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Amorphous and crystalline SiC nanoparticles were synthesized via laser ablation of SiC micro-sized powder in water and ethanol. X-ray and HRTM analysis showed the amorphous nature of SiC nanoparticles with an average particle size of 44 nm in water and crystalline 6H-SiC polytype nanoparticles with an average size of 18 nm in ethanol. The direct and indirect bandgap of SiC nanoparticles were determined from UV–visible absorption spectra. PL emission characteristics were studied and crystalline SiC nanoparticles exhibit tunable PL emission covering UV to the visible region.

This communication reports hydrothermal synthesis of molybdenum trioxide (MoO3) with long microsheets morphology and their gas sensing characteristics through clad-modified fiber optic gas sensor technique. Synthesized material is subjected to characterization analysis including XRD, SEM and Raman Spectra. Spectral analysis on the gas sensing characteristics reveal that MoO3 microsheets exhibit good gas response to methanol at room temperature. Gas sensing mechanism is also discussed.

This communication reports multiferroic perovskite, nano crystallite BiFeO3 coated clad modified PMMA Fiber optic sensor functioning at room temperature and sensing Toxic gas in the environment. The porous BiFeO3 nanocrystalite clusters synthesized through solvothermal process and its structure, composition and morphology are analysed using XRD, EDAX and SEM. The crystallites were in agglomerated dimensions with pores up to 500 nm, average particle size 30 nm with rombohedral crystal structure. And it is used in the Fiber optic sensor modifying the original PMMA clad. Spectral response for BiFeO3 clad modified sensor is observed for Ammonia, Ethanol and Methanol, and the better sensitivity is found for Ammonia at room temperature compared to the other two vapours ethanol and Methanol.

We report on the growth of large size organic single crystal of a C2-symmetric bis amide molecule, N,N′ bis(4-nitrophenyl)-(1R,2R)-diaminocyclohexane (BNDC) for the first time. Optical quality BNDC single crystals of sizes 1.7 × 1.9 × 0.5 cm3 and 1.5 × 0.5 × 0.2 cm3 are successfully grown from mixed solvents by varying the molar ratios. The physical properties of the as-grown BNDC crystals are studied and discussed in detail. From the powder X-ray diffraction study, the lattice parameters of the as-grown BNDC crystal are determined to be a = 10.237 A, b = 12.827 A and c = 13.622 A (α = β = γ = 90°) which matches with the reported CCDC file (155122). BNDC crystal melts at 212 °C and no phase change behavior is observed. BNDC crystal shows good optical transmittance between 519 and 2000 nm. The slim P–E hysteresis loop reveals soft magnetism in BNDC crystal. The presence of ferroelectric domains is visualized using AFM. We demonstrate the THz generation in BNDC crystal for the first time using Ti:Sapphire Laser with a wavelength of 800 nm of 140 femtosecond pulses with 80 MHz repetition rate. We employed optical rectification technique for THz generation, and efficiency of generated power of the electric field for BNDC crystal was of the order of 10–4 V at 700 mW incident laser power.

Friction welding of tube-to-tube plate using external tool (FWTPET) 1 is an innovative friction welding process wherein a friction stir welding tool is used to join tube and tube plate. This work investigates the combined effects of tool rotation speed and plunge duration in terms of a parameter named Total Welding Rotation (TWR) 2 , on the quality of FWTPET joints. A mathematical model is proposed to understand the upper and lower limits of TWR, beyond which the process is inclined to give defective joints. This model is verified using experimental studies on joints between AA6061 plate and AA1060 tube. The welded specimens are non-destructively evaluated using Digital Radiography (DR) 3 and Phased Array Ultrasonic Testing (PAUT) 4 , which show that above and below certain TWR values the process leads to defective joints.

