Revisiting Lebedev’s century-old experiment

As reported by Lebedev, the endothermic impact of borosilicate crown glasses is within the temperature area of 550 to 610 °C. The best heating temperature in Lebedev’s experiments is 700 °C. That is a lot decrease than 1200 °C, the place the endothermic impact of silica glass could be noticed. That’s the reason Lebedev didn’t discover the endothermic impact of pure silica in his experiments. The big distinction within the temperature areas of the endothermic impact between borosilicate crown glass and silica glass is as a result of distinction of their chemical composition. Sodium silicate glasses with numerous NatwoThe O focus can be utilized for instance the affect of chemical focus within the temperature area on endothermic results.

Determine 3a is the NatwoO-SiOtwo section diagram, displaying the variation of the liquidus temperature of the binary glass when the focus of sodium oxide variessixteen. Because the sodium oxide within the glasses will increase from 0 to 11.3% by weight, the liquidus temperature of the glasses decreases from 1713 to 1470 °C. As a result of the corresponding solidification crystal of those glasses is (upbeta)-cristobalite, which is identical as that of pure silica glass, sodium cations are usually not concerned in all the crystal formation course of, together with the formation of embryonic clusters. Sodium silicate glasses with a sodium oxide focus of lower than 11.3% by weight have the identical vital temperature Tc as pure silica glass at 1470 °C17. The transformation course of from dysfunction to order beneath Tc is predicted to take just a few hundred levels of the temperature vary to finish. Subsequently, the Tg of those glasses should be near 1200 °C, the identical as pure silica glass; and the endothermic impact of all these glasses ought to be noticed close to 1200 °C.

Determine 3a additionally reveals that the liquidus temperature for sodium silicate glasses within the composition vary of 11.3 to 24.5 wt% decreases from 1470 to 870 °C. The corresponding crystal on this temperature vary via which sodium silicate glass solidifies is (upbeta)-tridymite, no (upbeta)-cristobalite. The vital temperature Tc that separates the 2 totally different temperature areas is the polymorphic inversion temperature between the crystal (upbeta)-tridymite and (upbeta)-quartz, which is 870 °C17. Within the glass formation course of above 870 °C, the clusters fashioned are (upbeta)-tridymite embryos, no (upbeta)-Cristobalite embryos. Though the (upbeta)Embryonic clusters of tridymite have a special form and variety of sides than (upbeta)-cristobalite, nonetheless bear dysfunction to order transformation within the temperature area beneath 870 °C. As a result of the association of SiO4 tetrahedra within the base airplane of (upbeta)-the hexagonal construction of tridymite is identical as that of the (111) airplane of (upbeta)cristobalite face-centered cubic construction18, figs. 2a and b can be used for instance the stabilized construction of (upbeta)-Embryonic teams of tridymite fashioned within the sides. The ultimate temperature of this transition, Tg, is predicted to be a few hundred levels decrease than 870°C and could be decided experimentally. For instance, level T, indicated by an arrow in Fig. 3a, represents sodium silicate glass with 15 wt% NaOtwo. The liquidus temperature and demanding temperature of this explicit glass are present in Fig. 3a as 1340 and 870 °C, respectively. The temperature area of the endothermic impact of this glass could be decided from experimental warmth capability information. The warmth capability Cp of sodium silicate glass with 15 mol. of NaOtwo relying on the temperature is discovered from the references19.20 and is depicted in Fig. 3b. Since within the NatwoO-SiOtwo system, the compositions expressed in wt% and mol% differ little or no, the Cp information discovered above represents the thermal property of the glass offered by the purpose T in Fig. 3a. The sturdy improve in Cp from 480 to 560 °C in Fig. 3b signifies that warmth absorption will increase quickly inside the temperature area of 480 to 560 °C. This temperature vary of sodium silicate glass, displaying the endothermic impact, may be very near that noticed by Lebedev for borosilicate crown glass, as proven in Fig. 1.

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