On 2018-08-08 14:48:54
Calcination process of muffle furnace
The main physical and chemical changes in the calcination process of muffle furnace are as follows:
(1) Thermal decomposition. At higher temperature, the solid-phase reaction of oxides may take place to form an active combined state;
(2) By recrystallization, a certain crystal shape, crystal size, pore structure and specific surface can be obtained;
(3) The microcrystalline is sintered properly to improve the mechanical strength.
The main factors affecting the calcination process are calcination temperature, gas phase composition, thermal stability of the compound, etc. Therefore, according to the different thermal stability of various compounds (such as carbonates, oxides, hydroxides sulfides, oxysalts, etc.), by controlling the calcination temperature and gas phase composition, the composition of some compounds can be selectively changed or the crystal shape can be changed, and then the impurities can be removed and the useful components can be separated and enriched.
The principle of high-temperature muffle furnace calcination is the thermal dissociation or crystal transformation process of natural or artificial compounds; at this time, the compounds are thermally dissociated into a simpler compound or crystal transformation occurs. The thermal dissociation of carbonate is called calcination. The calcination operation can be used to directly process the mineral raw materials to meet the subsequent process requirements, and can also be used to prepare the chemical concentrate by the chemical beneficiation post-treatment to meet the user's requirements for products.
Muffle furnace: it's translated from English muffle furnace. Muffle means package, furnace means furnace, furnace. There are several general names of muffle furnace in China: electric furnace, resistance furnace, Maofu furnace and muffle furnace. Muffle furnace is a kind of general heating equipment. It can be divided into box furnace, tube furnace and crucible furnace according to its appearance and shape. There are domestic muffle furnaces and imported muffle furnaces according to nationality. According to the heating elements, there are: electric furnace wire muffle furnace, silicon carbon rod muffle furnace and silicon molybdenum rod muffle furnace; generally, they are divided into 900 degree series muffle  furnace, 1000 degree muffle furnace, 1200 degree muffle furnace, 1300 degree muffle furnace, 1600 degree muffle furnace and 1700 degree muffle furnace according to the rated temperature. According to the controller, it can be divided into the following categories: pointer table, ordinary digital display table, PID regulation control table and program control table; according to the insulation materials, it can be divided into two categories: ordinary refractory brick and ceramic fiber. Muffle furnace is a periodic operation mode, which is used by laboratories, industrial and mining enterprises and scientific research institutions for element analysis and determination, as well as general small steel parts for heat treatment such as quenching, annealing and tempering. High temperature muffle furnace can also be used for high temperature heating such as sintering, dissolution and analysis of metals and ceramics.
Maintenance and precautions of muffle furnace:
1. When muffle furnace is used for the first time or is used again after long-term shutdown, it must be dried. The oven drying time shall be at room temperature 200 ℃ for four hours. 200 ℃ to 600 ℃ for four hours. When in use, the high temperature of the furnace shall not exceed the rated temperature, so as to avoid burning the electric heating elements. It is forbidden to pour various liquids and soluble metals into the furnace. Maofu furnace is recommended to work below 50 ℃ of high temperature. At this time, the furnace wire has a long service life.
2. Muffle furnace and controller must work in the place with relative humidity no more than 85, no conductive dust, explosive gas or corrosive gas. When metal materials such as grease need to be heated, a large number of volatile gases will affect and corrode the surface of electric heating elements, so as to destroy and shorten their service life. Therefore, when heating, it is necessary to timely prevent and seal the container or properly open holes to eliminate.
3. Muffle furnace controller shall be limited to the range of 0-40 ℃ ambient temperature.
4. According to the technical requirements, regularly check whether the wiring of the electric furnace and controller is in good condition, whether the pointer of the indicator is stuck when it moves, and use the potentiometer to check the increase of the error of the instrument caused by the magnetic steel, demagnetization, expansion of the wire, the fatigue of the shrapnel, balance damage, etc.
5. Do not pull out the thermocouple suddenly in case of high temperature, so as to prevent the jacket from cracking.
6. Keep the furnace clean and remove oxides and other things in time.