IELTS® Academic Reading Practice 72

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Toughened Glass

In the summer of 1999, a large pane of toughened glass suddenly shattered in Cirencester, a town in the UK, falling from its frame in a shopping center’s roof at Bishop’s Walk. The day was August 2nd, and it was an especially hot one. In the wake of this incident, experts at the large glass manufacturer Pilkington, which had made the pane, examined the shattered fragments of glass and made a surprising discovery. They found that when the glass pane was manufactured, tiny nickel sulfide crystals had become trapped within it, thus causing the glass to shatter unexpectedly out of its frame.

According to the chairman of the standards committee at the Glass and Glazing Federation, a British trade association, and standards development officer at Pilkington Brian Waldron, “The glass industry is aware of the issue.” He maintains that this kind of incident is extremely unlikely to occur at all, stating “It's a very rare phenomenon.” On the other hand, some are skeptical of Waldron’s remarks. Barrie Josie, an engineer consulted to help investigate the incident at Bishop’s Walk, commented “On average I see about one or two buildings a month suffering from nickel sulfide related failures.” Meanwhile, experts continue recounting other similar events. Both Tony Wilmott of London-based consulting engineers Sandburg, as well as Simon Armstrong at CalTech Associates in Hampshire both have alluded to there being hundreds more of these cases. “What you hear is only the tip of the iceberg,” says Trevor Ford, a glass expert at Resolve Engineering in Brisbane, Queensland. “No-one wants bad press.” says Ford, who believes this is the real explanation for the downplaying of similar events.

Toughened glass is found everywhere, from cars and bus shelters to the windows, walls, and roofs of thousands of buildings around the world. It's easy to see why. This glass has five times the strength of standard glass, and when it does break it shatters into tiny cubes rather than large, razor-sharp shards. Architects love it because large panels can be bolted together to make transparent walls, and turning it into ceilings and floors is almost as easy. It is made by heating a sheet of ordinary glass to about 620°C to soften it slightly, allowing its structure to expand, and then cooling it rapidly with jets of cold air. This causes the outer layer of the pane to contract and solidify before the interior. When the interior finally solidifies and shrinks, it exerts a pull on the outer layer that leaves it in permanent compression and produces a tensile force inside the glass. As cracks spread better in materials under tension, the compressive force on the surface must be overcome before the pane will break, making it more resistant to cracking.

The problem starts when glass contains nickel sulfide impurities. Small amounts of nickel and sulfur are usually present in the raw materials used to make glass, and nickel can also be introduced by fragments of nickel alloys falling into the molten glass. As the glass is heated, these atoms react to form tiny crystals of nickel sulfide. Just a tenth of a gram of nickel in the furnace can create up to 50,000 crystals. 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 afterwards, 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.

When this happens, the crystals expand by up to 4%. And if they are within the central, tensile region of the pane, the stresses this unleashes can shatter the whole sheet. The period of time before failure occurs is unpredictable. It could happen just months after manufacture, or decades later, although if the glass is heated, by sunlight, for example, the process speeds up. Ironically, says Graham Dodd, of consulting engineers Arup in London, the oldest pane of toughened glass known to have failed due to nickel sulfide inclusions was in Pilkington's glass research building in Lathom, Lancashire. The pane was 27 years old. Data shows that the nickel sulfide problem is almost impossible to find. The picture is made more complicated by the fact that these crystals occur in batches. So even if on average, there is only one inclusion in 7 tonnes of glass, if you experience one nickel sulfide failure in your building, that probably means you've got a problem in more than one pane. Josie says that in the last decade he has worked on over 15 buildings with the number of failures into double figures.

One of the worst examples of this is Waterfront Place, which was completed in 1990. Over the following decade, the 40 story Brisbane block suffered a rash of failures. Eighty panes of its toughened glass shattered due to problems before experts were finally called in. John Barry, an expert in nickel sulfide contamination at the University of Queensland, analyzed every glass pane in the building. Using a studio camera, a photographer went up in a cradle to take photos of every pane. These were scanned under a modified microfiche reader for signs of nickel sulfide crystals. ‘We discovered at least another 120 panes with potentially dangerous inclusions which were then replaced,’ says Barry. ‘It was a very expensive and time-consuming process that took around six months to complete.’ Though the project cost $1.6 million (nearly £700,000), the alternative - re-cladding the entire building - would have cost ten times as much.




This reading practice simulates one part of the IELTS Academic Reading test. You should spend about twenty minutes on it. Read the passage and answer questions 31-40.
Questions 31-33
Choose the correct letter, A, B, C or D.

Write your answers in boxes 31-33 on your answer sheet.

