How Clean Combustion Provides Better Data Quality and Uptime

Inorganic materials, such as ceramics, cement or metals have properties that are affected by alloying or impurity elements. To illustrate, the hardness of steels, tensile strength, or other mechanical characteristics can be adapted by altering the concentration of carbon.

Moreover, sulfur-based contamination can also cause steels to become brittle, thus, it is vital that levels of carbon and sulfur can be precisely measured in such materials.

The most common process with which to calculate quantities of carbon and sulfur atoms in inorganic materials is known as the combustion method. This mode of analysis is based on the transformation of carbon and sulfur atoms into carbon dioxide and sulfur dioxide gases, identified using infrared sensors, following exposure to oxygen.

Induction heating, alongside accelerators like iron and tungsten, is used to achieve the very high required sample temperature of approximately 2,000 °C.

Conversely, traditional CS analyzers suffer face problems relating to the development of excessive levels of dust and fragments. These fragments are sputtered from the melt, which sticks to the top layer of the combustion tube. Additionally, tungsten oxide dust is created through the exothermic oxidation of tungsten, in which the gas flow is tainted and data quality is negatively affected.

This leads to the need for tiresome cleaning sessions, even with the use of autocleaners. As part of the time-consuming process of their manual cleaning, which must be undertaken at frequent intervals, autocleaner units must be broken down into their singular parts.

The inductar CS cube eliminates the need for these lengthy periods spent cleaning, with a pioneering design-build that offers clean combustion, a better quality of data, and a reduction in system downtime.

 

Clean Combustion

There are two inventive ideas behind the inductar CS cube’s ability to reduce dust and debris to minimum levels. To begin with, the ceramic crucibles feature distinctive shaping which differentiates them for crucibles used in comparable CS-analyzers (Figure 3).

The height and slenderness of the form ensure that melt droplets cannot be sputtered out of the ceramic crucible. This results in a longer lifespan for the glass combustion tube surface, as it is protected from exposure to sputter particles. Dust, meanwhile, is largely retained inside the ceramic cups.

In addition to this, the inimitable top-down carrier gas flow drives dust into the ceramic cups, and the sheath gas flow created shields the surface of the combustion tube. This keeps it almost clear of dust and debris (Figure 1). Time-consuming cleaning processes are kept to a minimum through this clever design which ensures debris and dust are held within the sample container.

As a result of the gas flow design of the inductar CS cube, along with the unique crucible, only low levels of thine dust are moved by the transporter gas. The adsorption of sulfur dioxide molecules by these metal oxide particles may lead to reduced measurement values and thus, a reduced accuracy of results.

To this end, a heated dust filter is mounted, which improves data quality levels by protecting the analytical gas stream from dust. The filter’s precise temperature can be adapted, allowing the ideal setting to be chosen by the user.

The dust filter may require cleaning after a number of cycles have been carried out, however, as with other upkeep on this system, this job can be carried out without tools and in seconds. The ability to carry out maintenance simply and rapidly allows for the greatest levels of system uptime, as well as being convenient for users.

Schematic picture of the gas flow in and around the ceramic crucible during combustion.

Figure 1. Schematic picture of the gas flow in and around the ceramic crucible during combustion.

Functional principle of the inductar CS cube.

Figure 2. Functional principle of the inductar CS cube.

Comparison of the advanced sample crucible of Elementar with a standard crucible.

Figure 3. Comparison of the advanced sample crucible of Elementar with a standard crucible.

Measurement Principle

In contrast to similar devices, a robotic arm is used to automatically slot the ceramic crucibles into the analyzer from the top. The ceramic cups are packed with samples made up of particles, chips or drillings. Additionally, the oxygen carrier gas current moves in a downward stream.

In this manner, a sheath gas flow is generated, which reduces the sticking of dust and fragments on the combustion tube to minimum levels. Moreover, the height of the ceramic crucible walls ensures minimum levels of sputtering of debris, resulting in clean combustion.

A programmable solid-state induction furnace is used to heat the samples to extremely hot temperatures. Following this, carbon and sulfur atoms mix with oxygen to become carbon monoxide, carbon dioxide, and sulfur dioxide.

A moisture trap and heated dust-trap cleanse the gas flow before it passes a wide-range IR sensor, which calculates the levels of sulfur dioxide in the gas flow (Figure 2). Therefore, the sulfur dioxide levels measured provide the data to calculate the concentration of sulfur atoms within the sample.

