Sasidharan Sankar

Hydrophobic and Metallophobic Surfaces: Highly Stable Non-wetting Inorganic Surfaces Based on Lanthanum Phosphate Nanorods.

Metal oxides, in general, are known to exhibit significant wettability towards water molecules because of the high feasibility of synergetic hydrogen-bonding interactions possible at the solid-water interface. Here we show that the nano sized phosphates of rare earth materials (Rare Earth Phosphates, REPs), LaPO4 in particular, exhibit without any chemical modification, unique combination of intrinsic properties including remarkable hydrophobicity that could be retained even after exposure to extreme temperatures and harsh hydrothermal conditions. Transparent nanocoatings of LaPO4 as well as mixture of other REPs on glass surfaces are shown to display notable hydrophobicity with water contact angle (WCA) value of 120° while sintered and polished monoliths manifested WCA greater than 105°. Significantly, these materials in the form of coatings and monoliths also exhibit complete non-wettability and inertness towards molten metals like Ag, Zn, and Al well above their melting points. These properties, coupled with their excellent chemical and thermal stability, ease of processing, machinability and their versatile photo-physical and emission properties, render LaPO4 and other REP ceramics utility in diverse applications.

Very Low Thermal Conductivity in Lanthanum Phosphate–zirconia Ceramic Nanocomposites Processed using a Precipitation–peptization Synthetic Approach

A wet chemical synthetic approach involving precipitation–peptization mechanisms was successfully adopted for the development of LaPO4–ZrO2 nanocomposites with the ZrO2 content varying in the 5–20 wt% range. Stoichiometric lanthanum phosphate, formed as nanofibrils during the precipitation reaction with orthophosphoric acid, was subsequently transformed into nanorods of ∼10 nm width and 98% TD for the LaPO4–10 wt% ZrO2 composition upon sintering at 1600 °C. The addition of ZrO2 to LaPO4 impeded densification and grain growth inhibition of up to 50% was obtained for LaPO4–20 wt% ZrO2 nanocomposites. Furthermore, the nanocomposites indicated very low thermal conductivity values (1 W m−1 K−1) compared to single phase LaPO4. The non-reactivity of LaPO4 and ZrO2 at high temperatures and the low thermal conductivity values of LaPO4–ZrO2 render them effective for high temperature thermal insulation applications.

Bifunctional lanthanum phosphate substrates as novel adsorbents and biocatalyst supports for perchlorate removal.

Porous lanthanum phosphate substrates, obtained by an environmentally benign colloidal forming process employing methyl cellulose, are reported here as excellent adsorbents of perchlorate with >98% efficiency and with 100% reusability. Additionally, the effectiveness of such substrates as biocatalyst supports that facilitate biofilm formation of perchlorate reducing microbes (Serratia marcescens NIIST 5) is also demonstrated for the first time. The adsorption of perchlorate ions is attributed to the pore structure of lanthanum phosphate substrate and the microbial attachment is primarily ascribed to its intrinsic hydrophobic property. Lanthanum phosphate thus emerges as a dual functional material that possesses an integrated adsorption/bioremediation property for the effective removal of ClO4(-) which is an increasingly important environmental contaminant.

Modeling and surface texturing on surface roughness in machining LaPO4–Y2O3 composite

ABSTRACT In this work, lanthanum phosphate with a 20% yttria (LaPO4/Y2O3) composite prepared by an Aqueous Sol–Gel process is machined using an Abrasive Water Jet Machine (AWJM). The machinability of this composite is studied by varying the input parameters namely Jet Pressure (JP), Stand-Off Distance (SOD), and Traverse Speed (TS) on Surface finish. Garnet of 80 mesh size is used as an abrasive with a flow rate of 85 g/min. The microstructural characterization study reveals the presence of new element YPO4. This element enhances the machinability and reduced porosity in the composite. Microscopy examinations on the machined surface reveals that partial overlapping at low JP, poor surface finish at high JP and SOD, forged deficiency at maximum SOD and TS. The minimum levels of all input parameters are influenced to obtain acceptable Ra. Atomic Force Microscopy (AFM) on the kerf surface shows micro wear track and peaks. The Multiple Regression Analysis (MRA) is developed for Ra to check the adequacy. From the Analysis of Variance (ANOVA), SOD has a significant effect on Ra with a contribution of 53%. The influence of JP and TS on Ra is found to be 31% and 15%, respectively.

