I. INSTRUCTION
Coal tar pitch is an anode raw material that binds the coke particles together during the production of carbon anodes used in aluminum industry. During the baking process, pitch undergoes pyrolysis. The thermal decomposition of pitch results in the release of volatiles and the formation of pitch-coke, namely, carbonized pitch. Carbonized pitch exhibits different structure than that of coke due to its properties, mixing, and compacting conditions used as well as the heat treatment that it is subjected to during anode fabrication. The structure of carbonized pitch and its interface with coke particles have a significate influence on the strength and reactivity of baked anodes. Reference Tosta, Inzunza and DeYoung1,Reference Neyrey, Edwards, Anthony Ross, Vogt and H. Kvande2
Polarized light microscopy is a well-known method that is used for the examination of polished surfaces of metallurgical cokes. Reference Hays, Patrick and Walker3–Reference White10 Optical textural units of varying size and color can be seen on the polished coke surface due to the interaction between the structure and the incident light. Reference Hays, Patrick and Walker4 Two types of optical structure of carbonized pitch (isotropic and anisotropic) can be identified by optical microscopy depending on pitch composition and baking conditions. The granular texture in carbonized pitch under polarized light exhibits stronger physical bonding with coke due to stronger possibility of forming chemical bond with coke particles compared to that of carbonized anisotropic pitch. Therefore, carbonized pitch with relatively granular structure is preferred for anode production due to more favorable anode strength. Reference Jones and Bart11,Reference Adams, Mathews, Schobert and Peterson12 Moreover, disordered carbonized coke has less open porosity that protects the underlying coke from air/CO2 oxidation better than a more ordered anisotropic carbonized coke in addition to obtaining anode with better strength with this type of pitch. Reference Tosta, Inzunza and DeYoung1,Reference Neyrey, Edwards, Anthony Ross, Vogt and H. Kvande2 Because of the similar hardness and composition of coke and carbonized pitch in baked anodes, their optical shapes and structures are similar. This makes it difficult to distinguish carbonized pitch from the coke particles and to identify their interface on the polished surface of the sample by this technique.
Scanning electron microscopy (SEM) is also used to characterize the structure of different metallurgical cokes Reference Hays, Patrick and Walker3,Reference Hays, Patrick and Walker4,Reference Marsh, Forrest and Pacheco6,Reference Patrick, Shaw and Willmers9 and carbonized pitches Reference Hays, Patrick and Walker3,Reference Hays, Patrick and Walker5 on fractured or etched surfaces. SEM examination on fractured surface can reveal the true three-dimensional nature of texture but cannot quantify its textural composition. This can be successfully determined by examining the etched surfaces with a point-counting technique, which facilitates the correlation of textural composition with carbon properties. The principle of etching technique is based on the etchants' preferential reaction with carbon materials, which creates various morphological characteristics. Therefore, the choosing the type of etchant and etching conditions is critical to produce a suitable surface for SEM examination.
Various etchants were used to etch coke and carbon material surfaces for SEM examination. Argon ion was used successfully as an etchant for polished coke surfaces by Patrick et al. Reference Patrick, Shaw and Willmers9 Etching of coke fibers in oxygen plasma is reported by Barnet and Norr. Reference Barnet and Norr13 Atomic oxygen, a useful and traditional etchant for cokes and carbon materials, was utilized by several researchers to characterize the structure of carbons and graphite. Reference Hays, Patrick and Walker3–Reference Marsh, Forrest and Pacheco6 Atomic oxygen reacts preferentially with the optical isotropic texture in metallurgical coke. Reference Marsh, Forrest and Pacheco6 The carbon textural constituents observed by microscopy on the etched surface using atomic oxygen correlated well with the coke strength. Reference Hays, Patrick and Walker4 Etching of baked anode by atomic oxygen provided textural information on carbonized pitch which served to explain the mechanical properties of the corresponding laboratory anode. Reference Hays, Patrick and Walker3,Reference Hays, Patrick and Walker5 Coke and carbonized pitch as well as the textural composition of carbonized pitch were successfully identified and differentiated in these studies. However, the anodes used were made of fine petroleum coke with a narrow range of particle size distribution (+75–150 µm) in the laboratory. The commercial carbon anodes containing coke particles with a wide range of particle size distribution were not studied. The strong oxidizer, chromic acid, was also used as etchant to obtain cokes and carbon surfaces and compare with those etched using atomic oxygen. Reference Marsh, Forrest and Pacheco6 The study revealed that chromic acid oxidized preferentially the anisotropic carbon whereas atomic oxygen etched better the isotropic carbon.
