Influence of Surface Treatment on the Shear Bond Strength of Ceramics Fused to Cobalt-Chromium

Purpose: To evaluate the influence of surface treatment on the shear bond strength between a Co-Cr alloy and two ceramics.Materials and Methods: Forty-eight metal cylinders were made (thickness: 4 mm, height: 3.7 mm) according ISO TR 11405. The 48 metallic cylinders were divided into four groups (n = 12), according to the veneering ceramic (StarLight Ceram and Duceram Kiss) and surface treatments: air-particle abrasion with Al(2)O(3) or tungsten drill (W). Gr1: StarLight + Al(2)O(3); Gr2: StarLight + W; Gr3: Duceram + Al(2)O(3); and Gr4: Duceram + W. The specimens were aged using thermal cycling (3000 x, 5 to 55 degrees C, dwell time: 30 seconds, transfer time: 2 seconds). The shear test was performed with a universal testing machine, using a load cell of 100 kg (speed: 0.5 mm/min) and a specific device. The bond strength data were analyzed using ANOVA and Tukey's test (5%), and the failure modes were analyzed using an optical microscope (30x).Results: The means and standard deviations of the shear bond strengths were (MPa): G1 (57.97 +/- 11.34); G2 (40.62 +/- 12.96); G3 (47.09 +/- 13.19); and G4 (36.80 +/- 8.86). Ceramic (p = 0.03252) and surface treatment (p = 0.0002) significantly affected the mean bond strength values.Conclusions: Air-particle abrasion with Al(2)O(3) improved the shear bond strength between metal and ceramics used.

Opaque Layer Firing Temperature and Aging Effect on the Flexural Strength of Ceramic Fused to Cobalt-Chromium Alloy

Purpose: To evaluate the effect of the opaque layer firing temperature and mechanical and thermal cycling on the flexural strength of a ceramic fused to commercial cobalt-chromium alloy (Co-Cr). The hypotheses were that higher opaque layer temperatures increase the metal/ceramic bond strength and that aging reduces the bond strength.Materials and Methods: Metallic frameworks (25 x 3 x 0.5 mm(3); ISO 9693) (N = 60) were cast in Co-Cr and airborne-particle abraded (Al(2)O(3): 150 mu m) at the central area of the frameworks (8 x 3 mm(2)) and divided into three groups (N = 20), according to the opaque layer firing temperature: Gr1 (control)-900 degrees C; Gr2-950 degrees C; Gr3-1000 degrees C. The opaque ceramic (Opaque, Vita Zahnfabrick, Bad Sackingen, Germany) was applied, and the glass ceramic (Vita Omega 900, Vita Zahnfabrick) was fired onto it (thickness: 1 mm). While half the specimens from each group were randomly tested without aging (water storage: 37 degrees C/24 hours), the other half were mechanically loaded (20,000 cycles; 50 N load; distilled water at 37 degrees C) and thermocycled (3000 cycles; 5 degrees C to 55 degrees C, dwell time: 30 seconds). After the flexural strength test, failure types were noted. The data were analyzed using 2-way ANOVA and Tukey's test (alpha = 0.05).Results: Gr2 (19.41 +/- 5.5 N) and Gr3 (20.6 +/- 5 N) presented higher values than Gr1 (13.3 +/- 1.6 N) (p = 0.001). Mechanical and thermal cycling did not significantly influence the mean flexural strength values (p > 0.05). Increasing the opaque layer firing temperature improved the flexural bond strength values (p < 0.05). The hypotheses were partially accepted.Conclusion: Increasing of the opaque layer firing temperature improved the flexural bond strength between ceramic fused to Co-Cr alloy.

Methanogenic potential and microbial community of anaerobic batch reactors at different ethylamine/sulfate ratios

Methylamine and sulfate are compounds commonly found in wastewaters. This study aimed to determine the methanogenic potential of anaerobic reactors containing these compounds and to correlate it with their microbial communities. Batch experiments were performed at different methylamine/sulfate ratios of 0.71, 1.26 and 2.18 (with respect to mass concentration). Control and experimental runs were inoculated with fragmented granular sludge. The maximum specific methane formation rates were approximately 2.3 mmol CH4 L-1 g TVS-1 day-1 for all conditions containing methylamine, regardless of sulfate addition. At the end of the experiment, total ammonium-N and methane formation were proportional to the initial concentrations of methylamine. In the presence of methylamine and sulfate, Firmicutes (46%), Deferribacteres (13%) and Proteobacteria (12%) were the predominant phyla of the Bacteria domain, while Spirochaetes (40%), Deferribacteres (17%) and Bacteroidetes (16%) predominated in the presence of methylamine only. There was no competition for methylamine between sulfate-reducing bacteria and methanogenic archaea.

