Thomas Hübert

Thermal stability of TiN thin films investigated by DTG/DTA

The paper demonstrates the scope of the differential thermal analysis coupled with the thermal gravimetry as an express method for estimation of thin film protecting ability and oxidation kinetics. Oxidation of an iron foil protected by the PVD titanium nitride thin film coating was investigated as well as non-isothermal oxidation of PVD thin films of TiN (two types of the preparation procedure), (Ti,Nb)N and (Ti,Al)N isolated from a substrate by dissolving them in an acid. Additions of aluminium and niobium are expected to improve chemical, thermal and biomedical properties of thin films for their technical application. It was established that the addition of niobium decreases, whereas the addition of aluminium not only increases the thermal stability of TiN coatings, but also changes the oxidation mechanism. It was demonstrated that the TiN film oxidation is a many-staged process depending on the heating rate. An opportunity of a quite formal treatment for getting Kissingers estimation of kinetics parameters of different oxidation stages is also demonstrated.

A Colour Ripeness Indicator for Apples

Ripeness and senescence of climacteric fruits are strongly related to the emission of ethylene gas. The ethylene emission of apples can be detected by a new developed ripeness indicator. This indicator is based on the reduction effect of ethylene causing colour changes in selected metal ions. The used molybdenum (Mo) chromophores change under the impact of ethylene in a colour spectrum from white/light yellow to blue because of a partial reduction of Mo(VI) to Mo(V). The sensitivity of molybdenum colour change reactions can be varied by composition and pH values (pH 1.4–pH 1.5) of used ammonium molybdate solution and thus adopted to different fruits and storage conditions. The indicator can be combined with a colour recognition sensor for quantitative measurements of colour change in the frame of the L*a*b* model. The b*-coordinate, reflecting changes from yellow to blue, and the luminance L* continuously vary with increasing ethylene emission. Results obtained with the indicator system were compared with direct determination of ethylene concentrations by gas chromatography (GC-FID). Furthermore, a descriptive sensory test was used to estimate the degree of ripeness. The indicator can be applied for ripeness gauge on single fruit or in paperboard crates.

Amorphous and nanocrystalline SrTiO3 thin films

Abstract The interdependence of stoichiometry, structure and optical properties is discussed for SrTiO3 thin films prepared by chemical sol-gel process and physical vapour deposition (PVD). Both sol-gel and PVD coatings have a thickness of 50 to 500 nm and a homogeneous structure with an average grain size ranging from 15 to 30 nm and increasing to 50–250 nm after heat treatment to 700 °C. The molar ratio Sr to Ti to O is close to 1:1:3. The films are amorphous but, after annealing at temperatures above 450 °C, they have a polycrystalline structure. Optical properties were measured and data were compared with bulk material values. The films have a lower refractive index and absorption index in a 300–800 nm wavelength range by comparison with SrTiO3 single crystal data. This is due to the different preparation techniques resulting in changes in structure and lower film density.

Fire retardancy of sol–gel derived titania wood-inorganic composites

Sol–gel technology was applied in tailoring novel wood-made-inorganic composites with improved thermal and fire properties. In practice, composites materials were prepared by impregnating pine sapwood wood with nano-scaled precursor solutions derived from titanium(IV) isopropoxide followed by a thermal curing process. Thermal and fire properties were evaluated by thermal analysis and cone calorimetry, whereas flammability was specified by oxygen index (LOI) and UL 94 test. Peak heat release rates were moderately reduced indicating fire retardance potential in terms of flame spread attributed to the appropriate protection layer action of the titania-based depositions. LOI (oxygen index) values of these composites were increased up to 38 vol.% in comparison to 23 vol.% for untreated wood. The flame retardancy performance depends on the fire scenario and is strongly influenced by wood loading and crack-free deposition of the titania layers inside the composite.

Geographical provenience differentiation and adulteration detection of cumin by means of electronic sensing systems and SPME-GC-MS in combination with different chemometric approaches

The detection of the aroma and flavour volatile compounds of spices is key in product quality control. Accordingly, it is necessary to develop new electronic sensing systems for food adulteration control and authenticity assessment for protecting customers health. In this work, the capability of the E-nose and VE-tongue in combination with SPME-GC-MS to correctly discriminate between several cumin samples of different geographical origins and to detect their adulteration, by using unsupervised and supervised chemometric tools, was evaluated. Regarding the aroma profile, eleven volatile compounds were characterized by SPME-GC-MS; all of them were found in cumin powder while only eight are found in cumin seeds. The main volatile compounds detected were β-pinene, m-cymene, γ-terpinene, cuminaldehyde and cuminic alcohol, in different proportions depending on the cumin sample form (seed or powder). In summary, the results obtained are sufficiently encouraging as a starting point for the development of new electronic sensing systems with more improvement in the reliability of the sensors performance as well as chemometric tools in order to deal with a complex dataset.

