3.2 Titanium dioxide (TiO2)

drying the precipitates after subsequent washing with water. The solvent for processing zircon sand, as shown in Table 3, depends on the purposed powder. Zircon sand can be processed to obtain nano-zircon, silica, or nano-zirconia powders. The calcination temperatures were selected after inspecting the thermal data

Precursor Calcination

Mg HCl MgCl2 700 Pure MgO 98

Ti HCl TiCl4 200 < T < 700 TiO2

Ceramic Materials ‐ Synthesis, Characterization, Applications and Recycling

MgCl2

Dissolution of metal powders in acid to produce nanocrystalline oxide powders.

temperature (°C)

Product Crystallite size

anatase

TiO2 rutile

rutile

MgTiO3

>800 TiO2

700 Pure

(nm)

96–114

6–96

>200

65

instrumental correction using an annealed Y2O3 as suggested previously. The relative weight fraction of phase i at each depth was determined by:

The structure, composition, and nanocrystallinity of the powders were examined using CuKα X-ray diffraction (XRD) data to which the Rietveld-based Rietica [25] and Material Analysis Using Diffraction (MAUD) [26] softwares were employed. The former was applied for phase composition calculation according to the "ZMV" method, while the latter for average crystallite size estimation by implementing the Thomson-Cox-Hastings [14] model in a pseudo-Voigt peak-shape function after

where si denotes the Rietveld scale factors of sample i and n is the number of the

Calcination temperature (°C)

— 100 (drying) ZrSiO4 160<sup>a</sup>

ZrOCl2 700 ZrO2 20

NaOH Na2SiO3 100 (drying) Am. SiO2 — HCl Na2SiO3 900 Cristobalite >500

phases. Zi is the number of formula unit of phase i (calculated from the refined

lattice parameters) with mass Mi in the unit cell volume Vi.

Dissolution of natural zircon mineral to produce high-purity oxide powders.

precipitate

Mineral Acid/base Precursor/

Milling in ethanol

NaOH + HCl

ð1Þ

Product Crystallite

size (nm)

40b

from the precursors.

ZrSiO4 (zircon sand)

Unmilled powder.

Milled powder for 10 h at 150 rpm.

a

b

46

Table 3.

Metal powder

Mg

Table 2.

Acid/ base

Ti HCl Mixture of TiCl4 and

DTA/TG plot of the dried Ti-dissolved solution is given in Figure 4. The XRD patterns of the calcined powders are presented in Figure 5. Similar behavior in the phase formation of MgO was found here for the Ti-dissolved powders. Significant mass release occurs and followed by crystallite formation. Interestingly, the dried Ti-dissolved powder has already exhibited rutile with a relatively low degree of crystallinity as indicated by low diffraction intensities. The crystallinity becomes clearer at higher calcination temperatures. Pure rutile is achieved at 400°C, but anatase forms above 600°C. In most cases, the formation of anatase occurs at a

Figure 2. DTA/TG plot of the Mg-dissolved dried powder.

#### Figure 3.

X-ray diffraction patterns (CuKα radiation) of the calcined Mg-dissolved powders. Symbols: B = bischofite (MgCl26H2O), M = magnesia (MgO, also known as periclase).


#### Table 4.

Phase weight fraction and MgO crystallite size of the calcined Mg-dissolved powders extracted from XRD data.

XRD peaks imply the nanometric crystal size of the products [28]. MAUD software

Phase weight fraction and TiO2 crystallite size of the calcined Ti-dissolved powders extracted from XRD data.

X-ray diffraction patterns (CuKα radiation) of the calcined Ti-dissolved powders. Symbols: A = TiO2 anatase,

Rutile Anatase Rutile Anatase

Temperature (°C) Relative weight fraction (%) Crystallite size (nm)

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

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

200°C 100 — 6 (1) — 400°C 100 — 11(1) — 600°C 97.96(5) 2.04(1) 22(1) 98(2) 700°C 99.08(5) 0.92(1) 96(3) 114(6)

Synthesis of MgTiO3 powder can be performed following the schematic diagram

[26] estimated crystallite size of rutile and anatase in the samples which are

given in Figure 2. The detailed explanation of the synthesis has been reported elsewhere [29]. In principle, the magnesium powder was dissolved in hydrochloric acid at room temperature stirring to obtain a light yellow solution, while the titanium powder was prepared similarly but at around 60°C to give a purple solution. Both solutions were then stirred at around 75°C for 4 h to ensure homogenous mixing prior to drying at 105°C to produce granular agglomerates. Phase and microstructure analyses were performed on the manually ground agglomerates after calcination at various temperatures. Figure 6 shows the XRD patterns of calcined powders for 1:1 Mg:Ti ratio at different temperatures. As can be seen from the figure, only MT (COD ID 01-079-0831, hexagonal), MgO (periclase, 00-045- 0946, cubic), and rutile (01-078-2485, tetragonal) were present in all samples. This result shows that our dissolution method can hinder the formation of other magnesium titanate phases such as MgTi2O5 [30, 31] or Mg2TiO4 [32]. However, the

3.3 Magnesium titanium oxide or magnesium titanate (MgTiO3)

presented in Table 5.

Figure 5.

Table 5.

49

R = TiO2 rutile,T = undetected phase.

