Showing papers by "National Aerospace Laboratories published in 2015"

PZT to Lead Free Piezo Ceramics: A Review

Abstract: The growth of piezo science is phenomenal since the discovery of piezoelectricity in 1880. Among various piezoelectric materials, lead zirconate titanate (PZT) is a very popular and exhaustively studied piezo system which allows synthesis of large number of materials with wide range of properties due to formation of solid solutions over large range of Zr:Ti ratio. Also, this system accommodates wide range of dopants for modification of crystal structure. Due to this versatile nature, PZT has emerged as very popular among users and researchers worldwide. However, considering the toxicity of lead oxide, development of lead free piezo ceramics is encouraged in recent years. Some lead free piezo material systems such as BNT, BKT, KNN, BZT-BCT have been explored. However, development of lead free piezo devices and their performance in comparison with PZT devices are yet to be established. At this juncture, it was felt that an article reviewing the current status of development of piezo materials highlighting t...

Dielectric and piezoelectric properties of PVDF/PZT composites: A review

Abstract: Smart materials, which exhibit piezoelectricity, find an eclectic range of applications in the industry. The direct piezoelectric effect has been widely used in sensor design, and the inverse piezoelectric effect has been applied in actuator design. Ever since 1954, PZT and BaTiO3 were widely used for sensor and actuator applications despite their toxicity, brittleness, inflexibility, etc. With the discovery of PVDF in 1969, followed by development of copolymers, a flexible, easy to process, nontoxic, high density alternate with high piezoelectric voltage coefficient was available. In the past 20 years, heterostructural materials like polymer ceramic composites, have received lot of attention, since these materials combine the excellent pyroelectric and piezoelectric properties of ceramics with the flexibility, processing facility, and strength of the polymers resulting in relatively high dielectric permittivity and breakdown strength, which are not attainable in a single phase piezoelectric material. The current review article is an attempt to provide a compendium of all the work carried out with reference to PVDF-PZT composites. The review article evaluates the effect of grain size, content and other factors under the purview of dielectric and piezoelectric properties while evaluating the sensitivity of the material for sensor application. POLYM. ENG. SCI., 55:1589–1616, 2015. © 2015 Society of Plastics Engineers

Evaluation of corrosion resistance and self-healing behavior of zirconium–cerium conversion coating developed on AA2024 alloy

Abstract: In the present investigation, a zirconium–cerium conversion coating (ZrCeCC) was developed on aerospace aluminum alloy (AA2024) by simple immersion technique. Zirconium conversion coating (ZrCC) was also prepared for comparison. Surface morphology of ZrCC and ZrCeCC specimens exhibited smooth and cracked patterns respectively. Elemental analysis showed the presence of Zr and Ce in ZrCeCC specimen. XPS results indicated the presence of multiple oxidation states of Zr and Ce in the developed coatings. Potentiodynamic polarization results revealed the corrosion current density (icorr) values obtained for both coatings (between 0.6 and 0.85 μA/cm2) were lower than bare specimen (1.2 μA/cm2). However, ZrCeCC specimen exhibited the lowest icorr value of about 0.46 μA/cm2 after 168 h of immersion in 0.6 M NaCl solution. EIS studies showed that higher coating resistance (Rcoat) value was obtained for ZrCeCC even after 168 h of immersion. The results obtained from simulated scratch cell test revealed a continuous increase in charge transfer resistance (Rct) value for bare specimen which was exposed along with ZrCeCC in 0.1 M NaCl solution. The self-healing behavior of ZrCeCC was confirmed from all electrochemical tests. After 168 h of neutral salt spray exposure, the surface of ZrCeCC was almost comparable with the conventional chromate conversion coating.

