Formation of pearlitic banded structures in ferritic-pearlitic steels

The conditions for ferrite and pearlite banding in strip and plate made of structural steels were investigated. Factors found to influence the formation of banded structures were the cooling rate during the γ/α-transformation, the former austenite grain size, and the work-hardened condition of the former austenite. Analyses with the aid of an electron beam microprobe made it possible to demonstrate that the carbon-rich bands correspond locally with banded manganese enrichments, yet that they do not form before the course of the γ/α-transformation as a result of secondary segregation. It was possible to explain the mechanism of action of the influencing factors on the basis of this model.     

The formulation and use of mixed collectors in sulphide flotation

Mixtures of collectors have been widely used for many years in sulphide flotation, and a range of performance benefits have been reported for many different systems. The combinations of collector types have varied, as have the ratios that have been used. Synergistic effects have been obtained (greater than the sum of the parts) and in some cases the mechanisms of this improved behaviour have been identified. These benefits have been attributed to increased carrying capacity of the froth phase, faster kinetics, and more successful recovery of middling or coarse particles. It is the interaction between the various components of the mixed collector system, rather than the individual main effects, that dominate the performance benefits. The process benefits include increased paymetal recoveries and grades – as well as increased rates of recovery whilst using lower dosages of reagents. Various mechanisms have been reported and are discussed. These have been shown to affect different composition/liberation classes and sizes of mineral particles. In recent years, automated quantitative mineralogy and surface analysis technology such as ToF-SIMS have enabled the development of better information, to establish what aspect of the process has been affected. This has been successful mostly for use in a diagnostic capacity. Candidate selection for the mixed collector suite is presently based on experience and contextual knowledge. Predictive properties from these systems are a desirable future goal. Currently optimum combinations are preferably identified experimentally at laboratory scale prior to any plant trial. It is recommended that such laboratory work be performed using a factorial design with replicates and quality controls, such as may be delivered from High-Confidence Flotation Testing. The purpose of this paper is to summarise and review current theory and practice in the usage of mixtures of collectors in sulphide flotation – both in the application and in research in order to develop insights and guidelines to develop a methodology for use in a predictive capacity. A case study demonstrating this approach will be published at a later date.     

Design and measurement of small recovery gains: A case study at Raglan concentrator

The appearance of a significant amount of liberated fine pentlandite in the Raglan tailings, during a campaign to demonstrate future ore behaviour, called attention to a recovery opportunity. This opportunity was identified by a statistical benchmark survey of the operation during that campaign, and QEMSCAN measurement of these survey samples. This development was caused by escalating ore treatment rates and different characteristics in future ore sources. It was thus proposed to change the selection of collector from potassium amyl xanthate (PAX) to potassium isobutyl xanthate (PIBX). Laboratory scale flotation testwork, using high-confidence flotation testing, followed. The PIBX showed much faster flotation than the PAX. Nickel yield to first rougher concentrate was increased from 23.5% to 44.2%. The Raglan flowsheet bypasses this first rougher concentrate directly to final concentrate. Thus there was an expectation that overall performance would improve at plant scale when using PIBX. A designed plant trial was implemented in 2007 to measure and confirm the performance gain. This trial design used on–off switching following a 3-month baseline data block of normal operations using PAX. This layout provided checking of standard PAX performance prior to and during the trial. Thereafter, they were used to evaluate the trial blocks using PIBX. This trial format was deliberately designed so as to overcome the effects of autocorrelation in the operations data. In this way, small but significant metal recovery gains may be measured and proven in a plant trial. The paper describes the case study to show that this approach successfully blocks out autocorrelation in time, which is an obstacle in analysing concentrator operations data. The results showed that the PIBX had produced clear and statistically significant recovery gains for Ni, Cu, Pt and Pd. Adjusted for feed and concentrate grades, these recovery gains were: Ni: 1.04%, Cu: 1.01%, Pt: 2.67% and Pd: 1.79% in absolute terms.     

Silicon matrix disorder in amorphous hydrogenated silicon alloys

The authors report a detailed investigation of correlations between Urbach energies from photothermal deflection spectroscopy and Raman half-widths of transverse optic (TO)-like Si-Si modes as a measure of silicon matrix disorder in glow-discharge amorphous hydrogenated silicon (a-Si:H) and a-SiGe:H, as well as in glow-discharge and sputtered a-SiC:H and a-SiN:H. A corresponding decrease in TO full width at half-maximum (FWHM) and Urbach energy E₀ for soft deposition techniques yields bond angle distributions as narrow as 8.5° for the best a-Si:H films. Even at the lowest levels of nitrogen incorporation, simultaneous increases in E₀ and TO-like half-widths indicate that lattice distortions occur due to threefold coordination of nitrogen in the a-Si:H matrix. In contrast, no deviation of silicon TO-FWHM could be detected in a-SiC:H of up to 35 at.% of carbon content, whereas Urbach edges broaden in a well-known manner that is interpreted in terms of -CH₃ incorporation into the amorphous network. Diborane doping and sputter deposition, however, give rise to lattice distortions in a-SiC:H, which reflects changes in the carbon coordination     

