Thermal expansion characteristics of a titanium modified austenitic stainless steel: measurement by high-temperature X-ray diffraction and modelling using Grüneisen formalism

The thermal expansion of a titanium modified, swelling resistant austenitic stainless steel designated as D9 is studied by measuring the lattice parameter as a function of temperature in the range 300-1300 K by high-temperature X-ray diffraction technique. The thermal expansion data thus obtained is in reasonable agreement with the typical thermal expansion values reported for similar nuclear grade austenitic stainless steels. However, at temperatures exceeding 900 K, the measured thermal expansivity exhibits a pronounced non-linear increase due partly to the precipitation of complex carbide and intermetallic phases. The high-temperature thermal expansion data obtained in the present study are augmented by modelling the low-temperature thermal expansion behaviour by Grüneisen formalism.     

Experiments on slider lubricant interactions and lubricant transfer using TFC sliders

Future magnetic storage density targets (>4 Tb/in. ²) require subnanometer physical clearances that pose a tremendous challenge to the head disk interface (HDI) design. A detailed understanding of slider-lubricant interactions at small clearances and contact is important to not only address magnetic spacing calibration and long term HDI reliability but also to meet additional challenges imposed by future recording architectures such as heat assisted magnetic recording (HAMR). In this work, the behavior of the disk lubricant is investigated through controlled tests using TFC sliders which are actuated to proximity (i.e. backoff) and into contact (i.e. overpush) on one specific half of the disk per rotation by synchronization with the spindle index. Observations for lubricant distribution in contact tests (i.e. overpush) reveal an accumulation of lubricant on the disk near the onset of contact suggesting a migration of lubricant from the slider to the disk as the slider approaches the disk. Experiments also reveal that there is a similar deposition of lubricant even in the absence of contact for backoff tests. Furthermore, light contact tests result in significant lubricant rippling and depletion with associated slider dynamics. The lubricant rippling frequencies correlate well with the slider’s vibration frequencies. Interestingly, strong overpush may lead to stable slider dynamics (for certain air bearing designs) that is also associated with noticeably lower lubricant distribution (compared to the light contact case), and the greatest lubricant changes are observed only at the onset and the end of contact. This paper reveals the complex nature of slider-lubricant interactions under near-contact and contact conditions, and it highlights the need for further studies on the topic to help design a HDI for recording architectures of the future.     

13C CP/MAS NMR Spectroscopy of Native and Acid Modified Starches

¹³CP/MAS NMR spectroscopic studies of some starches from cereals (wheat, maize and finger millet), pulses (green gram, chick pea), tuber (potato) and root (tapioca), and their respective acid (HCI, HNO₃) modified starches were carried out. While cereal starches exhibited a triplet signal for their anomeric carbons, pulse, tuber and root starches showed doublets. Line width changes in signals indicated that debranching in the above modified starches led to narrowing of C₆ signals (more pronounced in the case of potato and tapioca starches) and were consistent with the release of branching strains. Potato starch, both native and modified, was found to be different from other starches as inferred from the chemical shift values for their anomeric carbons and line shape. The dihedral angle (ϕ′2) calculated from chemical shift values for C₁ and conformation of dihedral angel (x) as predicted from chemical shift of C₆ are discussed with respect to structural organization.     

Synthesis of nanoparticles of barium lanthanum hafnium oxide by a modified combustion process

Barium lanthanum hafnium oxide, a complex perovskite ceramic, has been synthesized as nanoparticles by a modified combustion process for the first time. The Ba, La, and Hf ions required for the formation of Ba2LaHfO5.5 were obtained in solution by dissolving in boiling nitric acid a stoichiometric mixture of BaCO3, La2O3, and HfO2 that had been heated at 1200 degrees C for 4 h. By complexing the ions with citric acid and using ammonia as fuel, it was possible to get Ba2LaHfO5.5 as nanoparticles in a single-step combustion process. The powder obtained by the present combustion process was characterized by X-ray diffraction, BET surface area analysis, differential thermal analysis, thermogravimetric analysis, infrared spectroscopy, and scanning and high-resolution transmission electron microscopy. According to the results of X-ray and electron diffraction, the powder synthesized through the combustion process showed single-phase barium lanthanum hafnium oxide. The transmission electron microscopic investigations showed a grain size of 42 nm, with a standard deviation of 8 nm. The nanoparticles of Ba2LaHfO5.5 synthesized by the present combustion technique could be sintered to > 97% of the theoretical density at a relatively low temperature of 1425 degrees C. Scanning electron microscopic studies on the sintered Ba2LaHfO5.5 samples showed that the final grain size of the sintered specimen was < 500 nm.     

Plackett-burman design for determining the preference of Rhizomucor miehei lipase for FA in acidolysis reactions with coconut oil

The preference of lipase (EC 3.1.1.3) from Rhizomucor miehei in the incorporation of 11 FA, ranging from C10∶0 to C22∶6, into coconut oil TAG during acidolysis was studied by applying the Plackett-Burman experimental design. Enzymatic acidolysis reactions were carried out in hexane at 37°C for 48 h with coconut oil (0.1 M) and a mixture of 11 FA at a TAG to FA molar ratio of 1∶1. Lipase was used at the 5 wt% level. The incorporation of FA into coconut oil TAG was determined by GC. The lipase showed preference for long-chain saturated FA for incorporation into coconut oil TAG. The FA with 18 carbon atoms showed a high incorporation rate (18∶1>18∶1>18∶3). The lipase showed the least preference for the incorporation of 12∶0, which occurs in maximal concentration (46%), whereas the most preferred FA, 18∶0, occurs at a very low concentration (<2%) in coconut oil. The overall preference of lipase for the incorporation of different FA into coconut oil TAG was 18∶0>18∶2, 22∶0>18∶1, 18∶3, 14∶0, 20∶4, 22∶6>16∶0>12∶0≫10∶0.     

