Magnetite | Additives feature
Dr Chris DeArmitt of LKAB Minerals argues that magnetite deserves a higher profile as a useful functional filler that can enhance the properties of polymers in a wide variety of ways
Magnetite: exploring the multi-functional filler
Magnetite is probably the most interesting and useful filler you’ve never heard of. As with all materials, its applications stem from its properties. So, what are the most noteworthy properties of magnetite? It has a high density of 5.2 g/cm3
, and it is a hard
material with a Mohs hardness of around 6. Magnetite is both electrically and thermally conductive, plus it has an unusually high specific heat capacity. The black, lustrous mineral is also extremely pure and inert. This article will take a look at each of these proper- ties in turn and see how they lead to real-world applications for this specialty mineral filler.
Increasing density Density is perhaps not the most glamorous of proper- ties, but there are many applications requiring a dense filler. These vary from counterweights for washing machines to ballast and bowling balls. Traditionally, barium sulphate has filled the role of
www.compoundingworld.com high density filler – it has a density of 4-4.5 g/cm3 .
However, over the past decade, magnetite has become more popular as it has a higher density of 5.2 g/cm3
and
is therefore more effective. In some applications, adding mass is the sole goal, but sometimes other benefits are in focus. For example, adding heft creates the perception of a high-quality product. As a result, magnetite is used in cosmetics packaging, synthetic leather and household appliances to add luxury feel (haptics). Compound densi- ties up to 3.0 g/cm3
are attainable using magnetite. Dense fillers can also be used for sound and
vibration damping. Typically, high levels of a dense filler – up to around 80% by weight – are added to a soft, high-loss polymer that deforms by non-elastic/viscous flow. Magnetite has been used by major automotive companies for decades in injection moulded parts, for example in PA or PP, and as soft sheets to isolate the cabin from road noise, or in strategically placed polyurethane spray foam.
August 2015 | COMPOUNDING WORLD 63
When dispersed in oil, Magnetite forms a
ferro-fluid or magneto-rheo- logical fluid
s
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