrosion resistance, etc., are analyzed using various bond promoters and excellent in the class of insulative coatings. The effect of various diluents on the curing is observed and then finalized the suitable diluents for spray coating. The coating forms hard silica char, which in turn protect the surface from further high temperatures. A scheme for painting the metallic and non-metallic articles is also established for ease of application to the user.

Structural epoxy adhesive was investigated for its thermal stability and degradation behaviour in a thermo-oxidative environment by thermogravimetry analysis (TGA). Non-isothermal TGA was performed at temperatures between 30 and 600°C utilizing different heating rates. The ageing characteristics of material were determined by an accelerated ageing study using isothermal TGA at different temperatures for 5% threshold conversion. The activation energies from both non-isothermal TGA and isothermal TGA were estimated and the activation energy values for 5% degradation from both the methods were in good agreement. The epoxy adhesive with titanium dioxide as filler showed a shelf life exceeding 13 years at ambient conditions (27°C). Additionally, the lap shear strength of the adhesive joint was also tested after treating the samples at 70°C with 90% relative humidity to evaluate the hydrothermal effect on adhesive joint.