Microstructure of Bentonite in Iron Ore Green Pellets

Sodium-activated calcium bentonite is used as a binder in iron ore pellets and is known to increase strength of both wet and dry iron ore green pellets. In this article, the microstructure of bentonite in magnetite pellets is revealed for the first time using scanning electron microscopy. The microstructure of bentonite in wet and dry iron ore pellets, as well as in distilled water, was imaged by various imaging techniques (e.g., imaging at low voltage with monochromatic and decelerated beam or low loss backscattered electrons) and cryogenic methods (i.e., high pressure freezing and plunge freezing in liquid ethane). In wet iron ore green pellets, clay tactoids (stacks of parallel primary clay platelets) were very well dispersed and formed a voluminous network occupying the space available between mineral particles. When the pellet was dried, bentonite was drawn to the contact points between the particles and formed solid bridges, which impart strength to the solid compac

Thermoresponsive Pentablock Copolymer on Silica : Temperature Effects on Adsorption, Surface Forces, and Friction

The adsorption of hydrophilic or amphiphilic multiblock copolymers provides a powerful means to produce well-defined "smart" surfaces, especially if one or several blocks are sensitive to external stimuli. We focus here on an A-B-A-B-A copolymer, where A is a cationic poly((3acrylamido-propyl)-trimethylammonium chloride) (PAMPTMA) block containing 15 (end blocks) or 30 (middle block) repeat units and B is a neutral thermosensitive water-soluble poly(2-isopropyl-2-oxazoline) (PIPOZ) block with 50 repeat units. X-ray reflectivity and quartz crystal microbalance with dissipation monitoring were employed to study the adsorption of PAMPTMA(15)-PAMPTMA(30)-PIPOZ(50)-PAMPTMA(15) on silica surfaces. The latter technique was employed at different temperatures up to 50 degrees C. Surface forces and friction between the two silica surfaces across aqueous pentablock copolymer solutions at different temperatures were determined with the atomic force microscopy colloidal probe force and friction measurements. The cationic pentablock copolymer was found to have a high affinity to the negatively charged silica surface, leading to a thin (2 nm) and rigid adsorbed layer. A steric force was encountered at a separation of around 3 nm from hard wall contact. A capillary condensation of a polymer-rich phase was observed at the cloud point of the solution. The friction forces were evaluated using Amontons' rule modified with an adhesion term.Peer reviewe

Scanning probe microscopy studies of interaction forces between particles: emphasis on magnetite, bentonite and silica.

