Foamed glass is widely used as thermal insulation material due to its characteristics such as low density, low thermal conductivity, low water absorption, good chemical stability, good frost resistance, non-combustibility, sound absorption, easy processing and forming, and easy paste construction. Sound absorption material. Foam glass is generally made of waste glass as the main raw material by sintering method, it can also be added to some perlite, volcanic ash, fly ash and other natural minerals or industrial waste.
Hard wire is solid waste produced during the production of glass fiber. Since no good treatment has been found, landfills have long been used for treatment. The purpose of this study is to develop foamed glass using waste glass fiber hard wire as the main raw material, comprehensively utilize industrial waste, protect the environment, and explore its foaming mechanism.
1. Foaming agents are anthracite, coke, limestone, and soda ash, all of which are industrial products. Stabilizing agents A and B are chemically pure reagents, and the binders are industrial water glass and polyvinyl alcohol.
Oxide Content 1.2 Sample preparation The finely ground glass powder, foaming agent, and foam stabilizer are accurately weighed, mixed thoroughly, and then an appropriate amount of binder is added. The mixture is pressed, formed, dried, and baked into the furnace. The firing process includes preheating, sintering, foaming, and annealing.
1.3 Performance Measurement and Foaming Mechanism Study The foam glass samples prepared with different compositions and different preparation conditions were mainly measured for their bulk density, pore size, observation aperture morphology and distribution, and the relationship between composition, preparation conditions and quality of foam glass. The main physical properties such as bulk density, compressive strength, thermal conductivity, and water absorption were determined for samples with good test results.
The TG and DTA curves of various foam glass batch materials were measured using a WCT-2 microcomputer differential thermograph, and the effects of various additives and the foaming mechanism were studied. The heating rate was 10 t/mi. 2. As can be seen from Table 2, the waste glass was used. As a main raw material, fiber stiff wires are added with appropriate foaming agents, foam stabilizers, and binding agents, and a reasonable technological system can be used to prepare foamed glass that meets the requirements of quality. The prepared foam glass has a moderate bubble diameter, a uniform distribution, a small density and thermal conductivity, and a high compressive strength.
After a lot of experimental research, suitable batch materials were obtained: coke and soda ash were suitable as foaming agents. The optimal dosages were 1.5% and 2.5% respectively. Stabilizing foams A and B needed to be used in combination. The appropriate dosage was 2% each. Suitable sintering process parameters are: foaming temperature 850T, foaming time 40mk, sintering temperature range Table 2 Foam Glass Main Physical Properties Bulk Density Aperture Compressive Strength Mass Water Absorption Thermal Conductivity 2.2 Foaming Mechanism From the Coke 2 shown The TG and DTA curves for % of blowing agent batch materials show that in the temperature range of 500 to 650 T, the DTA curve has a distinct exothermic peak, which is the result of the oxidation of fixed carbon in coke, with a peak top temperature of 591. This exothermic effect has a significant weight loss process on the TG curve. The weight loss rate is 1.94%. The weight loss before 120T is mainly due to the exclusion of residual water. The subsequent weight loss is due to the decomposition and oxidation of the binder and foam stabilizer in the batch. The shape of the TG and DTA curve of the anthracite powder with 2% as the blowing agent is similar to that of the coke compound, except that the temperature range of the oxidation exotherm and the weight loss is wider than that of the coke and is not concentrated. The exothermic peak top temperature on the DTA curve is 581T:, and the weight loss rate in the 500-650X: temperature range is 1.67%. The TG and DTA curves of the batch materials with limestone 2% and soda ash 2% as foaming agents, respectively Shown at. It can be seen from the figure that there is a significant weight loss process on the TG curve due to the elimination of residual water below 100T. The temperature at which soda starts to decompose is low and the decomposition temperature range is wide. The apparent weight loss of soda ash from 290 began to appear, and it was almost completed until about 700 T. The weight loss rate was 0.86% within this temperature range. The limestone batch had a significant weight loss process in the temperature range of 690-770t. The weight loss rate is 0.75%. Due to the effects of other ingredients in the batch, the limestone's thermal decomposition temperature is reduced, and the liberated gas is concentrated, basically within this temperature range. In addition, from the DTA curves shown, the TG and DTA curves for the soda ash and limestone batch materials should be in the thermal decomposition temperature range of the limestone ig curve. There is a significant endothermic process on the mA curve, only the temperature rises to this temperature. After the upper limit of the range, the pattern of the heat absorption valley is not complete due to the baseline drift of the instrument. Soda ash has a low decomposition temperature, a wide range of decomposition temperatures and a small amount of heat, so the thermal effect is not significant. And due to the complex physical and chemical changes in the heating process of other ingredients in the batch, in this temperature range, the DTA curve appears more complex changes.
From the characteristics of the above-mentioned changes of carbon and carbonate blowing agents in the heating process, it can be seen that under the action of other components of the batch material, the foaming agent actually starts to decompose or oxidize before the batch material is sintered. . Since the green body has started to sinter at this time, most of the gases generated by the decomposition or oxidation of the foaming agent escape out of the green body, and part of the gas is trapped inside the green body due to sintering of the green body, forming numerous closed microscopic bubbles. As the temperature rises and the sintering process continues, the gas pressure within the microbubbles increases as the blowing agent continues to evolve gas, the temperature rises, and the confinement of the sintered body.
