Normas morales y violencia en el matrimonio

by considering the time taken for.bubble nucleation and growth to enable the establishment of the well defined crater-like structure.

4.3 Decarburization at 1400° C.

From the preliminary experiments'which were carried out at 1400° C the data obtained were insufficient to enable a

decarburization trend to be established. A series of experi­ ments was therefore followed with the aim of obtaining, and if possible, establishing such a trend. Shorter intervals of time were predetermined for the required experiments based on previous results. The aim again being to follow changes in decarburization to within closer variations w i t h time. As

expected from previous experiments a great number of experiments was needed in order to define a.trend during decarburization but successful droplets were obtained up to 11 and 12 minutes of reaction time. Four slags were chosen for this set of experi­ ments, Fayalite and 141,25'.85% and 31% CaO contents. Fayalite and 14% CaO slags showed greater scatter of results as

compared wit h high (25 and 311) CaO contents. Scattered results were expected and therefore duplicate or triplicate

experiments were carried out so as to define the path followed • by decarburization.1- The data obtained from decarburization of an FeO-4.26$C alloy w i t h fayalite slag are shown in fig . 38 and those for decarburization w i t h 14!CaO in fig.39. From visual observations fayalite slag showed greater signs of

quenched crucibles. Tlie reacted droplets were of spherical shape but there were no signs that bubble nucleation (i.e. cratered surface) had taken place on the surface. Overall diameters were greater for reacted droplets as compared with initial sample. Signs of internal nucleation were found when crushing the droplets for chemical analysis. Due to the

scattered results obtained no further experiments were made at 1400° C with these two slags. . ;

The results from decarburization of an Fe-4.35%C alloy with 31.94$CaO slag are shown in fig.40 and those for an Fe-4.02$C alloy decarburized in 25.85%CaO slag are shown in fig.41. The same smooth, trend was found for these two slags at 1400° C as in the 1300° C decarburization reactions. ’ By continuing che trend followed by the data obtained Ci.e.

assuming the decarburization rate to continue in the same fashion) it may be seen from the graphs that in order to obtain low carbon levels, reaction times of a b o u t ‘15 min would be required for high lime contents.

The reacted droplets w i t h final carbon levels under 2.2|C were completely covered w i t h craters. The internal surfaces

(when exposed by subsequent fracture) clearly showed craters where bubble nucleation must have taken place.

4.4 Experiments at 1500° C.

The experimental arrangement used at 1240° C, 1300° C

... .. .. * - - ...

and 1400° C was found adequate for the study of decarburization with various CaO-FeO-SiC^ slags, although at 1400° C m a n y

difficulties were found. By scrutiny of the rates of decarb- urization for the above mentioned experiments it is seen that

an increase in temperature causes an increase in the rate of decarburization for corresponding slags. Also due to the short time required for the carbon content to attain levels below 1%, a series of experiments was envisaged to carry out decarburization reactions at temperatures of 1500° C which could perhaps require only a small number of experiments to establish the trend followed.

4.4.1 Crucibles for decarburization at 1500° C« Due to the highly reactive slags under which decarburi­ zation reactions were being studied it became necessary to adopt crucibles which could withstand the 1500° C temperature proposed.

Two options were open, the use of either zirconia cruc- ibles or, as in the case of iron crucibles, the use of a zirconia coating on a refractory crucible. The two options could be followed with stabilized zirconia crucibles, and, depending on the results obtained, (i»e * reaction times,

foaming of slag, scatter in results) the same type of experi­ ments with a zirconia-coated refractory crucible could be continued. Stabilized zirconia crucibles of 40mm ID x 40 m m high were initially used. Because the crucibles are prone to

thermal shock it became necessary to support them inside

graphite crucibles .to prevent any run-out or slag from attacking the working tube. Graphite rods were machined to give a

crucible 100 mm high. 42 mm internal diameter and 1.5mm wall thickness. The graphite crucibles were held with. Pt-Pt/10% Rh. wire with a lead of about 16cm above the crucible and subsequently

4.4.2 DecarburizaLion at 1500° C.

Due to the small volume provided by the zirconia crucibles the slag to metal ratio was set at 20:1. The size of the

metallic sample was maintained at one gram. Slags used in the 'present experiments varied from fayalite to 20.681 and 2 8.2!CaO.

Preheating of the zirconia crucibles was carried out in incre­ ments of approximately 150° C every 5 min. The system

(crucible + sample + slag) was held at a final preheating temp­ erature of 1000° C for 10 min giving a total preheating time of 50 min. The system was then taken to the reaction temperature of 1500° C where the melting time for the slags was always of the order of 30 to 45 sec. A considerable degree of turbulence took place during the first three minutes but generally sub­ sided after 3.5 min. The foamed slag in most cases reached the top of the zirconia crucible, the latter usually remained visible for most of the reaction time indicating this, that the slag did not rise above 40mm height.

The data obtained are plotted in figures 42 to 44 for the three slags used. Decarburization rates obtained from

fayalite reactions were found to be far slower than expected for a reaction at a temperature of 1500° C.

In the following trials a 20.68ICa0 slag was used to

decarburize Fe-4.12!C alloys. The results obtained indicated a fast decarburization rate down to carbon levels of about 2%

-after which the reaction seems to drastically slow down.

After 10 min of reaction the results become scattered and tend