**3. X-ray tomography and fluorescence microscopy**

Many different cross-sectional views are created suing X-rays. These are then assembled to create a 3D image of the object. The size of the pixels which are created in this manner so created are in micrometers and hence the word, microtomography. It should be noted that the 3D model is a virtual model and is not in real time. These pixel sizes have also resulted in the terms high-resolution X-ray tomography, micro-computed tomography (micro-CT or μCT) and similar terms. In today's terminology, tomography automatically implies computer tomography.

**Figure 11** illustrates the features of a slag-based geopolymer using the X-ray microtomograph. Furthermore, histogram, **Figure 11**, also depicts particle size distribution. In general, fly ash-based polymers have been studied by Das et al. and characterized by X-ray tomography [14].

The X-ray tomography shows the distribution of phases. Slag particles can be clearly seen as a white product. There also seem to be some cracks, which, if allowed to propagate, could lead to premature failure of the component in use (**Figure 12**).

According to The Royal Chemical Society, X-Ray Fluorescence is an imaging technique where a beam of X-rays is directed at the specimen-Rays are emitted

#### **Figure 11.**

*X-ray microtomography scan of a sodium silicate-activated binder (80% slag/20% metakaolin, activat) (b) a histogram depicting volume of pixels of the volume of interest.*

#### **Figure 12.**

*X-ray fluorescence micrographs of a sodium metasilicate-activated binder (75% slag/25% metakaolin) [13].*

due to transitions and the intensities of the X-rays emitted due to are detected as a function of wavelength and position. As these energies are element-specific, X-ray fluorescence microscopy can be used to determine spatially resolved elemental composition.

The X-Ray fluorescence image shown above shows different emitted colors for inner gel and for outer gel. As can be seen, the differences in Ca/Si ratio also can be mapped based upon the color.

### **4. Nuclear magnetic resonance (NMR) spectra**

**Nuclear magnetic resonance** (**NMR**) is a physical phenomenon in which nuclei in a strong static magnetic field are perturbed by a weak oscillating magnetic field. This field is very close to the surface. It does not involve electromagnetic interactions or waves and respond by producing an electromagnetic signal with a frequency characteristic of the magnetic field at the nucleus. This process occurs near resonance. As we are aware, during resonance, two frequencies have to match, and the resultant frequency is far ahead in intensity compared to the two participating frequencies. When the oscillation frequency matches the intrinsic frequency of the nuclei, which depends on the strength of the static magnetic field, the chemical environment and the magnetic properties of the isotope involved; in practical applications with static magnetic fields up to ca. 20 tesla, the frequency is similar to VHF and UHF television broadcasts (60–1000 MHz). NMR results from specific magnetic properties of certain atomic nuclei. Nuclear magnetic resonance spectroscopy is widely used to determine the structure of organic molecules in solution and study molecular physics, crystals as well as noncrystalline materials. NMR is also routinely used in advanced medical imaging techniques, such as in magnetic resonance imaging (MRI).

Nuclear magnetic resonance spectra can be used to identify elemental groups. Each group has a characteristic shift in wavelength. The shifts for different geopolymers are shown in **Figure 14**.

**Figure 13** depicts wavelength shift [15].

**Figure 14** depicts the difference between amorphous and semi-crystalline geopolymers. Mathematical analysis has been done on these peaks, and Gaussian peak deconvolution has been used to characterize short range order in T-O-T bonds,

**31**

workers [18, 19].

