Synthesis of A1PO4, LaPO4 and KTiOPO4 by flash combustion

Fine particle AlPO4, LaPO4 and KTiOPO4 have been prepared by the flash combustion of aqueous solutions containing metal nitrate, ammonium hydrogen phosphate, ammonium nitrate or ammonium perchlorate and carbohydrazide or tetraformal trisazine. When rapidly heated at 400 °C, the solution containing the redox mixtures ignites to undergo self-propagating, gas-producing, exothermic reactions. Formation of crystalline phosphates was confirmed by powder X-ray diffraction patterns and IR spectra. The metal phosphates formed are fine and have 20�78 m2 g?1 surface area.

CoMn2O4 spinel from a MOF: synthesis, structure and magnetic studies

A hydrothermal reaction of Mn(OAc)(2)center dot 4H(2)O, Co(OAc)(2)center dot 4H(2)O and 1,2,4 benzenetricarboxylic acid at 220 degrees C for 24 h gives rise to a mixed metal MOF compound, CoMn2(C6H3(COO)(3))(2)], I. The structure is formed by the connectivity between octahedral CoO6 and trigonal prism MnO6 units connected through their vertices forming a Kagome layer, which are pillared by the trimellitate. Magnetic susceptibility studies on the MOF compound indicate a canted anti-ferromagnetic behavior, due to the large antisymmetric DM interaction between the M2+ ions (M = Mn, Co). Thermal decomposition studies indicate that the MOF compound forms a tetragonal mixed-metal spinel phase, CoMn2O4, with particle sizes in the nano regime at 400 degrees C. The particle size of the CoMn2O4 can be controlled by varying the decomposition temperature of the parent MOF compound. Magnetic studies of the CoMn2O4 compound suggests that the coercivity and the ferrimagnetic ordering temperatures are dependent on the particle size.

Nano structured carbon nitrides prepared by chemical vapour deposition

Nanostructured carbon nitride films were prepared by pyrolysis assisted chemical vapour deposition(CVD). A two zone furnace with a temperature profile having a uniform temperature over a length of 20 cm length has been designed and developed. The precursor Azabenzimidazole was taken in a quartz tube and evaporated at 400 degrees C. The dense vapours enter the pyrolysis zone kept at a desired temperature and deposit on the quartz substrates. The FTIR spectrum of the prepared samples shows peaks at 1272 cm(-1) (C-N stretching) and 1600 cm(-1) (C=N) confirms the bonding of nitrogen with carbon. Raman D and G peaks, are observed at 1360 cm(-1) and 1576 cm(-1) respectively. XPS core level spectra of C 1s and N 1s show the formation of pi bonding between carbon and nitrogen atoms. The size of the nano crystals estimated from the SEM images and XRD is similar to 100 nm. In some regions of the sample a maximum of 57 atom % of nitrogen has been observed.

Influence of Substrate Temperature and Deposition Rate on Structural and Mechanical Properties of Shape Memory NiTi Films

NiTi thin films deposited by DC magnetron sputtering of an alloy (Ni/Ti:45/55) target at different deposition rates and substrate temperatures were analyzed for their structure and mechanical properties. The crystalline structure, phase-transformation and mechanical response were characterized by X-ray diffraction (XRD), Differential Scanning Calorimetry (DSC) and Nano-indentation techniques, respectively. The films were deposited on silicon substrates maintained at temperatures in the range 300 to 500 degrees C and post-annealed at 600 degrees C for four hours to ensure film crystallinity. Films deposited at 300 degrees C and annealed for 600 degrees C have exhibited crystalline behavior with Austenite phase as the prominent phase. Deposition onto substrates held at higher deposition temperatures (400 and 500 degrees C) resulted in the co-existence of Austenite phase along with Martensite phase. The increase in deposition rates corresponding to increase in cathode current from 250 to 350 mA has also resulted in the appearance of Martensite phase as well as improvement in crystallinity. XRD analysis revealed that the crystalline film structure is strongly influenced by process parameters such as substrate temperature and deposition rate. DSC results indicate that the film deposited at 300 degrees C had its crystallization temperature at 445 degrees C in the first thermal cycle, which is further confirmed by stress temperature response. In the second thermal cycle the Austenite and Martensite transitions were observed at 75 and 60 degrees C respectively. However, the films deposited at 500 degrees C had the Austenite and Martensite transitions at 73 and 58 degrees C, respectively. Elastic modulus and hardness values increased from 93 to 145 GPa and 7.2 to 12.6 GPa, respectively, with increase in deposition rates. These results are explained on the basis of change in film composition and crystallization. (C) 2010 Published by Elsevier Ltd

