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In this study we present the results of in vivo measurements of the mercury concentration in organs of occupationally exposed persons by the use of X-ray fluorescence analysis (XRF). The mercury concentration in the right kidney was measured in 20 occupationally exposed workers and 12 referents. The detection limit for the individual persons varied with the kidney depth (mean 26 μg/g, range 12-45 μg/g), was exceeded in nine of the exposed workers but in none of the referents. The mean kidney mercury concentration (including estimated concentration values below the detection limit) was 24 μg/g in the group of exposed workers (group MDC 5 μg/g) and for the group of referents no detectable concentration (mean 1 μg/g) was found (group MDC 6 μg/g). The mean urinary mercury excretions for the two groups were 34 and 1.7 μg per g creatinine. X-ray fluorescence measurements made on liver (n = 10) and thyroid (n = 8), in some of the exposed workers, revealed no measurable mercury concentrations.
The oxidation resistance of TiAl-alloys can be improved by several orders of magnitude by fluorine doping of the surface zone of the material. The oxidation mechanism changes from the formation of a thick mixed oxide scale to a protective alumina layer. This fluorine treatment influences only the surface region of the components so that the bulk properties are not affected. Recent results achieved with TiAl-components showed the potential of a fluorine treatment for the use of TiAl in several high temperature applications. Turbine blades for aero engines made of TiAl were treated with fluorine by different methods and their performance during high temperature oxidation tests in air is shown. Further on by selective local fluorination a structured oxide scale develops on TiAl above 800°C. A simple high temperature activation cause the formation of areas covered by a thin alumina layer alternating with a thick mixed oxide scale where no fluorine was applied before oxidation. The aim is to reproduce a shark-skin pattern (tiny parallel ridges) on the surface in order to minimize the aero dynamic resistance of turbine blades rotating in a gas flow. Different methods used for this attempt and the corresponding results are also presented.
Alloys based on aluminium and titanium are possible materials for several high temperature applications. The use of TiAl would increase the efficiency of e.g. aero turbines, automotive engines and others due to their properties, among others low specific weight and good high temperature strength. The oxidation resistance is low at temperatures above approximately 800°C so that no long term use of TiAl-components is possible without improvement of the oxidation behaviour. Small amounts of halogens in the surface zone of TiAl-samples lead to a dramatic improvement of the oxidation resistance at temperatures up to 1100°C for more than 8000 hours in air. In this paper results of the work on the halogen effect over the last years are presented. The results of thermogravimetric measurements, thermocyclic oxidation tests of small coupons and thermodynamic calculations for different atmospheres (e.g. air, H2O, SO2) are shown and the halogen effect mechanism is discussed. The postulated mechanism is in good agreement with the results of the oxidation tests. The limits of the halogen effect will also be mentioned. Predictions for the halogenation of TiAl-components can be given so that the processing can be planned in advance.
Intermetallic titanium aluminides solidifying via the disordered β-phase are of great interest for several high-temperature applications in automotive and aircraft industries. In this paper the thermocyclic oxidation behavior of three β-solidifying γ-TiAl-based alloys at 800°C and 900°C in air, with and without fluorine treatment, is reported for the first time. The behavior of the well-known TNM alloy (Ti-43.5Al-4Nb-1Mo-0.1B, in at.%) is compared with that of two Nb-free model alloys which contain different amounts of Mo (Ti-44Al-3Mo and Ti-44Al-7Mo, in at.%). During thermocyclic high-temperature exposure in air a mixed oxide scale develops on all three untreated alloys. Small additions of fluorine in the subsurface region of the alloys change the oxidation mechanism from mixed oxide scale formation to alumina at both temperatures. The oxidation resistance of the fluorine treated samples was significantly improved compared to the untreated samples.
Orthorhombic titanium-based Ti2AlNb alloys cannot be used above a temperature limit of about 800°C due to accelerated oxidation and environmental embrittlement. This embrittlement is caused by the high oxygen solubility which deteriorates the mechanical properties. Even if these materials possess an Al content up to ca. 25at.% no protective alumina layer is formed. Instead a non-protective fast growing mixed scale is found. Several attempts have been made to increase their operation temperature e.g. by coatings but none has proven sufficiently protective so far. One new way presented in this paper is to enrich Al in a narrow surface zone by using a powder pack process (aluminization) followed by a fluorination step. Exposure tests at elevated temperature have shown that the aluminized specimens form an alumina layer during exposure in oxidizing environments. Due to the gradient in the Al-concentration interdiffusion with the substrate and the Al-rich diffusion zone occurs which lowers the Al concentration in the diffusion zone. If the Al content drops below a critical value, Ti oxides will also form, which deteriorates the protection provided by the alumina scale. The subsequent fluorination triggers the fluorine effect which stabilizes the protective alumina layer. Untreated specimens are covered with a thick non protective scale and exhibit oxygen ingress in the subsurface zone while treated specimens reveal a thin protective alumina layer and no inward diffusion of oxygen. In this paper results of exposure tests of untreated and treated orthorhombic Ti2AlNb alloys will be presented and compared with the Nb-free α2-phase Ti3Al and Nb-containing Ti3Al-based alloys.
