Influence of abrasives and graphite on processing and properties of sintered metallic friction materials

In this study, the influence of abrasives (size and morphology) and graphite on the processing and properties of friction materials were investigated. Friction materials based on bronze matrix, graphite as solid lubricant and different abrasives (silica, mullite and zircon) were prepared following two routes. On the one hand, following the traditional P/M technology (pressing-sintering) and on the other hand, using an alternative P/M route, which consists on sintering a powder blend free deposited in a mold and subsequently cold pressing. Sinterability, microstructure and physical-mechanical properties of the processed friction materials have been studied. Tribological and wear tests were carried out on a pin-on-disc system at different loads and sliding speeds using samples of 20 mm in diameter. Results show that the influence of abrasives size is especially relevant in the alternative P/M route, where materials including fine abrasives present unsuitable properties. Graphite also plays an important role on tribological behavior, in this work it has been found that friction materials with 4 wt.% graphite have better tribological properties than those with 2 wt.% graphite, despite having lower density and mechanical resistance

Milling Process of Petroleum Coke for Sintered Steel Applications

The effect of milling on different properties of a petroleum coke has been evaluated. The material was subjected to planetary milling at two different rates (400 and 600 rev min-1) for different times up to 48 h. The milled material was characterised by scanning electron microscopy, X-ray diffraction, sieve analysis, thermal analysis, chemical analysis, specific surface area and compressibility has been undertaken. The results show that the milling produces a very quick loss of the crystal structure of the coke and a rapid comminution, which lead to large increases in specific surface area and compressibility losses. The coke has shown a high activity through the milling process, absorbing a great quantity of oxygen. The increase in milling time shifts its thermal decomposition to lower temperatures.Authors want to acknowledge the financial support of Spanish Education Ministry, through Project PTR1995-0724-OP.Publicad

Adiponectin, leptin, and IGF-1 are useful diagnostic and stratification biomarkers of NAFLD

[EN] Background: Nonalcoholic fatty liver disease (NAFLD) is the most common chronic liver disease where liver biopsy remains the gold standard for diagnosis. Here we aimed to evaluate the role of circulating adiponectin, leptin, and insulin-like growth factor 1 (IGF-1) levels as non-invasive NAFLD biomarkers and assess their correlation with the metabolome. Materials and Methods: Leptin, adiponectin, and IGF-1 serum levels were measured by ELISA in two independent cohorts of biopsy-proven obese NAFLD patients and healthy-liver controls (discovery: 38 NAFLD, 13 controls; validation: 194 NAFLD, 31 controls) and correlated with clinical data, histology, genetic parameters, and serum metabolomics. Results: In both cohorts, leptin increased in NAFLD vs. controls (discovery: AUROC 0.88; validation: AUROC 0.83; p < 0.0001). The leptin levels were similar between obese and non-obese healthy controls, suggesting that obesity is not a confounding factor. In the discovery cohort, adiponectin was lower in non-alcoholic steatohepatitis (NASH) vs. non-alcoholic fatty liver (AUROC 0.87; p < 0.0001). For the validation cohort, significance was attained for homozygous for PNPLA3 allele c.444C (AUROC 0.63; p < 0.05). Combining adiponectin with specific serum lipids improved the assay performance (AUROC 0.80; p < 0.0001). For the validation cohort, IGF-1 was lower with advanced fibrosis (AUROC 0.67, p<0.05), but combination with international normalized ratio (INR) and ferritin increased the assay performance (AUROC 0.81; p < 0.01). Conclusion: Serum leptin discriminates NAFLD, and adiponectin combined with specific lipids stratifies NASH. IGF-1, INR, and ferritin distinguish advanced fibrosis.CR was funded by FEDER through the COMPETE program and by national funds through Fundação para a Ciência e a Tecnologia (PTDC/MED-FAR/29097/2017—LISBOA-01- 0145-FEDER-029097) and by European Horizon 2020 (H2020- MSCA-RISE-2016-734719). This work was also supported by Fundação para a Ciência e Tecnologia (PD/BD/135467/2017) and Portuguese Association for the Study of Liver/MSD 2017. JB was funded by Spanish Carlos III Health Institute (ISCIII) (PI15/01132, PI18/01075 and Miguel Servet Program CON14/00129 and CPII19/00008), co-financed by Fondo Europeo de Desarrollo Regional (FEDER), Instituto de Salud Carlos III (CIBERehd, Spain), La Caixa Scientific Foundation (HR17-00601), Fundación Científica de la Asociación Española Contra el Cáncer, and European Horizon 2020 (ESCALON project: H2020-SC1-BHC-2018-2020)

Influence of abrasives and graphite on processing and properties of sintered metallic friction materials