An optimum interference mitigating combining scheme for the CDMA downlink with the same complexity as MRC

This letter presents a new optimum interference mitigating combining (OIMC) scheme for the code-division multiple-access downlink RAKE receiver. The OIMC scheme optimizes the RAKE weights and maximizes the signal-to-interference-plus-noise ratio (SINR) at the RAKE combiner output. Unlike other interference mitigation schemes, the new scheme does not need to estimate the interference or data correlation matrix (and its inverse) of the received signal to render a reliable and low complexity receiver. The OIMC scheme mitigates interference by inversely proportionately weighting the finger output by its associated interference power, while simultaneously mitigating multipath fading. The interference power is found to be directly related to the finger's associated multipath channel gain, rendering the OIMC scheme with the same order of complexity as a maximal ratio combining (MRC) scheme. Under realistic channel conditions, simulation results show that the proposed OIMC scheme always outperforms MRC with a gain of up to more than 1 dB.     

Der Einfluß von Temperaturgradienten auf das dilatometrische Verhalten von unlegierten Eisenwerkstoffen mit niedrigem Kohlenstoffgehalt im Verlauf der α-γ-Umwandlung

Kontinuierliche Aufnahme der Längenänderung von reinem Eisen, Armco-Eisen und Stahl St 35.8 im Verlauf der α-γ-α-Umwandlung in Abhängigkeit vom Temperaturgradienten zwischen 0 und 35°C/cm. Deutung der Meßergebnisse mit Hilfe der ebenen Phasengrenzfläche. Bleibende Längenänderung nach mehrfachem Durchlaufen der Phasenumwandlung und deren Deutung.     

Automatic Snoek-type bending-oscillation pendulum to determine carbon and nitrogen dissolved in strip steel specimens

Snoek-pendulum for measuring the amount of dissolved interstitial elements in steels, used on a larger scale, therefore working automatically as bending oscillation pendulum with strip material specimens. Additional equipment for quenching specimens from elevated temperatures. Examples for application.     

Influence of thermomechanical treatment on the modification of austenite structure

As a substantial subject of the work reviewing the effect of thermomechanical treatment (TMT) on the γ/&-transformation of steel, this paper gives a survey of the metallurgical processes in the austenite as a consequence of hot deformation. These processes determine the properties of the austenite structure from which the transformation takes place. The dynamic and static recrystallization which refine the coarse grain formed during reheating are treated. For the case that at most minimal recrystallization occurs, the deformation structures arising from hot deformation are described under the aspect of their roll as nucleation sites for the γ/&-transformation.     

Effect of novel water-soluble polymeric forms of sorbic acid against Fusarium oxysporum f.sp. radicis-cucumerinum

New controlled release water-soluble formulations of sorbic (2,4-hexadienoic) acid were prepared and their inhibitory activity on mycelium growth of Fusarium oxysporum f.sp. radicis-cucumerinum was evaluated. The new products are epoxidized polymers of polyvinylpyrrolidone (PVP) containing covalently bonded sorbic acid (polymeric esters of sorbic acid) and complexes of PVP with hydrogen bonded sorbic acid, characterized by controlled release of sorbic acid. It was shown that the polymeric complexes of sorbic acid with PVP were more effective fungicidal agents than sorbic acid polymeric esters. In all cases the activity of polymeric derivatives (esters and complexes) was increased by lowering the molecular weight of the polymeric carriers. Controlled release formulations of these polymeric derivatives are new promising products due to their low toxicity, wide range of efficient concentrations for application and ability to regulate lyophilicity. Our data contribute to the understanding of the action mechanism of various polymeric sorbic acid formulations and can result in products which are particularly suitable for food and feed protection applications.     

Determination and Modelling of the Influence of Cooling in the Coil on the Mechanical Properties of Hot Strip Steels with Bainite

The phenomenon of bainite formation in the hot strip mill for unalloyed steels and the influence of the complex cooling process have hardly been dealt with in literature. Only two useful model equations were found, namely according to Suehiro et al. [4] for the determination of the strength parameters R_p0.2 and R_m of annealed bainite, and according to Umemoto et al. [2] for the calculation of the tensile strength R_m of bainite formed during the isothermal holding temperature. These equations could be optimized by structural complements and modification of the coefficients by adjusting them to the own measured values. For building up the necessary data base, experimental methods were developed, involving the use of a computerized deformation dilatometer. The results thus obtained can be applied to the industrial practice.