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2. Evaluation of the effect of two training regimes on the resumption of the ovarian activity by analysis of faecal 20a-hydroxyprogesterone in trotter mares

Author

Renaville R., Portetelle D., Bolelli G., Gerin D., Prandi A., and Messina M.

Subjects
Mare, cyclic activity, 20a-hydroxyprogesterone, faeces, training, Biotechnology, TP248.13-248.65, Environmental sciences, GE1-350
Abstract

Onset of cyclic ovarian activity in mares, after seasonal anoestrus is characterized by the appearance of the first heat and thebeginning of seasonal breeding activity. The aim of this work was to evaluate the effect of different training regimes on theresumption of ovarian activity by analysis of 20a-hydroxyprogesterone in faeces. Sixteen trotter mares, housed in singleboxes, were allocated into two groups: in group A, mares (n = 8) were trained outside for one hour each day while in groupB (n = 8), the mares were remained inside their boxes all day. Faecal and plasma samples were collected every Monday andFriday morning from the 16th of February until the 13th of May and stored at -20 °C until used for hormone assay. Plasmalevels of progesterone and faecal level of 20a-hydroxyprogesterone were measured by radioimmunoassay. In group A, theonset of cyclic activity occurred one month earlier than in group B (P < .001). Moreover, during the reproductive season, theresumption of the cyclic activity was more gradual in group Athan in group B, in which cyclic activity was enhanced betweenthe 15th and 30th of April. In conclusion, 20a-hydroxyprogesterone concentrations in faeces can be used to evaluate cyclicactivity in mares. Resumption of cyclic ovarian activity was positively affected by regular physical work.

Published
1998

42. Comparison of shear bond strengths between a mica-based glass-ceramic and human dentin using three different resin cements

Author

Srichumpong, T, Suputtamongkol, K, Thongpun, N, Phokhinchatchanan, P, Angkulpipat, S, Prasertwong, S, Bolelli, G, Veronesi, P, Leonelli, C, Heness, G, Chaysuwan, D, Srichumpong, T, Suputtamongkol, K, Thongpun, N, Phokhinchatchanan, P, Angkulpipat, S, Prasertwong, S, Bolelli, G, Veronesi, P, Leonelli, C, Heness, G, and Chaysuwan, D

Abstract

Three resin cements, RelyX™ Ultimate, Panavia F2.0 and RelyX™ U200, were evaluated for their bond strengths between a mica glass-ceramic and human dentin. This research shows that a self-etch dental cement resin system, Panavia F2.0 provided the best bond strength. The glass-ceramic was produced and phases analysed. Biaxial flexural strength and hardness were measured and found to be comparable to that of human enamel and dentin. Bond strength was measured before and after thermocycling. Thermocycling was found to reduce the bond strength. Thermocycling reduced the shear bond strengths of all adhesives by 50–60%. The two-way ANOVA test was used to analyse the data (p = 0.05). Failure modes were analysed, showing failure predominately at the cement/glass-ceramic and dentin/resin cement interfaces. Failure modes changed after thermocycling. The resin cement bond between the dentin and mica glass-ceramics interfaces was examined for failure by optical microscopy (OM) and scanning electron microscopy (SEM).

Published
2019

44. Properties of HVOF-sprayed Stellite-6 coatings

Author

Sassatelli, P. (Paolo), Bolelli, G. (Giovanni), Lassinantti Gualtieri, M. (Magdalena), Heinonen, E. (Esa), Honkanen, M. (Mari), Lusvarghi, L. (Luca), Manfredini, T. (Tiziano), Rigon, R. (Rinaldo), Vippola, M. (Minnamari), Sassatelli, P. (Paolo), Bolelli, G. (Giovanni), Lassinantti Gualtieri, M. (Magdalena), Heinonen, E. (Esa), Honkanen, M. (Mari), Lusvarghi, L. (Luca), Manfredini, T. (Tiziano), Rigon, R. (Rinaldo), and Vippola, M. (Minnamari)

Abstract

Stellite-6 coatings were deposited onto AISI 304 stainless steel substrate by gas-fueled HVOF spraying, systematically varying the process parameter settings. By operating the HVOF torch with a fuel-rich mixture, dense coatings (<1% porosity) are produced, containing up to ≈3 vol% oxide inclusions. A substantial amount of a Cr-rich f.c.c. phase is found, mainly produced by quenching of molten lamellae, and distinct from the equilibrium, Co-based f.c.c. solid solution retained in unmelted particles. These coatings exhibit pseudo-passive behavior and survive 5 cycles (100 h) of the Corrodkote test (ASTM B380-97) with no substrate corrosion. Coatings obtained from oxygen-rich mixtures, on the other hand, contain fewer oxide inclusions but also greater porosity, and do not protect the substrate against corrosion. The wear behavior of the coatings is less influenced by deposition conditions. In ball-on-disk dry sliding tests, all coatings exhibit wear rates of 2-3 × 10⁻⁵ mm³/(N·m), higher than those reported for bulk or clad Stellite, because of interlamellar delamination. Strain-induced, “martensitic” phase transformation from the f.c.c. structure to a h.c.p. one is observed over a 1-2 μm depth below the contact surface. Additional tribo-oxidation is onset when frictional heat dissipation has heated the wear debris enough to trigger its reaction with the environment. Correspondingly, a transition to a regime of higher friction occurs (from ≈0.6 to ≈0.8). At 400 °C, lamellar delamination is suppressed but wear rates rise to 5-8 × 10⁻⁵ mm³/(N·m) because of abrasive and adhesive wear. At 800 °C, a dense “glaze” tribofilm is formed by sintered debris particles, firmly bonded to a thermally grown oxide scale on the underlying metal surface. The “glaze” protects the coating, lowering the wear rate to ≈1 × 10⁻⁵ mm³/(N·m) and the friction coefficient to <0.45. Under high-stress particle abrasion conditions, wear rates of ≈1 × 10⁻³ mm³/(N·m) are found.

