3.4 Zircon (ZrSiO4)

presence of periclase and rutile shows that the product is not pure MT. In terms of XRD line peaks, the MT patterns exhibit broadened peaks, particularly at lower temperatures indicating that it is in nanometric crystallite size [17]. The average XRD crystallite size of the MT nanocrystals is between 76 2 nm (600°C) and 150 4 nm (800°C). Figure 7 shows a typical TEM micrograph of the MT crystallites. The micrograph shows inhomogeneous crystallite size ranging between 50 and 120 nm—being the dominating size is around 80 nm. Therefore, the TEM result supports that of XRD, where the hexagonal morphology of the crystallites confirms

X-ray diffraction patterns (CuKα radiation) of the calcined (Mg,Ti)-dissolved powders at various calcination temperatures: (a) 600, (b) 700, and (c) 800°C. symbols: MT = MgTiO3, R = rutile, P = periclase (MgO).

Ceramic Materials ‐ Synthesis, Characterization, Applications and Recycling

Figure 6.

Figure 7.

50

TEM micrograph of MT powder after calcination at 600°C.

Synthesis of ZrSiO4 powder was performed by making use of natural zircon sand which was collected from District of Kereng Pangi in Central Kalimantan. To obtain a pure zircon powder, the sand was subject to several processing steps including magnetic separation, reaction with HCl followed with NaOH, and finally washing and drying. The XRD patterns of the samples after each processing are presented in Figure 8. Several inferences can be drawn from the figure, for example, the dominating phase in the sand and powder is zircon (ZrSiO4, COD ID 900-2554). Furthermore, the highest intensity increases with the processing step, indicating that the crystallinity improves subsequently. Moreover, the undetected peaks disappear after reacting the sand with HCl. Investigation using XRF showed that the disappearance of the undetected XRD peaks in Sample (B) could be associated with the removal of unwanted substances such as Ti and Fe in the sand (Figure 9). However, Sample (B) contains silica quartz (COD ID 500-0035). The XRF data showed Zr:Si weight fraction ratio of approximately 3:2 which indicates that pure zircon powder has not been achieved since the ratio should be at approximately 3:1. Reaction with

#### Figure 8.

X-ray diffraction patterns (CuKα radiation) of (A) zircon sand, (B) zircon powder after magnetic separation and reaction with HCl, and (C) powder B after reaction with NaOH and washing. Symbols: Z = zircon, ZrSiO4; S = silica (SiO2), quartz; T = undetected.

ceramics, that is, 15 GPa [34] versus 3 GPa [35]. Therefore, zirconia balls would presumably be able to mill zircon powder. The XRD patterns of the milled zircon powders at various milling time are presented in Figure 11. Milling has no effect on the detected phase, that is, it remains zircon, and resulted in lower but broader peak intensity. The XRD peak broadening was caused by crystallite size and nonuniform effects after milling. These XRD characters were investigated using MAUD software [26] and came across at a conclusion that the synthesized zircon powder exhibited smaller crystallite size after milling, that is, from 173 nm before milling to 162 and finally to 45 nm after milling for 5 and 10 h, respectively. TEM images of the unmilled and 10 h milled zircon powders are shown in Figure 12. These images

Synthesis of High-Purity Ceramic Nano-Powders Using Dissolution Method

DOI: http://dx.doi.org/10.5772/intechopen.81983

SEM image (SEI mode, left) and its energy-dispersive elemental mapping (right) of the purified zircon powder

confirm the success of the synthesis of the nano-sized zircon powder.

annealing at 200°C for 2 h.

Figure 11.

53

Z = zircon, ZrSiO4.

Figure 10.

(sample C).

The software also allowed the extraction of a nonuniform strain of the milled powder, and the results showed that longer milling induced more strains as also observed by others [36, 37] for different metal oxides. The strain values for the zircon powders are 2, 3, and 6 <sup>10</sup><sup>4</sup> for the unmilled and 5 and 10 h for milled samples, respectively. These values dropped significantly to as low as 2 <sup>10</sup><sup>4</sup> after

X-ray diffraction patterns (CuKα radiation) of milled zircon powder at various milling times. Symbol:

#### Figure 9.

X-ray fluorescence atomic weight fractions of (a) zircon sand, (B) zircon powder after magnetic separation and reaction with HCl, and (C) powder B after reaction with NaOH and washing.

