Pellet Cores Research Articles

The Effect of Design and Size of the Fluid-Bed Equipment on the Particle Size-Dependent Trend of Particle Coating Thickness and Drug Prolonged-Release Profile

The focus of the current work is to study and demonstrate the impact of the design, the scale, and settings of fluid-bed coating equipment on the differences in pellet coating thickness, which in case of prolonged-release pellets dictates the drug release. In the first set of coating experiments, the pellet cores were coated with the Tartrazine dye with the aim of estimating the coating equipment performance in terms of coating thickness distribution, assessed through color hue. In the second set, drug-layered pellets were film-coated with prolonged-release coating and dissolution profile tests were performed to estimate the thickness and uniformity of the coating thickness among differently sized pellets. In both study parts, film coating was performed at the laboratory and the pilot scale and essentially two types of distribution plate and different height adjustments of the draft tube were compared. The dye coating study proved to be extremely useful, as the results enable process correction and the optimal use of the process equipment in combination with the appropriate process parameters. Preferential film coating of larger drug-containing pellets was confirmed on the laboratory scale, while on the pilot scale, it was possible to achieve preferential coating of smaller pellets using rational alternatives of settings, which is desirable in terms of particle size-independent drug release profile of such prolonged-release dosage forms.

Review on Starter Pellets: Inert and Functional Cores.

A significant proportion of pharmaceuticals are now considered multiparticulate systems. Modified-release drug delivery formulations can be designed with engineering precision, and patient-centric dosing can be accomplished relatively easily using multi-unit systems. In many cases, Multiple-Unit Pellet Systems (MUPS) are formulated on the basis of a neutral excipient core which may carry the layered drug surrounded also by functional coating. In the present summary, commonly used starter pellets are presented. The manuscript describes the main properties of the various nuclei related to their micro- and macrostructure. In the case of layered pellets formed based on different inert pellet cores, the drug release mechanism can be expected in detail. Finally, the authors would like to prove the industrial significance of inert cores by presenting some of the commercially available formulations.

Towards a Better Understanding of Verapamil Release from Kollicoat SR:IR Coated Pellets Using Non-Invasive Analytical Tools.

The aim of this study was to gain deeper insight into the mass transport mechanisms controlling drug release from polymer-coated pellets using non-invasive analytical tools. Pellet starter cores loaded with verapamil HCl (10% loading, 45% lactose, 45% microcrystalline cellulose) were prepared by extrusion/spheronization and coated with 5% Kollicoat SR:IR 95:5 or 10% Kollicoat SR:IR 90:10. Drug release was measured from ensembles of pellets as well as from single pellets upon exposure to acetate buffer pH = 3.5 and phosphate buffer pH = 7.4. The swelling of single pellets was observed by optical microscopy, while dynamic changes in the pH in the pellet cores were monitored by fluorescence spectroscopy. Also, mathematical modeling using a mechanistically realistic theory as well as SEM and Raman imaging were applied to elucidate whether drug release mainly occurs by diffusion through the intact film coatings or whether crack formation in the film coatings plays a role. Interestingly, fluorescence spectroscopy revealed that the pH within the pellet cores substantially differed upon exposure to acetate buffer pH = 3.5 and phosphate buffer pH = 7.4, resulting in significant differences in drug solubility (verapamil being a weak base) and faster drug release at lower pH: from ensembles of pellets and single pellets. The monitoring of drug release from and the swelling of single pellets indicated that crack formation in the film coatings likely plays a major role, irrespective of the Kollicoat SR:IR ratio/coating level. This was confirmed by mathematical modeling, SEM and Raman imaging. Importantly, the latter technique allowed also for non-invasive measurements, reducing the risk of artifact creation associated with sample cutting with a scalpel.

Microstructure and Porosity Evolution During the Reduction, Softening and Melting of Iron-Bearing Materials