Preparation of different basic Si-MCM-41 catalysts and application in the Knoevenagel and Claisen-Schmidt condensation reactions

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

High-velocity oxyfuel Cr3C2-NiCr replacing hard chromium coatings

Comparative wear and corrosion properties of Cr3C2-NiCr (CC-TS) (a high-velocity oxyfuel [HVOF]) and hard chromium (HC) coating's obtained on a steel substrate have been studied. The structural characterization was done before and after measurements by optical microscopy, scanning electron microscopy, and scanning white light interferometry. Wear and corrosion properties were evaluated by ball on disk (ASTM G99-90), rubber wheel (ASTM G65-91), and electrochemical measurements of open circuit and polarization curves. The best corrosion and wear resistance was for the CC-TS obtained by HVOF. The open-circuit potential values measured for both samples after 18 h of immersion we're: -0.240 and -0.550 V, respectively, for CC-TS and HC, versus Ag/AgCl,KClsat. Three orders of magnitude lower volume loss were found for CC-TS (HVOF) after friction tests compared with HC.

Comparative study of Cr3C2-NiCr coatings obtained by HVOF and hard chromium coatings

In the present work the corrosion resistance of micro-cracked hard chromium and Cr3C2-NiCr (HVOF) coatings applied on a steel substrate have been compared using open-circuit potential (E-OC) measurements, electrochemical impedance spectroscopy (EIS) and polarization curves. The coatings surfaces and cross-section were characterized before and after corrosion tests using optical microscopy (OM) and scanning electron microscopy (SEM). After 18 h of immersion, the open-circuit potential values were around -0.50 and -0.25V/(Ag vertical bar AgCl vertical bar KClsat) for hard chromium and Cr3C2- NiCr, respectively. The surface analysis done after 12 h of immersion showed iron on the hard chromium surface inside/near surface cracks, while iron was not detected on the Cr3C2-NiCr surface even after 18 h. For longer immersion time hard chromium was more degraded than thermal sprayed coating. For hard chromium coating a total resistance values between 50 and 80 k Omega cm(2) were measured and two well-defined time constants were observed, without significant change with the immersion time. For Cr3C2-NiCr coating the total impedance diminished from around 750 to 25 k Omega cm(2) as the immersion time increased from 17 up to 132 h and two overlapped time constants were also observed. Polarization curves recorded after 18 h of immersion showed a lower current and higher corrosion potential for Cr3C2-NiCr coating than other samples studied. (c) 2005 Elsevier Ltd. All rights reserved.

Spectroscopic characterization of the reduction and removal of chromium (VI) by tropical peat and humin

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Cr3C2-NiCr and WC-Ni thermal spray coatings as alternatives to hard chromium for erosion-corrosion resistance

Cr3C2-NiCr and WC-Ni coatings are widely used for wear applications at high and room temperature, respectively. Due to the high corrosion resistance of NiCr binder, Cr3C2-NiCr coatings are also used in corrosive environments. The application of WC-Ni coatings in corrosive media is 14 not recommended due to the poor corrosion resistance of the (pure Ni) metallic matrix. It is well known that the addition of Cr to the metallic binder improves the corrosion properties. Erosion-corrosion performance of thermal spray coatings is widely influenced by ceramic phase composition, the size of ceramic particles and also the composition of the metallic binder. In the present work, two types of HVOF thermal spray coatings (Cr3C2-NiCr and WC-Ni) obtained with different spray conditions were studied and compared with conventional micro-cracked hard chromium coatings. Both as-sprayed and polished samples were tested under two erosion-corrosion conditions with different erosivity. Tungsten carbide coatings showed better performance under the most erosive condition, while chromium carbide coatings were superior under less erosive conditions. Some of the tungsten carbide coatings and hard chromium showed similar erosion-corrosion behaviour under more and less erosive conditions. The erosion-corrosion and electrochemical results showed that surface polishing improved the erosion-corrosion properties of the thermally sprayed coatings. The corrosion behaviour of the different coatings has been compared using Electrochemical Impedance Spectroscopy (EIS) and polarization curves. Total material loss due to erosion-corrosion was determined by weight loss measurements. An estimation of the corrosion contribution to the total weight loss was also given. (c) 2007 Elsevier B.V. All rights reserved.

Black and green pigments based on chromium-cobalt spinels

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Evaluation of solid sampling high-resolution continuum source graphite furnace atomic absorption spectrometry for direct determination of chromium in medicinal plants

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Nanoporous of W/WO3 Thin Film Electrode Grown by Electrochemical Anodization Applied in the Photoelectrocatalytic Oxidation of the Basic Red 51 used in Hair Dye

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Assessment of chromium contamination in the Monte Alegre stream: a case study

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Photoelectrocatalytical degradation of basic blue 41 dye using nanoporous semiconductor of Ti/TiO2

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Nitrate role in basic cation leaching under no-till

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Electrochemical behavior of metallic chromium in chloride media

The electrochemical behavior of metallic chromium in aqueous solutions containing chloride ions at different pH was studied by means of open-circuit potential vs. time measurements, cyclic voltammetry and electrochemical impedance spectroscopy. The composition of the surface oxides was analyzed by XPS. For solutions with pH<3 the formation of a passive layer occurs via a dissolution/precipitation process while for pH>3 the mechanism changes. XPS analysis revealed that Cr2O3 basically constitutes the passive layer.