A preliminary comparison of the corrosion behaviour of additively and conventionally manufactured 18Ni300 maraging steel for moulds

ABSTRACT: The corrosion behaviour of a maraging steel 18Ni300 manufactured by Laser Powder Bed Fusion (L-PBF) was compared to that of a conventional tool steel. Electrochemical test conditions were chosen to approximate the corrosive environments encountered during injection moulding of polyvinyl chloride (PVC) parts. The corrosion behaviour of the steel produced by both routes was evaluated before and after an ageing treatment at 510 ºC for six hours. Cuboid specimens were fabricated and a polished area of 100 mm2 was immersed in a 0.1M HCl solution for 7 days. Open circuit potential (OCP) and polarization curves were used to monitor the material exposed to the corrosive environment. The obtained results indicate that the conventionally produced aged steel is less susceptible to corrosion and that the steel manufactured by L-PBF (not aged condition) showed better resistance to pitting.info:eu-repo/semantics/publishedVersio

Smart coating for detection of early-stage corrosion of steel

ABSTRACT: The work describes the investigation of LDH-based nanoadditives for early-stage corrosion detection of steel, and subsequent development of a multi-layer functional protection coating. A systematic study on the level of degradation and the detected colorimetric signal was performed using electrochemical characterisation. The protection properties and detection functionality were also studied in conditions relevant to exploitation of metallic structures.info:eu-repo/semantics/publishedVersio

Um roteiro para a produção de metal duro com maior resistência à corrosão

RESUMO: Com o objetivo de racionalizar o desenvolvimento de compósitos de metal duro com maior resistência à corrosão, realizou-se um estudo sistemático da influência de vários parâmetros que determinam o seu desempenho. Neste trabalho apresentam-se resultados da influência de parâmetros relacionados com a constituição do material (tipo de ligante e tamanho de grão de carboneto de tungsténio - WC) e de parâmetros do ambiente de serviço (pH e temperatura). O estudo socorreu-se principalmente de métodos electroquímicos e de análise da superfície.info:eu-repo/semantics/publishedVersio

Corrosion behaviour of WC hardmetals with nickel - based binders

Cobalt is the standard binder in tungsten carbide (WC) hardmetals due to its compatibility with the WC phase, resulting in composites with exceptional hardness and wear resistance. However, their corrosion resistance is not satisfactory in many applications, leading to the early deterioration and failure of tools and equipment. In this work, the corrosion of WC hardmetals with three alternative binders (FeCoNi, NiCrCoMo and NiCrMo) is compared with a benchmark WC-Co composite, using electrochemical techniques such as open circuit potential (OCP) monitoring, polarisation curves and electrochemical impedance spectroscopy (EIS), assisted by scanning electron microscopy (SEM).publishe

Redução electroquímica de iões de terras raras e o seu efeito na corrosão de metais

RESUMO: Os iões de terras raras estão entre os inibidores de corrosão de nova geração mais promissores. No entanto, foram encontradas condições onde a corrosão é acelerada na presença destes iões [1]. O caso mais relevante devido à sua importância é o aumento da corrosão do zinco no par galvânico zinco-ferro. Esse aumento está associado a uma reacção catódica adicional inesperada que é observada nas curvas de polarização obtidas experimentalmente. Esta nova redução corresponde a corrente catódica adicional que aumenta a oxidação do ânodo do par galvânico. Nesta comunicação analisa-se o impacto prático desta aceleração no par Zn-Fe e no aço galvanizado e procura-se identificar a natureza da nova reacção catódica.info:eu-repo/semantics/publishedVersio

Isoperimetric problems of the calculus of variations with fractional derivatives

In this paper we study isoperimetric problems of the calculus of variations with left and right Riemann-Liouville fractional derivatives. Both situations when the lower bound of the variational integrals coincide and do not coincide with the lower bound of the fractional derivatives are considered.Comment: Submitted 02-Oct-2009; revised 30-Jun-2010; accepted 10-May-2011; for publication in the journal Acta Mathematica Scienti

Effects induced by Apis mellifera venom and its components in experimental models of nociceptive and inflammatory pain

