Effect of carbides on the austenite grain growth characteristics in 1Cr-1C and 6Cr-1Mo-1C steels

The nature of carbidesvis-a-vis austenite grain growth characteristics in a ball-bearing steel (1Cr-1C) and in a wear-resistant steel (6Cr-1Mo-1C) is reported. Quantitative EPMA analysis was used to determine the type of carbides andin situ examination of austenite grain growth was carried out in a hot-stage microscope. The grain size against temperature plots indicated an initial stage of slower normal grain growth, followed by the abnormal growth, or, grain coarsening beyond a critical soaking temperature. The M₃C type of carbides containing a small amount of chromium could inhibit grain coarsening up to 1223 K in 1Cr-1C steel, whereas the alloy carbides of the M₇C₃ type with a substantial amount (about 35 mass%) of chromium were more effective in restricting grain growth even up to 1273 K in the 6Cr-1Mo-1C steel. In addition, the grain sizes obtained in the latter steel were found to be considerably smaller than those of the former variety at all soaking temperatures investigated.     

Special cause management: A knowledge-based approach to statistical process control

In this paper we discuss a set of software tools developed to support the tasks associated with managing special causes of variation in a manufacturing process. These tasks include the detection of significant changes in process variables, a diagnosis of the causes of those changes, the discovery of new causes, the management of performance data, and the reporting of results. The software tools include automatic recognition of out-of-control features in critical process variables, rule-based diagnosis of special causes, a model-based search for symptoms where a diagnosis is not possible, and automated reporting aids. It is hoped that these tools will enhance the efficiency of special cause management.     

Is there ferromagnetic to spin-glass transition in PdAuFe alloys?

Electrical resistivity studies on several (Pd_1–x Au _x )_99.93Fe_0.07 alloys between 25 mK and 1 K are reported. The experiments reveal interesting features of the impurity spin polarization with the addition of Au atoms to pure PdFe_0.07 alloy. Forx<0.28 the ternary alloys exhibit a familiarT ² dependence for belowT _c , indicative of complex magnetic behavior. For still higher Au concentrations, resistivity maxima occur in these alloys, reflective of short-range magnetic ordering. Arguments are presented to show that this is strongly suggestive of spin-glass-type freezing at lower temperatures, as is observed in many canonical metallic spin-glasses.     

Comparative nutritional quality of palmstearin-liquid oil blends and hydrogenated fat (vanaspati)

An attempt was made to use high-melting lowdigestible fat palmstearin as a vanaspati substitute by blending it with polyunsaturated fatty acid-rich liquid oils. This blending produced fat products of zero-trans fatty acid content and melting points below the human body temperature, so that they can be digested easily. The new blended products were fed to male albino rats (Charles Foster strain); the coefficients of digestibilities were 94.2% for palmstearin and rapeseed oil blend, 95.1% for palmstearin and sunflower oil blend, and 96.2% for palmstearin and soybean oil blend, which were somewhat better than the digestibility coefficient of conventional vanaspati (93.6%). Feeding experiments for three months showed comparable results in terms of serum lipid profiles. The blended products significantly increased the total cholesterol level but not the free cholesterol level in serum and liver of rats when compared with those of the conventional vanaspati group of rats.     

Cool plasma functionalization of nano-crystalline diamond films

It was demonstrated that an atmospheric pressure dielectric barrier glow discharge system is a powerful tool for the surface functionalization of nano-crystalline diamond films. Diamond film functionalization was performed in minutes using plasma discharges generated with fluorine containing gases. The chemical bonds formed between reactive species generated in the plasma and diamond surface were confirmed by FTIR and XPS analysis. Following plasma treatment, XPS analysis revealed a high concentration of F on the diamond surface, nearly 50 atomic percent. FTIR analysis revealed the presence F-bands related to CF₃ (CF₂) stretching vibrations and symmetric and asymmetric CF₂ vibrations. It was concluded that atmospheric pressure dielectric barrier glow discharge is a highly effective means to fluorinate diamond surfaces within a modest time.     

