Mössbauer and X-ray diffraction studies of two dry and hydrated portland cements and their clinker

(Hydroxy)apatite on cement: insights into a new surface treatment

“…[41][42][43][44][45] However, the higher CS values for the abiotic treated cement sample are consistent with the view that the average Fe 3+ coordination number is higher than in the other two samples and consequently there may be small differences in the partitioning of iron between the hydrated phases containing iron. [41][42][43][44][45] The overall absorption intensity for the abiotic HAp samples is similar to that of the untreated cement, indicating a higher iron content than the biogenic HAp sample. This suggests that the HAp layer covering the cement is thinner in the abiotic sample than in the biogenic sample as it is diluting the Fe signal less, which is confirmed by EPMA imaging (as described below, Fig.…”

“…All 57 Fe Mössbauer spectra could be fitted with two doublets (D1: centre shift: 0.26-0.42 mm s -1 , quadrupole splitting: 0.41-0.49 mm s -1 , and D2: centre shift: 0.23-0.45 mm s -1 , quadrupole splitting: 1.21-1.61 mm s -1 , Table 2). These doublets (within experimental uncertainties and taking into account the low signal-to-noise ratio) indicate the existence of at least two different paramagnetic Fe 3+ sites and that all of the observed iron is present as ferric iron in all three of the cement samples [41][42][43][44][45] . The hyperfine parameters from fitting the Mössbauer spectra associated with the cement samples are all fully consistent with values for cement from Harchand et al (D1: centre shift: 0.278 mm s -1 , quadrupole splitting: 0.428 mm s -1 , and D2: centre shift: 0.285 mm s -1 , quadrupole splitting: 1.667 mm s -1 , Table 2).…”

“…41 A significant proportion of the iron in hydrated OPC resides in the calcium aluminoferrite phases and its hydration products. Multiple researchers [41][42][43][44][45] have shown that room-temperature 57 Fe Mössbauer spectroscopy of hydrated OPC produces complex spectra with 3 or more components, due to the hydration products, including ettringite, iron substituted monosulphoaluminate and C-S-H, hydrogarnet and partlyunresolved magnetic components. [43][44][45] However, given the low signal-to-noise ratio obtained for our Mössbauer spectra, plus the absence of any weakly-(or strongly-) magnetic signals (which would give rise to spectral components at more positive and negative velocities than were observed), fitting with 2 doublets has been considered sufficiently robust to enable any significant differences arising between the samples to be identified.…”

“…Table 2 Mössbauer parameters for the biogenic and abiotic treatment, the untreated cement coupon and four literature standards: a) six-and four-fold coordinated Fe 3+ within the structure of hydroxyapatite (D1 and D2, respectively) and surface bound Fe 2+ (D3) 47 ; b) six-and four-fold coordinated Fe 3+ within calcium aluminoferrite (D1), labile iron component of C-S-H and iron in hydrogarnet (D2) and non-labile iron component of C-S-H 44,45 (D3); c)Fe 3+ within ordinary Portland cement in four-and six-fold coordinated sites (tetrahedral and octahedral D1 and D2, respectively) likely within the structure of calcium aluminoferrite 41 ; and d) Fe 3+ in four-and six-fold, or ordered and disordered six-fold coordinated sites within structure and on the surface of ferrihydrite (D1 and D2, respectively). 48 The number in brackets represents uncertainty in the last decimal place.…”