Look through the text. Get ready to speak about brasses, bronzes and aluminum alloys

There are many applications of non-ferrous metals in an unalloyed state, but in most cases some alloying element is added. Non-ferrous metals may be mixed in various proportions to form many alloys, the main of them being brasses, bronzes and aluminum alloys.

Brasses are yellowish or reddish alloys of copper and zinc in different proportions (about 60 per cent copper and 40 per cent zinc, but some brasses contain as high as 90 per cent copper with only 10 per cent zinc). An addition of tin makes brasses stronger. Brasses are very ductile and may be treated without heating them. They are corrosion-resistant and are used for making musical instruments, bearings, etc.

Bronze is an alloy containing primarily copper and tin, but other elements may be added to the alloy to increase its properties such as hardness and resistance to wear. The most common bronzes are known as straight bronze, phosphor bronze and manganese bronze. Straight bronze is a mixture of copper and tin, but there are many bronzes that contain zinc and lead, especially cheap mixtures.

Alluminum alloys. Aluminum is used extensively for castings that are to be light in weight, light in colour, or mut not rust. As aluminum is too soft for making castings, it is necessary to mix some other metals with it.The metals that alloy freely with aluminum are copper, zinc and iron.Usually, where aluminum alloys are made, aluminum predominates.

Unit 14

1. Memorize the following words:

draw into jewelry tarnish precious account for (зд) valuable spark equipment powder ignition sheet thickness similar discover rare inch craft

вытягивать в ювелирные изделия тусклый ценный объяснять ценный искра оборудование порошок зажигание лист толщина подобный обнаружить редкий дюйм (2, 54 см) ремесло

витягувати ювелірні вироби тьмяний коштовний пояснювати цінний іскра обладнання порошок запалювання лист товщина подібний виявити рідкий дюйм ремесло

1. Practise the reading of the following words:

Jewelry, powder, valuable, precious, rare, account, draw, equipment, scarcity, metallurgist, thermometer, catalyze, least, measure, photographic, bromide, palladium, rhodium, ruthenium, iridium, osmium, lustrous.

1. Read and translate the text:

Precious Metals

Why are some metals so much more valuable than others? Gold, silver and platinum have been highly valued for centuries because of their scarcity, beauty and high qualities. The result of the rush for these metals was death, blood and tragedy.

To metallurgists the most exciting discovery made by the Spaniards was the finding of platinum in the silver mines of Mexico. At that time the new metal could not be melted by any known method, though it was possible to make a very realistic imitation gold from it. Later it joined the group of precious metals and is now used for jewelry and in industry. Its high melting point makes it suitable for electrical contacts where the heat of sparks would melt other metals. Its resistance to corrosion is of great value for chemical industry. Platinum is used in jewelry, laboratory equipment, electrical contacts and electrodes, platinum resistance thermometers, dentistry equipment, and catalytic converters. The most common use of platinum is as a catalyst in chemical reactions. It has been employed in this application since the early 1800s, when platinum powder was used to catalyze the ignition of hydrogen. Platinum is also used in the petroleum industry as a catalyst in a number of separate processes.

Gold is the most malleable of all the metals. It can be hammered into sheets so thin that 250 of them would equal the thickness of a sheet of paper. It is also the most ductile metal. One gram of gold can be drawn into a wire 1.8 miles in length. There was an ancient craft of gold-beating, a process by which gold was beaten between skins until it was reduced to a very thin sheet. The Egyptians could produce sheets only one five-thousandth of an inch thick, and used them for gilding wooden statues and for other decorative purposes.

Gold is the least chemically active of all metals and does not combine with oxygen to form rust. This ability to resist corrosion makes it very durable, i.e. it may last for centuries. Pure gold is too soft to be used in jewelry so it is usually alloyed with other metals. The proportion of gold in an alloy is measured in karats. Pure gold is 24 karats. A 14 karat gold ring is an alloy of about 58% of gold and small percentages of copper and silver.

Silver is similar to gold in many ways. Like gold, it is very malleable and ductile and so it is also used for jewelry. Silver differs from gold in that it is more reactive and tarnished when exposed to sulfur in the air. (Silver sulfide, a black deposit, forms on its surface). Pure silver is too soft and so it is usually alloyed with copper to increase its hardness and durability. Sterling silver is 92.5 percent silver and 7.5 percent copper. Silver is used for coins and for photographic films because certain compounds of silver, such as silver bromide, reflect light. Silver is the best conductor of electricity known.

Palladium is a chemical element with the chemical symbol Pd and an atomic number of 46. Palladium is a rare lustrous silvery-white metal that was discovered in 1803 by William Hyde Wollaston, who named it after the asteroid Pallas.

Palladium, along with platinum, rhodium, ruthenium, iridium and osmium form a group of elements known as the platinum group metals (PGMs). Platinum group metals have similar chemical properties, but palladium has the lowest melting point and is the least dense of these precious metals.

The unique properties of palladium and other platinum group metals account for their widespread use. One in four goods manufactured today either contains platinum group metals or had platinum group metals play a key role during their manufacturing process.

1. Find in the text English equivalents for these words and word-combinations:

імітація золота; найнижча точка плавлення; відомий метод; дорогоцінні метали; висока точка плавлення; хімічна промисловість; подібні хімічні властивості; ювелірна прикраса; втрачати блиск (окислюватися); срібло вищої проби; фотоплівка; срібні копальні, широке застосування, унікальні властивості, відбивати світло, нафтова промисловість.

1. Answer the following questions.

1. What are precious metals valued for?

2. Where was platinum found by Spaniards?

3. Where is platinum used now?

4. Why can platinum be used for electrical contacts?

5. Why is it easy to hammer gold into thin sheets?

6. Why can gold last for centuries?

7. What are the properties of silver?

8. What colour is silver sulfide?

9. Where is silver used?

10. 10.What do you know about palladium?

6. Fill in the blanks with suitable words from those given below: