Carbon/Sulfur & Oxygen/Nitrogen/Hydrogen Analysis

Index

Principle

History of EMIA/EMGA

Key components

Pro's and Con's of EMIA/EMGA analyzers

Principle

C/S analyzers refers to products that measure Carbon and Sulfur in inorganic materials. Alternative denomination is Elemental Analyzers even if only 2 elements are measured. ISO standards talk about Infrared Absorption Method after combustion. HORIBA uses the acronym EMIA, which stands for Element Material Infrared Analyzer.

O/N/H analyzers refers to products that measure Oxygen, Nitrogen, and Hydrogen in inorganic materials. Depending on the model, 1, 2 or 3 gases are measured.  Alternative denomination is also Elemental Analyzers. ISO standards describe the principle as Inert Gas Fusion Technique. HORIBA uses the acronym EMGA, which stands for Element Material Gas Analyzer.

C/S & O/N/H analyzers measure inorganic solid samples such as small blocks, chips, powders or granulates. The principle of these instruments is to heat the sample to very high temperature to ensure complete combustion and to carry the gases generated to detectors where the elements will be measured. Therefore, EMIA & EMGA combine high performance furnaces and specific detection systems.

For EMIA, a flow of Oxygen is used to carry CO, CO2 and SO2 to the detection system while for EMGA a flow of inert gas is used to carry H2, N2 and CO (produced with reaction of oxygen with a graphite crucible).

There are 3 different types of furnaces depending on the instrument and the application:

  • Resistance furnace (EMIA): The sample is placed into a ceramic boat and slowly heated. This type of furnace allows for precise temperature control. It is preferred to differentiate accurately the element from the surface and from the bulk of the material as it allows for very precise temperature control.
  • Induction furnace (EMIA): The sample is introduced into a ceramic crucible, mixed with accelerators to facilitate combustion and heated by induction. If the exact temperature in the crucible is not known with this type of furnace, it remains possible to control the applied current and to adjust it to optimize the method. It is preferred for total carbon measurement and high throughput.
  • Impulse furnace (EMGA): The sample is introduced into a graphite crucible that is placed between 2 electrodes. A very high current is generated and maintained to melt the sample and generate gases. The output current of the furnace is monitored and can be automatically optimized to separate surface contamination from bulk content.


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The table below summarizes the principle for each element and instrument.

ElementCarrier gasFurnaceCruciblePrincipleDetection techniqueModel
CO2InductionCeramic crucibleOxidation / Generates CO and CO2

NDIR

EMIA Pro / Expert
ResistanceCeramic boatEMIA Step
SO2InductionCeramic crucibleOxidation / Generates SO2NDIREMIA Pro / Expert
ResistanceCeramic boatEMIA Step
OHeImpulseGraphite crucibleInert gas fusion, reduction / Generates CO and CO2NDIREMGA 930/920
NHeGraphite crucibleInert gas fusion, reduction / Generates N2TCDEMGA 930/920
HHeGraphite crucibleInert gas fusion, reduction / Generates H2 + conversion to H2ONDIREMGA 930
ArGraphite crucibleInert gas fusion, reduction / Generates H2TCDEMGA 921


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Below are synopsis of EMIA and EMGA instruments

EMIA C/S analyzer synopsis

EMIA C/S analyzer synopsis

EMGA O/N/H analyzer synopsis

EMGA O/N/H analyzer synopsis

EMGA H analyzer synopsis

EMGA H analyzer synopsis

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History of EMIA/EMGA

C/S & O/N/H analyzers are strongly needed in metallurgical laboratories as these 5 elements are critical for materials’ performance and lifetime and as no alternative technique is able to reach the expected levels of sensitivity and accuracy and is able to cope with the fast analysis time related to the manufacturing environment.

The EMIA and EMGA Series were developed in the 80’s by HORIBA as an answer to Japanese steel manufacturers asking for high reliability instruments for their plants. Based on its core technology of gas analyzer as a worldwide leader in gas analysis for automotive and environment, and combined with advanced electric furnaces, HORIBA started to provide instruments for metallurgy. HORIBA has now a 40 years long experience in providing high-end instruments that ensure high performance, ease-of-use along with reliability and are used not only for metallurgical applications but also for semiconductor, battery materials, ceramics, glass, catalysts, solders, rare earths, electrical components and more.

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Key components

EMIA and EMGA consist in the generation of gases from the sample under specific conditions and in the measurement of the gases emitted using NDIR or TCD. Key components are the furnace that is the source for gas generation and the detectors allowing the measurement of these gases.

Furnace

There are 3 types of furnaces used for gas generation on EMIA and EMGA. Carbon and Sulfur can be analyzed using induction or resistance furnace. Oxygen, Nitrogen and Hydrogen are using an impulse furnace. Below is a description of these different furnaces.

Induction furnace

The ceramic crucible in which the sample and accelerators are introduced is surrounded by an induction coil. Heating is performed by electromagnetic induction under a flow of oxygen and high temperature is reached, typically over 2300°C. The reaction of carbon and sulfur with oxygen at high temperature generates CO, CO2 and SO2.

The exact temperature of the sample is not known with an induction furnace, however it is possible to control the applied current and change it during an analysis cycle to optimize the measurement.

The following example illustrates this function and shows a steel sample polluted with base oil. The Temperature curve in red refers to the applied current. A low temperature level is set to release the carbon from the surface of the sample that is due to contamination and a higher level for the analysis of the bulk carbon and sulfur after steel is melted.

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Resistance furnace

The sample is placed into a ceramic boat that is positioned in the middle of a horizontal furnace where temperature is uniform. Heating can be done up to 1450°C and is performed using a resistance and a thermocouple for temperature control. In a resistance furnace the exact temperature at the sample is controllable and can be changed during a measurement. As for the induction furnace, heating is done in a flow of oxygen and the reaction of carbon and sulfur with oxygen at high temperature generates CO, CO2 and SO2.

