Tim H. Muster

Enhanced efficiency fertilisers: a review of formulation and nutrient release patterns.

Fertilisers are one of the most important elements of modern agriculture. The application of fertilisers in agricultural practices has markedly increased the production of food, feed, fuel, fibre and other plant products. However, a significant portion of nutrients applied in the field is not taken up by plants and is lost through leaching, volatilisation, nitrification, or other means. Such a loss increases the cost of fertiliser and severely pollutes the environment. To alleviate these problems, enhanced efficiency fertilisers (EEFs) are produced and used in the form of controlled release fertilisers and nitrification/urease inhibitors. The application of biopolymers for coating in EEFs, tailoring the release pattern of nutrients to closely match the growth requirement of plants and development of realistic models to predict the release pattern of common nutrients have been the foci of fertiliser research. In this context, this paper intends to review relevant aspects of new developments in fertiliser production and use, agronomic, economic and environmental drives for enhanced efficiency fertilisers and their formulation process and the nutrient release behaviour. Application of biopolymers and complex coacervation technique for nutrient encapsulation is also explored as a promising technology to produce EEFs.

Applications and Limitations of Scanning Kelvin Probe Force Microscopy for the Surface Analysis of Aluminum Alloys

The surface properties of aluminum alloy 2024-T3 (AA2024-T3) sheet after several surface treatments were investigated using scanning Kelvin probe force microscopy (SKPFM) and scanning electron microscopy (SEM). Treatments included boiling water, sodium chloride solution, and a chromate-free deoxidizing solution. The ability of SKPFM to resolve contact potential differences on both polished and rolled AA2024-T3 surfaces has been evaluated. While sensible data could be obtained on rolled sheet surfaces, SKPFM on pitted surfaces proved to be problematic. The inability of the scanning tip to accurately trace the surface topography resulted in erroneously high contact potential differences. Polished AA2024-T3 was analyzed by SEM before and after oxide growth. Carbon deposits on polished AA2024-T3 occurring during SEM analysis were revealed as areas with contact potential contrast using SKPFM. The influence of oxide thickening on contact potential differences was explored for AA2024-T3 and pure copper foil. The applicability of SKPFM for studying intermetallic features on other aluminum and other common engineering alloys is discussed.

Products Formed during the Interaction of Seawater Droplets with Zinc Surfaces II. Results from Short Exposures

This paper reports on a study in which fine seawater droplets were placed on zinc surfaces for periods of 15 min to 6 h. After each exposure, droplets were either extracted from the specimens or allowed to evaporate in laboratory conditions. Scanning electron microscopy (SEM)-energy-dispersive spectroscopy, X-ray microdiffraction, and SEM―focused ion beam studies were undertaken on the specimens after exposure, as was in situ Raman spectroscopy on zinc covered with a saline droplet. Approximately 30 min after droplets were placed on the surface, a thin moisture layer (termed the secondary spreading film) spread out from the central droplet. As a function of position and time, oxide development in the central region was initially slow; however, after ∼30 min, a significant local attack of the underlying microstructure occurred. Correspondingly, precipitate phases developed on top of the oxide, which produced an oxide consisting of three bands: an irregular zone with a localized metal attack and significant voids at the metal/oxide interface, overlaid by a relatively void-free layer, which in turn was overlaid by a porous zone. At the edge of the drop (before the secondary spreading), oxide growth was much faster, and the deposition of phases that precipitate in solutions appeared critical. We discuss the chemistry and identification of the various phases and the implications of oxide formation to the electrochemical processes occurring in drops.

Products Formed during the Interaction of Seawater Droplets with Zinc Surfaces: I. Results from 1- and 2.5-Day Exposures

This paper reports on a study in which fine seawater droplets were placed on zinc surfaces for periods up to 2.5 days. At the end of each exposure, the droplets were either extracted from the specimens or allowed to evaporate in laboratory conditions. Scanning electron microscope-energy-dispersive spectroscopy, X-ray diffraction studies (including mapping), and Fourier transform infrared and Raman spectroscopy were carried out on the specimens after exposure and on the dried extractions. It was observed that soon after the droplets were placed on the surface, a thin moisture layer (termed the secondary spreading film) spread out from the central droplet. X-ray analysis indicated the presence of gordaite and simonkolleite in the center of the drop when the droplet volume was maintained. However, during droplet evaporation a wider range of species was detected, including boyleite, zinc chlorate hydrate, and sodium zinc chloride hydrate. In the secondary spread region, an amorphous phase with a composition and morphology consistent with zinc hydroxy carbonate was present. The phase analysis is supported by electrochemical data and by analysis of changes in droplet chemistry with time. A synthesis of the data permits a description of the processes leading to the phase development. The implications to atmospheric corrosion are discussed.

Photoluminescence enhancement of carbon dots by gold nanoparticles conjugated via PAMAM dendrimers

Carbon dots (CDs) have many fascinating fluorescent properties, however, their low quantum yield limits their applications. In this study, the photoluminescence (PL) of CDs in the vicinity of gold nanoparticles (Au NPs) is enhanced significantly due to the surface plasmon resonance (SPR) of the Au NPs. This is achieved by conjugating Au NPs and CDs to dendrimers (PAMAM) through an amidation reaction, resulting in the formation of the Au-PAMAM-CD conjugates. The maximum 62-fold enhancement was obtained with an optimized molar ratio between Au NPs, PAMAM, and CDs. In this process, PAMAM, which serves as a spacer, can keep Au NPs and CDs at an appropriate distance for PL enhancement. The adjustment of the amount of Au NPs or CDs linked to PAMAM can induce the optimum PL enhancement. This strategy can be easily applied to different metal-space-fluorophore systems to enhance the fluorescence of fluorophores.

