Identical Process Conditions Research Articles

Nitrogen diffusivity in expanded austenite

Expanded austenite is a metastable phase formed after nitrogen insertion into austenitic stainless steel, at elevated temperatures between 350 and 400 °C with nitrogen contents between 5 and 30 at.%, thus leading to a lattice expansion of up to 13%. The layer thickness can vary up to a factor of ten for different alloys at identical process conditions. The main part of the nitrogen depth profiles can be described by an complementary error function. However, close to the end of the profile, a rather sharp decrease of the nitrogen content is found. Calculating the concentration dependent nitrogen diffusivity, it can be shown that this kink corresponds to steep increase of the diffusivity by nearly a factor of ten. A systematic study of different steel grades is presented, trying to correlate the diffusivities with the alloying content and to predict the ‘suitability’ of austenitic stainless steel for nitriding.

Underlayer work function effect on nucleation and film morphology of chemical vapor deposited aluminum

The dependence of early stage of dimethylaluminum hydride (DMAH)-sourced aluminum chemical vapor deposition on underlayer material was investigated. Identical process conditions were used to deposit the aluminum on TiN, TaN and Ti-W surfaces. Surface coverage and particle densities of aluminum deposited on TiN were much greater than those deposited on Ti-W or TaN. Work function measurements performed on the three metal surfaces suggest that the difference in nucleation rate on TiN compared to TaN and Ti-W is due its increased ability to donate electrons to the DMAH decomposition process.

Hydrodynamic characteristics and mixing behaviour of Sclerotium glucanicum culture fluids in an airlift reactor with an internal loop used for scleroglucan production.

The filamentous fungus, Sclerotium glucanicum NRRL 3006, was cultivated in a 0.008 m(3) airlift bioreactor with internal recirculation loop (ARL-IL) for production of the biopolymer, scleroglucan. The rheological behaviour of the culture fluid was characterised by measurement of the fluid consistency coefficient (K) and the flow behaviour index (n). Based on these measurements, the culture fluid changed from a low viscosity Newtonian system early in the process, to a viscous non-Newtonian (pseudoplastic) system. In addition, reactor hydrodynamics and mixing behaviour were characterised by measurement of whole mean gas hold-up (epsilon(g)), liquid re-circulation velocity (U(ld)) and mixing time (t(m)). Under identical process conditions, the effects of the viscosity of the culture fluid and air flow rate on epsilon(g), U(ld) and t(m) were examined and empirical correlations for epsilon(g), U(ld) and t(m) with both superficial velocity U(g) and consistency coefficient K were obtained and expressed separately. The correlations obtained are likely to describe the behaviour of real fungal culture fluids more accurately than previous correlations based on Newtonian or simulated non-Newtonian systems.

Removal of divalent heavy metal mixtures from water by Saccharomyces Cerevisiae using crossflow microfiltration

The removal of heavy metal ions, Ni 2+, Cu 2+ and Pb 2+ using yeast ( Saccharomyces cerevisiae) as carriers in a crossflow microfiltration is investigated. The effects of yeast cell and electrolyte concentrations on the transient and steady-state permeate flux and metal ion rejections are established. It is found that the metal ion rejection reaches a plateau if yeast cell concentration is greater than ∼2 g/l as a result of cell aggregation. The binding affinity of the metals to yeast cell is Pb 2+>Cu 2+>Ni 2+, which is also reflected in the metal ion rejection under identical process conditions. Because of the formation of yeast cell flocks in the presence of Pb 2+, permeate flux is also higher for this metal. The presence of NaCl decreases both rejection and permeate flux for Ni 2+ and Cu 2+ but not for Pb 2+. When binary or ternary metal mixtures are used, the rejection of the individual metals is reduced except that of Pb 2+. It is found that the pseudo-gel concentration is unaffected by the presence of metal ions.

Comparison of Hydrodenitrogenation of Basic and Nonbasic Nitrogen Compounds Present in Oil Sands Derived Heavy Gas Oil

The hydrodenitrogenation of oil sands-derived heavy gas oil has been conducted in a trickle bed reactor over a commercial Ni−Mo/Al2O3 catalyst in the temperature range of 365−415 °C, pressure in the range of 65−88 bar, liquid hourly space velocity in the range of 0.5−2 h-1. The hydrogen/heavy gas oil ratio has been changed from 400 to 1000 mL/mL. The study was conducted to determine the effects of these variables on the relative rates of conversion of total, basic, and nonbasic nitrogen compounds. It was observed that rate of conversion of nonbasic nitrogen compounds was lower than that of basic nitrogen compounds under identical process conditions. The pressure and hydrogen/heavy gas oil ratio have a more significant effect on the conversion of nonbasic nitrogen compound as compared to their effect on the conversion of basic nitrogen compounds. The effect of excess hydrogen sulfide on the conversion of basic and nonbasic nitrogen compounds has also been studied by adding butanethiol in the feed gas oil. An increase in the quantity of butanethiol decreases the conversion of both basic and nonbasic nitrogen compounds. It was also observed that in the region of higher space time (about 1.5−2 h), the conversion of nonbasic nitrogen compound increased at a sharp rate as compared to that of basic nitrogen compounds. This may be possibly due to the generation of more basic nitrogen compounds from the nonbasic ones. The kinetics of the conversion of nitrogen compounds has also been studied in the present work.