Following this, an additional furnace is used to oxidize sulfur dioxide and carbon monoxide, forming sulfur trioxide and carbon dioxide. A sulfur trioxide trap is used to eliminate sulfur trioxide from the gas flow.

Finally, a further wide-range IR detector is used to measure the concentration of carbon dioxide and to thus, determine the total quantity of carbon atoms within the sample. On finishing, the ceramic crucible is automatically detached from the device.

Experimental

To show the lasting steadiness of the inductar CS cube, 200 cycles have been carried out in sequence, requiring no contact with the instrument beyond refilling the autosampler. An integrated 89-position autosampler was used, allowing the operation of the inductar CS cube without a user in attendance.

For the samples, a weight of 0.5 g was measured into the ceramic crucibles followed by 2 g of W/Sn accelerator. These crucibles were positioned on the automatic sample feeder and a sequence of several analyses was begun.

The samples were automatically examined by the inductar CS cube and additional samples were weighed by the user at the same time. Some 200 samples were analyzed in an 8.5 hour period. With an additional 89 analyses carried out overnight, a single operator can thus analyze 289 samples in just one day.

This is made possible with the greatly reduced need for maintenance work, now requiring just three minutes each in the morning and afternoon.

Sample throughput and work scheme for the inductar CS cube.

Figure 4. Sample throughput and work scheme for the inductar CS cube.

Results

The built-in optical camera offers a qualitative analysis of the level of dust and debris which leaves the ceramic crucibles. In Figure 5, the combustion tube can be seen prior to the first analysis, following 10 cycles, and following 200 cycles. It is easy to see that extremely low quantities of dust and no sputter particles at all adhere to the surface of the combustion tube. This endorses the effective and dependable minimization of dust and debris within the system on a qualitative level.

As well as examining the visual effects, a qualitative examination was also used to confirm the consistent and clean combustion by examining the analysis data. The carbon and sulfur levels of a variety of materials for the measurement series of 200 successive analyses can be seen in Figure 6.

To demonstrate this more clearly, from 200 analyses, the outcomes of just five consecutive analyses at intervals of 50 cycles are plotted against cycle numbers. These values can all be seen to fall within a slender range, endorsing the reliability of the carbon and sulfur values.

The creation of dust and debris would lead to adsorption of gaseous sulfur dioxide molecules at the surface of fine metal oxide particles. Therefore, when the dust is created, it could be expected that there would be lower sulfur concentrations with a higher cycle number.

However, the lack of any pattern with higher cycle numbers verifies that the determination of carbon and sulfur is not affected by metal oxide dust. These strongly reproducible results endorse the steady and consistent combustion process over longer timeframes.

The combustion tube of the inductar CS cube after 0, 10 and 200 cycles.

Figure 5. The combustion tube of the inductar CS cube after 0, 10, and 200 cycles.

Time series of carbon and sulfur content of different materials analyzed with the inductar CS cube. The solid line depicts the average C or S concentration for the complete time series, the dashed lines the 3 sigma standard deviation of the measurements.

Figure 6. Time series of carbon and sulfur content of different materials analyzed with the inductar CS cube. The solid line depicts the average C or S concentration for the complete time series, the dashed lines the 3 sigma standard deviation of the measurements.

Summary

This demonstration showed that over 200 analyses can be carried out without the need for any tiresome cleaning processes. The dust and fragments which are formed in the combustion process are largely captured within the sample container. Subsequently, an autocleaner unit is superfluous, as they have a tendency to fail and necessitate further manual cleaning.

A heated dust filter effectively filters the fine dust, which is transported by the carrier gas. This guarantees a high purity analytical gas stream and leads to reliable and accurate results. This reduction in dust and fragments not only improves the measurement results but also minimizes the need for time-consuming cleaning processes.

All Elementar instruments employ a distinctive tool-free clamp connection system, which allows maintenance to be carried out simply and quickly, making the inductar CS cube not only immensely user-friendly but also extremely reliable, with minimal system downtime.

The study and dependable automated sample feeder allow for completely automatic use without user attendance, offering the greatest working efficiency.

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This information has been sourced, reviewed and adapted from materials provided by Elementar Analysensysteme GmbH.

For more information on this source, please visit Elementar Analysensysteme GmbH.

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