Pulsed laser ablation in liquid technique (PLAL) had started getting attention in late 1990, particularly for the production of the nanomaterials due to its easy handling and room-temperature synthesis process. Soon after the initial demonstration of nanomaterials generation from the PLAL technique, PLAL gradually becomes a green, facile and inexpensive method for the generation of ultrapure carbon nanomaterials (CNMs). In the past two decades, different allotropic forms of CNMs have been fabricated by using PLAL techniques such as graphene/graphene oxide nanosheet, carbon nanotubes, graphene oxide quantum dots, nanodiamonds, carbogenic nanoparticles, polyynes and carbon-encapsulated metal-based nanoparticles. In this review article, we offer a comprehensive discussion on the progress achieved in the design and development of the PLAL method for the production of CNMs only (the year 1998–2020). Firstly, we have introduced the different types of PLAL methods widely used for CNMs fabrication. Secondly, the different types of factors affecting the physicochemical (structural, morphological, optical) properties of CNMs and the efficiency of CNMs production from PLAL method have been summarized in detail. The laser parameters and experimental conditions of the PLAL method, that affecting the physicochemical properties and efficiency of CNMs production are laser wavelengths, pulse duration and repetition rate, ablation duration, per-pulse energy density (fluence), PLAL setup design and nature of solvents. The results from different spectroscopic techniques for each kind of CNMs have been discussed thoroughly, to unambiguously differentiate the structural integrity of the CNMs from one another. Finally, the uses of CNMs for different applications in the present time, existing challenges in the PLAL methods and the future outlook of laser-assisted synthesized CNMs for novel applications were also discussed.

Conventional Friction welding is a well-established solid state welding process. However, this method has a limitation that it is not suitable for tube to tube plate welding. An innovative variant of this process, named Friction welding of tube to tube plate using an external tool (FWTPET) is gaining popularity in industrial applications as a potential alternative to its fusion welding counter parts. This process can be used to join not only similar but also dissimilar metals. The major parameters of this process include the speed of rotation of the tool, plunge depth and plunge duration. In this work, the effect of plunge duration and tool rotational speed on the quality of FWTPET process is investigated using visual examination and microhardness analysis of tube to tube plate joints between two grades of Aluminium alloys welded under various conditions. The results of the visual inspection are used to examine the parameters for optimal flash deposition without causing excessive internal material loss. The effect of plunge duration and tool rotation speed, on the microhardness of the weld, is also studied in this work and the results show that at higher plunge durations and tool rotational speeds, the micro hardness tends to drop. Microstructural analysis shows that the grain coarsening happens due to dynamic recrystallization, similar to that in Friction Stir Welding.

Friction welding of tube-to-tube plate using external tool (FWTPET) is a novel variant of friction welding process for joining tubes to tube plates. This process has the capability of producing leak proof joints between similar or dissimilar materials. Being a solid state welding process FWTPET has a significant advantage that it is free from fusion related defects usually seen in conventional tube to tube plate joining alternatives which use fusion welding methods. Hence this process offers a strong potential for applications in several sectors including automotive, marine, aerospace etc. However, in order to establish FWTPET for industrial applications it is required to develop suitable Non-Destructive Evaluation (NDE) methods for detection and characterization of the defects. In this study, the defects in FWTPET joints welded between 6 mm thick AA 6061 plate and 2 mm thick AA 1060 tube under various conditions are investigated using two advanced volumetric NDE methods, namely Digital Radiography (DR) and Phased Array Ultrasonic Testing (PAUT). This study shows the capability of these volumetric NDE methods to assess the quality of FWTPET joints, and to reveal significant information about the conditions which lead to defect formation. This work also brings out the effect of the parameters of FWTPET using theoretical model and NDE results, and in turn suggests the parametric combinations which could offer defect free joints.