The use of light weight structural materials such as titanium in transport systems like aero planes leads to a significant reduction in fuel consumption. However, titanium and its alloys cannot be used at elevated temperatures above 500°C for several reasons. Today aero engine compressors are made of a mixture of light Ti- and heavy Ni-alloys. The improvement of Ti-alloys to withstand the conditions in the high pressure compressor i.e. temperatures above 500°C would enable the manufacturing of a compressor from titanium as a whole with all its associated benefits. Intermetallic TiAl-alloys are another class of light weight materials for several high temperature applications. The use of TiAl as low pressure turbine (LPT) blades in the last sections of a large jet engine could save up to 150 kg of weight. In the last sections of the LPT the temperature is quite moderate (max. 650°C). The improvement of the high temperature capability of TiAl would allow its use in hotter sections of the engine with additional weight reduction. Similarly, the response performance of TiAl-turbocharger rotors in automotive engines would be much faster compared to the heavy Ni-based alloys used today. Furthermore higher rotation speeds are possible. Due to the novel so called fluorine effect the oxidation mechanism of TiAl can be altered. Fluorine-treated TiAl-components are protected by an alumina layer formed during high temperature exposure in oxidizing environments. This effect can be transferred to Ti-base materials if they are enriched with aluminum in a thin surface zone. The concepts and the results of high temperature exposure experiments of treated Ti- and TiAl-specimens are presented in this paper. They are discussed in the view of a use for real components.
Above 750-800°C oxidation becomes a serious life time issue for the new group of intermetallic light-weight high temperature alloys based on titanium aluminides (TiAl). Fast growing titanium oxide competes with protective alumina as a surface scale in the oxidation reaction by which the formation of a slow-growing protective oxide scale is prevented. The key to the development of alloys with sufficient oxidation resistance is the understanding of the thermodynamic and kinetic situation during the oxidation process. The latter is influenced by the type of alloying elements, the Al- and Ti-activities in the alloy, the oxidation temperature and the environment (e.g. dry or humid air, etc.). This paper provides a comprehensive summary of the oxidation mechanisms and the parameters influencing oxide scale formation. Besides the role of metallic alloying elements, the halogen effect will also be discussed. The paper finishes with recent results concerning the prevention of oxidation-induced room temperature embrittlement of TiAl alloys.
The nature of human–animal interactions is an important factor contributing to animal welfare and productivity. Reducing stress during routine husbandry procedures is likely to improve animal welfare. We examined how the type of early handling of calves affected responses to two common husbandry procedures, ear-tagging and disbudding. Forty Holstein–Friesian calves (n = 20/treatment) were exposed to one of two handling treatments daily from 1 to 5 weeks of age: (1) positive (n = 20), involving gentle handling (soft voices, slow movements, patting), and (2) negative (n = 20), involving rough handling (rough voices, rapid movements, pushing). Heart rate (HR), respiration rate (RR) and behaviour (activity, tail flicking) were measured before and after ear-tagging and disbudding (2 days apart). Cortisol was measured at −20 (baseline), 20 and 40 min relative to disbudding time. There were no significant treatment differences in HR, RR or behaviour in response to either procedure. However, the following changes occurred across both treatment groups. HR increased after disbudding (by 14.7 ± 4.0 and 18.6 ± 3.8 bpm, positive and negative, respectively; mean ± s.e.m.) and ear-tagging (by 8.7 ± 3.1 and 10.3 ± 3.0 bpm, positive and negative, respectively). After disbudding, there was an increase in RR (by 8.2 ± 3.4 and 9.3 ± 3.4 breaths/min, positive and negative, respectively), overall activity (by 9.4 ± 1.2 and 9.9 ± 1.3 frequency/min, positive and negative, respectively) and tail flicking (by 13.2 ± 2.8 and 11.2 ± 3.0 frequency/min, positive and negative, respectively), and cortisol increased from baseline at 20 min post procedure (by 10.3 ± 1.1 and 12.3 ± 1.1 nmol/l positive and negative, respectively). Although we recorded significant changes in calf responses during ear-tagging and disbudding, the type of prior handling had no effect on responses. The effects of handling may have been overridden by the degree of pain and/or stress associated with the procedures. Further research is warranted to understand the welfare impact and interaction between previous handling and responses to husbandry procedures.
