a) Give 2 reasons for not using metals / alloys as the main aggregate in refractory materials. b) True or false? Motivate your choice. i) A freeze lining is a type of refractory lining. ii) The freeze lining in a PGM smelter protects the copper cooler from sulphidation. iii) Water cooling of the shell of a pyrometallurgical unit that is lined with MgO bricks, can be detrimental if a water leak develops. iv) Anglo American Platinum has replaced MgO bricks with Al2O3Cr2O3 based bricks close to the copper coolers to alleviate the problem of MgO hydration. v) The thickness of the backlining of a specific unit will need to be thicker in the case where MgOC bricks are used in the working lining, rather than MgO bricks, for the same shell temperature (assume the original working lining thicknesses are the same)