Klaartje De Buysser

Aqueous CSD approach for the growth of novel, lattice-tuned LaxCe1−xOδ epitaxial layers

Lanthanum–cerium oxide (LCO) films were deposited on Ni-5%W substrates by chemical solution deposition (CSD) from water-based precursors. LCO films containing different ratios of lanthanum and cerium ions (from CeO2 to La2Ce2O7) were prepared. The composition of the layers was optimized towards the formation of LCO buffer layers, lattice-matched with the superconducting YBa2Cu3Oy layer, useful for the development of coated conductors. Single, crack-free LCO layers with a thickness of up to 140 nm could be obtained in a single deposition step. The crystallinity and microstructure of these lattice-matched LCO layers were studied by X-ray diffraction techniques, RHEED and SEM. We find that only layers with thickness below 100 nm show a crystalline top surface although both thick and thin layers show good biaxial texture in XRD. On the most promising layers, AFM and (S)TEM were performed to further evaluate their morphology. The overall surface roughness varies between 3.9 and 7.5 nm, while the layers appear much more dense than the frequently used La2Zr2O7 (LZO) systems, showing much smaller nanovoids (1–2 nm) than the latter system. Their effective buffer layer action was studied using XPS. The thin LCO layers supported the growth of superconducting YBCO deposited using PLD methods.

Structure and phase transition of Sn-substituted Zr(1−x)SnxW2O8

A conventional solid state reaction between ZrO2, SnO2 and WO3 was used to prepare the negative thermal expansion material Zr(1−x)SnxW2O8. The strong negative thermal expansion over a broad temperature range, which is well known for the pure zirconium tungstate compound, is also demonstrated in this substituted material. However, the order–disorder phase transition of the cubic materials was shown to shift towards lower temperatures, dependent on the degree of Sn4+-substitution, by dilatometry and temperature variable X-ray diffraction. This is attributed to the lower bond strength of the Sn–O bond in comparison to the Zr–O bond. The unit cell parameters of the material are significantly smaller due to the insertion of smaller Sn4+-cations on the Zr4+-position in the structure. For one composition (x = 0.3), the structure of Zr(1−x)SnxW2O8 was studied by neutron diffraction at two temperatures, 293 K and 473 K, corresponding to respectively the low temperature α-, and high temperature β-polymorph of Zr(1−x)SnxW2O8. The refined structures were found to be similar to that of ZrW2O8 at the same temperatures. Variable temperature X-ray diffraction of the same sample was used to establish the phase transition temperature, by refining the fractional occupancy of the possible tungstate orientations with temperature.

X-ray photoelectron spectroscopy (XPS) depth profiling for evaluation of La2Zr2O7 buffer layer capacity

Lanthanum zirconate (LZO) films from water-based precursors were deposited on Ni-5%W tape by chemical solution deposition. The buffer capacity of these layers includes the prevention of Ni oxidation of the substrate and Ni penetration towards the YBCO film which is detrimental for the superconducting properties. X-ray Photoelectron Spectroscopy depth profiling was used to study the barrier efficiency before and after an additional oxygen annealing step, which simulates the thermal treatment for YBCO thin film synthesis. Measurements revealed that the thermal treatment in presence of oxygen could severely increase Ni diffusion. Nonetheless it was shown that from the water-based precursors’ buffer layers with sufficient barrier capacity towards Ni penetration could be synthesized if the layers meet a certain critical thickness and density.

Highly crystalline nanoparticle suspensions for low-temperature processing of TiO2 thin films

In this work, we present preparation and stabilization methods for highly crystalline TiO2 nanoparticle suspensions for the successful deposition of transparent, photocatalytically active TiO2 thin films toward the degradation of organic pollutants by a low temperature deposition method. A proof-of-concept is provided wherein stable, aqueous TiO2 suspensions are deposited on glass substrates. Even if the processing temperature is lowered to 150-200 °C, the subsequent heat treatment provides transparent and photocatalytically active titania thin layers. Because all precursor solutions are water-based, this method provides an energy-efficient, sustainable, and environmentally friendly synthesis route. The high load in crystalline titania particles obtained after microwave heating opens up the possibility to produce thin coatings by low temperature processing, as a conventional crystallization procedure is in this case superfluous. The impact of the precursor chemistry in Ti(4+)-peroxo solutions, containing imino-diacetic acid as a complexing ligand and different bases to promote complexation was studied as a function of pH, reaction time and temperature. The nanocrystal formation was followed in terms of colloidal stability, crystallinity and particle size. Combined data from Raman and infrared spectroscopy, confirmed that stable titanium precursors could be obtained at pH levels ranging from 2 to 11. A maximum amount of 50.7% crystallinity was achieved, which is one of the highest reported amounts of anatase nanoparticles that are suspendable in stable aqueous titania suspensions. Decoloring of methylene blue solutions by precipitated nanosized powders from the TiO2 suspensions proves their photocatalytic properties toward degradation of organic materials, a key requisite for further processing. This synthesis method proves that the deposition of highly crystalline anatase suspensions is a valid route for the production of photocatalytically active, transparent films on heat-sensitive substrates such as polymers.

