75 Years of Silicones

In 1947, WACKER became the first European company to start working on silicones. Today, the Group is the world’s second-largest manufacturer of these high-performance plastics, which are now ubiquitous in our everyday lives. Here, we look back at the time when the future was taking shape in the most modest of circumstances – in a wooden barracks in Burghausen.

In this furnace, we are producing at least 1,000 kilograms [of silanes] a month, and soon, when we have a further reactor, it will be two to three tons.” “Try to make 200 to 300 tons as soon as you can.” That was the advice given in late 1950 to one Dr. Siegfried Nitzsche by the former managing director, Dr. Johannes Hess, shortly before his death on February 3, 1951. And Dr. Nitzsche, despite all the naysayers, took the advice – and in so doing earned the right to be called the “father of WACKER silicones.” For, according to Nitzsche’s own recollections, even the board of management back then took the view that “we’ll be happy if we can generate a million marks in sales.”

That WACKER has long since left such modest goals behind is due in no small part to the tireless efforts of Dr. Nitzsche and his unstinting perseverance. Today, WACKER SILICONES is the largest business division of Wacker Chemie AG, notching up sales approaching three billion euros.

The most important of the silanes mentioned in that exchange between Director Hess and Dr. Nitzsche, namely dimethyldichlorosilane, is the precursor to about 2,800 silane and silicone-containing products at WACKER and is produced at Burghausen, Nünchritz and Zhangjiagang. WACKER is thus the undisputed number-two player in the global market for silicones.

The circumstances in which Dr. Nitzsche began his work on silanes and silicones at the Burghausen site in 1947 are worth examining, as they reveal why WACKER countenanced the idea of engaging with this new business area in the first place and the resistance which Dr. Nitzsche initially faced.

The route followed by Dr. Nitzsche to obtain silicones also proceeded via dimethyldichlorosilane. In the early 1940s, the Chemical Institute in Jena, where he was preparing for his postdoctoral qualification, had received an order from the German Army for the “siliconization of iron pipes.” It is not hard to fathom that these were intended for use as heavy artillery. While working on this task, Dr. Nitzsche’s laboratory assistant suffered a mishap: water came into contact with the sensitive dimethyldichlorosilane, hydrolysis occurred, and Dr. Nitzsche was unable to distill off the resulting oily product – not even at 360 °C. Upon cooling, a rubber-elastic product was obtained, which remained stable even when heated to red-hot temperatures. Without knowing it, Dr. Nitzsche had just made his first silicone rubber. Other, less-talented chemists would have dismissed the incident and returned to the task at hand. But Dr. Nitzsche was fascinated and had now found the subject area for his postdoctoral thesis: “Heat-resistant, silicon-containing plastics.”

Later, in spring 1947, when Dr. Nitzsche was released from an American internment camp for German scientists, he received an invitation from the German Chemical Society. He was asked to deliver a plenary lecture on his thesis subject at its first post-war conference in Heidelberg. Among the audience were two representatives from Wacker Chemie: Chief Chemist Dr. Wolfgang Gruber and Director and Senior Engineer Dr. Eduard Kalb. Dr. Gruber would later describe the event in his memoirs, which were published under the title “Gratwanderungen (Balancing Acts).”

“Here I managed to do the company a great service by recruiting Dr. Siegfried Nitzsche, who gave a very good lecture on silicones, for the Burghausen plant. I had already suggested to Director Hess that we study the field of silicones, because the raw materials fall within our sphere of activity and we could easily get our hands on them (copper-silicon alloys, methyl chloride, possibly silicon tetrachloride). Nitzsche had previously had a job application turned down by the WACKER board in Munich, but this decision was quickly reversed. In just a few years, annual sales of silicones soared into the millions of deutschmarks and the number of articles rose to 100 and beyond!”

Dr. Nitzsche joined WACKER in Burghausen on August 2, 1947, and immediately set about working on WACKER silicones.

What were the raw materials that Dr. Gruber was referring to? Back in 1947, silicon, a semi-metal, was already a longstanding “old familiar” at WACKER. In fact, Elektrobosna, a predecessor company established by Alexander Wacker, had owned a patent for the production of elemental silicon. And before the war, WACKER’s portfolio included numerous alloys for the processing of steels, including calcium silicon, ferrosilicon and calcium aluminum silicon. In the 1930s, WACKER’s plants accounted for two-thirds of German demand for ferrochrome alloy. So, in 1947, the company had access to silicon and was experienced at handling both it and, of course, the hydrogen chloride needed for the production of methyl chloride from methanol.

