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    Add: No.238, Qiushe Road, Qiushe Industrial Park, Tongli Town, Wujiang District, Suzhou City, Jiangsu, 215200, P.R.China

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Silica Sol Casting Capillary Microstructure Decision

Silica sol is a high quality water-based binder commonly used in investment casting. Because of its shell does not require chemical hardening,Silica Sol Casting  high temperature strength, high temperature resistance to deformation ability, easy to dubbed high-quality liquid than the high-quality paint, since the sixties of last century was introduced after the investment casting, shelling technology The development of the relevant theory is very fast, but the published literature [1] mostly on the shell process and process parameters control and the choice of refractory materials and other aspects of the investment casting process shell micro Structural analysis has not yet seen the relevant reports.

       In this paper, the change of the microstructure of the shell in the process of silica sol casting is discussed from the perspective of colloidal chemistry,Silica Sol Casting so as to provide some effective theoretical guidance for the optimization of the shell technology.

2. Introduction to professional terms

      Some technical terms in the field of chemistry and casting the understanding of the field is not the same, for the convenience of discussion, we unified the use of colloidal chemistry to understand the terminology, and the use of narrow understanding. The briefing is as follows:

2.1 colloid

      First colloid is not a special substance, nor is the nature of matter, but the existence of a special state of material. The colloidal system is characterized by a certain size of the dispersed phase particles (the diameter of the dispersed phase particles is 1 to 100 nm), and there is a significant physical interface between the colloidal particles and the dispersion medium. Therefore,Silica Sol Casting the colloidal system is a two-phase or multi- Uneven dispersion system.

2.2 sol

      From the definition of colloids, colloidal systems can be formed in dispersed media in different states as long as the particle sizes of the dispersed phases of different aggregates are between 1 and 100 nm. In addition to the dispersed phase and dispersion medium are gas and can not form colloidal system, the remaining eight kinds of dispersion system can form a colloid system. When the dispersion medium is solid, it is called solid sol; when the dispersion medium is gas, it is called aerosol, and the colloidal dispersion system with liquid dispersion is called liquid sol or sol.        

2.3 Gel

     Also known as jelly. The colloidal particles in the sol can be connected to each other under certain conditions to form a space network structure, the structure of the gap filled with liquid as a dispersion medium, regardless of the amount of liquid, this will lose the liquidity of the dispersion system called gel. Fresh gel called wet gel, when the liquid in the gel all lost also known as the gel, is the dry gel, the structure of the dry gel inside the filling is full of gas.

    Gels are filled with water when the liquid is called water.

     Gel has a certain geometric shape, with a solid mechanical properties, such as strength, elasticity and yield value. But from the internal structure, it is different from the usual solid, which consists of solid-liquid two-phase composition, but also has some properties of the liquid, such as ions in the fresh hydrogel diffusion rate close to the diffusion rate in aqueous solution The This shows that the fresh hydrogel,Silica Sol Casting the dispersed phase and dispersion medium are continuous phase, which is the structural characteristics of the gel.

2.4 capillary phenomenon

       The continuous dispersed phase forms the solid skeleton of the gel, and the continuous dispersion medium forms the fluid portion of the gel, forming the particle size of the colloid so that the gel has a microstructure of the capillary. Capillary phenomenon refers to the liquid inside the fine tubular object, due to the adhesion between the liquid and the wall and the liquid itself, the difference between the cohesion in the vertical tube within the rise or fall phenomenon, and the role of these two forces is the capillary force The role.

     The gel structure of fresh gel is filled with liquid dispersion medium. With the progress of gel drying, the gel will change from liquid-solid two-phase to liquid-solid three-phase, and the final liquid phase will be replaced by gas phase and become dry gel The The permeability of the visible shell is determined by the microstructure of the capillaries of the gel. It is also seen that the drying process is a very critical and important link in the gel formation process and that the factors related to the gel drying rate will ultimately affect the gel capillary Of the microstructure.

2.5 gelling

      A certain concentration of sol in the appropriate conditions to form a gel process known as gel.

During the gelation process of silica sol, the capillary structure of the colloidal silica gel was formed by hydrogen bonding. The hydroxylation of the hydroxyl group was formed by the hydrogen bond in the late stage. After drying, the hydrogen bond was continuously formed into the covalent bond of the silica and the three-dimensional growth of the micelles, but the crosslinking speed in each direction was different , The cross-linking density will be different, and ultimately the formation of heterogeneous, with complex micro-area,Silica Sol Casting dendritic polymer structure of the gel.


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Address: No.238, Qiushe Road, Qiushe Industrial Park, Tongli Town, Wujiang District, Suzhou City, Jiangsu, 215200, P.R.China
Tel: +86-512-633758+86-608
 Fax:86-512-63370558
 E-mail:szxsjm@sohu.com
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