Fine-grained Bulk Research Articles

Formation of Peripheral Coarse Grain in Thin-Walled Al–Mg–Si Extrusion Profiles

Investigations on microstructure and texture development during processing of Al–Mg–Si sheet and extrusion profiles focused on describing and modelling the changes in the bulk. However, understanding the evolution of microstructure in the sub-surface region is highly relevant, as this governs material performance under corrosion and bending deformation, which are crucial applications in mobility and transportation. The aim of this study was to correlate the effect of alloy composition and extrusion parameters to the formation of texture and peripheral coarse grain (PCG) layer. For this, five alloys of the AA6xxx class with varying content of dispersoid forming elements were extruded at increasing extrusion speeds into thin-walled hollow profiles. The microstructure at a plane section was investigated by means of EBSD and characterized in terms of distinct texture component distribution. It was shown that with increasing grain boundary mobility, through adapting dispersoid content and extrusion speed, the PCG layer grows into a fine-grained bulk. This growth of the PCG layer is only counter-acted upon, when the grain boundary mobility in the bulk is high enough, so that extensive growth of Cube oriented grains occurs. The PCG layer shows distinct orientations related to langle 101rangle ||rm{TD}, so that a possible mechanism for the orientation selection during grain growth is proposed.

NUMERICAL SIMULATION OF THE PROCESS OF AERODYNAMIC SEPARATION OF FINE-GRAINED BULK MATERIAL

Various methods can be used to numerically simulate the aerodynamic separation of fine-grained bulk material, including discrete element methods, finite element methods, and bounded domain methods. In all these methods, these equations are solved numerically, and the results are used to determine the trajectories and velocities of air and particles. The Discrete Element Method (DEM), on the basis of which the study will be conducted, is designed for modeling the granular flow of materials. The purpose of the research is to simulate the movement of fine-grained loose material under the influence of air flow and calculate the parameters of its aerodynamic separation in the Simcenter STAR-CCM+ software package. The following were selected as physical models: gas, two-dimensional, separated flow, gradients, ideal gas, isothermal fluid energy equation, unsteady implicit, turbulent, Reynolds averaging of the Navier-Stokes equation, K-Epsilon turbulence model, admissible two-layer K-Epsilon, wall distance, double layer for any y+, gravity, Lagrangian multiphase, DEM discrete element model, multiphase interaction. As a result of the numerical simulation of the movement of fine-grained loose material under the influence of the air flow in the Simcenter STAR-CCM+ software package, the distribution of their components in the area of the separator was constructed. The following parameters were adopted as research factors: the diameter of the particles of the liquid fraction and impurities d, the particle supply speed f, the air flow speed v. Based on the results of the processing of the obtained data set in the Wolfram Cloud software package, the patterns of changes in the position of the intersection line of the distribution of two fractions (distance x) and the content of impurities δ in the liquid zone of separation from research factors were established. The presented detailed method of numerical modeling can be used to study other methods of separation of fine-grained loose materials.

Manufacturing of fine-grained structures by multilevel kinking mechanism through a novel periodic undulating compression method: An example 7075 aluminum alloy

Combining the advantages of high strength and excellent plasticity, fine-grained bulk materials have gained superiority and potential to manufacture lightweight components. However, the efficient preparation of large-sized fine-grained materials remains a challenge, which further hinders their industrial applications. In this study, a novel approach named periodic undulating compression (PUC) and a multilevel kinking mechanism based on this approach were proposed for the fabrication of large-sized fine-grained materials. Compared with conventional severe plastic deformation (SPD) approaches, PUC can realize multi-pass deformation of large-sized materials without changing the dies and can homogeneously accumulate relatively high strain in a single pass deformation. Furthermore, large amounts of kinking band are generated at 350 °C, which improves the conversion of dislocations to grain boundaries, and effectively promotes grain refinement. Due to the complex flow trajectories of materials, and matrix refinement during PUC deformation, the texture intensity can be effectively inhibited with increasing deformation passes. Experimental results indicate that multilevel kinking bands are more efficient at inhibiting the texture intensity than continuous dynamic recrystallization (CDRX). Therefore, the production of ultrafine grained materials for industrial applications is possible with PUC.

