Thermogravimetric analysis

Scientists use a special tool to study things.

It works like a tiny scale inside a hot oven. We put a sample on the scale. Then, we make the heat go up. As things get hot, they might change. Some things might lose weight. This happens when they burn or break apart. We watch the weight and the heat. This helps us see how strong a material is. It can even help us study new metals for space!

Scientists use a tool called a thermogravimetric analyzer.

This tool helps us study how materials change with heat. It works like a tiny scale inside a hot oven. The scale is a precision balance. It measures the mass, or weight, of a sample. A furnace heats the sample up. Scientists can change the heat at a steady rate. They can also change the air around the sample. They might use a vacuum or special gases.

As the sample gets hot, it may change. It might break apart or burn. These changes often cause the sample to lose weight. This is called thermal decomposition. Scientists use a TGA curve to see these changes. This is a graph that shows weight over time.

This tool is very useful for many things. It helps us study polymers. Polymers are materials like plastics, paints, and fuels. TGA shows if a polymer is thermally stable. This means it can stay strong even when hot. NASA uses TGA to study copper alloys. They want to find metals for engines in space. They need to know if the metal will stay strong in oxygen.

Thermogravimetric analysis, or TGA, is a clever way to study materials.

It helps scientists see how things change when they get hot. By measuring mass, or weight, over time, we learn a lot. This method shows us physical changes like absorption or desorption. It also shows chemical changes like thermal decomposition. Thermal decomposition is when a substance breaks down because of heat. This tool is vital for understanding how many different materials behave.

How does this work step by step? A scientist puts a sample into a small pan. This pan sits on a precision balance inside a furnace.

The furnace heats the sample as the temperature changes. This can happen at a steady rate. The machine also controls the atmosphere around the sample. It might use air, a vacuum, or special gases. The balance continuously weighs the sample during this whole process.

Scientists use different types of TGA for different jobs. Isothermal TGA keeps the temperature the same while weighing the sample. Quasistatic TGA raises the temperature in separate, steady steps. Dynamic TGA heats the sample in a continuous, linear way.

These methods help create a TGA curve. This curve is a graph of mass versus temperature or time. It helps us see exactly when a material begins to degrade. We can even use a DTG curve to find specific points of interest.

This tool is very useful for studying polymers. Polymers include things like plastics, paints, and even fuels.

Most polymers melt or break down before 200 °C. However, some special polymers can withstand 300 °C in air. Other stable polymers can reach 500 °C in inert gases. TGA also helps NASA study copper alloys. NASA wants to use these alloys in combustion engines. They need to know if the metal stays strong in oxygen.

Many scientists use TGA along with other tools. It can be paired with mass spectrometry for gas analysis. This lets researchers measure the weight of each part that breaks off. TGA can reach temperatures as high as 1000 °C. Some other tools, like DTA, can go even higher to 1600 °C. While TGA measures weight, DTA measures temperature differences. Both tools help us understand the amazing world of materials.

Thermogravimetric analysis, often called TGA, is a vital method of thermal analysis. It allows scientists to measure the mass of a sample as the temperature changes over time. This process reveals how materials react to heat through physical or chemical changes. Physical phenomena include phase transitions, absorption, adsorption, and desorption. Chemical phenomena include chemisorptions, thermal decomposition, and solid-gas reactions like oxidation or reduction. By tracking weight changes, researchers can understand the fundamental nature of a substance.

The mechanism of TGA relies on a specialized instrument called a thermogravimetric analyzer. This device contains a precision balance and a sample pan. The pan is placed inside a furnace that has programmable temperature controls. As the furnace heats the sample, the balance continuously measures its mass. The temperature usually increases at a constant rate to trigger a thermal reaction. Scientists can also control the atmosphere surrounding the sample during this process. They might use ambient air, a vacuum, or inert gases. Other options include oxidizing, reducing, corrosive, or carburizing gases. They may even use liquid vapors or a self-generated atmosphere.

There are three distinct types of thermogravimetry used depending on the research goal. The first is isothermal or static thermogravimetry. In this method, the sample weight is recorded at a constant temperature over time. The second type is quasistatic thermogravimetry. This technique raises the temperature in sequential steps. These steps are separated by isothermal intervals where the mass reaches stability. The third type is dynamic thermogravimetry. In this approach, the sample is heated in an environment where the temperature changes in a linear manner.

Data from these tests is compiled into a TGA curve. This is a plot where the y-axis shows mass or the percentage of initial mass. The x-axis represents either temperature or time. Scientists often use the first derivative of this curve, known as the DTG curve. The DTG curve helps determine inflection points for deeper interpretations. This data is essential for materials characterization through decomposition patterns. It allows researchers to see exactly how and when a material loses its structure.

One major application of TGA is evaluating thermal stability. If a species is thermally stable, there will be no observed mass change in a specific temperature range. A lack of slope in the TGA trace indicates little or no mass loss. TGA also identifies the upper use temperature of a material. Beyond this point, the material will begin to degrade. This is especially useful for studying polymers like thermoplastics, thermosets, and elastomers. Most polymers melt or degrade before reaching 200 °C. However, some thermally stable polymers can withstand 300 °C in air. In inert gases, these special polymers can reach 500 °C without losing strength.

NASA uses TGA for important research on advanced copper alloys. They are studying these alloys for possible use in combustion engines. Scientists must check for oxidative degradation, which occurs when copper oxides form in oxygen-rich atmospheres. Understanding resistance to oxidation is vital because NASA wants to reuse shuttle materials. TGA can also detect inconsistencies in materials like unpurified carbon nanotubes. If these nanotubes contain metal catalysts, they may undergo combustion. This causes a rapid temperature change and a dramatic slope change in the DTG plot. Such deviations can help diagnose if a sample is anisotropic. For example, testing the top and bottom of a sample can reveal if particles have undergone sedimentation.

Finally, TGA is often used in combination with other analytical methods. It can be coupled with Fourier-transform infrared spectroscopy (FTIR) and mass spectrometry. This allows for gas analysis as the sample decomposes. The analyzer can heat samples to temperatures as high as 1000 °C during these tests. This helps measure the weight percentage of each resulting mass change. While TGA measures weight, another method called Differential Thermal Analysis (DTA) measures temperature differences. DTA can reach higher temperatures, sometimes as high as 1600 °C. Together, these tools provide a complete picture of how matter behaves under heat.