31. The crystals expand within the glass due to…

32. Why do crystals of nickel sulfide remain in the glass after manufacturing?

33. Which of the following speeds the process which leads to toughened glass failure?

Questions 34-38
Complete the summary using the list of words, A-N, below.
  1. compression
  2. after
  3. warm
  4. heating
  5. before
  6. slowly cooling
  7. nickel sulphide
  8. rapidly cooling
  9. cold
  10. cool
  11. tension
  12. heat
  13. compressive
  14. tensile

The manufacturing process of toughened glass involves  ordinary glass and keeping it there for a time, before the outside of the glass. This leads to the outer layer contracting the inner layer. The end result is glass which is under on the outside, and under on the inside.  In order to break the glass, the compressive force must first be exceeded.

Questions 39-40
Do the following statements agree with the information given in the reading passage? In boxes 39-40 on your answer sheet, write

TRUE   if the statement agrees with the information
FALSE   if the statement contradicts the information
NOT GIVEN   if there is no information on this.

39. There is plenty of documented evidence available about the incidence of nickel sulphide failure.

40. Toughened glass has the same appearance as ordinary glass.




Answer Sheet
1
N/A
2
N/A
3
N/A
4
N/A
5
N/A
6
N/A
7
N/A
8
N/A
9
N/A
10
N/A
11
N/A
12
N/A
13
N/A
14
N/A
15
N/A
16
N/A
17
N/A
18
N/A
19
N/A
20
N/A
21
N/A
22
N/A
23
N/A
24
N/A
25
N/A
26
N/A
27
N/A
28
N/A
29
N/A
30
N/A
31
32
33
34
35
36
37
38
39
40


Reading Passage Vocabulary
Toughened Glass


In the summer of 1999, a large pane of toughened glass suddenly shattered in Cirencester, a town in the UK, falling from its frame in a shopping center’s roof at Bishop’s Walk. The day was August 2nd, and it was an especially hot one. In the wake of this incident, experts at the large glass manufacturer Pilkington, which had made the pane, examined the shattered fragments of glass and made a surprising discovery. They found that when the glass pane was manufactured, tiny nickel sulfide crystals had become trapped within it, thus causing the glass to shatter unexpectedly out of its frame.

According to the chairman of the standards committee at the Glass and Glazing Federation, a British trade association, and standards development officer at Pilkington Brian Waldron, “The glass industry is aware of the issue.” He maintains that this kind of incident is extremely unlikely to occur at all, stating “It's a very rare phenomenon.” On the other hand, some are skeptical of Waldron’s remarks. Barrie Josie, an engineer consulted to help investigate the incident at Bishop’s Walk, commented “On average I see about one or two buildings a month suffering from nickel sulfide related failures.” Meanwhile, experts continue recounting other similar events. Both Tony Wilmott of London-based consulting engineers Sandburg, as well as Simon Armstrong at CalTech Associates in Hampshire both have alluded to there being hundreds more of these cases. “What you hear is only the tip of the iceberg,” says Trevor Ford, a glass expert at Resolve Engineering in Brisbane, Queensland. “No-one wants bad press.” says Ford, who believes this is the real explanation for the downplaying of similar events.

Toughened glass is found everywhere, from cars and bus shelters to the windows, walls, and roofs of thousands of buildings around the world. It's easy to see why. This glass has five times the strength of standard glass, and when it does break it shatters into tiny cubes rather than large, razor-sharp shards. Architects love it because large panels can be bolted together to make transparent walls, and turning it into ceilings and floors is almost as easy. It is made by heating a sheet of ordinary glass to about 620°C to soften it slightly, allowing its structure to expand, and then cooling it rapidly with jets of cold air. This causes the outer layer of the pane to contract and solidify before the interior. When the interior finally solidifies and shrinks, it exerts a pull on the outer layer that leaves it in permanent compression and produces a tensile force inside the glass. As cracks spread better in materials under tension, the compressive force on the surface must be overcome before the pane will break, making it more resistant to cracking.

The problem starts when glass contains nickel sulfide impurities. Small amounts of nickel and sulfur are usually present in the raw materials used to make glass, and nickel can also be introduced by fragments of nickel alloys falling into the molten glass. As the glass is heated, these atoms react to form tiny crystals of nickel sulfide. Just a tenth of a gram of nickel in the furnace can create up to 50,000 crystals. 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 afterwards, 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.

When this happens, the crystals expand by up to 4%. And if they are within the central, tensile region of the pane, the stresses this unleashes can shatter the whole sheet. The period of time before failure occurs is unpredictable. It could happen just months after manufacture, or decades later, although if the glass is heated, by sunlight, for example, the process speeds up. Ironically, says Graham Dodd, of consulting engineers Arup in London, the oldest pane of toughened glass known to have failed due to nickel sulfide inclusions was in Pilkington's glass research building in Lathom, Lancashire. The pane was 27 years old. Data shows that the nickel sulfide problem is almost impossible to find. The picture is made more complicated by the fact that these crystals occur in batches. So even if on average, there is only one inclusion in 7 tonnes of glass, if you experience one nickel sulfide failure in your building, that probably means you've got a problem in more than one pane. Josie says that in the last decade he has worked on over 15 buildings with the number of failures into double figures.

