Synthetic Emeralds Grown by IG Farben: Historical Development and Properties Related to Growth Technology

摘要

Developments in emerald synthesis occurred over a period of nearly five decades (1911-1958) at a facility in Bitterfeld, Germany, operated primarily under the name IG Farben. Initial experiments involving the flux method of growth performed by H. Wild in Idar-Oberstein led to collaborations with Bitterfeld scientist *0. Dreibrodt in the 1910s and 1920s. Almost two decades of research then ensued, culminating in a breakthrough by H. Espig of IG Farben in 1929 that permitted the growth of larger synthetic emerald crystals. A standard synthesis process was developed between 1930 and 1935, and production on a limited scale lasted until 1942. Although the possibility of restarting production was explored in the 1950s, those initiatives were abandoned without further operations. The evolution of the company's flux-growth technology from the first trials before 1914 through the standardized production after 1935 is recorded in variations in the properties of the resulting synthetic emeralds. While Cr was always present as a colour-causing trace element, in later eras Ni was added as well. Growth was performed in platinum crucibles with the nutrient at the bottom, seeds centrally located in a molybdate melt and silica plates floating on top of the melt. To create a barrier between the seeds and the silica plates, a platinum net was originally employed but was subsequently replaced by a platinum baffle. Natural beryl seeds were used in the early years, followed by flat synthetic emerald plates. As a consequence, the morphology of the synthetic emerald crystals changed from prismatic to thick tabular or short prismatic.