Christos G. Aneziris

Virus Removal in Ceramic Depth Filters Based on Diatomaceous Earth

Ceramic filter candles, based on the natural material diatomaceous earth, are widely used to purify water at the point-of-use. Although such depth filters are known to improve drinking water quality by removing human pathogenic protozoa and bacteria, their removal regarding viruses has rarely been investigated. These filters have relatively large pore diameters compared to the physical dimension of viruses. However, viruses may be retained by adsorption mechanisms due to intermolecular and surface forces. Here, we use three types of bacteriophages to investigate their removal during filtration and batch experiments conducted at different pH values and ionic strengths. Theoretical models based on DLVO-theory are applied in order to verify experimental results and assess surface forces involved in the adsorptive process. This was done by calculation of interaction energies between the filter surface and the viruses. For two small spherically shaped viruses (MS2 and PhiX174), these filters showed no significant removal. In the case of phage PhiX174, where attractive interactions were expected, due to electrostatic attraction of oppositely charged surfaces, only little adsorption was reported in the presence of divalent ions. Thus, we postulate the existence of an additional repulsive force between PhiX174 and the filter surface. It is hypothesized that such an additional energy barrier originates from either the phages specific knobs that protrude from the viral capsid, enabling steric interactions, or hydration forces between the two hydrophilic interfaces of virus and filter. However, a larger-sized, tailed bacteriophage of the family Siphoviridae was removed by log 2 to 3, which is explained by postulating hydrophobic interactions.

Control of the size, shape and composition of highly uniform, non-agglomerated, sub-micrometer β-tricalcium phosphate and dicalcium phosphate platelets.

Calcium phosphates (CaPs) are widely used as bone graft substitutes but are inherently brittle, hence restricting their use to mechanically protected environments. Combining them with a tough polymer matrix could potentially lead to a composite with load-bearing properties. However, the highest mechanical properties can only be achieved if the CaP particles possess very precise features: they should be uniform in size and shape, non-agglomerated, elongated and thin. The aim of the present study therefore was to assess a novel method to produce such particles. This involved the precipitation of CaP particles in ethylene glycol at moderate temperatures (90-170 °C) and the variation of different reaction parameters (temperature, concentration, pH, etc) to study their influence on particle composition, size, shape and dispersion was studied. As a result, two main CaP phases were obtained as well-dispersed and highly uniform platelets in the form of: (i) β-tricalcium phosphate (β-TCP) hexagonal prisms and (ii) monetite (DCP) flat parallelepipeds. The size dispersion was the narrowest for β-TCP (standard deviation/mean < 5%) whereas the aspect ratio was the highest for DCP (up to 25). In both cases, the thickness of the platelets was below 300 nm which should be ideal for the synthesis of strong CaP-based composites.

In Situ Observation of Collision between Exogenous and Endogenous Inclusions on Steel Melts for Active Steel Filtration

In a confocal scanning laser microscope, interactions between exogenous and endogenous inclusions on steel melts have been investigated. Higher capillary long-range attraction forces as well as higher acting lengths of the capillary forces between exogenous and endogenous particle pairs have been observed in comparison to endogenous inclusions pairs. The contribution of the roughness of the exogenous inclusions to the capillary attraction forces has been discussed and a surface filter design for a higher filtration efficiency of steel melts has been proposed.

Improved virus removal in ceramic depth filters modified with MgO.

Ceramic filters, working on the depth filtration principle, are known to improve drinking water quality by removing human pathogenic microorganisms from contaminated water. However, these microfilters show no sufficient barrier for viruses having diameters down to 20 nm. Recently, it was shown that the addition of positively charged materials, for example, iron oxyhydroxide, can improve virus removal by adsorption mechanisms. In this work, we modified a common ceramic filter based on diatomaceous earth by introducing a novel virus adsorbent material, magnesium oxyhydroxide, into the filter matrix. Such filters showed an improved removal of about 4-log in regard to bacteriophages MS2 and PhiX174. This is explained with the electrostatic enhanced adsorption approach that is the favorable adsorption of negatively charged viruses onto positively charged patches in an otherwise negatively charged filter matrix. Furthermore, we provide theoretical evidence applying calculations according to Derjaguin-Landau-Verwey-Overbeek theory to strengthen our experimental results. However, modified filters showed a significant variance in virus removal efficiency over the course of long-term filtration experiments with virus removal increasing with filter operation time (or filter aging). This is explained by transformational changes of MgO in the filter upon contact with water. It also demonstrates that filter history is of great concern when filters working on the adsorption principles are evaluated in regard to their retention performance as their surface characteristics may alter with use.

Pitfalls of local and quantitative phase analysis in partially stabilized zirconia

The addition of selected elements into the host structure of ZrO2 stabilizes the tetragonal and cubic phases of zirconia, which are, in their undoped binary form, only stable at high temperatures. From the crystallographic point of view, the increasing amount of the stabilizer causes a continuous transition of the tetragonal zirconia to its cubic modification. In partially stabilized zirconia, local concentration gradients of the stabilizer are frequently present as a consequence of the production process, which results in a coexistence of zirconia domains having different degrees of tetragonality. The presence of the local concentration gradients in such samples and the continuous nature of the phase transformation are features important for many technological applications, but their analysis is not straightforward. Furthermore, these features complicate the quantitative phase analysis in partially stabilized zirconia. For the example of zirconia partially stabilized by magnesium, this contribution illustrates the capabilities and limitations of X-ray and electron backscatter diffraction. In particular, the ability of these experimental methods to reveal the gradual lattice distortion that is associated with the cubic to tetragonal phase transformation in zirconia and the reliability of the quantitative phase analysis are discussed. In this context, it is shown to what extent the choice of the microstructure model influences the result of the phase analysis.