Inhibition of Rhizomucor miehei and Candida rugosa lipases by D-glucose in esterification between L-alanine and D-glucose

A detailed kinetic study of the esterification of D-glucose with L-alanine catalyzed by lipases from Rhizomucor miehei (RML) and Candida rugosa (CRL) showed that both lipases follow the Ping-Pong Bi-Bi mechanism, in which L-alanine and D-glucose bind in subsequent steps releasing water and L-alanyl-D-glucose, with competitive substrate inhibition by D-glucose at higher concentrations leading to the formation of dead-end lipase.D-glucose complexes. An attempt to obtain the best fit of this kinetic model through curve fitting yielded good approximates of the apparent values of four important kinetic parameters: for RML-k(cat)=0.29+/-0.028x10(-3) M h(-1) mg(-1), K(m L-alanine)= 4.9+/-0.51x10(-3) M, K(m D-glucose)=0.21+/-0.018x10(-3) M, and K(i D-glucose)=1.76+/-0.19x10(-3) M; for CRL-k(cat)= 0.75+/-0.08x10(-3) M h(-1) mg(-1), K(m L-alanine)=56.2+/-5.7x10(-3) M, K(m D-glucose)=16.2+/-1.8x10(-3) M, and K(i D-glucose) =21.0+/-1.9x10(-3) M.     

Pramila Rao · D. Sujatha · K. Rathina Raj · S. Vishwanatha · K. Narasimhamurthy · P. Saibaba · D. Narasimha Rao · S. Divakar

 Subchronic toxicity dietary studies were conducted in albino rats on the safety aspects of residual β-cyclodextrin in egg samples treated for cholesterol removal at concentrations of 250, 125 and 20 ppm for a period of 90 days. Daily food intake, body weight gain, relative organ weights, histopathology, haematology and serum enzyme activities were studied. The study however, did not reveal any toxicity at any of the levels tested. It can therefore be concluded from the present study that β-cyclodextrin-treated egg samples do not cause any toxicity. Received: 28 September 1999     

Thermal stability of CeO<Subscript>2</Subscript>/ZrO<Subscript>2</Subscript> multilayer thin films prepared by pulsed laser deposition

Multilayers of CeO₂/ZrO₂ thin films were deposited on Si (100) substrates using pulsed laser deposition at an optimized oxygen partial pressure of 3×10⁻² mbar and at room temperature. The CeO₂ layer thickness was 10 nm, while the ZrO₂ layer thickness was varied as 10, 20 and 30 nm. CeO₂ and ZrO₂ layers were deposited alternately to obtain 25 bilayers. High temperature x-ray diffraction (HTXRD) results showed that the multilayer films had cubic ceria and tetragonal ZrO₂. Thermal expansion coefficients were calculated for CeO₂ and t-ZrO₂ and found to increase with the decrease of ZrO₂ layer thickness. The cross sectional transmission electron microscopy (XTEM) of CeO₂/ZrO₂ multilayer also indicated that ceria was found to be in cubic phase while zirconia contained predominantly tetragonal phase along with cubic phase in thermally annealed specimen.     

Palladium‐nanoparticle intercalated vermiculite for selective hydrogenation of α,β‐unsaturated aldehydes

Palladium nanoparticles were generated in the interlamellar region of swelling 2:1 type vermiculite clay using an adsorption excess isotherm. An adsorption excess isotherm was constructed for vermiculite after exchanging the exchangeable Na⁺ ions in the interlamellar region using a binary liquid mixture (ethanol:toluene). Based on adsorption excess isotherm, 1% w/w palladium was intercalated into the interlamellar space of vermiculite. The Pd‐intercalated vermiculite was characterized by X‐ray diffraction, transmission electron microscopy and atomic absorption spectroscopy. The 1% w/w Pd‐intercalated vermiculite was tested for its catalytic activity towards selective hydrogenation reactions involving some α,β‐unsaturated carbonyl compounds using a pulse reactor and its catalytic activity was compared with commercial 1% Pd/C. The intercalated catalyst was found to be very selective towards the desired product of unsaturated alcohols. Copyright © 2007 Society of Chemical Industry     

Studies of interfaces in Al65Cu20Fe15

The study of interfaces in quasicrystalline alloys is relatively new. Apart from the change in orientation, symmetry and chemistry which can occur across homophase and heterophase boundaries in crystalline materials, we have the additional, exciting possibility of an interface between quasicrystalline and its rational approximant. High resolution electron microscopy is a powerful technique to study the structural details of such interfaces. We report the results of a HREM study of the interface between the icosahedral phase and the related Al₁₃Fe₄ type monoclinic phase in melt spun and annealed Al₆₅Cu₂₀Fe₁₅ alloy.