Article Review: Characterization of porosity and defect imaging in ceramic tile using ultrasonic inspections
Elif Eren, Semra Kurama and, Igor Solodov
Ceramics International 38 (2012) 2145–2151

Non Destructive Testing (NDT) are methods or techniques which can be applied to analyze the properties of materials without causing permanent damage to the test material. NDT has been adopted by various industries as a quicker way to detect defects in products during manufacturing processes, to avoid delays caused by more conventional methods. The article reviewed is a study by a group of investigators from Anadolu University, Turkey and University Stuttgart, Germany to assess ultrasound testing as a possible NDT for application in quality control during manufacturing and processing of ceramic tile. The physical properties under scrutiny are porosity and defect imaging.

Ultrasonic testing, a common NDT method for metallic and non-metallic materials, was employed by the group in their study. In this type of NDT, ultrasonic waves of low amplitude are propagated through the tiles and time of travel and intensity of waves are measured. Aim of the study: characterization of porosity, detection and imaging of different types of defects in ceramic tiles by applying three different ultrasonic approaches. Flaws in the tiles were achieved by inclusion of a piece of aluminum foil in one tile and a piece of paper in another before sintering them at high temperature. Aluminum foil melts and diffuses intothe tile structure, while the paper burns and creates a void in the tile. A third defective tile was sintered at a lower temperature to create a more porous tile. Analyses between defective and non-defective portions of the tiles were compared.

From the results the group makes the following conclusions: their first approach, A-scan analysis (a form of ultrasonic testing), can be used for detection of different types of defects in ceramic tile. Whether the defect is a distinct void (created by the burned paper) or a weak non-homogeneity (caused by the infiltration of melted aluminum foil), the A-scan catches the change in amplitude of the backwall echo caused by the defect. Measurement of ultrasonic wave velocity (second approach) is recommended as a reliable tool for characterization of porosity. The group also predicts that their third approach, ultrasonic frequency response,can be an indicator of porosity and potentially can be used for quantification of porosity (after more work and calibration).

The imagings developed by these techniques are high quality visual observations, though a bigger sample size and some statistical analysis would be necessary to affirm the results reported. The charts and images included in the article are very clear and can be easily interpreted, especially the images of the tile with melted aluminum foil and the tile with the void created by paper. This group has also published other articles detailing NDT methods for detection of different defects. A correlation, when established between such a qualitative approach and conventional quantitative methods such as ASTM C373 (Archimedes technique was used by the group in the study) can be used as an effective way for detection of defects without losing time. A drawback of this kind of NDT is detection without differentiation of both open (connected) and closed (non-connected) pores. Initially applied in industries to provide safer, less expensive materials and systems, NDT has fast gained popularity in various industries for flaw detection and evaluation in quality control. While the article stresses that such methods are effective and conventional methods difficult in the quality control of ceramic tile manufacturing, there is no discussion on whether implementing such techniques are cost effective or not.

If interested in more information about this research, please contact Dr. Jyothi Rangineni at Tile Council of North America.