3,205 research outputs found
Heat Treatment Effects on the Tribological Performance of HVOF-Sprayed Co-Mo-Cr-Si Coatings
No full textThe tribological behavior of high-velocity oxyfuel sprayed Co-28%Mo-17%Cr-3%Si coatings, both as sprayed and after heat treatments at 200, 400, and 600 °C for 1 h, has been studied. The as-sprayed coating contains oxide stringers and is mostly amorphous. It has low hardness (∼6.7 GPa) and toughness and undergoes adhesive wear against 100Cr6 steel. The friction coefficient increases up to ∼0.9, so the flash temperature reaches a critical oxidation value; then, friction decreases and increases again. This phenomenon occurs periodically. Much adhesive wear occurs in the first stage. Abrasive wear prevails against alumina pin: the coating wear rate is lower because it possesses good plasticity. Thermal effects still occur. The 600 °C treatment causes formation of submicrometric crystals. Hardness increases (∼8.8 GPa), adhesive wear is prevented, the friction coefficient has no peaks. Against the alumina pin, wear rates remain similar to the as-sprayed case. Nevertheless, the friction coefficient has no peaks and its final value is lowered (from 0.84 to0.75)
Tribological properties of HVOF as-sprayed and heat treated Co–Mo–Cr–Si coatings
No full textHVOF-sprayed Co–28%Mo–17%Cr–3% Si alloy tribological performance was tested in the as-sprayed condition and after thermal treatments at 200, 400, 600°C for 1 h. As-sprayed coating possesses low hardness, undergoes adhesive wear against 100Cr6steel and displays an high-friction coefficient causing relevant thermal effects. The 600°C-heat treatment increases microhardness, thus preventing adhesive wear and reducing friction
Bioluminescent bacteria as bioindicators in environment
No full textWith the developments in science of the last decades the environmental consciousness has greatly increased. In every place where man has an influence on the environment which is not a naturally occurring one should be surrounded with procedures to lower it’s environment impact.
In vivo luminescence is a sensitive indicator of xenobiotic toxicity: if noxious substances are present, the bacterial luminescence decreases proportionally to their concentration.
References:
Girotti, S., Ferri, E.N., Bolelli, L., Sermasi, G., Fini, F. Applications of bioluminescence in analytical chemistry. In: “Chemiluminescence in Analytical Chemistry”, A.M. Garcia-Campaña, W.R.G. Baeyens, Eds. New York, Marcel Dekker, 247-284, 2001.
S.Girotti, L. Bolelli, A.Roda, G.Gentilomi, M.Musiani. “Improved detection of toxic chemicals using bioluminescent bacteria”. Anaytica Chimica Acta, 471, 113-120, 2002
Heat treatment effects on the corrosion resistance of some HVOF-sprayed metal alloy coatings
No full textThe present study evaluates the effects of a 600 °C, 1 h heat treatment on the corrosion resistance of threeHigh Velocity Oxygen Fuel (HVOF) flame-sprayed alloy coatings: a Co–28Mo–17Cr–3Si (similar to Tribaloy-800) coating, a Ni–20Cr–10W–9Mo–4Cu–1C–1B–1Fe (Diamalloy-4006) coating and a Ni–32Mo–16Cr–3Si–2Co (similar to Tribaloy-700) coating. Electrochemical polarization tests and free corrosion tests wereperformed in 0.1 M HCl aqueous solution. The corrodkote test (ASTM B380-97R02) was also performed, toevaluate the coatings qualitatively. The heat treatment improves the corrosion resistance of the Co–28Mo–17Cr–3Si coating and of the Ni–20Cr–10W–9Mo–4Cu–1C–1B–1Fe coating by enhancing their passivationability. The precipitation of sub-micron sized secondary phases after the treatment may produce galvanicmicrocells at intralamellar scale, but the beneficial contribution provided by the healing of the very small but dangerous interlamellar defects (normally present in thermal spray coatings but not detectable usingordinary scanning electron microscopy) prevails. The effect on Ni–32Mo–16Cr–3Si–2Co coatings is moreambiguous: its sensitivity to crevice corrosion is worsened by the heat treatment
Alkaline water better than plain water? A critical review
No full textPE2. ALKALINE WATER BETTER THAN PLAIN WATER? A CRITICAL REVIEW
Emanuele MORGANTI,1 Luca BOLELLI,1 Giuseppe NOVELLI,2
Chris FREEMAN,2 Stefano GIROTTI1
1Department of Pharmacy and Biotechnology FaBiT, Via San Donato 15, Alma Mater Studiorum - Università di Bologna, Bologna,40127, Italy
2CULLIGAN ITALIANA SPA, Cadriano di Granarolo Emilia, Bologna, 40057, Italy
Water is the basic element of living beings. No other substance is more important for human body than water. In fact, in the reference man, 60% of body weight (BW) (about 45 L) is represented by total body water (TBW) [1]. Some people believe that alkaline water can help to drain toxins more efficiently than regular tap water, leading to better health and fitness. Alkaline water has a higher pH level than plain water. Proponents say that it can neutralize acid in bloodstream, boost the metabolism and help the body to absorb nutrients more effectively. Some even say that alkaline water can help prevent diseases and slow the aging process. An investigation in the scientific literature has been done to verify these claims. The main consideration that could be done is that the alkalinity in ionized water is due to the sodium hydroxide formed during electrolysis if salt is the electrolyte in the water. Most alkaline water representatives do not like to admit this, but when the sodium hydroxide enters the stomach, it is immediately neutralized by the strong stomach acidity back into water and salt ions. There is no reason to expect that the water formed when the alkaline hydroxide ion is neutralized will retain any special characteristics (even if it had some in the beginning) or that dissolved salt, which results from the neutralization process, will have any special properties when it is absorbed. The alkalinity level of the incoming water relative to the acidity of the stomach acid and to the pH the body's well-buffered blood is negligible. This means that there would be almost no resulting effect on pH of the body. The EFSA (European Food Safety Authority) does not authorize any health assertion about alkaline water because is not based on solid scientific data [2]. In conclusion, at this moment, there is no credible evidence in standard medical or scientific literature to support claims that alkaline water has any greater health effects or health benefits than drinking regular water.
