**2.2 Natural fiber-reinforced geopolymers for construction and passive cooling systems**

In a recent research, vascular natural fiber is used to improve the properties of end products to be used for more than one purpose. The use of natural fibers such as *Luffa cylindrica* fibers (LCF) as reinforcements for geopolymers has several objectives. In addition to improving mechanical properties, these vascular fibers improve the microstructural properties of the resulting material. In this research,

**Figure 3.** *The schematic diagram of the research methodology [11].*

**Figure 4.** *XRD patterns corresponding to kaolin and the resultant geopolymer [11].*

geopolymers (Sk-geopolymer) and LCF-reinforced geopolymers (LG composite) were made for reference and polymer composites using fiber as a reinforcing material with volume percentage of 10% as shown in **Figure 3**. The composition of the Sk-geopolymer was reported in our previous work [11].

As can be seen from X-ray tests, **Figure 4**, kaolinitic soil is transformed to an amorphous geopolymer gel as a result of the calcination at 750°C and the subsequent geopolymerization reactions [11, 16, 17]. These XRD results are in agreement with the SEM images as reported in **Figure 5**. The kaolin layers in **Figure 5A** break down by the geopolymerization process to obtain geopolymers with a semi-uniform nano-pore network as shown in **Figure 5B**. We also note the presence of bundles of tubes forming LC fiber. Both phases, whether the porous geopolymeric matrix or vascular LCF, help to increase the surface moisture of the material, which helps in the applications of passive cooling systems, especially in hot and dry regions.

On the other hand, we note that introducing LCF contributed significantly in improving the mechanical properties of geopolymeric products, where the

**5**

**Figure 6.**

**Figure 5.**

*Introductory Chapter: Case Studies of Functional Geopolymers*

*SEM images of the precursor (A), geopolymer matrix (B), and the LCF cross section (C) [8, 11].*

*Mechanical and physical properties of geopolymers (Sk-geopolymer) and geopolymer composite (LG-composite): Compressive strength (A), Bulk density (B), and Stress-strain curve (C) [11].*

*DOI: http://dx.doi.org/10.5772/intechopen.90363*

*Geopolymers and Other Geosynthetics*

**4**

**Figure 3.**

**Figure 4.**

*The schematic diagram of the research methodology [11].*

*XRD patterns corresponding to kaolin and the resultant geopolymer [11].*

Sk-geopolymer was reported in our previous work [11].

geopolymers (Sk-geopolymer) and LCF-reinforced geopolymers (LG composite) were made for reference and polymer composites using fiber as a reinforcing material with volume percentage of 10% as shown in **Figure 3**. The composition of the

As can be seen from X-ray tests, **Figure 4**, kaolinitic soil is transformed to an amorphous geopolymer gel as a result of the calcination at 750°C and the subsequent geopolymerization reactions [11, 16, 17]. These XRD results are in agreement with the SEM images as reported in **Figure 5**. The kaolin layers in **Figure 5A** break down by the geopolymerization process to obtain geopolymers with a semi-uniform nano-pore network as shown in **Figure 5B**. We also note the presence of bundles of tubes forming LC fiber. Both phases, whether the porous geopolymeric matrix or vascular LCF, help to increase the surface moisture of the material, which helps in the applications of passive cooling systems, especially in hot and dry regions. On the other hand, we note that introducing LCF contributed significantly in improving the mechanical properties of geopolymeric products, where the

#### **Figure 5.** *SEM images of the precursor (A), geopolymer matrix (B), and the LCF cross section (C) [8, 11].*

#### **Figure 6.**

*Mechanical and physical properties of geopolymers (Sk-geopolymer) and geopolymer composite (LG-composite): Compressive strength (A), Bulk density (B), and Stress-strain curve (C) [11].*

#### **Figure 7.** *HFO granules (point 1) in the geopolymeric matrix (point 2).*

#### **Table 3.**

*Concentration (ppm) of leached metals from crude HFO and HFP geopolymer matrix after immersion in pH = 7 for 1 day.*

compressive strength was doubled as shown in **Figure 6A**. It was observed also that the density of products was reduced by up to 10%, **Figure 6B**, thanks to the addition of vascular LC fiber as reinforcement. This reduction in density is due to the fact that these fibers exhibit low bulk density compared to the geopolymer matrix. The most important influence for LC fibers on the mechanical properties of geopolymers is to significantly increase the tensile strength as shown in **Figure 6C**. Brittle geopolymer matrix also acquires the ductile failure thanks to LC fibers.