The performance of the blast furnace is strongly affected by the position and thickness of the cohesive zone, which is largely influenced by the high-temperature properties of the iron-bearing materials. During its reduction, softening and melting, ferrous materials undergo major microstructure changes and its understanding is essential to develop new raw-materials, technologies, and models. In this study, the behavior of reduction, softening and melting of a lump ore, an acid pellet, and a sinter was characterized by softening and melting (S&M) experiments. After that, to access the samples’ structural transformations, interrupted S&M tests were carried out up to four different conditions based on contraction and pressure loss levels. The obtained products were characterized according to its density (true and apparent), porosity (open, closed and total), phase composition by X-ray diffraction and microstructure (reflected light microscopy and electron scanning microscopy). From the S&M test results, three main regions of reduction were characterized, namely: solid/gas reduction, reduction retardation, and melting reduction. In the solid/gas reduction, samples open porosity increased, with reduction following the shrinking core model. On the region of reduction retardation, a sharp decrease in open porosity was identified together with the diminishing of the reduction rate, which occurred due to the iron shell porosity being clogged due to the slag transfer from the particles’ cores to its periphery. At the melting exudation region, reduction retardation ceased and exudation of the ferrous slag lead to a peak of reduction. The lower the reduction degree of the samples at this stage, the higher the consumption of carbon. Furthermore, at 10 pct contraction, a pseudo-globular wustite structure interspersed with slag was observed for the pellet and sinter cores. At 50 pct contraction, the previous structure coalesced to form a globular shape wustite in a well-connected slag matrix.

Colon targeted bioadhesive pellets of curcumin and cyclosporine for improved management of inflammatory bowel disease.

The objective of the present work was to develop and optimize multiparticulate pH-dependent bioadhesive pellets of curcumin and cyclosporine for the management of intestinal bowel disease (IBD). The bioadhesive sustained release pellets were intended for targeting the affected site for an improved therapeutic effect. Bioadhesive pellet cores of curcumin and cyclosporine were formulated using Carbopol 940 (CP940) and hydroxypropyl cellulose (HPC-H) by the extrusion/spheronization method, and drug delivery to the colon was controlled by the pH-sensitive polymer Eudragit® S100. Microcrystalline cellulose (Avicel PH101) was found to be the best forming agent for pellet core. The ratio of CP940 to HPC-H was kept at 1:1 to achieve 100% bioadhesion. The in vitro dissolution profiles of coated pellets depicted that 12.327 ± 0.342% of curcumin and 14.751 ± 0.112% of cyclosporine were released at the end of 6h (at pH6.8), whereas 71.278 ± 0.100% of curcumin and 76.76 ± 0.195% of cyclosporine were released at the end of 24h (at pH7.4). The drug release profile was found to follow zero-order kinetics for both drugs. The selected formulation was evaluated on an acetic acid-induced ulcerative colitis in the rat model to evaluate the efficiency of drug-loaded pellets coated with Eudragit®S100. The pharmacodynamic study revealed the therapeutic efficacy of Eudragit®S100-coated pellets of curcumin and cyclosporine in alleviating the conditions of the acetic acid-induced colitis model as reflected by weight gain as well as improvement of clinical, macroscopic and microscopic parameters of induced colitis, as compared with free curcumin and cyclosporine. The combination of curcumin and cyclosporine has been proven to have a synergistic effect for the successful management of IBD when used in a low dose as compared with individual drugs with high doses. Hence, curcumin- and cyclosporine-loaded bioadhesive pellets may act as a promising targeted drug delivery system in the management of IBD. Graphical abstract.

A mechanistic understanding of compression damage to the dissolubility of coated pellets in tablets

Damage to the drug diffusion coat barrier of controlled release pellets by the compaction force when preparing multiple-unit pellet system tablets is a major concern. Previous studies have shown that pellets located at the tablet axial and radial peripheral surfaces were more susceptible to damage when compacted due to the considerable shear encountered at these locations. Hence, this study was designed to assess with precision the impact of pellet spatial position in the compact on the extent of coat damage by the compaction force via a single pellet in minitablet (SPIM) system. Microcrystalline cellulose (MCC) pellet cores were consecutively coated with a drug layer followed by a sustained release layer. Chlorpheniramine maleate was the model drug used. Using a compaction simulator, the coated pellets were compacted singly into 3 mm diameter SPIMs with MCC as the filler. SPIMs with individual pellets placed in seven positions were prepared. The uncompacted and compacted coated pellets, as SPIMs, were subjected to drug release testing. The dissolution results showed that pellets placed at the top-radial position were the most susceptible to coat damage by the compaction force, while pellets positioned within the minitablet at the middle and upper quadrant positions showed the least damage. The SPIM system was found to be effective at defining the extent of coat damage to the pellet spatial position in the compact. This study confirmed that coated pellets located at the periphery were more susceptible to damage by compaction, with pellets located at the top-radial position showing the greatest extent of coat damage. However, if the pellet was completely encrusted by the cushioning filler, coat damage could be mitigated. Further investigations were directed at how the extent of coat damage impacted drug release. Interestingly, small punctures were found to be most detrimental to drug release whilst coats with large surface cuts did not completely fail. A damaged pellet coat has some self-sealing ability and failure is not total. Thus, this study provides a deeper understanding of the consequence of coat damage to drug release when sustained release coated pellets are breached.

