Drickamer apparatus

Drickamer apparatus. A high-pressure apparatus, also known as a Drickamer anvil cell, is a device used to generate static pressures in the gigapascal range for materials research. It was pioneered by American physical chemist Harry George Drickamer in the mid-20th century and represents a significant development between simpler anvil designs and more complex multi-anvil systems. The apparatus is renowned for its ability to achieve very high pressures while accommodating relatively large sample volumes compared to other high-pressure devices, facilitating a wide range of physical measurements.

History and development

The apparatus is named for its principal developer, Harry George Drickamer, a professor at the University of Illinois at Urbana-Champaign who made seminal contributions to high-pressure science throughout his career. His work built upon earlier foundational designs like the Bridgman anvil, invented by Percy Williams Bridgman, who won the Nobel Prize in Physics for his high-pressure research. Drickamer's key innovation in the 1950s and 1960s was the refinement of the opposed-anvil geometry with improved containment and force distribution. This development occurred alongside other major high-pressure technologies, such as the belt apparatus and the later invention of the diamond anvil cell at the National Bureau of Standards. The Drickamer apparatus filled a crucial niche, enabling pioneering studies on the electrical and optical properties of materials under extreme conditions, which contributed to advancements in fields like solid-state physics and geophysics.

Design and components

The core design features two opposed, hardened anvils, typically made from materials like tungsten carbide or sintered diamond, which are driven together by a large press. The anvils have flat, parallel faces, and the sample is placed within a gasket or chamber assembly between them. This gasket, often made from a compressed material like pyrophyllite or a metal, serves to contain the sample and transmit pressure uniformly. The entire assembly is frequently housed within a hydraulic or mechanical press capable of delivering immense uniaxial force. Support rings, often constructed from high-strength steel alloys, surround the anvils to prevent catastrophic failure by containing radial stress. This robust construction distinguishes it from more delicate devices like the diamond anvil cell and allows for the use of larger anvil tip areas.

Operating principles

The apparatus operates on the principle of uniaxial compression, where force from a press is applied directly to the backs of the two opposed anvils. This force is concentrated onto the smaller anvil faces, generating immense pressure on the sample chamber confined between them according to the formula P = F/A. The gasket material flows plastically under pressure, creating a sealed environment that supports the sample and prevents extrusion. Pressure calibration is achieved using established internal standards, such as the phase transitions of certain metals like bismuth or the fluorescence shift of ruby chips, a technique also employed in diamond anvil cell experiments. The device can maintain static high-pressure conditions for extended durations, allowing for in-situ measurements of various physical properties while the sample is under load.

Applications in high-pressure research

The Drickamer apparatus has been extensively used to investigate the behavior of materials under extreme pressures. It has been instrumental in studying pressure-induced phase transitions in elements, semiconductors, and ionic compounds, providing data critical for understanding planetary interiors, including the Earth's mantle and core. Researchers have employed it to measure electrical resistivity, Hall effect, and optical absorption in materials, contributing to the development of high-pressure superconductors and novel electronic materials. Institutions like the Carnegie Institution for Science and various national laboratories have utilized these devices for geophysical and materials synthesis research. Its capability to house larger samples has also made it valuable for preliminary studies before using more spatially constrained methods like X-ray diffraction in synchrotron facilities such as the Advanced Photon Source.

Advantages and limitations

A primary advantage of the Drickamer apparatus is its ability to achieve high pressures, often exceeding 30 GPa, on relatively large sample volumes, which simplifies the integration of electrical probes and other diagnostic tools. Its robust and mechanically simple design allows for durable and sustained experiments. However, significant limitations exist. The pressure field, while high, is not as hydrostatic as in a liquid-medium diamond anvil cell, leading to potential shear stresses on samples. The maximum attainable pressure is generally lower than that achievable with modern diamond anvil cell techniques, which can reach pressures of the megabar range. Furthermore, optical access is more restricted compared to transparent diamond anvils, limiting certain spectroscopic applications. Despite these constraints, the apparatus remains a vital and historically important tool in the portfolio of high-pressure research methods.