The research is in three broad areas:

1. Design by molecular modeling and the selection and testing of tailor-made specialty chemicals for improved plant performance by optimizing the process chemistry;

2. Optimization of industrial-scale unit operations using advanced modeling and simulation tools;

3. Development of technologies for economically viable and environmentally acceptable strategies for recycling, utilization and management of industrial and municipal wastes.

The interdisciplinary team works closely with its industrial partners and clients to deliver implementable solutions in a timely and cost-effective manner. Recently several projects related to these three areas have been implemented, leading to significant benefits to our industrial partners.

We present salient findings of our work carried out during the year in one of the in-house innovation research initiatives, namely, synthesis and processing of nano-particles for producing nano-structured products.

Synthesis and Processing of Nano Particles

We initiated research in two important and complementary areas:

1. Processes for bulk synthesis of nanoparticles amenable to easy scale-up and 

2. Colloidal processing of nanoparticles, comprising sub-processes like dispersion, consolidation and sintering of nanoparticles for producing nanostructured products.

The choice of these areas was based on a critical examination of the current status of the field and the strengths of our group in particle science and technology.

In order to translate the relevant physics and chemistry involved in production and processing of nanoparticles on the laboratory scale to successful technologies for producing commercially usable products, it is necessary to employ engineering concepts like scalability, reliability, reproducibility, standardization, productivity in process engineering design, control and optimization.

We have explored the method of producing metal nano-particles in an aqueous medium through a chemical reduction route. Silver particles of 136 nm size were obtained as stable suspensions (Figure 1).

One of the most difficult engineering challenges in the production of large nanostructured products from nanopowders lies in achieving full densification while retaining the nano structure in a defect-free microstructure. It is therefore important to understand the phenomena underlying dispersion, consolidation and sintering of nano-particles in order to model, simulate, optimize and control the fabrication processes. Close control of pore size and pore size distribution (narrow distribution is better) is the key to restrict grain growth and thus retain nanostructures in the final product.

Our approach involves the following three important steps

1. Design of suitable additives to enhance dispersion of nanopowders in aqueous suspensions, using advanced molecular modelling techniques;

2. Optimization of experimental conditions for arriving at a preferred consolidation technique which can provide a green compact having a finer pore size and a narrower pore size distribution;

3. Optimization of time-temperature sintering cycle (full densification at minimum grain growth) using a simulator based on the population-based modelling approach.

By a judicious combination of fabrication process conditions, namely, the choice of the dispersant and its dosage, appropriate consolidation technique (pressure casting) and an optimized sintering cycle, it was possible to achieve 95% density in the final product sintered at 1300oC having a grain size of around 100 nm only, from a Zirconia nanopowder of 70 nm size. Efforts are in progress to enhance the sinter density using a population balance simulator to optimize time-temperature sintering cycles for achieving full densification with minimum grain growth.

Similarly, starting with a relatively coarse fraction of zirconia nanopowder having a crystallite size of 30 to 60 nm (characterized by TEM) but available in aggregated form (laser scattering particle size of 738 nm), it was possible to obtain a sinter density of 97% (sintered at 1300oC for 4 hours) in the final product and a mean grain size of 210 nm

It is interesting to note that detailed porosimetry studies showed a bimodal pore size distribution with peaks at 90 nm and 15 nm in the green compact, which on sintering shifted to 12 nm and 7 nm respectively. Efforts are in progress to eliminate the coarser pores in order to enhance the densification kinetics