Mechanical and thermal properties of a nanopowder talc compound produced by controlled ball milling
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A powdered compound constituted by over the 95% of talc Mg3Si4O10(OH)2 with MgCO3 and CaMg(CO3)2 as minor phases was mechanically deformed by compaction and shear to a nanosized particulate (crystallite size ~5 nm) in a specifically built planetary ball mill. The mechanical milling was conducted in a controlled thermodynamic environment (25 °C and 0.13 Pa) by using low mechanical load to minimise amorphisation of the material. Mechanical τ(ε) shear analysis and thermo-structural modifications of the nanostructured talc particulate were investigated after selected milling times (0, 1, 5 and 20 h). At the very early stages of milling (1 h) layer flattening, lamination and texturing of the talc particles occurred. For prolonged milling (up to 20 h), a progressive reduction of the TOT talc stacking layer coherence, from about 20–5 nm, and an increase of (001) microstrain from about 0.6–2.2 × 10−2 nm, as a non-linear function of the treatment time, were observed. A progressive increase of the specific surface area up to 28 m2/g as a consequence of the particle size reduction took place at intermediate milling times (5 h) and reduced to about 10 m2/g at prolonged milling (20 h). Even the thermo-structural behaviour of the particulate was significantly modified. For 20-h milled talc, a severe decrease of the dehydroxylation temperature from about 900–600 °C was observed with a concomitant anticipation of the recrystallisation of talc into MgSiO3 (enstatite). The τ(ε) behaviour of the compound was strongly affected by the milling treatment changing from a shear-softening regime (untreated and 1 h) to a shear-hardening one (20 h). The observed changes of talc are of great importance to understand the rheology and the thermal transformation kinetics of talc compounds and can be exploited in those industrial applications that required milling of talc, such as in the production of talc-polymers nanocomposites or in medium–high-temperature ceramic processes.
KeywordsTalc Mg3Si4O10(OH)2 Microstrain Ball milling Ceramic compound Nanomaterials
IMIFABI S.P.A (Milan, Italy) is kindly acknowledged for the supply of the talc raw material. University of Bologna is also thanked for the support of the research.
- Bošković SB, Gašić MČ, Nikolić VS, Ristić MM (1968) The structural changes of talc during heating. Proc Br Ceram Soc 10:1–12Google Scholar
- Calafato A, Dellisanti F, Valdrè G (2006) Relationship between structural properties and experimental shear test of KGa-1, KGa-2 and commercial kaolin under high normal pressure. Paper presented at 4th Mediterranean clay meeting, Ankara, Turkey, 5–10 Sep 2006Google Scholar
- Dellisanti F, Calafato A., Pini G.A, Valdrè G (2005) The role of water on development of scaly cleavage and geomechanical behaviour. Results from experimental shear deformation. Paper presented at conference Geoitalia 2005, Spoleto, Italy, 21–23 Sep 2005Google Scholar
- Eberl DD, Drits V, Srodon J, Nuesch R (1996) MudMaster: a program for calculating crystallite size distribution and strain from the shapes of X-ray diffraction peaks. USGS, Open File Report 96-171, BoulderGoogle Scholar
- Evans BW, Guggenheim S (1988) Talc, pyrophyllite and related minerals. In: Bailey SW (ed) Hydrous phyllosilicates (exclusive of micas). Review of mineral geochemistry. Mineralogical Society of America, Washington, pp 225–294Google Scholar
- Gregg SJ (1968) Surface chemistry study of comminuted and compacted solids. Chem Ind 11:611–617Google Scholar
- Klug HP, Alexander LE (1974) X-ray diffraction procedures. Wiley, New YorkGoogle Scholar
- Krumm S (1996) WINFIT 1.0—a computer program for X-ray diffraction line profile analysis. Acta Univ Carol Geol 38:253–261Google Scholar