APPLICATION OF NUCLEAR TECHNIQUES TO STUDY SYNTHETIC SANDSTONES MICROSTRUCTURE PROPERTIES

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1 2009 International Nuclear Atlantic Conference - INAC 2009 Rio de Janeiro,RJ, Brazil, September27 to October 2, 2009 ASSOCIAÇÃO BRASILEIRA DE ENERGIA NUCLEAR - ABEN ISBN: APPLICATION OF NUCLEAR TECHNIQUES TO STUDY SYNTHETIC SANDSTONES MICROSTRUCTURE PROPERTIES Leonardo C. Marques, Jaquiel S. Fernandes, and Carlos R. Appoloni 1 Physics Department (CCE / State University of Londrina) Campus Universitário Londrina, PR leocarma@yahoo.com.br jaquielfernandeso@yahoo.com.br appoloni@uel.br ABSTRACT X-ray microtomography was employed to evaluate ceramic samples microstructure, which were manufactured with similar characteristics of sandstones. The three ceramic sets studied have the following composition and permeability: 99.7 % of SiO 2 and (46 ± 9) md; 99.7 % of SiO 2 and (550 ± 20) md; 85 % of SiO 2 and 15 % of Al 2 O 3 and (82 ± 2) md. For the acquisition of microtomographic data of the samples, a Skyscan model 1172 µ-ct scanner was used. The first ceramic kind was scanned at 1.73 μm resolution and average total porosity values from 25.7 to 30.1 % were found. The second one was scanned at 0.64 μm resolution and average total porosity values from 48.4 to 51.0 % were found. The third one was scanned at 1.28 μm resolution and average total porosity values from 28.2 to 30.6 % were found. A comparison was made between the porosity results by microtomography and gamma ray transmission methodology employing an Am-241 source. The porous size distribution was also measured for the three kinds of samples. Besides the 2D sections obtained through the scanning, a partial reconstruction of the volume was also accomplished. 1. INTRODUCTION Knowledge of the porous structure of amorphous materials is of fundamental importance in calculating geometrical parameters such as total porosity, pore size distribution and physical parameters relating to fluid flow inside void space. Ceramics are materials thoroughly used in industrial production, such as filters and thermal insulator. The microstructure knowledge of these materials is of great importance to their manufacture. A non-destructive methodology normally used is the gamma ray transmission. It permits the measurement of parameters as density and porosity of studied material. It is a great tool to simple researches without necessity to know the inner profile of body. X-ray microtomography also is a non-destructive methodology. It is related with structural parameters determination of materials, such as porosity and pore size distribution of 2D and 3D images. Through microtomography images is possible to evaluate the inner structure of scanned bulk. In this paper, X-ray microtomography was used to evaluate the microstructure of ceramic samples to simulate sandstones.

2 2.1. Samples and Equipment 2. MATERIALS AND METHODS Analyses were done with ceramic samples manufactured by the TechMat Tecnologia de Materiais Ltda, a company INT/RH [1]. The samples were mainly manufactured with SiO 2, presenting a permeability of (46.0 ± 9.2) md for ceramic I kind, (550 ± 20) md for ceramic II kind and (82 ± 2) md for ceramic III kind. The chemical composition of the ceramic samples is given in Table 1. Table 1. The chemical composition of ceramic samples Compound (%) SiO2 Al2O3 Fe2O3 CaO MgO K2O ceramic I and II ceramic III For the microtomographic experiment, one parallelepiped with 0.6 x 0.6 x 1.2 cm was cut of an original parallelepiped with 1 x 1 x 3 cm dimensions. This procedure was done for each ceramic kind to facility the acquisition. Table 2 summarizes the main acquisition parameters. Table 2. Acquisition parameters used for X-ray microtomography. Sample Spatial Exposition Angular Voltage Resolution Time Step (kv) (μm) (ms) (degrees) Frames ceramic I ceramic II ceramic III Besides parameters showed in Table 2, all of acquisitions were accomplished with 1048 x 2000 pixels on CCD camber and aluminum filter of 1 mm thickness to minimize the beam hardening [2]. An 1172 Skyscan scanner was used to perform the experiment. It possesses an X-ray tube with W anode operated at kv voltage range at the 10 W power. The detector is a 10 Mp (mega pixels) CCD camera coupled to the scanner. This set is able to differentiate dimension objects smaller than 1 μm. This equipment is installed in CENPES/PETROBRAS. In this work, two specifics software were used. One to reconstruct 2D images based on acquired projections, NRecon, and another one to analyses the parameters in 2D images, Imago. The NRecon software belongs to Skyscan-pack and the Imago software was developed at the Laboratory of Porous Media and Thermophysical Properties (LMPT), Department of Mechanical Engineering, Federal University of Santa Catarina in association with Engineering Simulation and Scientific Software (ESSS).