[1] L. Petraccia et al., Clinical Nutrition 25 (2006) 377–385.
[2] EU Register on nutrition and health claims: http://ec.europa.eu/nuhclaim
BIOLUMINESCENT BACTERIA AND BIOREMEDIATION
No full textThe increasing sensibility of both public and private institutions to the problem of contamination of industrial area, vacant sites, abusive tips has risen a new interest about decontamination of polluted sites. The choice of the best strategies of regeneration of an area must consider the characteristics of the site and the costs as regards to hazard/benefits, in particular, the costs of bioremediation and management of the area. One of the most promising and cheap strategies for hydrocarbons recovery is the acceleration of the natural process of biodegradation of these compounds in situ. Hydrocarbons can be degraded by various micro-organisms as bacteria and mushrooms.
Bioluminescent bacteria (BLB) emit light when they find themselves in an optimal environment. If noxious substances are present, the luminescence decrease. Thus, the presence of toxic substances can be evaluated [1-2]. The bioluminescent bacteria toxicity test is simple and, compared to other bioassays, it is less time consuming, with a sensitivity within the same order of magnitude and allows to obtain results in a direct way.
The BLB test was applied to samples of soil collected near a refinery at different depth levels and distances from the industrial plan. The microbial population of the soil was studied. The samples were then treated with different species of bacteria degrading hydrocarbons, both autochthonous (already present in the soil) or commercial, or with mixture of them.
The bioluminescent bacteria were exposed to the samples for 12-20 hour. The acute and chronic biotoxicity was determined, following light emission for 60 minutes or for some hours (10-15), respectively. The acute toxicity is generally due to powerful or available toxicants, as heavy metal ions, while compounds with a slow penetration mechanism to enter bacterial cells or acting on bacteria reproduction are usually responsible for chronic biotoxicity.
All the untreated samples proved to inhibit the luminescence as shown in Figure 1, where the perceptual inhibition at 60 minutes is reported (black values in figure). After the treatment with bacteria degrading hydrocarbons, only the samples collected at the deepest levels still inhibited the light emission (for example S2 720), while superficial specimens no longer inhibited the luminescence (for example S1C1).
Figure 1: Inhibition (%) of the light emission of different soil samples before and after the treatment with hydrocarbons degrading bacteria.
The BLB assay proved to be sensible at toxic substances and suitable to be applied to the control of bioremediation of contaminated area after treatment by bacteria degrading hydrocarbons. The use of a microplate assay allowed the simultaneous, rapid and at low cost analysis of numerous samples.
The assay also allowed to optimise the mix of bacteria degrading hydrocarbons, starting from the species directly developed in real conditions in polluted grounds, selecting and improving them.
References
[1] Girotti S., Ferri E.N., Bolelli L., Sermasi G., Fini F. Applications of Bioluminescence in Analytical Chemistry. In: Chemiluminescence in Analytical Chemistry Garcìa-Campaña A.M.& Baeyens W.R.G. Eds., Marcel Dekker Inc., New York, 2001, 247-84.
