**4. Inventions of DACs and MAA**

In the past 50+ years, two major static high-pressure techniques have been developed in mineral physics laboratories by earth scientists desiring to replicate in the laboratory the P–T conditions of Earth's deep interior: the diamond-anvil cell (DAC) and the multi-anvil apparatus (MAA). These two static technique are both useful and very complementary, although have occasionally been viewed as competitive. Higher pressures and large sample volumes can be achieved either through the use of larger tonnage hydraulic rams in MAAs or by increasing the culet size of DACs, and thus experimental conditions of the two techniques will eventually merge.

### **Figure 5.**

*a. Geotherm with P–T ranges compared with the P–T regions achievable with diamond anvil cells (and various types of heating) and with LVP (large-volume presses, aka multi-anvil apparatus). b. Temperature and pressures achievable in difference types of large-volume apparatus.*

The diamond-anvil cell (DAC) was invented at the National Bureau of Standards [NBS] under the direction of Alvin Van Valkenburg and his colleagues in 1958. For the subsequent developments of the DAC, see the excellent review by William Bassett [6]. In the same time period, Tracy Hall invented the first multi-anvil apparatus, a tetrahedral-anvil machine; such MAA have evolved progressively [7] and can now achieve pressures close to 100 GPa at high temperatures. With the advent of synchrotron radiation facilities in the early 1980s, many of these DAC and MAA devices have been utilized in conjunction with *in situ* X-ray diffraction.

In **Figure 5a** and **b**, we illustrate the pressure and temperature ranges achievable with the diamond anvil cells and multi-anvil apparatus and compare those with the P–T ranges of the geotherm of the Earth.

In **Figure 6**, the regions of the Earth's interior (Crust, Upper mantle, Lower mantle, Outer core and Inner core) accessible to difference types of high-pressure apparatus: Belt, Split-Sphere, DIA and DAC are illustrated.

With the aid of high-pressure devices such as diamond anvil cells and multi-anvil apparatus, scientists have been able to explore the crystallographic transformations which the principal minerals of the upper mantle undergo as they are buried deeper in the Earth's interior. Thus, olivine, garnet, clinopyroxene and orthopyroxene of the upper mantle evolve to mixtures of (Mg, Fe)O-ferropericlase and Ca- and (Mg, Fe, Al)-SiO3-perovskites [the latter recently named bridgmanite] in the lower mantle. In the vicinity of the outer core, the bridgmanite transforms to a post-perovskite phase which has not yet been found in nature (see **Figure 7a**, courtesy of Stas Sinogeikin and **Figure 7b**, courtesy of Nick Schmerr and Ed Garnero).

In addition to experiments using static multi-anvil apparatus or diamond anvil cells, many scientists have utilized dynamic shock wave techniques to measure the physical properties of minerals at high pressures and temperatures. In **Figure 8**, the shock wave gun at Caltech is shown; it was originally built by Thomas Ahrens and is now under the supervision of Paul Asimow.

### **Figure 6.**

*Regions of the Earth's interior accessible to different types of high-pressure apparatus: Belt, Split-sphere, DIA and DAC.*

*Mineral Physics DOI: http://dx.doi.org/10.5772/intechopen.102326*

**Figure 7.**

*a. Evolution of minerals in the earth from the upper mantle to the core. Courtesy of Stas Sinogeikin. b. Upper mantle seismic discontinuities: Mineral phase boundaries. Courtesy of Nick Schmerr and Ed Garnero.*

In a paper now in press entitled "New analysis of shock-compression data for selected silicates", Thomas Duffy has illustrated one of the important uses of shock wave experiments:

"The study of minerals under shock compression provides fundamental constraints on their response to conditions of extreme pressure, temperature, and strain rate and has applications to understanding meteorite impacts and the deep Earth. The recent development of facilities for real-time *in situ* X-ray diffraction studies under gun- or laser-based dynamic compression provides new capability for understanding

### **Figure 8.**

*Static (multi-anvil press and diamond anvil cell) high-pressure devices illustrated with the dynamic shock-wave gun at Caltech.*

the atomic-level structure of shocked solids. Here traditional shock pressure-density data for selected silicate minerals (garnets, tourmaline, nepheline, topaz, and spodumene) are examined through comparison of their Hugoniots with recent static compression and theoretical studies. The results provide insights into the stability of silicate structures and the possible nature of high-pressure phases under shock loading. This type of examination highlights the potential for *in situ* atomic-level measurements to address questions about phase transitions, transition kinetics, and structures formed under shock-compression for silicate minerals."

Experiments are not the only solution to finding progress. In the figure above is a quote by Artem Oganov:

"High-pressure experiments are extremely difficult".

Thus, he resorts to the computer for theoretical calculations.

"Recent progress in theoretical mineral physics based on the *ab initio* quantum mechanical computation method has been dramatic in conjunction with the rapid advancement of computer technologies. This technique solves electronic structures and chemical bonding natures of materials highly accurately and became practical after the beginning of this century. It is now possible to predict thermodynamic stability, elasticity, and transport properties of complex minerals quantitatively with uncertainties that are comparable or even smaller than those attached in experimental data under high pressure and high temperature. These calculations under *in situ* high-pressure (*P*) and high-temperature (*T*) condition allow us to construct *a priori* mineralogical models of the deep Earth and have opened a new generation in solid geophysics and geochemistry". (Taku Tsuchiya, personal communication, 2021).
