440
Ind. Eng. Chem. Fundam. 1984, 23, 440-446
depend on the firing atmosphere and temperature, and the solubility limits indicated in Figure 2 are determined in air at 1100 "C. ZnO and Cu20.Cr203are not compatible and on firing they form Zn0.Cr203 and Cu20. The tie lines determine the compatible tetrahedra in the quaternary system ZnOCuO-Cu-Cr203. Registry No. ZnO, 1314-13-2; Crz03,1308-38-9; CuO, 1317methanol, 67-56-1. 38-0;CuzO, 1317-39-1; Literature Cited Abadk, M. F.; Qadalla, A. M. Trans. J. Br. Ceram. Soc. 1976, 75(4), 74-77. Bulko. J. P.; Herman, R. G.; Kller, K.; Simmons, G. W.J. Phys. Chem. 1979, 83, 3118-22. Chapple, F. H.; Stone, F. S. Proc. 8r. Ceram. Soc. 1964, 7 , 45-58. Gadalla, A. M.; White. J. Trans. Br. Ceram. SOC. 1984, 63(10), 535-52. Goroshko. 0. N.; Lavrova, V. V.; Rusov, M. T.; Ryzhak, I. A. Katal. Katal. 1975, 73,92.
Herman. R. G.; Kller, K.; Simmons, G. W.; Finn, B. P.; Bulko, J. B. J. Catal. 1978, 56, 407-29. Ishil, T.; Furruichl. R.; b r a . Y. J. Thennal Anal. 1877, 7 7 , 71-80. Johnson, R. E.; Muan, A. J . Am. &ram. Soc. 1888, 57, 432. Kr-r, F. A. "The Chemistry of Imperfect Crystals", North-Holland Publlshlng Company: Amsterdam, 1964. Kubota, 8.J. Am. Ceram. Soc. 1861, 44(5), 247. Mehta, S.; Simmons, G. W.;Klier, K.; Herman, R. G. J. Catal. 1979, 57, 339-60. Ol'shanskll, Y. I.; Shlepov, V. K. Wl.Akad. Naukk SSSR 1953, 97, 583. Purl, V. K.; Awasthl, R. B.; Choudhary. R. L.; Qangull, N. C.; Ghosh, S. K.; Sen, S. P. fertilzer Techno/. ( I d i a ) 1976, 73(2-3), 158-61. Schiavelio, M.; Pepe, F.; DeRosi, S. Z . Phys. Chem. (frankfurt am Main) 1874, 92, 109-24. Shirashi, T. "ham Kogyokoto Semmon Gekko Kuo, Rikogaku Hen 1981, 17. 45.
WIIIlams,~R.J. J.; Cunningham, R. E. Ind. f n g . Chem. Rod. Res. Dev. 1974, 73,49-60.
Receiued for review May 5, 1983 Accepted April 9,1984
The Quaternary System Cr,O,-MgO-CuO-Cu,O in Air and Its Bearing on the Performance of Copper Melting Furnaces Ahmed M. Gadalla" and Nalla A. L. Mansour Chemical Engineering Department, Texas A&M University, college Station, Texas 77843
The quaternary system was studied by construcing four sections, three of constant magnesia content and the fourth having a MgO/Cr203ratio of 1: 1. The existing conjugation tetrahedra were flxed and the corresponding reactions were established. MgOCr,O, dissolves copper oxldes and excess MgO and Cr203forming a wide range of solid solutions. Cu2Mg03 takes Cr2O3 in its lattice and its stability drops. I n the presence of Cr203, the solubility of decreases the stabili copper oxides in periclase decreases. CuO-C~O,enters into the spinel phase. Cu20-Cr203 of guggenite giving Cu20 and spinel at 1035 C. Partial melting with isothermal oxygen pickup occurs at about 1120 OC in mixtures poor in Cr2O3. Increasing the Cr2O3 content in chrome-magnesite bricks increases the a refractoriness due to the formation of solid solutions, but above saturation refractoriness. Magnesite bricks have h the liquid phase is formed and it penetrates the perlclase grains.