Texture evolution in commercially pure titanium after warm equal channel angular extrusion

Texture development in commercially pure titanium during equal channel angular extrusion (ECAE) through Routes A, Be and C has been studied up to three passes at 400 C. Textures were measured using X-ray diffraction, while the microstructural analyses were performed using electron back-scattered diffraction as well as transmission electron microscopy. Occurrences of dynamic restoration processes (recovery and recrystallization) were clearly noticed at all levels of deformations. Finally, the textures were simulated using a viscoplastic polycrystal self-consistent (VPSC) model. Simulations were performed incorporating basal, prismatic and pyramidal slip systems as well as tensile and compressive twinning. The simulated textures corroborate well with experimental textures in spite of the occurrence of dynamic restoration processes. (C) 2010 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

(Ba3MTiMO9)-Ti-III-O-V (M-III = Fe, Ga, Y, Lu, M-V = Nb, Ta, Sb) perovskite oxides Synthesis, structure and dielectric properties

We describe the synthesis structures and dielectric properties of new perovskite oxides of the formula (Ba3MTiMO9)-Ti-III-O-V for M-III = Fe Ga Y Lu and M-V = Nb Ta Sb While M-V = Nb and Ta oxides adopt disordered/partially ordered 3C perovskite structures where M-III/Ti/M-V metal-oxygen octahedra are corner connected the M-V = Sb oxides show a distinct preference for the 6H structure where Sb-V/Ti-IV metal-oxygen octahedra share a common face forming (Sb Ti)O-9 dimers that are corner-connected to the (MO6)-O-III octahedra The preference of antimony oxides (Sb-V 4d(10)) for the 6H structure which arises from a special Sb-V-O chemical bonding that tends to avoid linear Sb-O-Sb linkages unlike Nb-V/Ta-V d(0) atoms which prefer similar to 180 degrees Nb/Ta-O-Nb/Ta linkages - is consistent with the crystal chemistry of M-V-O oxides in general The dielectric properties reveal a significant difference among Mill members All the oxides with the 3C structure excepting those with Mill = Fe show a normal low loss dielectric behaviour with epsilon = 20-60 in the temperature range 50-400 degrees C the M-III = Fe members with this structure (M-V = Nb Ta) display a relaxor-like ferroelectric behaviour with large E values at frequencies <= 1 MHz (50-500 degrees C) (C) 2010 Elsevier Masson SAS All rights reserved

Microstructure evolution and hardness variation during annealing of equal channel angular pressed ultra-fine grained nickel subjected to 12 passes

The microstructure, thermal stability and hardness of ultra-fine grained (UFG) Ni produced by 12 passes of equal channel angular pressing (ECAP) through the route Bc were studied. Comparing the microstructure and hardness of the as-ECAPed samples with the published data on UFG Ni obtained after 8 passes of ECAP through the route Bc reveals a smaller average grain size (230 nm in the present case compared with 270 nm in 8-pass Ni), significantly lower dislocation density (1.08 x 10(14) m(-2) compared with 9 x 10(14) m(-2) in 8-pass Ni) and lower hardness (2 GPa compared with 2.45 GPa for 8-pass Ni). Study of the thermal stability of the 12-pass UFG Ni revealed that recovery is dominant in the temperature range 150-250A degrees C and recrystallisation occurred at temperatures > 250 A degrees C. The UFG microstructure is relatively stable up to about 400 A degrees C. Due to the lower dislocation density and consequently a lower stored energy, the recrystallisation of 12-pass ECAP Ni occurred at a higher temperature (similar to 250 A degrees C) compared with the 8-pass Ni (similar to 200 A degrees C). In the 12-pass Nickel, hardness variation shows that its dependence on grain size is inversely linear rather than the common grain size(-0.5) dependence.

Absorption-resorption heating cycles with the new working pairs R21-NMP and R21-DMA

The new working pairs, R21-NMP and R21-DMA, find potential application as working pairs for the single stage Resorption Heat Pump (RHP) and the Resorption Heat Transformer (RHT) cycles. A thermodynamic cycle analysis with these pairs shows that single stage RHPs have high COPs in their entire range of operation. RHTs show higher temperature boosts (up to 47 K) than the simple absorption heat transformers. Absorber temperatures of up to 400 K can be achieved in a single stage RHT system using R21 as the refrigerant. However, absorption-resorption systems have inherent limitations on the range of operating temperatures. Besides, they necessitate a higher pump work as compared to simple single stage absorption heating systems.