Intermetallic titanium aluminides are potential materials for application in high temperature components. In particular, alloys solidifying via the β-phase are of great interest because they possess a significant volume fraction of the disordered body-centered cubic β-phase at elevated temperatures ensuring good processing characteristics during hot-working. Nevertheless, their practical use at temperatures as high as 800°C requires improvements of the oxidation resistance. This paper reports on the fluorine effect on a multi-phase TiAl-alloy in the cast and hot-isostatically pressed condition at 800°C in air. The behavior of the so-called TNM material (Ti-43.5Al-4Nb-1Mo-0.1B, in at %) was compared with that of two other TiAl-alloys which are Nb-free and contain different amounts of Mo (3 and 7 at%, respectively). The oxidation resistance of the fluorine treated samples was significantly improved compared to the untreated samples. After fluorine treatment all alloys exhibit slow alumina kinetics indicating a positive fluorine effect. Results of isothermal and thermocyclic oxidation tests at 800°C in air are presented and discussed in the view of composition and microstructure of the TiAl-alloys investigated, along with the impact of the fluorine effect on the oxidation resistance of these materials.
The potential of platy nanofillers like clays in polymer nanocomposites is mostly determined by their aspect ratio. The degree of improvement that may be achieved in respect to reinforcement, gas-barrier properties and flame retardancy critically depends on the aspect ratio. Thus, increasing the aspect ratio is highly desirable in order to explore the full potential of the clay filler. Mechanical shear stress as generated in the grinding chamber of a stirred media mill (ball mill) induced an efficient exfoliation of highly hydrated and therefore ‘shear-labile’ synthetic Mg-fluorohectorite in aqueous dispersion. The attainable degree of exfoliation can be tuned and controlled through the shear forces applied by changing process parameters such as solid content and grinding media diameter. Characterization and evaluation of the exfoliation efficiency during milling was achieved by combining and cross-validating data obtained by powder X-ray diffraction (XRD), static light scattering (SLS), specific surface area measurements applying the Brunauer-Emmett-Teller (BET) equation, and scanning electron microscopy (SEM). This led to the identification of optimal processing parameters, allowing for control of the degree of exfoliation and, consequently, the aspect ratio of the nanoplatelets. Not surprisingly, besides exfoliation, increasing the magnitude of the shear stress also resulted in some reduction in platelet size.
The clay platelets obtained showed a high average aspect ratio (>600), several times greater than that of original synthetic fluorohectorite. The increase of aspect ratio was reflected in a significant enhancement of both specific surface area and cation exchange capacity (CEC) of the external basal surfaces. This method has substantial advantages compared to microfluidizer processing with respect to feasibility, batch size and particle diameter size preservation. The exfoliated nanoplatelets obtained by milling have great potential to improve mechanical properties of polymer layered silicate nanocomposites (PLSN).
Enhanced acquisition and delayed extinction of fear conditioning are viewed as major determinants of anxiety disorders, which are often characterized by a dysfunctional hypothalamic–pituitary–adrenal (HPA) axis.
In this study we employed cued fear conditioning in two independent samples of healthy subjects (sample 1: n=60, sample 2: n=52). Two graphical shapes served as conditioned stimuli and painful electrical stimulation as the unconditioned stimulus. In addition, guided by findings from published animal studies on HPA axis-related genes in fear conditioning, we examined variants of the glucocorticoid receptor and corticotropin-releasing hormone receptor 1 genes.
Variation in these genes showed enhanced amygdala activation during the acquisition and reduced prefrontal activation during the extinction of fear as well as altered amygdala–prefrontal connectivity.
This is the first demonstration of the involvement of genes related to the HPA axis in human fear conditioning.
Studies have suggested that moderate alcohol consumption is associated with a reduced risk of CVD and premature mortality in individuals with diabetes mellitus. However, history of alcohol consumption has hardly been taken into account. We investigated the association between current alcohol consumption and mortality in men and women with diabetes mellitus accounting for past alcohol consumption. Within the European Prospective Investigation into Cancer and Nutrition (EPIC), a cohort was defined of 4797 participants with a confirmed diagnosis of diabetes mellitus. Men and women were assigned to categories of baseline and past alcohol consumption. Hazard ratios (HR) and 95 % CI for total mortality were estimated with multivariable Cox regression models, using light alcohol consumption (>0–6 g/d) as the reference category. Compared with light alcohol consumption, no relationship was observed between consumption of 6 g/d or more and total mortality. HR for >6–12 g/d was 0·89 (95 % CI 0·61, 1·30) in men and 0·86 (95 % CI 0·46, 1·60) in women. Adjustment for past alcohol consumption did not change the estimates substantially. In individuals who at baseline reported abstaining from alcohol, mortality rates were increased relative to light consumers: HR was 1·52 (95 % CI 0·99, 2·35) in men and 1·81 (95 % CI 1·04, 3·17) in women. The present study in diabetic individuals showed no association between current alcohol consumption >6 g/d and mortality risk compared with light consumption. The increased mortality risk among non-consumers appeared to be affected by their past alcohol consumption rather than their current abstinence.