Introduction Studying the attack of refractories used in copper melting and refining furnaces is not as difficult as that used in the extraction process. While in copper melting furnaces the slag consists primarily of copper oxides, in copper converters consideration must be given to modes of attack both by ferrous silicate and by copper oxides. To throw light on the corrosion problem in copper melting furnaces, phase relationship in relevant systems should be studied. Previous work by Gadalla et al. (1963) and Gadalla and White (1964a*b*C) on the systems CuO-Cu20-Si02, CuOCU~O-A~~ CuO-Cu20-Mg0, O~, and CuO-Cu20-Cr203explains the reason for the superiority of refractories containing MgO or Cr203 over silica and aluminosilicate refractories in melting copper and they recommended using chrome-magnesia or magnesia-chrome refractories. The present study is carried out to determine the optimum composition which can resist fluxing by copper oxides. Previous Work The System Cu0-Cu20-Mg0. Trojer (1958) and Riby and Hamilton (1961) reported the formation of a binary compound in basic refractory bricks and named it 'guggenite". They assumed that it has the composition 0198-4313/84/1023-0440$01.50/0
CuMg02. Gadalla and White (1964b) proved that guggenite is an intermediate binary phase of composition near to Cu2Mg0,. Later Drenkhahn and Mueller-Bouchbaum (1975) confirmed the existence of Cu2Mg03and reported that it is orthorhombic. Gadalla and White (1964b) found that this compound is more stable than CuO and dissociates in air isothermally at 1060 "C with loss of oxygen giving CuzO and magnesia. They proved that contrarily to silica and alumina, where a liquid phase is formed at 1060 "C and at 1230 "C, respectively, as soon as copper oxide is added, no liquid is formed with magnesia unless the copper oxide content (taken as solid solution by magnesia) exceeds 35.7 wt %. The System Cu0-Cu20-CrzOp During service in copper refineries, Rigby and Hamilton (1961, 1962) and Ust'yantsev et al. (1971) reported the existence of copper chromite which is formed from the reaction of copper oxide with free Cr203or with Cr203in the spinel phase that contains mainly magnesium chromite. The latter was found to decompose in the presence of copper oxides and silica. Gadalla and White (1964c), however, investigated the system at different oxygen partial pressures. In air, in the presence of excess CuO, the spinel Cu0.Cr203 has a low stability and forms Cuz0.Cr2O3with oxygen loss at about 890 "C but in the presence of Cr2O3,CuOCr203 0 1984 American Chemical Society
Ind. Eng. Chem. Fundam., Vol. 23,No. 4, 1984 441
U
1 6 7 % M q 0 167%Cr,O,. 666%Cu 0
z
a9 l
.
O
h
05
5O%CuO. 30 %Cr,O,.
0.5
800
I
05 I
8 0
900
,
.
,
.
I
,
1000 Temperature 'C
I
,
,
I
j
900
1000 Temperature C
1100
Figure 2. Dissociation curves for mixtures having 20% (molar) MgO.
,
1100
Figure 1. Dissociation curves for mixtures lying in the section Mg0-Cr203-Cu0-Cuz0: (A) contains initially 20% (molar) MgO. Crz03-80% CuO; (B)contains initially 40% Mg0.Crz03-60% CuO.
remains stable up to 1100 "C above which it dissociates isothermally with oxygen loss giving Cuz0.Crz03and CrzOs. They concluded that the presence of Crz03 in a basic refractory is beneficial since the copper oxide content expressed as CuO must exceed 51.5 w t ?% before a liquid phase is present at any temperature up to 1560 "C. The System Crz03-Mg042u0-Cuz0.In view of the X-ray examination of the mixtures fired in this system, Ust'yantsev et al. (1972) reported the formation of the spinel Mg0.Crz03 first; at 960 "C guggenite appears and at 1045 "C it disappears. They reported that below 1026 "C Mg0.Crz03, Cu20.Crz03and CuO coexist and above 1026 "C Mg0.Crz03, CuzO, and Cuz0.Crz03coexist until melting occurs. Recently Pressley and White (1979) studied the phase relationships between MgO-Crz03and copper oxide in air at 1400 "C by quencing technique. Their system can be considered an isothermal section in the quaternary Crz03-Mg0-Cu0-Cuz0 lying near the ternary Crz03-Mg0-Cuz0. Experimental Procedure AR grade cupric oxide, magnesia, and chromic oxide were used as starting materials. The former was found to dissociate in air in the solid state at 1026 "C to CuzO with oxygen loss. AR grade magnesia was calcined to constant weight at 1140 "C before use. Chromic oxide was prepared from chromium trioxide (stated by the supplier, BDH,to contain not less than 99% CrzO3) by heating in a direct flame until all the brown fumes were driven off, and then it was heated in a muffle furnace at 1100 "C. The spinel Mg0.Crz03was prepared by weighing out the appropriate amounts of MgO, and Crz03 and was repeatedly fired to 1600 "C with intermediate grinding until the reaction was complete. Completion of reaction was followed by microscopic examination. The mixtures were prepared by weighing out the appropriate amounts of Mg0.Crz03 and CuO to study the section MgO~Cr,03-CuO-Cuz0. To investigate the behavior of sections having constant MgO composition, the appropriate amounts of MgO-CrzO3(and Crz03or MgO) as well as CuO were prepared. The mixtures were fired for a lengthy period (at least 24 h) at 800 "C to allow for any solid state reaction in the ternary Mg0-Cr203-Cu0 (i.e., formation of CuO-Crz03,CuzMg03,and solid solu-