When the temperature rises to the foaming temperature, the glass gradually softens, the resistance to the bubble wall movement decreases, the bubble volume expands, and the gas pressure in the bubble gradually decreases until the gas pressure in the bubble is balanced with the external pressure. At this point, the foam glass has the largest volume and the smallest bulk density. After the end of foaming, due to the decrease of temperature during the annealing process, the volume of the gas in the bubbles will gradually decrease, and the volume of the foam glass will decrease accordingly, and the bulk density will increase accordingly. In theory, when the temperature drops to the glass strain point, the particles in the glass can basically not migrate and adjust, and the volume of the foam glass will be fixed. In fact, when the temperature drops to the glass transition point or slightly above the temperature, the volume and shape of the foam glass are already substantially fixed.
From the amount of residual gas in the foam glass (calculated based on the density of foam glass and glass and taking into account the temperature effect) and the amount of gas evolved after the foaming agent is completely decomposed, a simple calculation can be made. The foam obtained by using 2% of soda ash as a foaming agent can be known. In glass, the amount of residual gas in the bubbles is only about 28% of the amount of gas evolved from the blowing agent in the batch, and most of the gas evolved by the blowing agent escapes out of the body. Therefore, foam glass made from waste glass fiber hard wire is based on the fact that the glass softens at the foaming temperature to expand the volume of bubbles enwrapped in the sintered body and further decompose the foaming agent to generate a foam glass.
2.3 The function of foam stabilizers and the role of foam stabilizers are mainly to prevent small bubbles from combining with each other to form large bubbles or to form connected pores. It is generally believed that the foam stabilizer stabilizes the air bubbles by increasing the viscosity of the glass and lowering the surface tension of the glass. In addition, foam stabilizers are often fluxes, which can form eutectics with other ingredients in the batch at lower temperatures to promote sintering, so that the gas evolved by the blowing agent stays more in the body. , It is helpful to obtain foam glass with small volume density and uniform pore size.
Under the same foaming conditions, foamed glass without foam stabilizer has a small number of small pores and its density is as high as 850 kg/m 3 , although it has been completely softened inside and the surface melted to the required viscosity for foaming. This is because there is no stability. The firing temperature of the foam formulation is relatively high, and most of the gas evolved by the foaming agent escapes the body before the body is sintered. Only a small amount of gas that has been decomposed after the green body is sintered remains in the green body to form bubbles.
Using two kinds of foam stabilizers A and B, the amount of one of them was fixed at 2%, and the relationship between the density of the foam glass produced after varying the amount of the other and the amount of blowing agent was seen. From the figure, it can be seen that when a foam stabilizer is used alone, the density of the foam glass is relatively low, and the effect is not good. When two foam stabilizers are used in combination, the density of foam glass is the lowest when the amount of foam stabilizer B is 2%. When the amount of the foam stabilizer A is 1.5% or less, the density of the foam glass is significantly reduced. Since then, its use has continued to increase, although the density of foam glass has continued to decline, but the decline has slowed. In view of the quality and cost of foamed glass, suitable dosages of foam stabilizers A and B are 2% each, because the two foam stabilizers used can increase the viscosity of the glass and reduce the surface tension of the glass in addition to the fluxing effect. At the foaming temperature, the relatively low viscosity and low surface tension can prevent the small bubbles from being combined with each other to form large bubbles and stabilize the bubbles, resulting in a foam glass having a small bulk density and a small and uniform bubble diameter.
The use of these two foam stabilizers together improves the viscosity and reduces the surface tension better than the use of only one foam stabilizer, and the effect is best when the amount of the two foam stabilizers is a certain proportion.
The relationship between the foam stabilizer concentration and the density of the foam glass 2.4 The effect of the bonding agent From the above-mentioned foaming mechanism, it can be seen that the factors affecting the sintering of the green body have a great influence on the quality of the foam glass, such as reducing the particle size of the glass powder, Increasing the glass powder specific surface area can significantly reduce the sintering temperature W and the bulk density of the foam glass. In addition, the addition of an appropriate amount of binder into the batch to form a compact body can also significantly promote sintering and reduce the bulk density of the foamed glass. After the dry batch material without any binder was placed in the mold and compacted by a little pressure, the obtained foam glass had only a small amount of small bubbles, and the bulk density was 760 kg/m3. The water-containing glass and the polyvinyl alcohol aqueous solution were used as a binder, respectively. forming. The experimental results show that the binding effect of the two binding agents is similar, the bulk density of the green body is significantly lifted compared to the non-bonding agent, and both the green blank strength and the dry blank strength can meet the process requirements. The bulk density of the resulting foamed glass is about 300 kg/m3. This shows that after the addition of a binder and pressure molding, the powder particles contact closely, the reaction cross-sectional area increases, and sintering can be promoted. In addition, the resistance of the blowing agent to evolve gas out of the body is greatly increased, thereby allowing more gas to stay in the body, reducing the bulk density of the glass foam and improving the quality of the crucible.
3 Conclusion The use of waste glass fiber hard wire as the main raw material to add appropriate foaming agent, foam stabilizer and binder, using a reasonable process system, can be prepared with a smaller bulk density, compressive strength than 篼, low thermal conductivity Foam glass.
The foaming mechanism of the foamed glass is as follows: at the foaming temperature, the glass softens the volume expansion of the bubbles entrapped in the sintered body and the continuous decomposition of the foaming agent increases the volume of the green body and generates a foam foaming agent to facilitate the fluxing and improvement. The proper use of the glass melt properties can significantly improve the quality of the foamy glass. The addition of a binder and compression molding promotes sintering and therefore has a positive effect on the quality of the foam glass.
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