Comparison of Weibull and normal probability distribution of flexural strength of dense and porous fired clay

In this research, dense and porous fired clay were produced at a firing temperature of 1300°C. The flexural strength data of the dense and the porous fired clay were determined using three point bending test. Two-parameter Weibull and normal probability distributions were used to estimate the reliability of the flexural strength data of the dense and the porous fired clay. From the result, the Weibull probability distribution scale parameter for the dense (36.31MPa) and Porous (18.85MPa) fired clay are higher than the mean strength value for the dense (33.84MPa) and the porous (17.87MPa) of the normal distribution. Distributions of flaws in the dense and the porous fired clay have a significant effect on the Weibull and normal distribution parameters. The fractured surface of the dense fired clay shows a random distribution of cracks while that of the porous fired clay shows a distribution of pores in the morphology. The normal distribution considers failure at 50% of the flexural strength data while Weibull probability distribution is failure at 62.3% of the strength data. Therefore, two-parameter Weibull is the suitable tool to model failure strength data of the dense and porous fired clay

Characterisation of nanocrystalline diamond coating deposited via hot filament chemical vapour deposition method with various seeding methods

A nanocrystalline diamond bilayer has been deposited via hot filament chemical vapour deposition method. The bilayer has been produced by two different deposition parameters. The first is by limiting microcrystalline diamond growth and the second layer by pulsing additional oxygen gas into the system. The two layers become indistinguishable after the deposition ends. The pretreatment of the substrate, tungsten carbide has been varied i.e. its various seeding sizes (<0.1 μm synthetic, <0.5 μm synthetic, <0.25 μm natural, <0.5 μm natural, and <1 μm natural); with and without hammering by silicon carbide. This set up is highly similar to that of previous work however the different deposition time has caused the microcrystalline diamond layer to be nanocrystalline diamond instead. Results presented are the optical and SEM (up to 100,000x magnification) images of both planar and cross-section of the diamond layer. AFM gave topographical analysis of the diamond layer. The results show that the thickness is about 1.7 μm, top layer diamond about 100 nm in size and are indeed diamonds by XRD and Raman

Dispersion of polymeric-coated–silica aerogel particles in unsaturated polyester composites: effects on thermal-mechanical properties

The thermal-mechanical properties of unsaturated polyester (UP) composite were enhanced by the dispersion of silica aerogel (SA) with preserved pores. Low-cost SA was prepared from rice husk via the sol-gel process and ambient pressure drying. A new method was proposed to encapsulate the hydrophobic aerogel surface pores with hydrophilic polyvinyl alcohol (PVA) film using the fluidized-bed coating process. The dispersion of PVA-coated aerogel with preserved pores in the polyester matrix resulted in an increase of specific compressive strength (44.1 MPa · cm3 g−1), thermal insulation (0.23 W m−1 K−1), and thermal stability (Tonset = 310°C), but decreased the glass transition temperature (Tg = 260°C)

Effects of silica aerogel particle sizes on the thermal–mechanical properties of silica aerogel–unsaturated polyester composites

Silica aerogels with a surface area as high as 773 m2 g−1 and a density of 0.077 g cm−3 were produced from rice husk via sol–gel process and ambient pressure drying. A particulate composite material was prepared by adding silica aerogel particles of three different particle sizes (powder, granules and bead) to unsaturated polyester resin with a fixed volume fraction of 30%. Thermogravimetric and thermal conductivity studies revealed that silica aerogel composites were having higher thermal stability and thermal insulation than the neat resin. It was suggested that the preservation of aerogel pores from resin intrusion is important for better thermal properties. Larger silica aerogel particles have more porous area (unwetted region) which results in a lower degradation rate and lower thermal conductivity of the base polymer. However, the addition of silica aerogel into resin has reduced the tensile modulus of the polymer matrix where smaller particle size displayed higher toughness than those with bigger particle size

The effect of atmospheric plasma spray distance of the agglomerated maerogel coated on Inconel 625 substrate

