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第一段
1 .Listen to part of a lecture in a materials science class.
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第二段
1 .So what's the first thing that comes to mind when we talk about uses for copper? Tammy?
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第三段
1 .The penny. It's made of copper.
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第四段
1 .Okay, good one. But what's a one cent coin worth these days?
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2 .You might get back change.
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3 .Like if you go to the store and give the cashier 5 dollars for something that costs 4 dollars 98 cents,
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4 .you'll get 2 cents back, but 2 cents does not buy much.
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5 .The value of the penny in terms of what it'll buy has gotten so low that there's actually a move afoot to eliminate the coin from US currency.
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6 .But there's more to it.
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第五段
1 .As Tammy implied, the penny looks like it's solid copper.
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2 .It is reddish orange with a bright metallic luster when it's new, but that's just the copper plating.
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3 .The penny's not solid copper.
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4 .In actuality, it is almost 98 percent zinc.
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第六段
1 .But given the rising value of both these metals, each penny now costs about 1.7 cents to produce.
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2 .So it generates what is called negative Seigniorage.
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第七段
1 .Negative seigniorage is when the cost of minting a coin is more than the coin's face value.
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2 .Even though the penny generates quite a bit of negative seigniorage,
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3 .there is concern that if it's eliminated,
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4 .we'll need more nickels, because more merchants might start setting prices in five-cent increments, 4 dollars 95 cents and so on.
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5 .So we need a trusty five-cent piece that can be minted economically.
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6 .But the nickel's negative seigniorage is even worse than the pennies.
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7 .Each nickel costs the US mint 10 cents to produce.
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第八段
1 .Also, some of us are pretty attached to pennies for whatever reason, nostalgia, and then those collectors.
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2 .And people, if they see a penny on the sidewalk, they'll pick it up and think: it is my lucky day!
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第九段
1 .Another scenario is that, without pennies, merchants, instead of charging 5.98,
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2 .might round up the price to an even five dollars.
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3 .So consumer goods would become slightly more expensive.
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4 .But on the other hand, some cash transactions would be more convenient for consumers.
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5 .And as I said, the government would save money if pennies were eliminated.
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第十段
1 .But wouldn't the copper industry suffer financially if the US government stopped buying copper to make pennies?
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第十一段
1 .But how much copper do pennies actually contain?
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第十二段
1 .How much...Oh, got it, right.
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第十三段
1 .So what else comes to mind when you think about copper?
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2 .What else is copper used for?
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第十四段
1 .I know that copper can be shaped into all sorts of things:
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2 .sheets, tubing, and my cousin's house has a copper roof.
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第十五段
1 .Yes, like gold and silver, copper is extremely malleable,
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2 .but it's not a precious metal, it's far less expensive than gold or silver.
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3 .It's also a superb conductor of electricity so you can stretch it into wires which go into appliances and even car motors.
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第十六段
1 .Copper also has superior alloying properties, it's...you know, when it's combined with other metals.
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第十七段
1 .For instance, how many of you play a brass instrument, like a trumpet or a trombone?
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第十八段
1 .Well, brass is an alloy of copper and zinc.
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2 .If your trombone was made of pure copper or pure zinc, it wouldn't sound nearly as beautiful as a brass trombone.
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第一十九段
1 .Another alloy, a combination of copper and nickel, resists corrosion.
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2 .It does not rust, even with prolonged exposure to water.
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第二十段
1 .But what about the Statue of Liberty in New York Harbor?
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2 .It's made of pure copper, but it turned green.
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3 .Isn't that a sign of corrosion?
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第二十一段
1 .Indirectly. If copper's exposed to damp air, its color changes from reddish orange to reddish brown.
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第二十二段
1 .But in time, a green film, called a patina, forms and the patina actually serves to halt any further corrosion.
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2 .It is one reason that ship hulls are made of copper-nickel alloys.
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3 .These alloys are also hard for the barnacles to stick to.
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4 .If these little shellfish adhere to the hull of a ship, it produces drag, slowing the vessel down.
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第二十三段
1 .Copper's also a key material used in solar heating units and in water desalination plants,
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2 .which will play increasingly important roles in society.
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第二十四段
1 .Bottom line: if you are a copper miner, you won't lose any sleep should the penny get...
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2 .if you'll excuse the expression, pinched out of existence.
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