Polycapillary Parallel-beam Optical System (Mechanical Components)
Shimadzu Analytical & Measuring Center
The term "polycapillary" indicates multiple (poly) fine glass tubes (capillaries) that guide X rays. X rays generated by a point source are accepted at a high solid angle by the polycapillaries, and emerge as a parallel beam at the opposite end. This optical system utilizes the X rays generated by the X-ray tube more efficiently than the standard (concentrating) method (the Bragg-Brentano Method), to achieve higher diffraction X ray intensities. The parallel-beam polycapillary method used in the optical system ensures that the angle of diffraction does not change due to displacements of the sample measurement surface. This characteristic allows highly sensitive and accurate measurements of samples with curved or irregular surfaces and improves the separation of the diffracted lights and shift in the angles of diffraction inherent in the concentrating method. These features of the polycapillary parallel-beam optical system permit the direct measurement of complex-shaped samples, such as mechanical components.
Measurement of Zeolite Catalyst
he measurement of a zeolite catalyst used to purify automobile emissions is presented here as an example of the measurement of an irregular surface. As shown at the bottom of Fig. 4, the standard (concentrating) method results in a shift in the angles of diffraction and separation of the diffracted lights. The shift in the angles of diffraction to lower angles is assumed to result from superimposition with diffraction lights reflected from the inside of holes in the sample, as shown in Fig. 1. Conversely, the angular positions of the diffracted lights measured using the polycapilary parallel-beam method perfectly match ICDD database card No. 46-1600 Mg2Al4Si5O18 (represented by lines in the diagram), confirming that the measurement was unaffected by the sample shape. The high diffraction intensity allows small peaks to be captured.
Measurement of a Welding Bead
Fig. 5 shows the measurement results on the corroded area of a welding bead. Oxides including Fe2O3 and FeO were detected but magnetite (Fe3O4) was the principal component of the corrosion products. The a-Fe detected close to the angle of diffraction 2q = 45°C) is thought to be the base metal. Easy quantitative identification (simple calculation using the I/Ic corundum ratio from the IC_DD database card) was conducted using search software to determine the quantitative values. This indicates that the polycapillary method extends the range of measurable samples, as measurements are unaffected by surface irregularities. The extremely high diffraction intensity attainable is expected to enhance the search accuracy.
Measurement of Residual Austenite in Steel Balls
Fig. 7 shows quantitative measurements to determine the residual austenite in approximately 2 mm-diameter miniature steel ball bearings. A dramatic drop in diffraction intensity occurred with the standard method, as only the apex of the sample surface contributed to the diffraction due to the high curvature of the sample surface. However, the polycapillary method is able to detect diffracted lights from a wide area, permitting highly sensitive measurements that confirmed the diffracted lights for the g -(200). (220) planes (top row, Fig. 7). Quantitative analysis using the method of direct comparison obtained a mean value of 1.01% for the five diffracted lights. This result indicates that the polycapillary parallel-beam method is extremely effective for detecting small peaks from samples with highly irregular surfaces.