Influence of smectite suspension structure on sheet orientation in dry sediments: XRD and AFM applications

The structure-building phenomena within clay aggregates are governed by forces acting between clay particles. Measurements of such forces are important to understand in order to manipulate the aggregate structure for applications such as dewatering of mineral processing tailings. A parallel particle orientation is required when conducting XRD investigation on the oriented samples and conduct force measurements acting between basal planes of clay mineral platelets using at. force microscopy (AFM). To investigate how smectite clay platelets were oriented on silicon wafer substrate when dried from suspension range of methods like SEM, XRD and AFM were employed. From these investigations, we conclude that high clay concns. and larger particle diams. (up to 5 μm) in suspension result in random orientation of platelets in the substrate. The best possible laminar orientation in the clay dry film, represented in the XRD 0 0 1/0 2 0 intensity ratio of 47 was obtained by drying thin layers from 0.02 wt.% clay suspensions of the natural pH. Conducted AFM investigations show that smectite studied in water based electrolytes show very long-range repulsive forces lower in strength than electrostatic forces from double-layer repulsion. It was suggested that these forces may have structural nature. Smectite surface layers rehydrate in water environment forms surface gel with spongy and cellular texture which cushion approaching AFM probe. This structural effect can be measured in distances larger than 1000 nm from substrate surface and when probe penetrate this gel layer, structural linkages are forming between substrate and clay covered probe. These linkages prevent subsequently smooth detachments of AFM probe on way back when retrieval. This effect of tearing new formed structure apart involves larger adhesion-like forces measured in retrieval. It is also suggested that these effect may be enhanced by the nano-clay particles interaction

Morphology and internal structure of Antarctic cosmic dust spherules: Possible links to meteorite fusion crusts

Petrographic and SEM comparison of the outer morphology of different Antarctic spherules with their internal structure helped to distinguish those spherules that resulted from melting of micrometeorites from the ablation products of meteorites. A chain of possible transformations beginning with unmelted micrometeorites was recognized. Such structural transformations could begin from unmelted cosmic dust of olivine aggregates through granular spherules, to vitrophyric spherules with ghost-olivine glassy ovoidal objects, to vitrophyric, and to skeletal spherules. The fusion crusts of meteorites studied, showed that ablation can also produce a variety of spherules. Achondrites could produce glassy smooth, and internally compact holohyaline spherules, whereas chondrites could generate spherules of the rough glazed, dendrite decorated morphological types

TEM, XRD, and Thermal Stability of Adsorbed Paranitrophenol on DDOAB Organoclay

Water purification is of extreme importance to modern society. Organoclays through adsorption of recalcitrant organics provides one mechanism for the removal of these molecules. The organoclay was synthesised through ion exchange with dimethyldioctadecylammonium bromide labeled as DDOAB of formula (CH3(CH2)17)2NBr(CH3)2. Paranitrophenol was adsorbed on the organoclay at a range of concentrations according to the cation exchange capacity (CEC) of the host montmorillonite. The paranitrophenol in solution was analysed by a UV-260 spectrophotometer at 317nm, with detection limits being 0.05mg/L. The expansion of the montmorillonite was studied by a combination of X-ray diffraction and transmission electron microscopy. Upon adsorption of the paranitrophenol the basal spacing decreased. The thermal stability of the organoclay was determined by a combination of thermogravimetry and infrared emission spectroscopy. The surfactant molecule DDOAB combusts at 166, 244 and 304 degrees Celsius and upon intercalation into Na-montmorillonite is retained up to 389 degrees Celsius thus showing the organoclay is stable to significantly high temperatures well above the combustion/decomposition temperature of the organoclay

Sodium Aluminosilicate Solid Phase Specific Fouling Behaviour

Process heat transfer equipment fouling due to sodium aluminosilicate precipitation is a serious problem that confronts high-level nuclear waste liquor and Bayer process alumina processing plants. The fouling of 316 stainless steel substrate by thermodynamically stable and unstable sodium aluminosilicate polytypes: amorphous solid, zeolite A, sodalite and cancrinite crystals, been has studied in an isothermal, batch precipitation system at 65 °C. Fouling invariably occurred via heterogeneous nucleation, crystal growth and particulate adsorption processes, accompanied by solution-mediated, phase transformation and morphological changes. For the thermodynamically stable cancrinite fouling, the amount of scale deposited increased systematically with increasing crystallization time before levelling off as a result of depleted supersaturation. Where the deposited scale involved a less stable phase (e.g., amorphous, zeolite A), transformation to a more stable phases (e.g., sodalite/cancrinite) occurred. The scale layer coverage/growth characteristically increased and then decreased in a periodic manner. The periodicity of this unusual behaviour appeared to be directly and kinetically related to polytypic phase transformation of amorphous to zeolite A, zeolite A to sodalite and sodalite to cancrinite

