| Sodium water glass adhesive is composed of binding agents, curing agents, fillers and additives. With the advantages of non-inflammability, acid resistance, non-toxic, simple process, low cost, etc, it has been widely used in fireproof insulating materials, acid resistant mortar, refractory coating, casting, mold and other fields. However, its shortcomings, such as low bonding strength, poor water resistance and poor heat resistance limit its more wide application. Therefore, its improvement of bonding strength, water resistance and heat resistance is necessary. In this work, coarse grained filling material will be used as reinforcing material to improve heat resistance, composite fine grained filling material will be used as jointing material to improve mechanical properties and water resistance.The effects of factors such as the modulus and baume of sodium water glass, the amount of curing agent, the type, composition and grain size of filling materials on performance of the adhesive are investigated. A series of experiments have been carried out to select the most suitable raw materials for the adhesive, including sodium water glass solution with a modulus value of 2.8 and a baume of 45 (as binding agent), sodium fluorosilicate Na2SiF6 (as curing agent), bauxite with 90 mesh of granularity (as coarse grained filling material), silica fume with 1250 mesh of granularity and cast stone powder with 600 mesh of granularity ( as fine grained filling material). According to the results of single factor test and orthogonal experiment, the following optimal formulation is achieved: sodium water glass 45 g, sodium fluorosilicate 6.75 g, bauxite 80 g, silica fume 28 g, cast stone powder 12 g. On that basis, the curing conditions of the adhesive have been investigated. The optimum curing process is that the adhesive is heated to 130℃at the rate of 12℃/min, and the temperature is kept for three hours, then, treated three times with 50% sulfuric acid with an interval of 12 h. In this way, the mechanical strength of the adhesive is increased by 17% to 22%.The performance tests of prepared samples are carried out. Results show that the mechanical properties of the modified adhesive can reach 6.87 MPa, and the unmodified can reach 5.03 MPa, with an increase of 36.6% in the mechanical properties. The water resistance remain-strength rate of the modified adhesive can reach 95%, and the unmodified can reach 88%, with an increase of 7% in the water resistance properties. Heat resistance remain-strength rate of the modified adhesive can reach 87.9%, the unmodified can reach 74%, with an increase of 13.9% in the heat resistance properties. The modified cost is 800 yuan / t, commercially available product is 1200 yuan / t, with an reduce of 33.3% in the cost. Furthermore, the modifying mechanism of the adhesive is analyzed by means of SEM, TG-DTA and XRD. Making use of SEM, it is found that the original adhesive appeared many cracks on the surface, but the modified one denser and smoother, which resulted in an obvious improvement of its mechanical strength. The measurement results of TG-DTA indicate that the modified adhesive do not decompose until 900℃and its residual strength is two times more than the original one at 600℃, improving the high-temperature performance significantly. XRD indicated that both coarse grained filling material and fine grained filling material are only mixed into the binding agent without any chemical reaction. Compared with the likewise products, the modified adhesive possesses obvious technical and economical superiority, so its market prospect is extremely broad. |
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