There are different terms (anisotropic, lamellar, isotropic, and granular) to describe the texture of coke and carbonized pitch in the literature studies. Reference Hays, Patrick and Walker3–Reference Marsh, Forrest and Pacheco6 The terms isotropic and granular are used for the similar pitch textures. In this article, granular was used to represent this type of structure.
Although the etchants stated above are suitable to etch carbon materials, most of them need specific and expensive apparatus, which are not available in most laboratories. In addition, the chemicals used such as chromic acids are toxic and carcinogenic and difficult to dispose after etching. Therefore, the object of the present study is to develop a simple, fast, cheap, and convenient method for etching baked anode surfaces to facilitate the structural analysis. To obtain information on carbonized pitch structure, air etching experiments were carried out. Mildly oxidizing conditions were used to remove the less etch resistant portions of the carbon and to expose the more resistant crystalline structure so that it can be analyzed with a scanning electron microscope. An attempt was made to compare the textures of carbonized pitch on fractured, polished and etched surfaces using SEM with the aim of identifying suitable etching technique. The differences in the textures and topography of pure carbonized pitch as well as carbonized pitch and its interface with coke in baked anodes, which were produced in the laboratory using an anode recipe similar to that of industry, were investigated.
II. EXPERIMENTAL
A. Carbon materials
Anode was produced in the laboratory using an anode recipe similar to that used in industry. The chemical and physical properties of coal tar pitch and fresh petroleum coke are presented in Table I. The commercial petroleum coke, butt, recycled anodes, and coal tar pitch were mixed at a certain temperature and the anode paste was vibro-compacted to obtain green anode. Then, the anode covered by packing coke was baked in a furnace available at the carbon laboratory of the University of Quebec at Chicoutimi (UQAC). The anodes were baked using heating rate of 11 °C/h and a soaking time of 8 h at the maximum temperature of 1100 °C. The same coal tar pitch, used as binder in anodes, was also carbonized alone (pure carbonized pitch) in an electrically heated vertical furnace using the same baking conditions. The carbonization was carried out under oxygen-free nitrogen atmosphere to prevent the oxidation of carbon materials. The sample was allowed to cool in nitrogen before being prepared for etching and characterization.
Physical and chemical properties of petroleum coke and coal tar pitch used in the study.
B. Specimen preparation
For hot air etching and microscopic examination, baked anode and pure carbonized pitch samples were mounted into the epoxy liquid resin. After curing, the excess epoxy resin was cut away and the sample surface was polished by a Struers polisher to create a scratch free surface. The polished samples were first examined with optical microscopy. Then, they were cut to 10 × 10 mm2 blocks. Thereafter, the small samples were ultrasonically cleaned and dried in the oven at 80 °C for 17 h to remove humidity before etching.
C. Carbon etching
Hot air was chosen as etching medium primarily due to the differences in air reactivities of carbon with different compositions and textures. Thermogravimetric analyzer (TGA), which is also used for air reactivity tests, was used to expose the polished samples to hot air. It is a safe, simple, and effective method.
During each test, one polished specimen from baked anode and one sample of pure carbonized pitch were subjected to hot air. The samples were suspended into the TGA and subjected to air flow of 6 mL/min at 525 °C. The period of effective air etching was found to be around 20 min. At this time, the interfaces between coke particles and carbonized pitch in baked anodes were visible and suitable surfaces were obtained for microscopic examination. A series of tests with etching periods of up to 55 min showed that there was no additional benefit of using longer etching times for microscopic analysis of samples.
D. Optical microscope assessment
The optical microscope allows the examination of a larger surface area compared to the area analyzed with the SEM technique, and sample does not need to be coated. The polished pure carbonized pitch samples were examined under a polarizing microscope using Nikon Eclipse ME600P (Nikon Inc., Melville, NY) optical microscope and analyzed with the Clemex Vision 4.0 image analysis software to study their components. The etched baked anode samples were investigated by optical microscope.
E. SEM examination
All the samples were dried and vacuumed to remove moisture in the pores of carbon before SEM examination. The fractured, etched, and nonetched baked anode and pure carbonized pitch were mounted onto the surface of an aluminum block using electrically conducting paste and sputter-coated with a palladium/gold layer to have electrically conductive surface. The samples were scanned using a SEM (JSM 6480LV; JEOL Ltd., Tokyo, Japan) and the images of representative parts of the carbon surfaces were taken at different magnifications.
