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Análise termogravimétrica (ATG) Determinação de umidade em susbtâncias secas, de componentes voláteis e de cinzas.

Thermogravimetric analysis or thermal gravimetric analysis (TGA) is an analytical method that has been developed over a century ago and maintained its basic principles throughout its history. At its core, TGA determines the mass loss of a sample as a function of time, temperature and, if applicable, surrounding atmosphere.

Parameters which typically are measured via TGA are:

% Moisture

% Volatile

% Cinzas

% Lost on ignition

With advanced instrumentation and measurement techniques the precision of TGA measurements has significantly enhanced. As a result, TGA has solidified its status as an important analytical tool over the years.

In contemporary applications, this quantitative technique yields critical insights into the curing reactions and decomposition processes occurring during material heat treatment. TGA's versatility allows the examination of sample behaviour under both inert and oxidative conditions, depending on the equipment and methodology employed. This enables TGA to deliver temperature-dependent data on a wide array of physical phenomena, including phase transitions, adsorption, and desorption, as well as chemical processes like chemisorption, thermal decomposition, and solid-gas reactions such as oxidation and reduction.

Consequently, TGA stands as a vital method for understanding material properties and reactions under varying thermal conditions.

Thermogravimetric Analysis Principle

As the measuring principle of (automated) TGA is based on the change in mass as a function of temperature, the essential components of a thermogravimetric analysis instrument remain the same, regardless of which device is used: 

  • Thermal treatment of the samples requires a furnace chamber, which can vary in size and shape depending on the design of an analyser.
  • Built-in balance detects the weight of the sample at predefined time intervals.
  • An external gas supply is required if the measurements are to be carried out either under inert conditions or in an oxidative atmosphere. Combination of different gas environments is also conceivable, whereby in this case the device is set so that it switches between different gas environments depending on the measurement settings.
  • A connected computer with the corresponding software, which is designed to record and evaluate the collected measuring points.

The core concept of the thermogravimetric analysis is to measure how the weight of a material changes as it is heated, cooled, or held at a constant temperature. However, the behaviour of the sample does not depend exclusively on the temperature program used. The atmosphere in the sample chamber also has a decisive influence on the mass change mechanism. In an inert environment using gases such as nitrogen or argon, for example, materials lose weight as the temperature rises. This may involve evaporation, sublimation, dissociation, desorption or decomposition. The presence of a continuous gas flow in the furnace chamber prevents the possible occurrence of back reactions that could influence the result. In this way, samples can be tested for moisture content, volatile components or thermal stability. When thermogravimetric analysis (TGA) is conducted under oxidative conditions (oxygen atmosphere or air), this leads for the most part in more pronounced mass loss compared to inert conditions due to combustion or oxidation processes. The decomposition patterns of the material offer insights into its oxidative stability by observing the rate of the mass loss during the reaction. In addition, the residue obtained by oxidative reactions can provide information on inorganic components of the sample, such as ash content, for example. Overall, TGA under oxidative conditions provides information regarding material performance, stability, and safety in oxidative environments.

The functional principle of thermal gravimetric analysis using the ELTRA THERMOSTEP can be summarized as follows:

  • The initial sample weight is determined.
  • The sample is heated to a temperature range of 40 °C to 1,000 °C.
  • Based on the sample type, temperature, and atmosphere, the sample undergoes drying, oxidation, or loss of volatile components, leading to a reduction in weight (in rare cases an increasing of weight due to oxidation is possible).
  • When the mass of the sample remains constant under the selected conditions, it is again weighed, and the mass change is documented.

MAСRO vs. MICRO TGA

Most thermogravimetric analysis instruments available in the market fall into one of two categories: Micro or Macro TGAs. The main distinction between these categories is the size of the sample they are intended to analyse. Micro TGAs, which feature a smaller furnace chamber, are tailored for analysing samples in the range of micrograms to a few milligrams and usually measure only one sample simultaneously for TGA parameters. On the other hand, Macro TGAs, like the ELTRA THERMOSTEP, are designed to handle multiple larger samples, up to several grams each.

With a large furnace chamber multiple measurements can be carried out by Macro TGA simultaneously and larger sample quantities reduce measurement uncertainty due to potential inhomogeneity of the sample. For this reason, Macro TGAs are more suited for industrial applications or when the bulk properties of a material are of interest, whereas Micro TGAs are often used in research applications with studying materials only being available in small quantities. 

Coupled Techniques (mainly used in combination with MICRO TGAs): For enhanced detection and analysis of volatiles, thermogravimetric analysis (TGA) can be coupled with gas analysis techniques such as Fourier Transform Infrared Spectroscopy (FTIR), Mass Spectrometry (MS), or Gas Chromatography (GC). These techniques allow for the real-time analysis of gases evolved during the TGA run.

TGA-FTIR: Identifies functional groups in the evolved gases, providing insights into the composition of volatiles.

TGA-MS: Offers mass-to-charge ratio information, helping to identify the molecular structure of evolved gases.

