Today, most rockets are fueled by hydrazine, a toxic and hazardous chemical comprised of nitrogen and hydrogen. Those who work with it must be kitted up in protective clothing. Even so, around 12,000t of hydrazine is released into the atmosphere every year by the aerospace industry
Now, researchers are in the process of developing a greener, safer rocket fuel based on metal organic frameworks (MOFs), a porous solid material made up of clusters of metal ions joined by an organic linker molecule. Hundreds of millions of connections join in a modular structure.
Robin Rogers, formerly at McGill University, US, has worked with the US Air Force on hypergolic liquids that will burn when placed in contact with oxidisers, to try get rid of hydrazine. He teamed up with Tomislav Friščić at McGill who has developed ways to react chemicals ‘mechanochemically’ – without the use of toxic solvents.
The pair were interested in a common class of MOFs called zeolitic imidazole frameworks, or ZIFs, which show high thermal stability and are usually not thought of as energetic materials.
They discussed the potential of using ZIFs with the imidazolate linkers containing trigger groups. These trigger groups allowed them to take advantage of the usually not accessible energetic content of these MOFs.
The resulting ZIF is safe and does not explode, and it does not ignite unless placed in contact with certain oxidising materials, such as nitric acid, in this case.
Authorities continue to use hydrazine because it could cost millions of dollars to requalify new rocket fuels, says Rogers. MOF fuel would not work in current rocket engines, so he and Friščić would like to get funding or collaborate with another company to build a small prototype engine that can use it.
2019 has been declared by UNESCO as the Year of the Periodic Table. To celebrate, we are releasing a series of blogs about our favourite elements and their importance to the chemical industry. Today we look at arsenic and some of its effects.
What is arsenic?
Arsenic is a chemical element found in nature – low levels of arsenic are found in water, air and soil – in man-made products. As arsenic is distributed throughout the environment, people have high exposure to elevated levels of inorganic arsenic through contaminated drinking water, as well as exposure to arsenic through oceans, food and insecticides.
Is arsenic harmful?
Arsenic can occur in an organic and inorganic form. Organic arsenic compounds are less harmful to our health, whereas, inorganic arsenic compounds (e.g those found in water) are carcinogens, which are highly toxic and dangerous. Arsenic contamination of groundwater has led to arsenic poisoning which affects the skin, liver, lungs and kidneys.
Prominently, arsenic has attracted much attention in Bangladesh, as 21.4% of all the deaths in a highly affected area were caused by levels of arsenic surpassing WHO’s provisional guideline value of 10 μg/L.
Long-term exposure to low doses of arsenic can cause a negative interference in the way cells communicate, which may minimise their ability to function, subsequently playing a role in the development of disease and causing an increase in health risks.
For example, cells use phosphate to communicate with other cells, but arsenate, which is one form of arsenic, can replace and imitate phosphate in the cell. This damages cells so they can not generate energy and impairs the ability of cells to communicate.
The health risks of arsenic in drinking water. Video: EnviroHealthBerkeley
Symptoms of arsenic poisoning can be acute, severe or chronic depending on the period of exposure and method of exposure. Symptoms may include vomiting, abdominal pain and diarrhoea, and long-term exposure can lead to cancers of the bladder and lungs.
Certain industries may face exposure to arsenic’s toxicity, but the maximum exposure to arsenic allowed is limited to 10 micrograms per cubic metre of air for every 8-hour shift. These industries include glass production, smelting, wood treatment, and the use of pesticides. Traces of arsenic can also be found in tobacco, posing a risk to people who smoke cigarettes and other tobacco products.
A global threat
Arsenic is naturally found in the Earth’s crust and can easily contaminate water and food.
WHO has ranked arsenic as one of the top 10 chemicals posing a huge threat to public health. WHO is working to reduce arsenic exposure, however, assessing the dangers on health from arsenic is not straightforward.
As symptoms and signs caused by long-term exposure to inorganic arsenic varies across population groups, geographical regions, as well as between individuals, there is no universal definition of the disease caused by this element. However, continuous efforts and measures are being made to keep concentrations as low as possible.