Asad Ullah Khan

Rheological studies of aqueous stabilised nano-zirconia particle suspensions

In the present investigation aqueous suspensions of nano- and colloidal range particles are stabilised by changing the ambient pH. Rheology is used to establish the stability of the suspensions and it is found that the rheology of the suspensions is strongly dependent on the pH values. The viscosity is highest close to the iso-electric point of the powders. At the iso-electric point the net surface charge on the powder particles is zero and is the cause of the high viscosity. Away from the iso-electric point, the particles are charged, giving rise to a double layer phenomenon and causing the reduction in viscosity. It is also found that increasing the solid contents of the suspensions reduces the pH region of low viscosity.

Synergistic effect of Chitosan-Zinc Oxide Hybrid Nanoparticles on antibiofouling and water disinfection of mixed matrix polyethersulfone nanocomposite membranes

Antifouling polyethersulfone (PES) membranes for water disinfection were fabricated by incorporating varying concentrations of carbohydrate polymer chitosan and Zinc oxide hybrid nanoparticles (CS-ZnO HNPS). The CS-ZnO HNPS were prepared using chemical precipitation method and were characterized using SEM, XRD and FTIR. The membranes were then fabricated by incorporating nanoparticles of CS-ZnO HNPS with three different concentrations of 5%, 10% and 15% w/w in the casting solution of PES through phase inversion method. The influence of nano-sized CS-ZnO HNPS on the properties of PES was characterized to study morphology, contact angle, water retention, surface roughness and permeability flux. The membranes with the maximum concentrations of 15% HNPS resulted in larger mean pore sizes and lowest contact angle value as compare to the pristine PES membrane. The prepared membranes exhibited significant water permeability, hydrophilicity and prevention against microbial fouling. The prepared membranes were observed to have significant antibacterial as well as antifungal properties due to the synergistic effect of chitosan and ZnO against both bacteria of the type of S. Aureus, B. Cereus, E. coli, and fungi such as S. typhi, A. fumigatus and F. solani.

Effect of concentration of Surfactant on the Exfoliation of Graphite to Graphene in Aqueous Media

Graphite was exfoliated to graphene by tip sonic using sodium cholate as a surfactant in the presence of Millipore water as a medium. The use of water as a solvent for exfoliation purposes is very important due to its environmentally friendly nature and almost no cost, contrary to organic media. Two different concentration ratios of surfactants are used in the present work. As a result, graphene dispersions with two different concentrations of 5 mg/ml and about 7 mg/ml respectively were obtained in aqueous media. It was observed that the optimum concentration of surfactant has an effective role in the exfoliation of graphite to graphene. Concentrations of graphene dispersions were studied through UV spectroscopy, while Raman spectroscopy, Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM) were used to study the quality of the exfoliated graphene flakes.

Rheological Characterization of Alumina Ceramic Suspensions in Presence of a Dispersant and a Binder

The rheological responses of aqueous alumina suspensions, stabilized with an organic polyvalent salt dispersant called “Aluminon,” and including a poly(vinyl) alcohol (PVA) binder, are described in this study. It is observed that the addition of PVA, without any dispersant does not significantly influence the rheology. However, in the presence of the dispersant the rheology is affected significantly. At a given concentration of the dispersant, the viscosity, the storage and loss modulii all increase with the PVA concentration. Also, for a given concentration of the PVA, the viscosity, the storage and loss modulii values increases as the concentration of the dispersant is increased. At relatively low PVA concentrations, an excess concentration of the dispersant, causes flocculation of the particles in the suspension by a reduction of the electrostatic (double layer) effect. On the contrary, at higher concentrations of the PVA the flocculation of the suspension occurs via a depletion mechanism.

Direct comparison between rotational and extrusion rheometers

The use of cone and plate rotational rheology to characterize the flow properties of concentrated dispersion and extrusion methods to determine the rheological properties of pastes have become established rheometric techniques. Direct comparison between the results obtained from the two techniques has not previously been demonstrated. In this article the results of such a comparison using established experimental methods and associated analysis are reported. It is found that for most samples investigated the difference in the calculated values of shear stress at a shear rate of 5/s is <10%. Data for a series of slurries, composed of various solid fractions of lime waste, are reported over a shear rate of 0-10/s. The computed results for two techniques are shown to be, within the experimental error, identical over this shear rate range.

Mechanism of Corrosion and Erosion Resistance of Plasma‐ Sprayed Nanostructured Coatings

There has been a dramatic increase in recent years in a demand for tough, wear‐ resistant, abrasion, erosion, and corrosion‐resistant coatings for petroleum, chemical, aerospace industry, and processes encountering harsh environments such as paper and pulp equipment (the ball valve for high‐pressure leaching). Whereas sufficient informa‐ tion on mechanical properties, such as abrasion, wear, and fatigue, has been gathered over the years, work on the resistance of these coatings to erosion and corrosion is seriously lacking. In the work reported, it has been shown that nanostructured TiO2 coatings offer superior physical and mechanical properties compared to conventional TiO2 coatings. Three different types of plasma‐sprayed titanium dioxide coated samples on mild steel substrate were employed for investigation. The feedstocks used were Sulzer Metco nanopowders designated as AE 9340, AE 9342, and AE 9309. Powder 9340 was a precursor. The corrosion resistance of nanostructured TiO2 coating was dictated largely by surface structure and morphology. The distribution and geometry of splat lamellae, contents of unmelted nanoparticles, and magnitude of porosity are the important factors that affect corrosion resistance. TiO2 showed excellent resistance to corrosion in 3% NaCl. The maximum corrosion rate was observed to be 4 mils per year as shown by polarization potential and weight loss studies. The erosion‐corrosion resistance of the plasma‐ sprayed nanostructured titanium dioxide coatings depends largely upon the character‐ istics of feed powder and its reconstitution. Dense, uniform, and evenly dispersed nanostructured constituents provide a high coating integrity, which offers high resistance to erosion‐corrosion. A mechanism of erosion‐corrosion is explained in the chapter with a schematic diagram. The findings show that the nanostructured TiO2 coatings offer superior resistance to corrosion, erosion, and environmental degradation.