0 %Cu 0 Figure 3. The system MgO-Cr203-Cu0 showing the compositions in mole percentage of the campatible phases. Mixtures which started dissociation over a range of temperature are indicated by (0);those which started dissociation isothermally at 1024 "C are indicated as ( O ) ,and those which started dissociation isothermally at 1042 O C are indicated as (0). Cr
tions) without any oxygen loss. Dissociation curves of the prefired mixtures were determined using the thermobalance, the mixtures being heated to constant weight at progressively increasing temperatures in alumina crucibles lined with platinum foil. Typical examples of the dissociation curves obtained are shown in Figures 1and 2. The atomic ratio O/Cu, calculated from the weight losses, was plotted against temperature which was measured with an accuracy of *3 "C. In calculating O/Cu ratio, oxygen contributed to the mixture by MgO and Crz03was ignored so that the value of the ratio is a direct index of the state of oxidation of copper. X-ray diffraction patterns were compared with ASTM cards to determine the existing phases and to confirm the conclusions deduced from the dissociation curves.
Results and Discussion In this quaternary system four sections were investigated; three at constant MgO composition (10, 20, and 50 molar %). The fourth is a section passing through Mg0.Crz03, CuO, and Cu20.
442
Ind. Eng. Chem. Fundam., Vol. 23,No. 4, 1984 MgO
50%Mg0 50 % C r 2 0 3
%1/2CU2O
Figure 5. Section in the quaternary system having 50% molar MgO.
A
o/dl2cUfi
Figure 4. The system MgO-Cr203-1/2Cu20 showing compatible
phases existing as the mixtures cross the quaternary system.
The System Mg0-Cr203-Cu0. This system represents the face of the quaternary corresponding to complete oxidation of copper. The compositions investigated were plotted on this ternary (Figure 3) and were classified according to their behavior on heating. The solubility limits for the nonstoichiometric phases; periclase (MgO solid solution), guggenite (Cu2Mg03solid solution), and Cu0.Cr203solid solution were drawn from the ternary system CuO-Cu20-Mg0 and Cu0-Cu20-Cr203in air obtained by Gadalla and White (1964b,c). Those mixtures giving isothermal loss imply the existence of four condensed phases and the existence of a tie tetrahedron. The bases of the two tetrahedra at 1024 and 1042 "C will be triangle a-bCuO and a-b-c. Point c was fixed tentatively and it is shown within the triangle since at high temperature MgO takes both copper oxides and a limited amount of CrzO3 in solution as indicated by Alper et al. (1964). The presence of a continuous series of spinel solid solutions extending from Mg0.Cr203to Cu0.Crz03was based on Rigby and Hamilton's (1961) findings and on the absence of isothermal steps in mixtures lying to the left of "a-CuO". Accordingly, mixtures in the region Mg0.Cr203-Cr2O3-CuO.Cr2O3 consist, at temperatures below 1024 "C, of two condensed phases; spinel and CuO. Mixtures in the region a-b-CuO consist of spinel phase of composition "a", CuO, and guggenite of composition "b" implying that CrzO3 dissolves in guggenite. They started losing weight at 1024 "C due to dissociation of CuO to CuzOgiving an isothermal tetrahedron, spinel-guggenite-Cu0-Cu20 (see later). Mixtures in the region a-b-c consist of spinel phase of composition "a", periclase of composition "cn, and guggenite of composition "b". They lost weight isothermally at 1042 "C indicating the presence of an isothermal tetrahedron, spinel-periclase-guggenite, and Cu20. Accordingly, guggenite dissociated at 1042 "C instead of 1060 "C, implying that on taking Cr203in solid solution the stability of guggenite decreases. It should be mentioned that this result supports the observation of Ust'yantsev et al. (1972) that guggenite disappears at 1045 "C. It also evident that Mg0.Cr203-Cu0 is not a true binary and accordingly the section Mg0.Cr203-CuO-Cu,0 is not a true ternary system (quasiternary). T h e System Mg0-Cr203-Cuz0. This system represents one face of the quaternary system when the com-