Microstructure and Tensile Properties of Fine-Grained Bulk Copper Fabricated by Thermomechanical Consolidation of Copper Nanopowder/Micron-Sized Powder Blend

Samples of fine structured Cu were fabricated by spark plasma sintering (SPS) of compacts of Cu nanopowder/micron-sized powder blend with a ratio of 3:7 by weight, and one of the SPSed samples was further processed by hot extrusion. The microstructures of the as-SPSed and the as-extruded samples and the tensile properties and fracture behavior of the as-extruded sample were studied. It was found that the microstructures of the samples consist of a concoction of ultrafine and coarse grains with high dislocation densities (~1015 m-2) as a result of microstructural evolution during material processing. Some nanograins were oxidized to form Cu2O particles residing around the coarse grains. Extrusion of the SPSed sample increases its microhardness from 70 HV to 90 HV. The electrical conductivity of the as-extruded sample reaches 87% international annealed copper standard (IACS), and its tensile properties are 200 MPa for yield strength, 218 MPa for ultimate tensile strength and 9% for elongation to fracture. The tensile test specimens from the as-extruded sample exhibit nearly ideal plastic deformation and undergo ductile fracture, suggesting that the fine-grained copper is a highly desirable material for high strength electrical conductors.

Modeling of a bulk material stress state in a conical hopper hole under vibration action

A model of a fine-grained bulk material stress state in a conical hopper hole under vibration during material unloading is proposed. For the study, it is used a model of a discrete medium based on a balance of a small thickness elementary volume, in which the stress redistribution occurs by opening an outlet at the hopper bottom. A formula for determining the material radial stress in the discharge conical hopper hole is obtained, taking into account all force factors influencing the bulk material behavior. The influence of humidity, shape and geometric parameters of the hopper, and vibration intensity on the change of the bulk material stress state is investigated. As a result, the efficiency of vibration to improve the conditions of the fine-grained bulk material leakage from the hoppers is established.

Justification of vibrating hopper hole parameters during fine grained bulk material unloading

Purpose. The leakage process of the fine grained bulk material (BM) from the unloading hopper is considered. As known the BM behaviour during the unloading process is directly related to the material stress state (active or passive) inside the hopper, which depends on the physical and mechanical bulk material properties, as well as hopper geometric parameters. At the boundary of the transition from the cylindrical part to the conical part of the unloading hopper hole, the horizontal stresses that precede the leakage of the material increase sharply. The use of vibration reduces horizontal stresses in the hopper and thus improves the bulk product fluidity. Also, the use of vibration reduces the probability of the free-fall arch formation over the outlet. Therefore, the present paper is aimed at developing the mathematical model of the fine grained bulk material flow under the vibration action from the conical hopper hole. Methodology. It is used one of the methods of studying the BM behavior, namely the analysis of the stress state of the conditionally stationary (pseudo-stationary) layer of the product and the force balance equation in the free-fall arch is made for further study of the geometric parameters of the unloading hole. Findings. In this paper, the mathematical model of the BM behavior in the conical hopper hole is developed. Since the most determining factor influencing the hopper productivity is the outlet diameter, so based on the developed model, it is established relationships that allow determining all parameters that affect the diameter. Graphical dependences are obtained, which allow to estimate the influence of the angle inclination of the hopper hole walls on the value of the hopper outlet size at active and passive stress states. The dependence of the diameter of the unloading hopper hole on the BM properties is also established. The BM properties directly affect the initial shear resistance of the material. The influence of vibration on the unloading hole geometry is presented. Originality. The pseudo-immobile layer of bulk product is considered in the developed mathematical model, and it is investigated how vibration affects the BM behavior in this layer. Practical value. The practical value of this paper lies in the possibility of further mathematical modeling of the influence of the BM properties, hopper geometric dimensions and vibration on the product behavior in the material leakage process from the hopper. The results of the studies, presented in the form of graphs, can be used during the vibrating hopper design and the selection of rational modes of hopper operation.

Improvement of the design of the aeration device of the pneumatic chamber pump

The production of building materials is a complex technological process involving the processing of raw materials with various physical and mechanical properties, as well as using a variety of degrees of complexity of technological equipment and auxiliary mechanisms. High-pressure pneumatic transport has found application in construction, refractory, chemical and other industries. It is widely used for transportation of fine-grained bulk materials such as cement, alumina, soda, apatite, ash, clay, synthetic products, mineral fertilizers. The process of pneumatic transportation occurs due to the action of compressed air on the material being moved. However, at the same time, as a rule, there are through channels in the material layer, which leads to an increased consumption of compressed air, part of the unloaded material remains at the bottom of the pump chamber, which reduces productivity. Due to the fact that some fluidizing devices can form through channels in the material layer and given the large volumes of material being transported, it is necessary to solve issues to improve the efficiency of pneumatic chamber pumps and reduce the consumption of compressed air required for transporting bulk materials. This can be achieved by organizing effective fluidization of the material, that is, uniform mixing of the transported material with air.

