Acid Corrosion Behavior of Sol–Gel‐Prepared Mullite Ceramics With and Without Addition of Lanthanum

Abstract

The corrosion behavior of pure and lanthanum doped, sol-gelderived, mullite ceramics in nitric acid aqueous solutions with various concentrations was investigated and compared. Samples sintered at a temperature of 1600°C for 4 h were characterized using powder X-ray diffraction, SEM, and energy dispersive X-ray spectroscopy. The corrosion behavior was explored by measuring the amount of eluted ions using atomic absorption spectrophotometry and inductively coupled plasma optical emission spectrometry (ICP-OES). The doped sample was found to be more susceptible to dissolution in the corrodent, having higher leaching rates. The amounts of eluted lanthanum ions were in order of magnitude higher than amounts of silicon and aluminum. Those phenomena were attributed to the incorporation of lanthanum in the glassy phase, forming SiO 2 -La 2 O 3 -rich glassy phase, which can dissolve in corrodent more easily than SiO 2 -rich glassy phase in the pure sample.

Optimization of Alumina Ceramics Corrosion Resistance in Nitric Acid

“…According to previous studies [ 5 , 7 , 16 , 29 , 30 ], three factors (input variables) that impact the chemical stability of ceramics in acidic solutions were selected: temperature, concentration and immersion time in HNO 3 . Each factor was varied at three levels with five replicates, which were conducted at the center point ( Table 2 and Table 3 ).…”

Tuning pore structure of corrosion resistant solid-state-sintered SiC porous ceramics by particle size distribution and phase transformation

“…Residual strengths of SiC supports after 200 h of corrosion in 20 wt.% H2SO4 and NaOH solutions at 90 °C are shown in table 2. The average strengths of supports all remain ≥92.5% of their initial strengths, suggesting that SiC supports sintered with or without B4C additive possess the desired corrosion resistance in hot acidic/basic solutions, which is considerably superior to the supports reported in previous literature [11][12][13][14][15][16][17]. Moreover, a representative SiC support sintered with 1 wt.% B4C at 2200 °C shows unconspicuous variation of flexural strength as the corrosion time increases (Fig.…”

“…By contrast, other low cost ceramic supports such as cordierite and mullite appear more susceptible to dissolution in corrodent [10,14]. Cordierite is not resistant to thermal acidic solution due to the quick dissolution of Mg and Al [10], while mullite is not stable in hot acidic and basic solutions [15][16][17].…”

Electrospun mullite nanofibers derived from diphasic mullite sol

“…The peaks of alumina phase are not very obvious because of the poor level of structural order. Some studies also suggested that this transient phase was Al–Si spinel (a solid solution between alumina and silica) which exhibits broad peaks very similar to those of alumina phase. Further research should be done to confirm this phase transformation.…”

“…Although many groups, such as Lin, Zadeh, and Peng, have successfully fabricated nanoscale mullite fibers by electrospinning a monophasic mullite sol, the results indicated that mullite nanofibers derived from the monophasic sol cannot be used at high temperatures (higher than 1400°C) due to the dramatic growth of mullite grains and therefore is unsuitable for being used as the starting material for the fabrication of mullite nanofibrous ceramics. Mullite sol can be divided into the monophasic sol and the diphasic sol according to their homogeneity, and the general agreement of the extensive works is that the homogeneity level of mullite sols actually controls the phase transformation sequence, mullite formation temperature, as well as the properties of sintered bodies. Monophasic sols are constituted of long Al‐O‐Si linkages with molecular homogeneity and crystallize mullite phase directly based on the Al‐O‐Si fundamental structure at a low temperature (∼980°C); however, the generated grains would grow dramatically at high temperature, which would consequently influence the fiber mechanical properties.…”