NaOH was subsequently done to form liquid Na2SiO3 precursor which can be easily removed by sieving. The sieved slurry was then washed and dried to obtain pure zircon powder (Sample (C)). The SEM image and its energy-dispersive elemental mapping of Sample C are shown in Figure 10. The figures indicate the high crystallinity and high purity of the powder. These facts show that the dissolve method which comprises magnetic separation, HCl reaction, washing-filtering, NaOH reaction, another washing-filtering, and drying of natural zircon sand may produce high-purity, single-phase zircon powder.

An effort to process the zircon powder to achieve zircon nano-powder has been accomplished. The mechanical zirconia ball-milling was chosen. Well-sintered partially stabilized zirconia ceramics exhibit much higher Vickers' hardness than zircon Synthesis of High-Purity Ceramic Nano-Powders Using Dissolution Method DOI: http://dx.doi.org/10.5772/intechopen.81983

Figure 10. SEM image (SEI mode, left) and its energy-dispersive elemental mapping (right) of the purified zircon powder (sample C).

ceramics, that is, 15 GPa [34] versus 3 GPa [35]. Therefore, zirconia balls would presumably be able to mill zircon powder. The XRD patterns of the milled zircon powders at various milling time are presented in Figure 11. Milling has no effect on the detected phase, that is, it remains zircon, and resulted in lower but broader peak intensity. The XRD peak broadening was caused by crystallite size and nonuniform effects after milling. These XRD characters were investigated using MAUD software [26] and came across at a conclusion that the synthesized zircon powder exhibited smaller crystallite size after milling, that is, from 173 nm before milling to 162 and finally to 45 nm after milling for 5 and 10 h, respectively. TEM images of the unmilled and 10 h milled zircon powders are shown in Figure 12. These images confirm the success of the synthesis of the nano-sized zircon powder.

The software also allowed the extraction of a nonuniform strain of the milled powder, and the results showed that longer milling induced more strains as also observed by others [36, 37] for different metal oxides. The strain values for the zircon powders are 2, 3, and 6 <sup>10</sup><sup>4</sup> for the unmilled and 5 and 10 h for milled samples, respectively. These values dropped significantly to as low as 2 <sup>10</sup><sup>4</sup> after annealing at 200°C for 2 h.

Figure 11.

X-ray diffraction patterns (CuKα radiation) of milled zircon powder at various milling times. Symbol: Z = zircon, ZrSiO4.

NaOH was subsequently done to form liquid Na2SiO3 precursor which can be easily removed by sieving. The sieved slurry was then washed and dried to obtain pure zircon powder (Sample (C)). The SEM image and its energy-dispersive elemental mapping of Sample C are shown in Figure 10. The figures indicate the high crystallinity and high purity of the powder. These facts show that the dissolve method which comprises magnetic separation, HCl reaction, washing-filtering, NaOH reaction, another washing-filtering, and drying of natural zircon sand may produce

X-ray fluorescence atomic weight fractions of (a) zircon sand, (B) zircon powder after magnetic separation and

reaction with HCl, and (C) powder B after reaction with NaOH and washing.

X-ray diffraction patterns (CuKα radiation) of (A) zircon sand, (B) zircon powder after magnetic separation and reaction with HCl, and (C) powder B after reaction with NaOH and washing. Symbols: Z = zircon,

Ceramic Materials ‐ Synthesis, Characterization, Applications and Recycling

An effort to process the zircon powder to achieve zircon nano-powder has been accomplished. The mechanical zirconia ball-milling was chosen. Well-sintered partially stabilized zirconia ceramics exhibit much higher Vickers' hardness than zircon

high-purity, single-phase zircon powder.

Figure 8.

Figure 9.

52

ZrSiO4; S = silica (SiO2), quartz; T = undetected.

Figure 12. TEM micrographs of unmilled (left) and 10 h milled zircon (right) powders.
