SKIN... what to use for a sustainable home: metallurgy 101
After much debate, the new addition to the Melaver residence has a skin that it can call its own and call "itself" sustainable. After starting with a pure zinc product much debate about its origins , recycled content, and its nature in general were questioned. Everything from stainless steel to galvalume were considered, but after some fact finding, COPPER became our material of choice.
read further to debate the metals in contention:
sample of copper panel
patina after years of exposure
Copper
* Copper has an infinite recyclable life. Copper, by itself or in any of its alloys, such as brass or bronze, is used over and over again.
* Known worldwide copper resources are estimated at nearly 5.8 trillion pounds of which only about 0.7 trillion pounds (12%) have been mined throughout history. Nearly all of that is still in circulation, because copper’s recycling rate is higher than that of any other engineering metal.
* Each year in the U.S.A., nearly as much copper is recovered from recycled material as is derived from newly mined ore. When you exclude wire production, most of which uses newly refined copper, the amount of copper used by copper and brass mills, ingot makers, foundries, powder plants and other industries shows that nearly three-fourths (72%) comes from recycled copper scrap. Of the copper used in architectural applications, nearly 100% is recycled.
* More then half of this scrap is “new” scrap, such as chips and turnings from screw machine production... the remainder is “old” scrap, such as discarded electric cable, junked automobile radiators or even ancient Egyptian plumbing.
* Copper’s recycling value is so great that premium-grade scrap normally has at least 95% of the value of the primary metal from newly mined ore.
* The U.S. does not depend on foreign copper... we are completely self-sufficient.
Steel, Galvanized Steel, & Stainless Steel
* Steel has an infinite recyclable life.
* The overall recycling rate for steel is approximately 71%. Approximately 98% of steel used in architectural and construction applications is recycled.
* Scrap has become the steel industry's single largest source of raw material because it is economically advantageous to recycle old steel into new steel. In light of this, steelmaking furnaces have been designed to consume steel scrap.
* In the past 50 years, approximately 50 percent of the steel produced in this country has been recycled through the steelmaking process.
* The life of zinc-containing products is variable and can range from 10-15 years for cars or household appliances, to over 100 years for zinc sheet used for roofing. Street lighting columns made of zinc-coated steel can remain in service for 40 years or much longer, and transmission towers for over 70 years. All these products tend to be replaced due to obsolescence, not because the zinc has ceased to protect the underlying steel. For example, zinc coated steel poles placed in the Australian outback a hundred years ago are still in excellent condition.
The presence of zinc coating on steel does not restrict steel's recyclability and all types of zinc-coated products are recyclable. Zinc coated steel is recycled along with other steel scrap during the steel production process - the zinc volatilizes and is then recovered.
Zinc
* Zinc is a valuable commodity in the marketplace because, unlike many other materials zinc can be recycled again and again and still maintain its physical and chemical properties.
This means that much of the zinc you use today was first used years ago.
* Over 6.5 million metric tons of zinc slab, oxides, powders and dusts are consumed each year in the Western World, two million of which come from recycled zinc. In the United States, the Bureau of Mines estimates that with enhanced recovery, recycled zinc will account for 40% of total consumption by 2000.
* Zinc, the 27th most common element in the Earth's crust, is fully recyclable. At present, approximately 70% of the zinc produced originates from mined ores and 30% from recycled or secondary zinc. The level of recycling is increasing in step with progress in zinc production technology and zinc recycling technology.
* Today, over 80% of the zinc available for recycling is recycled. Zinc is recycled at all stages of production and use - for example, from scrap that arises during the production of galvanized steel sheet, from scrap generated during manufacturing and installation processes, and from end-of-life products.