The influence of the lewis number on the dynamics of chemically reacting systems

The influence of Lewis number on stability and oscillations for stirred tanks, catalytic wires and gauzes, and catalyst particles is determined quantitatively. The mathematical structure is discussed and illustrated by example. Relaxation oscillations are found to be the natural asymptote to the bifurcating limit cycles as Le → 0.     

The theory and practice of safe handling temperatures

Many hot objects which may be touched or handled every day can cause either discomfort, pain or burning of the skin. The precise effect will depend on the Contact Temperature tC, an intermediate value between the hot object and the skin temperature. The value of tC varies with the material, and is governed by the Contact Coefficient b, a property of the material which has a wide range of values from metals to plastics. In the experiments with 48 female subjects, surface and contact temperatures for three materials were measured over a wide range, and subject reactions recorded on a five-point comfort scale. From the heat conduction theory outlined, and using the calculated values of b for the three materials, the predicted safe surface temperatures were determined. These predicted values were then compared with the observed temperatures and with those recommended in British Standards.     

STEADY STATE AND DYNAMIC MODELLING OF A PACKED BED REACTOR FOR THE PARTIAL OXIDATION OF METHANOL TO FORMALDEHYDE II. EXPERIMENTAL RESULTS COMPARED WITH MODEL PREDICTIONS

Heterogeneous and pseudohomogeneous two-dimensional models are compared to steady state and dynamic experimental data from a packed bed reactor for the partial oxidation of methanol to formaldehyde over an iron oxide-molybdenum oxide catalyst. Highly effective parameter estimation software was used to fit selected model parameters to large sets of experimental data so as to obtain small residuals. Heat transfer parameters which were successful in matching data from experiments without reaction were not capable of fitting data from experiments with reaction, and it was necessary to increase the radial heat transfer for higher temperatures or reaction rates. Axial composition profile data was represented by estimating the preexponential factors and activation energy in a half-order redox rate expression for methanol oxidation. After some decline in catalyst activity, a time-varying axial catalyst activity profile was determined from the data. A redox-type rate expression for the oxidation of formaldehyde to carbon monoxide was proposed to fit the data. The dynamics of the reactor temperature profile were accurately represented by the model. The heterogeneous and pseudohomogeneous models gave similar results in fitting experimental data, although the parameters determined for the two models were somewhat different.     

The quasi-steady-state approximation in continuous stirred tank reactors

The Quasi-steady-state-approximation (QSSA) applied lo continuous stirred tank reactors (CSTR) is examined. The induction period is found to be somewhat longer and the error in the QSSA larger than for batch reactors. This error is usually insignificant except when CSTR conversions are low. An alternative approximation is proposed for this case. The errors in the QSSA are also illustrated for the well known cases of Enzyme and Free-Radical polymerization kinetics.     

Novel electron beam‐modified surface‐coated silica fillers: Physical and chemical characteristics

A novel process of surface modification of silica fillers has been performed by coating with an acrylate monomer, trimethylol propane triacrylate (TMPTA) and with a silane coupling agent, triethoxy vinyl silane (TEVS), followed by electron beam irradiation of these coated fillers. The surface‐modified fillers have been characterized by Fourier‐Transform Infrared Analysis (FTIR), Electron Spectroscopy for Chemical Analysis (ESCA), Contact angle measurements by dynamic wicking method, Scanning Electron Microscopy (SEM), Energy dispersive X‐ray spectroscopy (EDX), Transmission Electron Microscopy (TEM), Fractal studies, Thermogravimetric analysis (TGA), and X‐ray diffraction (XRD) studies. Presence of the acrylate and the silane coupling agent on the modified fillers is confirmed from the above studies. The contact angle measurements suggest a significant improvement in hydrophobicity of the treated fillers, which is supported by water flotation test. After irradiation and acrylate treatment an increase in filler aggregation is observed, which is not as significant in the case of silanized silica filler. However, XRD studies demonstrate that the entire modification process does not alter the bulk properties of the fillers. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 2255–2268, 2002