X-Ray Powder Diffraction

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X-Ray Powder Diffraction

XRD analysis of clinker has been used in cement studies for the past 60 years, and applied in phase abundance analysis over the past 40 years. ASTM 1365 [4] details a standard test method for quantitative phase abundance analysis using XRD (QXRD). X-ray powder diffraction patterns provide phase, chemical, and crystal structure information data that may afford greater understanding of cement property / performance relationships. However, XRD analysis of clinker has proven difficult as the large number of phases results in substantial peak overlap. There is also difficulty in securing suitable pure phase reference standards. This may be addressed using the Rietveld method for X-ray powder diffraction [5]. Public domain code General Structure Analysis System (GSAS) was used to refine the powder diffraction data [6].

The Rietveld method allows standardization of powder diffraction analysis through use of calculated reference diffraction patterns based upon crystal structure models. The result is a set of refined crystal structure models for each phase in the clinker. From these data one can obtain pattern intensity information that may be related to phase abundance. Additional data on the chemical and structural properties of each phase may also be explored relative to selected performance properties. This can be used in research, and for quality-control in cement production, and is now being used to analyze the NIST Reference Clinkers. This method is acceptable under ASTM C1365 where a user is required to qualify their instrument and procedure.

Initial crystal structure models were taken from the literature [7-11]. These models are being incorporated into a cementitious materials crystal structure database currently in development. This database (Figure 2) is a compilation of published structures of cement and related phases, including crystalline phases in mineral admixtures.

Figure 2. Crystal structure database (in preparation) entry for belite (-form).

Phase: -Dicalcium Silicate	Formula: Ca₂SiO ₄	ICDD: 33-302 (larnite)

Reference:	K.H. Jost, B. Ziemer and R. Seydel "Redetermination of the Structure of -Dicalcium Silicate," Acta Cryst. (1977). B33, 1696-1700

Symmetry:	Monoclinic P2₁/n	Z: 4	Mass, Formula Unit: 3.326 g cm^-3

Cell Parameters (Å)
a 5.502	b 6.745	c 9.297	= 94.59°	Vol (Å³ ): 343.9



Atomic Parameters
	x	y	z	B (Å²)

Ca(1)	0.2738	0.3428	0.5694	0.38
Ca(2)	0.2798	0.9976	0.2981	0.30
O(1)	0.2864	0.0135	0.5599	0.91
O(2)	0.0202	0.7492	0.6919	0.67
O(3)	0.4859	0.6682	0.6381	0.63
O(4)	0.1558	0.6710	0.4264	0.62


Average interatomic distances
Si - O:	1.63 Å ,	Ca - O:	2.88 Å


Typical bulk belite composition (from Taylor '90, Cement Chemistry)
Na₂O	MgO	Al₂O ₃	SiO₂	P₂O₅	SO₃	K₂O	CaO	TiO₂	Mn ₂O₃	Fe₂O₃

0.1	0.5	2.1	31.5	0.2	0.1	0.9	63.5	0.2	0.0	0.9
This reference: (K_0.01 Na_0.005 Ca_0.975 Mg_0.01)₂ (Fe_0.02 Al_0.06 Si_0.90 P_0.01 S_0.01)O_3.96

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