Tuning the Pore Geometry of Ordered Mesoporous Carbons for Enhanced Adsorption of Bisphenol-A

Mesoporous carbons were synthesized via both soft and hard template methods and compared to a commercial powder activated carbon (PAC) for the adsorption ability of bisphenol-A (BPA) from an aqueous solution. The commercial PAC had a BET-surface of 1027 m2/g with fine pores of 3 nm and less. The hard templated carbon (CMK-3) material had an even higher BET-surface of 1420 m2/g with an average pore size of 4 nm. The soft templated carbon (SMC) reached a BET-surface of 476 m2/g and a pore size of 7 nm. The maximum observed adsorption capacity (qmax) of CMK-3 was the highest with 474 mg/g, compared to 290 mg/g for PAC and 154 mg/g for SMC. The difference in adsorption capacities was attributed to the specific surface area and hydrophobicity of the adsorbent. The microporous PAC showed the slowest adsorption, while the ordered mesopores of SMC and CMK-3 enhanced the BPA diffusion into the adsorbent. This difference in adsorption kinetics is caused by the increase in pore diameter. However, CMK-3 with an open geometry consisting of interlinked nanorods allows for even faster intraparticle diffusion.

Aqueous ZrO 2 and YSZ Colloidal Systems through Microwave Assisted Hydrothermal Synthesis

In this paper, the formation of ZrO2 and yttria-stabilised-zirconia (YSZ) aqueous colloidal systems via microwave assisted hydrothermal synthesis is studied. Microwave synthesis allows a fast screening of the influence of different parameters such as time and temperature. The temperature varied from 140 °C up to 180 °C and the used reaction time varied from 5 min up to 1 h. The synthesised zirconia nanoparticles have a particle size of 50 nm confirmed by TEM. A 1H NMR (nuclear magnetic resonance) study helped to understand the stabilization mechanism of the synthesised particles. By the addition of ytrrium ions into the zirconia colloidal solution, YSZ could be formed via an additional thermal treatment. Hereby, the samples are heated up to 400 °C for 1 h. YSZ colloidal solutions are synthesised by making use of complexing agents such as nitrilotriacetic acid, ethylenediaminetetraacetic acid and citric acid to control the hydrolysis and condensation of both ions to avoid non-stoichiometric phases. The ratio of Zr/Y in the particles is quantified by XRF. The amorphous structure of those particles necessitates an additional thermal treatment up to 600 °C during 1 h in order to obtain crystalline YSZ.

Influence of aqueous precursor chemistry on the growth process of epitaxial SrTiO3 buffer layers

In this Article, epitaxial thin films of SrTiO3 were prepared on single crystalline (100) LaAlO3 by an aqueous chemical solution deposition method. By using different chelating agents to stabilize the metal ions in water, the impact of the precursor chemistry on the microstructural and crystalline properties of the films was studied. Thorough investigation of the precursor by means of infrared and Raman spectroscopy as well as thermogravimetric analysis revealed that stable precursors can be obtained in which strontium ions can be either free in the solution or stabilized by one of the chelating agents. This stabilization of strontium ions appeared to be essential in order to obtain single phase SrTiO3 films. Precursors in which Sr(2+) remained as free ions showed SrO microcrystal segregation. Precursors in which both metal ions were stabilized gave rise to strongly textured, dense, and terraced SrTiO3 films, allowing subsequent deposition of YBa2Cu3O7-δ with superior superconducting performances.

Feasibility Study of the Use of Concrete Sludge As Alternative Raw Material for Portland Clinker Production

AbstractThis study aims to examine the use of concrete sludge from water treatment installations of ready-mixed concrete plants as an alternative raw material for portland clinker kilns, and to enumerate possible limitations. By its extensive and representative collection of concrete sludge samples data, it may also be used for other investigations. The chemical variations of this sludge were evaluated by gathering 87 sludge samples over a period of two years. Furthermore, a treatment phase was proposed. Numerical simulations were conducted based on the chemistry of a representative concrete sludge sample, before and after a specific treatment phase, together with classic raw materials of three reference clinker factories to investigate the influence of the sludge on the clinker meal composition. Based on these simulations, experimental clinkers were produced, which were fully analyzed and evaluated for possible mineralogical influences. Based on the findings of this investigation, it was concluded that s...

Discovery of a novel, large pore phase in a bimetallic Al/V metal–organic framework

A new series of bimetallic COMOC-2(V)/DUT-5(Al) frameworks are developed and fully characterized. Electron paramagnetic resonance and transmission electron microscopy confirm the homogeneous dispersion of Al/V in the entire framework. The study of the flexibility by means of CO2 pressure dependent XRPD and high pressure sorption reveals the co-existence of two different large pore phases and a narrow pore phase in the entire pressure regime.

Thickness characterization toolbox for transparent protective coatings on polymer substrates

The thickness characterization of transparent protective coatings on functional, transparent materials is often problematic. In this paper, a toolbox to determine the thicknesses of a transparent coating on functional window films is presented. The toolbox consists of a combination of secondary ion mass spectrometry and profilometry and can be transferred to other transparent polymeric materials. A coating was deposited on designed model samples, which were characterized with cross-sectional views in transmission and in scanning/transmission electron microscopy and ellipsometry. The toolbox was then used to assess the thicknesses of the protective coatings on the pilot-scale window films. This coating was synthesized using straightforward sol-gel alkoxide chemistry. The kinetics of the condensation are studied in order to obtain a precursor that allows fast drying and complete condensation after simple heat treatment. The shelf life of this precursor solution was investigated in order to verify its accordance to industrial requirements. Deposition was performed successfully at low temperatures below 100 °C, which makes deposition on polymeric foils possible. By using roll-to-roll coating, the findings of this paper are easily transferrable to industrial scale. The coating was tested for scratch resistance and adhesion. Values for the emissivity (ε) of the films were recorded to justify the use of the films obtained as infrared reflective window films. In this work, it is shown that the toolbox measures similar thicknesses to those measured by electron microscopy and can be used to set a required thickness for protective coatings.