#### Figure 4. DTA/TG plot of the Ti-dissolved dried powder.

lower temperature than rutile [8, 10]. In our study, the formation of rutile is more spontaneous than anatase possibly due to the type of precursor and its environment. A similar result was observed by others [27]. It is also worth noting that the broad

Synthesis of High-Purity Ceramic Nano-Powders Using Dissolution Method DOI: http://dx.doi.org/10.5772/intechopen.81983

#### Figure 5.

X-ray diffraction patterns (CuKα radiation) of the calcined Ti-dissolved powders. Symbols: A = TiO2 anatase, R = TiO2 rutile,T = undetected phase.


#### Table 5.

Phase weight fraction and TiO2 crystallite size of the calcined Ti-dissolved powders extracted from XRD data.

XRD peaks imply the nanometric crystal size of the products [28]. MAUD software [26] estimated crystallite size of rutile and anatase in the samples which are presented in Table 5.

### 3.3 Magnesium titanium oxide or magnesium titanate (MgTiO3)

Synthesis of MgTiO3 powder can be performed following the schematic diagram given in Figure 2. The detailed explanation of the synthesis has been reported elsewhere [29]. In principle, the magnesium powder was dissolved in hydrochloric acid at room temperature stirring to obtain a light yellow solution, while the titanium powder was prepared similarly but at around 60°C to give a purple solution. Both solutions were then stirred at around 75°C for 4 h to ensure homogenous mixing prior to drying at 105°C to produce granular agglomerates. Phase and microstructure analyses were performed on the manually ground agglomerates after calcination at various temperatures. Figure 6 shows the XRD patterns of calcined powders for 1:1 Mg:Ti ratio at different temperatures. As can be seen from the figure, only MT (COD ID 01-079-0831, hexagonal), MgO (periclase, 00-045- 0946, cubic), and rutile (01-078-2485, tetragonal) were present in all samples. This result shows that our dissolution method can hinder the formation of other magnesium titanate phases such as MgTi2O5 [30, 31] or Mg2TiO4 [32]. However, the

lower temperature than rutile [8, 10]. In our study, the formation of rutile is more spontaneous than anatase possibly due to the type of precursor and its environment. A similar result was observed by others [27]. It is also worth noting that the broad

Temperature Weight fraction (%) Crystallite size (nm)

Ceramic Materials ‐ Synthesis, Characterization, Applications and Recycling

X-ray diffraction patterns (CuKα radiation) of the calcined Mg-dissolved powders. Symbols: B = bischofite

MgCl2.6H2O (bischofite)

400°C — 100 — 90(12) 500°C 18.5 81.5 99(5) 97(5) 700°C 100 — 98(5) — 800°C 100 — 98(3) —

Phase weight fraction and MgO crystallite size of the calcined Mg-dissolved powders extracted from XRD data.

MgO (periclase) MgCl2.6H2O (bischofite)

MgO (periclase)

(MgCl26H2O), M = magnesia (MgO, also known as periclase).

Table 4.

Figure 3.

Figure 4.

48

DTA/TG plot of the Ti-dissolved dried powder.

the structure of the phase. In conclusion, the simple dissolution method is very

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

The influence of excessive Mg [33] to produce higher-purity MT was investigated further by XRD for samples which were calcined at 800°C [29]. It has been shown that excessive addition of Mg up to 3% reduces the amount of rutile (R), while above 6% addition causes vanishing rutile but the appearance of periclase (M). This result implies that the method can be easily used to control the amount of MT by varying Mg:Ti ratio without the introduction of MgTi2O5 or Mg2TiO4 which was found when other methods were used [30, 32]. The results explained the role of excessive Mg in the formation of high-purity MT. The amount of MT can achieve as high as 99.4 3.6% in the 6% excessive Mg sample with rutile as the sole residual or 97.5 3.5% in the 3% excessive Mg sample with periclase as also the only residual. An excessive Mg around 5–6% is therefore envisaged to give MT with the highest

The formation of MT at 600°C with 1 h dwelling time was incomplete, with the weight fraction of rutile and periclase that was about 17.2 and 17.4%, respectively, while increasing calcination temperature improves such formation. The effect of calcination dwelling time on the completeness of the MT formation was then examined [29]. It was reported that the formation of MT is significantly improved by prolonged calcination as proven by the MT molar fraction around 65% (equivalent with around 82% by weight) for 1 h to 82% (90% by weight) for 4 h. It was also found that the crystallite size of MT was invariant to dwelling time at values around

Therefore, the dissolution method has been successfully implemented to produce high-purity MT nanocrystals. Sub-nanometric MT crystals were achieved from Mg-Ti hydrochloric acid solutions mixing with 6% excessive Mg followed by calcination at 800°C for 1 h. Meanwhile, prolonged calcination at 600°C significantly improved the MT formation up to 82% (molar) and retained its nanometric

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

potential to produce bi-cationic nanocrystals.

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

3.3.2 Effect of calcination dwelling time

crystallite size at around 76 nm.

3.4 Zircon (ZrSiO4)

51

76 nm as indicated by insignificant changes on the XRD line.

3.3.1 Effect of excessive Mg

purity [29].

#### Figure 6.

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).

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

Figure 7. TEM micrograph of MT powder after calcination at 600°C.

the structure of the phase. In conclusion, the simple dissolution method is very potential to produce bi-cationic nanocrystals.
