Losses burn a ceramic object is a quantity that can be measured on the shrinking (size) due to the burning object. It was not just because of the evaporation of free water, but because of the changing nature of the chemical and physical properties of clay into ceramic permanently. Soft clay when mixed with water easily parsed and plastic, but after being burned into a hard stony clay and water-resistant and shrink in size compared to the size of the time before burning.
Things That Cause Losses Fuel Occurrence
In the process of burning ceramic objects will be a process as follows:
a. Evaporation of residual water forming
Although it has been drained, but the amount of water vapor still remain in the pores of the ceramic objects and will only evaporate when objects The burned. After that there was shrinkage because all particles closer together to fill the pores.
To avoid the outbreak of objects ceramics were burned as a result of water vapor pressure and shrinkage suddenly, the temperature rise at the initial stage of combustion should done slowly. At a temperature of 1000C-1500C all water formers have been lost. At that stage, it can be said that drying process is considered complete.
b. Evaporation of water chemistry
Subsequent changes that occur in the process of burning clay at a temperature of 3500C is water chemistry of clay started out. Understanding water chemistry should not be confused as a water-forming, water pores plasticity or water that evaporates during drying. Water chemistry is a part of the molecular structure of clay and not affected by temperatures below 3500C.
When expressed as a percentage, clay-containing water chemicals by 14% of the total weight. Water chemistry should be sufficient to vaporized in the combustion, so as to prevent the collection vapor pressure which is likely to break down objects. At the time of clay bodies had been burned at a temperature of 5000C, the process will occur dehydration so it is no longer soluble in water or decompose. Clay also will lose plasticity and becomes very brittle so it is not may be recycled or used again.
c. Complete combustion (oxides) compounds of carbon, carbonate and sulfate.
Another important change that occurred in the clay mass during the initial combustion is oxidation or burning completely all non-clay component in oxide compounds, including, among others, organic materials containing carbon and sulfate compounds. Process all ingredients typically oxides would be perfect on the combustion temperature 9000C.
Because the amount of these minerals is relatively small, it is usually burning oxide can be carried out without a problem. Because oxidation of the three elements above, then the shrinkage fuel will also occur as a result of the movement of clay particles to occupy the space left by these elements.
d. occurrence of quartz inversion
All clays contain certain quartz in bulk. Quartz can disos ialisasikan as complementary mineral clay nature. Quartz can also be added to the clay in the form of sand white (flint). Quartz crystals have a number of different forms- depending on the temperature difference.
When the temperature changes, the crystal- quartz crystal to adjust to be slightly different structure and followed by a volume change. Therefore, when the temperature of 5730C was achieved, quartz crystal changes the shape of the alpha (c) to beta (d). This change was followed by a slight volume expansion (2%) and vice versa, during cooling, ie at a temperature of 5730C, crystal quartz changed back from beta to alpha or back to form crystals accompanied by the original volume shrinkage. Though changes in a relatively small volume of the mineral quartz, the temperature rise burning must be done slowly to prevent the outbreak objects were burned.
e. occurrence of vitrification process
Vitrification process is a melting process silica materials into glass which then enters the pores and make all solidified particles. Agency bervitrifikasi ceramic objects that have been in perfect becomes porous and become watertight. Clay will menggelas at different temperatures, depending on the composition.
A type of red clay, for example, containing many elements of iron and other mineral impurities, can be burned into a hard and solid at a temperature of about 1000 0 C and may melt into a liquid glass at a temperature of 1250 0 C. Depreciation continues during vitrification.
Shrinkage is due to the reduced particle size, especially when the particles are approaching the melting point and arrangement of particles increasingly menggelas. Losses burn an object ceramics can exceed 10%. Shrinkage is diverse, large or size depending on the temperature level vitrifikasinya. Clay will melt usually preceded by bubbling phases, boiling and at this point probably will swell in size.
Case This is called over-firing or too mature. T anah clay mass that has completely burned and mature can be seen from the level of violence, pressure strength, power density or water-resistant, resistant to friction and can be seen from the color and texture.