Sta 449f3 synchronous thermal analyzer

To further analyze the effect of LDHs on the hydration products and the microstructure of the cement pastes in the sulfate environment, typical samples (after 180 d immersion in 5.0 wt.% Na₂SO₄ solution) were detected by XRD, TGA, SEM, and MIP, respectively. XRD analysis was performed by a Rigaku Smartlab 9kw advance powder X-ray diffractometer with 1.54 Å Cu Ka radiation at a scanning speed of 10 °/min from 5° to 50°. TGA was carried out using a NETZSCH STA 449F3 Synchronous Thermal Analyzer at a heating speed of 10 °C/min from 30 to 800 °C in a flowing nitrogen atmosphere. The microscopic morphology of the samples was observed using a Zeiss Sigma 300 scanning electronic microscope. Before the test, the typical flaky samples were coated with a 10 nm thick gold film. MIP was tested using a Micromeritics Auto Pore V 9620 mercury porosimeter with a maximum pressure of 60,000 psi.

One sample was selected from each group of samples after curing: A, B, C, D, E, and F, plus the control group. A total of seven samples were tested; the samples were placed in an oven for drying, crushed, passed through a 200-mesh sieve, and used for XRD (Hefei, China), TGA (Hefei, China), and SEM (Hefei, China) to analyze the chemical bonds and chemical components in the cured samples.
XRD patterns were obtained using a Rigaku D/Max-2005 V diffractometer with Cu-Kα scanning from 5 to 80° 2θ. The components in the samples were identified by comparison with standards established by the International Center for Diffraction Data.
The instrument used in the TGA test was a STA449F3 synchronous thermal analyzer manufactured by NETZSCH, Germany. During the test, the atmosphere was nitrogen (flow rate 50 mL/min), the temperature range was set from 25 °C to 1000 °C, and the heating rate was 5 °C/min. The FTIR test used a Nicolet iS50 FTIR spectrometer manufactured by Thermo Fisher Scientific. The sample was prepared via the tableting method during the test, and the measurement range was 4000~400 cm⁻¹.
SEM imagery was obtained to provide direct evidence of reaction product analyses. Samples of approximately 5 × 5 × 5 mm were selected; they were initially freeze-dried before their surfaces were cleaned and then coated with gold, in preparation for SEM analysis.