[2] Girotti S., Bolelli L., Roda A., Gentilomi G., Musiani M., Improved detection of toxic chemicals using bioluminescent bacteria”. Analytica Chimica Acta, 2002, 471, 113-120
Control of microbial contamination in drinking water from microfiltering dispensers by dialysis ultrafilters
No full textAbstract. Tap water filtering devices are widely employed to improve odor and taste of tap water, or to obtain refrigerated or sparkling drinking water. The presence of disinfectants-resistant bacteria in tap water is responsible of the biofilm formation inside tubes and tanks. The consequent contamination of dispensed water is a well-known hygiene problem because of the quite constant presence of potentially pathogenic bacteria likes P. aeruginosa. In this study, we tested the technical feasibility and effectiveness of the addition to different commercial devices of a packaged polysulphone fibers filter. We aimed to find a simple solution to implement the quality of the delivered water. Water contamination levels were determined in a wide selection of microfiltered water dispensers and we selected among them a representative group of 10 devices, new or in use. The packaged ultrafilter was introduced in about half of them, to monitor, when possible, in parallel the contamination levels and flow rate of a couple of identical units, with and without the filter. The placement of the dialysis filters resulted feasible at different positions along the water circuits of the variously designed filtration units. Delivered water resulted completely free from bacteria when the filter was placed exactly at, or very close to, the outlet in spite of the inner surfaces contamination. This performance was not obtained in presence of a more or less long tract of water circuits downstream the ultrafilter: a significant but not complete reduction of the plate count numbers was observed. The filters worked in continue over the whole study period, ten months, showing exactly the same efficiency. Moreover, the flow rate in presence of the filter was quite unaffected. The addition of this kind of filter to already in use water dispensers was technically easy, and its use can be recommended in all cases a simple but reliable water sanitization is requested
HVOF-sprayed WC-CoCr coatings on Al alloy: Effect of the coating thickness on the tribological properties
No full textThe microstructure, the micromechanical properties, the wear behaviour and the impact resistance of WC-CoCr cermet coatings, deposited onto an aluminium alloy substrate by High Velocity Oxygen-Fuel (HVOF) flame-spraying, were examined as a function of the coating thickness, which was varied between 50 mu m and 150 mu m by performing different numbers of scans of the HVOF torch in front of the substrate. The coatings became denser and significantly harder as the number of torch scans increased: the analysis of single WC-CoCr splats by combined SEM and Focused Ion Beam (FIB) techniques enabled the interpretation of the mechanisms underlying this phenomenon. In accordance to such densification, the sliding wear resistance increased with the number of torch scans, as abrasive grooving and brittle failure mechanisms were progressively suppressed. The resistance to cyclic impact was also enhanced. In comparison to anodised films, the WC-CoCr coatings appeared much more resistant against wear and cyclic impact; specifically, three torch scans seem enough to produce a coating having suitable characteristics. (C) 2009 Elsevier B.V. All rights reserved
The management and exploitation of naturally light-emitting bacteria as a flexible analytical tool: A tutorial
No full textConventional detection of toxic contaminants on surfaces, in food, and in the environment takes time. Current analytical approaches to chemical detection can be of limited utility due to long detection times, high costs, and the need for a laboratory and trained personnel. A non-specific but easy, rapid, and inexpensive screening test can be useful to quickly classify a specimen as toxic or non toxic, so prompt appropriate measures can be taken, exactly where required. The bioluminescent bacteria-based tests meet all these characteristics. Bioluminescence methods are extremely attractive because of their high sensitivity, speed, ease of implementation, and statistical significance. They are usually sensitive enough to detect the majority of pollutants toxic to humans and mammals. This tutorial provides practical guidelines for isolating, cultivating, and exploiting marine bioluminescent bacteria as a simple and versatile analytical tool. Although mostly applied for aqueous phase sample and organic extracts, the test can also be conducted directly on soil and sediment samples so as to reflect the true toxicity due to the bioavailability fraction. Because tests can be performed with freeze-dried cell preparations, they could make a major contribution to field screening activity. They can be easily conducted in a mobile environmental laboratory and may be adaptable to miniaturized field instruments and field test kits
A comparison between corrosion resistances of some HVOF-sprayed metal alloy coatings
No full textThis study compares the corrosion resistance of one Co–based alloy coating, namely Co–28Mo–17Cr–3Si (similar to Tribaloy-800), four Ni-based alloy coatings, namely Ni–17Cr–4Fe–4Si–3.5B–1C (Diamalloy-2001), Ni–20Cr–10W–9Mo–4Cu–1C–1B–1Fe (Diamalloy-4006), Ni–22Cr–9Mo–4Nb–5Fe (similar to Inconel-625), Ni–32Mo–16Cr–3Si–2Co (similar to Tribaloy-700), and a (WC-12Co)–33Ni–9Cr–3.5Fe–2Si–2B–0.5C cermet–Ni alloy blend coating. They were produced by liquid-fuelled HVOF spraying onto AISI1040 steel plates. Electrolytic hard chrome (EHC) plating was characterised as a reference material, to verify whether some HVOF coatings are suitable as an EHC replacement. The microstructure of the coatings was examined by SEM and XRD. Electrochemical polarization tests and free corrosion tests were performed in 0.1 M HCl aqueous solution; the corrodkote test (ASTM B380-97R02) was also performed, to rank coatings qualitatively.The lowest corrosion current densities (Icorr) were recorded for EHC and Tribaloy-700. The latter coating contained few secondary phases and little porosity; the damage was mainly due to corrosion activation along lamellae boundaries. Diamalloy-2001 exhibited the highest Icorr and was significantly damaged after the polarization test, as its multi-phase microstructure had triggered severe galvanic corrosion. During free corrosion in 0.1 M HCl, Tribaloy-700 and Diamalloy-4006 retained rather stable polarization resistance (Rp), whereas the Rp of EHC decreased significantly. Tribaloy-700 survived 40 h of corrodkote test with no apparent damage and EHC underwent limited pitting corrosion. All other coatings had visible corrosion. The Inconel-625 coating failed to protect the substrate after 20 h of testing, due to inadequate processing conditions
- …