In this report, silver nanoparticles (Ag-NPs) were prepared by pulsed laser ablation of the silver nitrate salt solution using Nd:YAG laser. Trisodium citrate (TSC) is used as a stabilizing/reducing agent for nanoparticles. Under different laser ablation durations, the morphology of nanoparticles changed. Nanoparticles showed the average size ranging from 5 to 31 nm for 20–80 min of ablation. The theoretical and experimental estimation of the particle sizes is done. Butterfly-shaped silver nanoparticles have been tested for the room-temperature clad-modified fiber optic gas sensors sensitivity with ammonia and ethanol gas. The clad-modified optical fiber sensor exhibits distinct linear variation in the spectral peak intensity with the ammonia concentration (0–500 ppm). The characteristics of the gas sensors when exposed to ethanol and ammonia gases were used for studying the sensor selectivity. The results exhibited good sensor response and selectivity for ammonia with sensitivity of 64 counts/ppm and sensitivity percentage of 27%, whereas for ethanol, sensitivity of 9.5 counts/ppm and sensitivity percentage of only 4% were observed.

This paper reports on the fiber optic gas sensing characteristics of clad-modified Cu-doped ZnO nanopowder for the detection of ammonia, ethanol, methanol and acetone gases at various concentration (0–500 ppm). Pure and Cu-doped (1, 3 and 5 mol%) ZnO samples were fabricated and characterized for its structural, optical and morphological properties. Among the samples studied, the sensor containing 5 mol % Cu shows very good response to acetone with the highest gas sensitivity when compared with other gases. Moreover, it exhibits fast response/recovery time (12 and 15 s) and good selectivity.

In recent years, there is a great demand for ecofriendly, light weight and cost effective composites. Basalt fiber is one such naturally available fiber which offers exceptional properties over glass fibers. In this study a Basalt fiber reinforced composites were fabricated by vacuum bagging technique. Thermal properties of these composites were determined using infrared thermography. In-depth and in-plane thermal diffusivity were determined by using pulse thermography and space resolve method, respectively. The in-plane thermal diffusivity was determined in the transmission and reflection modes. In-depth thermal diffusivity was validated with Light flash method.

The long pulse thermography is a suitable technique for detection and quantification of defects in low thermal conducting materials, especially for composites. Basalt fiber reinforced epoxy composite is studied for determining defect depths using long pulse thermography. Flat bottom holes with specified depths and sizes are made in the composite for simulating delamination defects. Thermal images of the specimen are studied to obtain thermal contrast and characteristic peak time. A relation between the slope peak time and defect depth by peak derivative method is obtained analytically for long-pulsed thermography. Defect sizing is determined from the full- width- half- maximum approach. Experimental and numerical results are presented and analyzed.

The gas sensing characteristics of nanocrystalline samarium oxide (Sm2O3) clad modified fiber optic gas sensor are reported with and without a carrier gas (air) in the radiation mode (detection of a light radiating from the clad modified surface) and transmission mode (detection of a light transmitted through the fiber) for ammonia, ethanol, methanol and acetone gases. When the carrier gas present, the sensor output in the radiation mode increases for methanol and ammonia whereas it decreases for ethanol and acetone with the increase in the gas concentration. It is reverse, in the case of, the transmission mode. When there is no carrier gas, the sensor output decreases in the radiation as well as transmission modes for all gases. The dynamic characteristics of the gas sensor are presented.

Sensing characteristics of Ho (1, 3 and 5% mol) – doped Bi 2 O 3 clad-modified fibre optic gas sensor are studied for ammonia, ethanol, methanol and acetone gases at ambient temperature. Bi 2 O 3 doped with all concentrations of Ho shows good gas response to acetone, whereas, 1% and 3% mol of Ho show to methanol. Ammonia and ethanol show very poor gas response for all the doping concentrations. The highest gas sensitivity and gas selectivity property are shown with 3% mol of Ho with acetone. Time response characteristics of the sensor are also reported.

Cr2O3-SnO2 heterojunction nanocomposites were prepared via chemical precipitation method. The prepared samples were characterized by X-ray diffraction (XRD), Transmission electron microscopy (TEM), UV-Vis diffuse reflectance spectra and Field Emission Electron Microscopy (FESEM). The XRD spectrum confirms the presence of both tetragonal rutile SnO2 and rhombohedral corundum Cr2O3 structure. Further investigation into the gas sensing performances of the prepared Cr2O3-SnO2 nanocomposites exhibited an enhanced sensitivity towards VOPs such as isopropanol, acetone, ethanol and formaldehyde. Especially, isopropanol vapor sensor shows excellent sensitivity at an operating temperature of 100 °C. The highest sensitivity for Cr2O3-SnO2 heterojunction nanocomposites indicate that these materials can be a good candidate for the production of high-performance isopropanol sensors.

