Ph.D., associate Professor Lydmila Ignatovich

Belarussian State University of Technology, Belarus.

Ph.D., associate Professor Lydmila Dubovskaya

Belarusian State Academy of Arts, Belarus.

Influence of the interaction of hardener and mineral binding THE STRENGTH OF COMPOSITE

Introduction. It is known that the waste from wood processing industries often burned, but the calorific value of the sawdust is low enough and the use of soft waste in this capacity is the least economically expedient in relation to other types of wood fuel. There is more rational use of waste wood - as a raw material for the production of composite materials in the mineral binder. A good mineral binder is a liquid glass, which has high adhesion to wood, low cost and availability of raw materials. Significant disadvantages of liquid glass are its low water resistance. Improve the adhesive properties of sodium silicate and water resistance can be achieved by modifying hexafluorosilicate sodium, which also accelerates the process of setting and hardening of the liquid glass.

The main part. In order to identify the reaction products hexafluorosilicate sodium silicate in the presence of sawdust and without electron microscopic analysis were and IR spectroscopic studies of the initial components and products of their interaction. Infrared absorption spectra of the test compounds were recorded in the frequency range of 400-4000 cm-1 by direct analysis of individual substances without mixing with KBr. Spectra were obtained with single-beam FT-IR spectrometer "FTIR-8601 PC". In the analysis we recorded the IR absorption spectra of the compounds considered in the general case, the number of absorption bands related to the vibrations of the ion or molecule, and the frequency range of their occurrence. The results of these studies suggest that the basis of the interaction of the starting compounds (water glass and Na2SiF6) is a chemical reaction oc-Penitent by equation 1:

2(Na₂O·3,2SiO₂∙nН₂О) +2Na₂SiF₆ ® 8NaF + SiF₄↑+ 7,4(SiO₂∙nН₂О) (1)

The reaction of proceeds sufficiently quickly (within 10-15 minutes) and irreversible. Since the content of NaF in the solid product interaction (TPR) Na2SiF6 and Na2SiO3 24 hours was the same as after the 10-minute interaction, the solid product and the parent compounds were analyzed for silicon content by electron microscopy analysis using scanning microscope with a microprobe, which allows to determine the chemical composition of the element by element of the objects. It was found that the total of the total silicon in the initial product (Na2SiF6) + (Na2SiO3) is 25.28 wt.%. This exceeds the total silicon content in the solid product interactions on the value of 12.39 wt.%. This difference corresponds exactly to the total silicon content in the gaseous product of interaction. The above scheme can be balance (Equation 2):

(Si Na₂SiF₆+ Si Na₂SiO₃) - Si = Si SiF₄ (2)

Or, based on 100 wt. h of liquid glass and 16 wt. h hexafluorosilicate sodium balance in distribution of silicon is (Equation 3):

(5,51 + 2,38) – 6,7 = 1,20 wt. % (3)

The presence of silica in the solid product is confirmed by the interaction of the initial components of IR spectroscopic studies. IR spectra were analyzed products are shown in Figure 1. Confirmation that the mixture and Na2SiO3 Na2SiF6 in the presence of H 2 O is the reaction of interaction, leading to destruction and SiF62-SiO32-anions to form SiO2, is the absence in the IR spectrum of the mixture Na2SiF6 Na2SiO3 absorption bands corresponding to the vibrations of the anion SiF62--733, 494 and 475 cm and SiO32-1018, 900, 770, 474, 436 cm (Fig. 1). View of the IR spectrum of a mixture Na2SiF6 Na2SiO3 after the interaction is almost identical to the IR spectrum of amorphous SiO2. The absence in the IR spectrum of the mixture and Na2SiO3 Na2SiF6 absorption bands corresponding to the vibrations of NaF, due to the fact that its content of impurities NaF (equation) below the lower limit of detection of its appropriate instruments [1].

The study results assume that the adhesion of the particles of wood composite [2] due to the formation of a stable crystal structure (Fig. 2), consisting of molecules of SiO2 ∙ 2H2O and NaF, formed by the interaction of sodium hexafluorosilicate (Na2SiF6) and sodium silicate (Na2SiO3) for the above-given reaction. At the same time, the IR spectra of composite materials designed purpose [2] found the absorption bands corresponding to vibrations of the anion SiF62-730, 490 and 474 cm (Figure 2). This indicates the presence of sodium hexafluorosilicate in the resulting materials. Above will most likely reaction of Na2SiO3 Na2SiF6 and adding filler - sawdust - occurs is not completely due to possible steric hindrance arising from the interaction of components and wood bonding with each other [3].

Fig. 1 IR absorption spectra1 2Na2O • SiO2 · nH2O + 2 Na2SiF6; 2 - amorphous SiO2

Fig. 2 IR absorption spectra1 sawdust, 2 - the material of construction of 3 - insulating material

Conclusion. Improving the strength of materials produced by small pieces of wood and water glass in the presence of sodium hexafluorosilicate, due to the formationnew hydrogen bonds with the wood due to their participation in shaping the structure of fluoride ions present in the anion SiF62-and have greater electronegativity. [4]

Increase the water resistance of such materials sposobstvovuet reduction of hydrophilic hydroxyl groups, clearly visible when comparing the IR spectra of the "Silk-K", "Silk-E" and the original wood (wood of the absorption band of the 3000 - 3700 cm-1 is much deeper and wider ). [3]

Literature

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2. Дубовская, Л.Ю. Композиционный материал на основе древесных отходов и минерального вяжущего / Л.Ю. Дубовская, А.А. Янушкевич // Известия Белорусской инженерной академии. – 2004 – №2. – С. 29 – 30.

3. Карклинь В.Б. ИК-спектроскопия древесины и её компонентов / В.Б. Карклинь, Е.Э. Охерина // Химия древесины. – 1981. – №4. – С. 38 – 44.

4. Жбанков, Р.Г. Инфракрасные спектры целлюлозы и её производных / Р.Г. Жбанков. – Минск, 1964. – 338 с.