In terms of raw materials, then, Dr. Nitzsche was off to a fairly good start. But in the immediate aftermath of the war, there were still shortages on all fronts elsewhere. Dr. Nitzsche found it hard to get his hands on personnel, equipment, the requisite laboratory and production rooms and even specialist literature. For example, it was from an article in the popular science magazine Reader’s Digest that he learned about the progress being made in the field of silicones in the US. Another difficulty was the patent situation. General Electric (GE) held the important patents for the production of silanes, and another US company, Dow Corning Corporation (DC), had secured the rights to the key steps for processing these into silicones.

Fortunately, both companies were interested in working with European companies on the production and marketing of silicone products. Aside from with WACKER, they concluded contracts with Rhône-Poulenc and Bayer AG. The key licensing agreements with DC were signed in 1951 and those with GE in 1953. And so it came about that the first brochures marketing WACKER’s own silicones were published in 1951, in parallel with a catalog in which WACKER acted as the general agent for DC silicones.

Further developments in silanes took a leap forward from 1950 on, with the recruitment of two new key employees, Dr. Ewald Pirson and Dr. Manfred Wick. As of 1949, the following products were already available: silicone fluids, oil emulsions, antifoam agents, impregnating agents, pastes and release agents. 1952 saw the appearance of the first silicone rubber grades, followed in 1953 by masonry protection agents – applications which were basic back then but which can still be found in WACKER SILICONES’ product portfolio today in a much more advanced and sophisticated form. By 1959, more than 100 different silicone products were under development.

As demand for silicones rose, the plant in Burghausen expanded. The first production facility had long been too small and was pulled down. Significant sums were invested from the mid-1960s to gradually expand silicone production. The plant was extended in the west and north to create an integrated production system. The idea is to waste nothing and make use of everything. WACKER was thus able to run low-waste and efficient production lines even then.

“On June 26, 1972, the new North Plant started up production of silane.” This report in the plant magazine was something of an understatement. In reality, it was a much more spectacular affair that in subsequent years would be systematically expanded with further facilities to form what is now Burghausen’s integrated siloxane production plant. The plant featured a revolutionary, unenclosed reinforced-concrete design and the first vestiges of automated control in the guise of a control room.

At 51.1 meters, the silane distillation columns erected in 1972 were the tallest of their kind in Burghausen. Recently, after 50 years’ service, they were replaced by a new silane column, which, at more than 70 meters, towers above them.

Around about the same time, in the early 1970s, Dr. Günter Kratel at the Kempten plant of WACKER’s subsidiary ESK developed a filler: HDK^® pyrogenic silica, which also turned 50 in 2022. This extremely versatile material can be found in a swath of wholly disparate applications and, among its many uses, has more or less become the default reinforcing filler for WACKER’s silicone rubber.

As early as 1978, a separate HDK^® plant was built in Burghausen and hooked up to the integrated silicon production network. What makes this so interesting is that HDK^® is itself obtained from byproducts from silane synthesis and is thus part of the integrated production network operated by the WACKER SILICONES and WACKER POLYSILICON divisions. The “silane byproducts” from silane synthesis are pyrolyzed at over 1,000 °C in a hydrogen-oxygen flame, and cool to form flocs that have the basic structure of silicon dioxide (SiO2). In other words, a substance with the same composition as sand. Unlike sand, HDK^® from WACKER has a massive surface area that serves as the source of its unique properties. A large bag of HDK^® weighs just ten kilograms.

There are very few chemical reactions that give a 100-percent yield of the intended product. This fact underlies one of the key advantages of integrated production at WACKER. Over the decades, chemists and engineers have succeeded in taking a great many byproducts generated in various processes and using them, for example, as starting materials for other products.

Today, demand for WACKER HDK^® is so great that it is produced not only in Burghausen, but also in Nünchritz, Zhangjiagang and Charleston. HDK^® is therefore a prime example of how, at WACKER, one little cogwheel meshes with another. Waste from silicone production is thus transformed into a new sales product which may not be visible in our living environment, but is nevertheless omnipresent.

It would go beyond the bounds of this article to list all the other WACKER silicone sites that emerged worldwide in the decades that followed. However, two fully integrated sites deserve a mention, because they have something in common with Burghausen: they each boast a complex that produces silanes by the Müller-Rochow method.

The first is Nünchritz, which has already been mentioned briefly. Founded in 1900 as the Weißig plant of Chemische Fabrik von Heyden, it operated in former East Germany first as VEB Schwefelsäure und Ätznatronwerk and then, following the work of Richard Müller, as VEB Chemiewerk Nünchritz. After the fall of the Berlin Wall, the plant was initially taken over by Hüls AG in 1990, which sold it to Wacker Chemie a few years later in 1998. Since then, as a result of continuous investment in its expansion, Nünchritz is now the largest WACKER site in Germany after Burghausen.