The effects of the treatment conditions on the dissolution profile of ethylcellulose coated pellets

Due to the additional particle coalescence in the coating, changes in the dissolution profile occur over time in the formulations coated by aqueous ethylcellulose latex. Dry thermal treatment (DT) of the coating can be used as a prevention of this process. Alternatively, it is advisable to take advantage of the synergistic effect of high humidity during wet treatment (WT), which substantially accelerates the film formation. This can be a problem for time-controlled systems, which are based on the coating rupture due to the penetration of water into the core causing the increase in the system volume. This process can begin already during the WT, which may affect the coating adversely. The submitted work was focused on the stability testing of two pellet core compositions: pellets containing swelling superdisintegrant sodium carboxymethyl starch (CMS) and pellets containing osmotically active polyethylene glycol (PEG). Another objective was to identify the treatment/storage condition effects on the pellet dissolution profiles. These pellets are intended to prevent hypoglycemia for patients with diabetes mellitus and therefore, besides the excipients, pellet cores contain 75% or 80% of glucose. The pellet coating is formed by ethylcellulose-based latex, which provides the required lag time (120–360 min). The sample stability was evaluated depending on the pellet core composition (PEG, CMS) for two types of final pellet coating treatment (DT or WT). Scanning electron microscopy and Raman microspectroscopy revealed the penetration of glucose and polyethylene glycol from the core to the PEG pellet surface after WT. For the CMS sample, significant pellet swelling after WT (under the conditions of elevated humidity) was statistically confirmed by the means of stereomicroscopic data evaluation. Therefore, the acceleration of dissolution rate during the stress tests is caused by the soluble substance penetration through the coating in the case of PEG pellets or by dosage form volume increase in the case of CMS pellets. The observed mechanisms can be generally anticipated during the stability testing of the ethylcellulose coated dosage forms. The aforementioned processes do not occur after DT and the pellets are stable in the environment without increased humidity.

Pellet patented technology for fast and distinct visual detection of cholinesterase inhibitors in liquids

The main objective of the presented research was to prepare an innovative carrier as a filler for detection tubes in the form of double-coated pellets with a very significant color transition during the detection of cholinesterase inhibitors such as nerve agents, organophosphorus or carbamate insecticides in liquids that is observable visually and also spectrophotometrically at 412 nm. The pellet cores were prepared by the extrusion/spheronization method. Consecutively, two different coats were applied on the pellet cores in the coating device using the Wurster column method. To increase the color change intensity, the second semipermeable coat based on Eudragit® RL was applied on top of the first coat, which was formed by butyrylcholinesterase immobilized in hydroxypropyl methylcellulose. Prepared samples differing in thickness of the second coat were evaluated for their quality parameters, enzymatic activity and inhibition. The detection mechanism was based on the standard Ellman’s colorimetric reaction. It was observed that the semipermeable coat prevented leaching of the enzyme into the solution and led to an increased intensity of color transition from white – yellow to white – deep yellow/orange, thus enabling a more accurate visual detection. This system allows easy, rapid and safe identification of cholinesterase inhibitors in liquids, especially chemical warfare agents.

Analysis of pellet coating uniformity using a computer scanner

A fast method for pellet coating uniformity analysis, using a commercial computer scanner was developed. The analysis of the individual particle coating thicknesses was based on using a transparent orange colored coating layer deposited on white pellet cores. Besides the analysis of the coating thickness the information of pellet size and shape was obtained as well. Particle size dependent coating thickness and particle size independent coating variability was calculated by combining the information of coating thickness and pellet size. Decoupling coating thickness variation sources is unique to presented method. For each coating experiment around 10000 pellets were analyzed, giving results with a high statistical confidence. Proposed method was employed for the performance evaluation of classical Wurster and swirl enhanced Wurster coater operated at different gap settings and air flow rates.