III. RESULTS AND DISCUSSION
A. Pure carbonized pitch
The appearance of principle solid particles in green pitch and pitch heated to 500 °C in nitrogen medium is illustrated in Figs. 1(a) and 1(b), respectively. The SEM image in Fig. 1(a) shows the primary quinoline insoluble (QI) particles mixed with the agglomerated submicron particles on flattened and polished green pitch sample surface. The appearance of these agglomerated submicron particles is similar to that of carbon black reported in the literature study. Reference Hays, Patrick and Walker5 However, there is no carbon black particle in industrial pitches. They might be submicron QI particles or other components present as particles at room temperature in green pitch. The submicron particles may be identified by extracting particles from pitch and then examining with SEM, which requires further study. The other softer components of green pitch have been removed preferentially leaving the harder QI particles by polishing. Direct assessment of particles in the micrographs shows that all particles are less than 1 µm in diameter. The micrographs also indicate that the green pitch used in this study does not contain mesophase which is 10–20 μm in size. Reference Hays, Patrick and Walker5 Mesophase was formed during the carbonization of the pitch. This is confirmed by the micrograph in Fig. 1(b) illustrating the spherical morphology of mesophase spheres on the surface of pitch carbonized at 500 °C in nitrogen medium. This appearance of mesophase was observed on the top surface of the sample. It is expected that QI particles, surrounding the mesophase spheres during their formation, will prevent the particle growth and cause the distortion of their surfaces. However, these mesophase spheres were observed on the top surface of the calcined pitch sample. The solid QI particles are usually heavier than the rest of the pitch components which are in liquid state. Therefore, they accumulate at the bottom of the sample. Due to the lack of QI particles on the top of the sample, the perfect mesophase spheres can be formed on the sample surface. The mesophase spheres were larger than 5 μm in size. Although the spherical nature of mesophase particles is evident in Fig. 1(b), it was not possible to detect a nematic structure. Reference Marsh14 During the pyrolysis of the pitch, carbon constituents undergo intramolecular and/or intermolecular rearrangements and condensation reactions as the temperature increases. This results in the growth and the coalescence of the mesophase [see Fig. 1(b)] and the formation of semi-coke and finally the formation of carbonized pitch shown in Figs. 2 and 4.
SEM images of (a) primary QI particles and (b) mesophase spheres in pitch carbonized at 500 °C.
Micrographs of pure carbonized pitch: (a) optical microscopy image of polished surface (A: anisotropic, I: isotropic texture), (b) SEM image of polished surface, (c) general views of fractured surface, (d) different textural components visible in fractured surface (G: granular, L: lamellar), (e) granular texture, and (f) lamellar texture on etched surface.
To investigate the structure of carbonized pure coal tar pitch, the polished, fractured, and etched sample surfaces were examined using optical microscopy and/or SEM [Figs. 2(a)–2(f)].
The appearance of the carbonized pitch observed from Fig. 2(a) exhibits both optical anisotropic and granular textures, which are in agreement with results of carbonized pitch-coke presented in the literature study. Reference Marsh14 The observed surface textures are similar to those found in metallurgical cokes. Reference Hays, Patrick and Walker5 It was proposed by Hays et al. Reference Hays, Patrick and Walker5 that the texture of carbon materials can be lamellar, granular, and intermediate (mixture of lamellar and granular), which can be identified with SEM. The granular material could form due to the insertion of QI particles in anisotropic material, which interrupts the growth of anisotropic texture. Therefore, it can be said that the origin of the granular material is small anisotropic material (mosaics) associated with the QI agglomerates formed during pitch carbonization. It is not possible to observe clearly these textural components on the surface of polished pure carbonized pitch sample shown in Fig. 2(b). Therefore, the attempt was made for examining the fractured surface [see Figs. 2(c) and 2(d)]. It was observed from the SEM results with a large magnification that the carbonized pitch in the current work contains only two different components, namely, lamellar (position L) and granular (position G) as can be seen in Fig. 2(d). The appearance of the granular component with primary QI particle accumulated in certain regions of carbonized pitch is clearly visible from the SEM image in Fig. 2(d), which shows the details of the fractured carbonized pitch surface. Although the corresponding fractured surface shown in Fig. 2(d) does not show the detailed texture of lamellar component, the some characteristics can be seen for the two components. The percentage of different