Scanning probe microscopy (SPM), such as the atomic force microscope (AFM), using colloidal probes is a highly suitable technique to probe single particle-particle interactions in aqueous solution. The interaction force between a colloidal probe on the AFM cantilever and sample surface is measured. Ultrasmall intermolecular and surface forces, down to the piconewton level, can reliably be measured under controlled experimental conditions with AFM. The interaction between magnetite, bentonite and silica particles plays an important role in many different applications. One important application is in the steel production process where high-quality iron ore pellets are used. Moreover, the interaction between magnetite nanoparticles with Ca2+ ions and with silica particles has high importance in several medical applications and for nanoelectronics. It is known and widely studied that particle surface properties significantly affect the particle dispersion and aggregation. Also, the particles are often treated in aqueous suspensions or in moist conditions prior to the final aggregation, for instance in a pelletizing processes. Thus, different dissolved chemical species may modify the magnetite, bentonite and silica surfaces, which causes the surface properties to change. However, the exact mechanism how the dissolved chemical species influence the direct particle-particle interaction and particle adhesion is not well known.The main focus of this thesis was the study of magnetite particle force interaction with natural and synthetic magnetite, silica and bentonite particles in aqueous solution with SPM. In addition, complimentary methods, such as scanning electron microscopy (SEM), vertical scanning interferometry (VSI), energy dispersive spectroscopy (SEM-EDS), x-ray diffraction (XRD) and electrophoresis techniques were used for surface morphology investigation, chemical characterization, determination of atomic structure and measurements of zeta-potential. The particle interaction forces were examined in solutions with various Ca2+ ion concentrations and in NaCl solution to determine the effect of Ca2+ ions on the surface properties. Also, the effect of pH at various concentrations was studied. The colloidal probes in the studies were natural magnetite and bentonite particles, micrometer-sized spherical silica particles. Sample surfaces were natural magnetite particles, smooth layers of synthetic magnetite nanoparticles and bentonite flakes.Qualitative changes in adhesion forces, i.e. interaction trends, and forces on approach for magnetite-magnetite, magnetite-silica, magnetite-bentonite and bentonite-silica interaction systems with an increase of Ca2+ ion concentration and pH were measured and evaluated. The interaction trends were consistent in most cases with zeta-potential measurements. Possible surface modification and formation of calcium silicates and calcium carbonates at pH 10 on the magnetite surfaces was discussed. The long-range repulsive interaction, similar to a steric-like interaction, was observed in the interactions for bentonite-silica and magnetite-silica systems, likely due to the swelling of bentonite layers and rising of bentonite flakes from the surface. The rising of bentonite flakes in water was verified with cryo-scanning electron microcopy investigation. Furthermore, the measured adhesion forces were compared with calculated adhesion forces, which were evaluated with the use of a few contact mechanics models. The comparison revealed discrepancies, which could be explained by the particle surface roughness. Additionally, a comparison of VSI and AFM techniques for surface characterization was performed on samples possessing sharp periodic surface structures and three stage plateaux honed cast iron surface. This comparison is of high relevance to the accurate calculation of tribological surface roughness parameters. Moreover, force measurements on biological samples and between magnetic particles are also briefly discussed in the thesis.The work within this thesis shows that SPM methods can be successfully applied to measure and predict forces between natural particles, such as magnetite and bentonite, in solution. The obtained and presented results are new and of high interest in applications where the knowledge of the dispersion and aggregation of studied particle interaction is important.Godkänd; 2014; 20140422 (illdob); Nedanstående person kommer att disputera för avläggande av teknologie doktorsexamen. Namn: Illia Dobryden Ämne: Fysik/Physics Avhandling: Scanning Probe Microscopy Studies of Interaction Forces Between Particles: Emphasis on Magnetite, Bentonite and Silica Opponent: Associate Professor/Reader Neil Thomson, Department of Oral Biology, Leeds Dental Institute/School of Physics and Astronomy, University of Leeds, UK, Ordförande: Biträdande professor Nils Almqvist, Avd för materialvetenskap, Institutionen för teknikvetenskap och matematik, Luleå tekniska universitet Tid: Onsdag den 18 juni 2014, kl 10.00 Plats: E632, Luleå tekniska universite

Surface characterization and force measurements applied to industrial materials with atomic force microscopy

