Preparation and characterization of adherent autocatalytically deposited nickel coating on carbon fiber

In the present study carbon fibers were successfully coated with nanocrystalline nickel using an acidic bath by electroless plating method. Coating thickness obtained was about 1.5 microns beyond that there was coating delamination. Coated fibers were characterized for various properties such as morphology, composition, structure, phase transformation temperature, resistivity and tensile strength. Field emission scanning electron microscope (FESEM) studies revealed that the coating showed nodular morphology. Energy dispersive analysis of X-ray (EDAX) showed that the coating containing about 10.5 wt.% P with balance Ni. Structural studies carried out on these coated fibers exhibited two major diffraction peaks and were assigned as C (002) and Ni (111). Differential scanning calorimetry (DSC) studies on these coated fibers exhibited a single exothermic peak at 3510C. Activation energy obtained for the crystallization process of high P deposit is about 215.9 kJ/mol. Bulk resistivity was measured using four-probe technique over a single coated fiber and the obtained value was around 3.2 μΩ-m. Tensile strength of these coated fibers were also carried out and observed that not much variation found in the strength of coated and uncoated fibers

Wettability of Y2O3: A relative analysis of thermally oxidized, reactively sputtered and template assisted nanostructured coatings

The wettability of reactively sputtered Y2O3, thermally oxidized Y-Y2O3 and Cd-CdO template assisted Y2O3 coatings has been studied. The wettability of as-deposited Y2O3 coatings was determined by contact angle measurements. The water contact angles for reactively sputtered, thermally oxidized and template assisted Y2O3 nanostructured coatings were 99°, 117° and 155°, respectively. The average surface roughness values of reactively sputtered, thermally oxidized and template assisted Y2O3 coatings were determined by using atomic force microscopy and the corresponding values were 3, 11 and 180 nm, respectively. The low contact angle of the sputter deposited Y2O3 and thermally oxidized Y-Y2O3 coatings is attributed to a densely packed nano-grain like microstructure without any void space, leading to low surface roughness. A water droplet on such surfaces is mostly in contact with a solid surface relative to a void space, leading to a hydrophobic surface (low contact angle). Surface roughness is a crucial factor for the fabrication of a superhydrophobic surface. For Y2O3 coatings, the surface roughness was improved by depositing a thin film of Y2O3 on the Cd-CdO template (average roughness = 178 nm), which resulted in a contact angle greater than 150°. The work of adhesion of water was very high for the reactively sputtered Y2O3 (54 mJ/m2) and thermally oxidized Y-Y2O3 coatings (43 mJ/m2) compared to the Cd-CdO template assisted Y2O3 coating (7 mJ/m2)

Drilling of carbon epoxy composite using nanocrystalline nickel alloy coated tools

This paper is concerned with the effect of auto-catalytically deposited Nickel alloy coating on the machining performance of High Speed Steel (HSS) drill bits in the drilling of carbon composite. The present work is focussed on the performance comparison of nanocrystalline Nickel-Boron (Ni-B) coated and uncoated HSS twist drill bits of size 5 & 6 mm by evaluating tool wear, hole deviation error, extent of delamination, surface roughness of the hole when drilling carbon epoxy laminate. In addition to this the coating was also characterized by ICP-OES (Inductively Coupled Plasma), FESEM (Field Emission Scanning Electron Microscope), DSC (Differential Scanning Calorimetry) and NHT (Nanohardness Test) to study the composition, surface morphology, phase transformation behavior and nanohardness respectively. The coating showed typical nodular morphology in as-deposited condition. The activation energy required for the Ni-B coating to convert from meta-stable phase to stable crystalline phase was found out to be 160.4 kJ/mol. The coating showed the surface hardness of 1118HV30mN and 1445HV30mN in as-deposited and heat-treated conditions

Synthesis of Carbon Nanotubes by Single Zone Pyrolysis Technique

Multi-walled carbon nanotube (MWNT) and combination of single-walled (SWNT) and MWNT were synthesized using pyrolysis assisted chemical vapor deposition method. A single hot zone furnace was used for the synthesis of carbon nanotubes at various temperatures in the range of 750-900C. The as-prepared CNT consisted of carbonaceous impurities and traces of transition metal contents. The as-prepared CNT was oxidized at 500C and then treated with hydrochloric acid which resulted in pure CNT with a purity of 95%. The carbon nanotubes were characterized using field emission scanning electron microscopy (FESEM) and micro-Raman spectroscopy techniques. FESEM images clearly showed the presence of carbon nanotubes and the diameters of the MWNT prepared at various temperatures were in the range of 35-100 nm. The Raman spectroscopy data also showed the presence of D, G and 2D peaks which confirm the presence of CNT

