Mineral wool
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Mineral wool, also known as mineral cotton, silicate cotton, stone wool, slag wool, rockwool, and rock wool, is an inorganic substance used for insulation and filtering.
Mineral wool is a furnace product of molten rock, at a temperature of about 1600°C, through which is blown a stream of air or steam. More high tech production techniques are based on spinning molten rock (lava) on high speed spinning wheels. (compare with candy floss) The final product is a mass of fine intertwined fibres with a typical diameter of 6 to 10 micrometres. Mineral wool may contain a binder and an oil to reduce dusting and making it water repellant (hygro phobic). It is a poor conductor of heat and sound, is fire-proof and insect-proof, and therefore is ideal as a building insulation. Other uses are in resin bonded panels, growth medium in hydroponics,filler in compounds for gaskets,brake pads,in plastics in the automotive industry and as a filtering medium.
Precautions need to be made when handling a fibre product as it can be absorbed into the body by inhalation. It can also irritate the eyes, skin and respiratory tract. Prolonged exposure could lead to long term effects and it is considered a possible carcinogen to humans. This effect may depend upon the fibre diameter and length, chemical composition and persistence within the body.
High bio soluble fibres (HT-fibres) are produced that do not cause damage to the human cell. IARC (the International Agency for Research on Cancer)has reviewed the carcinogenity of man made mineral fibres in Oktober 2002. These newer bio soluble materials have been tested for carcinogenicity and most are found to be non-carcinogenic, or to cause tumours in experimentals animals only under very restricted conditions of exposure. The IARC Monographs working group concluded that only the more biopersistent materials remain classified by IARC as possible human carcinogens (Group 2B). These include refractory ceramic fibres, which are used industrially as insulation in high-temperature environments such as blast furnaces, and certain special-purpose glass wools not used as insulating materials. In contrast, the more commonly used vitreous fibre wools including insulation glass wool, rock (stone) wool and slag wool are considered not classifiable as to carcinogenicity to humans (Group 3).
The EU risk and safety phrases associated with this material in general are:
- R38 – Irritating to the skin
- R39 – Danger of very serious irreversible effects
- R40 – Possible risk of irreversible effects
- S36/37 – Wear suitable protective clothing and gloves.
All European produced rock (stone)wool and glass wool is bio soluble and R39 and R40 do not apply. For these products only the risk phrase R38 remains. This irritation to the skin however is not a chemical irritation but only a temporal mechanical irritation, comparable with exposure of the skin to straw, grass or hay.
Use in Hydroponics
Mineral wool is used in hydroponics for its ability to hold large quantities of water and at the same time maintain a high percentage of air as well. This aids root growth and nutrient uptake. The fibrous nature of mineral wool also provides a good mechanical structure to hold the plant stable. Mineral wool has a high pH, which is not suitable to plant growth. This requires correcting or conditioning. Conditioned mineral wool has a stable pH over long periods of time.