The paper reports the preparation and fiber optic gas sensing characteristic of clad modified Zn3(VO4)2 nanopowder. Ultrafine zinc vanadate nanopowder was obtained by surfactant assisted solution combustion method. The structural characterization and morphological studies of Zn3(VO4)2 nanoparticles were done by X-ray diffraction, scanning electron microscope, transmission electron microscope, FT-IR spectra and diffuse reflectance spectra (DRS). Clad modified fiber optic gas sensors made from Zn3(VO4)2 nanopowder demonstrate good sensitivity to ammonia gas at room temperature. Gas sensing behavior of this material to various other reducing gases such as ethanol, methanol and acetone has also been studied. Results reveal that nanocrystalline Zn3(VO4)2 has the highest sensitivity to ammonia with a fast response and a recovery time of 46.8 and 59.0 min respectively.

We investigate an organic nonlinear optical (NLO) crystal, (2-(2-hydroxy-3-methoxystyryl)-1-methylquinolinium-4-methylbenzenesulfonate (O-HMQ) suitable for Terahertz applications. The present study elaborates the synthesis, crystal structure, thermal stability and dielectric and transmission properties of O-HMQ crystal at terahertz frequencies. O-HMQ is successfully synthesized in our Laboratory. H1-NMR and FTIR results revealed the molecular structure. O-HMQ single crystals of size 7 × 3 × 3 mm3 are grown from methanol solution by solvent evaporation technique. Single crystal X-ray diffraction data shows that O-HMQ belongs to a monoclinic crystal structure with space group C 2/c. The melting point analysis shows a phase transition around 72°C and a mesophase. The temperature-dependent dielectric study has been carried out for different frequencies ranging from 1kHz to 1 MHz proved the phase transition. The real part of the dielectric constant (erʹ), imaginary part (ei″) and dielectric loss (tanδ) are estimated. Further, we demonstrate Terahertz (THz) transmission characteristics of our as-grown O-HMQ single crystal using 50 fs ultra-short two-color laser plasma source in a broad spectral range of 0.1–50 THz, proving its suitability for THz related applications.

In order to study the response of poly(vinyl alcohol) based composite films under UV radiations, polymer-based films of ZnO, GO and ZnO/rGO powders were prepared by solution casting technique at room temperature. The prepared samples were characterized by powder X-ray diffraction, UV–Visible absorption spectroscopy, atomic force microscopy and Raman spectroscopic technique. The photo-sensitivity of the films towards UV radiation were studied by current–voltage measurements (IV) under visible and UV irradiation. The electric field produced by the UV radiation can pull the holes to the surface while at the surface the adsorbed oxygen ions will trap the photo-generated holes by the recombination of surface electrons and holes, which results in the increase of photocurrent gain. A better response was observed for the ZnO/rGO polymer composite film due to large surface roughness and localized electrons in the GO sheet.

Carbon nanoparticles (CNPs) were prepared by laser ablation of activated carbon (4% ash) in water + ethanol solution (5:2 by volume). Average particle size of about 14 nm was observed and CNPs exhibited a crystalline structure. When 2 mL of NaOH (0.185 M) was added to water + ethanol solution, the average particle size was about 4 nm and the amorphous structure was observed. Photoluminescence (PL) of synthesized CNPs in the absence of NaOH showed spectral peak intensity in the blue region (466 nm) whereas it shifted to the green region (515 nm) for CNPs synthesized with NaOH. The PL of both CNPs exhibited excitation dependent. FWHM of PL spectra of CNPs decreased with increase in the excitation wavelength for a solution without NaOH whereas it increased initially and then decreased for CNPs synthesized with NaOH.

