what's the difference between fused zirconia and chemical grade zirconia,

The term fused zirconia refers to the zirconia grains which are melted by heating above their melting point therefore the surface of these grains is in a fused state and it is nearly theoretically dense. One would expect better thermo mechanical properties from fused grains. Where as chemical grade is generally refered to zirconia prepared by chemical precipitation or decomposition of zirconium salts and such grains show high surface porosity hence they are prone to liquid metal wetting.


 Refractoriness is all about purity. A fused grade will contain fewer of the glass forming impurities which reduce the refractoriness of high melting point materials like zirconia. Hence you will have cleaner grain boundaries less prone to chemical attack, high temperature creep etc. In extreme applications, go for fused grade every time. Of course there are grades of fused materials as well, so you have to go by the quantities and types of impurities present in the chemical analysis to be sure that you're getting a quality product.


Price wise:
It can expected the fused grade to be more expensive. But there are different grades of fused zirconia, as with any other fused material. The fused material obtained from the centre of the melted mass is expected to contain the least contaminants and companies will often sell this material at the highest price whilst sell the material obtained from the outside of the melt at a lower price.
Whether it's better depends upon what use of it and how essential the place it is. That is, it could be cost effective to use the lower grade of zirconia in certain applications. Usually any containment vessel is zoned and the highest grade, fused materials only used in the high wear areas.


Crystal Size :
Cristal size is a major difference. Fused ZrO2 is slowly cooled, thus allowing for better formed and larger crystals than chemical ZrO2.


Lattice Size: 
There can not be major difference in the lattice parameters of the fused and chemical grade calcined zirconia but it may vary by from 5to 6% because the chemical grade is expected to have high vacancy or interstitial concentration hence it may show larger lattice parameter.Since in the fused zirconia the imputities are segregated to the surface of grains during solidification therefore it show lattice corresponding to that of pure zirconia crystal.

how Manganese cause Magcarbon refractory erosion?

1) Rich MnO slags can lead to Mn-rich metallic particles and solid solution with Mg (and, indeed, carbon oxydation) at the interface between slag and lining. 
Anyway, this is seldom the first cause of erosion: it generally occurs after the lining has been weared for some other reason (i.e. slags unsaturated in MgO or rich in FeO).


2) Mn presence in converter causes erosion faster, as it behaves acidic, makes the liquid less viscous, penetrates the pores and joints and reacts with MgO at the contact point. For Mn steel, different of configuration of MgC brick is used.


3) it is observed that after a low grade ore(high impurity i.e Mn,Si) converter life is almost reduced and high erosion profile is being observed. 
as my observation high Mn slag is very fluid and do not cover the converter lining after slag splashing. reducing use of iron ore as coolant may help.


MnO + SiO2 = very low melting and corrosive liquid. 

I suppose primary wear area limiiting converter life will be the trunnions. Trunnions can be zoned with higher quality MgO containing bricks - MgO purity should be 97.5 minimum and of largest MgO crystal size available. Graphite should be 10-20% and have coarse flaked quality -- exact amount of graphite is function of sracp charge; hot metal chemistry; gunning practice; slag viscosity etc. A good start would be 15% C. Metal additions should be aluminum and silicon metal which will form carbides for added strength and corrosion resistance. 

Turkish fused MgO is superior to Chinese fused MgO especially for corrision resistance - crystal size is larger and grain chemistry is more homogeneous. 

Some other thoughts: 

The operator should be adding enough lime/limestone/dolomitic lime to maintain slag basciity at a > 3:1 lime:silca ratio and some MgO is helpful to reduce slag liquidity and reactability. 

Reblows will be especialy harmful as added FeO can result and FeO+MnO+SiO2 is a refractory solvent that is very aggressive. So effort should be taken to control reblowing to minimum. 

Overblowing such that temperature is overheated should be controlled. 

Corriosive slag should be slagged off shortly after tap. 

A high purity MgO gun mix and laser readings to identify low spots for added gunning maintenance will extend service life. 

Do practice slag splashing; a special lance is used to inject nitrogen after tap - the slag is made more refractory prior to the nitrogen splasing by addition of dolomitic lime. 