The influence of Mo addition on the microstructure and its thermal stability for electrodeposited Ni films

An investigation was conducted to study the effect of molybdenum (Mo) alloying on the grain size and lattice defect structure in nanocrystalline nickel (Ni) films processed by electrodeposition. Moreover, the influence of saccharin addition to the electrolyte bath on the microstructure of Ni-Mo layers with low and high Mo contents was studied. It was found that the higher Mo content resulted in a larger dislocation density and twin fault probability as well as a smaller grain size. The addition of saccharin to the bath resulted in a further increase in the density of both dislocations and twin faults. It was also revealed that Mo alloying improved the thermal stability of the nanostructure in Ni films while saccharin addition yielded a reduction of stability. The reasons for these opposite behaviors were discussed in detail. In addition, the defect structure and its stability in Ni-Mo layers were compared with that for fine-grained bulk samples with the same composition but processed by severe plastic deformation.

Signal or noise? Isolating grain size effects on Nd and Sr isotope variability in Indus delta sediment provenance

Radiogenic elements, such as neodymium (Nd) and strontium (Sr), are commonly used to decipher the provenance and weathering histories of bulk siliciclastic sediments worldwide, although increasing evidence for diagenetic and sediment transport-driven bias of isotope signatures calls into question the utility of bulk isotope compositions as effective tools. This study evaluates grain size-dependence and variability of Nd and Sr compositions in the Indus delta of Pakistan, documenting both a significant isotopic evolution and coarsening upward sequence during the last deglaciation (~15 ka). Grain size analysis, trace element geochemistry, and Nd and Sr geochemistry are determined for bulk and separate grain size fractions (<63 μm, 63–125 μm, 125–250 μm, >250 μm) from four core sampling sites with similar provenance. Isotopic compositions are controlled by grain size distribution, in turn variably controlled by size fraction mineralogy. Fine-grained bulk sediment Nd isotope compositions are primarily dictated by the finest (<125 μm) sediments enriched in Nd-bearing monazite and allanite, with coarser bulk sediments influenced by mica. The most abundant grain size fraction drives bulk sediment Sr isotope compositions, with the finest grain size fractions indicating strong control by potassium feldspar, mica, epidote, and/or volcanogenic clay minerals. Over the last 15 k.y., resolvable provenance-driven trends are confidently identified in Nd isotope compositions. Long-term trends remain consistent with previous findings although the isotopic shift in delta compositions must be less than previously envisaged (~4 vs. 0.69–1.91 εNd units). Although considerable variability is observed in bulk Sr isotope compositions, <63 μm and 63–125 μm fraction 87Sr/86Sr compositions evolve in parallel through time and show fractionation by ~0.005–0.01 as a result of grain size. Within the isotopically diverse Indus drainage system, bulk isotopic compositions are estimated to deviate on average no than ±1.04 εNd units and ±0.0099 for 87Sr/86Sr values for any sediment as a result of mineralogy, grain size distribution, and analytical error. Isotopic excursions beyond these uncertainties can be unambiguously assigned to either a change in upstream provenance and/or chemical weathering.

A detrital record of the Nile River and its catchment

This research uses analyses from Nile catchment rivers, wadis, dunes and bedrocks to constrain the geological history of NE Africa and document influences on the composition of sediment reaching the Nile delta. Our data show evolution of the North African crust, highlighting phases in the development of the Arabian–Nubian Shield and amalgamation of Gondwana in Neoproterozoic times. The Saharan Metacraton and Congo Craton in Uganda have a common history of crustal growth, with new crust formation at 3.0 – 3.5 Ga, and crustal melting at c. 2.7 Ga. The Hammamat Formation of the Arabian–Nubian Shield is locally derived and has a maximum depositional age of 635 Ma. By contrast, Phanerozoic sedimentary rocks are derived from more distant sources. The fine-grained (mud) bulk signature of the modern Nile is dominated by input from the Ethiopian Highlands, transported by the Blue Nile and Atbara rivers. Detrital zircons in the Nile trunk are predominantly derived from Phanerozoic cover rocks. Most detritus from the upstream White Nile is trapped in the Sudd marshes and contributes little to the Nile trunk. Therefore, the White Nile downstream is dominated by locally derived Phanerozoic cover. The White Nile proximal to the Gezira Fan is influenced by the fan's Blue Nile signature. Supplementary material : Sample information, analytical methods and data tables are available at https://doi.org/10.6084/m9.figshare.c.3569490

