Evolution of properties of parts during MIM and sintering of recycled oxide particles

Metal injection moulding (MIM) is an established process for high volume production of complex shaped metallic parts using commercially available feedstocks. The characteristics of parts after moulding, debinding, and sintering cannot be simply predictable from raw materials because the properties get altered with the process parameters and the corresponding levels of porosity during processing steps. In this study, physical properties, microstructure, and mechanical properties of the MIM parts have been characterised to understand the evolution of strength during various steps in MIM processing. Feedstocks with different binder loading show a considerable difference in physical as well as mechanical characteristics. During sintering of parts which have solid loading of grinding sludge, simultaneous in situ reduction and densification takes place, whereas only densification occurs in carbonyl iron parts. It is, therefore, possible to make complex shaped parts of different levels of porosity from downgraded shop floor metallic waste.     

Homogeneous asymmetric hydrogenation ofo-chloroacetophenone to enantiomerically pureo-chloro-(1-phenyl)ethanol catalyzed by BINAP-Ru(II) complex

The BINAP-Ru(II) catalyst (2,2-bis(diphenylphosphino)-1,1-binaphthyl)chloro(p-cymene)rutheniun chloride is found to be highly active and enantioselective for homogeneous asymmetric hydrogenation of o-chloroacetophenone to optically pureo-chloro-(1-phenyl)ethanol. In contrast to results of Noyori and coworkers, no organic and inorganic bases are required to obtain high activities and enantioselectivities     

Synthesis of submicron size silver powder for passive components application

Submicron silver powder was prepared from AgNO₃ by a chemical reduction method in the presence of a mixture of caprylic acid and triethanolamine as a surfactant. Hydrazine hydrate (N₂H₄·H₂O) is preferred as a reducing agent. A spherical silver powder with an average particle size of about 150 nm was achieved. Effort was also made to correlate the crystal structure and microstructure evolution of the prepared powders with the resultant thick film characteristics.     

Non-monotonic lattice parameter variation with crystallite size in nanocrystalline solids

An anomalous dependence of the lattice parameter on the crystallite size of nanocrystalline ball-milled powders of metals was observed: lattice contraction followed by lattice expansion with decreasing crystallite size. These data were determined by application of detailed X-ray diffraction measurements. To this end the lattice parameters of the metals investigated – nickel, copper, iron and tungsten – were precisely determined by correcting for influences of stacking faults, in the face-centred cubic metals, as well as by correcting for instrument-related aberrations. The non-monotonic variation of the lattice constant was interpreted as the result of two competing mechanisms: interface-stress-induced contraction vs. expansion as a result of the stress field generated at the crystallite boundary due to the increased excess free volume in the crystallite boundary upon decreasing crystallite size.     

Hydrazine method of synthesis of γ-Fe2O3 useful in ferrites preparation. Part III – study of hydrogen iron oxide phase in γ-Fe2O3

Direct current electrical conductivity () measurements as a function of temperature have been carried out on -Fe₂O₃ prepared from precursors, iron (II) carboxylatohydrazinates, -FeOOH and hydrazinated -FeOOH. The conductivity variation obeys an Arrhenius equation, _I = \_oe^- E / kT and the plots of log versus 1/T of the as prepared -Fe₂O₃, which are in general linear, during the very first heating up to 350°C and cooling to room temperature (RT) do not overlap. This indicates a hysteresis behavior of conductivity, thereby suggesting involvement of two different conductivity mechanisms. When the heat treated sample was equilibrated in a known partial pressure of moisture at 200°C and then conductivity measured from RT, the log plots during heating and cooling did not overlap and a hysteresis behavior similar to the as prepared -Fe₂O₃ is observed again in the conductivity. Water is considered to be crucial during the synthesis of -Fe₂O₃ through magnetite, Fe₃O₄. Protons, H⁺, are thought to be introduced in the spinel Fe₃O₄ making it defective and the oxidation product of this is -Fe₂O₃ which retains few protons in its spinel structure. From the structural similarity of such proton incorporated -Fe₂O₃ and lithium ferrite, LiFe₅O₈, (Fe³⁺)₈ [Fe³⁺ ₁₂ Li¹⁺ ₄]O₃₂, a formula HFe₅O₈, (Fe³⁺)₈ [Fe³+₁₂H¹+₄]O₃₂ is suggested. A hydrogen iron oxide of formula H_1-xFe_5+x3O₈, where x 0.1 is probably formed as a maximum limit. Protons are removed during the very first heating of the as prepared sample in the present studies and hence the conductivity of proton free -Fe₂O₃ is different and therefore a hysteresis behavior is observed. Moisture equilibration reintroduces the protons. The lithiated samples in the present studies were found to substitute for protons in -Fe₂O₃ and no hysteresis behavior is observed in such samples even after moisture equilibration.     