DNA Photocleavage and Cytotoxic Properties of Ferrocene Conjugates

Ferrocenyl conjugates 2-ferrocenylimidazophenanthroline (1) and 2-ferrocenylimidazophenanthrene (2) were prepared, characterized, and their photoinduced DNA cleavage and photocytotoxic activity were studied. 2-Phenylimidazophenanthroline (3) was used as a control species. Compound 2 was characterized by X-ray crystallography. The interaction of the compounds with double-stranded calf thymus DNA (CT DNA) was studied. The compounds show good binding affinity to CT DNA with K-b values of approximately 10(5) M-1. Thermal denaturation data suggest the groove binding nature of the compounds. The redox-active compounds show poor chemical nuclease activity in the presence of hydrogen peroxide and glutathione (GSH). Compound 1 exhibits significant DNA photocleavage activity in visible light of 476 and 532 nm. Compound 3 shows only moderate DNA cleavage activity. The positive effect of the ferrocenyl moiety is demonstrated by the DNA photocleavage data. Mechanistic investigations reveal the formation of superoxide as well as hydroxyl radicals as the active species. The photocytotoxicity of the compounds in HeLa cells was studied upon irradiation with visible light (400-700 nm). Compound 1 shows efficient photocytotoxic activity with an IC50 value of 13 mu M, while compounds 2 and 3 are less active with IC50 values of > 50 and 22 mu M, respectively.

A study of microstructure and wear behaviour of TiB2/Al metal matrix composites

The present paper deals with the study of microstructure and wear characteristics of TiB2 reinforced aluminium metal matrix composites (MMCs). Matrix alloys with 5, 10 and 15% of TiB2 were made using stir casting technique. Effect of sliding velocity on the wear behaviour and tribo-chemistry of the worn surfaces of both matrix and composites sliding against a EN24 steel disc has been investigated under dry conditions. A pin-on-disc wear testing machine was used to find the wear rate, in which EN24 steel disc was used as the counter face, loads of 10-60N in steps of 10N and speeds of 100, 200, 300, 400 and 500 rpm were employed. The results showed that the wear rate was increased with an increase in load and sliding speed for both the materials. However, a lower wear rate was obtained for MMCs when compared to the matrix alloys. The wear transition from slight to severe was presented at the critical applied loads. The transition loads for the MMCs were much higher than that of the matrix alloy. The transition loads were increased with increase in TiB2 and the same was decreased with the increase of sliding speeds. The SEM and EDS analyses were undertaken to demonstrate the effect of TiB2 particles on the wear mechanism for each conditions.

Variation of surface flashover voltage in SF6 with pressure

Surface flashover characteristics of solid spacers in a rod-plane configuration have been investigated in SF6, at pressures to 400 kPa, for switching impulse voltages to determine the effect of spacer, spacer materials and polarity of applied impulses. The effect of spacer material on the flashover voltage is not significant. For negative polarity impulses, the influence of the spacer is also insignificant. But for positive polarity impulses, at pressures < 200 kPa, the spacer efficiency becomes > 1.0. On the other hand, at pressures > 200 kPa, the presence of spacer drastically reduces the flashover voltage of the system. At about atmospheric pressure also, the spacer efficiency in air has been found to be > 1.0, with the same electrode geometry.

A model for heat transfer in a honey bee swarm

A swarm is a temporary structure formed when several thousand honey bees leave their hive and settle on some object such as the branch of a tree. They remain in this position until a suitable site for a new home is located by the scout bees. A continuum model based on heat conduction and heat generation is used to predict temperature profiles in swarms. Since internal convection is neglected, the model is applicable only at low values of the ambient temperature T-a. Guided by the experimental observations of Heinrich (1981a-c, J. Exp. Biol. 91, 25-55; Science 212, 565-566; Sci. Am. 244, 147-160), the analysis is carried out mainly for non-spherical swarms. The effective thermal conductivity is estimated using the data of Heinrich (1981a, J. Exp. Biol. 91, 25-55) for dead bees. For T-a = 5 and 9 degrees C, results based on a modified version of the heat generation function due to Southwick (1991, The Behaviour and Physiology of Bees, PP 28-47. C.A.B. International, London) are in reasonable agreement with measurements. Results obtained with the heat generation function of Myerscough (1993, J. Theor. Biol. 162, 381-393) are qualitatively similar to those obtained with Southwick's function, but the error is more in the former case. The results suggest that the bees near the periphery generate more heat than those near the core, in accord with the conjecture of Heinrich (1981c, Sci. Am. 244, 147-160). On the other hand, for T-a = 5 degrees C, the heat generation function of Omholt and Lonvik (1986, J. Theor. Biol. 120, 447-456) leads to a trivial steady state where the entire swarm is at the ambient temperature. Therefore an acceptable heat generation function must result in a steady state which is both non-trivial and stable with respect to small perturbations. Omholt and Lonvik's function satisfies the first requirement, but not the second. For T-a = 15 degrees C, there is a considerable difference between predicted and measured values, probably due to the neglect of internal convection in the model.

