02.03.2022 by Erwin Kaisersberger

Gas Analysis Systems Coupled to NETZSCH Instruments: How it all started

NETZSCH-Gerätebau GmbH consists of over half a century of development experience in coupling technology. In the month of March, find out in a historical summary how it all began, which systems were used then and which are used today, and read exciting contributions from our long-standing customers and partners.

NETZSCH-Gerätebau GmbH consists of over half a century of development experience in coupling technology. In the month of March, find out in a historical summary how it all began, which systems were used then and which are used today, and read exciting contributions from our long-standing customers and partners.

Photos: Hardly changed: Erwin Kaisersberger in the 80s (right) and 2000s (left)

In 1973, physicist Erwin Kaisersberger joined NETZSCH and was initially responsible for applications & sales in Germany and abroad. Further career stages followed as Head of Applications Laboratory, Head of Technical Sales and “Senior Scientist” in the worldwide Service & Applications Support Team. Beginning in 2007, he worked for the company as a freelance consultant before he went into his well-deserved retirement in 2012 – after 39 working years. In those last five years, he dedicated all of his energy specifically to the area of TGA-GC-MS coupling.

Erwin Kaisersberger has compiled the history of coupling gas analysis systems to NETZSCH instruments for us:

Starting Point in 1970

As you can see from the account of the STA history in the anniversary article for February 2022, the first NETZSCH STA with model number 429 was introduced in 1970. This took place on the occasion of the International Engineering Fair in Brno (fall 1970), which at that time and still many years later was an important marketplace for business with Eastern European countries, among others.

Until 1970, NETZSCH favored the philosophy that it was better to work separately with DTA and TGA, since for DTA, faster heating rates were effective in obtaining larger peaks; for TGA, on the other hand, slower heating rates were preferred in order to determine mass changes in a state as close as possible to equilibrium. The simultaneous application of DTA and TGA to a single sample under identical conditions, however, quickly became established.

With the introduction of the STA 429, which was designed to be vacuum- and gas-tight from the beginning, we entered a new market segment and were in immediate competition with other Western European manufacturers; this was also the case in Eastern Europe with the derivatograph (Paulik and Erdey). Particularly in the higher temperature range, NETZSCH was able to bring in its long-standing experience in the fields of inorganics, minerals and ceramics.  

Even before 1973, NETZSCH had a wide-ranging production program, as stated in the dilatometer brochure from 1973 (anniversary article from January 2022). This also included continuously operating gas detection instruments for coupling with the gas-tight models for DTA, TGA, STA and dilatometers. Of course these gas detectors, which registered changes in the Conduttività TermicaThermal conductivity (λ with the unit W/(m•K)) describes the transport of energy – in the form of heat – through a body of mass as the result of a temperature gradient (see fig. 1). According to the second law of thermodynamics, heat always flows in the direction of the lower temperature.thermal conductivity (EGA), gas density (EGD) or radioactivity (ETA) of a sample gas during an experiment, were not quite satisfactory despite their simplicity and the fact that some of them had high detection sensitivity: They only showed that gases had evolved or been absorbed, but not which ones!

Gas identification, however, was as current a topic at that time as it is today. But which gas analysis systems were initially available? The focus of the development work quickly turned to the quadrupole mass spectrometer due to its compactness and high detection sensitivity (1960: Invention of the quadrupole mass filter by the German physicist and later Nobel Prize winner, Wolfgang Paul, and his coworker, Helmut Steinwedel, at the University of  Bonn).

Basic design of a quadrupole mass filter

Since 1970, instrument development at NETZSCH was also directed toward more compact dimensions with smaller and thus faster furnaces, reduced sample chambers for better gas purging and vacuum tightness to achieve clean gas atmospheres at the samples. This was a basic requirement for the sensible coupling of sensitive gas analysis systems. Also beginning in 1970, electronics developed by Karl Bayreuther and his team in-house at NETZSCH were used in the instruments’ control systems. This made the instruments more flexible and more precise, especially in temperature control and measurement data acquisition.

Temperature control system 400
Interface 414 for computer coupling; a Mini-DTA 404 M with computer operation was already introduced in 1973 at the Achema Fair in Frankfurt a. M.

