CS200989B1 - Method for the quality determination of sodium silicate aqueous solution - Google Patents

Description

The present invention provides a method for determining and controlling the quality of an aqueous sodium silicate solution, particularly for the foundry and chemical industries. Traditionally, the quality of waterglass is judged only by its density and silicate modulus. The production of waterglass and methods of its control remained practically unchanged from the very beginning of industrial use of this raw material.

The water glass test methods used so far can only give a very rough picture of the properties important for the foundry use of this raw material. Using traditional methods it is not possible to assess reactivity, gelation rate, nature of gel formed, system stability. These properties of the waterglass decide, for example, on the technological properties of the foundry mixtures, such as workability, strength, shelf life, abrasion resistance, disintegration, etc. water glasses of the same module and density may have completely different foundry properties. By simply checking the module and the density, it is not possible to detect water glasses which cause a change in the technological properties which result in core cracking, increased abrasion or degradation or other defects occurring after the introduction of a new water glass supply.

These problems with insufficient stability of waterglass properties also occur in the chemical industry in the production of silica gel, where the properties of the resulting

200 9Θ9

200 989 product, although the modulus and density of the water glass used meet the requirements.

The aforementioned drawbacks are eliminated by the method of determining the aqueous solution according to the invention, which is characterized in that the solution is titrated with acid and the amount of acid just required to effect coagulation is determined. For the titration, it is preferable to use 1N hydrochloric acid, the coagulation threshold being the minimum amount of acid at which there is an apparent coagulation.

When an electrolyte is added to the colloidal solution, the ionic strength of the dispersion medium increases, exchange adsorption between the ions of the outer layer of the bilayer and the ions of the added electrolyte, thereby reducing the electrokinetic potential of the particles. At some point the adhesion forces outweigh the electrostatic repulsive forces and coagulation occurs. The amount of electrolyte at which coagulation occurs is referred to as the coagulation threshold. Thus, the coagulation threshold is proportional to the content of stabilizing Na ⁺ ions in the external portion of the electrical bilayer of particles. For evaluating an aqueous sodium silicate solution, the coagulation threshold can be determined using various acids. Most preferred is 1N HCl.

The method of evaluating the quality of an aqueous sodium silicate solution, in particular in foundries, enables to accurately determine the necessary binder content and the corresponding amount of hardener and thus eliminate unjustified operating reserves, which results in savings of raw materials and casting and reducing labor in the casting treatment plant. In addition, the evaluation method based on the determination of the coagulation threshold makes it possible to determine in advance the length of the production cycle (mix pot life, model removal time) and the course of strength increase, or to adjust the production cycle length to the desired state . For a waterglass manufacturer, the quality evaluation method of the present invention allows improved uniformity of properties across batches and reduces the assortment of many product types to several types differing in the graded coagulation threshold.

Example 1

The quality of the aqueous sodium silicate solution was evaluated by the coagulation threshold method as follows:

Weigh 10.0 g of the test aqueous sodium silicate solution into a 150 ml beaker. While stirring, hydrochloric acid 1 N HCl was added until gelation occurred. The gelation was clearly observable on the change in solution viscosity. A characteristic of the aqueous sodium silicate solution is the coagulation threshold in mmol / lCl / g.

Example 2

In accordance with the procedure in Example 1. 1, a coagulation threshold of 150 samples of aqueous sodium silicate solution was determined. The coagulation threshold was in a wide range: 0.2 to 4.0 mmol / g. The importance of the evaluation of the aqueous sodium silicate solution by the coagulation threshold method is confirmed by the relationships to the technological properties of the mixtures obtained for the above

200 98 sample file:

P = 0.80 + 0.88 A,

R = 13.44. e * ^{O 43} \ where P is a bond of an aqueous sodium silicate solution (MPa) K is ro2psdsvo3t 3měsí after casting (J) and A is the threshold coagulant (mmol / g).

Claims (2)

OBJECT OF THE INVENTION A method for determining the quality of an aqueous sodium silicate solution, characterized in that the solution is titrated with acid and the amount of acid just required to induce coagulation is determined, 2. A process according to claim 1, wherein the titration is mono-normal hydrochloric acid.