A new type of fiber optic gas sensor is proposed by detecting a light radiated from a region of cladding modified with metal oxide (nanocrystalline ZnO). The intensity of radiated light is found to vary with different gasses and concentrations. Sensing characteristics are studied for ammonia, methanol, ethanol and acetone gasses. Gas sensitivity of the proposed sensor is compared with clad-modified fiber optic gas sensor. The new sensor exhibits enhanced sensitivity. Time response characteristics of the sensor are reported.

Multiferroic perovskite bismuth ferrite is synthesized by a co-preparation method here and characterized by X-ray diffraction(XRD), diffused reflections spectroscopy(DRS), scanning electron microscopy(SEM) and transmission electron microscopy(TEM) analysis. Clad modified fiber optic gas sensors made from BFO nanopowder demonstrate good sensitivity to ethanol gas at room temperature. Gas sensing behavior of this material to various concentration of ethanol in 0 ppm, 100 ppm, 200ppm and 300 ppm has been studied. Results reveal that nanoparticles BFO has the highest sensing to 300 ppm with a response and a recovery time of 10.5 and 20.3 min, respectively.

The present study employed laser ablation to obtain fluorescent carbon nanoparticles (CNPs) using inexpensive and easily available Bougainvillea alba flower juice extract as the source. The laser ablation of flower juice extract was carried out using 355 nm wavelength of Nd: YAG pulsed laser for 60 min. HR-TEM studies showed the presence of both larger (about 60 nm) and smaller size (about 10 nm) CNPs and average particle size was found to be about 25 nm. Crystalline structure was also observed in CNPs, whose interplanar lattice spacing was 0.27 nm, indicating the contracted lattice spacing from usual graphitic structure. XRD and Raman analysis showed that the crystalline CNPs correspond to non-perfect graphitic carbon structure. Optical spectroscopic studies revealed the down-conversion of photoluminescence emission at 485 nm under the excitation wavelength of 400 nm. The average fluorescence lifetime of carbon nanoparticles was estimated as 1.1 ns from time-resolved spectroscopy. The CNPs were found to be non-toxic to human vein endothelial cells and internalized into the cells with high intensity up to 24 h. Two distinct PL emissions were observed with the large particles emitting at the longer wavelength localized predominantly in the cytosol and smaller particles emitting at the shorter wavelength concentrated on the nuclear membrane. The results suggest that the CNPs are biocompatible and have the potential for bioimaging applications.

Bismuth tungstate (Bi2WO6) nanomaterials were synthesized through hydrothermal method. XRD and SEM studies on synthesized nanomaterials showed crystal structure as orthorhombic phase and surface morphology as nanochips with rectangular shape, respectively. As prepared bismuth tungstate nanoparticles were used to modify a portion of the cladding of PMMA optical fiber and their gas sensing characteristics were studied at room temperature for various concentrations (ppm) of ammonia, ethanol, and methanol. The gas sensor exhibited good response to methanol.

Traditionally, CNPs directly obtained from nanosecond pulsed laser ablation (ns-PLA) in an organic solvent like ethanol, isopropyl alcohol and acetone, possess toxic characteristics with excellent fluorescent properties. However, water-soluble CNPs are found to be non-toxic with weak fluorescent properties. In this study, a post-ablation method was utilized to achieve water-soluble fluorescent CNPs. Initially, the colloidal Eth-CNPs solution was obtained from ns-PLA of charcoal powder in the ethanol, which was subsequently dried at room temperature and then dispersed in water to achieve the final water-soluble CNPs (W-CNPs). The High-resolution Transmission Electron Microscopy (HRTEM) image analysis of W-CNPs shows quasi-spherical size particle distribution with an average particle size found to be around 21 nm. XPS studies of charcoal powder and W-CNPs confirm the creation of fluorescent emissive defects state on the surface of W-CNPs under laser ablation in ethanol. Photoluminescence studies of W-CNPs demonstrated the wavelength-dependent PL emission, with peak PL emission in the blue region of the visible spectrum. In vitro studies indicated the non-toxic nature of the W-CNPs at low and high concentration (1, 5 and 10% v/v) in human cardiomyocytes. Herein, the W-CNPs obtained from post-ns-PLA was found to exhibit both blue and green fluorescence in the cardiomyocytes and hence, it can be exploited as a fluoro probe in bioimaging applications.