positions reach an O/Cu ratio of 0.5. The compositions investigated were plotted on the ternary MgO-Cr2031/2Cu20(Figure 4). Those mixtures which approach this face at the end of an isothermal step at 1042 OC are indicated by dark circles while those approaching the face at the end of a step at 1035 "C are indicated by open circles. This means that the triangle, ~ - C - ~ / ~ C U is ~the O, end face of the tie tetrahedron at 1042 "C joining the compositions of spinel-guggenite-Cu0 and Cu20. The triangle m-Cu2O.Cr2O3- 1/zCu20is the base for another tie tetrahedron occuring at 1035 "C which will be discussed later. Each conjugation tetrahedron containing a liquid p h a e has one of its planes lying near this section with the liquid composition inside the quaternary. This conclusion was based on the results which showed that after the compositions reached an O/Cu ratio of about 0.5, partial melting occurred isothermally with oxygen pickup; mixtures reaching the triangle a - ~ - l / ~ C u ~gave O isothermal pickup of oxygen at 1120 "C while those reaching the triangle ~ - C U ~ O C ~ , O ~ - ~picked /~CU up~oxygen O at 1125 "C. The present results obtained in various sections were used to construct these two tie tetrahedra which were projected on this face as will be shown later. It should be noted that 1/2Cu20was taken instead of Cu20to facilitate locating the points and to obtain all the dissociation paths parallel to the base Cr203-C!uO-1/2Cuz0 (and to the edge Cu0-'/,Cu2O). Results of Mixtures Containing 50% MgO. The dissociation paths for the five mixtures having initially 50% MgO will lie in a plane parallel to the system Cr203-Cu0-1/2Cu20 passing through the stoichiometric composition of MgOCr203. All the mixtures behave like that shown in Figure 1B. From Figures 3 and 4 it is evident that they cross the tie tetrahedron connecting periclase "c", spinel "a", guggenite "b", and Cu20. A t low temperatures the mixtures consist of a periclase, spinel, and guggenite. The compositions reached at various temperatures are shown in Figure 5. Points d and h were taken from Figure 3 and the dissociation paths are the thin parallel lines. At the end of the monovariant situation at 1042 "C the composition reaches the line "df", thus approaching the face Mg0-Cr203-Cu20 (Figure 4) and the mixtures consist of periclase "c", spinel "a", and Cu20;i.e., at 1042 "C guggenite dissociates as discussed above. On further heating slight oxygen loss appears up to 1120 O C . A t 1120 "C isothermal oxygen pickup occurs. The compositions reached at the beginning and at the end of this step fix the triangle g-f-e which is the intersection of the present section with the tie tetrahedron joining the phases coexisting under equilibrium at 11.20 "C. Behavior of Mixtures Containing 20% MgO. The dissociation curves of nine mixtures containing initially
Ind. Eng. Chem. Fundam., Vol. 23, No. 4, 1984
A
20%Mg0 8 0 % Cr,O, SSS = Spinel Solid S o l u t i o n C'K= Cu~O~CrI03 C 2 M =Guggenite M = Periclase
443
,Ao 0
%CU,O
Figure 6. Section in the quaternary system having 20% molar MgO.
5, 10, 15, 20, 25, 30, 35, 40, and 45 molar % Cr2O3 were investigated. The reaction paths for these mixtures lie in a plane parallel to the system Cr203-Cu0-1/zCu20passing between the composition of MgOCr203and the guggenite with the composition "b" (Figure 3). Figure 2 (A and B) shows the features obtained in mixtures containing from 22 to 47% Cr203 On the other hand, Figure 1A shows the features obtained in mixtures containing Cr203 between points "r" and "q" and Figure 1B shows the features obtained between points "p" and "q". While the composition of the breaks on the dissociation curves represented the composition reached when the dissociation path of a mixture crosses a phase boundary, the compositions reached at the beginning and at the end of any isothermal vertical step fix the points at which the dissociation curve crosses a tie tetrahedron joining four condensed phases. These points were plotted in Figure 6. On connecting the compositions reached isothermally, the intersection between the present section and the tetrahedra is obtained. Accordingly, a triangle or an irregular quadrilateral shape must be obtained at any monovariant situation, when four condensed phases coexist in equilibrium. To understand this section better the hypothetical system MgO-Cr203CuO-Cu20 was constructed and it is shown in Figure 7 after ignoring the solid solubility. The conjugation triangles established in the four faces of the quaternary are drawn and accordingly the quaternary is divided to the following tie tetrahedra: MK-CK-C'K-K, MK-C'K-CCK, MK-C'K-C-C', MK-C-C'-C2M, and MK-C2M-C'M, where M = MgO, K = Cr203,C = CuO, and C' = Cu20. This over simplified picture gives different reactions than that obtained in Figure 6. Moreover, the third and fourth tetrahedra correspond to the same reaction, i.e. 2cuo
F=
cu20
+ '/202
(1)
Accordingly, a quaternary tie line must be added to connect C2M and C'K and in this case section "A" represents the behavior of constant composition of MgO lying between Mg0.Cr203 and MgO, which was was shown in Figure 5. Section "B" represents the shapes obtained when this section (above C2Mbut below MK) intersects five tie tetrahedra. Section "C" represent the relationships in mixtures having constant MgO content lower than that of guggenite. According to this idealized case the quaternary is divided into the following six volumes. (1)MK-CK-C'K-K, where three condensed phases are in equilibrium. A spinel solid solution (SSS) containing Mg0.Crz03in Cu0.Cr203coexists with Cu20.CrzO3and
Figure 7. The system MgO-Cr20sCu0-Cu20showing the tie lines, tie triangles, tie tetrahedra, and three sections having constant MgO content (ignoring the solid solution).