One of the worst examples of this is Waterfront Place, which was completed in 1990. Over the following decade, the 40 story Brisbane block suffered a rash of failures. Eighty panes of its toughened glass shattered due to problems before experts were finally called in. John Barry, an expert in nickel sulfide contamination at the University of Queensland, analyzed every glass pane in the building. Using a studio camera, a photographer went up in a cradle to take photos of every pane. These were scanned under a modified microfiche reader for signs of nickel sulfide crystals. ‘We discovered at least another 120 panes with potentially dangerous inclusions which were then replaced,’ says Barry. ‘It was a very expensive and time-consuming process that took around six months to complete.’ Though the project cost $1.6 million (nearly £700,000), the alternative - re-cladding the entire building - would have cost ten times as much.

 
IELTS Academic Reading Tips for Success
These are general tips that will appear on all reading questions.

Tips to improve your reading speed
To get a high score on the IELTS reading section, you need to have a fast reading speed. To have a fast reading speed, you need to improve your vocabulary and practice dissecting sentences. One strategy to dissect a sentence is to look for the subject and verb of the sentence. Finding the subject and verb will help you better understand the main idea of said sentence. Keep in mind, a common feature of a IELTS reading passage is to join strings of ideas to form long compound sentences. This produces large chunks that students have a hard time absorbing. Do not get overwhelmed by its length, just look for the subject and verb, the rest of the ideas will flow.


Keep in mind, having a slow reading speed makes skimming or scanning a reading passage more difficult. The process of quickly skimming through a reading passage for specific keywords or main ideas is a requirement for you to employ successful reading strategies to improve your IELTS reading score. In other words, skimming and scanning are critical skills to ensure you complete all questions in the allotted time frame.
IELTS Reading Strategies
Once you can read and comprehend a passage with a rate of, at least, 220 words per minute, you'll be ready to start implementing our strategies. All too often, students spend too much time reading the passages and not enough time answering the questions. Here is a step by step guide for tackling the reading section.

  1. Step 1: Read questions first

    One of the most common mistakes that candidates make when approaching the reading exam is reading every single word of the passages. Although you can practice for the exam by reading for pleasure, "reading blindly" (reading without any sense of what the questions will ask) will not do you any favors in the exam. Instead, it will hurt your chances for effectively managing your time and getting the best score.

    The main reason to read the questions first is because the type of question may determine what you read in the passage or how you read it. For example, some question types will call for the "skimming" technique, while others may call for the "scanning" technique.

    It is important to answer a set of questions that are of the same question type. You'll need to determine which question type you want to tackle first. A good strategy would be to start with the easier question type and move on to more difficult question types later. The Easiest question types are the ones where you spend less time reading. For example, the Matching Heading question type is an easier one because you only need to find the heading that best describes the main idea of a paragraph. An example of a difficult question type would be Identifying Information. For this question type, you'll need to read each paragraph to find out if each statement is TRUE, FALSE, or NOT GIVEN according to the passage.

    Here is a table that lists the difficulty levels for each question type. Use this table as a reference when choosing which question type you want to tackle first.


    Difficulty level Question Type
    Easy Sentence Completion
    Short answer
    Medium Matching Features
    Multiple choice
    Matching Headings
    Summary, Table, Flow-Chart Completion
    Difficult Matching Sentence Endings
    Matching Information
    Identifying Information (TRUE/FALSE/NOT GIVEN)
    Identifying Viewer's claims (YES/NO/NOT GIVEN)

  2. Step 2: Read for an objective

    After you've read the questions for the passage, you will be able to read for an objective. What does this mean? For example, if you come across a question that includes the year "1896", you can make a note of when this year comes up in the text, using it to answer the question later on. There are two reading techniques that will help you stay on track with reading for an objective. The first one, skimming, is best defined as reading fast in order to get the "gist", or general idea, or a passage. With this technique, you are not stopping for any unfamiliar words or looking for specific details. The second technique, scanning, is best defined as reading for specific information. With this technique, you are not reading for the overall gist, but rather, specific information. Notice how each of these techniques has a specific objective in mind. This will help you find information more quickly.

  3. Step 3: Take notes

    As you're reading for an objective, you should also be making notes on the margins of the passage, placing stars next to key information, or underlining things that you believe will help you answer the various questions. This will make it easier for you to check back when you are asked certain things in the questions. Choose whichever note-taking system is right for you - just make sure you do it!

  4. Step 4: Answer wisely

    After you've read the questions, read the passage, and have taken any appropriate notes, you you should have located the part of the text where you where you need to read carefully. Then just read carefully and think critically to determine the correct answer.

IELTS Reading Question Types
 
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