Artículos de revistas
Phenomenon of primary and secondary extinction in textured material
Autor
KRYSHTAB , T. G.
PALACIOS GÓMEZ, J.
MAZIN , M. O.
Institución
Resumen
SE PROPONE UN NUEVO MÉTODO DE DIFRACCIÓN DE RAYOS X PARA EL CÁLCULO MÁS EXACTO DE FIGURAS POLARES PARA LA DETERMINACIÓN DE LA FUNCIÓN DE DISTRIBUCIÓN DE ORIENTACIONES DE CRISTALITOS (CODF) EN MATERIALES CON TEXTURA, INTRODUCIENDO UNA CORRECCIÓN PARA LA INTENSIDAD INTEGRADA DEL HAZ DIFRACTADO DEBIDA AL FENÓMENO DE EXTINCIÓN. ADEMÁS, PARA EL CASO DE LA DIFRACCIÓN SIMÉTRICA DE BRAGG DE UNA MUESTRA TEXTURADA EN FORMA DE PLACA DE ”ESPESOR INFINITO”, SE DESARROLLA UNA SOLUCIÓN SIMPLE PARA LA SEPARACIÓN Y DETERMINACIÓN DE LOS PARÁMETROS DE EXTINCIÓN PRIMARIA Y SECUNDARIA, LAS CUALES PUEDEN ESTAR PRESENTES SIMULTÁNEAMENTE. LA DETERMINACIÓN DE ESTOS PARÁMETROS DA INFORMACIÓN ADICIONAL DE LA ESTRUCTURA DE LOS CRISTALITOS Y NOS PERMITE EVALUAR EL TAMAÑO PROMEDIO DE LOS SUBGRANOS Y SU DESORIENTACIÓN RESPECTIVAMENTE [1]. DE LA TEORÍA DE LA DIFRACCIÓN DINÁMICA SE DEMUESTRA QUE LA LONGITUD DE EXTINCIÓN, QUE ESTÁ DIRECTAMENTE RELACIONADA CON EL FENÓMENO DE EXTINCIÓN PRIMARIA, EN LA GEOMETRÍA DE BRAGG PARA LA POLARIZACIÓN (PERPENDICULAR), ES INDEPENDIENTE DE LA LONGITUD DE ONDA USADA PARA UNA REFLEXIÓN DADA. POR OTRA PARTE, LA CONTRIBUCIÓN ADICIONAL DE LA EXTINCIÓN SECUNDARIA DEPENDE DE LA LONGITUD DE ONDA DE LOS RAYOS X DEBIDO AL CAMBIO DEL COEFICIENTE DE ABSORCIÓN EFECTIVA. CONSIDERANDO ESTE HECHO, SE REALIZA EL CÁLCULO DE LA DENSIDAD DE POLOS Y LOS PARÁMETROS DE EXTINCIÓN PRIMARIA Y SECUNDARIA USANDO LA MISMA REFLEXIÓN FUERTE PARA DOS LONGITUDES DE ONDA DIFERENTES Y EN EL CASO DE UNA DE ESTAS LONGITUDES DE ONDA, PARA UNA REFLEXIÓN DE SEGUNDO ORDEN. PARA CONFIRMAR EL MÉTODO PROPUESTO FUERON MEDIDAS UNA MUESTRA DE ALUMINIO PARCIALMENTE LAMINADO EN FRÍO Y UNA MUESTRA DE POLVO DE ALUMINIO. AHÍ FUERON OBTENIDOS: LA DENSIDAD CORREGIDA DE POLOS, LOS VALORES DE LA EXTINCIÓN PRIMARIA Y SECUNDARIA Y LOS TAMAÑOS PROMEDIOS DE LOS DOMINIOS COHERENTES Y EL ÁNGULO PROMEDIO DE DESORIENTACIÓN DE LOS SUBGRANOS EN LAS DIRECCIONES SELECCIONADAS. LOS RESULTADOS MUESTRAN QUE LA CARACTERIZACIÓN PRECISA POR DIFRACCIÓN DE RAYOS X DE MATERIALES CON TEXTURA REQUIERE LA CONSIDERACIÓN EN GENERAL DEL FENÓMENO DE EXTINCIÓN PRIMARIA ASÍ COMO DE LA SECUNDARIA.AbstractA NEW X-RAY DIFFRACTION METHOD IS PROPOSED FOR A MORE EXACT CALCULATION OF POLE FIGURES TO DETERMINE THE CRYSTALLITE ORIENTATION DISTRIBUTION FUNCTION (CODF) IN TEXTURED MATERIALS, BY THE INTRODUCTION OF A CORRECTION OF THE INTEGRATED INTENSITY OF THE DIFFRACTED BEAM DUE TO THE PHENOMENON OF EXTINCTION. BESIDES, FOR THE CASE OF A SYMMETRICAL BRAGG REFLECTION FROM AN ”INFINITELY THICK” FLAT PARALLEL PLATE TEXTURED SAMPLE A SIMPLE SOLUTION IS DEVELOPED FOR THE PROBLEM OF SEPARATION AND DETERMINATION OF PRIMARY AND SECONDARY EXTINCTION PARAMETERS, WHICH CAN BE PRESENT SIMULTANEOUSLY. THE DETERMINATION OF THESE PARAMETERS GIVES ADDITIONAL INFORMATION ABOUT CRYSTALLITE STRUCTURE AND ALLOWS US TO EVALUATE THE AVERAGE SUBGRAINS SIZE AND THEIR DISORIENTATION, RESPECTIVELY [1]. IN THIS WORK, ACCORDING TO THE DYNAMIC DIFFRACTION THEORY, IT IS SHOWN THAT THE EXTINCTION LENGTH, WHICH IS DIRECTLY CONNECTED WITH THE PHENOMENON OF PRIMARY EXTINCTION, IN THE BRAGG GEOMETRY FOR POLARIZATION (PERPENDICULAR) IS INDEPENDENT ON THE WAVELENGTH USED FOR A GIVEN REFLECTION. ON THE OTHER HAND, THE ADDITIONAL CONTRIBUTION FROM SECONDARY EXTINCTION DEPENDS ON X-RAYS WAVELENGTH DUE TO THE CHANGE OF EFFECTIVE ABSORPTION COEFFICIENT. CONSIDERING THIS FACT, THE CALCULATIONS OF POLE DENSITY AND THE PARAMETERS OF PRIMARY AND SECONDARY EXTINCTION ARE PERFORMED USING THE SAME STRONG REFLECTION FOR TWO DIFFERENT WAVELENGTHS AND, FOR ONE OF THESE WAVELENGTHS, A SECOND ORDER OF REFLECTION. FOR CONFIRMATION OF THE PROPOSED METHOD A PARTIALLY COLD ROLLED ALUMINUM SAMPLE AND AN ALUMINUM POWDER STANDARD SAMPLE WERE MEASURED. THE CORRECTED POLE DENSITIES, THE VALUES OF PRIMARY AND SECONDARY EXTINCTION AND THE AVERAGE SIZES OF PERFECT COHERENT AREAS AND AVERAGE ANGLE OF DISORIENTATION OF SUBGRAINS IN THE SELECTED DIRECTIONS WERE OBTAINED. THE OBTAINED RESULTS SHOW THAT THE PRECISE X-RAY DIFFRACTION CHARACTERIZATION OF TEXTURED MATERIALS REQUIRES THE CONSIDERATION, IN GENERAL, OF PRIMARY AS WELL AS SECONDARY EXTINCTION PHENOMENON. A NEW X-RAY DIFFRACTION METHOD IS PROPOSED FOR A MORE EXACT CALCULATION OF POLE FIGURES TO DETERMINE THE CRYSTALLITE ORIENTATION DISTRIBUTION FUNCTION (CODF) IN TEXTURED MATERIALS, BY THE INTRODUCTION OF A CORRECTION OF THE INTEGRATED INTENSITY OF THE DIFFRACTED BEAM DUE TO THE PHENOMENON OF EXTINCTION. BESIDES, FOR THE CASE OF A SYMMETRICAL BRAGG REFLECTION FROM AN ""INFINITELY THICK"" FLAT PARALLEL PLATE TEXTURED SAMPLE A SIMPLE SOLUTION IS DEVELOPED FOR THE PROBLEM OF SEPARATION AND DETERMINATION OF PRIMARY AND SECONDARY EXTINCTION PARAMETERS, WHICH CAN BE PRESENT SIMULTANEOUSLY. THE DETERMINATION OF THESE PARAMETERS GIVES ADDITIONAL INFORMATION ABOUT CRYSTALLITE STRUCTURE AND ALLOWS US TO EVALUATE THE AVERAGE SUBGRAINS SIZE AND THEIR DISORIENTATION, RESPECTIVELY [1]. IN THIS WORK, ACCORDING TO THE DYNAMIC DIFFRACTION THEORY, IT IS SHOWN THAT THE EXTINCTION LENGTH, WHICH IS DIRECTLY CONNECTED WITH THE PHENOMENON OF PRIMARY EXTINCTION, IN THE BRAGG GEOMETRY FOR POLARIZATION (PERPENDICULAR) IS INDEPENDENT ON THE WAVELENGTH USED FOR A GIVEN REFLECTION. ON THE OTHER HAND, THE ADDITIONAL CONTRIBUTION FROM SECONDARY EXTINCTION DEPENDS ON X-RAYS WAVELENGTH DUE TO THE CHANGE OF EFFECTIVE ABSORPTION COEFFICIENT. CONSIDERING THIS FACT, THE CALCULATIONS OF POLE DENSITY AND THE PARAMETERS OF PRIMARY AND SECONDARY EXTINCTION ARE PERFORMED USING THE SAME STRONG REFLECTION FOR TWO DIFFERENT WAVELENGTHS AND, FOR ONE OF THESE WAVELENGTHS, A SECOND ORDER OF REFLECTION. FOR CONFIRMATION OF THE PROPOSED METHOD A PARTIALLY COLD ROLLED ALUMINUM SAMPLE AND AN ALUMINUM POWDER STANDARD SAMPLE WERE MEASURED. THE CORRECTED POLE DENSITIES, THE VALUES OF PRIMARY AND SECONDARY EXTINCTION AND THE AVERAGE SIZES OF PERFECT COHERENT AREAS AND AVERAGE ANGLE OF DISORIENTATION OF SUBGRAINS IN THE SELECTED DIRECTIONS WERE OBTAINED. THE OBTAINED RESULTS SHOW THAT THE PRECISE X-RAY DIFFRACTION CHARACTERIZATION OF TEXTURED MATERIALS REQUIRES THE CONSIDERATION, IN GENERAL, OF PRIMARY AS WELL AS SECONDARY EXTINCTION PHENOMENON.