It is observed in this research that the LCF geopolymer composites have attracted mechanical and physical properties. In addition, the presence of multiple structures of porous networks, whether the geopolymeric matrix or the vascular LC fibers, plays an active role in the manufacture of passive cooling materials. Thus, these materials can be used as construction materials and in reducing the energy consumed in the indoor conditioning.

**7**

*Introductory Chapter: Case Studies of Functional Geopolymers*

use as construction materials in specific applications.

**3. Conclusions**

**Author details**

Mazen Alshaaer

**2.3 Immobilization and stabilization of toxic wastes in geopolymers**

Geopolymers have been used in recent years as a matrix for immobilization and stabilization of toxic wastes. The finished products can be used for specific construction purposes as well. Therefore, this geopolymerization process achieves several goals at once. In this study [18], heavy oil fly ash (HFO) containing toxic elements such as Ni, Cr, Pb, etc. was added to the geopolymeric matrix as a filler. As can be seen in **Figure 7**, the granules of the HFO are fixed in the geopolymers. The resultant HFO geopolymer exhibits mechanical properties comparable with pure geopolymer [18]. As for the examination of the immobilization of toxic elements, it is observed in **Table 3** that these elements were fixed in the geopolymeric matrix and they were not leached in water after a full day of immersion in water. Accordingly, this research achieves several objectives: the use of geopolymers in the recycling of HFO as a waste and the stabilization of toxic elements, in addition to its

There are several challenges and drawbacks facing the commercialization of geopolymers as an alternative to conventional cement and other conventional materials in construction. One important strategy to overcome these challenges is the manufacture of functional geopolymers with multiple uses. Three different applications of polymers in the fields of water purification, passive cooling systems, and waste recycling were presented in this introductory chapter. It is noticeable that the results are of great importance in many applications and confirm that this strategy will play a key role in the commercialization of geopolymers as products

with multiple uses in engineering and environmental applications.

Department of Physics, College of Science and Humanities in Al-Kharj,

© 2020 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium,

Prince Sattam Bin Abdulaziz University, Al-Kharj, Saudi Arabia

\*Address all correspondence to<EMAIL_ADDRESS>
provided the original work is properly cited.

*DOI: http://dx.doi.org/10.5772/intechopen.90363*


**Author details**

Alfredo Ramírez‐Reveco1\*, Jorge Luis Hernández2 and Pablo Aros1,3

\*Address all correspondence to<EMAIL_ADDRESS>
1 Laboratory of Cryobiology and Spermatic Function Analysis, Animal Science Institute, Faculty of Veterinary Science, Austral University of Chile, Valdivia, Chile

2 Center of Artificial Insemination, Faculty of Veterinary Science, Austral University of Chile, Valdivia, Chile

3 School of Veterinary Medicine, Faculty of Veterinary Science, Austral University of Chile, Valdivia, Chile


**6. Mass transfer with external forces in oxide crystal growth**

In crystal growth, steady convection is always desired because it is helpful for mass transfer and thus provides an enhanced renewal of the melt/solution in the region near the crystallization interface. However, when the temperature gradient gets larger enough, the convective flow may become oscillatory or even turbulent, which inevitably gives rise to generation of striations. In some cases, the unsteady flow may be suppressed by external force such as rotation, vibration or magnetic field. In this part, some experimental results will be given about the effect of external forces on mass transport during oxide crystal growth.