Increasing demands on technical components for high-temperature applications (e.g. tur-bine blades) promote new developments not only in the field of alloy design, but also in surface engineering. This paper shows that it is possible to structure the surface of intermetallic titanium aluminides in-situ by locally controlled oxidation of the material due to selective doping with fluorine. The aim is to reproduce a shark-skin pattern (parallel riblets with valleys in between) in order to improve the surface aerodynamics. Riblets with widths in the single digit μm range have been generated. The nucleation process, the aspect ratio and the stability of the generated micro-structures are discussed as a function of the substrate composition and the oxidation conditions.
Intermetallic TiAl-alloys can replace the heavier Ni-based superalloys in several high temperature applications with regards to their mechanical properties, however they can not be used at temperatures above 800°C in oxidizing environments for longer times because of insufficient oxidation resistance. Despite an Al-content of about 45 at.% in technical alloys, no protective alumina layer is formed because the thermodynamic stabilities of titanium oxide and aluminum oxide are of the same order of magnitude. Therefore a mixed TiO2/Al2O3-scale is formed which is fast growing so that the metal consumption rate is quite high. On the other hand the formation of a slow growing alumina layer is promoted by a fluorine treatment. This so called fluorine effect leads to the preferential intermediate formation of gaseous aluminum fluorides at elevated temperatures if the fluorine content at the surface stays within a defined concentration range. These fluorides are converted into solid Al2O3 due to the high oxygen partial pressure of the high temperature service environment forming a protective pure Al2O3 surface scale. In this paper results of high temperature oxidations tests of several technical TiAl-alloys will be presented. Different F-treatments e.g. dipping or spaying which are easy to apply have been used and their results will be compared. The mass change data of the F-treated specimens are always lower than those of the untreated ones. Post experimental investigations such as light microscopy, scanning electron microscopy and energy dispersive X-ray analysis reveal the formation of a thin alumina layer on the F-treated samples after optimization of the process while a thick mixed scale is found on the untreated samples. The results will be discussed in view of an optimized procedure and the future use of TiAl-components in high temperature environments.
To improve the insufficient oxidation resistance of Titanium Aluminides at temperatures above 750°C the fluorine effect offers an innovative way. The focus of this paper is to define the fundamental material variables for the fluorine effect related to the macroscopic behaviour (oxidation resistance) and its long time stability.
The thermodynamic model predicted the fluorine effect for the TiAl within a corridor of total fluorine amount in terms of partial pressures. To realize the fluorine effect the required F-concentration [in at.-%] within the near surface region had to be found. Using fluorine ion implantation several fluences within 5e15 and 5e17 F cm-2 were implanted with an energy of 20 keV. The implantation depth profiles were calculated by using the Monte Carlo simulation code T-DYN and verified experimentally by using the non-destructive PIGE - technique (Proton Induced Gamma-ray Emission). After oxidation tests at 800°C – 1000°C a value of 2e17 F cm-2 / 20 keV was determined as an optimal implantation parameter set. Following these results the maximal fluorine concentration was identified to be a fundamental material variable for starting the alumina formation with a required fluorine amount of about 40-45 at.-%. However this maximum fluorine concentration showed a rapid decrease to values less than 5 at.-% only after a few hours of oxidation (900°C and 1000°C) followed by a slow decrease. Therefore the maximum fluorine concentration Cmax – now located at the metal/oxide – interface – was identified to be a fundamental parameter for the long time stability. An exponential decay function containing a constant term of about 1 at.-% was found to describe the time behaviour of Cmax for isothermal and cyclic oxidation (900°C, 1000°C). Because the alumina scale on the surface acts as a diffusion barrier for fluorine, the stability of Cmax is strongly influenced by the F-diffusion into the metal. From the F-depth profiles the diffusion coefficient of fluorine into the TiAl at 900°C was determined as a fundamental parameter for the long-term stability of Cmax showing a value of 1.56e-15cm2/s.