How to improve the moisture absorption resistance of sodium water glass sand
The sodium water glass is an aqueous solution of sodium silicate, and the molecular formula is Na2O·mSiO2. The m in the formula of sodium water glass is called the modulus of water glass, and represents the molar ratio of Na2O and SiO2, which is a very important parameter. So how does the sodium water glass sand type absorb moisture resistance? Let's take a look at it along with Xiaobian.
The sodium water glass sand core hardened by CO2 or heating is assembled in the clay wet type. If it is not poured in time, the strength of the sand core will be drastically reduced, not only creeping or even collapse; in a humid environment, storage and release The core of the sand is also significantly reduced in strength. Table 1 shows the strength values of CO2 hardened sodium water glass cores placed in a relative humidity of 97% for 24 h. The reason for the loss of strength in a humid environment is due to the re-hydration of soda water glass. Na+ and OH in the sodium water glass binder matrix absorb moisture and etch the matrix, and then break the silicon-oxygen bond Si—O—Si, resulting in a significant decrease in the bond strength of the sodium water glass sand.
The measures to solve this problem are:
1. Add lithium water glass to sodium water glass, or add inorganic additives such as Li2CO3, CaCO3, ZnCO3 to sodium water glass, which can form relatively insoluble carbonates and silicates, and can reduce free sodium ions. Therefore, the moisture absorption resistance of the sodium water glass binder can be improved.
2. Adding a small amount of organic material to the sodium water glass or adding an organic substance having a surfactant action. When the binder is hardened, the hydrophilic Na+ and OH- ions in the sodium water glass gel are replaced by an organic hydrophobic group, or Combined with each other, the exposed organic water-based base improves moisture absorption.
3. Increase the modulus of the water glass because the high modulus water glass is more resistant to moisture absorption than the low modulus water glass.
4. Add a starch hydrolyzate to the sodium water glass sand. A better method is to modify the sodium water glass with a starch hydrolyzate.
In summary, the sodium water glass sand type anti-hygroscopicity can be improved. The larger the m-value of the sodium water glass, the higher the viscosity of the water glass, and the higher the water glass modulus, the sodium water glass sand type. The higher the moisture absorption resistance.
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