New strategies for the Hofmann reaction

Some new strategies, such as the use of hydrotropes, surfactants, co-solvent, etc., were applied to the Hofmann reaction of fatty amides to obtain isocyanates, amines and carbamates. Additionally, some industrially important aromatic amines were synthesised.     

Solid Circulation Rate in Recirculating Fluidized Bed

Recirculating fluidized bed (RCFB) is a spouted bed with a draft tube at the center. This is used for a variety of operations such as incineration, coal and heavy crude oil gasification, grain drying, blending and mixing, etc. Solid circulation rate is an important parameter for any circulation system, and it describes the efficiency of operation. Mathematical models do not always predict the circulation rates accurately. Hence, there is a need to measure the circulation rates directly. Most of the methods (for direct measurement) reported are either costly, involving high expertise and sophisticated equipment, or time consuming. A butterfly valve arrangement can measure the solid circulation rate accurately and quickly. It is sturdy, and the cost/expertise involvement is the bare minimum. Solid circulation rates measured directly using the butterfly valve arrangement are compared with the solid circulation rates computed based on the particle velocity and the operating voidage in the downcomer bed. Solid circulation rates measured directly are in close comparison (mostly within a deviation of 10%) with the computed circulation rates.     

Performance Prediction of an RCFB Incineration System

Incineration, in spite of being a costly option, is widely used for the treatment and disposal of solid, liquid, and gaseous wastes. Use of fluidized beds paved the way for less polluting incinerators. Circulating fluidized bed systems can burn low-heat-content watery wastes without (or with minimum) auxiliary fuel. Equations of heat transfer and heat balance for different zones of a recirculating fluidized bed (RCFB) incineration system are presented along with a computational procedure to predict the performance details of the system. The method presented is applied to compute the performance of an RCFB incineration system burning distillery spent wash. Results show that RCFB incinerators are capable of burning a spent wash of solids content considerably lower than 60%. The incineration units in operation at present concentrate spent wash to about 60% solids content in external evaporators for autogenous burning. This costly and difficult operation can be minimized by the use of RCFB for incineration.     

Comparison of the surface and catalytic properties of rare earth‐promoted CaO catalysts in the oxidative coupling of methane

Rare earth (viz. La, Ce, Sm, Nd and Yb) promoted CaO catalysts have been investigated, comparing their surface properties (viz. surface area and basicity/base strength distribution) and catalytic activity/selectivity in the oxidative coupling of methane at different reaction conditions (temperatures, 650–800 °C, CH₄/O₂ ratios, 2.0–8.0 and space velocity, 51 360 cm³ g^?1 h^?1). The surface properties and catalytic activity/selectivity are strongly influenced by the rare earth promoter and its concentration. Apart from the Sm‐promoted CaO catalyst, both the total and strong basic sites (measured in terms of CO₂ chemisorbed at 50° and 500 °C respectively) are decreased due to the promotion of CaO by rare earth metals (viz. La, Ce, Nd and Yb). The catalytic activity/selectivity is strongly influenced by the temperature, particularly below ?700 °C, whereas at higher temperature no further effect is seen. The La₂O₃? CaO, Nd₂O₃? CaO and Yb₂O₃? CaO catalysts showed high activity and selectivity, and also their results are comparable. Among the catalysts, Nd‐promoted CaO (with Nd/Ca = 0.05) showed the best performance (19.5% CH₄ conversion with 70.8% C₂₊ selectivity) in the oxidative coupling of methane. A close relationship between the surface density of total and strong basic sites (measured in terms of CO₂ chemisorbed at 50° and 500 °C respectively) and the C₂₊ selectivity and/or C₂₊ yield has been observed. Copyright © 2005 Society of Chemical Industry     

Citrate gel route for synthesis of dense pyrochlores

The solid solution of pyrochlore oxides, Nd₂Zr_xTi_2−xO₇ (x = 0.2, 0.4, 0.6, 0.8 and 1.0) was synthesized by citrate gel method and the conventional ceramic method. The results indicate that the citrate gel method gives pyrochlore phase formation at a much lower temperature and better morphology of the product oxides as compared with the ceramic method. The dc conductivity study was carried out on some samples to understand the defects, if any, in the lattice of the solid solution Nd₂Ti_xZr_2−xO₇ (x = 0.2, 0.4, 0.6, 0.8 and 1.0) on substitution of Zr by Ti. The formation of defects in the lattice on substitution of Zr by Ti, was explained on the basis of XPS studies.