Esomeprazole magnesium enteric-coated pellet-based tablets with high acid tolerance and good compressibility

The aim of this study was to develop esomeprazole magnesium (EMZ-Mg) enteric-coated pellets and pellet-based tablets, as well as to investigate the effects of pellet size and compression method on acid tolerance, content uniformity, compressibility, and stability of preparations. This study used two types of pellet cores, namely, microcrystalline cellulose (MCC) core with a particle size of 150–300 μm and sucrose core with a particle size of 600–700 μm. Enteric-coated pellets, which consisted of a drug-free core, a drug layer, a sub-coating layer (hydroxypropyl methylcellulose, 6 cps), and an enteric-coating layer (Eudragit®L30D-55), were prepared by using a bottom-spray fluidized bed-coating technique. Pellet-based tablets were prepared by using a direct compression method or a wet granulation method. The acid tolerances of the two types of enteric-coated pellets (MCC and sucrose cores) reached up to 98% in simulated gastric fluid (pH 1.0) within 2 h, and the dissolution rates in simulated intestinal fluid (pH 6.8) reached up to 85% of the labeled amount within 15 min. When compressed into tablets, the pellets based on MCC core (smaller particle size) displayed a significantly higher acid tolerance (up to 92%) compared with the pellets based on sucrose core (larger particle size). In addition, the MCC core-based tablets (F8), especially those prepared by using a granulation method, showed higher drug content uniformity and compressibility than the sucrose core-based tablets (F10), and no lamination phenomenon was observed during compression. The crystallinity of EMZ-Mg was altered during drug layering process, and some physicochemical interactions were observed between the drug and excipients. Moreover, the two types of enteric-coated pellets showed a relatively high stability after storage under high temperature and strong light. However, they showed poor stability under high humidity, resulting in remarkable degradation of active compound. The EMZ-Mg enteric-coated pellets and pellet-based tablets were successfully developed, and reduction in pellet size and wet granulation reduced the differences in content uniformity and better protected the pellet coating from damages during compression.

The interprocess NIR sampling as an alternative approach to multivariate statistical process control for identifying sources of product-quality variability

We are presenting a new approach of identifying sources of variability within a manufacturing process by NIR measurements of samples of intermediate material after each consecutive unit operation (interprocess NIR sampling technique). In addition, we summarize the development of a multivariate statistical process control (MSPC) model for the production of enteric-coated pellet product of the proton-pump inhibitor class. By developing provisional NIR calibration models, the identification of critical process points yields comparable results to the established MSPC modeling procedure. Both approaches are shown to lead to the same conclusion, identifying parameters of extrusion/spheronization and characteristics of lactose that have the greatest influence on the end-product’s enteric coating performance. The proposed approach enables quicker and easier identification of variability sources during manufacturing process, especially in cases when historical process data is not straightforwardly available. In the presented case the changes of lactose characteristics are influencing the performance of the extrusion/spheronization process step. The pellet cores produced by using one (considered as less suitable) lactose source were on average larger and more fragile, leading to consequent breakage of the cores during subsequent fluid bed operations. These results were confirmed by additional experimental analyses illuminating the underlying mechanism of fracture of oblong pellets during the pellet coating process leading to compromised film coating.

Development of oral site-specific pellets containing flavonoid extract with antioxidant activity

Herbal medicines are recognized as an effective treatment of common diseases, mainly associated with oxidative stress. Therefore developing drug delivery systems of these biological active ingredients are gaining interest. Parsley (Petroselinum crispum L.) is a well-known culinary herb and its leaf contains high amount of apigenin, therefore it is suitable as a natural source of this flavonoid. Apigenin possess many health effects such as antioxidant, anti-inflammatory and anticancer activities. Unfortunately, these benefits are limited due to the low water solubility and bioavailability, it was recently classified as BCS II group compound. Therefore the aim of this study was to develop a carrier system for Petroselinum crispum extract, containing high amount of apigenin. Microcrystalline cellulose inert pellet cores were chosen and enteric coatings were applied. The produced multiparticulates had spherical shape, narrow size distribution and low moisture content. 10% (w/w) Eudragit® L 30 D-55 and 15% (w/w) Eudragit® FS 30 D coating was adequate for the modified release in vitro. The layered pellets demonstrated antioxidant activity. It was concluded that development of oral site-specific pellets containing flavonoid extract successful and the therapeutic effectiveness could be hypothesized.