A novel approach to formulate high flux multifunctional ultrafiltration membranes from photocatalytic titania composite precursors on multi-channel tubular substrates

Anatase rich titanium dioxide ultrafiltration membranes with high filtration rates have been successfully developed on multi-channel tubular alumina substrates via aqueous sol–gel method from titania–alumina composite precursors containing 30 wt% alumina. The composite membrane material exhibited anatase phase stability above 800 °C and retained a BET surface area of 64 m2 g−1 even after calcination at 700 °C. Supported membranes on multi-channel substrates with an active layer thickness of 4 μm gave a water flux value of 215 L m−2 h−1 coupled with 80% rejection of Bovine Serum Albumin (BSA) with molecular weight 66 kD at 2 bar pressure. This is much higher compared to a flux of 27 L m−2 h−1 obtained for a single component titania membrane layer. The composite membrane materials showed excellent photocatalytic activity under UV irradiation such that a solution containing Methylene Blue (MB) dye showed 96% dye degradation within 2 h. Porous disc shaped substrates coated with the active titania composite layer showed methylene blue degradation of 44% under identical conditions. The present results point towards an excellent pathway for the development of multifunctional ultra-filtration membranes for water purification and also for other separation applications where separation together with photocatalysis will be of great importance.

Abrasive Waterjet Cutting of Lanthanum Phosphate—Yttria Composite: A Comparative Approach

The objective is to study the effect of Silicon Carbide (SiC) and Garnet of each 80 mesh size when used as abrasives while on machining LaPO4 + 20%Y2O3 composite in Abrasive Waterjet Machining (AWJM). The output responses, namely, Material Removal Rate (MRR), Kerf Angle (KA) and Surface Roughness (Ra) are measured with varied input parameters of Jet Pressure (JP), Stand-Off Distance (SOD), and Traverse Speed (TS). MRR and KA are found to be high in Garnet and better Ra in SiC. Microscopy examination on kerf surface reveals that failure is due to the development of internal stress and repetitive cyclic load of hard SiC abrasive. It leads to grain boundary and plastic deformation. Machining using Garnet tends to crush and squeeze the composite that guides to the formation of microcrack and weak grain bond. This study reveals that the use of SiC abrasive gives an acceptable range of output response than Garnet.

Effect of abrasive waterjet machining on LaPO4/Y2O3 ceramic matrix composite

LaPO4/Y2O3 composite is identified as potential materials that possess low thermal conductivity and superior hardness and finds its application as high thermal barrier material and also a functional material. The objective of the study is to exhibit the correlation of three independent parameters of AWJM on LaPO4/Y2O3 composite prepared by Aqueous Sol-Gel process by response surface method (RSM). Jet pressure (JP), stand-off distance (SOD) and traverse speed (TS) are taken as the three independent parameters of AWJM. Effects of these parameters are measured and validated through three dependent responses of material removal rate (MRR), Kerf angle (KA) and surface roughness (Ra). To perform the experimental observations, central composite design (CCD) of L20 orthogonal array is used. Garnet of 80 meshes is used as abrasive. The microstructure of the cut region has plastic deformation surface with micro wear track and crack. Through RSM, it is identified that the three independent parameters have equal contributions on MRR and KA, where SOD has a significant effect on Ra.

Mathematical modelling on multiple variables in machining LaPO 4/Y 2O 3 composite by abrasive waterjet

Abrasive water jet machine (AWJM) cutting technology is used to process many engineering materials which have low toughness and poor thermal conductive property. In this study, LaPO4/Y2O3 ceramic composite, that possesses no phase transformation at high operating temperature and good thermal barrier material, is used. AWJM with garnet of 80 mesh size as abrasive is characterised with various process parameters. Here, material removal rate (MRR), kerf angle (KA) and surface finish (Ra) are investigated by using the three influencing parameters such as jet pressure (JP), stand-off distance (SOD) and traverse speed (TS). L27 orthogonal array is used to record the experimental observations. The empirical model is developed by multilinear regression analysis (MRA) for MRR, KA and Ra. Analysis of variance (ANOVA) and response tables show the influences and the contribution of each independent variable over the dependent response.