Brazil's state-run oil company Petroleo Brasileiro SA, or Petrobras said on Friday its board of directors voted to make Luiz Nelson Guedes de Carvalho chairman until January 31. Guedes has been serving as interim chairman since September when he assumed the top board spot after a decision by Murilo Ferreira, chief executive of Brazilian mining company Vale SA, to step down temporarily. Ferreira made his departure permanent in November.