Análise microestrutural e de fases de um carbeto cementado dopado com terras-raras sinterizado por fase líquida

Abstract

O presente trabalho tem como objetivo principal a caracterização microestrutural e de fases de carbeto cementado (WC/10Co) dopado com terras-raras (La2O3 e CeO2). Este carbeto cementado é largamente utilizado como ferramenta de corte. Foram preparadas diversas misturas de WC/10Co com adições de até 3% em peso de La2O3 e CeO2 da fase cobalto. Os pós misturados foram submetidos a prensagem uniaxial em 200 MPa numa matriz cilíndrica (fi = 10 mm). Os compactos foram sinterizados sob vácuo em 1400ºC durante 60 min. A densidade relativa das peças foi determinada. As peças sinterizadas foram submetidas a ensaios de difração de raios-X e microscopia eletrônica de varredura via elétrons secundários. Os resultados mostraram que para as condições estudadas a adição de elementos de terras-raras influenciou positivamente a densificação do carbeto cementado WC/10Co durante o processo de sinterização. A microestrutura sinterizada das peças não sofreu modificações significativas com a adição dos elementos de terras-raras estudados.

Green Grabbing in the Matopiba Agricultural Frontier

“…Matopiba is a territory defined by state-sanctioned private capital and corporate businesses (Mathias 2017) and the Brazilian state, legally recognising it as an agricultural frontier (ibid.). This official recognition has enabled the expansion of agribusiness through public investments in infrastructure (roads, railways, ports, hydroelectric plants), in agricultural research and technical support (Gomes 2020;Azerêdo and Mitidiero Jr 2020), and through the support of state governments (Silva et al 2021).…”

“…Self-registration, in line with environmental regulation, has been done to validate and formalise irregular land tenures. These self-registrations in the national platform of CAR, or SICAR, have been neither validated nor inspected by the environmental authorities (OCF 2019), making these cadastres automatically 'valid' and without any control (Gomes 2020;Silva 2021).…”

“…This cadastre would allow the Federal Government and state agencies to monitor and inspect rural properties and the fulfilment of environmental regulations. However, this original purpose was diverted and the tool for environmental regularisation became an instrument for green grabbing (Gomes 2020;Silva 2021).…”

“…Environmental legislation is distorted, as the private owner declares a 'Legal Reserve' (20 per cent of land in the Cerrado, particularly in Matopiba) on other people's land. The cadastre is a legal requirement but also a way for discharging environmental obligations and costs such as restoring or compensating the deforestation of a Legal Reserve (Gomes 2020). Silva (2021 has demonstrated this process of appropriation and green grabbing, tracking the cadastres in CAR, but also in SNCI and SIGEF.…”

“…54 No. 1 February 2023 'Frontier Territories: Countering the Green Revolution Legacy in the Brazilian Cerrado' Matopiba since 2015, referring to the Cerrado as an 'open frontier' and a business opportunity in the states of Maranhão, Tocantins, Piauí, and Bahia (Gomes 2020;Silva et al 2021).…”