Cr203 A curve is obtained in crossing this volume and the following reaction takes place 2CuOCr203(S.S.) Cu20.Cr203+Cr203+ 1/202 (2) (2) Mk-CK-C'K-C, where three condensed phases are in equilibrium. A spinel solid solution of MgOCr203in Cu0.Cr203 coexists in equilibrium with Cu20.Cr203and CuO. A curve is thus obtained in crossing this volume and the following reaction occurs Cu0.Cr203(S.S.) + CuO 2 Cu20Cr203+ 1/202 (3) (3) MK-C'K-C-C2M, where four phases (spinel solid solution, Cuz0Cr2O3,guggenite and CuO) coexist in equilibrium giving a monovariant situation. A vertical step is obtained in the dissociation curve due to the reaction 4CuO + MgOCr203+ Cu20.Cr203+ 2CuO.MgO (S.S.) 1/202 (4)
+
This reaction occurs in air at 1024 "C. (4) C'K-C2M-C-C' where the four phases Cu20Cr203, guggenite, CuO, and Cu20 coexist in equilibrium giving a monovariant situation. On crossing this tie tetrahedron an isothermal oxygen loss occurs at 1026 "C due to reaction 1. (5) MK-C2M-C'K-C' where the four phases (spinel, guggenite, Cu20.Cr203and Cu20)coexist in equilibrium giving a monovariant situation. On crossing this tie tetrahedron an isothermal oxygen loss occurs at 1035 "C due to the reaction Cu20Cr203(S.S.) + 2CuO.MgO (S.S.) MgOCr203(S.S.) + 2Cu20 + 1/202 (5)
(6) MK-C2M-M-C' where the four phases (spinel, guggenite, periclase, and CuzO) coexist in eqiulibrium giving a monovariant situation. On crossing this tie tetrahedron an isothermal oxygen loss occurs at 1042 "C due to the reaction 2CuO.MgO (SA) + C U ~ O + MgO (S.S.) + ' / 2 0 2 (6) Comparing section "B" in Figure 7 with that obtained in Figure 6, it is evident that the spinel exists as a quaternary phase having MgOCr203and CuOCr203as well as Cu20in solid solution. This solid solution extends over a wide composition range (Figure 6 and Figure 2 A) causing the two-phase regions (spinel solid solution-Cu0) to exist over a wide volume as is evident from the mixtures initially containing 25, 30, 35, 40, and 45% Cr2O3. For mixtures approaching the Mg0-Cr203-Cuz0 face partial melting occurs with isothermal oxygen pickup. Mixtures containing initially up to 20% Cr203have an
444
Ind. Eng. Chem. Fundam., Vol. 23, No. 4, 1984 10 %MgO 90 %C r2 0
A. Mg0.Cr203
~
20
MgO
1/2Cup1 %CU,O
Figure 8. Section in the quaternary system having 10% molar MgO.
