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| 2. |
- Sundararajan, G., et al.
(författare)
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A Comparative Study of Tribological Behavior of Plasma and D-Gun Sprayed Coatings under Different Wear Modes
- 1998
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Ingår i: Journal of Materials Engineering and Performance. ; 7:3, s. 343-351
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Tidskriftsartikel (refereegranskat)abstract
- In recent years, thermal sprayed protective coatings have gained widespread acceptance for a variety of industrial applications. A vast majority of these applications involve the use of thermal sprayed coatings to combat wear. While plasma spraying is the most versatile variant of all the thermal spray processes, the detonation gun (D-gun) coatings have been a novelty until recently because of their proprietary nature. The present study is aimed at comparing the tribological behavior of coatings deposited using the two above techniques by focusing on some popular coating materials that are widely adopted for wear resistant applications, namely, WC-12%Co, Al2O3, and Cr3C2-NiCr. To enable a comprehensive comparison of the above indicated thermal spray techniques as well as coating materials, the deposited coatings were extensively characterized employing microstructural evaluation, microhardness measurements, and XRD analysis for phase constitution. The behavior of these coatings under different wear modes was also evaluated by determining their tribological performance when subjected to solid particle erosion tests, rubber wheel sand abrasion tests, and pin-on-disk sliding wear tests. The results from the above tests are discussed here. It is evident that the D-gun sprayed coatings consistently exhibit denser microstructures and higher hardness values than their plasma sprayed counterparts. The D-gun coatings are also found to unfailingly exhibit superior tribological performance superior to the corresponding plasma sprayed coatings in all wear tests. Among all the coating materials studied, D-gun sprayed WC-12%Co, in general, yields the best performance under different modes of wear, whereas plasma sprayed Al2O3 shows least wear resistance to every wear mode.
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| 5. |
- de Leeuw, N.H., et al.
(författare)
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Modeling the competitive adsorption of water and methanoic acid on calcite and fluorite surfaces
- 1998
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Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 14:20, s. 5900-5906
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Tidskriftsartikel (refereegranskat)abstract
- Atomistic simulation techniques were used to investigate the interaction between the minerals calcite and fluorite with water and methanoic acid. The relative adsorption energies suggest that methanoic acid preferentially adsorbs onto fluorite surfaces, while adsorption of water is energetically preferred over methanoic acid on the calcite cleavage plane in agreement with experiment. The coverage and configuration of adsorbed methanoic acid on the surfaces depends largely on lattice spacing between the cations, and bridging between surface calcium atoms is highly favored. These findings have given an insight into interactions at the atomic level which indicate that modeling techniques should be capable of predicting adsorption behavior and designing collector molecules, which is of central importance to the mineral processing technique of flotation
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| 7. |
- Jonsson, B J, et al.
(författare)
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Method to extract the critical current density and the flux-creep exponent in high-T-c thin films using ac susceptibility measurements
- 1998
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Ingår i: Physical Review B Condensed Matter. - 0163-1829 .- 1095-3795. ; 58:9, s. 5862-5867
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Tidskriftsartikel (refereegranskat)abstract
- High-precision ac susceptibility measurements have been made on high-quality Hg-1212 thin films. A method to analyze chi(1)'(T,H-0,f) and chi(1)" (T,H-0,f) and extract the temperature dependence of the critical current density J(c)(T), as well as the temperature and field-dependent flux-creep exponent n(T,H-0), is presented. With specific measurements at external ac fields Ho in the range 7-100 Oe(rms) we determine the temperature dependence of the critical current density from a single temperature scan. The obtained temperature dependence, J(c)(T), is found to be in good agreement with data obtained from measurements using the traditional "loss-maximum" approach. In addition we present a method to extract the temperature and ac field-dependent flux-creep exponent n(T,H-0) from a set of temperature scans taken at different cc fields and driving frequencies. The observed power law describing the frequency dependence of chi' is consistent with a current-dependent effective activation energy of the form U(J)= U(0)ln(J(c)/J). Furthermore, the flux creep is found to increase with ac field and with temperature except at about 20-30 K below T-c, where our data suggest a slowing down of the flux creep.
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| 8. |
- Meenakshi, S, et al.
(författare)
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High-pressure studies on YNi2B2C at room temperature
- 1998
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Ingår i: PHYSICAL REVIEW B-CONDENSED MATTER. - : AMERICAN PHYSICAL SOC. - 0163-1829. ; 58:6, s. 3377-3380
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- The electronic and lattice structure, and equation of state behavior of YNi2B2C has been investigated by electrical resistivity, thermoelectric power, and angle-dispersive x-ray-diffraction measurements. The electrical resistance under pressure has also b
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| 13. |
- Rao, K. Hanumantha, et al.