Hydrophobicity — A Green Technique for Enhancing Corrosion Resistance of Alloys

The corrosion phenomenon is as old as the age of the planet. The cost of corrosion has risen alarmingly with industrial progress and it is estimated to be around 300 billion dollars or 3 to 4.5% of the GNP of developed nations. Thousands of alloys have been developed to control corrosion, which is a major consideration in the development of new ferrous and non-ferrous alloys. Several corrosion control techniques such as inhibitor treatment, coatings, cathodic protection, alloying additions, and designing for corrosion protection have been developed to combat corrosion. Despite their merits, techniques such as inhibition treatment and coatings are limited by their adverse effect on the environment because of their volatile organic components. Due to an increasing‐ ly alarming carbon footprint, there is a growing global concern to keep the environ‐ ment clean. Hence, a great need exists to replace the current control methods by ecofriendly methods. The potential of the green technology of hydrophobicity has therefore been exploited to control corrosion by fabricating hydrophobic surfaces on alloys and these surfaces have shown highly promising results. This technology offers a novel method to control corrosion of metals, alloys, polymers and composites.

7Effects on Thermal and Ablative Properties of Phenolic Resin (Novolac) Blended Acrylonitrile Butadiene Rubber

In this work we investigated the ablative response and thermal properties of phenolic resin (PR) blended acrylonitrile butadiene rubber (NBR) composites. PR was added to NBR in the proportion of 0, 5, 10, 20, 30, 40 and 50 phr by means of two-roll laboratory mill. PR remarkably improved ablation resistance and thermal properties of NBR/PR composite. The linear and mass ablation rates reduced to 21.3 % and 26.1 % respectively. The char content deposition increased from 0.19 to 26.8 %. Char layer produced by PR, obviously reduced the erosion rate of the NBR/PR composite relative to neat NBR (without PR). Detailed morphological studies of the composite and post-test (ablation) microstructure of char revealed that higher loading of PR in the rubber composite produced dense char layer firmly intact to the substrate. Furthermore, thermal stability of the composite improved by 22–23 ºC, however, thermal conductivity of the composite slightly increased by 0.115 W/mK for 50 Phr of PR loading as compared to the neat.

Redox balance and DNA fragmentation in arsenic-exposed occupational workers from different industries of Pakistan

Occupational exposure accounts for a contact between workers and different toxicants. Present study was designed to measure the arsenic-induced DNA fragmentation and oxidative stress in exposed workers. Blood, hair, and nail samples were collected from welding, brick kiln, furniture, pesticide, and paint industries (n = 50/industry) of Pakistan along with 200 controls. DNA damage was calculated using DNA fragmentation assay. Antioxidant enzymes (CAT, SOD, GPx) were measured using ELISA. Results revealed that arsenic exposure induced DNA fragmentation in brick kiln, furniture, and welding industries. Enzyme activity was reduced in five industries compared to control. In exposed group, significant depletion of enzymes was observed in furniture, welding, and brick kiln workers. Based on age and time of exposure, significant difference was observed in welding and brick kiln group. Smokers of exposed group showed significantly reduced levels of enzymes compared to controls. Arsenic deposition was observed higher in the hair, nail, and blood samples of exposed group (P < 0.001) compared to control. Likewise, lead and cadmium contents were higher in the blood samples of industrial workers compared to control. This study suggests increased trend of cellular damage and oxidative stress in occupational workers profoundly in welding, furniture, and brick kiln industries. Moreover, this study recognizes the contribution of age, exposure time, and smoking status toward arsenic-induced oxidative stress and DNA fragmentation.

Harnessing Green Engineering for Eco-Friendly Housing and Utilities in South-Asian Countries

This paper reviews the recent development in green materials employed for eco-friendly construction in the context of developing countries, where climatic change and limited resource demand cost effective and sustainable materials of construction. The paper reviews some of the important fundamentals on which green engineering is based and shows how the advantages offered by green materials can be harnessed for societal, economic and technological benefits. The proliferation of nanotechnology in construction has filled many of the holes left by traditional technologies. The mountain and hilly regions is the primary target in South Asia in this review as these areas in Pakistan and similar geographical regions are still far behind in harnessing the benefits of green engineering. New methods of collection of safe drinking water, using Nano materials and treatment of snow melted and rain water are reviewed. The design of roofs in cold and snow bound areas and new green materials developed for such areas are also discussed. The article describes the latest Nano eco-friendly materials which may be employed to minimize energy, increase life cycle and decrease carbon foot points for longer and healthier lives. This paper also dwells on the proper use of green Nano materials for constructing houses in developing countries.