On Wed, 27 Jan 1999 09:41:22 -0500 David J Killick wrote:
> From: David J Killick <[log in to unmask]>
> Date: Wed, 27 Jan 1999 09:41:22 -0500
> Subject: RE: Effect of Titanium in Iron Ore
> To: "[log in to unmask]" <[log in to unmask]>
>
> The Schlakenatlas/Slag Atlas (Dusseldorf: Verlag Stahleisen M.B.H., 1981)
> contains several viscosity plots for titania in blast furnace slags - see
> in particular pages 201, 203, 207 and 213. The underlying data are of
> varying age and may not be entirely reliable.
>
> If I remember correctly a short tutorial on the subject that Ned Rehder
> gave me some years ago, a slag needs to have viscosity under 6 poise to
> tap freely. Blast furnace slags are basically CaO + Al2O3 + SiO2, assuming
> that enough CaO was added as lime to take up all the gangue (if not, some
> of the FeO in the charge will be sacrificed to mop up the excess SiO2 +
> Al2O3). The plots in the slag atlas, especially those on p. 207, show that
> the viscosity of these slags is marginal (6 or above) at 1400C. The
> addition of TiO2 clearly DECREASES the viscosity, as Ian Freestone notes,
> and thus makes slags flow more freely - see in particular figure 42 0n p.
> 207.
>
> If TiO2 doesn't have adverse effects on slag viscosity, then why are
> modern blast furnace operators so careful to exclude it from the charge?
> The cut-off value for TiO2 in modern blast furnace feed is 1%. (At
> Phalaborwa in South Africa, which is a copper mine, the magnetite in the
> ore is segregated by Ti content - that under 1% is sold, that above is
> dumped in huge heaps. They spray these with molasses to keep the finely
> ground ore from blowing, so they act as a Mecca for flies !) The ore above
> 1% TiO2 can't be sold because in a modern blast furnace the TiO2 would be
> reduced into the iron metal, as in the case cited by Peter Hutchinson -
> not because of any effect on the viscosity of the slag.
>
> In answer to James Brothers then, I think that the TiO2-slag question is a
> red herring. If you are looking for technical reasons for failure, try
> looking instead at the difficulties of achieving sufficiently high
> fluidity in CaO/SiO2/Al2O3 slags (usually with some MgO as well) in cold
> blast furnaces. There could be many reasons for failure to attain
> sufficent temperature - damp charcoal, for example, poor furnace design
> (leading to "bridging" of the mid-shaft by sintered ore) and lack of skill
> on the part of the operators, as in charging incorrect proportions or
> trying to tap too soon, resulting in the freezing of slag in the taphole.
>
> ----------------------
> David J Killick
> Associate Professor, Department of Anthropology
> University of Arizona, Tucson, AZ 85721-0030
> Phone (520)621-8685; FAX 621-2088
> [log in to unmask]
> http://www.mse.arizona.edu/faculty/killick.html
>
> David Killick and Robert Gordon have I think adequately
covered the matter. An added minor note is that modern blast
furnace operators don't want TiO2 in slag because some of
it reduces and then forms titanium nitride inclusions during
steelmaking; and cleanliness of steel is now an obsession
for good reasons.
Ned.
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