CEPT (B) de la Región Educativa B 1 Ubicación.

been immersed for 120 s, The indistinct melt - cylinder interface developed a cored or zoned phase (dark grey) adjacent to, and within the globular wftstite zone. The mole proportions of oxides present on the dark grey col­ oured region were.2(MgO~FeO):1 SiO^. A mineralogical

notation described by Berry and Mason (-**43) has been used to define the olivine series Mg„Fen ' .SiO- to represent the Forsterite (2Mg0,Si0 2) and Fayaiite (2Fe0.Si0p) end

members. This series is referred to as the Fo - Fa olivine series. The mole fraction of one end member automatically fixes the value of the other member (Fig. 45* p. 2 9 4). The

terminology cf forsterite (Fo) has been used throughout this section to describe the composition of the phase. The magnesia values obtained from the oxide distribution pro­ file in Plate 78 (p. 349 ) showed a progressive forsterite

enrichment towards the cylinder, ranging from F o ^ to

fuse Fo - Fa olivine phase formed, Plate 79 (p. 350 ). Isolation of the granular olivine phase and progressive resorption occurred at the margin between melt and globu­ lar wustite.

The reaction interface for the pill test was rep­ resented as illustrated in Plate 80 (p. 351 ). The mole proportions and mole fractions of phases derived from oxide concentrations suggested some 4 - component assem­

blages, The possibilitjr that simultaneous measurement of twro or more phases occurred at some of the analysis points cannot be overruled due to the spot size used. The pro­ portion's of Fo - Fa olivine phases were low in the sample

and this may have been as a consequence of the low volume of melt available for reaction. The reacted parts of the '•crucible” • were composed of dicalcium silicate and magnesio-

wiistite, and produced a similar interface to that of a

dolomitic lime cylinder immersed in a correspondingly large volume of melt.

The addition of 5 mass % MgO to the melt produced a well developed Fo - Fa olivine zone which followed closely the contours of the globular wftstite margin after a cylin­ der immersion time of 360 s, Plate 81 (p. 352), Penetra­ tion of melt into the cylinder was limited to the margin after a 15 and 360 s immersion period. The Fo - Fa oli­ vines (Fo^) represented by the dark grey coloured areas of the melt (Plate 81) showed signs of resorption within a calcic olivine phase.

Four zones were distinguishable in a composition profile represented by the hard burnt dolomitic lime cyl­

inder in Plate 82 (p. 353). Analysis point 1 indicated a lime rich fayaiite phase (C - F - S) which persisted into the'well developed cored Fo - Fa olivine region, adjacent to the globular wustite and Fo - Fa assemblages. A crack separated the reacted cylinder from the melt in­ terface after the cylinder had cooled. Analytical points 3, 4, 7 and 8 (Plate 82, p.353 ) indicated a gradual en­

richment of the forsterite (Fo) component towards the cylinder interface, progressing from F o ^ r il' ° 7 1 an(^

F o ^ respectively.

The melt cylinder interface concentrations of FeO and MgO have been compared at immersion times of 15f 120 and 3-60 s using the oxide concentration results, Figs. 48 and 49 (p«297 )«. Composition profiles were related to the same melt - cylinder interface position and adjusted to an

it

equivalent scale. Phases composed of wustite globules or dicalcium silicate were ignored, Analytical points that may possibly have represented mixed phases were also ig­

nored. The profiles in Figs. 48 and 49 may be envisaged as a mean free path from the melt through to the cylinder.

The concentration of FeO decreased rapidly towards the melt cylinder interface and rose sharply again due to the formation of magnesiowustite. The widest zone of FeO depletion occurred within the 120 s immersed sample. Mag­

nesia (MgO) produced a corresponding increase in concen­ tration towards the cylinder interface for all three im­ mersion periods. A compatible phase of MgO and FeO formed within the cylinder (magnesiowustite) but a divergent rel­ ationship existed when both oxides diffused into the melt.

The relationships were equated with the formation of mag­ nesium silicates containing quantities of FeO (Fo - Fa olivine) and CaO - FeO silicates which were liquid under the prevailing isothermal conditions.

4c 3.3.2 Lime,

An immersion period of 15 s produced a well devel­ oped CaO concentration gradient between a usoftn "burnt lime C3'linder and an iron silicate melt, Plate 83 (p.354 ).

Lime (CaO), silica (Si02) and iron oxide (FeO) contents of the melt remained relatively constant up to the inter­ face with dicalcium silicate (C^S) which formed a barrier approximately 1 0jjm thick. The silica concentration gra­ dient indicated an’absence of SiO^ in the zone between the C^S barrier and the lime cylinder. The silica - free zone coincided with a FeO - CaO association corresponding to the phase calciowustite (CF*)„

An extended static immersion period of 540 s pro-? duced a 200 /im wide reaction interface containing C^S and a 2-phase region of wustite and.calciowustite, Plate 84 (p« 355 )« Silica showed the same distribution pattern to that in the' 15 s immersed cylinder (Plate 83, p«>354 )•

A lime cylinder reacted with an iron silicate melt containing 5 mass % MgO produced a granular dicalcium zone, with magnesia reaching a 10 mass % level at the melt - cylinder interface after a 15 s immersion period, Plate 85 (p. 356 ). The level of* magnesia fell to around

2 mass % MgO between the C^S and lime cylinder interface. Silica showed a progressive depletion from the melt, C^S

and tricalcium silicate (C..S) phases, and only a trace occurred in the iron oxide - rich phase adjacent to the cylinder. The distribution of lime indicated a. steep concentration gradient from the edg*e of the reacted cyl­

inder into the melt, Plate 85 (p.356). A cylinder im­ mersed for 360s in a 5 mass % _{MgO - iron silicate melt} produced a mixed zone 150 ,um wide of CpS, C^S and OF’ phases, Plate 86 (p.357). Magnesia remained at the 5 mass % _{MgO level close to the melt “ CpS boundary but} was reduced to between 1 and 2 mass % _{MgO within the} CpS - lime cylinder interface.

The oxide concentrations derived from the analyses of phases produced by the melt - cylinder reactions have

.

been plotted across the 1300°C isothermal section of the CaO - ’FeO1 - SiOp phase diagram (Figs. 50a and b, p.298).

Lime cylinders immersed in magnesia free and 5 mass % _MgO- iron silicate melts have been compared at varying times. The reaction of lime with an iron silicate melt produced a displacement of the melt composition towards the CaO - SiOp edge of the CaO - ’FeO’ - SiOp isothermal diagram. The formation of solid calcium silicate phases produced a liquid enriched in FeO relative to the bulk melt, and the oxide composition plots moved across to the FeO corner of the diagram. At this position, the liquid phase was cap­ able of reacting directly with the lime cylinder,(Figs. 50a and b, p. 298). Magnesia enriched iron silicate melts produced a similar type of reaction but the reaction pro­ file was deflected into the tricalcium silicate phase field before the composition moved across to the FeO corner of

4*3*4 Dissolution Experiments.

4* 3.4.1 Dolomitic lime cylinders,,

The results of the immersion experiments on static and rotated dolomitic lime cylinders are tabulated in Tables 31 and 32 (p. 256). The results are presented

graphically in Figs. 51 and 52 (p. 299 ) and represent

plots relating the mass % of lime (CaO) and magnesia (MgO)

recorded in rhe bulk synthetic slag after analysis against