Introduction
Laboratory practice is aims to give students skills of theoretical principles to concrete questions of silicate technology. For example, all basic types of silicate technology at thermal treatment of initial material include a step of substances in a solid state works «Research of firm phase reaction between silica and magnesium oxide», and calcite, and silica will serve understanding these processes.
An important role in technological processes belongs to the structural transformation of separate components. Polymorphic transfer of silica and alumina influences on the interaction in firm phases in ceramic, glass and cement mixture. They have special significance in fire brick production.
The work in studying of influence on the transformation degree of silica such factors as velocity of heating, mineralizers and others is devoted to these questions.
Any raw material of silicate technology can be described with sufficient degree of approach in appropriate balance system. Therefore construction of diagrams condition and experimental research of model systems will give a deep understanding of processes occurring at heating of ceramic, glass and cement mixtures.
Laboratory work № 1 Synthesis of sodium silicates
Aim of the work – to define of solubility of sodium silicates
Theoretical information
Waterless sodium silicates
In the system of Na2O-SiO2 formation of three double chemical compounds is observed: sodium orthosilicate 2Na2O·SiO2, melting with decomposition; sodium methasilicate Na2O-SiO2 and sodium disilicate Na2O·2SiO2, melting without decomposition (figure 1).
Figure 1. Diagram of the state of two-component system Na2O- SiO2
The most slightly melted eutectic, melting at 793ºC, is formed in individual system of sodium bisilicate and silica. The composition of this eutectic is Na2O – 26,1 and SiO2 – 73,9 mass %.
The typical peculiarity of sodium silicates is their slight solubility in water. Therefore sodium silicates have significance to produce two-component soluble glass.
Glass sodium silicate or soluble glass has a composition Na2O·mSiO2, where – silicate module changes from 1 to 4.
Synthesis of sodium silicate
In industry soluble glass is produced by boiling in bath furnaces of mixture consisting of quartz sand, soda or sodium sulphate (in the presence of reducing agent - carbon) by reactions:
Technique of experiment
As raw material the local quartz sand and technical soda are used. The quartz sand and soda are weighed on technical balance in the given ratio and carefully mixed up. The weight of mixture makes 50 g (0.05 kg). Mixture is placed in previously prepared crucible. In avoidance of adhesion silicate - lump to internal walls crucible is previously covered with a layer of alumina.
The boiling is made in muffle furnace at temperature 9000С during an hour.
Then solubility of silicate - lump is determined.
Definition of solubility of glassy alkaline silicates depending on temperature
At studying of solubility of glassy alkaline sodium silicates, potassium silicates and others of various dispersability at different temperatures to set dependence between temperature and solubility of these silicates at solubilization in water nonautoclave way is used.
Weight of silicate powder of an investigated fraction in 1 g filled up in glass , placed in the thermostat. In this glass distilled water is previously poured in amount of 50 ml. The temperature of water in the thermostat is brought to the given temperature of the experiment with the help of an electroheater and adjusted with the help of mercury heating controller and an electronic relay. In the glass with the test of a powder of silicate glass mixer rotating from the electromotor is inserted.
At the end of dissolving, during an hour, the device is on, glass is taken from the thermostat, the content of the glass is diluted with hot distilled water and filtered by the funnel of Byuhner under the vacuum through a dense ash-free filter. The insoluble residual is washed out by distilled water three times on the filter the residual after appropriate drying is baked in the weighed porcelain crucible in electromuffle at temperature the 950-10000С up to constant weight.
Processing of results
The result of definition is calculated by the formula:
Where: Н0 - insoluble residual in weight % in relation to absolutely dry silicate;
а – weight of crucible, g;
ВВ - initial damp weight of the tested silicate, g;
А – content of hygroscopic moisture in researched silicate, %
Received filtered material after separation of the insoluble residual is transfered in the measuring flask in the capacity of 250 ml and distilled water up is added up to a notch.
Aliquot part (25 mlof this filter is titrate by 0.1 N solution of НСl and methyl-orange.
The content of sodium oxide in the tested alkaline silicate is calculated under the formula:
Where: a - number ml 0.1 N НСl, for titration of aliquot part of silicate solution;
k - correction factor for 0.1 N НСl;
0.0031 - transitive factor from ml 0.1 N НСl to Nа2О;
n - dilution of solution;
ВС - absolutely dry weight of the tested silicate in g;
Н0 - insoluble residual, %
The content of silica in the tested alkaline silicate is determined:
%SiO2=100 - %Na2O
Silica module of silicates is defined under the formula:
Where: 1.0323 - factor for transition from per cents to moles.
Devices and reagents
1. Counter balance
2. Porcelain crucibles
3. Glass
4. Thermostat
5. Glass mixer
6. Commercial soda
7. Quartz sand
8. Silicate - lump
9. Distilled water
10. Ash-free filter
Questions for self-checking: 1. Sodium silicates and their typical peculiarities.
2. Define the temperatures of the beginning of mixtures melting in individual systems Na2O-Na2O·SiO2, Na2O·SiO2- Na2O·2SiO2 and Na2O·2SiO2- SiO2.
3. Production of glass sodium silicate (soluble glass).
4. Definition of silica module of soluble glass.
5. Define the temperature of melting of glass sodium silicate of the following composition Na2O·2,85·SiO2