Improved electrochemical performance of Na0.67MnO2 through Ni and Mg substitution

Abstract: Incorporating nickel and magnesium into P2–Na0.67MnO2 is expected to suppress Jahn–Teller active Mn3+ ions, increase the average potential of the electrode through Ni4+/Ni2+ redox couples and stabilize M–O layers resulting in a smooth cycling profile with better capacity retention. In this communication, P2–Na0.67Ni0.25Mg0.1Mn0.65O2 is reported as the cathode material for rechargeable Na-ion batteries. It reversibly intercalates ∼0.52 moles of Na per formula unit in the voltage region of 1.5–4.2 V at C/10 rate which corresponds to a specific capacity of 140 mA h g−1. X-ray photoelectron spectroscopy has attributed the origin of the capacity in this phase to both Ni and Mn redox species active at different potential ranges. Substituting part of Mn with Ni and Mg increases the average potential of Na0.67MnO2 and improves the energy density of Na0.67Ni0.25Mg0.1Mn0.65O2 to 335 W h kg−1.

Graphitic-carbon nitride support for the synthesis of shape-dependent ZnO and their application in visible light photocatalysts

Abstract: Shape-dependent synthesis of ZnO has been developed on the surface of g-C3N4 following a simple and reproducible strategy. Initially, graphitic-carbon nitride (g-C3N4) was synthesized by pyrolysis of urea which was further used to grow ZnO nanostructures via refluxing conditions. Different hydrolyzing agents, such as hexamethylenetetramine (HMT) and ammonia were used to synthesize dumbbell and cone structures, respectively. Apart from hydrolyzing agents, cetyltrimethylammoniumbromide (CTAB) was also used as a growth controlling agent. Structural, morphological and optical characterizations of the as-synthesized materials were performed by using FESEM, TEM, XRD, XPS, UV-vis etc. techniques. After successful synthesis, the as-synthesized heterostructures were explored as visible light driven photocatalysts towards organic pollutant (methylene blue and phenol) degradation. The photocatalytic performances of bare ZnO, dumbbell and cone structures of g-C3N4/ZnO as well as g-C3N4, have been examined thoroughly. Photocatalytic results revealed that g-C3N4/ZnO heterostructures exhibit a higher efficiency under the illumination of visible light as compared to pure g-C3N4. Superior photodegradation activity of the g-C3N4/ZnO heterostructure originated from the synergistic effect and high charge separation at the interface of g-C3N4 and ZnO has also been discussed.

Noble metal ions in CeO2 and TiO2: synthesis, structure and catalytic properties

Abstract: In the past four decades, CeO2 has been recognized as an attractive material in the area of auto exhaust catalysis because of its unique redox properties. In the presence of CeO2, the catalytic activity of noble metals supported on Al2O3 is enhanced due to higher dispersion of noble metals in their ionic form. In the last few years, we have been exploring an entirely new approach of dispersing noble metal ions on CeO2 and TiO2 matrices for redox catalysis. In this study, the dispersion of noble metal ions by solution combustion as well as other methods over CeO2 and TiO2 resulting mainly in Ce1−xMxO2−δ, Ce1−x−yTixMyO2−δ, Ce1−x−ySnxMyO2−δ, Ce1−x−yFexMyO2−δ, Ce1−x−yZrxMyO2−δ and Ti1−xMxO2−δ (M = Pd, Pt, Rh and Ru) catalysts, the structure of these materials, their catalytic properties toward different types of catalysis, structure–property relationships and mechanisms of catalytic reactions are reviewed. In these catalysts, noble metal ions are incorporated into a substrate matrix to a certain limit in a solid solution form. Lower valent noble metal-ion substitution in CeO2 and TiO2 creates noble metal ionic sites and oxide ion vacancies that act as adsorption sites for redox catalysis. It has been demonstrated that these new generation noble metal ionic catalysts (NMIC) have been found to be catalytically more active than conventional nanocrystalline noble metal catalysts dispersed on oxide supports.