Development of protocatechualdehyde proliposomes-based sustained-release pellets with improved bioavailability and desired pharmacokinetic behavior for angina chronotherapy

The present study was aimed to develope a proliposomal formulation to decrease the hepatic first-pass metabolism of protocatechualdehyde (PD), followed by pellet coating to modify the drug release for angina chronotherapy. PD proliposomes were prepared by depositing PD-phospholipid complex on mannitol powders to improve the drug encapsulation. Afterwards, the PD proliposomes were prepared into pellet cores via extrusion-spheronization using 10% κ-carrageenan as pelletization aid prior to the development of PD sustained-release pellets (PD-SRPs). Eudragit® NE 30D was chosen as coating material and the desired drug release profile of PD-SRPs was calculated for formulation optimization by deconvolution based on the circadian rhythm of variant angina. A high similarity factor (f2=85.72) was achieved when the coating weight was 30% and the sustained release behavior also prevented the destruction of liposomes by gastric fluids. Pharmacokinetic studies revealed a basically consistent trend between the actual and the predicted plasma concentration-time curve with absolute percent errors (%PE) of concentrations <10% in 2–12h. Meanwhile, a relative bioavailability of 200% was achieved compared with pure PD. Therefore, the development of proliposomes-based PD-SRPs was an effective strategy to provide both improved oral bioavailability and desired drug plasma concentration-time course for angina chronotherapy.

Importance of air bubbles in the core of coated pellets: Synchrotron X-ray microtomography allows for new insights

High-resolution X-ray microtomography was used to get deeper insight into the underlying mass transport mechanisms controlling drug release from coated pellets. Sugar starter cores were layered with propranolol HCl and subsequently coated with Kollicoat SR, plasticized with 10% TEC. Importantly, synchrotron X-ray computed microtomography (SR-μCT) allowed direct, non-invasive monitoring of crack formation in the film coatings upon exposure to the release medium. Propranolol HCl, as well as very small sugar particles from the pellets' core, were expulsed through these cracks into the surrounding bulk fluid. Interestingly, SR-μCT also revealed the existence of numerous tiny, air-filled pores (varying in size and shape) in the pellet cores before exposure to the release medium. Upon water penetration into the system, the contents of the pellet cores became semi-solid/liquid. Consequently, the air-pockets became mobile and fused together. They steadily increased in size (and decreased in number). Importantly, “big” air bubbles were often located in close vicinity of a crack within the film coating. Thus, they play a potentially crucial role for the control of drug release from coated pellets.

Oral delivery of insulin via polyethylene imine-based nanoparticles for colonic release allows glycemic control in diabetic rats

In this study, insulin-containing nanoparticles were loaded into pellet cores and orally administered to diabetic rats. Polyethylene imine-based nanoparticles, either placebo or loaded with insulin, were incorporated by extrusion and spheronization technology into cores that were subsequently coated with three overlapping layers and a gastroresistant film. The starting and coated systems were evaluated in vitro for their physico-technololgical characteristics, as well as disintegration and release performance. Nanoparticles-loaded cores showed homogeneous particle size distribution and shape. When a superdisintegrant and a soluble diluent were included in the composition enhanced disintegration and release performance were observed. The selected formulations, coated either with enteric or three-layer films, showed gastroresistant and release delayed behavior in vitro, respectively. The most promising formulations were finally tested for their hypoglycemic effect in diabetic rats. Only the nanoformulations loaded into the three-layer pellets were able to induce a significant hypoglycemic activity in diabetic rats. Our results suggest that this efficient activity could be attributed to a retarded release of insulin into the distal intestine, characterized by relatively low proteolytic activity and optimal absorption.

Application of ethyl cellulose, microcrystalline cellulose and octadecanol for wax based floating solid dispersion pellets

The present study aimed to develop and optimize the wax based floating sustained-release dispersion pellets for a weakly acidic hydrophilic drug protocatechuic acid to achieve prolonged gastric residence time and improved bioavailability. This low-density drug delivery system consisted of octadecanol/microcrystalline cellulose mixture matrix pellet cores prepared by extrusion-spheronization technique, coated with drug/ethyl cellulose 100cp solid dispersion using single-step fluid-bed coating method. The formulation-optimized pellets could maintain excellent floating state without lag time and sustain the drug release efficiently for 12h based on non-Fickian transport mechanism. Observed by SEM, the optimized pellet was the dispersion-layered spherical structure containing a compact inner core. DSC, XRD and FTIR analysis revealed drug was uniformly dispersed in the amorphous molecule form and had no significant physicochemical interactions with the polymer dispersion carrier. The stability study of the resultant pellets further proved the rationality and integrity of the developed formulation.