The thesis focuses on the application of force measurements with atomic force microscopy (AFM) on materials with a few surface contacts/asperities and chemically modified surfaces. The technique allows measurements of ultra-small intermolecular and surface forces, down to the piconewton level. The force measurements between surfaces of well-defined geometry are often used to measure and model the interaction between different systems of charged and neutral surfaces in various environments. However, detailed knowledge of the contacting surface profile geometry and surface properties is required to model the fundamental forces involved in the interaction. The preparation of such well-defined and idealized surfaces is often time consuming and the surfaces may not possess the behavior and properties of a source material in real processes, such as in industry. Moreover, external factors such as magnetic fields, ionic strengths and pH-values in a solution, may further complicate the evaluation. Hence, it is desirable to explore and develop techniques for trustable measurements of forces between “real” surfaces. These are often a complex composition of various force interactions and multiple surface contacts.The AFM probe technique was explored to measure force interactions between “real” particle surfaces. The work shows the applicability of the AFM technique to study the interaction forces despite the forecasted difficulties with the roughness of the particles.A technique to measure the adhesion and work of adhesion from AFM force curves was implemented and used. The thermal tune method was implemented in our commercial NT-MDT microscope to determine cantilever spring constants. The force interactions between natural microsize (m-s) magnetite particles and synthetic nanosize (n-s) magnetite particles were studied in calcium solution with concentrations of 1, 10, 100 mM and at pH values 4, 6 and 10. The changes in force interactions, due to variations in calcium concentration and pH were investigated. The adhesion force change with the concentration and pH was similar for m-s/m-s and m-s/n-s systems, and the adhesion force increased with the concentration at pH 6, except for the highest calcium concentration of 100 mM at pH 10. It was found that the magnetite surface modification could appear at the highest calcium concentration at pH 10. Moreover, the thesis contains preliminary results of the force interaction study between natural and synthetic bentonite-magnetite particles in calcium solution with concentrations of 1, 10 and 100 mM at pH 6.The influence of roughness on the calculation of contact mechanics parameters were studied with AFM and Vertical Scanning Interferometry (VSI). This is important for future development of a model to describe and characterize the force interaction between samples with multiple surface contacts. It was found that the optical artifacts, induced by VSI, have a large influence on all the roughness parameters calculated on the calibration grids, which represent extreme surface topographies.Godkänd; 2012; 20120502 (illdob); LICENTIATSEMINARIUM Ämnesområde: Fysik/Physics Examinator: Docent Nils Almqvist, Institutionen för teknikvetenskap och matematik, Luleå tekniska universitet Diskutant: Docent Aji P Mathew, Institutionen för teknikvetenskap och matematik, Luleå tekniska universitet Tid: Fredag den 1 juni 2012 kl 10.00 Plats: E632, Luleå tekniska universite

Research data supporting Improving OFF-State Bias-Stress Stability in High-Mobility Conjugated Polymer Transistors with an Antisolvent Treatment

Data to accompany "Improving OFF-State Bias-Stress Stability in High-Mobility Conjugated Polymer Transistors with an Antisolvent Treatment" by Nguyen et al. The zip folder contains subfolders labelled with the figure numbers that can be referred to in the paper. All the subfolders contain raw data either in a .txt or .csv format. The imAFM data from Figure 4 is in .imp (intermodulation) format. Data analysis was carried out using python as described in methods and figure captions of the paper.FlexEnable CASE fundin

Chemical milling of cast Ti-6Al-4V and Ti-6Al-2Sn-4Zr-2Mo alloys in hydrofluoric-nitric acid solutions

The behavior of cast Ti-6Al-4V and Ti-6Al-2Sn-4Zr-2Mo during chemical milling in hydrofluoric-nitric (HF-HNO3) acid solutions with 1:3 and 1:11 molar ratios was investigated using electrochemical and atomic force microscopy (AFM) techniques. Faster corrosion rate in 1:3 solutions was measured for Ti-6Al-4V than for Ti-6Al-2Sn-4Zr-2Mo, whereas in 1:11 solution Ti-6Al-2Sn-4Zr-2Mo exhibited higher corrosion rate. Scanning Kelvin probe force microscopy measurements revealed difference in the Volta potential between the a-laths and the ß-layers in the Widmansttäten microstructure indicating operation of microgalvanic cells between the microconstituents when in contact with HF-HNO3 solution. The AFM topography measurements demonstrated faster corrosion of the a-laths compared to the ß-layers, in both alloys. In 1:3 solutions, higher a/ß height difference was measured in Ti-6Al-4V, whereas in 1:11 solution, the difference was higher in Ti-6Al-2Sn-4Zr-2Mo. The results revealed that the chemical milling behavior of the two investigated alloys is controlled by the microscopic corrosion behavior of the individual microconstituents.Postprint (published version

Label-free detection of polystyrene nanoparticles in Daphnia magna using Raman confocal mapping