Plasma-based Radar Cross Section Reduction

Abstract: The concealment of aircraft from radar sources or stealth is achieved either through shaping, or radar absorbing coatings, or engineered materials, or plasma, etc. Plasma-based stealth is a radar cross-section (RCS) reduction technique associated with the reflection and absorption of incident electromagnetic (EM) wave by the plasma layer surrounding the structure. Plasma cloud covering the aircraft may give rise to other signatures such as thermal, acoustic, infrared, or visual. Thus it is a matter of concern that the RCS reduction by plasma enhances its detectability due to other signatures. This needs a careful approach toward the plasma generation and its EM wave interaction. This book presents a comprehensive review of the plasma-based stealth, covering the basics, methods, parametric analysis, and challenges toward the realization of the idea. The book starts with the basics of EM wave interactions with plasma, briefly discusses the methods used to analyze the propagation characteristics of plasma, and its generation. It presents the parametric analysis of propagation behavior of plasma, and the challenges in the implementation of plasma-based stealth technology. This review serves as a starting point for graduate and research students, scientists, and engineers working in the area of low-observables and stealth technology.

Wear and corrosion resistant properties of electrodeposited Ni composite coating containing Al2O3–TiO2 composite powder

Abstract: Electrodeposited Ni composite coatings containing ceramic particles have been widely investigated due to their improved mechanical, wear and corrosion resistant properties over plain nickel coatings. The application of one of the most widely studied plasma spray powder, Al2O3–13 wt-%TiO2, has not been explored in electrodeposited nickel composites. In the present study, Ni/Al2O3–13 wt-%TiO2 coatings have been electrodeposited using physically mixed commercial Al2O3 and TiO2 powders. The microhardness, wear and corrosion resistant properties of the coatings have been investigated. It was found that the area fraction of particles incorporated in the nickel matrix was very high at lower current density, and the corresponding composite coating exhibited a maximum microhardness (∼580 HK). Interestingly, corrosion resistance of Ni/Al2O3–13 wt-%TiO2 composite coating was similar to that reported for Ni/TiO2. The wear behaviour of Ni/Al2O3–13 wt-%TiO2 coating was in between Ni/Al2O3 and Ni/TiO2 coatings a...

Active radar cross section reduction : Theory and applications

Abstract: This book discusses the active and passive radar cross section (RCS) estimation and techniques to examine the low observable aerospace platforms. It begins with the fundamentals of RCS, followed by the dielectric, magnetic and metamaterials parameters of the constituent materials and then explains various methods and the emerging trends followed in this area of study. The RCS estimation of phased array including the mutual coupling effect is also presented in detail in the book. The active RCS reduction is carefully touched upon through the performance of phased arrays, sidelobe cancellers and mitigation of multipath effect. Providing information on various adaptive algorithms like least mean square (LMS), recursive least square (RLS) and weighted least square algorithms, the authors also mention the recent developments in the area of embedded antennas, conformal load bearing antenna, metamaterials and frequency selective surface (FSS) based RCS reduction.

High-Temperature Piezoelectrics with Large Piezoelectric Coefficients

Abstract: High-temperature piezoelectric materials are of interest for sensors and actuators in various industrial applications in which the devices are exposed to high temperature. A lot of research has been conducted in this area to bring forth a suitable piezoelectric material having a high Curie temperature for suitable usage at a high temperature with good piezoelectric properties. This report is an attempt to review the state of the art in high-temperature piezoelectric materials, covering their issues and concerns at elevated temperatures. Among the non-ferroelectric crystal classes, langasite and oxyborate crystals retain their piezoelectricity up to a very high temperature, but their piezoelectric coefficient is much smaller compared to a standard piezoelectric material such as lead zirconate titanate. A similar trend has also been observed in ferroelectric crystal class which shows poor piezoelectricity but retains it until a high temperature. Recent studies on solid solutions of bismuth-based oxides and lead titanate with the chemical formulae Bi(Me3+) O3-PbTiO3 and Bi(Me1Me2)O3-PbTiO3 (Me3+ represents a trivalent cation and Me1 and Me2 are cations having a combined valency of 3) show a much application potential of these materials due to improved piezoelectric property and high Curie temperature. BiScO3-PbTiO3, Bi(Mg0.5Ti0.5)O3-PbTiO3, (Bi(Ni0.5Ti0.5)O3-PbTiO3 and Bi(Zn0.5T0.5)O3-PbTiO3 are some interesting high-temperature piezoelectrics from the group of Bi(Me3+)O3-PbTiO3 and Bi(Me1Me2) O3-PbTiO3 which shows superior piezoelectric properties at high temperatures. Among the lead-free piezoelectrics, (K0.5Na0.5)NbO3 demands a special interest for further studies due to its plausible good piezoelectric property at elevated temperature.

