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- Sol-gel (7)
- Hydrogen detection (4)
- Electronic nose (3)
- SPME-GC-MS (3)
- Voltammetric electronic tongue (3)
- Wood protection (3)
- ANOVA (2)
- Adulteration detection (2)
- Carbon black (2)
- Coulometric sensors (2)
Organisationseinheit der BAM
Different electronic sensor systems coupled with multivariate data analysis were applied to characterize and classify seven saffron samples and to verify their declared geographical origin. The proposed electronic sensing consists of a low-cost electronic nose (E-nose) based on metal oxide semiconductor sensors and a voltammetric electronic tongue (VE-tongue) based on voltammetric sensors. The ability of multivariable analysis methods such as Principal Component Analysis (PCA), Hierarchical Cluster Analysis (HCA) and Support Vector Machines (SVMs) to classify the saffron samples according to their geographical origin have been investigated. Both PCA and HCA have shown an overlapping of E-nose responses. Moreover, the SVM analysis of the E-nose database reached a 66.07% success rate in the recognition of the saffron sample odour. On the other hand, good discrimination has been reached using PCA and HCA in the VE-tongue characterization case, besides a 100% accuracy in the saffron flavour recognition was attained. To validate the proposed electronic sensing systems, analytical chemical methods such as SPME-GC-MS and UV-Vis spectrophotometry were used. These analytical methods could be helpful tools to identify the composition of volatile compounds of the analysed saffron samples. Moreover, UV-Vis spectrophotometry was also used to determine the non-volatile profile of the samples from different geographic origins. It is demonstrated that the electronic sensing systems' findings are in a satisfactory correlation with the analytical methods. In the light of these results, we might say that the electronic systems offer a fast, simple and efficient tool to recognize the declared geographical origin of the saffron samples.
Planar coulometric sensors were tested in humidified synthetic air at various gas temperatures. Generated frost point temperature in the gas ranged from -30 °C to -60 °C and were measured by coulometric sensors and in addition by a calibrated dew point hygrometer. The gas temperatures, which were measured by a calibrated Pt100 sensor, were set to -20 °C, 0 °C, 23 °C, 40 °C, 50 °C, and 60 °C during the experiments. Empiric nonlinear functions were calculated between the generated humidity and the sensor signals. In comparison to the measured signals at 23 °C, the sensor signals were lower at the other gas temperatures. The measurements at 60 °C showed indistinct results due to a great signal noise. The response behavior of the sensors was similar at 23 °C, 40 °C and 50 °C. In contrast to that, the sensors reacted slowly at a gas temperature of -20 °C and 0 °C. In summary, with coulometric sensors it was possible to measure continuously trace humidity with an expanded uncertainty below 2 K.
Trace humidity was measured by using miniaturized planar coulometric sensors in technical gases such as hydrogen, nitrogen, helium, nitrous oxide, and synthetic air. Frost point temperatures tf in the gases ranged from −60 °C to −30 °C, which is equivalent to a vapour mole fraction xv from 10 μmol mol−1 to 376 μmol mol−1. In addition, the generated humidity was determined by using a precision dew point hygrometer as reference. Nonlinear calibration functions were calculated that correlated electric current (sensor signal) and reference humidity. Parameters of functions were tested with one-way analysis of variances (ANOVA) to prove if all used sensors had a similar behavior in the same gas during experiments. Results of ANOVA confirmed that averaged functions can be applied for trace humidity measurement in nitrogen, helium, nitrous oxide, and synthetic air. The calculated functions were negligibly different for nitrogen, helium, and synthetic air. In humidified nitrous oxide, a minor change of parameters was observed due to lower electrical currents. In total contrast to that, the measured sensor signals were significantly higher in humidified hydrogen and each sensor required its own calibration function. The reason was a recombination effect that favoured multiple measurements of water molecules. Nevertheless, it was possible to measure continuously trace humidity in all tested gases by using coulometric sensors with an expanded uncertainty below 2 K (k = 2).
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 to −80°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=2 ) regarding frost point temperature.
The objective of this work is to report the improvement obtained in the discrimination of complex aroma and taste with subtle differences in odor and flavor, by the use of fast suitable procedures for the cases of measurements in the field demanding decision-making in real time. The proposed electronic sensing systems, formed by an E-nose and VE-tongue, were used to discriminate cumin cultivars from different geographical origins, as well as to quantify the cumin adulteration percentages by using unsupervised and supervised chemometric tools. Thus, the results obtained are sufficiently encouraging as a starting point for the development of new electronic sensing systems with more improvement such the reliability of the sensors’ performance as well as the chemometric tools in order to deal with a complex dataset.
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 crackfree
deposition of the titania layers inside the composite.
