Magnesia brick (Magnesite Brick) magnesian content is in the 90% above, alkalescent and fireproof material that gives priority to brilliant photograph with Fang Mei stone. Can divide commonly for agglomeration magnesia brick (say again firing magnesia brick) combine magnesia brick with chemistry (say not to burn magnesia brick again) two kinds big. Purity and firing the magnesia brick with high temperature, because grain of square magnesian stone is contacted directly, call direct union magnesia brick; The brick that makes for raw material with electric frit magnesia calls magnesia brick of electric frit recombine.
Magnesia brick has taller fireproof degree, function of very good broken bits of alkali resistance sex, loading bate begins temperature tall, but heatproof shake performance is poor. Agglomeration magnesia brick is raw material with making bricky magnesia brick, via smashing, burden, mix practice, after shaping, in 1550 ～ the high temperature of 1600 ℃ falls firing, high pure of goods firing temperature is in 1750 ℃ above. Irrigating magnesia brick is proper chemical bond is added in magnesia, via mixing refine, shape, dry and make.
The thermal conductivity of magnesia brick (coefficient of thermal conductivity) (Thermal Conductivity) , namely its deliver caloric capacity, express normally with coefficient of thermal conductivity. Thermal conductance expresses to transfer a process in energy in, inside unit time, below unit temperature gradient, the quantity of heat that unit area place passes.
1, the thermal conductance with different qualitative capable person often the difference is very big. Below normal temperature, the thermal conductance of all sorts of firebrick is OK from hundred arrive tens of (W ／ (M· ℃ ) ) , highest value and lowermost value differ close thousandfold. Lift as temperature, although the thermal conductance poor value of all sorts of firebrick tends reduce, but the difference is very big still. When be like 1000 ℃ , the thermal conductance of light qualitative silica is 0.35W ／ only (M· ℃ ) the left and right sides; Recrystallization carborundum goods is 17.5W ／ (M· ℃ ) the left and right sides; Black lead can be as high as 35W ／ (M· ℃ ) .
2, the thermal conductance of magnesia brick is divided outside sufferring temperature to affect, closely related as chemical as its still mineral composition and constituent structure. When firebrick is formed by crystal, the property of crystal has apparent effect to thermal conductance. Well-known, the thermal conductance of inorganic metalloid material compares a metal commonly a lot of lower. Because inorganic metalloid material and the metal that have metallic key are different,this is, have few free electron only. The heat conduction that causes by free electron in this kind of material is very finite, basically is degree of resonance of deviate of vibration of You Jing case and calm. Deviate resonance degree heals big, thermal conductance heals small. And degree of deviate of crystal lattice vibration is followed again make each constituent material rub the difference of Er quality increases and increase, the thermal conductance of simple substance is the so biggest (the thermal conductance of black lead is bigger depend on this) namely.
3, the crystal that has complex structure, bigger to the heat radiation action of crystal lattice, thermal conductance becomes smaller. Be like MgO, a12O3 and MgAl2O4 are brilliant waiting for an axis together, but because MgAl2O4 structure is complex, thermal conductance is inferior. Be different from tropism crystal, in the direction with the concentrated particle in edge crystal, thermal conductance is bigger. Like quartz particle of direction of edge C axis piles up more concentrated, its thermal conductance (13.6W ／ (M· ℃ ) ) it is about perpendicular at C axis direction person (7.2W ／ (M· ℃ ) ) 2 times. Be like the black lead of layer shape structure again, parallel is about at the thermal conductance of level direction 4 times at level direction more perpendicular.
4, if crystal is put in blemish, if fashion displacement solid solution when, because the regular sex of crystal structure is sufferred,destroy, cause hot scattering appearance, bring about thermal conductance to reduce. Other crystal blemish if room, the fault, also have similar effect. Same, as a result of the hot scattering phenomenon of crystal boundary, the thermal conductance of much brilliant material relatively single crystal person low; The material that fine grain makes is thicker grain constitutor is low. Foreign matter part is contained in material, because also produce scattering effect, reason also makes thermal conductance is reduced.
5, when
Firebrick
When vitreous photograph is being contained in, because the structure of noncrystalline does not have foreword, odds of the barge against between atom is big, reason and crystal photograph are compared, coefficient of thermal conductivity is inferior. When air hole is contained in firebrick, because aeriform thermal conductance is smaller than solid, follow the addition of porosity so, the thermal conductance of material is reduced. This is the main reason with porous material small thermal conductance.
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