A Review of Surface Functionalized Amine Terminated Dendrimers for Application in Biological and Molecular Sensing

Dendrimers are three dimensional nanosized synthetic molecules that have internal cavities and numerous surface groups. In recent times they have received increased attention in sensing applications. For dendrimers to be used as sensors, they most commonly require functionalization at their surface. This is because the surface is generally the first point of contact between the dendrimer and the outside world, hence surface functionalization serves to selectively home in on the target analyte. Further, sensor signals may be transmitted through surface functionalities e.g. fluorochromic molecules. It is therefore important to document surface functionalization approaches. Dendrimers with amine surface groups have the advantage of being able to be conjugated to other molecules via an amide linkage, which is one of the most fundamental and widespread chemical bonds in nature. In this paper we demonstrate the properties of dendrimers that make them so applicable to sensing. We review several methods for functionalizing dendrimers via an amide linkage, as well as present a review of surface functionalized polyamidoamine, polyamine, and polypeptide dendrimers that have been employed for biological, chemical and molecular sensing.

Microstructure of a Paint Primer - a Data-Constrained Modeling Analysis

Metallic aerospace components are commonly painted with a primer to improve their corrosion resistance. The primer contains a polymer matrix with embedded corrosion inhibitor and filler particles. Its performance is determined by the microscopic distributions of the particles. Various techniques have been used to quantify such distributions, including X-ray micro-computed tomography (CT). However, its success is sometimes limited by factors such as different particles having similar X-ray CT absorption properties and their size being smaller than the resolution of micro-CT. In this paper, we have performed two X-ray CT measurements on a paint primer sample consisting of SrCrO4 corrosion inhibitor particles and UV-absorbing TiO2 filler particles. Fe and Ti targets were used as X-ray sources with different spectral distributions. The measured CT data sets were used as constraints for a data-constrained microstructure modeling (DCM) prediction of the sample’s microscopic structures. DCM model predictions were compared with experimental elemental surface maps and showed reasonable degree of agreement, suggesting X-ray micro-CT combined with DCM modeling would be a powerful technique for detailing the dynamics of chromate-inhibited primers and other multiphase systems where the components are sensitive to incident X-ray energy.

Interaction of Ce(dbp)3 with surface of aluminium alloy 2024-T3 using macroscopic models of intermetallic phases

Abstract The mechanism of corrosion inhibition by cerium(III) dibutylphosphate [Ce(dbp)3] on aluminium alloy 2024-T3 (AA2024-T3) has been investigated using macroscopic models of the intermetallic (IM) phases in the alloy. Polished specimens of pure Al (99·999%) and the macroscopic IM phases Al2CuMg, Al7Cu2Fe and Al3Fe were each coupled to a large surface area of AA2024-T3 to simulate the interaction they experience in the alloy. Samples were immersed in 0·1M NaCl with 200 ppm Ce(dbp)3 for 24 h, and the resulting surfaces characterised by scanning electron microscopy, X-ray photoelectron spectroscopy, Rutherford backscattering spectroscopy and Raman spectroscopy. Ce(dbp)3 was found to interact differently with each of the different phases examined, providing evidence for a multifunctional corrosion inhibition mechanism.

Electron-Beam-Induced Carbon Contamination on Silicon: Characterization Using Raman Spectroscopy and Atomic Force Microscopy

Electron-beam-induced carbon film deposition has long been recognized as a side effect of scanning electron microscopy. To characterize the nature of this type of contamination, silicon wafers were subjected to prolonged exposure to 15 kV electron beam energy with a probe current of 300 pA. Using Raman spectroscopy, the deposited coating was identified as an amorphous carbon film with an estimated crystallite size of 125 A. Using atomic force microscopy, the cross-sectional profile of the coating was found to be raised and textured, indicative of the beam raster pattern. A map of the Raman intensity across the coating showed increased intensity along the edges and at the corner of the film. The intensity profile was in excess of that which could be explained by thickness alone. The enhancement was found to correspond with a modeled local field enhancement induced by the coating boundary and showed that the deposited carbon coating generated a localized disturbance in the opto-electrical properties of the substrate, which is compared and contrasted with Raman edge enhancement that is produced by surface structure in silicon.

Attachment Efficiencies of Salt Aerosols onto Infrastructure and Implications for Atmospheric Corrosion

To support a holistic approach to the modeling of atmospheric corrosion, an experimental program was undertaken to delineate the effects of relative humidity, wind speed, and infrastructure surface chemistry on the efficiency of salt aerosol retention. The fundamental adhesion between a salt crystal and a metal oxide surface was studied using colloid probe atomic force microscopy. The magnitude of adhesion was dependant upon the probe dimensions, surface chemistry, and relative humidity. Parallel experiments investigated the removal of salt particles/aerosols from both clean hydrophilic and hydrophobized glass slide surfaces in a wind tunnel. The efficiency of the removal of particulates from glass surfaces was found to be a function of relative humidity, and the influence of humidity and wind velocity appeared to be magnified by increasing the glass hydrophobicity. Furthermore, alterations in the glass surface chemistry led to notable differences in the size and distribution of adsorbed salts. The experimentally determined salt retention efficiencies enable current holistic lifetime prediction models to be updated and expanded, and provides insight into the ability of surface chemistry to control aerosol retention processes and thus atmospheric corrosion.