Luc Vandeperre

Gelatin gelcasting of ceramic components

Abstract Gelcasting is a new near net shaping technique, which has rapidly evolved from a laboratory invention towards industrial application. In gelcasting, a highly loaded but very fluid slurry consisting of powder, water, disperser and gelformer, is poured into a mould and subsequently gelled. Once gelation has taken place, the part is strong enough to retain its shape and can be demoulded, dried, calcined and sintered. A great advantage of the technique is that very complex shapes can be made with relative ease. In original gelcasting formulations, gelation was obtained through polymerisation of acrylamide monomers, which are classified as neuro-toxic. In this study, however, the feasibility of using a non-toxic gelformer (gelatin) will be reported. Relevant processing parameters such as slurry composition and preparation procedures, de-airing and gelation schedules are reported, along with results of sintering and resulting microstructures.

Magnesium-silicate-hydrate cements for encapsulating problematic aluminium containing wastes

Low pH cement systems for encapsulating legacy nuclear industry wastes containing aluminium metal are being developed using blends of MgO and silica fume (SF). The rheology of the binary system is significantly improved by addition of sodium hexa-metaphosphate (Na-HMP) which reduces the required w/s ratio. The addition of MgCO3 further controls the initial pH of the cement system and sand filler reduces shrinkage cracking. The physical, chemical and mechanical properties of the optimised MgO/SF cement system in terms of pH, setting time, microstructure, compressive strength, flexural strength and heat of hydration are reported and compared to the PC/BFS blended system currently used for waste encapsulation. The optimised MgO/SF cement and PC/BFS cement are also compared by monitoring the volume of H2 generated from binder samples containing Al metal strips. Al metal was firmly bound into MgO/SF samples and H2 gas was not detected, indicating that any corrosion reactions were very limited. It is concluded that the MgO/SF cement system has significant potential for encapsulating certain types of problematic wastes containing Al metal and may have uses in a range of other applications.

Production of pyroxene ceramics from the fine fraction of incinerator bottom ash

Incinerator bottom ash (IBA) is normally processed to extract metals and the coarse mineral fraction is used as secondary aggregate. This leaves significant quantities of fine material, typically less than 4mm, that is problematic as reuse options are limited. This work demonstrates that fine IBA can be mixed with glass and transformed by milling, calcining, pressing and sintering into high density ceramics. The addition of glass aids liquid phase sintering, milling increases sintering reactivity and calcining reduces volatile loss during firing. Calcining also changes the crystalline phases present from quartz (SiO2), calcite (CaCO3), gehlenite (Ca2Al2SiO7) and hematite (Fe2O3) to diopside (CaMgSi2O6), clinoenstatite (MgSiO3) and andradite (Ca3Fe2Si3O12). Calcined powders fired at 1080°C have high green density, low shrinkage (<7%) and produce dense (2.78 g/cm(3)) ceramics that have negligible water absorption. The transformation of the problematic fraction of IBA into a raw material suitable for the manufacture of ceramic tiles for use in urban paving and other applications is demonstrated.

Recycling disposable cups into paper plastic composites

The majority of disposable cups are made from paper plastic laminates (PPL) which consist of high quality cellulose fibre with a thin internal polyethylene coating. There are limited recycling options for PPLs and this has contributed to disposable cups becoming a high profile, problematic waste. In this work disposable cups have been shredded to form PPL flakes and these have been used to reinforce polypropylene to form novel paper plastic composites (PPCs). The PPL flakes and polypropylene were mixed, extruded, pelletised and injection moulded at low temperatures to prevent degradation of the cellulose fibres. The level of PPL flake addition and the use of a maleated polyolefin coupling agent to enhance interfacial adhesion have been investigated. Samples have been characterised using tensile testing, dynamic mechanical analysis (DMA) and thermogravimetric analysis. Use of a coupling agent allows composites containing 40 wt.% of PPL flakes to increase tensile strength of PP by 50% to 30 MPa. The Young modulus also increases from 1 to 2.5 GPa and the work to fracture increases by a factor of 5. The work demonstrates that PPL disposable cups have potential to be beneficially reused as reinforcement in novel polypropylene composites.

Properties of ceramics prepared using dry discharged waste to energy bottom ash dust

The fine dust of incinerator bottom ash generated from dry discharge systems can be transformed into an inert material suitable for the production of hard, dense ceramics. Processing involves the addition of glass, ball milling and calcining to remove volatile components from the incinerator bottom ash. This transforms the major crystalline phases present in fine incinerator bottom ash dust from quartz (SiO2), calcite (CaCO3), gehlenite (Ca2Al2SiO7) and hematite (Fe2O3), to the pyroxene group minerals diopside (CaMgSi2O6), clinoenstatite (MgSi2O6), wollastonite (CaSiO3) together with some albite (NaAlSi3O8) and andradite (Ca3Fe2Si3O12). Processed powders show minimal leaching and can be pressed and sintered to form dense (>2.5 g cm-3), hard ceramics that exhibit low firing shrinkage (<7%) and zero water absorption. The research demonstrates the potential to beneficially up-cycle the fine incinerator bottom ash dust from dry discharge technology into a raw material suitable for the production of ceramic tiles that have potential for use in a range of industrial applications.