Precipitation processes during non-isothermal aging of fine-grained AA2219

Fine-grained bulk AA2219 material was successfully manufactured by means of milling and hot compression/extrusion of metallic chips. Preliminary milling of the metallic scrap either for 8 or for 30 h was found to result in the development of two components of the material structure, i.e. a highly refined matrix and coarse remnants of unmilled chips. The average volume of the highly refined matrix reached 45% and 84% for materials milled for 8 h and 30 h (MA8h and MA30h samples), respectively. Hot compression tests confirmed high strength of preliminarily milled materials attributed to the grain refinement and properly carried out mechanical consolidation methods. An additional solid solution strengthening effect was observed for samples water-quenched after annealing at 808 K/300 min both for preliminarily milled materials and samples made from an industrial material (IM). However, subsequent hot deformation tests did not reveal noticeable hardening of the solution treated MA30h samples due to dynamic precipitation unlike in the case of IM samples. Transmission electron microscopy analyses may lead to the conclusion that the aging of solution treated MA material result in the growth of θ-type stable particles in heavily-refined areas without the preceding precipitation of metastable θ′ particles. Therefore, precipitation hardening of the tested MA-materials becomes inhibited with increased milling time.

Precipitation Processes during Non-Isothermal Ageing of Fine-Grained 2024 Alloy

Mechanical alloying and powder metallurgy procedures were used to manufacture very fine-grained bulk material made from chips of the 2024 aluminum alloy. Studies of solution treatment and precipitation hardening of as-received material were based on differential scanning calorimetry (DSC) tests and TEM/STEM/EDX structural observations. Structural observations complemented by literature data lead to the conclusion that in the case of highly refined structure of commercial 2024 alloys prepared by severe plastic deformation, typical multi-step G-P-B →θ” →θ’ →θ precipitation mechanism accompanied with G-P-B →S” →S’ →S precipitation sequences result in skipping the formation of metastable phases and direct growth of the stable phases. Exothermic effects on DSC characteristics, which are reported for precipitation sequences in commercial materials, were found to be reduced with increased milling time. Moreover, prolonged milling of 2024 chips was found to shift the exothermic peak to lower temperature with respect to the material produced by means of common metallurgy methods. This effect was concluded to result from preferred heterogeneous nucleation of particles at subboundaries and grain boundaries, enhanced by the boundary diffusion in highly refined structures. Transmission electron microscopy and diffraction pattern analysis revealed the development of very fine Al4C3 particles that grow due to the chemical reaction between the Al matrix and graphite flakes introduced as a process control agent during the preliminary milling of chips. Al4C3 nano-particles are formed at high temperatures, i.e. during hot extrusion and the subsequent solution treatment of the samples. Highly refined insoluble particles such as aluminum carbide particles and aluminum oxides were found to retard recrystallization and reduce recovery processes during solution treatment of preliminarily milled materials. Therefore, the as-extruded material composed of a milled part and chip residuals retained its initial bimodal structure in spite of solution heat treatment procedures. This points to a high structural stability of the investigated materials, which is commonly required for new technologies of high-strength Al-based materials production.

Accurate electron channeling contrast analysis of dislocations in fine grained bulk materials

Non-destructive, comprehensive dislocations characterization in fine grained Interstitial-Free Steel was realized for the first time by Accurate Electron Channeling Contrast Imaging “A-ECCI” in a Scanning Electron Microscope. Conventional Transmission Electron Microscopy g·b = 0 invisibility criterion and trace analysis were applied to determine Burgers vectors and line directions in this bulk material. This approach relies on the live collection of High Resolution Selected Area Channeling Patterns “HR-SACPs” using an innovative procedure to rock the beam with a remarkable spatial resolution of about 1 μm.