isothermal melting at 1120 “C corresponding to a monovariant situation which occurs when these mixutres cross the tie tetrahedron connecting periclase, spinel solid SOlution, Cu20, and a liquid phase. The present section cuts this tetrahedron in “DEFB”. On the other hand, mixtures containing initially from 20 to 38% Cr2O3 gave isothermal oxygen pickup at 1125 “C which similarly corresponds to a second tie tetrahedron joining, spinel solid solution, Cu20.Cr203,Cu20,and a liquid phase (monovariant situation). The intersection of this tetrahedron with the present section gives the triangle “ABC”. The behavior of mixtures containing up to 4 % Cr2O3 is shown tentatively in view of previous work on the terriary Mg0-Cu0-Cu20 and the present data on Cr203-MgOCuO shown in Figure 3. Behavior of Mixtures Containing 10% MgO. Seven mixtures containing initially 5,8, 10, 15, 20,30, and 40% Cr203were investigated and the composition of breaks as well as points of monovariant situations were used to construct the section shown in Figure 8. If the solid solubility is neglected the behavior of their mixtures can be deduced from section ”C” in Figure 7, having a magnesia content less than that required to form guggenite. This section contains the same regions discussed in the previous section as well as the tie tetrahedron joining guggenite, CuO, Cu20.Cr203and Cu20. Figure 8 is more complicated than the hypothetical cross section due to the existence of the extensive volume occupied by the spinel solid solution and the narrow temperature range over which the four tie tetrahedra (number 3,4,5, and 6) exist. Another difficulty is the existence of the guggenite composition just above this section thus fixing point P’, which represents the intersection of the added tie line guggenite-Cu20Cr203 with the present section, near the edge. The compositions of points t’, s’, r’, and q’ are taken from the ternary system MgO-Cr2Os-CuO shown in Figure 3, point H is taken from the ternary system Mg0-Cr203-Cu20 shown in Figure 4, and the points on the CuO-Cu20 edge are taken from the ternary system Mg0-Cu0-Cu20 determined by Gadalla and White (1964b). After crossing the various fields and appruaching the face Mg0-Cr203-Cu20, partial melting occurs with isothermal oxygen pickup at 1120 and 1125 “C. Mixtures consisting of periclase, spinel and Cu20 melt at 1120 “C. The present section intersects the tie tetrahedron existing at this temperature in the triangle “HLO” instead of the shape “BDEF” obtained with mixtures having 20% MgO. Mixtures consisting of spinel, Cu20.Cr203,and CuzO melt isothermally at 1125 “C, giving a second tie tetrahedron
CUD
20
.
LO
CUzO
60
%1/2CU,O
Figure 9. Section in the quaternary system having MgO/Cr203 molar ratio of 1:l represented as a quasiternary Mg0.CrzO3-Cu0cuzo.
which gives an intersection with the present section having the shape “HGIK” instead of the triangle “ABC” obtained in Figure 6. Behavior of Mg0.Cr203-Cu0 Mixtures. Eight mixtures consisting essentially of stoichiometric spinel MgOCr203and CuO were prepared and their behavior is shown in Figure 9. As is evident from Figure 3, these mixtures when fully oxidized intersect the tie line ”a-b” at point “T”implying that this section is nut a true ternary. At low temperature compositions poorer in CuO than “T” consist of spinel “a”, periclase “c”, and guggenite “b” (Figure 3) and their dissociation curves are similar to that shown in Fig. 1 B. Compositions richer in CuO than “T” consist of spinel “a”, guggenite “b”, and CuO and behave on heating as that shown in Figure 1A. Mixtures having initially less than 40% CuO started dissociation isothermally at 1042 “C due to the dissociation reaction of guggenite. This implies that on heating such mixtures below 1042 “C, the spinel dissolves CuO, until the composition “a” in Figure 3 is reached, and reacts with CuO forming small amounts of periclase and guggenite solid solutions with compositions “c” and “b”, respectively. On the other hand, mixtures having initially more than 40% CuO started dissociation isothermally at 1024 “C and below 1024 “C Mg0.Cr203 dissolves CuO to point “a” in Figure 3 and reacts with CuO precipitating guggehite with composition “b”. Referring to the hypothetical system shown in Figure 7, this section intersects the tie line Cu20Cr203-guggenite in the point V. Mixtures containing more than 40% CuO cross the tie tetrahedra: (a) SSS, C2M,C‘K and C occurring at 1024 “C; (b) C2M,C’K, C&C’ at 1026 “C; (e) C2M,MK, C’K and C’ at 1035 “C; and (d) M, SSS, C2M,C’ at 1042 “C. The reactions occurring on crossing these tetrahedra were discussed above. A t the end of the vertical step at 1042 “C, the mixtures consist of spinel solid solution, periclase, and Cu20. These mixtures are expected to melt partially with isothermal oxygen pickup on crossing the tie tetrahedron periclase, spinel, Cu20,and liquid at 1120 “C. This section intersects the above tetrahedron giving the triangle g’-N - 1/2Cuz0. As will be discussed in the melting relationships, the mixtures containing initially more than 75% CuO cross the tie tetrahedron at 1125 “C connecting spinel, Cu20.Cr2O3,Cu20, and liquid. This tetrahedron is intersected by the present section giving the triange Q-R-’/2Cu20. Melting Relationships in Air. From the four sections investigated it is evident that melting occurs isothermally
Ind. Eng. Chem. Fundam.. Vol. 23, No. 4. 1984 445 M4 0
T G T
. .. -
Figure IO. Projection of the tie tetrahedra correapondw to melting relationships on the face MgO-Cr&'/&O. 70
L
1130.C
Figure 12. Photomicrograph of mixture containing initially 50% Cu0:50% MgO molar (66.490 Cu033.6% MgO by weight). Sam2le equilibrated st 1100 "C and air-quenched. Dark grey rounded particles are perielase solid solution; light matrix mainly cuprous oxide. (Reflected light; 622X. unetehed).