1973: Coupling of Mass Spectrometers (MS)

The NETZSCH Group, comprised of the individual German companies Gebrüder NETZSCH-Anlagenbau, NETZSCH-Mohnopumpen, NETZSCH-Feinmahltechnik, NETZSCH-Newamatik, NETZSCH-Gerätebau and NETZSCH-Vertriebsgesellschaft, was in high spirits and celebrated its 100th anniversary on July 1, 1973 together with its foreign subsidiaries at what was reputed to be an “extremely opulent company party” in Selb. (I started working for NETZSCH-Gerätebau 100 years and one day after the foundation of NETZSCH; i.e., exactly the day after the 100-year celebration. To this day, I cannot answer the question as to why I was not there …)

Already in the early 70s, Balzers of Liechtenstein enjoyed a good reputation for their quadrupole mass spectrometers (QMS) for process control. NETZSCH-Gerätebau’s interest in collaborating with Balzers to develop an MS coupling for the STA 429 was very high and Balzers, in turn, was impressed by the open-mindedness at NETZSCH for optimization of integratable gas inlet systems. Thus, in the technical department of Gerhard Bräuer and his team, a gas inlet system consisting of a platinum capillary and a downstream platinum orifice plate was constructed.

This resulted in a mass spectrometer coupling that still functions at temperatures far above 1000°C and a mechanically high-precision modular component for installation in the 1600°C furnace of the STA 429.

Schematic of the MS coupling with platinum capillary and Pt orifice in the furnace of the STA 429
Platinum capillary with entrance funnel and radiation shields, aluminum oxide protection tube in front of it

1974: Introduction of the First and Unique NETZSCH-Balzers Mass Spectrometer Coupling

The exhaust for the new coupling interface is a two-stage rotary vacuum pump in the first stage (Pt capillary). The high level of vacuum necessary for exhausting the Pt orifice, the ion source and the quadrupole mass filter is provided by a diffusion pump with low-fragment (referring to the MS background spectrum) polyphenyl ether lubricant as a pumping medium.

The furnace, coupling system and high-vacuum pump are mounted on a vertical “lift” to allow free access to the sample carrier for sample change in the STA. There is even room for additional furnaces for “normal” STA tests.

The equipment was used at the University of Constance for the investigation of silicates and has been consistently, carefully and reliably maintained by the NETZSCH Service Department over many decades.

Left: Status 1974: NETZSCH STA 429 with platinum coupling system in the 1600°C furnace; above, the quadrupole system, the high-frequency source and a diffusion pump with shut-off valve are axially (i.e., vertically) arranged.

1974 also marks the foundation of a non-profit association for thermal analysis in the German-speaking area, GEFTA. Among others, two names played a decisive role in the founding of the new association: Prof.-Dr. Ing. Hans Lehmann from Clausthal-Zellerfeld and Dr. Wolf-Dieter Emmerich from NETZSCH in Selb, who persuaded several NETZSCH employees to also become founding members of GEFTA; this allowed the association to start with about 20 members.

The University of Constance was chosen as the venue for the 3rd annual GEFTA meeting as early as 1976, a tribute to the activities in the field of thermal analysis on-site. GEFTA had already been able to increase its membership to over 50 people and had become an integrating association of active thermal analysts and researchers parallel to the national organizations of neighboring countries.

1975: Beginning of a Tradition of Seminars on the Subject of Coupling Gas Analysis Systems

At the end of 1975, this mass spectrometer coupling with platinum capillary and orifice was introduced to a larger international group of interested parties on the occasion of an initial seminar entitled “NETZSCH-Balzers-MTA High-Temperature Coupling Systems” (MTA stands for mass spectrometric thermal analysis, an abbreviation no longer used today). Along with that, NETZSCH also realized a significantly simpler mass spectrometer coupling with steel capillary and platinum orifice, as offered later by Balzers as a separate gas inlet module, or in a compact solution with Thermostar. In this case, gas sampling was carried out at the gas outlet of the respective furnace, allowing coupling to all gas-tight instruments such as DTA, TGA, STA and dilatometers. A unique selling point over competitors’ offerings was the comprehensive and adjustable heating to 200°C of the gas outlet at the furnace.

So what were the next steps with the high-temperature coupling system?

The technical solution found, the practical execution and the detection sensitivity of the mass spectrometer in the ppm-range in combination with thermal analysis seemed more than adequate for all concerns and applications. Minor flaws in the experimental design and evaluation were behind the slow registration with the multi-channel dot printers, the relatively slow scanning speed of the mass spectrometer and the sometimes too numerous peaks in the background spectrum. Yes, there were also sometimes atoms, molecules, and compounds that simply did not find their way through the capillary and orifice, which were thermally destroyed on the way, or which couldn’t reliably be referred to from the MS peaks registered. Sometimes, meters-long recording paper webs had to be unrolled to find the “one” relevant recorder deflection of the MS signal.

