Chinese scientists on Monday unsealed a box of solid lubricant samples that were aboard the Shenzhou-7 spacecraft. They will study the material for the next six months.

"Two types of solid lubricant samples, after being exposed to outer space during the Shenzhou-7 mission, had shown obvious changes," said Liu Weimin, head of the Lanzhou Institute of Chemical Physics of the Chinese Academy of Sciences in northwest Gansu Province.

"The appearance of the two types of samples has either turned dark or become rougher," he said.

Solid lubricants are widely used in spacecraft to reduce friction because they withstand high temperatures.

Scientists hoped to improve the stability and lifetime of the materials by studying the test samples taken to outer space.

Liu said scientists would compare the samples with those exposed to a simulated space environment in the laboratory.

"We need to know how the lubricants react to being in a vacuum, atomic oxygen and low temperatures in outer space," he said.

If scientists discover the difference between the two exposed lubricants, they might be able to tell how other materials change in outer space, Liu said.

The solid lubricant samples, loaded outside the Shenzhou-7 capsule and retrieved by astronaut Zhai Zhigang during his spacewalk, weighed about 2.2 kg. They were exposed to outer space for 44 hours.

The Shenzhou-7 space module, carrying three taikonauts, landed safely by parachute on Sept. 28 in China's northern grasslands after a 68-hour flight. The mission included the first ever spacewalk by a Chinese astronaut.