Properties of plasma sprayed La2Zr2O7 coating fabricated from powder synthesized by a single-step solution combustion method

In recent years, rare earth zirconates with the general formula Ln2Zr2O7 have been investigated as futuristic thermal barrier coatings (TBCs). In the present study, the use of solution combustion process for the preparation of plasma sprayable grade La2Zr2O7 powder is reported. The powder was prepared by using urea as fuel in a single-step without using spray drying process. The powder was characterized for phase, morphology, flowability and particle size analysis by using powder X-ray diffractometry, field emission scanning electron microscopy (FESEM), a Hall flow meter and a particle size analyzer respectively. The powder was plasma sprayed and the phase purity of the plasma sprayed coating was analyzed by X-ray diffractometry. A Rietveld analysis of the coating was performed in order to understand the shift in the peak positions of the coating. The analysis revealed the coating to be a mixture of La2Zr2O7, La2O3 doped ZrO2 and ZrO2. The coating surface and cross-section were analyzed by FESEM. The density of the free-form of the coating was determined and the thermal conductivity of the coating was measured at 900 °C. The coating exhibited a conductivity value of 1.08 W m−1 K−1

Phase transformation behavior of nanocrystalline Ni–W–P alloys containing various W and P contents

In the present investigation, electroless (EL) ternary Ni–W–P coatings were prepared using hypophosphite based alkaline bath by varying sodium tungstate as tungsten source (5–80 g/L). Maximum amount of W incorporation (8.2±1 wt.%) was obtained when the bath contained about 20 g/L of tungsten source. At very high concentrations of W source in the bath the deposit contained about 4 wt.% W and 2 wt.% P. All the as deposited ternary coatings exhibited nodular surface morphology. X-ray diffractograms (XRD) obtained for as-deposited EL NiWP alloys indicated that crystallinity of the coatings increased with decrease in phosphorus content. Calculated grain size for the deposits varied from 1.2 to 12.7 nm when the tungsten source varied from 5 to 80 g/L in the bath. Higher crystallization temperatures were obtained due to codeposition in NiP matrix. Presence of metastable phases such as Ni5P2 and NiP apart from stable Ni and Ni3P was identified for the heat treated deposits (400 °C/1 h) containing lower amount ofWand higher amount of P. Whereas other ternary deposits after the heat treatment predominantly revealed face centered cubic (f.c.c.) Ni (111) peak. Activation energy for the crystallization of all the alloys has been carried out by modified Kissinger method. Microhardness measurements were carried out on all the deposits isothermally heat treated at 600 °C for 1

Solder reaction between electroless Ni-Sn-P and Sn-3.5Ag

In the present study electroless Ni-Sn-P (6-7 wt.% P and 19-21 wt.% Sn) coating was prepared on copper plates using an alkaline bath. Solder reaction with lead-free Sn-3.5Ag was investigated and compared with Ni-P (6-7 wt.%). Joint strength was studied by forming Ni-P/Sn-3.5Ag and Ni-Sn-P/Sn-3.5Ag micro tensile test specimens. Both Ni-P/Sn-3.5Ag and Ni-Sn-P/Sn-3.5Ag joints were thermally-aged at 180 °C up to 600 h to study their interfacial reactions and tensile properties upon aging. Formation of two interfacial compounds such as Ni3Sn4 and Ni13Sn8P3 was observed during the Ni-Sn-P/Sn-3.5Ag solder reaction. It was found that Sn atoms from the solder diffuse through the formed Ni3Sn4 layer to reach the Ni3Sn4/Ni-Sn-P interface, and react with the Ni-depleted region of the Ni-Sn-P layer to form the second IMC, Ni13Sn8P3. The tensile strength of the as-reflowed Ni-Sn-P/Sn-3.5Ag solder joints was found to be comparable to that of the as-reflowed Ni-P/Sn-3.5Ag solder joints. Both types of as-reflowed solder joints experience ductile failure in the bulk solder. The strength of Ni-P/Sn-3.5Ag joints drops significantly after aging for 400 h, while the strength of Ni-Sn-P/Sn-3.5A joints drops significantly after aging for 300 h. The Ni-P/Sn-3.5Ag solder joints aged for 400 h and 600 h experience brittle fracture at the Ni3Sn4/solder interface. The Ni-Sn-P/Sn-3.5Ag joints aged for 300 h, 400 h and 600 h experience brittle fracture not only at the Ni3Sn4/solder interface, but also through all of the interfacial layers (Ni3Sn4, Ni13Sn8P3 and Ni-Sn-P layers). It was also found that cracking of the metallization at some locations during long-term ageing has led to fast Sn diffusion and accelerated IMC growth at these locations which is responsible for the fast degradation of the Ni-Sn-P/solder joint strength

