X-ray diffraction analysis of clay minerals for brick clay, danish yellow and red brick clay

<p dir="ltr">X-ray diffraction (XRD) analysis was carried out with a PanAnalytical X’Pert PRO (CuKα radiation), wavelength of 1.54 Å, with operation settings 45 kV and 40 mA. Clay minerals in brick clay were identified using the glass slide method [44] on dried clay paste (< 2 μm). The brick clay was prepared through the following steps: 200 g of brick clay, without sand additives, was first dried at 40°C (for 7 days). CaCO3 was removed by mixing brick clay with 2 M acetic acid and left for 24 hours. The acetic acid was washed away with distilled water, and the samples were centrifuged (3000 rpm for 10 min), then dried for three days at 60°C. 20 g of brick clay was then mixed with 200 ml of 0.002M Na-pyrophosphate and rotated for 18 h. The samples were placed in an ultrasound for 15 min, then wet sieved through a 63 μm sieve. The fraction < 63 μm was transferred to an Andreasen pipette and filled with 0.002M Na-pyrophosphate, up to 20 cm. The Andrease pipette was shaken, and the slurry was left for 16.5h. After 16.5h, the top 20 cm, now containing the clay paste fraction (<2μm), was retained, and the excess water was removed by centrifugation (3000 rpm, 20 min). The clay paste was dried at room temperature in a fume cupboard. When dried, 0.03 g of the sample was mixed with 1.5 ml of distilled water and applied to a glass plate with a Pasteur pipette and left at room temperature until completely dry. The XRD measurements were performed on the dried sample, at four different conditions: 1) The glass plates were saturated with water; 2) saturated with ethylene glycol for a minimum of 2 days at 60°C; 3) ignited at 350°C for 2 h; 4) ignited at 550°C for 2 h. Before each measurement, the samples were cooled down to room temperature. The measurements were conducted by using the following programs: 1) Water saturated sample were measured between 2θ = 3-65°, with a slit of 15mm, step size 2θ = 2°, measuring time 21 min; 2) Ethylene glycolate sample: 2θ = 3-40°, 10mm, 2θ = 2°, time = 13 min; 3-4) Ignited samples: 2θ = 3-40°, 10mm, 2θ = 2°, time = 13 min</p>