Multiferroic systems are widely evaluated in gas sensing applications recently due to its multifunctional properties and cost effectiveness. In this study, pristine Bi2Fe4O9 (BFO) and 3% of Neodymium (Nd) doped mullite Bi2Fe4O9 (BNFO3) was synthesized using conventional solid state route. Further, energy dispersive spectroscopy (EDS) and X-ray photo electron spectroscopic (XPS) analysis, confirms the incorporation of Nd in BFO without any undesired chemical contamination. In addition, X-ray diffraction (XRD) studies revealed polycrystalline orthorhombic mullite structure of BFO with traces of mixed phases. Also, lattice distortion in BNFO3 was observed as a consequence of Nd doping, which is further confirmed by Raman spectra phonon modes. The gas sensing potential of BFO and BNFO3 samples were studied using clad modified fiber optic gas sensing setup with 4 different volatile gases (ammonia, ethanol, acetone and methanol) at varying concentrations (0–500 ppm). BNFO3 sensor showed highest sensitivity to ammonia gas with percentage sensitivity of about 20% for 500 ppm at room temperature. In addition, the sensor exhibited rapid response and recovery time of about 40 s and 48 s respectively compared to BFO. In brief, BNFO3 clad modified fiber optic sensor can potentially be utilized in sensing ammonia for industrial applications.

Nanocrystalline pure and potassium doped α-Fe2−x KxO3−δ (x = 0.03, 0.05) fiber optic gas sensors are proposed for sensing acetone, ethanol, methanol, and ammonia at room temperature. The nanostructured pure α-Fe2O3 and potassium doped α-Fe2−x KxO3−δ (x = 0.03, 0.05) were synthesized by conventional co-precipitation method and crystallite sizes were determined to be 6.02 nm for pure, 5.79 nm for 3%K-Fe2O3 and 3.97 nm for 5%K-Fe2O3. Synthesized nanostructures were characterized using characterization tools such as powder X-Ray Diffraction (XRD) for Structural phase composition, Fourier Transform Infrared Spectroscopy (FTIR) for functional group analysis and Scanning Electron Microscopy (SEM) for surface morphology, Energy-dispersive X-ray spectroscopy (EDX) for elemental analysis. UV–Vis spectroscopy showed optical characteristic properties exhibiting significant variation in absorbance for 5%K-Fe2O3. The gas sensitivity and selectivity characteristics were investigated for pure and doped materials. Time response of 5%K-Fe2O3 for all gases was taken. 5%K-Fe2O3 showed good gas selectivity and higher sensitivity towards acetone gas and gave relatively faster response. These substantiated the influence of potassium doping in α-Fe2O3 nanostructure.

Cr2O3-SnO2 heterojunction nanocomposites were prepared via chemical precipitation method. The prepared samples were characterized by X-ray diffraction (XRD), Transmission electron microscopy (TEM), UV-Vis diffuse reflectance spectra and Field Emission Electron Microscopy (FESEM). The XRD spectrum confirms the presence of both tetragonal rutile SnO2 and rhombohedral corundum Cr2O3 structure. Further investigation into the gas sensing performances of the prepared Cr2O3-SnO2 nanocomposites exhibited an enhanced sensitivity towards VOPs such as isopropanol, acetone, ethanol and formaldehyde. Especially, isopropanol vapor sensor shows excellent sensitivity at an operating temperature of 100 °C. The highest sensitivity for Cr2O3-SnO2 heterojunction nanocomposites indicate that these materials can be a good candidate for the production of high-performance isopropanol sensors.

