Thermal Expansion of Aragonite and its Atomic Displacements by Transformation into Calcite between 450°C and 490°C in Air, I

Kôzu, Shukusuké; Kani, Kôichi

doi:10.2183/pjab1912.10.222

Cited by 7 publications

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“…The second dehydration step was the major process in multistep thermal dehydration with c 2 = 0.77, which is attributed to thermal degradation of polymeric materials positioned between aragonite crystals. Thermal degradation of polymeric materials can produce the space for the volume increase in aragonite crystals [10][11][12]. A-C transformation of the biomineralized aragonite occurred at a low temperature, compared with that of mineral aragonite [5,13,14].…”

Section: Kinetic Relationship Between A-c Transformation and Multiste...mentioning

confidence: 99%

“…In crystallographic terms, the aragonite-calcite (A-C) transformation has been explained by a reorientation of the CO 3 group, accompanied by a variation in the distribution of the Ca atom from approximately hexagonal to cubic, close packings [9,10]. In addition, a detectable increase in the unit-cell volume has been observed during heating of aragonite samples [10][11][12][13]. Notably, in biomineralized aragonite, the thermally induced A-C transformation occurs in a lower temperature range, compared with mineral aragonite [5,13,14].…”

Section: Introductionmentioning

confidence: 99%

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Interplay between Thermally Induced Aragonite–Calcite Transformation and Multistep Dehydration in a Seawater Spiral Shell (Euplica scripta)

Tone

Koga

2023

Processes

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While heating a seawater spiral shell (Euplica scripta), thermally induced aragonite–calcite (A–C) transformation occurred within the temperature region of multistep thermal dehydration. Here, the kinetic interplay between the A–C transformation and thermal dehydration was studied as a possible cause of the reduction in the A–C transformation temperatures. The kinetics of the A–C transformation was systematically investigated under isothermal conditions by powder X-ray diffractometry and under linear nonisothermal conditions by Fourier transform infrared spectroscopy. The thermal dehydration was characterized as a partially overlapping, three-step process by thermogravimetry–differential thermal analysis coupled with mass spectroscopy for the evolved gases. The A–C transformation occurred in the temperature range of the final part of the second dehydration step and the initial part of the third dehydration step. The kinetics of A–C transformation and thermal dehydration were characterized by contracting geometry-type models, in which the respective transformations were regulated by a constant linear advancement rate and diffusional removal of water vapor, respectively. Based on the kinetic results, the mutual interaction of those thermally induced processes is discussed as a possible cause of the reduction in the A–C transformation temperature.

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