雅思阅读 114: Nacre and Greener Materials

Adapted from 'Mollusk shells could pave the way to greener materials', Scientific American, April 2026.

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Reading Passage

In 59 B.C.E. Julius Caesar gave his mistress a black pearl earring of such size and luster that it was chronicled by Roman writers. After all, pearls were a cornerstone of ancient Roman political and economic power. But today, nacre, the lustrous substance mollusks use to line their shells, is becoming prized once more, this time in materials science.

Nacre is a natural ceramic. Synthetic ceramics are found in everything from hip replacements to phone casings. They are strong, inert and able to withstand wear, corrosion and high temperatures. But as anyone who has dropped a mug knows, ceramics are also brittle and prone to shattering.

Nacre, on the other hand, is both strong and tough. Although its cells are 99 percent ceramic by volume, it resists crack propagation. It is composed of hexagonal crystals of aragonite, a calcium carbonate, arranged in overlapping layers resembling brick and mortar. The layers overlap out of alignment so joints do not line up, increasing hydrogen bonds and conferring strength. Where limestone is crumbly, nacres toughness comes from silklike proteins that weave between layers, providing elasticity to absorb fracture shock. Nacre is roughly 3,000 times tougher than its calcium carbonate building blocks.

Even with electron microscopy, nacre has proved difficult to manufacture synthetically. The one percent organic glue is critical. Researchers now try to replicate nacres internal architecture with different building blocks, testing these nacre-adjacent ceramics in next-generation nuclear reactors where resistance to fracture is essential.

Another problem is that ceramics are energy-intensive to make, with huge carbon emissions from high temperatures. Nature produces these composites at close to room temperature. Shu Yang of the University of Pennsylvania mimics the way bone forms: she creates 3D-printed organic scaffolds dipped in polymer coating, producing lightweight, porous materials that distribute stress. Such materials could be used in car bumpers or protective gear.

Researchers must not only mimic what evolution has produced but also copy natures methods and use renewable supplies. Even a creature as simple as a mollusk has much to teach us about how to build a greener world.

Questions 1-5

Choose the correct letter, A, B, C or D.

1. What is nacre? A. A type of plastic B. The lustrous substance lining mollusk shells C. A synthetic ceramic D. A metal alloy
2. How much of nacre is ceramic by volume? A. 50 percent B. 99 percent C. 10 percent D. 9 percent
3. What makes nacre tough? A. Hard glass B. Silklike proteins weaving between layers C. Metal fibers D. Plastic coating
4. How much tougher is nacre than its building blocks? A. 3 times B. 30 times C. 300 times D. 3,000 times
5. What is the problem with making ceramics? A. They are too soft B. They require high temperatures and emit much carbon C. They are too cheap D. They dissolve in water

Questions 6-10

Do the following statements agree with the information? Write TRUE, FALSE or NOT GIVEN.

6. Nacre is both strong and brittle.
7. Nacre is made of aragonite crystals.
8. Nacre has been easily manufactured synthetically.
9. Shu Yang uses 3D-printed scaffolds.
10. Natural ceramics form at very high temperatures.

Questions 11-13

Complete the summary. Choose ONE WORD ONLY.

Nacre is 99 percent ceramic but 1 due to proteins. The bricks overlap out of 2, increasing hydrogen bonds. Shu Yang grows ceramics on organic 3 at room temperature.

Answers

1. B 2. B 3. B 4. D 5. B
2. FALSE 7. TRUE 8. FALSE 9. TRUE 10. FALSE
3. tough 12. alignment 13. scaffolds

Key Vocabulary

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