0 '
0
230
8 20 10
MgO
1120
20
IO
So
80
Cr,03
%Cr203ndm
Figure 11. Molar percentage of copper oxide taken by Crp03-Mg0 refradoriea before a liquid phase appears at the indicated temperatures.
with oxygen pickup a t 1120 and 1125 "C. The shapes obtained in Figures 5,6,8, and 9 for melting were projected on the face, MgO-Cr,03-1/,Cu,0, in Figure 10. The two tetrahedra thus formed fix the compositions that melt completely giving liquid phases only. At 1120 OC, spinel of comwition "I", periclase 'k", C y 0 and a liquid phase, of composition Y mexist in equilibrium. At 1125 OC spinel of composition =mn,Cu20.Cr,03 "n", CuaO and a liquid phase of composition "X" coexist in equilibrium. It is evident from the above figure that periclase takes both Cr,O, and copper oxides in solid solution and the presence of Cr203decreases the solubility of CuO in MgO. Figure 11Was COnStruded to show the percentage of copper oxide taken by a ofMgO and cr,0, before a liquid Dhase will aDnear at 1120 and 1125 "C. It is evident that adding magnesia to Cr,Os enhances ita fluxing. Photomicrographs showed that in the absence of Cr,O, the periclase grains were rounded and separated by a matrix containing liquid (Figure 12) and the low dihedral angle suggests that the degree of penetration of the liquid phase between the grains was high. This implies that MgO in the refractory will dissolve copper oxides and resist fluxing. Above the saturation limit the liquid phase is corrosive and separates the gains. In the absence of MgO, on the other hand, interlocking laths of Cuz0.Crz03were formed (Figure 13) and the large dihedral angle indicates a small tencency for the liquid phase to penetrate between the solid phases. This implies that the presence of CrzO, in basic refractories retards fluxing due to the formation of a high melting compound and increases the refractoriness under load due to increasingthe dihedral angles and due to forming interlocking grains which tend to inhibit
.* ~
~
~~~
~~~
Figure 13. Photomicrograph of B mixture containing initially 80% Cu020% Cr,O, molar (67.5% CuO32.5% Cr20, by weight). Sample equilibrated at 1150 'C and air-quenched. Grey laths are Cu,OCr,O,; light matrix meinly cuprous oxide; dark areas are pores. light; 480xf
intergranular penetration of liquid copper oxides. Conclusions The spinel phase dissolves copper oxides forming a quaternary solid solution that extends over a wide range of compositions. When this solid solution is saturated, additions of CuO precipitate periclase and guggenite. the latter phase takes Cr,O, in solid solution thus decreasing its stability and above 1042 OC it dissociates to periclase and CuzO. In the presence of Cr,O,, the solubility of copper oxides in periclase decreases. With high CuO content, CuzOCr,03 appears and decreases the stability of guggenite by forming Cu,O and spinel a t 1035 "C. In air partial melting starts a t about 1120 'C and magnesia refractories (magnesitebricks) containing a molar ratio of MgO/Cr2O3higher than 9 1 have high refracto-
446
Ind. Eng. Chem. Fundam. 1904, 2 3 , 446-454
riness due to the formation of solid solution. With lower magnesia content a liquid phase appears that causes wetting and penetration between the grains of the refractory to take place, eventually leading to failure. On the other hand, with chromemagnesite bricks, the higher the Cr203content the higher is the corrosion resistance due to formation of the refractory Cu20.Crz03and its growth as interlocking laths in the liquid phase. Registry No. CuO,1317-38-0;periclase, 1317-74-4;gugganite, 67164-58-3;chromium copper oxide, 12017-79-7. Literature Cited
Drenkhahn, H.; Mueller-Bouchbaum, H. K. Z . Anorg. A/@. Chem. 1975, 418, 116. Gadalla, A. M.; Ford, W. F.; White, J. Trans Br. Ceram. SOC. 1963, 62, 54. Gadalla, A. M.; White, J. Trans. Br. Ceram. SOC. 1964, 63, 39. Gadalla, A. M.; White, J. Trans. Br. Ceram. SOC. I964b, 6 3 , 119. Gadalla, A. M.; White, J. Trans. Br. Ceram. SOC. 1964c, 6 3 , 535. Pressley, H.; White, J. Trans. J . Brit. Ceram. SOC. 1979, 7 8 , 4. Rigby, G. R.; Hamltton, B. J . Am. Ceram. SOC. 1961, 4 4 , 201. Rigby, G. R.; Hamliton, 8. Trans. Metall. SOC.AIME 1962, 224, 887. Trojer, F. Radex Rundsch. 1956, 7 , 365. Ust'yantsev, V. M.; Mar'evlch, V. P.; Perepelitsyn, V. A . Ogneuporv, 1971, 36,20. Ust'yantsev, V. M.; Mar'evich, V. P.; Lapachak, G. G. Izv. Akad. Nauk USSR, Neorg. Mater. 1972, 8 . 590.