Fine-Grained Bulk NiTi Shape Memory Alloy Fabricated by Rapid Solidification Process and Its Mechanical Properties and Damping Performance

A near-equiatomic NiTi shape memory alloy was fabricated by rapid solidification process through vacuum arc melting followed by vacuum suction casting in water-cooled thick copper mold. The rapidly solidified (or suction cast) NiTi alloy shows much finer grains and homogenous microstructure, in particular a uniform distribution of various fine precipitates, compared to the conventional cast one. The resultant alloy also exhibits the homogenous Ni distribution in the matrix of the alloy, allowing the martensitic transformation to take place throughout the NiTi alloy matrix simultaneously and resulting in sharper transformation peaks compared to the conventional cast alloy. Moreover, the suction cast NiTi alloy shows a significant improvement over the conventional cast one, in terms of possessing higher deformation recovery rates and displaying the increased compressive strength and damping capacity by 4% and 20%, respectively.

Comparison of thermoelectric performance of AgPbxSbTe20 (x = 20–22.5) polycrystals fabricated by different methods

Both vacuum melting and mechanical alloying (MA) were applied to the fabrication of AgPbxSbTe20 (x=20, 21 and 22.5) as a promising thermoelectric material to investigate the processing influence on its thermoelectric properties. The AgPbxSbTe20 compound powders were prepared by pulverizing the melted ingots or directly from MA, which were then consolidated to fine-grained bulk materials by spark plasma sintering (SPS). A high ZT value of 1.25 at 725K was observed in the AgPb20SbTe20 samples fabricated by both methods. Thermoelectric properties of all AgPbxSbTe20 compounds synthesized by vacuum melting method are nearly the same as that of those fabricated by MA combined with SPS in the whole measured temperature range. Considering the complexity of the melting method but with the same results as the MA–SPS method, the present work revealed that the MA–SPS process is more suitable for the fabrication of PbTe-based thermoelectric materials.

Step heating of 40Ar/ 39Ar standard mineral mixtures: Investigation of a fine-grained bulk sediment provenance tool

Quantitative techniques that link sediments to their sources are needed to understand a range of tectonic, climate, and anthropogenic driven Earth surface processes. Many provenance techniques exist for sand-sized material but fewer are available for fine-grained sediment archives. In this respect, bulk 40Ar/ 39Ar ages from silt-sized sediment show potential, but many questions remain about the significance of a bulk sediment 40Ar/ 39Ar age. We interrogate bulk sediment 40Ar/ 39Ar ages by step heating mixtures of well-constrained 40Ar/ 39Ar mineral standards crushed to silt-sized. Silt-sized end member components Alder Creek Sanidine, Taylor Creek Sanidine and Heidelberg Biotite all yield plateau ages within uncertainty of their coarse-grained counterparts. High-resolution step heating (as many as 43 steps) of the mineral mixtures shows that biotite degasses first at lower temperatures compared to the two sanidines that degas generally in concert. Concordant age steps develop at both low and high temperatures and the transition from the isotope signal being dominated by one mineral phase to another is clearly observed. We show that age spectra for the mineral standard mixtures can be modeled and predicted for all mixtures by assuming a (simplistic) Gaussian distributed release of Ar, and by using the degassing maxima, variance, K concentration, and 40Ar/ 39Ar age of each monitor mineral. Thus, bulk sediment 40Ar/ 39Ar ages can be robust indicators of the average cooling/crystallization age of all contributing K-bearing minerals to a depositional center. Furthermore, we discuss the potential to deconvolve individual mineral age populations by model inversion. The application of this bulk sediment provenance technique should not be considered a replacement for single grain analyses. It should be applied to environments that do not provide sand-sized sediment archives (e.g., distal terrigenous sedimentary archives) when information about source changes through time are more important than precise sediment source identification.

Rotary-Die Equal Channel Angular Pressing Method for Light Metals

A new ECAP process method called rotary-die ECAP (RD-ECAP) was developed to form fine-grained bulk materials such as aluminium alloys, magnesium alloys, aluminium composites, and titanium, all of which can be processed under conditions of 573-773K, at an approximately 0.9-2.4 mm/s punch speed of 300MPa or lower. By the RD-ECAP method, ECAP processing of up to 2 passes can be done without sample removal and samples processed over 30 cycles were obtained.