**Figure 14.**

**Figure 13.**

**5. FTIR spectra**

*Summary of Some Selected Characterization Methods of Geopolymers*

where T can be either Al or Si [15]. Fly ash and consolidated materials have been studied using NMR. The signals obtained are wide in nature, indicating a heteroge-

*The shift in wavelengths in the case of aluminum and silicon in aluminosilicate geopolymers. The first peak is* 

*for aluminum-based and the second peak is for silicon-based amorphous polymers [15].*

According to the 29Si RMN MAS spectra of fly ash-based geopolymer, the main shift equal to −94,66 ppm indicates the presence of Q4 (2 Al) and Q4 (3Al) units in the geopolymer matrix [17]. The shift equal to −107 ppm corresponding to the Q4 (0Al) coordination was less represented, which points to the Al penetration into the [SiO4] 4- skeleton. This interpretation of the NMR spectra is also shared by other

A schematic diagram of FTIR spectroscopy is reported in **Figure 15**. There is a broadband infrared source, which gives radiation. This radiation is split in the beam splitter. The split beam gets deflected onto the sample through a parabolic mirror.

neous distribution of Si atoms in these matrices [16].

*Shift in amorphous geopolymer as compared to semi-crystalline geopolymers [15].*

*DOI: http://dx.doi.org/10.5772/intechopen.82208*

*Summary of Some Selected Characterization Methods of Geopolymers DOI: http://dx.doi.org/10.5772/intechopen.82208*

#### **Figure 13.**

*Geopolymers and Other Geosynthetics*

composition.

**Figure 12.**

mapped based upon the color.

mers are shown in **Figure 14**.

**Figure 13** depicts wavelength shift [15].

**4. Nuclear magnetic resonance (NMR) spectra**

imaging techniques, such as in magnetic resonance imaging (MRI).

due to transitions and the intensities of the X-rays emitted due to are detected as a function of wavelength and position. As these energies are element-specific, X-ray fluorescence microscopy can be used to determine spatially resolved elemental

*X-ray fluorescence micrographs of a sodium metasilicate-activated binder (75% slag/25% metakaolin) [13].*

The X-Ray fluorescence image shown above shows different emitted colors for inner gel and for outer gel. As can be seen, the differences in Ca/Si ratio also can be

**Nuclear magnetic resonance** (**NMR**) is a physical phenomenon in which nuclei in a strong static magnetic field are perturbed by a weak oscillating magnetic field. This field is very close to the surface. It does not involve electromagnetic interactions or waves and respond by producing an electromagnetic signal with a frequency characteristic of the magnetic field at the nucleus. This process occurs near resonance. As we are aware, during resonance, two frequencies have to match, and the resultant frequency is far ahead in intensity compared to the two participating frequencies. When the oscillation frequency matches the intrinsic frequency of the nuclei, which depends on the strength of the static magnetic field, the chemical environment and the magnetic properties of the isotope involved; in practical applications with static magnetic fields up to ca. 20 tesla, the frequency is similar to VHF and UHF television broadcasts (60–1000 MHz). NMR results from specific magnetic properties of certain atomic nuclei. Nuclear magnetic resonance spectroscopy is widely used to determine the structure of organic molecules in solution and study molecular physics, crystals as well as noncrystalline materials. NMR is also routinely used in advanced medical

Nuclear magnetic resonance spectra can be used to identify elemental groups. Each group has a characteristic shift in wavelength. The shifts for different geopoly-

**Figure 14** depicts the difference between amorphous and semi-crystalline geopolymers. Mathematical analysis has been done on these peaks, and Gaussian peak deconvolution has been used to characterize short range order in T-O-T bonds,

**30**

*The shift in wavelengths in the case of aluminum and silicon in aluminosilicate geopolymers. The first peak is for aluminum-based and the second peak is for silicon-based amorphous polymers [15].*

#### **Figure 14.**

*Shift in amorphous geopolymer as compared to semi-crystalline geopolymers [15].*

where T can be either Al or Si [15]. Fly ash and consolidated materials have been studied using NMR. The signals obtained are wide in nature, indicating a heterogeneous distribution of Si atoms in these matrices [16].

According to the 29Si RMN MAS spectra of fly ash-based geopolymer, the main shift equal to −94,66 ppm indicates the presence of Q4 (2 Al) and Q4 (3Al) units in the geopolymer matrix [17]. The shift equal to −107 ppm corresponding to the Q4 (0Al) coordination was less represented, which points to the Al penetration into the [SiO4] 4- skeleton. This interpretation of the NMR spectra is also shared by other workers [18, 19].