In this study, the influence of abrasives (size and morphology) and graphite on the processing and properties of friction materials were investigated. Friction materials based on bronze matrix, graphite as solid lubricant and different abrasives (silica, mullite and zircon) were prepared following two routes. On the one hand, following the traditional P/M technology (pressing-sintering) and on the other hand, using an alternative P/M route, which consists on sintering a powder blend free deposited in a mold and subsequently cold pressing. Sinterability, microstructure and physical-mechanical properties of the processed friction materials have been studied. Tribological and wear tests were carried out on a pin-on-disc system at different loads and sliding speeds using samples of 20 mm in diameter. Results show that the influence of abrasives size is especially relevant in the alternative P/M route, where materials including fine abrasives present unsuitable properties. Graphite also plays an important role on tribological behavior, in this work it has been found that friction materials with 4 wt.% graphite have better tribological properties than those with 2 wt.% graphite, despite having lower density and mechanical resistance

Hot Pressing of Iron-based Friction Materials

Publisher Copyright: © European Powder Metallurgy Association (EPMA)Hot Pressing can be considered as efficient process for the fabrication of sintered friction materials. It also allows reducing the sintering temperature and avoiding springback during conventional cold pressing (and sintering) caused by the presence of graphite. Besides, a higher sintered density is obtained, improving the homogeneity and mechanical properties of the hot-pressed components. In a previous work [1], copper-based materials were studied, whereas new studies have been carried out for the fabrication of iron-based friction materials. Two different abrasive/graphite combinations have been used and analysed in terms of their sinterability, and tribological and wear behaviour. The reaction between one of the abrasives used (SiC) with the iron powders during hot-pressing has been also analysed by FEGSEM and XRD and its influence on the wear resistance has also been studied.Peer reviewe

Production of porous SiC by liquid phase sintering using graphite as sacrificial phase: Influence of SiO2 and graphite on the sintering mechanisms.

Porous silicon carbide (SiC) is a promising ceramic for high-temperature applications due to its unique combination of properties. In the present work, a fabrication route for porous SiC is presented using graphite spherical powder as sacrificial phase to introduce porosity. By varying the initial amount of sacrificial phase, high-performance SiC materials with porosities in the range 30-50% were manufactured and characterized in terms of microstructure, density, thermal conductivity and flexural strength. The materials were fabricated by liquid phase sintering in presence of 2.5 wt.% Al2O3 and Y2O3 as sintering additives. The results indicate that the SiO2 present in the starting SiC powders interacts with the sintering additives forming liquid phases that promote densification and weight loss. Besides, an Al-Si liquid phase is formed at higher sintering temperatures, whose contribution to densification is inhibited in presence of graphite due to the formation of Al-rich carbides

Thickness and (%) CaCO3 contents in the marl-limestone couplets of the Danian (Sopelana, Basque Arc)

The Sopelana sea-cliff section exposes, a continuous marl-limestone alternation from the Danes in the deep Basque Arc domain. The 95 rhythms studied represent ~1180 ka and correspond to ~20cm/20ka. The limestone layers are thicker than marls and the Fischer diagram detects several shifts of high sedimentation and some well-marked minimums. The high-resolution of the twelve limestone layers (<1cm/analysis; 317 analysis, 3.06 m) shows complex curves indicative of climatic fluctuations. The pink-white colour variations are indicative of accidental oxygenated water masses presence, without diagenesis influenc

Improvement of the thermo-mechanical properties of fine grain graphite by doping with different carbides

The possibilities for optimization of doped fine grain graphites with high thermal conductivity and high I thermal shock resistance are demonstrated at laboratory scale. A mixture of MCMB powder and different carbides (B4C, TiC, VC, ZrC and WC) was used as starting material. VC acts as catalyst of the graphitization at the lowest temperature, and ZrC is the most effective catalyst of all investigated carbides. A direct proportionality between the mean crystallite height, L-c, and the thermal conductivity at room temperature was found for all materials except for the B4C- and the ZrC-doped graphites. With increasing graphitization temperature the open porosity of all doped materials becomes gradually closed, suggesting the existence of a diffusion mechanism responsible for both the catalytic effect and the closing of the open porosity. The addition of carbides does not strongly influence the mechanical properties of pure graphite. A high ratio flexural strength to Young's modulus was achieved. (C) 2002 Elsevier Science B.V. All rights reserved

Improvement of the thermo-mechanical properties of fine grain graphite by doping with different carbides

The possibilities for optimization of doped fine grain graphites with high thermal conductivity and high I thermal shock resistance are demonstrated at laboratory scale. A mixture of MCMB powder and different carbides (B4C, TiC, VC, ZrC and WC) was used as starting material. VC acts as catalyst of the graphitization at the lowest temperature, and ZrC is the most effective catalyst of all investigated carbides. A direct proportionality between the mean crystallite height, L-c, and the thermal conductivity at room temperature was found for all materials except for the B4C- and the ZrC-doped graphites. With increasing graphitization temperature the open porosity of all doped materials becomes gradually closed, suggesting the existence of a diffusion mechanism responsible for both the catalytic effect and the closing of the open porosity. The addition of carbides does not strongly influence the mechanical properties of pure graphite. A high ratio flexural strength to Young's modulus was achieved. (C) 2002 Elsevier Science B.V. All rights reserved