Cyclic deformation and fatigue properties of very fine-grained metals and alloys

Bulk ultrafine-grained (UFG) metals and alloys prepared by techniques of severe plastic deformation (SPD), in particular by equal channel angular pressing (ECAP), exhibit exceptional mechanical properties. With respect to potential applications of this new class of very fine-grained bulk materials, the cyclic deformation and fatigue behaviour, relative to that of conventional grain size (CG) materials, is of crucial importance. In the present review, the research performed on the fatigue properties of very fine-grained bulk materials during the last decade will be discussed. Mainly bulk UFG materials prepared by ECAP will be considered and, to a smaller extent, also bulk truly nanocrystalline materials. The discussion will focus on simple materials and on more complex alloys and structural materials. Presentation of fatigue performance in total strain fatigue life diagrams has been found to be particularly suitable to compare the strong UFG and the more ductile CG materials in both the high cycle fatigue (HCF) and the low cycle fatigue (LCF) ranges. In general, the fatigue strength of UFG materials is enhanced considerably by grain refinement, in particular in the HCF regime. However, at the same time, the LCF performance is impaired by microstructural instabilities of the strongly hardened but less ductile UFG materials, as manifested in cyclic softening, fatigue-induced grain coarsening (by dynamic recrystallization at rather low homologous temperature!) and massive shear banding. These effects are discussed critically, also with respect to the effects of the route of ECAP-processing employed, the purity of the material – and the mode of fatigue testing. Remedies by mild annealing treatments which have been partially successful in improving the LCF strength by enhancing the ductility at the expense of a moderate loss of strength will be discussed. Examples of modelling of the cyclic deformation and fatigue properties will be presented, and some directions of future research will be outlined.

Wear-resistant ceramic and metal–ceramic ultrafine composites fabricated from combustion synthesised metastable powders

Abstract Dense Ti–Al2O3–TiC cermet and TiC–TiB2 ceramic composites have been fabricated by high-pressure high-temperature (HPHT) sintering starting from metastable nanostructured powders obtained by means of a technique based on the self-propagating high-temperature synthesis (SHS) process. The microstructural observations showed that an ultrafine microstructure was retained in the sintered composites thanks to the limited grain growth allowed by the short sintering duration of the HPHT method. The sintered TiC–TiB2 and Ti–Al2O3–TiC fine-grained bulk composites exhibited high values of hardness and Young modulus. The tribological characterization confirmed the good properties of both the materials in terms of wear-resistance and makes them very promising candidates for demanding applications. The influence of the ultrafine grain size on physical and tribological properties of the densified materials is discussed.

Evidence for biocycling from Ba/Ca, Sr/Ca, and 87Sr/86Sr in soils (Red Brown Earths) from South Australia

The impact of elemental cycling and biological fractionation in the soil–vegetation system was investigated for 6 Red Brown Earth soil profiles (Xeralfs and Xerults) from South Australia by comparing geochemical and 87Sr/86Sr data from bulk soils, soil exchange pool, and vegetation (grapes). In all 6 soil profiles from 3 different sites, Ba/Ca ratios of vegetation, soil exchange pool, and bulk soils were found to be a more robust biological fractionation indicator than Sr/Ca ratios. In the base-poor soils of the Coonawarra–Padthaway area of South Australia, the degree of weathering of soil material, as estimated by titania and alumina contents, correlated very well with the biological fractionation indicator Ba/Ca. Soil horizons with greater clay and titania content also had higher degrees of biological fractionation. Similar Red Brown Earth soils 400 km north in the Clare Valley showed either no, or poor, biological fractionation signature in their bulk soil. The Clare Valley soils have a stronger colluvial component and are richer in base cations than the Coonawarra and Padthaway sites. The main source of bulk soil material in the base-poor soils of the Coonawarra–Padthaway areas is dust, which has greatly influenced the base cation concentration, Ba/Ca ratios, and the strontium isotope ratios. Soils from Clare Valley, by comparison, are less intensely weathered and are thus not as dependent on dust and biocycling for their base cations. Biological fractionation has not left a discernible signature on the composition of the bulk soil. The exchange pools at all 3 sites are dominated by wetfall–dryfall sources, which in this coastal area are dominated by marine sources. For the base-poor soils of the Coonawarra–Padthaway area, the most likely major source of aeolian detritus is Murray River mud. The fine-grained component of this mud, with its organic matter content, relatively high base cation concentrations, and low strontium isotope ratios (Douglas et al. 1995) appears to have overwhelmed other dust sources and caused a homogenisation of the geochemical signature of fine-grained bulk soils in this area. Subsequent in situ weathering and neoformation following dust deposition were strongly influenced by exchange phase concentrations and ratios and resulted in an enhanced biological fractionation signature of the soils.