Received f o r review May 9, 1983 Accepted April 9, 1984
Alper, A. M.; McNally, R. N.; Doman, R. C.; Keihn, F. G. J. Am. Ceram. SOC. 1964, 47,30.
Mass Transfer Due to a Confined Laminar Impinging Axisymmetric Jet Hln-Sum Law and Jacob H. Masllyah' Department of Chemical Engineering, University of Alberta, Edmonton, Alberta, Canada T6G 2G6
Local mass transfer due to impingement of a confined laminar axisymmetric air jet onto a flat surface has been studied both theoretically and experimentally. Alter release from a cylindrical tube the axis of which is perpendicular to a target plate, the jet fluid is confined to flow radially outward in a channel between two parallel plates. The range of Reynolds number was 400 to 1900 and the jet-to-plate spacings were 2 and 4 times the jet nozzle diameter. The experimental study was carried out with double exposure holography and the theoretical study was made with the numerical solution of the transport equations using an upstream-weighted differencing scheme. In general, flow separation along the impingement plate occurred at a radial distance far away from the stagnation point. It was found that the variation of the local Sherwood number is similar to that of an unconfined jet in the stagnation flow region and in the wall jet region prior to flow separation. Beyond the flow separation region, the local Sherwood number is smaller than that for an unconfined jet.
Introduction Impinging jets of various configurations are frequently used in industrial equipment for their excellent heat and mass transfer characteristics. Drying of textiles and cooling of turbine blades are some of the important practical applications. Heat and mass transfer characteristics of impinging axisymmetric jets issuing from circular tubes have been studied rather extensively by Scholtz and Trass (1963,1970),Kapur and Macleod (1972,1974,1975),Saad et al. (1977), and Deshpande and Vaishnar (1982). The theoretical and experimental findings are well correlated in the stagnation-flow and in the wall-jet regions. However, of these studies, only the numerical study by Saad et al. (1977) considered the effect of the presence of a confinement plate, and their results were restricted in the region near the stagnation point. The effect of the presence of a confinement plate on the mass transfer due to a laminar two-dimensional jet has been studied by Law (1982,1984). A flow separation was found along the impingement plate in the region far away from the stagnation point, producing local minimum and maximum Sherwood numbers in the separation flow region. It is commonly known that heat and/or mass transfer from axisymmetric and two-dimensional jets have similar behavior, albeit there are significant quantitative differences. The objective of the present work is to study, both experimentally and numerically, the mass transfer characteristics of a confined laminar axisymmetric jet impinging on a flat plate. 0196-4313/84/1023-0446$01.50/0
Table I. Coefficients of Ea 1 rp
AI
A2
'43
WR
R2
-a
C
0 1
R3/Red 1/R R/RedSc
\Ir
0
0
Numerical Study The impinging jet system considered in the present study is shown in Figure 1. The air jet issues from a circular tube of diameter d with an average velocity of uj. The confinement plate is located parallel to and at a distance h from the impingement plate. The origin of the axisymmetric coordinate system is located at the center of the jet nozzle exit. The outflow region is chosen at a location sufficiently far away from the stagnation flow region where fully developed conditions can be assumed. The governing equations are the equations of motion in their vorticity-stream function form and the convectiondiffusion equation with the assumptions of steady state and incompressibleNewtonian fluid with constant physical properties. The pertinent equations can be represented by a general differential equation in the axisymmetric coordinate system as
0 1984 American
Chemical Society