In a resistance furnace, the sample can be slowly burned and programmable temperature curves can be set up. This allows to precisely separate signal from elements of the surface and of the bulk of a material.

Typical applications for resistance furnace include toner for copy machines or the measurement of free carbon in Silicon Carbide.

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Impulse furnace

Impulse furnace is used for O/N/H analyzers. The sample is placed in a graphite crucible that is positioned between 2 electrodes. A very high current is generated and maintained by a series of voltage pulses to melt the sample and the eventual fluxes inside the crucible. The crucible itself conducts electricity but does not melt as carbon sublimes at 5800°K only, higher than the melting temperature of all metals including W.

Surrounded by inert gas in the graphite crucible, elemental hydrogen H and oxygen O are reduced to H2 and O2 gases while the Oxygen reacts with the carbon from the crucible and generates CO.

The output current of the impulse furnace is monitored and it can possibly be changed during an analysis sequence to optimize the method and perform separation of surface contamination from bulk content or for the identification of different forms of the elements as shown in the example below.

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Monitoring the output current of the impulse furnace
Monitoring the output current of the impulse furnace.

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Non-dispersive infrared detector (NDIR)

Detection

EMIA and EMGA are using non-dispersive infrared detector (NDIR) and thermal conductivity detector (TCD).

Non-dispersive infrared detector (NDIR)

The main components of an NDIR sensor are an infrared light source, a sample chamber (cell), an optical filter and an infrared detector.

The gas in the sample chamber causes absorption of specific wavelengths according to the Beer–Lambert law, and the attenuation of these wavelengths intensity is measured by the detector to determine the gas concentration.

Carbon Monoxide Infrared Spectrum

An optical filter isolates the wavelength absorbed by the gas molecule of interest. The signal from the source is chopped or modulated to offset thermal background signals from the desired signal. NDIR detectors are used for CO2, CO, SO2 and H2O (when H is to be measured by NDIR). For CO2, two detectors are used with two optimum filters to measure both low and high concentrations with the best accuracy possible.

NDIR is a core technology of HORIBA who has pioneered NDIR analyzers to provide market leader instruments. It is currently used in multiple instruments covering a wide range of applications: Motor Exhaust Gas Analyzers, Ambient NOx Monitors and Stack Gas Analyzers.

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Thermal Conductivity Detector (TCD)

A TCD is using a Wheatstone bridge (see schematic below).

The reference cell is filled with the carrier gas only, the sample cell will see a change when the combustion takes place and the measured gas is carried and introduced in it.  

TCD has no selectivity – only a change in resistivity is measured. If more than one gas is introduced in the cell the measurement will be the result of changes in resistivity from all gases. Any gas that is not of interest must be carefully filtered prior detection to ensure accurate and reliable results.

TCD is used for measurement of N2 and can be used for H2, especially for applications requiring high sensitivity. 

The principle of operation requires that the measured gas and the carrier gas have very different conductivities for optimum sensitivity. Helium is required for the determination of nitrogen since argon thermal conductivity is too close to provide good sensitivity (see table below). The use of argon will lead to 100 times less sensitivity. For dedicated Hydrogen analyzer, argon is used as the difference is greater than with helium. The sensitivity by using TCD for H2 is better by a factor of at least 10 which explains why the TCD is the technique of choice for low hydrogen detection in the most demanding applications.

GasThermal conductivity (k/10-4Wm-1K-1)
He (as carrier)1649
N2 (target)294
Ar (as carrier)201
H2 (target)2033
A TCD is using a Wheatstone bridge.

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Pro's and Con's of EMIA/EMGA analyzers

EMIA and EMGA analyzers are unique as elemental analyzers as there is no technique able to provide analysis of C/S, O/N and H with such sensitivity and within few minutes. For example, ED-XRF cannot measured O, N and C and WD-XRF can measure C at % levels only. ICP-OES can determine about 70 elements of the periodic table but not C, O, N and H. Spark-OES instruments cannot measure H accurately and are not reaching the performance of EMIA and EMGA for both low and high levels of concentration.

EMIA and EMGA are flexible and can accept samples as powders, chips, small blocks or granulate and about 1g or less of sample is enough to perform the analysis. They provide high sensitivity and accuracy on a large dynamic range.

The EMIA Pro and Expert analyzers from HORIBA Scientific provides a unique design with a dustless furnace for improved MTBM (Mean Time Between Maintenance) allowing for up to 200 measurements without cleaning. The system provides also a higher throughput than standard instrument with a complete measurement cycle in 70 seconds and, thanks to a user-oriented design, a fast and easy maintenance, typically half of conventional models.

The EMIA Step is equipped with a newly designed dust filter providing easy maintenance, about 5 times faster than with conventional systems, as the dust doesn’t adhere to the piping after the furnace. In addition to facilitating maintenance, this system improves accuracy and sensitivity.

The EMGA Series is equipped with a dual sample/flux introduction mechanism allowing out-gassing of the flux at low temperature prior to the analysis. As a result, optimization of flux efficiency and blank reduction contribute to high accuracy measurements.

In addition, for both EMIA and EMGA, different levels of automation and accessories are available, from autosampler for unattended operation to the halogen trap for samples containing halogen elements such as Cl or Br.

A limitation of EMIA and EMGA is that they are not designed to handle liquid samples and cannot perform measurement of organic C, S, O, N and H.

Also, such instruments are not designed to perform measurements on the field or close to process and having them in transportable laboratory lead to an expensive solution due to the need of gases and high electrical current

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