Unlike Burghausen, Nünchritz does not have its own chlorine production. This highly reactive gas is needed for the production of chlorosilanes – which serve as intermediates in the production of silicones. This process re-generates the chlorine, which is then removed and reused. Every chlorine atom passes through the production loop a great many times. In Burghausen, chlorine is produced by electrolyzing rock salt sourced from the Group’s own salt mine in Stetten. Nünchritz, without its own supply of salt and therefore of chlorine, obtains chlorine-containing intermediates from Burghausen to replace the losses that inevitably arise even in an excellently designed integrated production system.

The gates to industrial-scale chemistry had already been opened up to silanes and silicones in 1942. In the middle of the Second World War, an American, Eugene Rochow, and a German, Richard Müller, working completely independently of one another, developed a way to produce liquid dimethyldichlorosilane direct from solid, powdery silicon and gaseous chloromethane. Figuratively speaking, this silane can be understood as a basic LEGO^® building block from which thousands of organosilicon compounds can be systematically synthesized.

Back then, Eugene Rochow was working for General Electric in Schenectady, New York, while Richard Müller, affectionately named “Silicon Richard” by his co-workers, was employed at the Chemische Fabrik von Heyden in Radebeul, Saxony. By the way, this factory also included the Weißig plant, which commenced production of silicones for the German Democratic Republic in 1953 to a design by Müller and his team. Today, it is known as the Nünchritz plant and, since 1998, has been one of the largest silicone plants operated by Wacker Chemie AG.

Even today, after more than 80 years, Müller-Rochow or direct synthesis is the only method in the world that is capable of producing dimethyldichlorosilane and hence silicones in commercially viable quantities. When one considers how much our lives are influenced by silicones, whose unique properties render them indispensable in countless everyday applications, it is surprising that the two inventors were never awarded the Nobel Prize in Chemistry. A late honor was forthcoming in 1992, though. On the occasion of the 50th anniversary of their synthesis, they were presented with the WACKER Silicone Award in Burghausen by Dr. Stroh, the then head of the Silicones division. Rochow was 83 years old at the time and Müller was 89.

Wacker Chemie AG also worked to ensure that it was vertically integrated. Silicon is not just a vital raw material for WACKER SILICONES, but is also an essential semi-metal needed by WACKER POLYSILICON in particular. In total, products containing silicon account for some 80 percent of WACKER’s current sales. So, the company’s decision to secure its own raw-material base by acquiring a captive production facility was certainly taken with an eye to the future.

To this end, in 2010, WACKER acquired a site in Holla, Norway, where quartz and coal are converted into silicon metal in huge furnaces. Silicon is the most abundant element in the earth’s crust after oxygen. Due to its very affinity for oxygen, however, it does not occur in elemental form anywhere, but primarily as silicon dioxide (SiO₂), i.e. quartz or quartz sand. From the outset, Holla was able to cover about one third of WACKER’s raw silicon requirements, with work ongoing to expand this capacity even further.

1947 – Getting Started: Work began on silanes and silicones

1949 – Production: Silane production began in Burghausen

1951 – Cooperation: Licensing agreement with Dow Corning

1953 – New Products: New Products Room-temperaturecuring and heat-curing silicones (RTV & HTV)

1954 – First Expansion: Expansion of the silicone facilities in the old plant

1959 – Portfolio: 100 different silicone products were being developed

1963 – Expansion: Production lines in the West Plant expanded

1965 – High-Ranking Visit: German Chancellor Ludwig Erhard visited Burghausen

1969 – USA: Stake acquired in SWS Silicones Corporation (Adrian)

1972 – Investments: The new silane distillation facility went on stream in the North Plant

1978 – Integrated Production: The first HDK^® facility in Burghausen to make use of byproducts

1980 – Innovation: Development of liquid silicone rubber (LSR)

1983 – Growth in Asia: Wacker Chemicals East Asia founded

1986 – Close to Customers: Construction started on the silicone manufacturing facility in Japan

1987 – Award-Winning: Presentation of the first WACKER Silicone Award

1992 – Patronage of the first “Silicone Days,” now a major industry gathering

1998 – New Sites: Nünchritz site purchased and a site in India founded

1999 – Focus on Asia: Wacker Asahikasei Silicone Ltd. joint venture (Japan)

2004 – Premiere in China: A silicone emulsions plant went on stream in Shanghai – the first time WACKER had produced silicones in China

2006 – Joint Venture: Ground-breaking ceremony for a joint WACKER/Dow Corning site in China

2008 – Eastern Europe: Production plant for ready-compounded SILMIX^® silicones in Czechia

2010 – Key Investments: A silicon-metal production plant was purchased in Norway and Lucky Silicones was bought in South Korea

2017 – R&D: Lab complex for developing innovative silicones (Ann Arbor, USA)

2022 – Efficiency: New distillation column added to Burghausen’s integrated siloxane production system