Micro- and nanoplastic pollution has emerged as a global environmental problem. Moreover, plastic particles are of increasing concern for human health. However, the detection of so-called nanoplastics in relevant biological compartments remains a challenge. Here we show that Raman confocal spectroscopy-microscopy can be deployed for the non-invasive detection of amine-functionalized and carboxy-functionalized polystyrene (PS) nanoparticles (NPs) in Daphnia magna. The presence of PS NPs in the gastrointestinal (GI) tract of D. magna was confirmed by using transmission electron microscopy. Furthermore, we investigated the ability of NH2-PS NPs and COOH-PS NPs to disrupt the epithelial barrier of the GI tract using the human colon adenocarcinoma cell line HT-29. To this end, the cells were differentiated for 21 days and then exposed to PS NPs followed by cytotoxicity assessment and transepithelial electrical resistance measurements. A minor disruption of barrier integrity was noted for COOH-PS NPs, but not for the NH2-PS NPs, while no overt cytotoxicity was observed for both NPs. This study provides evidence of the feasibility of applying label-free approaches, i.e., confocal Raman mapping, to study PS NPs in a biological system

Chemical milling of cast Ti-6Al-4V and Ti-6Al-2Sn-4Zr-2Mo alloys in hydrofluoric-nitric acid solutions

The behavior of cast Ti-6Al-4V and Ti-6Al-2Sn-4Zr-2Mo during chemical milling in hydrofluoric-nitric (HF-HNO3) acid solutions with 1:3 and 1:11 molar ratios was investigated using electrochemical and atomic force microscopy (AFM) techniques. Faster corrosion rate in 1:3 solutions was measured for Ti-6Al-4V than for Ti-6Al-2Sn-4Zr-2Mo, whereas in 1:11 solution Ti-6Al-2Sn-4Zr-2Mo exhibited higher corrosion rate. Scanning Kelvin probe force microscopy measurements revealed difference in the Volta potential between the a-laths and the ß-layers in the Widmansttäten microstructure indicating operation of microgalvanic cells between the microconstituents when in contact with HF-HNO3 solution. The AFM topography measurements demonstrated faster corrosion of the a-laths compared to the ß-layers, in both alloys. In 1:3 solutions, higher a/ß height difference was measured in Ti-6Al-4V, whereas in 1:11 solution, the difference was higher in Ti-6Al-2Sn-4Zr-2Mo. The results revealed that the chemical milling behavior of the two investigated alloys is controlled by the microscopic corrosion behavior of the individual microconstituents

Adsorption Behavior of Cellulose and Its Derivatives toward Ag(I) in Aqueous Medium : An AFM, Spectroscopic, and DFT Study

The aim of this study was to develop a fundamental understanding of the adsorption behavior of metal ions on cellulose surfaces using experimental techniques supported by computational modeling, taking Ag(I) as an example. Force interactions among three types of cellulose microspheres (native cellulose and its derivatives with sulfate and phosphate groups) and the silica surface in AgNO3 solution were studied with atomic force microscopy (AFM) using the colloidal probe technique. The adhesion force between phosphate cellulose microspheres (PCM) and the silica surface in the aqueous AgNO3 medium increased significantly with increasing pH while the adhesion force slightly decreased for sulfate cellulose microspheres (SCM), and no clear adhesion force was observed for native cellulose microspheres (CM). The stronger adhesion enhancement for the PCM system is mainly attributed to the electrostatic attraction between Ag(I) and the negative silica surface. The observed force trends were in good agreement with the measured zeta potentials. The scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), and attenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR) analyses confirmed the presence of silver on the surface of cellulose microspheres after adsorption. This study showed that PCM with a high content of phosphate groups exhibited a larger amount of adsorbed Ag(I) than CM and SCM and possible clustering of Ag(I) to nanoparticles. The presence of the phosphate group and a wavenumber shift of the P−OH vibration caused by the adsorption of silver ions on the phosphate groups were further confirmed with computational studies using density functional theory (DFT), which gives support to the above findings regarding the adsorption and clustering of Ag(I) on the cellulose surface decorated with phosphate groups as well as IR spectra.Validerad; 2015; Nivå 2; 20151112 (chuzhu)</p