textural components can be determined from such micrograph. The percentage of the granular material is around 50 in this specific sample shown in Fig. 2(d). However, large number of tests has to be carried out to determine the percentage of each component in pitch. Generally, the QI contents of the pitches are 5–10% weight percent. Hence, the percentage of granular component in pure carbonized pitch found in this study is greater than the QI contents of pitch. This is in agreement with the results reported by Hays et al. Reference Hays, Patrick and Walker5 They also showed that the portions of granular components present in two 9.7% primary QI-containing pitches exceeded their actual QI content after carbonization at 1000 °C. The implication seems to be that the granular components are not only composed of QI but also a small randomly-orientated granular matrix. The granular component increases with increasing QI but it is not equal to QI. Reference Hays, Patrick and Walker5 However, the nature of the lamellar texture on the fractured surface cannot be clearly seen from this micrograph. Thus, the surface of pure carbonized pitch was etched with hot air and inspected with SEM to get more detailed information and compare with that of pitch in baked anode. The SEM micrograph illustrating the appearance of granular component after etching is shown in Fig. 2(e). The primary QI particles are flattened, but they can be seen clearly from the micrograph in Fig. 2. The lamellar nature on pure carbonized pitch surface can also be easily identified from the etched sample as shown in SEM image [Fig. 2(f)], which is complementary to the information obtained from fractured surface in Fig. 2(d). The observed lamellar crack patterns are the effect of etchant. The differences in topography of etched surfaces reflect a difference in the structural units of the carbonized pitch studied [see Figs. 2(e) and 2(f)].
B. Structures of carbonized pitch in baked anodes
An optical microscope image with a magnification of 1000×, which shows a general view of a polished baked anode surface, is shown in Fig. 3(a). The presence of irregularly shaped interparticle pores in anode is clearly evident in this figure. These pores are the result of volatile release from pitch during baking. With increasing temperature, the anisotropic component in pitch grows in size and ultimately coalesces to form carbonized pitch, which has similar hardness and composition with those of calcined petroleum coke. Therefore, it is not possible to see the boundaries of coke particles and carbonized pitch on the polished baked anode surface by optical microscopy without etching. Furthermore, because of the small depth of focus and two-dimensional view of this method, the details of the pores are not clearly distinguished.
Optical microscopy images of (a) polished nonetched baked anode and (b) etched baked anode.
According to the literature study, the etching by atomic oxygen induces a surface topography which reflects the structural order of the surface material of baked anode specimen. Reference Hays, Patrick and Walker4 Etchants can attack the structural units differently. The differences in topography of the etched surfaces reflect the difference in the structural units of the carbon. Reference Hays, Patrick and Walker5 To improve the quality of microscopy analysis, the polished anode samples were etched by hot air in the present study. As indicated by the arrow in Fig. 3(b), it is possible to identify the contours of coke particles in optical microscopy images of baked anode samples with this method. This means the composition of baked anode can also be studied by means of various topographies created with the etchant. The effect of different etchants on carbon materials are not the same. The etchant used in this study attacks carbonized pitch easier than coke particle leaving the coke slightly raised on the etched surface. This difference can be attributed to the calcination of coke at high temperature (1200 °C), which makes coke more resistant to oxidation. The calcination temperature is higher than that of baking temperature (1100 °C), therefore, calcined coke and carbonized pitch have different properties such as crystalline length.
Due to the low magnification capacity of optical microscope, the texture of carbonized pitch is ambiguous in Fig. 3(b). Moreover, its small depth of focus requires highly even surface to obtain a clear image, which limits the utility of this method. The low magnification (1000×) SEM micrographs giving a general view of the polished and etched baked anode surfaces are presented in Fig. 4. No notable information can be observed from these images of polished but non-etched baked anode surface in regard to the structure of carbonized pitch and coke. Furthermore, it is difficult to differentiate the different carbons (coke and carbonized pitch) at this low magnification [see Fig. 4(a)].
SEM images of (a) polished nonetched baked anode, and (b–d) etched baked anode showing (b) lamellar texture, (c) intermediate texture, and (d) granular texture in carbonized pitch.
