Notas sobre la naturaleza del Estado capitalista

m elt-liq u id interface* I t varied from an almost m onolithic layer

(P late 80) to a th in broken rim (P late 8l) *

A fter only 13 seconds immersion, there was considerable w etting o f the lim e by the liq u id phase (P late 82). This liq u id had also penetrated and d isso lv ed parts of the 2 CaO.SiO^ m onolithic rim. After a reaction time of 30 seconds, i t was evident th at the melt

was also d issolvin g the p recip itated la y er (P late 83) . The d isso lu tio n o f 2 CaO.SiO^ could account for the iso la te d regions o f melt observed in the lim e-iron oxide liq u id phase (P late 84)*

4o3*2*3.1.1 Electron Probe A nalysis

P late 85 shows the lim e-m elt in terface of a specimen immersed for 45 seconds. Like flu o rin e , boron (Atomic Humber 5) could not be detected on the microprobe, so the accompanying X-ray images r e la te only to the d istr ib u tio n of calcium , iron and silic o n *

The p recip ita tio n o f 2 CaO.SiO^ did not prove to be a barrier for iron (oxide) which can be seen around the lime grq in s.

The d istrib u tio n o f s ilic o n was very sim ilar to that found w ith the f ir s t two systems i . e . a sharp drop in concentration at the

2 GaO.SiOg-liquid in terfa ce (Pig. 26). Consequently the concentration paths (P ig. 27) showed a sudden change toward the PeO corner.

4« 3* 2.3* 2 Large Lime P e lle ts

Large eqiuaxed p a r tic le s o f 2 Ca0.Si02 were observed along the m elt-liq u id in terfa ce (P late 86) o f a specimen immersed for 15 seconds. As the reaction time increased, there was a gradual tr a n sitio n from

a planar to a corrugated rim (P late 87)jr Along th e melt boundary, t lie re was extensive w etting and r eso lu tio n by the melt and the lim e- iron oxide liq u id . In some regions the liq u id had broken through to the melt (P late 8 8)0

4.3*3 Chemical Loss

Since both add itives are v o la tile at high tenperatures, separate checks were made on samples of m elt after heating to 1300°C for 1 hour. Instead of 10 \7t#> Bo0_, the analysis was 8 .7 TCo Bo0, and_{^ j 5} instead o f 10 Wtfo CaP^j the fin a l an alysis was 7<>4 OaP^o

4*4 Dicalcium S ilic a t e - F ayalite System

During probe an alysis o f the reaction zones, there was no d iscern ib le concentration gradient o f s ilic o n ( s ilic a ) from the bulk m elt towards the 2 GaO.SiOg la y er. The absence could be

associated -with the r ed istrib u tio n of oxides during s o lid if ic a t io n . However a sim ilar r e s u lt could be produced i f two concentration p r o file s (one towards and the other away from the 2 CaO.SiC^ layer) were superinposed one upon the other. To c la r ify the situ a tio n ,

syn th etic p e lle ts o f s ta b ilis e d 2 Ca0.Si02 were immersed in 2 PeO. S i02 a-b 1300°Go

4 .4 .1 Immersion Experiments

With no s o lid reaction product, the melt rapidly in filtr a te d the pore system o f the p e lle ts (P late 89)* Y/ithin a short time

(15 seconds) a large number o f twinned grains (horseshoe shaped) were e n tir e ly surrounded" .by the melt (P late 90). A fter 30 seconds

(P late 91) very l i t t l e s o lid 2 CaO.SiC^ remained.

4.4* 1*1 E lec tro n Probe A nalysis

Both the scanning images (P late 92) and the concentration p r o file s (Pig. 28) shewed com positional gradients for lim e and iron

oxide, w hile the s ilic a concentration remained constant across the reaction in ter fa c e .

4*4*1*2 D issolu tion K inetics

The r e su lts are tabulated in Table 18 and p lo tted grap h ically in P ig. 29* They in d icate a very high d isso lu tio n rate even though the p a r tia lly d issolved p e lle ts s t i l l had a th in layer o f s o lid if ie d melt adhering to the su rface.

5e D iscussion

The d eta iled discu ssion o f the r e su lts and observations is given for the purpose o f convenience under the follow in g headings: -

1. The D issolu tion o f Small Lime P e lle ts in F ayalite

2<> The E ffe c t o f Manganese Oxide . 3. The E ffe c t of Other Fluxes 4 o The E ffect o f P e lle t Rotation

5o The E ffe c t o f P e lle t Size 6. The Rate C ontrolling Mechanism

5ol The D issolu tion o f Small Lime P e lle ts in F ayalite

At 1300°C, the s o lid + liq u id phase field , of 2 CaO.SiO^ extends almast to the FeO corner of the CaO - FeO - SiO^ ternary system.' This means that CaO can never be at equilibrium w ith a melt o f composition JO Yft/o FeO - 30 WtSo SiOg. The only liq u id s which can c o ex ist w ith CaO at equilibrium are those along the lin e Le - Lf in F ig. 30. Although th e isothermal sectio n can provide u sefu l inform ation on phase assemblage, i t cannot p red ict the sp a tia l arrangement o f the phases. This in a b ility i s illu s tr a te d by -'die p o sitio n o f dicalcium

s ilic a t e r e la tiv e to th at o f lim e. YThile the isotherm al sectio n shows th at the phase f ie ld of tricalciu m s ilic a t e + liq u id separates the two phase fie ld s a t 1300GC; in p ractice the two phases were

separated by a liq u id rich in iron oxide (P late 13). -Within th is lim ita tio n , the 1300'C isothermal sec tio n w ill be used to illu s t r a t e how the composition o f the various phases change during the

d isso lu tio n o f lim e.

During the i n i t i a l reaction between lim e and fa y a lite , the

in te r fa c ia l liq u id composition moves from 2 F e0.Si02 towards L^

(Fig. 30) along the 2 F e0.Si02 - CaO iso p le th . When the com position of the reaction product has a CaO to S i^ molar ra tio o f 2:1 , 2 C a0.Si02

is p recip ita ted between the p e lle t and the melt* I n it ia lly the molar ra tio o f 2:1 occurs very c lo se to the GaO - 2 PeO.SiO^ in terface but as d isso lu tio n proceeds, the s o lid reaction product is p recip itated some distan ce away from the receding p e lle t* The p r e cip ita tio n of s o lid 2 CaO.SiO^ causes the composition o f the in te r fa c ia l liq u id to move towards the FeO corner as i t becomes enriched in the remaining components. The heterogeneous rea ctio n can be summarised as