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If
you live in a city that gets lots of snow and ice, then you're familiar
with road salt. Your city and local government likely has several
de-icing trucks that spread road salt on the highways, streets and
sidewalks to melt the ice. But how exactly does it work? 如果你生活在一座冰雪之城，那么你肯定對道路防結冰用鹽不陌生。你所在的城市和政府應該會有幾輛除冰車負責在高速公路、街道和人行道上撒鹽，以使路面的冰盡快融化。那么這背后的工作原理到底是什么？ First, road salt is simply halite
— rock salt — which is table salt in its natural form. The difference
is table salt goes through a lengthy purification process, while rock
salt does not. And because rock salt still has impurities, it's brown or
gray in color. 首先，道路用鹽就是石鹽，也被稱為巖鹽，即食鹽的天然形式。區別在于食鹽經過了漫長的純化工藝，而巖鹽則沒有。另外，由于巖鹽中還含有雜質，因此其呈現棕色或灰色。 Table salt：食鹽 Why Salt? 為什么選擇鹽？ Ice
forms when the temperature of water reaches 32 degrees Fahrenheit (0
degrees Celsius), and that includes ice on roadways. Road salt works by
lowering the freezing point of water via a process called freezing point
depression. The freezing point of the water is lowered once the salt is
added, so it the salt makes it more difficult for water to freeze. A
10-percent salt solution freezes at 20 degrees Fahrenheit (-6 Celsius),
and a 20-percent solution freezes at 2 degrees Fahrenheit (-16 Celsius). 當水溫達到32華氏度（或0攝氏度）時，就會形成冰，這也包括馬路上的冰。道路用鹽通過一種被稱為冰點降低的工藝來使水的冰點降低并從而發揮作用。當加入鹽后，水的冰點就會降低，因此鹽使水變得較難結冰。濃度為百分之十的鹽溶液會在20華氏度（零下6攝氏度）時結冰，而濃度為百分之二十的鹽溶液則會在2華氏度（零下16攝氏度）結冰。 The
key is, there has to be at least a tiny bit of water on the road for
freezing point depression to work. That's why you often see trucks
pre-treat roads with a brine solution (a mixture of salt and water) when
ice and snow is forecast. If the roads are dry and the DOT simply puts
down road salt, it likely won't make much of a difference. But
pre-treating with a brine solution can help ice from ever forming, and
will help reduce the amount of road salt trucks will need to spread to
de-ice later. 關鍵之處在于，要想使冰點降低發揮作用，馬路上必須要有水，哪怕是極少的水。這也是為什么當預報會出現冰雪天氣時，你會經常看到卡車會提前在路面上撒鹽溶液（鹽和水的混合物）。如果在路面干燥的情況下把道路用鹽撒上去，那很可能不會產生任何作用。但是提前在馬路上撒鹽溶液則有助于防止結冰，并從而減少隨后的撒鹽量。 Pros and Cons 優點和缺點 Rock
salt is one of the most widely used road de-icers, but it's not without
critics. For one, rock salt does have its limits. If the temperature of
the roadway is lower than about 15 degrees F (- 9 C), the salt won't
have any effect on the ice. The solid salt simply can't get into the
structure of the frozen water to start the dissolving process. In these
cases, the DOT typically spreads sand on top of the ice to provide
traction. 道路用鹽是適用范圍最廣的道路去冰材料之一，但是它也有一些負面的評價。首先，道路用鹽有局限性。如果路面的溫度低于15華氏度（零下9攝氏度），鹽對冰就不會有任何作用。固態鹽根本無法進入冰的內部以發揮融化的作用。在這種情況下，運輸部往往會把沙子灑在冰面上以增加摩擦力。 Rock
salt also has major environmental issues, including the sodium and
chlorine that leaches into the ground and water. And as we mentioned
earlier, because rock salt isn't purified and contains contaminants —
including lead, iron, aluminum and phosphorus — when it's spread, these
are spread as well. However, rock salt still remains the most widely
used and affordable de-icers available. And while there are other
chemical de-icers, too, none are 100 percent risk free. 道路用鹽還有非常嚴重的環境問題，包括鈉和氯會滲入到地面和水中。正如我們早些時候提到的，因為巖鹽沒有經過純化，因此還會含有污染物，比如鉛、鐵、鋁和磷-當撒下道路用鹽時，這些污染物也會被一同撒下。但是，道路用鹽仍然是應用最廣以及最經濟的去冰材料。盡管還有其他化學類的去冰材料，但是沒有哪一種是百分百安全的。 原文來源：HowStuffWorks 編輯：上海譯銳翻譯