A good strategy would be to plan for Continuous Improvement over several linings rather than thinking that one design change can be a silver bullet. Key is to study the wear profile, identify the wear mechanism and develop new lining design that addresses the wear area and wear meachanism; this should be repeated in several iterations over several linings as in "chaisng the hole". As one area is upgraded the weak link might move to another area of the vessel. EX: An upgrade of trunnions might shift the limiting zone to the cone or the slagline or the charge pad or the tap pad...

phenomenon of Alumina pick up by the liquid mould flux during Continuous Casting and how it affects the quality of cast strands?

The pickup of alumina in the mold causes the formation of calcium aluminates. Since there are a variety of different calcium aluminate morphs(each one with a higher melting temp.) over time the mold flux can and will begin to thicken up and the fluid lubrication on the strand mold faces can be interrupted causing surface defects & breakouts. Old timers used to throw Calcium flourides (spar) into the mold to liquify it but each time you do that you also increase the CA content which in turn will eventually thicken back up. Spar is a bad actor in the mold. In order to stay fluid there is a delicate chemical balance between CA & Al.

Why mag-c bricks is mostly prefer for ladle and EAF, why not spinel refractory?

EAF is all mag-carbon. Why it works well and zoning is done based on carbon level, anti-oxidant, graphite quality and magnesia grain quality. In steel ladles, however, mag-carbon is the solution in the slagline only. If the shop is in an alumina killed process, the common is alumina/magnesia carbon for the barrel and bottom. For silicon killed shops, the norm is dolomite (carbon bond normally) or magnesia carbon. The selection comes down to what works in the application and which technology is most cost effective. The later takes on a regional aspect. In fact one shop in ---- (blastfurnace not EAF) is using a bottom and barrel that is alumina magnesia castable with a mag-carbon slagline, why? Simple they maintain the barrel profile with shotcrete and recasting through many slaglines. In fact they only reline the barrel and bottom from the shell once a year!


MgO-C is more compatible with high lime fluid slag. Spinel is more neutral and performs well in molten metal contact.

In basic steel making process, the slag is high in lime. So the brick need to be compatible with the slag. So MgO.C is one of the brick suitable for ladle metal line & only brick suitable for slag line. Graphite addition provides nonwetting character, spalling resistance and additional corrosion resistance especially against FeO. Other bricks Al2O3-MgO-C (Al killed) & Dolo-C (Si-Killed) bricks are used mostly on metal line of ladle. Some ultra low-C, Al-killed steel customers use Al2O3-MgO castable & Spinel bricks in ladle metal line, prefab/precast ladle bottom depending on their plant practices. In EAF also basic slag & hot spots suits MgO.C bricks. It is also economic against spinel brick.

Benefits of using Steel Fibers and Organic Fibers in Refractory Castables and Monolithics

One of the most effective ways of improving the mechanical and thermal properties of refractory castables and other monolithic refractories is adding in suitable proportions of stainless steel fibers and organic fibers to the castable respectively.

Steel Fibers

Steel fiber reinforced refractory castables are very resistant to the tendency of the material to fall apart on thermal cycling. Stainless steel fibers greatly improve the flexural strength of the castable. And this added increase in ductility contributes significantly to the thermal shock and spalling resistance of the material. The fibers generally used are in size varying between 0.1 to 0.4 mm2 in cross-section & 20-40 mm in length. For monolithic SS is used either high chrome or high chrome nickel steels available in the market with different grades. One reason commonly reported that the thermal shock resistance of castables is greatly increased through addition of SS fibers because these fibers act as crack arresters, preventing cracks propagating. This is also possible that the microcracks caused by a mismatch in thermal expansion coefficients of matrix and fibers dissipate energy from larger cracks propagating as a result of thermal stress. However percentage of these fibers added becomes important because of two reasons as it has a direct impact on the fluidity of the castable, then it may also cause mixing difficult due to fiber-balling when added beyond 3% by volume. Another critical factor will be the maximum application temperature for the castable that those fibers present in the castable can resist oxidation (since these fibers can not perform beyond their melting temperature).

Organic Fibers

An effective means for improving the explosive spalling resistance of a castable is to add organic fibers to the formulation. It has been reported that the composition & concentration of fibers are not as important as melting temperature of the fiber, since these fibers after melting increase permeability at certain temp. & thereby reducing the explosive spalling tendency of the castables. The fibers generally used for this purpose are Polypropylene fibers, Polyester staple fibers, etc.
Because of these different advantages it have been found that both organic and SS fiber reinforced refractory castables provide substantial increase in service life and therefore, a considerable reduction in refractory maintenance cost and furnace down-time.