On the thermal stability and performance evaluation of Si doped transition metal nitride/oxide nanolayered multilayer-based spectrally selective absorber for high-temperature photothermal applications

Developing an absorber coating with high absorptance (α) in the solar spectrum region and low thermal emittance (ε) in the infrared region for concentrated solar power (CSP) applications, operating at temperatures >400 °C, is still a great challenge. Herein, we describe a multilayer solar selective coating on stainless steel 304 (SS 304) substrates with α of 0.954 and ε of 0.07. The multilayer solar selective coating consists of: (1) tungsten (W) infrared reflector layer, (2) titanium aluminum nitride (TiAlN) absorber layer, (3) titanium aluminum silicon nitride (TiAlSiN) absorber layer, (4) titanium aluminum silicon oxy-nitride (TiAlSiON) semi-absorber layer and (5) titanium aluminum silicon oxide (TiAlSiO) anti-reflection layer. The compositions of the individual layers have been selected in such a way that they easily form protective layers of Al2O3, TiO2 and SiO2 on the coating surface when exposed to high temperature in air. Further, addition of Si in different layers not only improves the thermal stability but also helps in densifying the microstructure of the layers. Moreover, the presence of multilayer structure hinders the formation of pinholes and pores along with columnar microstructure, a typical characteristic of the sputter deposited transition metal nitrides and oxides. This unique coating design, thus, leads to high spectral selectivity (α/ε) of 13.6 on SS 304 substrate along with thermal stability up to 600 °C for 1000 h in vacuum under cyclic heating conditions. These properties of the developed solar absorber coating demonstrate its suitability for evacuated receiver tubes in CSP plants

Tuning of deep level emission in highly oriented electrodeposited ZnO nanorods by post growth annealing treatments

Highly dense and c-axis oriented zinc oxide (ZnO) nanorods with hexagonal wurtzite facets were deposited on fluorine doped tin oxide coated glass substrates by a simple and cost-effective electrodeposition method at low bath temperature (80 °C). The as-grown samples were then annealed at various temperatures (TA = 100–500 °C) in different environments (e.g., zinc, oxygen, air, and vacuum) to understand their photoluminescence (PL) behavior in the ultra-violet (UV) and the visible regions. The PL results revealed that the as-deposited ZnO nanorods consisted of oxygen vacancy (VO), zinc interstitial (Zn i), and oxygen interstitial (Oi) defects and these can be reduced significantly by annealing in different environments at optimal annealing temperatures. However, the intensity of deep level emission increased for TA greater than the optimized values for the respective environments due to the introduction of various defect centers. For example, for TA ≥ 450 °C in the oxygen and air environments, the density of Oi defects increased, whereas, the green emission associated with VO is dominant in the vacuum annealed (TA = 500 °C) ZnO nanorods. The UV peak red shifted after the post-growth annealing treatments in all the environments and the vacuum annealed sample exhibited highest UV peak intensity. The observations from the PL data are supported by the micro-Raman spectroscopy. The present study gives new insight into the origin of different defects that exist in the electrodeposited ZnO nanorods and how these defects can be precisely controlled in order to get the desired emissions for the opto-electronic applications

Design and fabrication of thermally stable HfMoN/HfON/Al2O3 tandem absorber for solar thermal power generation applications

A new HfMoN(H)/HfMoN(L)/HfON/Al2O3 tandem absorber is designed and developed for high temperature solar thermal applications. The first absorber layer, HfMoN(H) is designed to have higher metallic content than the second HfMoN(L) layer. By varying the nitrogen flow rate, two different HfMoN layers with different refractive indices were deposited on SS substrates. The optical constants (n and k) measured using spectroscopic ellipsometry showed that HfMoN(H) and HfMoN(L) are the main absorber layers and HfON/Al2O3 acts as a double layer antireflection coating. The gradual decrease in the refractive indices from the substrate to the top resulted in increase in the absorptance, which was confirmed by the ellipsometric mesurements. The optimized four layer tandem absorber exhibited high absorptance ( = 0.94-0.95) and low thermal emittance (82C = 0.13-0.14). The four layer tandem absorber was thermally stable up to 600°C for 450 hrs and 650°C for 100 hrs in vacuum. Whereas, coatings heat-treated in air were thermally stable up to 475C for 34 hrs