TGA-GC: Separates the evolved gases, allowing for detailed compositional analysis.

 

Thermogram

Thermogram is a graphical representation of the obtained TGA measurement data that shows the relationship between the mass change of a sample and temperature or time under controlled conditions. Thermograms are unique for each compound and provide detailed insights into the thermal behaviour of materials, enabling the observation of decomposition, oxidation, dehydration, or other mass-altering reactions during thermal exposure. 

The Y-axis (vertical axis) in the diagram represents the sample weight, which can be displayed as either the percentage of the original mass remaining or the absolute mass in grams/milligrams. With proceeding analysis time, the change in the sample weight due to thermal treatment is plotted along this axis. Since the measuring principle of thermogravimetric analysis is based on weight change as a function of temperature and time, the X-axis (horizontal axis) therefore represents either temperature or time.

Interpretation of a Thermogram:

The thermogram generally consists of several consecutive sections of slopes and plateaus which allow the thermal behaviour of the respective materials to be analysed. 

Weight Loss (gain) Steps: As the sample is heated, it may undergo various processes such as dehydration (loss of water), decomposition (breakdown of the material), or oxidation (reaction with oxygen). These processes result in a decrease in the sample's mass, which appears as steps or slopes in the thermogram. It should be noted that in certain instances, particularly with metallic compounds, oxidation results in a higher oxidation state and an increase in the sample weight. 

 

An inert atmosphere, such as nitrogen or argon, is often used when the goal is to prevent oxidation or combustion of the sample. This environment is suitable for detecting the thermal decomposition products of the sample without interference from reactions with oxygen:

  • the first mass loss at temperatures around approx. 100°C is most likely due to the evaporation of water or residual solvents within the sample or on its surface.
  • at temperatures ranging from 200°C up to 600°C and sometimes even higher, thermal decomposition and release of volatile substances takes place.

 

 

 

An oxidative atmosphere (air or pure oxygen) is chosen when the interest lies in studying oxidative degradation or combustion products.

  • In the presence of oxygen or air materials may undergo oxidation, whereby this can already take place with temperatures starting at 100°C. Above approximately 300°C, organic substances experience oxidation, leading to a rapid decrease in mass, a process known as combustion. This is characterized by the emission of CO2 and various gases, resulting from the oxidation of the organic elements.

It is important to note that the exact temperatures and phenomena observed depend on the specific material type being analysed and on the experimental conditions.

 

 

Stability Regions: Flat regions or plateaus on the thermogram indicate temperatures where the sample's mass remains constant, suggesting thermal stability within that temperature range. 

Onset and Endset Temperatures: The temperatures at which a weight loss step begins, and ends are crucial for determining the thermal stability and decomposition temperatures of the material.

Comparado a medições não automatizadas com um forno mufla Vantagens da Análise Termogravimétrica (TGA)

Existem várias maneiras de realizar análises termogravimétricas, dependendo dos requisitos técnicos. Uma possibilidade é pesar cada amostra manualmente, colocá-la no forno de secagem ou mufla e depois pesá-la novamente. Se vários parâmetros precisam ser determinados (por exemplo, umidade e cinzas na farinha), são necessários vários fornos com diferentes temperaturas (105 °C e 550 °C), além de pesagens adicionais. Este método é bastante demorado. Uma alternativa muito mais conveniente e que economiza tempo é oferecida por instrumentos de análise termogravimétrica, como o TGA THERMOSTEP da ELTRA. Esses analisadores combinam forno e balança, permitindo a medição automatizada de uma variedade de parâmetros termogravimétricos. O usuário coloca várias amostras em cadinhos de cerâmica e as coloca no carrossel dentro do analisador, onde são pesadas pela balança integrada e analisadas automaticamente. De acordo com o programa selecionado, as amostras são secas ou reduzidas a cinzas até atingirem o peso constante desejado. Não é necessário realizar pesagem manual. Após a análise termogravimétrica ser concluída, os dados relevantes podem ser transferidos diretamente para um sistema de gerenciamento de informações de laboratório (LIMS).

Exemplo de uma medição automatizada de TGA

Também é possível executar um programa de análise complexa com um analisador termogravimétrico. Um exemplo: o carvão é seco a 105 °C (parâmetro: umidade), depois aquecido sob atmosfera de nitrogênio até 950 °C (parâmetro: componentes voláteis); após resfriamento até 750 °C, é queimado nesta temperatura sob atmosfera de oxigênio (parâmetro: cinzas). Todo o ciclo de análise é executado de forma totalmente automática, incluindo a documentação dos resultados da medição.

Thermogravimetric Analysis Applications and Industries

Due to its ability to precisely measure the mass change of a material as a function of temperature or time, thermogravimetric analysis (TGA) has become indispensable across a wide range of industries, being used for material characterization, quality control and research and development of novel products. TGA is thus carried out on a huge variety of samples, ranging from organic materials such as food, soil, wood, plastic and coal to inorganic materials such as cement or ceramics.