#### **6.1 Suppression of oscillatory flow by transverse magnetic field in NaBi(WO4)2 melt**

For oxide melt, oscillatory convection can be observed if the temperature gradient along the loop heater gets large enough. Fig. 21(a) shows a typical unsteady flow pattern of NaBi(WO4)2 melt. This pattern comprises one main trunk and the branches. The main trunk oscillates with time, and the arrows I, II represent the range of oscillation. Fig. 21(b) shows the schematic diagram of oscillatory pattern. The main trunk oscillates around the position A with the amplitude as shown by the bi-directional arrow 1. The oscillatory frequency reached about 10 Hz, and the amplitude was about 500 μm. Similar convective oscillations have also been observed in KNbO3, BaB2O4 and Bi12SiO20 melts or solutions suspended on a loop heater (Z. H. Liu et al., 1998; W. Q. Jin et al., 2004; Y. Hong et al., 2006).

When a 60 mT transverse static magnetic field is applied, the distinct attenuation of the oscillation is observed and arrows III, IV represent the range of oscillation as shown in Fig. 22(a). The main trunk oscillates around the position A with the amplitude (~200 μm) as shown by the bi-directional arrow 2 in Fig. 22(b), which is smaller than that as shown by arrow 1. So the oscillatory amplitude of main trunk decreased when the magnetic field is applied. The frequency of oscillation is measured to be about 4 Hz. This means that the instability of convective flow has been effectively reduced.

Interfacial Mass Transfer and Morphological Instability of Oxide Crystal Growth 549

(upper part) of the as-grown single crystal obtained with RMF in Fig. 23(c). It is simplified as a schematic drawing in Fig. 23(d). Since such curved lines are observed only at the upper part of the as-grown crystal, they are in correlated with the free surface at the top end of the melt. By contrast with the same position of the single crystal grown in the normal condition without RMF shown in Fig. 23 (b), no similar pattern can be observed on the free surface of the same position. Therefore, it can be concluded that the appeared pattern is definitely

Fig. 23. Bi12SiO20 crystals grown with (a) and without (b) rotation magnetic field, the regular

Optical microscopic observation reveals that the middle part of the crystal grown with RMF has no growth striations. On the other hand, a large number of growth striations could be clearly observed inside the crystal grown without RMF at the same position. This is due to the appearance of steady forced convection in the melt induced by magnetic field. As a result, the transport of heat and mass is enhanced and remains stable, and therefore the

**6.3 Improvement of crystallographic perfection in Bi12SiO20 crystal by axial vibration**  The authors have experimentally investigated the effect of axial vibration on the free surface flows in a vertical Bridgman model under isothermal conditions (X. H. Pan, 2005a, 2005b). Steady forced flows are obtained on the free surface of the liquid phase driven by pure axial vibration. Based on this hinting, axial vibration is introduced into the Bi12SiO20 crystal growth in our laboratory (Y. Zhang et al., 2008, 2009), in order to suppress the unsteady thermocapillary or buoyancy convections. Some results are described in the following. Axial vibration has been introduced in the growth of Bi12SiO20 single crystal by vertical Bridgman technique. The frequency of the axial vibration applied is 50 Hz and its amplitude varies. The quality of the Bi12SiO20 single crystal is identified by the high-resolution X-ray rocking curves as shown in Fig. 24. It can be found that the crystal grown with 70 μm

pattern (c) observed on the surface and its schematic drawing (d)

crystallographic perfection could be improved.

induced by the applied RMF.

Fig. 21. (a) Oscillatory flow pattern in NaBi(WO4)2 melt, (b) The schematic diagram of the flow pattern

Fig. 22. (a) Flow pattern in NaBi(WO4)2 melt under 60 mT transverse magnetic field, (b) The schematic diagram of the flow pattern

In general, attention has seldom been paid to the growth of oxide single crystals in applied magnetic fields since their electrical conductivity is extremely low even in the melt. It is normally assumed that the effect of the magnetic field to be applied is negligible in an oxide melt. However, above experimental result shows that 60 mT static magnetic field is strong enough to affect the mass flow of oxide melt. It should be emphasized that the oscillation of the thermocapillary flow could be completely suppressed by the 60 mT magnetic field if the temperature difference applied on the loop decrease. The suppression of magnetic field on the oscillation flow might be due to the Lorentz force induced by the interaction of dissociated ions with magnetic field (W. Q. Jin, 2007).

