Ramesh K. Guduru

Synthesis and characterization of Na0.44MnO2 from solution precursors

A simple, straightforward and less time consuming thermo-chemical conversion process was used to prepare submicron to micron size platelet/bar shaped single crystal powders of Na0.44MnO2 cathode material from an aqueous based solution precursor. Electrochemical characterization indicated a specific capacity close to the theoretical value (122 mA h g−1) with excellent cyclability.

A Brief Review on Multivalent Intercalation Batteries with Aqueous Electrolytes

Rapidly growing global demand for high energy density rechargeable batteries has driven the research toward developing new chemistries and battery systems beyond Li-ion batteries. Due to the advantages of delivering more than one electron and giving more charge capacity, the multivalent systems have gained considerable attention. At the same time, affordability, ease of fabrication and safety aspects have also directed researchers to focus on aqueous electrolyte based multivalent intercalation batteries. There have been a decent number of publications disclosing capabilities and challenges of several multivalent battery systems in aqueous electrolytes, and while considering an increasing interest in this area, here, we present a brief overview of their recent progress, including electrode chemistries, functionalities and challenges.

Synthesis and Microstructural Evolution of Amorphous/Nanocrystalline Steel Coatings by Different Thermal-Spray Processes

Amorphous/nanocrystalline coatings are useful in high strength and wear-resistant applications. In the present study, the microstructural evolution of a nanocrystalline high performance steel coatings developed by different spray processes along with a novel “hybrid thermal spray” technique was studied. The hybrid-spray process combines arc and high-velocity oxy-fuel (HVOF) techniques, in which the molten metal at the arcing tip is atomized and rapidly propelled toward the substrate by HVOF jet. This so-called hybrid concept offers the benefits of productivity of electric arc spray combined with improved coating densities of HVOF. The microstructural characterization of the hybrid-spray coatings was performed by x-ray diffraction, electron microscopy, and differential scanning calorimetry, and then compared with coatings of the similar material developed by plasma-, HVOF-, and arc-spray processes individually. The HVOF- and plasma-spray coatings showed amorphous structures with very fine nanocrystals embedded, whereas hybrid- and arc-spray techniques yielded completely crystalline coatings with grain size in the range of several nanometers. The final microstructures in different spray processes could be attributed to the precursor materials employed, process temperatures, and cooling rates during the deposition process.

Corrosion of Metal - Oxide Systems

Corrosion of materials occurs because of several factors; for example the application environment, operational conditions, presence of non-equilibrium phases, failure of the protective phases or layers in the materials, etc. In addition to the electro-chemical phenomena occurring in the corrosion process, operational conditions, such as temperature could influence the corrosion rates to different degrees depending on the materials involved. The effect of temperature is known to be severe on the corrosion phenomenon due to the dependence of corrosion rates on diffusion of materials. From the materials perspective, presence of non-equilibrium phases or second phases and their thermodynamic stability, microstructures, properties, and protective layers could affect the corrosion rates. Usually oxide systems are known for their protective behavior because of their stability and hindrance to the diffusion of different ionic species. Understanding their stability and role in prevention or slowing down of corrosion rates is, therefore, very important for engineers to design new material systems with desired properties and structures for corrosion resistant applications. Although metallic alloys with oxide second phase are extensively used in high temperature applications for creep resistance, literature suggests that addition of different kinds of oxide particles could help control the corrosion properties. In this chapter, an overview will be given on the corrosion behavior of different oxide systems and their role in corrosion resistant applications of the oxide particle embedded metallic systems in different environments, including low and high temperature applications.

Zinc oxide nanotips growth by controlling vapor deposition on substrates

ZnO nanotips structure fabrication was undertaken through controlled growth by chemical vapor deposition (CVD) method. Substrate position and deposition time role was investigated systematically by controlling the parameters such as temperature, flow rate, and growth pressure. The obtained result showed that ZnO nanorods undergo a sharp regrowth process with increase in ZnO vapor availability in the CVD reactor. The surface morphology and structural properties were investigated by using field-emission scanning electron microscopy and X-ray diffraction (XRD) techniques. The grown nanostructures were used for gas sensor fabrication to detect and to study the sensitivity effects of H2 and CO.

Mechanical Properties of Equal Channel Angular Extruded Magnesium Boride (MgB2) Powder in Tubes (PITs)

The MgB2 PITs, prepared by filling Fe tubes with MgB2 as a core, were processed through different number of passes at room temperature via Routes A, BA, C and BC. The mechanical properties of the PITs were measured in terms of density and hardness. The extent of the compaction was also studied through shear punch test. The shape of the compacts remains circular even after four passes via Route C & BC. Higher density and hardness along with higher USS is observed from the PITs of Route C compared to Route BC. The PITs processed through Route A and Route BA did not show sufficient compaction to carryout the density measurements. Thus, the current study shows that Route C is the optimal route; to attain good mechanical properties in ECAE processed MgB2 PITs with Fe tube.

Testing Techniques for Mechanical Characterization of Nanostructured Materials

Testing methods are reviewed that can be applied to the small sample sizes which result from many of the processing routes for preparation of nanocrystalline materials. These include the measurement of elastic properties on small samples; hardness, with emphasis on nanoindentation methods; the miniaturized disk bend test (MDBT); the automated ball indentation test (ABI); the shear punch test; and the use of subsize compression and tensile samples.