Discussions with prospects interested in the integrated MS-STA coupling led to new materials in the design of the gas inlet system in the furnace of the STA. For these applications, platinum was out of the question because of its catalytic effect on samples and the Reazione di DecomposizioneLa decomposizione è la reazione indotta termicamente con cui una sostanza chimica genera prodotti solidi e/o gassosi. decomposition products to be detected. High-purity sintered corundum tubes were selected which were expected to have good resistance for the operational temperature range. The challenges ahead like drilling small openings by laser (orifices) in the bottom of the tubes and soldering them to metal flanges were solved in cooperation with ceramic manufacturers and specialized institutes. A double orifice system was created.

Schematic of the high-temperature coupling system, consisting of concentric alumina tubes with orifice holes at the base of the tube

Interestingly, it was research on solid-state properties and the emerging technical ceramics, with problems such as the burnout of organic binders and volatility of inorganic SinteringSintering is a production process for forming a mechanically strong body out of a ceramic or metallic powder. sintering aids, that resulted in this double orifice solution.

1978: Deliveries of the STA 429 with Double Orifice System

The Max Planck Institute for Solid State Research, Stuttgart, Germany, was the first customer of our double-orifice coupling.

Another research area that became a focus of attention concerned the “safe” disposal of radioactive waste materials in the context of nuclear research. The Jülich Research Center (at that time still Jülich Nuclear Research Facility) purchased an STA 429 with double orifice system in order to research the gas release of vitrified waste materials. Prof. Dr. Reinhard Odoj (1973 – 2009 director for safety research and reactor technology at Jülich Research Center) and his colleague made a significant contribution to the optimization of high-temperature MS coupling for this area of application. One of the objectives was a gas inlet system that would allow for reliable detection of metal vapors such as cesium, selenium, tellurium, ruthenium oxides and silver (as reference substances with similar volatility to radioactive waste). The high-temperature MS coupling was significantly optimized for this application in cooperation with professors from the research center. The studies led to a dissertation with a description of the many individual steps up to a “skimmer coupling”, made of metal with greatly reduced distances between the sample, gas inlet and MS-ion source, all with a correspondingly short furnace.

The transfer of this “institute solution” to a commercially manufactured skimmer coupling system at NETZSCH was very sophisticated. Redesign of the furnace and search for optimum Skimmer materials for different operating temperatures and ranges are just some of the key points. Skimmers made of high-temperature resistant metal, quartz glass, alumina and glassy carbon were realized. Alumina and glass carbon subsequently proved to be the most versatile and practical for different temperature ranges and sample atmospheres.

Instrument development benefited from the fact that the furnace product range at NETZSCH had expanded from the low temperature range of -180°C to 2400°C, reliable turbomolecular pumps had begun being used for vacuum generation, and compact hoisting devices had also been designed.

STA 429 with 1600°C furnace on a standard hoisting device and 2400°C tungsten furnace on a newer motor-driven hoisting device.
Examples for Skimmer of alumina and of glassy carbon

1985: Introduction of the World’s First and Unique High-Temperature Coupling with Skimmer Gas Inlet System

Schematic of the Skimmer coupling in the high-temperature furnace with orifice in the protective tube and Skimmer tip at a short distance above. The cross-beam ion source of the quadrupole system is at a very short distance from the skimmer tip.
Newly designed setup of the mass spectrometer coupling with Skimmer inlet system on the STA 409 with turbomolecular pump and compact high-frequency source for the quadrupole system

In parallel to the further development of the orifice coupling to the Skimmer coupling outlined above, a new center of excellence for environmental, fuel and energy research was developed at the (Comprehensive) University of Paderborn, Department of Chemistry lead by Prof. Dr. Antonius Kettrup with an STA 429 MS double-orifice coupling. The very fruitful cooperation with Prof. Dr. Antonius Kettrup and his team also resulted in instrumental improvements (automatic pressure control at the inlet system) and redesign of instruments after the move of the research team to Neuherberg near Munich to what was then known as the GASS Research Center for Environment and Health. For environmental research (e.g., waste disposal, contaminated soils), a large=sample STA (sample volume up to 170 cm³) with possibilities for coupling mass spectrometers, FT-IR spectrometers and GC-MS instruments was built by NETZSCH within the framework of Bavarian research funding.

Macro STA 419 for samples in the 2- to 3-digit gram range and double-orifice coupling for MS

But what will happen next? What new developments will follow? Read more in the coming weeks…