Morphology and reduction kinetics of fluxed iron ore pellets

The present paper describes studies of the reduction and sintering behaviour, followed by examination of the structural changes taking place, during direct reduction of fluxed composite (ore plus coal) pellets. The kinetics and morphological aspects of the direct reduction of fluxed composite pellets are compared with those for the gaseous reduction of fluxed ore pellets without carbon addition. It is shown that the chemical reaction is the rate limiting factor for fluxed composite pellets, and the mass transport of reactant gas through the reaction product iron layer governs the overall reduction process in the case of fluxed ore pellets. Microscopic analysis of the fluxed composite pellets has indicated no tendency to form a reduction inhibition iron shell towards the end of the reduction, as found in the case of gaseous reduction of fluxed ore pellets under identical reduction process conditions. The effects of basicity, Fe/C, temperature, and other variables on morphological and microstructural changes in the directly reduced fluxed composite pellets have been experimentally investigated in the present work.

The Influence of Residual Stresses on the Mechanical Behaviour of ZrO<sub>2</sub>/Ni/AISI 316 Diffusion Bonds

In this paper the influence of residual stresses on the mechanical behaviour of zirconia/nickel/stainless steel AISI 316 diffusion bonds is described. A number of ZrO 2 /Ni/AISI 316 bonds was made under identical process conditions with Ni interlayers of different thickness. The strength of the combination was measured using shear strength testing. It appears that the bonded combination has a low strength, as residual stresses due to differences in thermal expansion between the different materials cause fracture in the zirconia during testing. The strength values have a relatively large scatter, yielding a low value of the Weibull modulus. To obtain insight in the residual stress distribution, finite element (FEM) calculations were carried out. From the results of these calculations, it can be concluded that the level of residual stress is rather high, especially in the ZrO 2 . The calculations of the stresses can be used to explain the type of failure of the diffusion bonded ZrO 2 /Ni/AISI 316 combinations.

Effect of Geometry on the Performance of Intermingling Nozzles

This study investigates the effect of nozzle geometry on the intermingling process. The dimensions of intermingling nozzles with single air inlets extended across the width of a rectangular yam channel are systematically varied. Nozzles with this cross-sectional shape prove to be easy to manufacture and efficient at intermingling. The performance is evaluated by visually inspecting the intermingled yarns and by measuring the nip fre quency. We have found that the performance of nozzles with large inlet widths is weakly dependent on yam channel geometry. The performance of nozzles with the smallest air inlet widths, on the other hand, is sensitive to yarn channel geometry. The smallest and largest yam channels we have considered give poor intermingling results. Control of the yam path is beneficial for the success and consistency of the intermingling process. Using yam guides to create a diagonal yarn path across the nozzle has the additional advantage of decreasing noise production. Our extended air inlet slot ensures continuous exposure of the yarn to the supply air stream across the entire width of the yarn channel in this arrangement. We also compare our designs with four industrial nozzles under identical process conditions. This study reveals similar trends for nip frequency and power consumption. The results agree with the broad trend established in the geometry study that the shape of the yam channel is not critical, provided the air inlet is large enough.

An Experimental and Numerical Investigation of Heat Transfer Fouling and Fluid Flow in Flat Plate Heat Exchangers

Recent investigations have shown that similar commercial heat exchanger plates with different corrugation patterns, fouled at very different rates under identical process conditions. These differences are attributed to the effects of flow distribution on fouling rates in the plate channels. Consequently, the effects of flow distribution on fouling were studied experimentally using flat heat exchanger plates with and without flow distributors. The aim of the different distributor designs was to obtain a more even flow distribution within the plate channels. Flow simulations were performed for different distributor designs and different plate shapes. Computational results compared well with those obtained experimentally.

Effect of Primary Particle Size on Granule Growth and Endpoint Determination in High Shear Granulators

ABSTRACT Three different grades of lactose monohydrate having widely differing mean particle sizes, yet similar tap densities, were granulated using a 25L instrumented Fielder mixer. The size distribution, porosity, and pore saturation of the wet granules were determined using a combination of “frozen granule” sieve analysis, mercury pycnometry, and oven drying. The granulating system was found to operate at quasi-steady-state, as granule growth ceased afler liquid addition was terminated. The resultant granule size distributions were strongly dependent on lactose grade. with coarser grades yielding larger granules for identical process conditions. In contrast. the magnitude of the power curves decreased with increasing primary particle size. Both of these observations are consistent with the fact that both the capillary and viscous interparticle fluid forces, which are believed to provide the main interparticle bonding forces in the wet mass, are inversely proportional to particle size.

Proteolysis of fusion proteins: stabilization and destabilization of staphylococcal protein A and Escherichia coli beta-galactosidase.