AbstractThe effects induced by Apis mellifera venom (AMV), melittin-free AMV, fraction with molecular mass < 10 kDa (F<10) or melittin in nociceptive and inflammatory pain models in mice were investigated. Subcutaneous administration of AMV (2, 4 or 6 mg/kg) or melittin-free AMV (1, 2 or 4 mg/kg) into the dorsum of mice inhibited both phases of formaldehyde-induced nociception. However, F<10 (2, 4 or 6 mg/kg) or melittin (2 or 3 mg/kg) inhibited only the second phase. AMV (4 or 6 mg/kg), but not F<10, melittin-free AMV or melittin, induced antinociception in the hot-plate model. Paw injection of AMV (0.05 or 0.10 mg), F<10 (0.05 or 0.1 mg) or melittin (0.025 or 0.050 mg) induced a nociceptive response. In spite of inducing nociception after paw injection, scorpion (Tityus serrulatus) or snake (Bothrops jararaca) venom injected into the dorsum of mice did not inhibit formaldehyde-induced nociception. In addition, AMV (6 mg/kg), but not F<10 (6 mg/kg) or melittin (3 mg/kg), inhibited formaldehyde paw oedema. Concluding, AMV, F<10 and melittin induce two contrasting effects: nociception and antinociception. AMV antinociception involves the action of different components and does not result from non-specific activation of endogenous antinociceptive mechanisms activated by exposure to noxious stimuli

Biochar impacts on runoff and soil erosion by water: a systematic global scale meta-analysis

Biochar application to soil has the potential to affect soil and vegetation properties that are key for the processes of runoff and soil erosion. However, both field and pot experiments show a vast range of effects, from strong reductions to strong increases in runoff and/or soil erosion. Therefore, this study aimed to quantify and interpret the impacts of biochar on runoff and soil erosion through the first systematic meta-analysis on this topic. The developed dataset consists of 184 pairwise observations for runoff and soil erosion from 30 independent studies but 8 of which just focused on soil erosion. Overall, biochar application to soil significantly reduced runoff by 25 % and erosion by 16 %. Mitigation of soil erosion in the tropics was approximately three times stronger (30 %) than at temperate latitudes (9 %); erosion reduction in the subtropical zone was 14 %, but not significantly different from either the tropical or temperate zones. Fewer reported field observations for runoff resulted in larger confidence intervals and only the temperate latitudes showed a significant effect (i.e. a 28 % reduction). At topsoil gravimetric biochar concentrations between 0.6 % and 2.5 %, significant reductions occurred in soil erosion, with no effect at lower and higher concentrations. Biochar experiments that included a vegetation cover reduced soil erosion more than twice as much as bare soil experiments, i.e. 27 % vs 12 %, respectively. This suggests that soil infiltration, canopy interception, and soil cohesion mechanisms may have synergistic effects. Soil amended with biochar pyrolyzed at >500 °C was associated with roughly double the erosion reduction than soil amended with biochar produced at 300–500 °C, which potentially could be related to the enhancement of hydrophobicity in the latter case. Our results demonstrate substantial potential for biochar to improve ecosystem services that are affected by increased infiltration and reduced erosion, while mechanistic understanding needs to be improved

Biochar boosts tropical but not temperate crop yields

Applying biochar to soil is thought to have multiple benefits, from helping mitigate climate change [1, 2], to managing waste [3] to conserving soil [4]. Biochar is also widely assumed to boost crop yield [5, 6], but there is controversy regarding the extent and cause of any yield benefit [7]. Here we use a global-scale meta-analysis to show that biochar has, on average, no effect on crop yield in temperate latitudes, yet elicits a 25% average increase in yield in the tropics. In the tropics, biochar increased yield through liming and fertilization, consistent with the low soil pH, low fertility, and low fertilizer inputs typical of arable tropical soils. We also found that, in tropical soils, high-nutrient biochar inputs stimulated yield substantially more than low-nutrient biochar, further supporting the role of nutrient fertilization in the observed yield stimulation. In contrast, arable soils in temperate regions are moderate in pH, higher in fertility, and generally receive higher fertilizer inputs, leaving little room for additional benefits from biochar. Our findings demonstrate that the yield-stimulating effects of biochar are not universal, but may especially benefit agriculture in low-nutrient, acidic soils in the tropics. Biochar management in temperate zones should focus on potential non-yield benefits such as lime and fertilizer cost savings, greenhouse gas emissions control, and other ecosystem services