Single crystals of pure, Mo and W doped KTP crystals were grown by flux technique. The grown crystals were subjected to various characterization studies such as EDX, powder XRD, FTIR and UV analysis. The SHG efficiencies of the pure and doped KTP crystals were measured by Kurtz–Perry technique and it was found that the doped KTP crystals exhibit higher values of SHG. Nonlinear refractive indexes were measured on different growth planes of pure and doped crystals by Z -scan method using a cw (continuous wave) He–Ne laser at 632.8 nm. The measured values of nonlinear refraction of different planes were in the order of 10 −12 cm 2 /W.

Defect depths are estimated in the basalt fiber reinforced composite using long pulse infrared thermography in the transmission mode. Defects of different sizes and depths are induced in the basalt fiber composite using flat bottom holes and their thermograms are analyzed. Contrast derivative and parker's method are used to predict the defect depths. The proportionality factor between peak contrast time and defect depth is determined analytically for contrast derivative method. It is observed that the contrast derivative method predicts the defect depths and is independent of the defect sizes, whereas the Parker's method predicts higher depth. The experimental results are in good agreement with numerical results.

The design of fiber optic sensor is based on a cladding modification methodology. A fiber-optic chemical sensor is developed by replacing a certain portion of the original cladding with a chemically sensitive material, specifically, calcinated gadolinium oxide (Gd2O3).Both the light absorption co-efficient and refractive index change upon exposure to chemical vapours of volatile organic compounds (VOCs) such as ammonia (NH3), ethanol (CH3CH2OH), and methanol (CH3OH). The spectral characteristics of the sensor were studied for different concentrations ranging from 0-500 ppm. These changes induced the optical intensity modulation of the transmitted optical signal. During interaction between the sensing material and VOCs, the output intensity is taken into account to detect the toxic VOCs present in the environment. This was systematically investigated by X-ray diffractometer (XRD) and SEM. The XRD analysis indicated that the calcinated Gd2O3 was formed in cubic structure with the crystallite size of 13 nm. ...

The organic nonlinear optical material of 4-bromo-4'chloro benzylidene aniline (BCBA) was synthesized and single crystal of BCBA was grown from acetone solution by solvent evaporation method at room temperature. Its three dimensional structure was elucidated from single crystal X-ray diffraction analysis at 173 K. Synthesized compound of BCBA was subjected to FTIR and (1)H and (13)C NMR spectral analyses. The range and percentage of optical transmission of BCBA was determined by UV-vis-NIR spectrum and its fluorescence spectrum was recorded using spectrofluorometer. The mechanical strength of the crystal was estimated using Vickers microhardness test on the (001) plane. Dielectric constant of the grown crystal was measured for various frequencies along (001) plane. The third order nonlinear optical properties of BCBA were investigated by Z-scan technique with He-Ne laser radiation of wavelength at 632.8 nm and the corresponding nonlinear refractive index, absorption coefficient and optical susceptibility were calculated.

Titanium nitride (TiN) coatings were deposited on mild steel (MS) by direct current reactive magnetron sputtering. With the aim of improving the corrosion resistance of TiN, an additional nickel interlayer was brush plated on the steel substrates before TiN film formation. The phases have been identified with X-ray diffraction analysis. The hardness values of TiN layers were found to increase with the increase in thickness of the Ni interlayer. The wear track investigations of TiN layers showed that the TiN/MS system was worn out by abrasive wear mechanism while on the film with Ni interlayer is by adhesive wear. It was found that the TiN/Ni/MS stack had a weaker tendency towards corrosion and higher corrosion resistance in 3·5%NaCl than the bare MS substrate, Ni/MS and TiN/MS specimen.

A new approach to probe the surface roughness of mild steel due to atmospheric corrosion using a fiber optic sensor system is described. The scattering principle is used to estimate the average surface roughness that is observed between 2.85 µm and 5.40 µm for the corroded surface and 0.11 µm and 0.16 µm for the polished surface respectively. The maximum sensitive region is estimated below the 0.10 mm for the polished surface. Specular and diffuse reflection is measured at normal incidence of fiber. Reflected intensity of corroded surface can be used to estimate the roughness, Ra. The rate of corrosion is determined by weight loss measurement technique and it is found to be linear with measured average roughness, Ra. This work suggests the possibility of using average surface roughness, Ra of atmospheric corroded mild steel to predict the approximated value of rate of corrosion.