The product yield of staphylococcal Protein A reached only 1.8% of the cell dry weight, while the corresponding value was 14% for a fusion protein composed of Protein A and Escherichia coli beta-galactosidase [1], when produced in the same E. coli host strain, with the same promoter and under identical process conditions. Measurement of the stability of Protein A in vivo showed that it was quickly degraded in the cell with a half-life of 30 min when the protein was expressed alone, but after fusion to beta-galactosidase, the Protein A part became considerably stabilized. In spite of the fast intracellular proteolysis of Protein A, few degradation products could be identified on Coomassie Brilliant Blue-stained SDS/PAGE gels after IgG purification, indicating an even faster degradation of the Protein A fragments. Such degradation products, however, accumulated during incubation of the disintegrated cells. Intracellular degradation intermediates could be demonstrated with the more sensitive Western-blot technique. This technique also revealed that a slow degradation took place not only in the Protein A moiety of the fusion protein, but also in the beta-galactosidase moiety. A control with native beta-galactosidase also showed a weak in vivo proteolysis of this molecule, but it was more stable in free form than in the fused form. This means that the proteolytically very sensitive Protein A was stabilized by fusion with beta-galactosidase, but the originally rather stable beta-galactosidase became slightly more susceptible to proteolysis after the fusion.

Comparison of fundamental properties of r.f.-sputtered TiN x and HfN x coatings on steel substrates

Titanium and hafnium based coatings in this work were sputtered on steel substrates in a r.f. sputtering unit with a diode arrangement. By feeding nitrogen in addition to the inert processing gas argon, TiN x and HfN x coatings were deposited under reactive sputtering conditions. Deposition pressure, nitrogen flow in the chamber and bias voltage on the substrates were systematically varied to get optimized coating systems. The coatings were investigated on their fundamental properties in order to compare titanium and hafnium based films, sputtered under identical process conditions. The results for hardness, deposition rate, internal stress, adhesion, structure, phase analysis and wear show that the properties of HfN x coatings are less influenced by the deposition process than the coatings of TiN x in the field of selected deposition parameters. The behavior of HfN x is comparable to TiN x , owing to a very similar crystal structure of the materials, but the conclusion of this present paper the well known TiN x has to be preferred for tribological applications in mechanical components.

Off-Axial, Gas-Jet-Assisted, Laser Cutting of 6.35-mm Thick Stainless Steel

A dual gas-jet, laser-cutting technique involving coaxial and off-axial oxygen gas flows was developed to cut 6.35-mm thick AISI 304 stainless steel plates with a 1.2-kW CO2 gas transport laser at a cutting speed of 12.7 mm/sec (30 in./min). Under identical process conditions, the single, coaxial gas jet could not cut the stainless steel although the cutting speed was reduced to 2.11 mm/sec (5 in./min). Thresholds of off-axial nozzle diameter, gas-impinging angle, oxygen pressure, and other process parameters were determined to obtain clean-cut edge quality (average dross height 0.25 mm). Experimental data coupled with a fluid-dynamics model of gas flow were presented to show the effectiveness of the dual gas-jet, laser-cutting method in achieving the maximum machining rate without deteriorating the quality of cut.

Schichtsynthese von Übergangsmetallnitriden mit ionenstrahlunterstütztem Aufdampfen

AbstractNitrides of titanium, chromium, molybdenum and tantalum were prepared by evaporation of the metal in an atmosphere of reduced nitrogen pressure under simultaneous irradiation with highly energetic nitrogen ions.—Chemical analysis showed that the elemental composition of the nitrides is strongly correlated with ion irradiation intensity and with chemical reactivity of the metal. Under identical process conditions titanium formed TiN, but chromium Cr2N. In case of molybdenum and tantalum X‐ray diffractometry revealed that by deposition under ion irradiation with high energy and beam intensity metastable nitrides with cubic structure could be formed.

Slurry phase Fischer-Tropsch synthesis with iron-manganese catalysts

Synthesis gas was reacted over different compositions of iron-manganese Fischer-Tropsch catalysts in a slurry reactor. The reactor operates in a back-mixed mode with a continuous flow of feed gas through the catalyst suspended in the liquid medium. Four catalysts with iron-manganese ratios of 57/43, 44/56, 22/78, and 10/90 were investigated at identical process conditions after a standard activation procedure. With time on stream for each catalyst system, hydrogenation of olefins occurred, along with olefin isomerization reactions. Activity, selectivity, and stability are discussed in general. Analyses of used catalyst samples are also reported.

Conversion of normal paraffinic hydrocarbons over high-fluorine catalyst

The feedstock was a 240-350~ gas oil cut. The studies were performed in a laboratory flow-type unit that has been described in [7], with unmodified and modified catalysts, the latter containing 10% fluorine by weight, under identical process conditions: temperature 400~ space velocity 1 h -z , pressure 30 kgf/cm 2, and hydrogen/hydrocarbon feedstock ratio i000 m3/m a. The catalytic action of the modified catalyst was evaluated on the basis of the change in distillation curve, hydrocarbon composition, and low-temperature properties of the liquid products.