3 2.2. Parameters Standard Procedure X-ray microtomography is based in inhomogeneous attenuation suffered for X-ray beam to be transmitted through matter. The characterization of this transmission is a linear attenuation coefficients map. Such as attenuation is written for Lambert-Beer law [3], as following: I μ x = I 0 e (1) The porous media showed in a binary microtomographic 2D image can be characterized by porous phase function Z(x) [4]: 1 when x belongs to porous space Z (x) = (2) 0 when doesn' t belongs to that one where x is the position. The porosity φ is the statistic media (related by ), as following: φ = Z( x) (3) For porous size distribution determination in 2D images, the measurement unit consists in porous superficial area. Therefore, the porous size distribution will be: φ φ(r) F(r) = φ (4) where φ is the total porosity of original image and φ (r) is the porosity of image after opening operation. 3. RESULTS AND DISCUSSIONS Figure 1 shows the 2D images for each ceramic scanned, where porous phase is presented in light gray shades and solid phase is presented in dark gray shades for ceramic I, on the contrary to ceramic s II and III, where the porous phase is presented in dark gray shades. Figure 1 also shows that the contrast resolution to ceramic II was that good as much as ceramic s I and III. The 2D images quantities obtained of scanning with chosen parameters were 978, 541 and 801 for ceramic I, II and III, respectively.

4 a b c Figure 1. (a) 34 2D image of ceramic I; (b) 918 2D image of Ceramic II and 100 2D image of Ceramic III. Figure 2 shows 2D images presented in Figure 1 binarized with Imago software. This software to relates white color as porous phase and black color as solid phase. Because of this, the 2D images of ceramic II and III were reversed. Besides, the 2D images of ceramic I were cut to eliminate white edges that will be related as porous phase. a b c Figure 2. (a) 34 2D image of ceramic I binarized at 146 gray shade; (b) 918 2D image of Ceramic II binarized at 109 gray shade and 100 2D image of Ceramic III binarized at 103 gray shade. Figure 3 shows the graphics of porosity for each 2D images for ceramic I and III. In Figure 3 (a), there wasn t any point out of 95 % confidence region. That shows a good homogeneity for ceramic I. Even though, some 2D images show porosity values higher due an irregularity in matrix. Already, in Figure 3 (b) it s possible to notice some porosity values out of 95 % confidence region, both above and below of this region.

5 a b Average Porosity (%) Average Porosity (%) 95 % Confidence % Confidence Porosity (%) D images Porosty (%) D Images Figure 3. Average porosity for each 2D image of (a) ceramic I and (b) ceramic III. Table 3 shows X-ray microtomography porosity results comparison with that one gamma ray transmission technique and manufacturer. Those results were showed with 95 %confidence. The results for Ceramic I set were in agreement to gamma ray transmission and manufacturer. The Ceramic II set results only had good agreement between gamma ray transmission and manufacturer. Because the manufacturer didn t supply particle density, it wasn t possible to obtain results for gamma ray transmission technique for Ceramic III set. It didn t supply the porosity value too. Table 3. Total porosity interval obtained for X-ray microtomography and gamma ray transmission, at 95 % confidence, and supplied by manufacturer. Sample X-ray Microtomography (%) Gamma ray Transmission (%) Manufacturer (%) ceramic I ceramic II ceramic III ** ** Figures 4 and 5 show porous size distribution of ceramic I and III kind. This distributions show that porous with dimensions lower than spatial resolution used weren t quantified. Figures 4 and 5 also show a porous size detail from 20 to 60 μm for ceramic I and from 10 to 50 μm for ceramic III.

6 30 0,6 Frequency (%) Frequency (%) 0,5 0,4 0,3 0,2 0,1 0, Ray (μm) Ray (μm) Figure 4. Porous size distribution for ceramic I from 0 to 50 μm and from 20 to 60 μm. Frequency (%) Freqüencia (%) 1,7 1,6 1,5 1,4 1,3 1,2 1,1 1,0 0,9 0,8 0,7 0,6 0,5 0,4 0,3 0,2 0,1 0, Raio (μm) Ray (μm) Figure 5. Porous size distribution for ceramic III from 0 to 50 μm and from 10 to 50 μm.

7 4. CONCLUSIONS Results for ceramic I show that X-ray microtomography is a good method to obtain porosity values of amorphous materials. However, results for ceramic II show that one has to be careful with the acquisition parameters choice. The comparison among parameters chosen for acquisition data gives direction that the contrast resolution could be better using 59 kv voltage and 8835 ms time resolution for ceramic II. There are samples which part of porosity isn t quantified because it possesses porous with size lower than the equipment spatial resolution. ACKNOWLEDGMENTS The authors thank CNPq for financial support and Capes/MEC for the scholarship. REFERENCES 1. TechMat: Tecnologia de Materiais Ltda, 2. R. A. Ketcham & W. D. Carlson, Acquisition, optimization and interpretation of X-ray computed tomographic imagery: applications to the geosciences, Computers & Geociences, vol. 27, pp , (2001). 3. V. Cnudde & P. J. S. Jacobs, Monitoring of weathering and conservation of building materials through non-destrutive X-ray computed microtomography, Environmental Geology, vol. 46, pp (2004). 4. IMAGO, Scientific Manual, Versão 2.1.4, 2002.