Energy sector

 

Coal, Biomass, Fuel Development: Quality control of coal, biomass and other fuels by analysing moisture, volatile content, combustible residue and ash content. Evaluating thermal behaviour and potential energy content.

Polymers and plastics industry, sealants

 

Studying thermal stability and degradation behaviour of polymers. Determination of compositional properties: filler content, polymer content, and moisture. 


Food industry

 

Determination of moisture and ash content and study of thermal properties in a wide range of food products.


Ciência ambiental

 

Análise dos componentes orgânicos e inorgânicos e avaliação do comportamento térmico e do potencial de conteúdo energético (como uma fonte potencial de energia alternativa) em vários tipos de resíduos.


Material science

 

Evaluating thermal stability and decomposition behaviour of ceramic, glass and advanced materials.


Indústria da construção

 

Análise de cimento e concreto: estabilidade térmica e comportamento de decomposição, determinação do teor de umidade. Análise da perda de CO2 de carbonatos no concreto. Betume: estudo do comportamento térmico e medição do teor de voláteis.


Wood

 

Wood: analysing thermal degradation patterns and determining the moisture, volatile and ash content.

Análise Elementar - FAQ

What is Thermogravimetric Analysis?

A análise termogravimétrica ou análise gravimétrica térmica (TGA) é um método analítico que mede a mudança de massa de uma amostra em função do tempo e da temperatura em uma atmosfera específica (inerte ou oxidativa). Este método é altamente sensível, tornando-se uma ferramenta importante para compreender uma ampla gama de propriedades e comportamentos de materiais durante o tratamento térmico. Ele fornece insights valiosos sobre reações de cura e processos de decomposição. Os parâmetros tipicamente medidos através da TGA incluem a porcentagem de umidade, substâncias voláteis, teor de cinzas e perda por ignição (LOI). Essas medições são cruciais para determinar a composição de um material, sua estabilidade térmica e seu comportamento durante o aquecimento, o que pode incluir fenômenos físicos (como transições de fase, adsorção e dessorção) e processos químicos (incluindo reações como oxidação e redução).

How does Thermogravimetric Analysis work?

Os instrumentos de análise termogravimétrica operam com base no princípio de medir e registrar mudanças de peso em um material à medida que ele passa por tratamento térmico em um ambiente controlado. Os componentes essenciais de um analisador TGA incluem uma câmara de forno para aquecer a amostra, uma balança integrada para medição de peso, um suprimento de gás externo para criar condições inertes ou oxidativas, e um computador com software para registrar e avaliar os dados. O peso da amostra é medido enquanto é aquecida, resfriada ou mantida a uma temperatura constante, sob condições inertes ou oxidativas, para obter informações sobre sua estabilidade térmica, teor de umidade, componentes voláteis e mais.

Why is Thermogravimetric Analysis important?

A análise termogravimétrica (TGA) é de grande importância em várias áreas de aplicações científicas e industriais, como o setor de energia, indústria alimentícia, indústria da construção, ciência ambiental e de materiais. Ela fornece dados importantes sobre a estabilidade térmica e a composição dos materiais. Ao compreender como um material se decompõe, reage ou muda de estado ao ser aquecido, pesquisadores e engenheiros podem tirar conclusões sobre sua capacidade de uso em determinadas áreas, sua durabilidade e como pode se comportar sob condições térmicas e atmosféricas variáveis. Na área de pesquisa e desenvolvimento, isso é essencial para projetar materiais com propriedades personalizadas, garantindo a segurança, eficiência e durabilidade desses novos produtos. Além disso, a TGA é uma ferramenta essencial para controle de qualidade. Ao garantir que os materiais atendam às suas propriedades térmicas e composição especificadas, os fabricantes podem manter a qualidade do produto, cumprir com os padrões regulatórios e evitar falhas potenciais durante a produção.

What are the advantages of Thermogravimetric Analysis compared to a muffle furnace?

Thermogravimetric analysis (TGA) offers several significant advantages over a muffle furnace. This includes automated measurement process, reducing the need for manual intervention such as weighing samples before and after heating. Unlike a muffle furnace thermogravimetric analysis instrument allows for continuous monitoring of mass change during the heating process, providing real-time measurement data. With pre-set material specific measurement applications automated analysis of samples at sequential specific temperature levels is possible.

Furthermore, TGA can operate under various controlled atmospheres (inert or oxidative). Control over the atmosphere is crucial for studying processes under inert conditions as well as oxidative or reductive behaviour of the materials. The TGA software can automatically calculate and present results such as moisture content, volatiles, ash content and loss on ignition (LOI), making the analysis process and the following calculation of the measured data easier for the operator.

Carbono / Nitrogênio Analisadores C-N

Carbono / Hidrogênio / Enxofre Analisadores C-H-S

Oxigênio / Nitrogênio / Hidrogênio Analisadores O-N-H

THERMOSTEP TGA Analisadores termogravimétricos

Analisadores Elementar


ELTRA offers elemental analyzers for a wide range of solid materials.


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