(författare)
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Flotation kinetics of apatite from magnetite
- 1999
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Ingår i: Beneficiation of Phosphate. - Littleton : Society for Mining, Metalurgy and Exploration. - 0873351789 ; , s. 103-125
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Bokkapitel (övrigt vetenskapligt/konstnärligt)abstract
- The influence of reagents dosage, pH, temperature, and particle size on the kinetics of apatite flotation response from magnetite has been investigated. The first-order models characterizing rectangular distribution and fast and slow distributions (F-S model) of floatabilities gave an excellent fit to the results of apatite flotation when compared to other models. However, the latter model is found to be better than the former in the goodness of fit and also in the description of flotation performance. The kinetic parameters in the F-S model are estimated by using a nonlinear least squares fitting program. The ratio of fast and slow rate constants is observed to be an important parameter for identifying the optimum levels of the variables and to outline the selectivity between apatite and magnetite. The influence of collector dosage is realized from the model parameters by relating it to the fraction of slow- floating particles. An attempt has been made to describe the apatite flotation behavior with the determined model parameters.
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| 16. |
- Su, Fenwei, et al.
(författare)
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Dephosphorization of magnetite fines - Part 1: Evaluation of flotation kinetic models
- 1998
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Ingår i: Mineral Processing and Extractive Metallurgy. - 0371-9553 .- 1743-2855. ; 107:SEPT/DEC, s. C95-C102
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Forskningsöversikt (refereegranskat)abstract
- Dephosphorization of magnetite fines by flotation in such a way as to minimize the fatty acid coating left on the magnetite surfaces is the principal technical challenge facing the mineral processing division of LKAB, Sweden. Modelling of flotation kinetics enables the influence of chemical and operational variables on apatite flotation from magnetite fines to be predicted. Five typical first-order flotation kinetic models are evaluated by statistical techniques, after an estimation of model parameters by a nonlinear least-squares fitting program, with use of the authors' own results and results taken from the literature. Evaluation of the models is based on two aspects: goodness of fit to the experimental results and suitability to describe the flotation behaviour. The first-order models with a rectangular distribution of floatabilities and with fast and slow floating components (F-S model) gave an excellent fit to the experimental results of apatite flotation when compared with the other models, the latter being superior not only in the goodness of fit to apatite flotation and other mineral flotation results but also in its description of flotation behaviour. The kinetic parameters (percentage recoveries and rate constants of fast and slow floating particles) in the F-S model have a physical significance and can thus be used for qualitative as well as quantitative interpretation of flotation performance. The influence of collector dose can be effectively included in the F-S model by making realistic simplifications and relating the collector dose to the fraction of slow floating particles. The ratio of fast and slow rate constants can be used to describe the selectivity of apatite flotation from magnetite.
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| 17. |
- Su, Fenwei, et al.
(författare)
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The influence of temperature on the kinetics of apatite flotation from magnetite fines
- 1998
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Ingår i: International Journal of Mineral Processing. - 0301-7516 .- 1879-3525. ; 54:3, s. 131-145
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Tidskriftsartikel (refereegranskat)abstract
- The influence of pulp temperature on the kinetics of apatite flotation from magnetite fines was studied using Atrac (fatty acid type) as collector and sodium silicate as dispersant at pH 8.5–9.0. The batch flotation tests were conducted in a specially designed temperature controlled flotation cell. A modified first-order model, incorporating two rate terms describing fast and slow-floating components, was applied to evaluate the flotation kinetics. The estimation of the model parameters was made by a non-linear least squares fitter program which is based on the Levenberg–Marquardt algorithm. Results indicate that increasing temperature from 10°C to 40°C decreases the phosphorous content in magnetite concentrate but with a simultaneous loss of magnetite recovery. At temperatures below 30°C, an increase in pulp temperature results increasing flotation rate of fast-floating particles and has a marginal effect on slow-floating particles. Above 30°C, the flotation rate of fast-floating particles decreases with increasing pulp temperature. Sodium silicate has a positive effect for increasing the phosphorous recovery and decreasing the phosphorous content in the magnetite concentrate at 20°C for all the levels of collector dosages. In the absence of sodium silicate, collector is active for both apatite and magnetite flotation. The higher selectivity between apatite and magnetite with an acceptable content of phosphorous in the magnetite concentrate is obtained at a moderate dosage of about 400 g/t sodium silicate. The optimum flotation conditions are: 50 g/t collector dosage, 350–400 g/t dispersant dosage, pH 8.5–9 and pulp temperature 25–30°C.
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| 18. |
- Yun, S H, et al.
(författare)
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Growth of a-axis-oriented HgBa2CaCu2Ox thin films by rapid quenching
- 1999
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Ingår i: Journal of Materials Research. - 0884-2914 .- 2044-5326. ; 14:8, s. 3181-3184
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Tidskriftsartikel (refereegranskat)abstract
- High-quality a-axis-oriented HgBa2CaCu2Ox superconducting thin films have been grown on (100) LaAlO3 substrates using a modified conventional method that contains a short annealing time of 5 min, rapid-quenching process, and an alternative encapsulated approach. We found that the preferred orientations of HgBa2CaCu2Ox thin films can be controlled by rapid quenching at specific temperatures: 800, 700, 600, and 500 degrees C. The films rapidly quenched in water from 700 degrees C during a cooling cycle showed predominantly a-axis orientation perpendicular to the film surface. Phase was confirmed by x-ray diffraction pole figures. The a-axis films exhibited a zero-resistance transition temperature >120 K, which is comparable to epitaxial c-axis-oriented films.
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