Kishor Purushottam Gadkaree

Whisker reinforcement of glass-ceramics

Silicon carbide whisker reinforcement of anorthite and cordierite glass ceramics has been studied. At 25 vol% whisker loading the flexural strengths increased from 65–103 MPa to 380–410 MPa, the fracture toughnesses increased from 1.0–1.5 MPa m1/2 to 5.2–5.5 MPa m1/2. The strengths decline to 240–276 MPa at 1200 °C. The reasons for the decrease in strength with temperature are discussed. Whiskers from two different sources with differences in diameters and aspect ratios were evaluated and the effect of the whisker morphology on the composite properties was studied. It was found that larger diameter, higher aspect ratio whiskers result in improved composite performance. The composites were also characterized in terms of their thermal properties, i.e. thermal expansions and thermal conductivities. The thermal expansion coefficient from 25–1000 °C for anorthite-based composite was 4.6×10−6 °C−1 and that for the cordierite-based composite was 3.62×10−6 °C−1. The thermal conductivities at 1000 °C were 3.75 and 4.1 Wm−1 K−1 for cordierite and anorthite composites, respectively.

Particulate-fibre-reinforced glass matrix hybrid composites

This study extends the concept of hybridization of glass matrix composites to fibre and particulate reinforcements. Hybridization of Nicalon®-glass matrix composites with silicon carbide particulates of mean diameters of 0.77, 1.5 and 6 μm was studied. The microcrack stress, transverse strength and interlaminar strengths improved significantly on hybridization. At the optimum loading of 7.5 wt % for 6 μm particle size the microcrack stress increased by 62%, transverse strength by 650% and interlaminar shear strength by 200%. The ultimate strength declined for this composite by 6%. The decline in ultimate properties was attributed to the damaged graphitic skin at the particle-fibre contact points.

41.4: AMOLED based on Silicon-On-Glass (SiOG) Technology

We have demonstrated that the single crystalline silicon films on the glass substrates can be utilized in the conventional mass production lines. The single crystalline Si layers were transferred to the 370 mm × 470 mm glass substrates using Silicon-On-Glass (SiOG) technology. Using the thin film transistor backplanes made by conventional CMOS technology, 2.4″ qVGA AMOLED with integrated circuits were successfully fabricated. A completed 2.4″ qVGA AMOLED module shows wide viewing angle (> 170°) and 73% color gamut. The advantages of SiOG technology and its significances will be presented.

Hybrid ceramic matrix composites

A model hybrid glass-matrix composite has been studied. The system investigated was Corning Code 1723 glass matrix (an alkaline earth aluminosilicate glass) with silicon carbide whiskers and Nicalon® fibres. It was found that a 10 wt % whisker loading of the matrix gave optimum composite properties. The optimized hybrid composite, when compared to an optimized non-hybrid composite, showed increases in microcrack yield stress from 330 to 650 MPa, interlaminar shear strength from 47 to 130 MPa, and transverse strength from 12 to 50 MPa, while the ultimate strength decreased from 965 to 900 MPa.

Silicon-on-Glass (SiOG) substrate technology: Process and materials properties

This paper is an introduction to a new Silicon-on-Glass substrate technology. The fabrication process and material properties of SiOG are presented. The semiconductor film has good electrical properties, comparable to other SOI technologies, and is strongly attached to a large area transparent substrate via an in-situ barrier layer compatible with FPD processing.

Glass-ceramic matrix composites with high oxidation embrittlement resistance

A new concept is introduced to minimize the oxidation embrittlement problem exhibited by Nicalon fibre-reinforced glass-ceramic matrix composites. A small amount of glass is added to the matrix and deforms at temperatures of interest to prevent microcrack formation. The graphitic interphase is thus shielded from an oxidative environment. The composites fabricated with the glass-doped matrices show excellent room- and elevated-temperature strengths and withstand high stresses at elevated temperatures in air for greater than 100 h without any deterioration in properties. The modulus of the glass-ceramic phase, the stiffness percentage of dopant glass and the process temperature were found to affect composite properties significantly.

Thermodynamics of Lithium Intercalation in Randomly Oriented High Graphene Carbon

This paper covers details of systematic investigation of the thermodynamics (entropy and enthalpy) of intercalation associated with lithium ion in a structurally novel carbon, called Randomly Oriented High Graphene (ROHG) carbon and graphite. Equilibrated OCV (Open Circuit Voltage) versus temperature relationship is investigated to determine the thermodynamic changes with the lithium intercalation. ROHG carbon shows entropy of 9.36 J·mol−1·K−1 and shows no dependency on the inserted lithium concentration. Graphite shows initial entropy of 84.27 J·mol−1·K−1 and shows a strong dependence on lithium concentration. ROHG carbon (from −90.85 kJ mol−1 to −2.88 kJ mol−1) shows gradual change in the slope of enthalpy versus lithium ion concentration plot compared to graphite (−48.98 kJ mol−1 to 1.84 kJ mol−1). The study clearly shows that a lower amount of energy is required for the lithium ion intercalation into the ROHG structure compared to graphite structure. Randomly oriented graphene platelet cluster structure of ROHG carbon makes it easier for the intercalation or deintercalation of lithium ion. The ease of intercalation and the small cluster structure of ROHG as opposed to the long linear platelet structure of graphite lead to higher rates of the charge-discharge process for ROHG, when used as an electrode material in electrochemical applications.

Performance of Novel Randomly Oriented High Graphene Carbon in Lithium Ion Capacitors

The structure of carbon material comprising the anode is the key to the performance of a lithium ion capacitor. In addition to determining the capacity, the structure of the carbon material also determines the diffusion rate of the lithium ion into the anode which in turn controls power density which is vital in high rate applications. This paper covers details of systematic investigation of the performance of a structurally novel carbon, called Randomly Oriented High Graphene (ROHG) carbon, and graphite in a high rate application device, that is, lithium ion capacitor. Electrochemical impedance spectroscopy shows that ROHG is less resistive and has faster lithium ion diffusion rates (393.7 × 10−3 S·s(1/2)) compared to graphite (338.1 × 10−3 S·s(1/2)). The impedance spectroscopy data is supported by the cell data showing that the ROHG carbon based device has energy density of 22.8 Wh/l with a power density of 4349.3 W/l, whereas baseline graphite based device has energy density of 5 Wh/l and power density of 4243.3 W/l. This data clearly shows advantage of the randomly oriented graphene platelet structure of ROHG in lithium ion capacitor performance.