Nano-structured silica aerogel, which is also known as maerogel, was synthesised from rice husk ash (RHA) by a Universiti Teknologi Malaysia (UTM) research team. This super lightweight solid (powder) material with low thermal conductivity was agglomerated into micro-size particles for use as a coating material. Sprayable maerogel coating has high potential for use in various thermal insulating applications such as in aeroengine turbine blade. The maerogel was coated on Inconel 625 via the atmospheric plasma spray (APS) method. Since the APS can deposit a wide range of coating powders and particle sizes with high deposition temperature, it has become a more suitable coating technique for maerogel coating. The coating spray distance of the APS was varied to study its effect on the maerogel coating in terms of microstructure, coating thickness, adhesion strength and thermal conductivity. The coating spray distance of 10 cm was the best spray distance, a parameter by which a homogenous microstructure with adequate coating thickness, adhesion strength and thermal conductivity was obtained

Microstructural evaluation and thermal oxidation behaviors of YSZ/NiCoCrAlYTa coatings deposited by different thermal techniques

In this paper, two coating techniques, the high velocity oxy-fuel (HVOF) and air plasma spray (APS) techniques, were used to deposit a bond coat of NiCoCrAlYTa on the Inconel 625 substrate, followed by applying a topcoat of yttria-stabilized zirconia (YSZ). The samples were preoxidized in an argon-controlled furnace at a temperature of 1000 °C for 12 and 24 h to characterize the microstructure of a thermally grown oxide (TGO) using the two coating techniques. The most suitable preoxidized samples were further tested for isothermal oxidation at 1000 °C for up to 120 h, and a hot corrosion test was performed at 1000 °C for up to 52 h or until spalling occurred. As-sprayed and oxidized samples prepared with different coating techniques were evaluated in terms of their microstructure using different characterization methods, such as field emission scanning electron microscopy (FESEM), variable pressure scanning electron microscopy (VPSEM), energy dispersive X-ray spectroscopy (EDS) equipped with energy dispersive X-ray and X-ray diffraction (XRD) analyses. In addition, the mechanical properties of these samples were evaluated using adhesion tests. The results show that the YSZ/NiCoCrAlYTa coating applied with the HVOF technique forms a more thin and continuous layer of TGO than that obtained when applying a YSZ/NiCoCrAlYTa coating using the APS technique, indicating that a severe brittle oxidation interface exists between the two layers. The results also indicate that the mechanical strength obtained from the adhesion test of the coated samples is observably affected by the oxidation behaviors obtained with the different deposition techniques chosen

Effects of varying electrodeposition voltages on surface morphology and corrosion behavior of multi-walled carbon nanotube coated on porous Ti-30 at.%-Ta shape memory alloys

The protection of the human muscle-skeletal system from the rapid degradation needs high corrosion resistance biocompatible scaffold materials. Based on this factor, this paper reports the surface morphology, structure and corrosion resistive traits of some multi-walled carbon nanotubes (MWCNTs) coated porous Ti-30 at.%-Ta shape memory alloys (hereafter coded as MWCNT-TTSMAs). The electrophoretic deposition (EPD) technique at various applied voltages was used to coat these alloys with MWCNTs. The structures and morphologies of the prepared samples were characterized at room temperature using the X-ray Diffraction (XRD), energy dispersive spectroscopy (EDS), Raman spectroscopy, Scanning Electron Microscope (SEM), Atomic Force Microscopy (AFM) and Transmission Electron Microscope (TEM) measurements. In addition, the corrosion resistance of the coated alloys was assessed via electrochemical impedance spectroscopy (EIS) in the simulated body fluid (SBF) solution. The thickness (increased from 10.05 to 25.93 μm), surface roughness (increased from 1.38 to 1.95 μm) and homogeneity of the coating was significantly affected by the increase in the applied voltages (0 to 50 V). The corrosion rate of the optimum coated specimens was 10 fold lower (0.0966 mm/year) compared to the uncoated one (0.9403 mm/year). The hydrophilic nature of the proposed MWCNT-TTSMAs affirmed their osseointegration potential to support the cell attachments. The mean water contact angle (WCA) of the coated samples indicated a hydrophilic surface with a value of 22° ± 6 compared to the uncoated sample that exhibited a hydrophobic surface with the WCA value of 96°. Thus, the surface of the MWCNTs tends to be hydrophilic, resulting in an improved surface wettability. Antibacterial activity test exhibited that TTSMAs presented minimal inhibition area toward Escherichia coli (E. coli), in contrast, using the MWCNT has shown an improvement in antibacterial performance