SEM with its large depth of focus is well suited to observe topography of the etched surface and identify the interface between carbonized pitch and coke particles by their texture and a discontinuity between the two materials as shown in Figs. 4(b)–4(d). This is in agreement with the results given in the literature study. Reference Hays, Patrick and Walker3 The carbonized pitch shows visible textural patterns while coke particle surface exhibits flat, less textured, and darker appearance after etching. This result confirms those obtained from optical microscope analysis that coke is more resistant to oxidation compared to pitch even after baking. Figures 4(b)–4(d) demonstrate different textural patterns of carbonized pitch. Due to the microcracks created by etching, parallel arrangements of short ridges and channels are visible in the carbonized pitch regions shown in Fig. 4(b). Corresponding view of the same component visible in etched pure carbonized pitch surface is given in Fig. 2(e). Therefore, it can be said that the structure of carbonized pitch is lamellar and it is easily identifiable in the micrographs. The lamellar arrangements are broken by the fine coke particles present in pitch as shown with arrows in Fig. 4(b). It is worth mentioning that the lamellar texture in carbonized pitch and the principal component of the petroleum coke, which also exhibits a lamellar texture on the anode surface, are easily distinguished after etching using the method developed in this study. This is a significant improvement compared to previous methods. Reference Hays, Patrick and Walker5 The textures of carbonized pitch in anode presented in Figs. 4(c) and 4(d) are different. Also, they differ from the lamellar texture shown in Fig. 4(b). However, the clear arrangement patterns of carbonized pitch in anode cannot be obtained from the micrographs in Figs. 4(c) and 4(d) at this low magnification of 1000×.
Furthermore, it can be seen that the components of carbonized pitch in baked anode shown in Fig. 4(d) has less damages and defects than those in Figs. 4(b) and 4(c) after etching. This indicates that the different textural components react differently with etchant, which permits to understand the differences in oxidation of different carbonized pitch structures and coke in baked anode. In turn, this might provide possibility to control and optimize the textures of carbonized pitch components in anode.
Figures 5(a)–5(c) show the higher magnification micrographs (5000×) illustrating the three different textural components of carbonized pitch in baked anode, corresponding to Figs. 4(b), 4(c), and 4(d), respectively. The nature of the lamellar component in the carbonized pitch in anode is clearly evident from the micrograph in Fig. 5(a). It exhibits smooth river patterns with arrangements of microcracks and carbon layers parallel to basal plane. The lamellar pattern on etched surfaces of pitch in baked anode and pure carbonized pitch shown in Fig. 2(f) appear identical, which help determine the lamellar component of pitch in baked anode. The appearance of lamellar component in Fig. 5(a) is in agreement with those reported in the literature study. Reference Hays, Patrick and Walker5 The growth of mesophase leads to the lamellar structure (anisotropic optical structure) in carbonized pitch. The presence of solids within the liquid phase of pitch influences significantly the enlargement pattern of the mesophase spheres. Reference Marsh14 Presence of large mesophase particles of several µm diameter may increase the size of the regions of coalesced lamellar structure around the particle surface. Reference Marsh14
SEM images showing different components of carbonized pitch on etched surface of anode: (a) lamellar; (b) intermediate; (c) granular.
The granular component in Fig. 5(c) shows poor, random, and distorted basal layer alignment with small pits and pores. The pit features appear to be due to the removal of QI particles during etching process. The granular carbonized pitch is composed of somewhat coalesced small spheres, which have appearance similar to that of mesophase spheres. Slight lamellar realignment of molecules seems to take place after coalescence. Same basal carbon layers are arranged like rays or radius of circles, which is the textural pattern of single sphere before coalescing with others. The characteristics of granular component observed from these micrographs are in agreement with the description given in the literature study. Mainly, two forms of granular components were observed, first one has poor alignment of basal layer due to mesophase coalescence and the second one has random alignment of basal layer of compressed sphere units alone. Reference Hays, Patrick and Walker3 No mesophase is present in the pitch-coke after calcination at high temperature. The form of sphere units present in the granular component [see Fig. 5(c)] is similar to the spherical form of mesophase but they are not mesophase spheres. Another effect of pitch solids on the growth pattern of mesophase spheres is the severe hindrance of coalescence by the small particles, such as primary QI et carbon black particles, which stick on the surface of spheres. Reference Marsh14 It was reported that the presence of primary QI or carbon black particles enhance the granular component at the expense of the other components. Reference Hays, Patrick and Walker5 These components differ markedly in appearance from the granular component of pure carbonized pitch shown in Fig. 2(e), which exhibits a grain-featured surface with visible QI particles after etching. The granular nature can be confirmed by its similarity to the granular component of carbonized pitch on etched baked anode as reported in the literature study. Reference Hays, Patrick and Walker5
The extent of basal layer alignment of intermediate component of carbonized pitch in baked anode shown in Fig. 5(b) appears to be between those of lamellar and granular components. The texture is considerably coarser than that of granular component presented in Fig. 5(c), which is similar to the observation of Hays et al. Reference Hays, Patrick and Walker5 Since there is no corresponding texture found in pure carbonized pitch, the intermediate textual form can be identified according to the characteristics reported in the literature studies, Reference Hays, Patrick and Walker3,Reference Hays, Patrick and Walker5 where the intermediate component is described as an elongated form of the granular component Reference Hays, Patrick and Walker5 and mixture of small distorted lamellae or elongated grains. Reference Hays, Patrick and Walker3 When the alignment of lamellar molecules is restricted during mesophase coalescence, intermediate components formed are less ordered than lamellar components. Reference Hays, Patrick and Walker3
Although the low percentage of pitch and the interference of fine coke particles with pitch makes the quantitative determination of different carbonized pitch components of in commercial anodes, it is still possible to quantify these components by eliminating its interference with fine coke particles as reported in the literature study Reference Hays, Patrick and Walker5 or by carrying out the analysis with a large number of samples having larger surface. Further study is needed to correlate the anode properties with the proportion of various structural components present in carbonized pitch of anode.