Combustion synthesis and properties of the NASICON family of materials

The fine-particle NASICON family of materials, MZr2P3O12(where M = Na, K, ½Ca and ¼Zr) and NbZrP3O12, have been prepared by the combustion of aqueous heterogeneous mixtures of stoichiometric amounts of metal nitrate, zirconyl nitrate, niobium phosphate, diammonium hydrogen phosphate, ammonium perchlorate and carbohydrazide (CH) at 400 °C. The formation of NASICON materials was confirmed by powder X-ray diffraction (XRD), IR, solid-state (31P) NMR spectroscopy and thermal expansion coefficient measurements. The combustion-synthesized NASICON powders have an average agglomerate size of 9�13 µm with a specific surface area varying from 8 to 28 m2 g�1. The powders pelletized and sintered in the range 1100�1200 °C for 5 h achieved 95�97% theoretical density and showed fine-grain microstructure. The coefficient of thermal expansion of a sintered compact was measured up to 500 °C and ranged from �1.5 × 10�6°C�1 to 1.0 × 10�6°C�1 depending on the composition.

Processing map for hot working of powder

The constitutive flow behavior of a metal matrix composite (MMC) with 2124 aluminum containing 20 vol pct silicon carbide particulates under hot-working conditions in the temperature range of 300 °C to 550 °C and strain-rate range of 0.001 to 1 s-1 has been studied using hot compression testing. Processing maps depicting the variation of the efficiency of power dissipation given by [2m/(m + 1)] (wherem is the strain-rate sensitivity of flow stress) with temperature and strain rate have been established for the MMC as well as for the matrix material. The maps have been interpreted on the basis of the Dynamic Materials Model (DMM). [3] The MMC exhibited a domain of superplasticity in the temperature range of 450 °C to 550 °C and at strain rates less than 0.1 s-1. At 500 °C and 1 s-1 strain rate, the MMC undergoes dynamic recrystallization (DRX), resulting in a reconstitution of microstructure. In comparison with the map for the matrix material, the DRX domain occurred at a strain rate higher by three orders of magnitude. At temperatures lower than 400 °C, the MMC exhibited dynamic recovery, while at 550 °C and 1 s-1, cracking occurred at the prior particle boundaries (representing surfaces of the initial powder particles). The optimum temperature and strain-rate combination for billet conditioning of the MMC is 500 °C and 1 s-1, while secondary metalworking may be done in the super- plasticity domain. The MMC undergoes microstructural instability at temperatures lower than 400 °C and strain rates higher than 0.1 s-1.

Design and realization of high-performance wave-pipelined 8×8 b multiplier in CMOS technology

Wave pipelining is a design technique for increasing the throughput of a digital circuit or system without introducing pipelining registers between adjacent combinational logic blocks in the circuit/system. However, this requires balancing of the delays along all the paths from the input to the output which comes the way of its implementation. Static CMOS is inherently susceptible to delay variation with input data, and hence, receives a low priority for wave pipelined digital design. On the other hand, ECL and CML, which are amenable to wave pipelining, lack the compactness and low power attributes of CMOS. In this paper we attempt to exploit wave pipelining in CMOS technology. We use a single generic building block in Normal Process Complementary Pass Transistor Logic (NPCPL), modeled after CPL, to achieve equal delay along all the propagation paths in the logic structure. An 8×8 b multiplier is designed using this logic in a 0.8 ?m technology. The carry-save multiplier architecture is modified suitably to support wave pipelining, viz., the logic depth of all the paths are made identical. The 1 mm×0.6 mm multiplier core supports a throughput of 400 MHz and dissipates a total power of 0.6 W. We develop simple enhancements to the NPCPL building blocks that allow the multiplier to sustain throughputs in excess of 600 MHz. The methodology can be extended to introduce wave pipelining in other circuits as well