Homogeneous functional Ni–P/ceramic nanocomposite coatings via stable dispersions in electroless nickel electrolytes

Stable nanoparticle dispersions in concentrated electrolytes are prerequisite for a variety of advanced nanocomposites prepared by deposition techniques. In this work we investigate the synthesis of electroless Ni-P/functional ceramic coatings from concentrated electrolytes containing functional nanoparticles such as TiO(2), α-Fe(2)O(3), ITO, and CeO(2). Stable nanoparticle dispersions in both low and high phosphorus electrolytes are achieved at plating temperatures (80-90 °C) by a generalized scheme employing comb-polyelectrolyte and antifreeze additives. Dispersion stability at room temperature is achieved in both low and high phosphorus EN media using anionic comb-polyelectrolyte surfactants with polyether side chain of 1100 g/mol. The optimal surfactant concentration is determined by zeta-potential and thermo-gravimetric analysis. Without additives the dispersions flocculate and sediment between 65 and 80 °C. Such phenomenon is believed to be associated with a critical flocculation temperature (CFT). The CFT is also weekly dependent on the particle type and the high ionic strength media. Addition of antifreeze additives such as propylene glycol and urea to the dispersions restores stability and increase the CFT for all particles. We estimate an average increase of the CFT by 1.5-2 °C per 1% additive for all particles and electrolytes. While the particle stabilization scheme is generalized in this work, the composite EN plating proved highly dependent on particle type. Baths containing ITO nanoparticles showed no plating reactions and those containing α-Fe(2)O(3) no nanoparticle co-deposition. In contrast, homogeneous Ni-P/TiO(2) and Ni-P/CeO(2) nanocomposites with up to 22 vol.% nanoparticles are produced. The possible application of the stabilization principles developed here for other functional nanocomposite systems is discussed.

Cellular Energy Absorbing TRIP-Steel/Mg-PSZ Composite: Honeycomb Structures Fabricated by a New Extrusion Powder Technology

Lightweight linear cellular composite materials on basis of austenite stainless TRIP- (TRansformation Induced Plasticity-) steel as matrix with reinforcements of MgO partially stabilized zirconia (Mg-PSZ) are described. Two-dimensional cellular materials for structural applications are conventionally produced by sheet expansion or corrugation processes. The presented composites are fabricated by a modified ceramic extrusion powder technology. Characterization of the microstructure in as-received and deformed conditions was carried out by optical and scanning electron microscopy. Magnetic balance measurements and electron backscatter diffraction (EBSD) were used to identify the deformation-induced martensite evolution in the cell wall material. The honeycomb composite samples exhibit an increased strain hardening up to a certain engineering compressive strain and an extraordinary high specific energy absorption per unit mass and unit volume, respectively. Based on improved property-to-weight ratio such linear cellular structures will be of interest as crash absorbers or stiffened core materials for aerospace, railway, or automotive applications.

Carbon Containing Castables and More

In terms of this work formulations of carbon bonded castables based on new binder approaches and nanoadditions will be demonstrated. The new binder system allows the manufacturing of water based magnesia carbon castables with the same properties and chemistry of pressed magnesia carbon bricks. This binder can be also applied in oxide castables offering them high refractoriness and workability during processing. According to the workability nano-additions improve significantly the spreading diameter of carbon castables and as a result their flowability.

Effect of the Filter Surface Chemistry on the Filtration of Aluminum

The influence of the filter surface chemistry of alumina skeletons on the filtration effect was tested with five different oxide coating materials (Al2O3, spinel, mullite, TiO2, and SiO2). All prepared filters were casted successfully under industrial conditions. The casted aluminum samples showed no contamination caused by the filters. The evaluation of the casted filters by means of SEM and EDX showed that the amount of inclusions in the area of the run in is larger than in the middle and the run out of the filter. The most non-metallic inclusions were found in the casted filters Al2O3+Al2O3 and Al2O3+spinel. The wetting experiments yielded for all tested materials a non-wetting behavior whereby Al2O3 and spinel showed higher wetting angle than mullite, TiO2, and SiO2.

Growth kinetics of hexagonal sub-micrometric β-tricalcium phosphate particles in ethylene glycol☆

Recently, uniform, non-agglomerated, hexagonal β-tricalcium phosphate (β-TCP) platelets (diameter≈400-1700nm, h≈100-200nm) were obtained at fairly moderate temperatures (90-170°C) by precipitation in ethylene glycol. Unfortunately, the platelet aspect ratios (diameter/thickness) obtained in the latter study were too small to optimize the strength of polymer-β-TCP composites. Therefore, the aim of the present study was to investigate β-TCP platelet crystallization kinetics, and based on this, to find ways to better control the β-TCP aspect ratio. For that purpose, precipitations were performed at different temperatures (90-170°C) and precursor concentrations (4, 16 and 32mM). Solution aliquots were retrieved at regular intervals (10s-24h), and the size of the particles was measured on scanning electron microscopy images, hence allowing the determination of the particle growth rates. The β-TCP platelets were observed to nucleate and grow very rapidly. For example, the first crystals were observed after 30s at 150°C, and crystallization was complete within 2min. The crystal growth curves could be well-fitted with both diffusion- and reaction-controlled equations, but the high activation energies (∼100kJmol(-1)) pointed towards a reaction-controlled mechanism. The results revealed that the best way to increase the diameter and aspect ratio of the platelets was to increase the precursor concentration. Aspect ratios as high as 14 were obtained, but the synthesis of such particles was always associated with the presence of large fractions of monetite impurities.