Study of the structural, thermal, optical, electrical and nanomechanical properties of sputtered vanadium oxide smart thin films

Abstract: Vanadium oxide thin films were grown on both quartz and Si(111) substrates, utilizing a pulsed RF magnetron sputtering technique at room temperature with the RF powers at 100 W to 700 W. The corresponding thicknesses of the films were increased from 27.5 nm to 243 nm and 21 nm to 211 nm as the RF power was increased from 100 W to 700 W for the quartz and silicon substrates, respectively. X-ray diffraction and field emission scanning electron microscopy were carried out to investigate the phase and surface morphology of the deposited films. The electronic structure and the vanadium oxidation states of the deposited films were investigated thoroughly by X-ray photoelectron spectroscopy. The as-grown films show only stoichiometric vanadium oxide, where vanadium is in V5+ and V4+ states. The phase transitions of the vanadium oxide films were investigated by the differential scanning calorimetric technique. The reversible i.e. smart transition was observed in the region from 337 °C to 343 °C. The average hemispherical infrared emittance of the deposited vanadium oxide films was evaluated by an emissometer in the wavelength range of 3 μm to 30 μm. The sheet resistance of the deposited films was measured by a two-probe method and the data were in the range of 106 to 105 Ω per square. The optical properties of the films, such as solar transmittance, solar reflectance and solar absorptance, as well as optical constants e.g. optical band gap, were also evaluated. Finally, mechanical properties such as the hardness and the Young’s modulus at the microstructural length scale were evaluated by employing a nanoindentation technique with a continuous stiffness mode.

Terahertz Antenna Technology for Space Applications

Abstract: The terahertz (THz) band provides a transition between the electronic and the photonic regions thus adopting important characteristics from these regimes. These characteristics corresponding with the progress in semiconductor technology has enabled researchers to exploit hitherto unexplored domains including satellite communication, biomedical imaging, security systems, etc. This book, explores the terahertz antenna technology toward implementation of compact, consistent, and cheap terahertz sources, as well as the high-sensitivity terahertz detectors. The advances in new materials and nanostructures such as graphene will be helpful in miniaturization of antenna technology while simultaneously maintaining the desired output levels. Terahertz antenna characterization of bandwidth, impedance, polarization, etc. has not yet been methodically structured and it continues to be a major research challenge. This book addresses these issues besides including the advances of terahertz technology in space applications worldwide, along with possibilities of using this technology in deep space networks.

Electromagnetic Techniques and Design Strategies for FSS Structure Applications [Antenna Applications Corner]

Abstract: Frequency-selective surfaces (FSSs) have a wide spectrum of applications in airborne platforms, wireless communication systems, medical imaging instruments, and high-power microwave systems. To employ finite, electrically large, and conformal FSSs for such applications, the development of an efficient electromagnetic (EM) design and analysis technique is essential, which is a challenging task in terms of computational complexity and requirements of highend computing platforms. In view of assessing the efficacies of various EM techniques for the design and analysis of FSS structures employed for planar and conformal surfaces, a brief review is presented here. Furthermore, the design strategies of novel FSS structures including metamaterial (MTM)-element FSSs are discussed for specific applications such as highperformance radomes, radar absorbing structures (RASs), and antennas. The complex issues associated with the EM design and analysis of FSS structures are also outlined for radomes, RAS, and antennas.