Smectite clay microstructural behaviour on the Atterberg limits transition

Particle space arrangement is a very important factor that determines the physico-mechanical properties of soil. Formations of three-dimensional (3D) structured networks within gelled or flocculated suspension may prevent clay particles and aggregates from building dense aggregates and by encapsulate water within the ultrathin and closed void network, lead to poor sludge dewatering. To better understand the water retention behaviour of smectite-rich clays, a microstructural investigation was conducted on Amcol Australian bentonite in aqueous suspension in near the liquid limit (LL) and the plastic limit (PL). The investigation was conducted with the aid of synchrotron-powered transmission X-ray microscope tomography (TXM), with subsequent computer reconstruction. Images from the microscopy studies were statistically analysed using the STatistical IMage ANalysing (STIMAN) system. The study found that clay particles form a spanned framework in which mineral particles, aggregates and water-filled voids assemble as hierarchic structural elements. The size of these structural elements was larger in the water suspension and subsequently became smaller as an effect of water loss in the suspension>liquid and>plastic limit conditions. The clay suspension structure was almost isometric, with a low anisotropy coefficient: K - 9%. This parameter increased to K - 17% in (LL) and increased further in (PL) conditions to K - 35%. Voids within structural elements were much smaller than the water filled inter-flock voids, with their median diameter 140nm (suspension), 120nm (LL) and 90nm (PL). Significant differences in Atterberg limits values were observed between powder freshly mixed with water and a seasoned sample. Therefore, careful consideration of the sample mineral composition, clay content and genesis must be given due to preparation for geotechnical examination

Micro-structure differences in kaolinite suspensions

SEM observations of the aqueous suspensions of kaolinite from Birdwood (South Australia) and Georgia (USA) show noticeable differences in number of physical behaviour which has been explained by different microstructure constitution.. Birdwood kaolinite dispersion gels are observed at very low solid loadings in comparison with Georgia KGa-1 kaolinite dispersions which remain fluid at higher solids loading. To explain this behaviour, the specific particle interactions of Birdwood kaolinite, different from interaction in Georgia kaolinite have been proposed. These interactions may be brought about by the presence of nano-bubbles on clay crystal edges and may force clay particles to aggregate by bubble coalescence. This explains the predominance of stair step edge-edge like (EE) contacts in suspension of Birdwood kaolinite. Such EE linked particles build long strings that form a spacious cell structure. Hydrocarbon contamination of colloidal kaolinite particles and low aspect ratio are discussed as possible explanations of this unusual behaviour of Birdwood kaolinite. In Georgia KGa-1 kaolinite dispersions instead of EE contact between platelets displayed in Birdwood kaolinite, most particles have edge to face (EF) contacts building a cardhouse structure. Such an arrangement is much less voluminous in comparison with the Birdwood kaolinite cellular honeycomb structure observed previously in smectite aqueous suspensions. Such structural characteristics of KGa-1 kaolinite particles enable higher solid volume fractions pulps to form before significantly networked gel consistency is attained

PDMS spreading morphological patterns on substrates of different hydrophilicity in air vacuum and water

In paper has been to investigate the morphological patterns and kinetics of PDMS spreading on silicon wafer using combination of techniques like ellipsometry, atomic force microscope (AFM), scanning electron microscope (SEM) and optical microscopy. A macroscopic silicone oil drops as well as PDMS water based emulsions were studied after deposition on a flat surface of silicon wafer in air, water and vacuum. our own measurements using an imaging ellipsometer, which also clearly shows the presence of a precursor film. The diffusion constant of this film, measured with a 60 000 cS PDMS sample spreading on a hydrophilic silicon wafer, is Df = 1.4 10-11 m2/s. Regardless of their size, density and method of deposition, droplets on both types of wafer (hydrophilic and hydrophobic) flatten out over a period of many hours, up to 3 days. During this process neighbouring droplets may coalesce, but there is strong evidence that some of the PDMS from the droplets migrates into a thin, continuous film that covers the surface in between droplets. The thin film appears to be ubiquitous if there has been any deposition of PDMS. However, this statement needs further verification. One question is whether the film forms immediately after forced drying, or whether in some or all cases it only forms by spreading from isolated droplets as they slowly flatten out

High porosity chained aggregates from the topsoil of the lunar regolith dust

The unusual behaviour of fine lunar regolith like stickiness and low heat conductivity is dominated by the structural arrangement of its finest fraction. Here, we show the previously unknown phenomenon of a globular 3D superstructure within the dust fraction of regolith. A study using the recently developed Transmission X-ray Microscopy (TXM) with tomographic reconstruction reveals a highly porous network of cellular voids in the finest dust fraction aggregates in lunar soil. Such porous chained aggregates are composed of sub-micron particles that form a network of cellular voids a few micrometers in diameter. Discovery of such a superstructure within the finest fraction of lunar topsoil enables a model of heat transfer to be constructed

AFM study of forces between silicon oil and hydrophobic-hydrophilic surfaces in aqueous solutions

An investigation has been made of the interactions between silicone oil and various solid substrates immersed in aqueous solutions. Measurements were made using an atomic force microscope (AFM) using the colloid-probe method. The silicone oil drop is simulated by coating a small silica sphere with the oil, and measuring the force as this coated sphere is brought close to contact with a flat solid surface. It is found that the silicone oil surface is negatively charged, which causes a double-layer repulsion between the oil drop and another negatively charged surface such as mica. With hydrophilic solids, this repulsion is strong enough to prevent attachment of the drop to the solid. However, with hydrophobic surfaces there is an additional attractive force which overcomes the double-layer repulsion, and the silicone oil drop attaches to the solid. A "ramp" force appears in some, but not all, of the data sets. There is circumstantial evidence that this force results from compression of the silicone oil film coated on the glass sphere