New Concrete Incorporates And Reduces Carbon Dioxide Emissions

Concrete surrounds us in our cities and stretches across the land in a vast network of highways. It’s so ubiquitous that most of us take it for granted, but many aren’t aware that concrete’s key ingredient, ordinary portland cement, is a major producer of greenhouse gases. Each year, manufacturers produce around 5 billion tons of portland cement — the gray powder that mixes with water to form the “glue” that holds concrete together. That’s nearly three-quarters of a ton for every person on Earth. For every ton of cement produced, the process creates approximately a ton of carbon dioxide, all of which accounts for roughly 7 percent of the world’s carbon dioxide emissions. And with demand increasing every year — especially in the developing world, which uses much more portland cement than the U.S. does — scientists are determined to lessen the growing environmental impact of portland cement production.

One of those scientists is Gaurav Sant of the California NanoSystems Institute at UCLA, who recently completed research that could eventually lead to methods of cement production that give off no carbon dioxide, the gas that composes 82 percent of greenhouse gases. Sant, an associate professor of civil and environmental engineering and UCLA’s Edward K. and Linda L. Rice professor of materials science, found that carbon dioxide released during cement manufacture could be captured and reused.

For every ton of cement produced, the process creates approximately a ton of carbon dioxide, all of which accounts for roughly 7 percent of the world’s carbon dioxide emissions.

The reason we have been able to sustain global development has been our ability to produce portland cement at the volumes we have, and we will need to continue to do so,” Sant said. “But the carbon dioxide released into the atmosphere creates significant environmental stress. So it raises the question of whether we can reuse that carbon dioxide to produce a building material.

During cement manufacturing, there are two steps responsible for carbon emissions. One is calcination, when limestone, the raw material most used to produce cement, is heated to about 750 degrees Celsius. That process separates limestone into a corrosive, unstable solidcalcium oxide, or lime — and carbon dioxide gas. When lime is combined with water, a process called slaking, it forms a more stable compound called calcium hydroxide.

And the major compound in portland cement is tricalcium silicate, which hardens like stone when it is combined with water. Tricalcium silicate is produced by combining lime with siliceous sand and heating the mixture to 1,500 degrees Celsius. Of the total carbon dioxide emitted in cement manufacturing, 65 percent is released when the limestone is calcined and 35 percent is given off by the fuel burned to heat the tricalcium silicate compound.

But Sant and his team showed that the carbon dioxide given off during calcination can be captured and recombined with calcium hydroxide to recreate limestone — creating a cycle in which no carbon dioxide is released into the air. In addition, about 50 percent less heat is needed throughout the production cycle, since no additional heat is required to ensure the formation of tricalcium silicate.

The study is published in the journal Industrial and Engineering Chemistry Research.


Worlds Like Earth Common In The Cosmos

A new way of studying planets in other solar systems – by doing sort of an autopsy on planetary wreckage devoured by a type of star called a white dwarf – is showing that rocky worlds with geochemistry similar to Earth may be quite common in the cosmos. Researchers studied six white dwarfs whose strong gravitational pull had sucked in shredded remnants of planets and other rocky bodies that had been in orbit. This material, they found, was very much like that present in rocky planets such as Earth and Mars in our solar system. Given that Earth harbors an abundance of life, the findings offer the latest tantalizing evidence that planets similarly capable of hosting life exist in large numbers beyond our solar system.

The more we find commonalities between planets made in our solar system and those around other stars, the more the odds are enhanced that the Earth is not unusual,” said Edward Young, a geochemistry and cosmochemistry professor at the University of California, Los Angeles (UCLA), who helped lead the study published in the journal Science. “The more Earth-like planets, the greater the odds for life as we understand it.”

The first planets beyond our solar system, called exoplanets, were spotted in the 1990s, but it has been tough for scientists to determine their composition. Studying white dwarfs offered a new avenue.

A white dwarf is the burned-out core of a sun-like star. In its death exoplanets, the star blows off its outer layer and the rest collapses, forming an extremely dense and relatively small entity that represents one of the universe’s densest forms of matter, exceeded only by neutron stars and black holesPlanets and other objects that once orbited it can be ejected into interstellar space. But if they stray near its immense gravitation field, they “will be shredded into dust, and that dust will begin to fall onto the star and sink out of sight,” said study lead author Alexandra Doyle, a UCLA graduate student in geochemistry and astrochemistry.

This is where that ‘autopsy’ idea comes from,” Doyle added, noting that by observing the elements from the massacred planets and other objects inside the white dwarf scientists can understand their composition.


How To Create Electricity From Snowfall

Researchers from University of California at Los Angeles (UCLA) and colleagues have designed a new device that creates electricity from falling snow. The first of its kind, this device is inexpensive, small, thin and flexible like a sheet of plastic.

The device can work in remote areas because it provides its own power and does not need batteries,” said senior author Richard Kaner, who holds UCLA’s Dr. Myung Ki Hong Endowed Chair in Materials Innovation. “It’s a very clever device — a weather station that can tell you how much snow is falling, the direction the snow is falling, and the direction and speed of the wind.”

The researchers call it a snow-based triboelectric nanogenerator, or snow TENG. A triboelectric nanogenerator, which generates charge through static electricity, produces energy from the exchange of electrons.

Static electricity occurs from the interaction of one material that captures electrons and another that gives up electrons,” said Kaner, who is also a distinguished professor of chemistry and biochemistry, and of materials science and engineering, and a member of the California NanoSystems Institute at UCLA. “You separate the charges and create electricity out of essentially nothing.”

Snow is positively charged and gives up electrons. Silicone — a synthetic rubber-like material that is composed of silicon atoms and oxygen atoms, combined with carbon, hydrogen and other elements — is negatively charged. When falling snow contacts the surface of silicone, that produces a charge that the device captures, creating electricity.

Snow is already charged, so we thought, why not bring another material with the opposite charge and extract the charge to create electricity?” said co-author Maher El-Kady, a UCLA assistant researcher of chemistry and biochemistry.

While snow likes to give up electrons, the performance of the device depends on the efficiency of the other material at extracting these electrons,” he added. “After testing a large number of materials including aluminum foils and Teflon, we found that silicone produces more charge than any other material.”

Findings about the device are published in the journal Nano Energy.