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Silica Sol Casting Has A Mechanical Nature Of The Solid

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

From the perspective of colloid chemistry, the change of the microstructure of the shell in the process of silica sol casting is discussed, and it is hoped that it will provide some effective theoretical guidance for the optimization of the shell technology.

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,Silica Sol Casting we unified the use of colloidal chemistry to understand the terminology, and the use of narrow understanding. The briefing is as follows:

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). There is a clear physical interface between the colloidal particles and the dispersion medium, so the colloidal system is a two-phase or multi- Uneven dispersion system.

Sol

      From the definition of colloid, as long as the particle size of different dispersed dispersed phase between 1 ~ 100nm, in different states of the dispersion medium can form colloidal system. In addition to the dispersed phase and the dispersion medium are gas and can not form a colloidal system,Silica Sol Casting 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; the colloidal dispersion system with liquid dispersion is called liquid sol or sol.

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.

    The gel structure is filled with water in the voids called water when it is called hydrogel.

     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,Silica Sol Casting such as ions in the fresh hydrogel diffusion rate close to the diffusion rate in aqueous solution The This shows that the fresh hydrogel, the dispersed phase and dispersion medium are continuous phase, which is the structural characteristics of the gel.

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,Silica Sol Casting 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 of.

     The gel structure of fresh gel is filled with liquid dispersion medium. As the gel dries, 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.


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