Measurement of Crystal Lattice Rotations under Nanoindents in Copper

A technique is described to measure the rotations of the crystal lattice in the deformed region around a nanoindent from volumes smaller than 3 × 10 −5 μm 3 . To demonstrate this method, a copper crystal has been indented on its (001) face to depths of 500 and 1300 nm. Cross-sections of nanoindents were prepared for transmission electron microscopy by focused ion beam milling, and rotations were measured about the [001], [010] and [100] axes using convergent beam electron diffraction.

3D Printing Bioinspired Ceramic Composites.

Natural structural materials like bone and shell have complex, hierarchical architectures designed to control crack propagation and fracture. In modern composites there is a critical trade-off between strength and toughness. Natural structures provide blueprints to overcome this, however this approach introduces another trade-off between fine structural manipulation and manufacturing complex shapes in practical sizes and times. Here we show that robocasting can be used to build ceramic-based composite parts with a range of geometries, possessing microstructures unattainable by other production technologies. This is achieved by manipulating the rheology of ceramic pastes and the shear forces they experience during printing. To demonstrate the versatility of the approach we have fabricated highly mineralized composites with microscopic Bouligand structures that guide crack propagation and twisting in three dimensions, which we have followed using an original in-situ crack opening technique. In this way we can retain strength while enhancing toughness by using strategies taken from crustacean shells.

Functionalised magnetic nanoparticles for uranium adsorption with ultra-high capacity and selectivity

The removal of radioactive contaminants from the environment for safe and efficient waste disposal is a critical challenge, requiring the development of novel selective and high-capacity sequestering materials. In this paper the design of superparamagnetic iron oxide nanoparticles (SPIONs) as highly efficient magnetic-sorbent structures for uranium (U(VI)) separation is described. The nanosorbent was developed by surface functionalisation of single crystalline magnetite (Fe3O4) nanoparticles with a phosphate-based complex coating. This new design allowed for the development of a magnetically separable ultra-effective sorbent, with a measured U(VI) sorption capacity of ∼2333 mg U per g Fe (1690 mg U per g Fe3O4 NP), significantly higher than everything previously reported. Based on TEM analysis, it is proposed that these properties are the result of a multi-layer ligand structure, which enables a high degree of U-incorporation compared to conventional surface-ligand systems. Moreover, the phosphate-NP construct ((PO)x-Fe3O4) shows exceptionally high specificity for the sequestration of U(VI) in solution at pH 7. Adsorption tests in the presence of competing ions, such as Sr(II), Ca(II) and Mg(II), showed high selectivity of the nanoparticles for U(VI) and extremely rapid kinetics of contaminant removal from solution, with the total amount of uranyl ions being removed after only 60 seconds of contact with the NPs. The results presented in this paper highlight the potential of such a phosphate-functionalised magnetic nanosorbent as a highly effective material for the remediation of U(VI) from contaminated water and industrial scenarios.

Control of Drying Shrinkage of Magnesium Silicate Hydrate Gel Cements

Cracks were observed when the magnesium silicate hydrate gel cement (prepared by 40% MgO/ 60% silica fume) was dried. This drying cracking is believed to be caused when unbound water evaporates from the binder. The shrinkage upon forced drying to 200 °C of mortars made up from a reactive magnesium oxide, silica fume and sand was measured using dilatometry. The magnitude of the drying shrinkage was found to decrease when more sand or less water was added to the mortars and can be as low as 0.16% for a mortar containing 60 wt% sand and a water to cement ratio of 0.5, which is of a similar order of magnitude as observed in Portland cement based mortars and concretes. A simple geometrical interpretation based on packing of the particles in the mortar can explain the observed drying shrinkages and based on this analysis the drying shrinkage of the hydration products at zero added solid is estimated to be 7.3% after 7 days of curing.

Production of Layered Double Hydroxides for Anion Capture and Storage

Technetium has a long half life of up to 2.13×10 5 years. It is separated from liquid waste streams with tetraphenylphosphonium bromide [1], which upon degradation releases Tc as the pertechnetate anion, TcO 4 − . Pertechnetate is highly mobile in groundwater and it is therefore highly desirable to capture and immobilise this anion within a solid for interim and ultimately long term storage. Layered Double Hydroxide (LDH) materials are known to possess excellent anion sorption capabilities due to their structure which consists of ordered positively charged sheets intercalated with interchangeable hydrated anions. The composition can be tailored to produce suitable precursors for ceramic phases by varying the divalent and trivalent cations and the anions. LDHs with the general formula Ca 1-x (Fe 1-y , Al y ) x (OH) 2 (NO 3 ) x . nH 2 O were produced by a co-precipitation method from a solution of mixed nitrates. Calcination leads to the formation of Brownmillerite Ca 2 (Al,Fe) 2 O 5 like compounds for temperatures as low as 400°C, this is close to the lowest temperature at which Tc is known to volatilise (310.6 °C Tc 2 O 7 ). It was shown that after calcining up to 600°C, the LDH structure is recovered in water allowing rapid ion capture to occur. This suggests that these materials have potential for both capture and as a storage medium for Tc.