Reducing copper leaching from treated wood by sol-gel derived TiO2 and SiO2 depositions

Abstract The antileaching efficacy of sol-gel-derived TiO2- and SiO2-based precursors has been evaluated through laboratory leaching trials with pine sapwood in two different ways. In a one-step process, wood was vacuum impregnated by the precursor solutions containing CuCl2. The copper (Cu) emission rates of the sol-gel-based impregnated woods were up to 70% lower than that of wood treated with pure CuCl2 solution at the same level of concentration. More improvement (80%) could be achieved in a two-step process, in which sol-gel precursors were introduced into an already CuCl2-treated wood. The refinement was attributed to several effects. In the one-step approach, Cu was embedded in the TiO2/SiO2 gels formed in the wood texture. During a two-step impregnation, gel layers that were formed in the wooden interior acted as an effective diffusion barrier. The sol-gel impregnations made wood more hydrophobic; therefore, the low amount of water that penetrated the cell wall was less efficient to leach out Cu.

Electronic Noses for the Quality Control of Spices

Abstract Spices are parts of plants, which are added to foodstuffs due to their natural flavoring. Their flavor is usually stimulated by a great number of volatile organic compounds. As natural products, the quality varies due to origin, seasons as well as processing and requires quality control. In addition to established methods, such as sensory and chemical analysis, electronic nose analysis has been developed to characterize various quality parameters of spices. Electronic noses are deployed for the discrimination between different types, provenience, and quality of spices. Furthermore, aroma intensity, aging effects, and mold infestation have been investigated. Electronic noses are used to characterize the impact of processing spices by milling or irradiation. Spice mixtures have been investigated in order to detect adulterations. In most cases, the deployment of electronic noses is performed in combination with other methods for reference such as sensory or chemical analysis.

Measurement uncertainty of coulometric trace humidity sensors

Abstract Especially trace amounts of water vapour in gases can be reliably determined by coulometric trace humidity sensors. The principle of these sensors is based on water vapour absorption in a hygroscopic layer and its subsequent electrolytic decomposition. The calibration of sensors was performed in the humidity range, expressed as frost point temperature, from − 30 ° C-30\hspace{0.1667em}^\circ \mathrm{C} to − 80 ° C-80\hspace{0.1667em}^\circ \mathrm{C}. This range is equivalent to volume fractions smaller than 376 µL·L−1. Generated humidity was measured with coulometric sensors and a chilled dew point hygrometer that was used as reference. An empirical non-linear function was found between sensor signal and measured reference humidity. This function consists of two parameters with a measurement uncertainty. Both calibration parameters were checked by means of one-way analysis of variance. It showed that gas specific function can be used for humidity measurement in nitrogen, hydrogen, dinitrogen monoxide, compressed and synthetic air. It is possible to determine trace humidity in all tested gases with an expanded uncertainty less than 2.1 K (coverage factor k = 2k=2) regarding frost point temperature.

Determination of safranal concentration in saffron samples by means of VE-Tongue, SPME-GC-MS, UV-Vis Spectrophotometry and multivariate analysis

An experimental investigation has been carried out to characterize and discriminate seven saffron samples and to verify their declared geographical origin using a voltammetric electronic tongue (VE-tongue). The ability of multivariable analysis methods such as Principal Component Analysis (PCA), Hierarchical Cluster Analysis (HCA) to classify the saffron samples according to their geographical origin have been investigated. A good discrimination has reached using PCA and HCA in the VE-tongue characterization case. Furthermore, cross validation and Partial Least Square (PLS) techniques were applied in order to build suitable management and prediction models for the determination of safranal concentration in saffron samples based on SPME-GC-MS and UV-Vis Spectrophotometry. The obtained results reveals that some relationships were established between the VE-tongue signal, SPME-GC-MS and UV-Vis spectrophotometry methods to predict safranal concentration levels in saffron samples by using the PLS model. In the light of these results, we can say that the proposed electronic system offer a fast, simple and efficient tool to recognize the declared geographical origin of the saffron samples.

P2.5.1 Long-Term Stability of the Low Energy Hydrogen Sensor

A silicon MIS-structure prepared with thin layers of the super-ionic conductor LaF3 and Pd is used to detect hydrogen. The sensor is able to detect hydrogen in a concentration range from below one ppm to the lower flammable limit in air which is 4 vol.-%. The chip operates at room temperature which results in an extremely low energy consumption compared to other hydrogen sensors. Only once per day a short heating pulse is necessary to reactivate the sensor chip. In cooperation with the BAM, a long-term experiment was carried out. The duration of the measurement was about three months, with a hydrogen exposure every two weeks. The sensor signal remained stable over the measured period.