Improved Durability of Wood Treated with Nano Metal Fluorides against Brown-Rot and White-Rot Fungi
(2022)
Low-water soluble metal fluorides such as magnesium fluoride (MgF2) and calcium Fluoride (CaF2) were evaluated for decay protection of wood. Initially, the biocidal efficacy of nano metal fluorides (NMFs) against wood destroying fungi was assessed with an in-vitro agar test. The results from the test showed that agar medium containing MgF2 and CaF2 was more efficient in preventing fungal decay than stand-alone MgF2 or CaF2. These metal fluorides, in their nanoscopic form synthesized using fluorolytic sol-gel synthesis, were introduced into the sapwood of Scots pine and beech wood and then subjected to accelerated ageing by leaching (EN 84). MAS 19F NMR and X-ray micro CT images showed that metal fluorides were present in treated wood, unleached and leached. Decay resistance of Scots pine and beech wood treated with NMFs was tested against Wood destroying fungi Rhodonia placenta and Trametes versicolor in accordance with EN 113. Results revealed that mass losses were reduced to below 3% in wood treated with the combination of MgF2 and CaF2.
It is concluded that NMFs provide full protection to wood even after it has been leached and can be used as wood preservatives in outdoor environments.
Fire retardancy effects in single and double layered sol-gel derived TiO2 and SiO2-wood composites
(2012)
Sol–gel derived TiO2 and SiO2-wood inorganic composites are prepared by direct vacuum infiltration of silicon and titanium alkoxide based precursors in pine sapwood in one or two cycles followed by a controlled thermal curing process. The resulting flame retardancy effect is investigated under two different fire scenarios using cone calorimetry and oxygen index (LOI). Heat release rates (HRR) especially the values for the second peak, are reduced moderately for all single layered composites. This effect is more pronounced for double layered composites where HRR was reduced up to 40 % showing flame retardancy potential in developing fires. Beside this, smoke release was lowered up to 72 % indicating that these systems had less fire hazards compared to untreated wood, whereas no meaningful improvement is realized in terms of fire load (total heat evolved) and initial HRR increase. However impressively, the LOI of the composites were increased up to 41 vol% in comparison to 23 vol% for untreated wood displaying a remarkable flame retardancy against reaction to a small flame. An approximate linear interdependence among the fire properties and the material loading as well as fire residue was observed. A residual protection layer mechanism is proposed improving the residue properties for the investigated composites.
During their growth on wood many fungi produce characteristic volatile organic compounds as secondary metabolites. These microbial volatile organic compounds (MVOCs) can be used as indicators of fungal growth even when such growth is concealed. In order to investigate the formation of these volatile metabolites on building materials, specimens of pine sapwood on agar media colonized by the dry-rot fungus Serpula lacrymans and a mixture of six moulds were examined. MVOCs from this fungal growth were studied over a period of up to half a year by ion mobility spectrometry (IMS) headspace analysis using a sensitive, portable IMS mini-device. The IMS headspace spectra from the growing fungal specimens obtained during this time span are differed from non-incubated wood specimens and indicate the presence of a mixture of MVOCs. The composition and amount of volatile metabolites of the fungi changed during cultivation. This was confirmed by a principal component analysis (PCA). Identification of different MVOCs in the headspace according to drift time and the mobility of ionized gaseous species in reference to GC-MS investigations were proposed. It was concluded that IMS can be used as a rapid and sensitive on-site method to indicate actively growing fungi concealed within wood.
Decay resistance of pine sapwood treated with titanium alkoxide solutions was tested against the brown-rot fungi Coniophora puteana and Poria placenta for exposure times of 10 and 16 wk. In practice, wood-specimens were vacuum-impregnated by alcoholic solutions of titanium alkoxide with concentrations in the range of 5–16 mass % (solid content in solution) and subsequently cured under different humidity conditions. Results reveal that treated wood degraded up to 5% in comparison to untreated one that deteriorated 38% and 50%, respectively against both wood-decay fungi. Even full protection (mass loss below 3%) was achieved against brown rot with titanium alkoxide solution containing solid content of around 5 mass% with a weight percentage gain (WPG) of 9 mass%. With increased concentration, fungal resistance decreased slightly which was associated with more cracks and imperfections formed in the deposited layers of titanium dioxide in the adjacent wood matrix. Thermal analysis verified that a considerable amount of precursor remained in the wood structure as un-hydrolyzed organic residues. These organics, being bioactive, had the tendency to induce similar fungicidal effects as those of conventional fungicides. The amount of organic residues is correlated with the decay resistance of the tested samples. In a prolonged decay test, mass losses of 16-wk incubated samples do not show behavior different from that of the wood samples incubated for 10 wk. This result implies that the decay protection is permanent and confirms further the fungicidal activity of titanium-alkoxide-treated wood.
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.