Hygro-thermo-electric properties of carbon nanotube epoxy nanocomposites with agglomeration effects

Abstract: In the present study, the effective electric, thermal, and moisture properties of carbon nanotube (CNT) epoxy composites are derived by considering the agglomeration effect of CNT concentrations in the epoxy matrix In this direction, the Voigt and Reuss homogenization method is adopted in the derivations It is well known from experiments that the CNT thermal and electrical conductivities and the epoxy hygro-thermal expansion coefficients have significant effects on the behavior of CNT nanocomposites Moreover, it has been experimentally proved that the agglomeration of CNTs in the matrix with high and low concentrations of the CNTs certainly affects the resistivity and, hence, the thermal expansion properties Therefore, the effective elastic, thermal, electrical, and moisture properties for the randomly distributed CNTs in the matrix has been derived in terms of the agglomeration volume fractions of CNTs In the effective relations, a single agglomeration parameter is considered to be active for a give

Effect of plasma nitriding on structure and biocompatibility of self-organised TiO2 nanotubes on Ti–6Al–7Nb

Abstract: TiO2 nanotubes formed by anodic oxidation of Ti–6Al–7Nb were nitrided in a nitrogen plasma. The samples were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), nano hardness testing (NHT) and field emission scanning electron microscopy (FESEM). The corrosion behaviour of the substrate, plasma nitrided substrate, substrate with self-organised TiO2 nanotubes (TNT) and with plasma nitrided TiO2 nano tubes (TNT + PN) was investigated through electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization studies in simulated body fluid (Hanks' solution). The investigations show that the native oxide on the sample is replaced by a self assembled nano array by an anodisation process. XPS spectra of the TNT plasma nitrided sample show the presence of oxy nitride and nitride on the surface. The nano hardness of the samples was increased after nitriding. FESEM images of samples immersed in Hanks' solution show that growth of calcium phosphate phases is more and the size of the deposits are larger on TNT and nitrided TNT samples, as compared to the untreated substrate. XPS spectra of TNT and nitrided TNT samples immersed in Hanks' solution show a higher amount of calcium, phosphorous and oxygen than on the substrate. Electrochemical studies show that nitriding decreases the corrosion resistance.

Cu/TiO2 thin films prepared by reactive RF magnetron sputtering

Abstract: Cu/TiO2 thin films were deposited on glass substrates by reactive RF magnetron sputtering technique. Crystalline structure, surface morphology and electronic structure were studied using X-ray diffraction (XRD), field emission scanning electron microscopy, atomic force microscopy and X-ray photoelectron spectroscopy (XPS). Transmittance and absorptance of these films were characterized by UV–Vis spectroscopy. XRD patterns demonstrate that TiO2 films deposited on glass substrate at 300 °C are observed to be in pure anatase phase, whereas Cu/TiO2 films are amorphous in nature at 300 °C substrate temperature. The crystallinity of Cu/TiO2 thin films decreases with increasing the dopant concentrations of Cu in TiO2 films. XPS studies show that Cu is in +2 oxidation state in all films. The optical band gap of Cu/TiO2 films decreases from ~3.3 to ~2.0 eV with the increase in the copper concentration. Further, antimicrobial studies of Cu/TiO2 films with ~3.9 at.% Cu exhibit high transmittance and best antimicrobial activity against E. coli and S. aureus compared to other doped films.

Flight validation of an embedded structural health monitoring system for an unmanned aerial vehicle

Abstract: This paper presents the design and flight validation of an embedded fiber Bragg gratings (FBG) based structural health monitoring (SHM) system for the Indian unmanned aerial vehicle (UAV), Nishant. The embedding of the sensors was integrated with the manufacturing process, taking into account the trimming of parts and assembly considerations. Reliable flight data were recorded on board the vehicle and analyzed so that deviations from normal structural behaviors could be identified, evaluated and tracked. Based on the data obtained, it was possible to track both the loads and vibration signatures by direct sensors’ cross correlation using principal component analysis (PCA) and artificial neural networks (ANNs). Sensor placement combined with proper ground calibration, enabled the distinction between strain and temperature readings. The start of a minor local structural temporary instability was identified during landing, proving the value of such continuous structural airworthy assessment for UAV structures.