#### **6.2 Effect of rotating magnetic field on Bi12SiO20 crystal growth**

In the following, the experiment results about bulk crystal growth by vertical zone-melting technique (VZM) in a rotation magnetic field (RMF) shall be demonstrated. Here Bi12SiO20 crystal is selected as model material due to its excellent photorefractive and electro-optical properties. More details about the RMF-VZM system is described in the reference (Y. Liu et al., 2010).

Fig. 23 shows the photographs of the Bi12SiO20 crystals grown by VZM. The crystal in Fig. 23(a) is grown with 25 mT and 50 Hz RMF and the one in Fig. 23(b) is obtained without RMF. A regular deep pattern with numerous curved lines is observed on the free surface

Fig. 21. (a) Oscillatory flow pattern in NaBi(WO4)2 melt, (b) The schematic diagram of the

Fig. 22. (a) Flow pattern in NaBi(WO4)2 melt under 60 mT transverse magnetic field, (b) The

In general, attention has seldom been paid to the growth of oxide single crystals in applied magnetic fields since their electrical conductivity is extremely low even in the melt. It is normally assumed that the effect of the magnetic field to be applied is negligible in an oxide melt. However, above experimental result shows that 60 mT static magnetic field is strong enough to affect the mass flow of oxide melt. It should be emphasized that the oscillation of the thermocapillary flow could be completely suppressed by the 60 mT magnetic field if the temperature difference applied on the loop decrease. The suppression of magnetic field on the oscillation flow might be due to the Lorentz force induced by the interaction of

In the following, the experiment results about bulk crystal growth by vertical zone-melting technique (VZM) in a rotation magnetic field (RMF) shall be demonstrated. Here Bi12SiO20 crystal is selected as model material due to its excellent photorefractive and electro-optical properties. More details about the RMF-VZM system is described in the reference (Y. Liu et

Fig. 23 shows the photographs of the Bi12SiO20 crystals grown by VZM. The crystal in Fig. 23(a) is grown with 25 mT and 50 Hz RMF and the one in Fig. 23(b) is obtained without RMF. A regular deep pattern with numerous curved lines is observed on the free surface

flow pattern

al., 2010).

schematic diagram of the flow pattern

dissociated ions with magnetic field (W. Q. Jin, 2007).

**6.2 Effect of rotating magnetic field on Bi12SiO20 crystal growth**

(upper part) of the as-grown single crystal obtained with RMF in Fig. 23(c). It is simplified as a schematic drawing in Fig. 23(d). Since such curved lines are observed only at the upper part of the as-grown crystal, they are in correlated with the free surface at the top end of the melt. By contrast with the same position of the single crystal grown in the normal condition without RMF shown in Fig. 23 (b), no similar pattern can be observed on the free surface of the same position. Therefore, it can be concluded that the appeared pattern is definitely induced by the applied RMF.

Fig. 23. Bi12SiO20 crystals grown with (a) and without (b) rotation magnetic field, the regular pattern (c) observed on the surface and its schematic drawing (d)

Optical microscopic observation reveals that the middle part of the crystal grown with RMF has no growth striations. On the other hand, a large number of growth striations could be clearly observed inside the crystal grown without RMF at the same position. This is due to the appearance of steady forced convection in the melt induced by magnetic field. As a result, the transport of heat and mass is enhanced and remains stable, and therefore the crystallographic perfection could be improved.


**4. Conclusions**

**Author Contributions:** Conceptualization, Z.L. and Y.H.; methodology, Z.L. and Y.H.; formal analysis, Z.L., Y.H., G.H. and X.G.; investigation, Z.L., X.G., G.H. and H.W.; data curation, Z.L. and Y.H.; resources, X.G. and H.W.; visualization, Z.L. and X.G.; writing—original draft preparation, Z.L.; writing—review and editing, Z.L., Y.H. and G.H.; funding acquisition, Z.L. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research was funded by the Natural Science Foundation of Xinjiang Uygur Autonomous Region (grant number: 2022D01B03), the Kashgar Science and Technology Plan Project (grant number: KS2021030) and the Horizontal Project of Kashi University (grant number: 022022184).

**Institutional Review Board Statement:** Not applicable.

**Informed Consent Statement:** Not applicable.

**Data Availability Statement:** The data used to support the findings of this study are included within the article.

**Conflicts of Interest:** The authors declare no conflict of interest.