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• 作者：Christopher L. Edwards ; Lawrence B. Alemany ; Andrew R. Barron
• 刊名：Industrial & Engineering Chemistry Research
• 出版年：2007
• 出版时间：July 18, 2007
• 年：2007
• 卷：46
• 期：15
• 页码：5122 - 5130
• 全文大小：311K
• 年卷期：v.46,no.15(July 18, 2007)
• ISSN：1520-5045

文摘

The determination of the relative concentrations of tricalcium silicate (C₃S) and dicalcium silicate (C₂S) withina cement sample is potentially important in the prediction of the setting properties of the cement. For modelsystems, we have demonstrated that the presence of a paramagnetic species in intimate (physical) contactwith an otherwise diamagnetic silicon-containing mineral can dramatically decrease the longitudinal relaxationtime T₁ and consequently allow for the rapid data collection of the ²⁹Si MAS NMR spectrum. Thus, it appearsthat, for cements, the T₁ values of C₃S and C₂S will be significantly altered because of the paramagnetic Fe³⁺present in the C₄AF matrix that makes intimate contact with each of the silicate phases. The presence of theparamagnetic C₄AF matrix thus allows for the rapid collection of spectra of cements. Experiments that mightotherwise take weeks or even months now take mere hours. Three methods of NMR relaxation have beenexamined and compared: inversion recovery, variable-delay Bloch decay, and saturation recovery techniques.Analysis of an API class H cement demonstrated that the saturation recovery method for analysis of ²⁹SiNMR data offers the best combination of accuracy, speed, and ease of processing. The saturation recoverymethod was used to determine the C₃S/C₂S ratios for eight different cements: three API class G cements andfive API class H samples. Determination of C₃S/C₂S ratios by NMR spectroscopy provides an effective methodof analysis for cements, owing to NMR spectroscopy's direct measurement of the minerals in question withoutthe assumptions of composition that are required with oxide analysis from X-ray fluorescence and applicationof the Taylor-modified Bogue equations. Given the importance of C₃S and C₂S (and hence their ratio) indefining the performance of cements, we propose that ²⁹Si MAS NMR spectroscopy represents a viable methodfor cement characterization.