Diamond laser heating

Temperatures as high as 2,500 K have been achieved by laser heating (LH). For such LHDAC experiments, the sample size was around 50-100 pm, the laser beam was focused to about 40 pm, and the synchrotron beam was microfocused to about 10 pm in diameter [70]. The photon-flux for the 14.4 keV ( Fe) synchrotron radiation at the focusing spot was about 10 photons s with a 1 meV energy bandwidth. This flux was reduced by a 5 mm path through diamond, via photo absorption, to 25% of its original value. For comparison the flux of the 21.5 keV radiation of Eu would be reduced to only 60%. 

Melting Curve of H20 to 90GPa Measured in a Laser-heated Diamond Cell. 

A short review on the development of laser heating in special applications under pressure has been published by Bassett (2001). A heating system to be used, with either ruby or YAG laser, under pressure in a diamond anvil cell has been described. Graphite to diamond and several silicate phase transformations have been studied. 

Very recently, Solozhenko [540] reported the high-pressure-high-temperature synthesis of cubic BC2N with in situ control of the reaction by x-ray diffraction measurement. The first high-density product has been obtained in a laser-heated diamond anvil cell (DAC). The starting material was g-BC N, prepared... 

R. Boehler, D. Errandonea, and M. Ross, The laser-heated diamond cell High P-T phase diagrams, in High Pressure Phenomena Proceedings of the International School of Physics Enrico Fermi, Course CXLVII, R. J. Hemley, G. L. Chiarotti, M. Bernasconi, and L. Ulivi, eds., lOS Press, Amsterdam, 2002, p. 55. 

W. A. Bassett and M. S. Weathers, Temperature measurement in a laser heated diamond anvil cell, in High-Pressure Research in Mineral Physics, M. H. Manghnani and Y. Syono, eds., American Geophysical Union, Washington, DC, 1987, pp. 129-134. 

Bassett WA (2001) Rev Sci Instrum 72(2) 1270. Workshop on Advances in Laser Heated Diamond Cell Techniques, Chicago, IL, 25-27 May 2000... 

Godward Univ. of California, Berkeley) and a team of researchers used a laser-heated diamond cel) (modified Mao-Bel type) in their research on the ullrahigh-pressure melting of lead. This study is pan of a project to characterize materials at ultrahigh pressures. Such data can be useful for a wide range of applications in (he planetary sciences and the physics of condensed matter,... 

The cubic y-modification has been recently observed under a pressure of 15 GPa and temperatures above 2000 K by the laser heating technique in a diamond cell [23] and in shock-wave compression experiments with pressures >33 GPa at 1800 K and >50 GPa at 2400 K [29]. This modification is often designated as the c-modification in the literature in analogy to the cubic boron nitride (c-BN). It has a spinel-type structure in which two silicon atoms are octahedrally coordinated by six nitrogen atoms, one silicon atom is coordinated tetrahedrally by four nitrogen atoms (Fig. 3c). The atomic coordinates for the cubic modification are given in Table 2. From calculations it is shown that this structure should have a high hardness similar to that of diamond and c-BN [23]. 

Jephcoat, A. P., Besedin, S. P. (1996) Temperature measurement and melting determination in the laser-heated diamond anvil cell. Phil. Trans. Roy. Soc. A, 354, 133-60. 

To be referred to next is the most modem diamond anvU type, generating pressures of order of 10 -100 GPa. The cell illustrated in Figure 6(e) consists of two gem diamonds with optically flat surfaces, between which a sample confined in a drilled hole of a thin metal gasket is sandwiched. To attain isostatic compression an inert gas or an organic liquid, like a 4 1 volume mixture of methanol and ethanol, is contained with the sample. The generated pressure is measured directly from the pressure shift of the fluorescence line of mby powder mixed with the sample. Temperatures to 5000 K can be obtained by laser heating. The quantity of sample confined in a typically 0.1-mm-wide hole is extremely small, just a few microcrystals. At present, research has focused on in situ observations using X-ray and other optical methods, rather... 

The e - y transition boundary was determined by measuring the resistance changes during the transition in a high-compression belt apparatus (Bundy, 1965) and in an internally heated diamond-anvil cell (Boehler, 1986 Mao et al, 1987). The boundary was also determined by in situ X-ray diffraction measurements in an internally heated diamond-anvil cell (Boehler, 1986 Dubrovinsky et al, 1998), in a laser-heated diamond-anvil cell (Shen et al, 1998), and in a multi-anvil apparatus (Funamori et al, 1996 Lfchida et al, 2001). The boundaries determined by Mao et al. (1987), Shen et al (1998), and Lfchida et al (2001) are in good agreement, but are all at —75 K higher temperature (or —2 GPa lower pressure) than the boundary determined by Funamori et al. (1996), Boehler (1986), and Bundy (1965). 

Experiments have established that there are four polymorphs in solid iron (a-, y-, S-, and s-phases). Saxena et al (1993) proposed a fifth iron phase (/3-phase) based on changes in thermal emission while laser heating the sample in a diamond-anvil cell. Boehler (1993) also observed similar changes in optical properties of iron in the same P-T range. Subsequent in situ X-ray diffraction measurements in the laser-heated diamond-anvil cell supported the occurrence of this new iron phase, although the structure of this phase is still under debate (Saxena et al, 1996 Yoo et al, 1996 Andrault et al, 1997, 2000 Saxena and Dubrovinsky, 2000). However, this phase was not observed in... 

The eutectic temperamre of the Fe-S binary system has been measured in a multi-anvil apparatus to 25 GPa (Fei et al, 1997, 2000 Li et al, 2001), and in a laser-heated diamond-anvil cell to 62 GPa (Boehler, 1996). Within the common pressure range, the diamond-anvil cell results are higher than the multi-anvil apparams results by as much as 400°. Despite the discrepancies, the existing data show that between... 

Shock-compressed carbon dioxide exhibits a strong slope change in the Hugoniot (recall Fig. 1), a clear indication of chemical reaction, at around 40 GPa and estimated temperature of 4500 K [1]. The previous theoretical calculation has confirmed that it is indeed due to chemical dissociation of carbon dioxide to elementary products such as diamond and oxygen. In recent diamond-anvil cell experiments [74], the similar dissociative products, lonstaleite diamond and oxygen have also been observed from the quenched products after laser-heating of CO2 samples at 67 GPa. The transition temperatures were estimated to be about 2500 K at 35 GPa, substantially lower than the estimated shock transition temperature 4500 K. 

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