Laser processed Si coatings with thickness in the range 100–150 μm were produced on AISI type 316L stainless steel substrate using a continuous wave CO2 laser. The experiments were done at a laser power between 1·5 kW and 1 kW, process speeds in the range 33·6–8·3 mm s−1, with a beam diameter of 1·6 mm. The microstructure of the laser processed coating consists of columnar dendrites and fine cellular structures. High temperature phases such as δ-ferrite and γ-austenite were found on the resolidified microstructure. The microanalysis technique demonstrated that the laser clad zone possessed a high concentration of Si. The crack free laser clad zone exhibited high hardness in the range 850–900 HV.

Laser surface alloying (LSA) of AISI 316L stainless steel with various compositions of Ni and SiC for different laser parameters was investigated. The hardness of the LSA layer was found to be a strong function of silicon content. The maximum hardness achieved was 733 HV. Columnar dendrites, equaxial dendrites and cellular structure were observed in the resolidified microstructure. XRD and EPMA studies were used to find different phases and elemental concentration, respectively.

Clad-modified with nanocrystalline metal oxide fiber optic gas sensors have been proposed for ambient temperature operation. The sensor output light intensity either increases or decreases when the gas concentration is increased. Study shows that optical properties of metal-oxides with air medium influence the gas sensing. Absorption characteristics of nanocrystalline metal oxides ( ZnO, Sm 2 O 3 and Ce doped ZnO etc., ) in air, methanol, ethanol and ammonia are analyzed as well as their effect on gas sensing.

Aluminum alloy LM13 was surface alloyed with Ni and Cr of different compositions (in wt.%) at various laser powers (1 kW, 1.5 kW, and 2 kW) using CW CO2 laser. Microhardness and microstructure of alloyed regions were examined. The study shows that surface alloying is achieved when the laser power is sufficiently high (1.5 kW). Microhardness increases appreciably when the Cr concentration is increased in the Ni-Cr composition. However, in the alloyed region, large variations in microhardness are observed with depth below the surface of the material. Microstructure exhibits needle structure when Ni-concentration is high and undergoes a phase transformation when Cr-concentration is increased. XRD analysis in the alloyed samples shows formation of intermetallic compounds.

7-Diethylamino-4-methylcoumarin(coumarin 1) exhibits two amplified spontaneous emission (ASE) bands in certain solvents under pulsed laser excitation though there is only one maximum in the fluorescence spectrum. In some solvents, it exhibits only one ASE band corresponding to the fluorescence maximum, while in other solvents, the ASE band is largely red-shifted from this maximum. These laser characteristics were studied in various solvents and also in binary solvent mixtures. The study shows that the above characteristics of coumarin 1 are due to the formation of a new type of emitting species under pulsed laser excitation and that this depends upon the properties of the solvent.

Fiber optic sensor based on cladding modification method for detecting various gas emissions such as ammonia methanol, and ethanol is proposed. The Ce doped ZnO annealed at 500 and 1200 °C are used as a gas sensing material. The spectral characteristics of the gas sensor are studied for different concentrations (0–500 ppm) of gases. The sensor exhibits a linear variation in the output light intensity with the concentration. The gas sensitivity and selectivity of the sensor is discussed briefly.

This paper deals with the study of Al-Si alloy laser melted with variable constituents of TiC and Fe coatings to generate TiC reinforced with Fe-Al matrix composite layer on it. This experimentation deals with the investigation of the quality of the composite layer generated by varying the process parameters and the coating composition. A superior composite layer is established when the variable processing parameters were of 2.5kW laser power and 1.5 m/min. scan speed for the coating composition of 25Fe-75TiC wt.%. This layer which consists of TiC reinforcement with Al-Fe matrix shows an average microhardness of about 750 HV and also exhibits pore and crack free surface. Bonding strength of the composite layer is also examined by the hardness test.