C. Interface between coke and carbonized pitch in baked anode
For pitch-bonded carbon anodes, the quality of the interface present between coke and pitch influences their strength properties. Reference Hays, Patrick and Walker15 The interface between coke and pitch in baked anode can be identified by careful examination of samples using SEM at high magnification on polished surfaces [see Figs. 6(a) and 6(b)]. No microcrack formation was observed between coke and pitch, indicating good bonding between coke and pitch for the sample studied. Possible interaction zones at the interface of coke and carbonized pitch may indicate reaction. The possibility of the presence of reaction products has been deduced based on the difference in the lightness of the surface at the interface compared to that of the coke surface. The spherical particles of carbonized pitch in baked anodes can be visually identified in a SEM micrograph [Fig. 6(d)] even after polishing the sample surface but there is no indication of the presence of an lamellar structure [Fig. 6(a)]. However, it is difficult to obtain detailed information about the interface from these micrographs. Hence, the etching of polished surface is necessary.
SEM images of interface between coke and carbonized pitch on polished surface (a and b) and on (c–e) etched surface in baked anode.
The etching method developed in this study can be used to obtain clear images of interfaces and interaction zones between coke and different textual components of carbonized pitch in baked anode [see Figs. 6(c)–6(e)]. Figure 6(c) reveals that the orientation of lamellae of lamellar component in carbonized pitch is parallel to the coke surfaces. This is in agreement with the results of coke structure reported in the literature study where the optical anisotropic materials in coke form lamellae parallel to insert surface. Reference Marsh14 However, the orientation of carbon basal plane of granular component of pitch is not uniform. This randomness is due to its textural characteristics [see Fig. 6(e)]. The isotropic structure in the granular component provides greater flexibility and diversity of chemical carbon chain along any plane for stronger bonding with coke particles, which can contribute to its higher fracture strength compared to those of the other components. This is confirmed by the results reported in the literature study, which indicate that anodes containing more granular carbonized pitch have higher strength. Reference Hays, Patrick and Walker3 The extensive crack development in lamellar component due to shrinkage of pitch during baking may reduce the mechanical properties of anodes. The surface energy of each textural component of coke is different and is considered to be important for its strength. Reference Hays, Patrick and Walker15 Therefore, the strength of carbonized pitch-bonded with coke may be also related to the surface energy of its components and their percentage.
IV. CONCLUSIONS
In this study, the texture of carbonized pitch and its interface with coke in baked anode were investigated. A new etching method was developed. This method, which uses hot air as etching medium, gave precise information on the textural composition of carbonized pitch. It is possible to measure the portions of the various components present in carbonized pitch and correlate them to the other properties of relevant anode. However, this requires the analysis of a large number of samples. The method has been proven be safe, simple, and effective for etching baked commercial anode samples for SEM examination. A study on the relation between the etched textural patterns and the pitch properties as well as the pitch content in baked anode is in progress.
ACKNOWLEDGMENTS
The technical and financial support of Aluminerie Alouette Inc. as well as the financial support of the National Science and Engineering Research Council of Canada (NSERC), Développement économique Sept-Îles, the University of Quebec at Chicoutimi (UQAC), and the Foundation of the University of Quebec at Chicoutimi (FUQAC) are greatly appreciated.