Published
2018

45. Mechanical properties and metallurgical features of new and ex vivo used Reciproc Blue and Reciproc.

Author

Generali, L., Puddu, P., Borghi, A., Brancolini, S., Lusvarghi, L., Bolelli, G., Consolo, U., and Pedullà, E.

Subjects
DENTAL equipment, SCANNING electron microscopy, ENERGY dispersive X-ray spectroscopy, FOCUSED ion beams, FRACTURE mechanics, TWO-way analysis of variance, DATA analysis
Abstract

Aim: To compare the mechanical properties and metallurgic features of new and used Reciproc Blue and Reciproc instruments. Methodology: A total of 120 R25 Reciproc Blue and R25 Reciproc instruments were used. The morphological, chemical, mechanical, thermal and phase composition characteristics of new and ex vivo used files were investigated by scanning electron microscopy (FEG‐SEM) with energy dispersive X‐ray spectroscopy (EDS), focused ion beam analysis (FIB), micro‐Raman spectroscopy, FEG‐SEM metallography, X‐ray diffraction (XRD), differential scanning calorimetry (DSC) and indentation tests. Usage‐induce degradation was evaluated. Ten new and ten used instruments per type were run until fracture occurred in a stainless steel artificial canal (60° angle of curvature, 4‐mm radius). Time to fracture and the length of the fractured fragment were recorded. Torque and angle of rotation at failure of ten new and ten used instruments for each type were measured according to ISO 3630‐1. The fracture surface of each fragment was examined. Two‐way analyses of variance was used to analyse the data statistically (α‐level 0.05). Results: SEM analysis revealed microcracks near the tip on both files after ex vivo usage tests. FIB imaging and micro‐Raman spectroscopy confirmed the presence of an oxide layer on the Reciproc Blue surface. There was no thinning of the coating after use. XRD revealed a reduction of martensite and R‐phase in Reciproc Blue after use. DSC analysis revealed different transformation temperatures for the instruments analysed. Reciproc Blue was significantly more flexible than Reciproc for both new and used samples (P < 0.05), and they were significantly more resistant to cyclic fatigue than Reciproc (P < 0.05). Ex vivo usage reduced the fatigue resistance of both files. Torsional resistance of Reciproc and Reciproc Blue was not reduced by simulated use (P > 0.05). Conclusions: The thermal treatment of Reciproc Blue was associated with a finer structure with smaller grains than Reciproc, which increased its fracture resistance and was also responsible for its reduced hardness and lower elastic modulus. Both files were safe during ex vivo usage in severely curved canals. [ABSTRACT FROM AUTHOR]

Published
2020
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49. Wear and corrosion behaviour of HVOF-sprayed WC-CoCr coatings on Al alloys

Author

Bolelli, G., Lusvarghi, L., Barletta, M., Karhail, V., Bolelli, G., Lusvarghi, L., Barletta, Massimiliano, and Bonferroni, B.

Subjects
Materials Chemistry2506 Metals and Alloys, Surfaces, Coatings and Films, Surfaces, Coatings and Films, Surfaces and Interfaces
Abstract

WC-CoCr coatings were HVOF-sprayed onto an AA6082T6 substrate. Thickness values between 50 μn and 150 μn were produced by stepwise increase of the number of torch scans. This increase makes the coatings not only thicker, but also denser. This is due both to peening effects and by modifications to the splat formation mechanism, investigated by FIB. Thanks to such densification, the hardness, the wear and impact resistance and the corrosion protectiveness of the layers increase with the number of torch scans. The largest improvement occurs from 2 to 3 torch scans. These coatings were also compared to anodized films: cermets have superior wear and impact resistance but offer less corrosion protection. Copyright © 2009 ASM International® All rights reserved.

Published
2009

50. Comparative study of the dry sliding wear behaviour of HVOF-sprayed WC-(W,Cr)2C-Ni and WC-CoCr hardmetal coatings

Author

Bolelli, G., Berger, L.-M., Bonetti, M., Lusvarghi, L., and Publica

Subjects
high temperature, indentation, nanoindentation, hardmetal coatings, sliding wear, thermal spray coatings
Abstract

Recent studies of HVOF-sprayed WC-(W,Cr)2C-Ni coatings indicated an applicability at temperatures above 600°C. Therefore, in the present paper the dry sliding wear behaviour of coatings prepared from one selected feedstock powder was studied up to 750°C and compared to a WC-10%Co-4%Cr coating as reference. Coatings were prepared onto stainless steel substrates by a liquid-fueled high velocity oxygen-fuel (HVOF) spray process. A Cr-W-Ni-C mixed matrix phase and chromium-rich large (W,Cr)2C grains were formed as a result of metallurgical reactions between the components WC, Cr3C2 and Ni during spraying; therefore, the resulting coating can be better designated as WC-(W,Cr)2C-Ni.The dry unidirectional sliding wear behaviour of the coatings, studied according to ASTM G99 against Al2O3 counterbodies at four different temperatures (25°C, 400°C, 600°C, 750°C) and at two sliding speeds, was interpreted on the basis of their microstructure, micromechanical properties and oxidation behaviour. The morphology and composition inside the wear scars were also studied by SEM and micro-Raman spectroscopy. The results show that the WC-(W,Cr)2C-Ni coating exhibits good wear resistance up to 750°C, whereas WC-CoCr, in spite of its very mild wear at low temperature, suffers from catastrophic oxidation at 750°C.

Published
2014

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