On 2nd August 199.9, a particularly hot day in the town of Cirencester in the UK, a large pane of toughened glass in the roof of a shopping centre at Bishops Walk shattered without warning and fell from its frame. When fragments were analysed by experts at the giant glass manufacturer Pilkington, which had made the pane, they found that minute crystals of nickel sulphide trapped inside the glass had almost certainly caused the failure.
These crystals can exist in two forms: a dense form called the alpha phase, which is stable at high temperatures, and a less dense form called the beta phase, which is stable at room temperatures. The high temperatures used in the toughening process convert all the crystals to the dense, compact alpha form. But the subsequent cooling is so rapid that the crystals don't have time to change back to the beta phase. This leaves unstable alpha crystals in the glass, primed like a coiled spring, ready to revert to the beta phase without warning.
Look at the following people and the list of statements below.
Match each person with the correct statement.
Write the correct letter in boxes on your answer sheet.
Complete the summary with the list of words below.
Write your answers in boxes on your answer sheet.
Toughened glass is favoured by architects because it is much stronger than ordinary glass, and the fragments are not as 18 .................... when it breaks. However, it has one disadvantage: it can shatter 19 ........................ This fault is a result of the manufacturing process. Ordinary glass is first heated, then cooled very 20 ....................... .
The outer layer 21 ....................... before the inner layer, and the tension between the two layers which is created because of this makes the glass stronger. However, if the glass contains nickel sulphide impurities, crystals of nickel sulphide are formed. These are unstable, and can expand suddenly, particularly if the weather is 22 ........................ If this happens, the pane of glass may break. The frequency with which such problems occur is 23 ....................... by glass experts. Furthermore, the crystals cannot be detected without sophisticated equipment.
warm sharp expands slowly
unexpectedly removed contracts disputed
cold moved small calculated detected quickly agreed
Do the following statements agree with the information given in Reading Passage 83?
In boxes on your answer sheet, write
if the statement agrees with the information
if the statement contradicts the information
if there is no information on this
Little doubt was expressed about the reason for the Bishops Walk accident.
Toughened glass has the same appearance as ordinary glass.
There is plenty of documented evidence available about the incidence of nickel sulphide failure.