# Silicon Compounds in Sponges
## 4 Results and Discussion
### Thermal Properties  
The thermal behavior of siliceous sponges was studied for two samples--1 and 9. Analysis of thermograms (Figure 14) shows that the decomposition of these samples in the region of 25-700 \({}^{\circ}\)C proceeds in three stages with some peculiarities, which will be considered in more detail. Decomposition of sample 1 (Figure 4a), weight--130 mg. At the first stage (25-180 \({}^{\circ}\)C), water is removed and, probably, some organic component. The weight loss in this temperature range is 3.1%. At the second stage (180-500 \({}^{\circ}\)C), first, thermal oxidative destruction occurs (above 180 \({}^{\circ}\)C), and at 410 and 440 \({}^{\circ}\)C there is a pronounced stepwise decomposition of individual inorganic compounds against the background of thermal oxidative destruction of organic substances. The decomposition temperatures suggest the presence of _Mg_(_OH_)\({}_{2}\) in the sample under study, the decomposition of which occurs at 410 \({}^{\circ}\)C into _Mg_O and _H_\({}_{2}\)_O, and _Ca_(_OH_)\({}_{2}\), which decomposes at 440 \({}^{\circ}\)C into _Ca_O and _H_\({}_{2}\)_O. At the third stage (500-700 \({}^{\circ}\)C), the carbonated residue burns out at a maximum rate at 540 \({}^{\circ}\)C. The mass of the mineral residue is 88.5%. The color of the residue is gray, irregular, with white needles. X-ray phase analysis of the remainder of sample 1 shows that it is X-ray amorphous (interplanar distance 3.96 A),  
Figure 14: Thermograms of the samples 1 (**a**) and 9 (**b**) (numbers according to Table 1). and the IR absorption spectrum (maxima of absorption bands (cm\({}^{-1}\)) at 470, 584, 798, 1103) corresponds to the spectrum of amorphous silica \(SiO_{2}\) obtained thermally, as, for example, sample 1 * in Table 4. Elemental analysis performed on a Shimadzu EDX 800 HS spectrometer confirms the formation of anhydrous silicon dioxide when sample 1 is heated to 700 \({}^{\circ}\)C. Thus, the content of water and organic components in sample 1 is 11.5%, and the content of the mineral residue is 88.5%. Decomposition of sample 9 (Figure 4b), weight--130 mg. At the first stage (25-160 \({}^{\circ}\)C), the sample is dehydrated at a maximum rate at 80 \({}^{\circ}\)C. The endothermic effect is observed on the differential thermal curve (DTA). Above 80 \({}^{\circ}\)C, a broad, mild exo effect begins, accompanying the process of protein denaturation (decomposition), according to [27]. The mass loss is 7.7%, which is almost 2.5 times greater than during the decomposition of sea sponge 1. At the second stage (160-390 \({}^{\circ}\)C), thermal oxidative destruction of protein components begins above 160 \({}^{\circ}\)C with a maximum rate at 260 and 290 \({}^{\circ}\)C. On DTA, this process is accompanied by an exo effect (shoulder at 290 \({}^{\circ}\)C and at 330 \({}^{\circ}\)C). Above 330 \({}^{\circ}\)C, thermal oxidative destruction of the formed new organic products and their carbonization occur, which proceeds up to about 390 \({}^{\circ}\)C. An inflection is observed on the TG weight loss curve. The total loss in the mass of volatile products at 390 \({}^{\circ}\)C is 36.2%, which is much higher than during the decomposition of sample 1. At the third stage (390-700 \({}^{\circ}\)C), the decomposition of the carbonated residue above 390 \({}^{\circ}\)C occurs, which is accompanied on the DTA curve by a broad intense exothermic effect with maxima at 490, 550, and 630 \({}^{\circ}\)C. The total weight loss at 700 \({}^{\circ}\)C is 61.9%. The mass of the mineral residue is 38.1%, which is 2.4 times less than in the decomposition of sample 1. The color of the residue is light gray, uniform. According to the X-ray phase analysis data, the residue, as with sample 1, is in the X-ray amorphous state, but with a slightly different position of the maximum of the amorphous peak (interplanar distance 4.00 A).