Improvement of mechanical properties of pellet containing tablets by thermal treatment

Batches of partially spray-dried lactose tablets with three different initial tensile strength (∼20N, ∼35N, ∼50N) were made. Changes along a 24h long thermal treatment at 100°C in tensile strength, friability, individual mass, water content, disintegration time, average free volume and wetting properties were evaluated. Caffeine containing gastroresistant pellets were gained by drug layering and filmcoating of inert microcrystalline cellulose pellet cores in fluid bed equipment. Shape, size, mechanical properties, drug content and dissolution profile of the coated pellets were determined. Batches of pellet containing tablets with three different pellet-filler ratios were compressed where partially spray-dried lactose was used as a filler-binder material.Characteristics of pellet containing tablets were evaluated before and after a 24h long thermal treatment at 100°C. Results shown that the poor initial mechanical properties (friability, tensile strength) were improved by thermal exposure while there were no remarkable alterations in drug release profiles.

Controlled delivery of a new broad spectrum antibacterial agent against colitis: In vitro and in vivo performance

Coated pellets and mini-tablets were prepared containing a new broad spectrum antibacterial agent: CIN-102, a well-defined, synergistic blend of trans-cinnamaldehyde, trans-2-methoxycinnamaldehyde, cinnamyl acetate, linalool, β-caryophyllene, cineol and benzyl benzoate. The aim was to provide a new treatment method for colitis, especially for Inflammatory Bowel Disease (IBD) patients. Since the simple oral gavage of CIN-102 was not able to reduce the pathogenic bacteria involved in colitis (rat model), the drug was incorporated into multiparticulates. The idea was to minimize undesired drug release in the upper gastrointestinal tract and to control CIN-102 release in the colon, in order to optimize the resulting antibiotic concentration at the site of action. A particular challenge was the fact that CIN-102 is a volatile hydrophobic liquid. Pellet cores were prepared by extrusion–spheronization and coated with polymer blends, which are sensitive to colonic bacterial enzymes. Mini-tablets were prepared by direct compression. The release of the main compound of CIN-102 (cinnamaldehyde, 86.7% w/w) was monitored in vitro. Optimized coated pellets and mini-tablets were also tested in vivo: in seven-week-old, male mice suffering from dextran sodium sulfate induced colitis. Importantly, both types of multiparticulates were able: (i) to significantly reduce the number of luminal and mucosal enterobacteria in the mice (the levels of which are increased in the disease state), and (ii) to improve the clinical course of the intestinal inflammation (decrease in the percentages of mice with bloody stools and diarrhea). Thus, the proposed coated pellets and matrix mini-tablets allowing for controlled CIN-102 release show a promising potential for new treatment methods of colitis.

Development of Process Analytical Technology (PAT) methods for controlled release pellet coating

This work focused on the control of the manufacturing process for a controlled release (CR) pellet product, within a Quality by Design (QbD) framework. The manufacturing process was Wurster coating: firstly layering active pharmaceutical ingredient (API) onto sugar pellet cores and secondly a controlled release (CR) coating. For each of these two steps, development of a Process Analytical Technology (PAT) method is discussed and also a novel application of automated microscopy as the reference method.Ultimately, PAT methods should link to product performance and the two key Critical Quality Attributes (CQAs) for this CR product are assay and release rate, linked to the API and CR coating steps respectively. In this work, the link between near infra-red (NIR) spectra and those attributes was explored by chemometrics over the course of the coating process in a pilot scale industrial environment. Correlations were built between the NIR spectra and coating weight (for API amount), CR coating thickness and dissolution performance. These correlations allow the coating process to be monitored at-line and so better control of the product performance in line with QbD requirements.

Formation and decomposition of C4F7 type calcium ferrites in superfluxed magnetite based pellets during oxidation and reduction

In the current work the reactions of magnetite based pellets with large additions of calcite (3%CaO) during reduction have been investigated. This made it possible to use both X-ray diffraction (XRD) and scanning electron microscopy (SEM) to detect reaction phases that normally occur in very small amounts. The main binding phase in the pellets after oxidation was (CaO,MgO,FeO)4(Fe2O3)7, whereas the one commonly reported in the literature is (CaO)(Fe2O3)2. During reduction at 500–700°C severe cracking occurred in these pellets, especially in the calcium ferrite phase. However, the decomposition of this phase began at 600°C, and therefore it is believed that the reason for the cracks is low strength of the phase itself, rather than weakness induced by reduction of the phase. Upon reduction of magnetite into wüstite at 800°C, the calcium began dissolving in the wüstite, and at 900°C porous calciowüstite had formed in the entire sample, except for some remaining magnetite left in the pellet cores.