Graphite Blend Research Articles

Stabilizing the Si/C blend anode by a multifunctional ternary composite binder

Si/C blend anodes hold great promise in commercialized high-energy-density (HED) Li-ion batteries but suffer from volumetric effects and electrode integrity deterioration. This study reports a ternary composite binder consisting of carboxymethyl cellulose (CMC), cationic polyacrylamide (CPAM), and styrene-butadiene rubber (SBR), which can significantly improve the cyclability of a Si@C/graphite blend anode. A high capacity retention of 92.9% after 100 cycles was achieved in a half cell. Moreover, the ternary binder proves suitable for a very high mass loading (4.9 mAh/g) electrode and is effective in a 2 Ah-level full cell, which delivers an excellent capacity retention of 80.6% after 500 cycles. The beneficial effects were ascribed to the multifunctional groups compatible with the surfaces of both Si and carbon, and the designed rigidness and elasticity which restricts and accommodates the volumetric effects of the Si/C blend anode simultaneously.

Understanding the Processability of Graphite Blend Electrodes with Silicon Nanoparticles

Li-ion batteries (LiBs) are one of the best solutions for energy storage due to their high capacity, high power, and cyclability1,2. The increasing need for energy storage to supply electric vehicles demands continuous innovation to optimize the LiBs, specifically the manufacturing parameters to fabricate these devices. The battery production requests improved materials, cell designs, greener manufacturing processes, and recycling3,4. For instance, developing an improved anode material could be a good approach for optimizing the LiB energy density. A blend of graphite and silicon is a promising negative electrode due to the combined stability of graphite with the high theoretical capacity of silicon5,6. Since adding silicon changes the manufacturing parameters already established for commercial graphite electrode fabrication, our goal is to understand the impact of the manufacturing process, such as the calendaring effect on the properties of the silicon/graphite blend electrodes. These electrodes were prepared with two different silicon percentages, 8%, and 15%, compared to pure graphite. We investigate the morphological changes, electrochemical aging, and tortuosity when decreasing the porosity from 55% to 30% for both electrodes to evidence the porosity threshold for obtaining adequate electrode properties. Manufacturing optimization is time and cost-consuming. Modeling approaches are an excellent choice to decrease LiB fabrication scraps. We are developing machine learning and physical models of the 3D silicon-graphite electrode fabrication process within our ARTISTIC project7, and these optimization results will help to validate them. S. Chu and A. Majumdar, Nature, 488, 294–303 (2012).J. B. Goodenough and K.-S. Park, J. Am. Chem. Soc., 135, 1167–1176 (2013).J. Li, J. Fleetwood, W. B. Hawley, and W. Kays, Chem. Rev., 122, 903–956 (2022).F. M. Zanotto et al., Batter. Supercaps, 5 (2022).M. T. McDowell, S. W. Lee, W. D. Nix, and Y. Cui, Adv. Mater., 25, 4966–4985 (2013).F. Jeschull et al., J. Electrochem. Soc., 167, 100535 (2020).C. Liu, O. Arcelus, T. Lombardo, H. Oularbi, and A. A. Franco, J. Power Sources, 512, 230486 (2021).

Impact of the manufacturing process on graphite blend electrodes with silicon nanoparticles for lithium-ion batteries

Correlating the input/output parameters of the manufacturing process aims to understand the link between the different steps of the Lithium-Ion Battery (LiB) electrode-making process. Fostering the interrelation of the properties in silicon/graphite blends for fabricating negative electrodes benefits the comprehension, quantification, and prediction of LiB output properties. Here, we report the impact of the manufacturing parameters during mixing, coating, and calendering on the properties of silicon/graphite blend negative electrodes. The mixing process was evaluated depending on the graphite content, where the viscosity increases with its percentage. Moreover, the slurry rheology directly impacts the electrode stability when the coating is done by using broader comma gaps. The calendering step evidences a porosity threshold necessary for adequate ionic resistance, tortuosity factor, and cycling life. Strong calendering increased the current collector adhesion, ionic resistance, tortuosity factor, and high cycling instability. On the other hand, better cyclabilities are obtained at moderate calendered electrodes, exhibiting the lowest ionic resistances and tortuosity factors.

Polyvinylidene fluoride‐poly(vinyl acetate)‐natural graphite blend nanocomposites: Investigations of electroactive phase formation, electrical, thermal, and wetting properties

AbstractSolution blended polyvinylidene fluoride (PVDF)‐20 wt% poly(vinyl acetate) (PVAc)‐natural graphite (NtGr) blend nanocomposites exhibit a very low electrical percolation threshold of less than 0.5 wt% NtGr due to the formation of graphite nanosheets. The electroactive gamma phase induced with and without NtGr in PVDF‐20 wt% PVAc blend film is confirmed by X‐ray diffraction, fourier transform infrared spectroscopy, and differential scanning calorimetry analyzes. The onset degradation temperature corresponding to PVDF in PVDF‐20 wt% PVAc blend nanocomposites is increased by 27°C when 1 wt% NtGr is incorporated into the blend, suggesting enhanced thermal stability of blend nanocomposites. Due to an increase in surface roughness of PVDF‐20 wt% PVAc‐3 wt% NtGr as evidence by field emission scanning electron microscopy analysis, the water contact angle increases to 141.6° from 83.44° for PVDF‐20 wt% PVAc blend. AC conductivity analysis suggests hopping conduction in PVDF‐20 wt% PVAc‐x wt% NtGr (x = 1, 3, 5) blend nanocomposites. The interjunction capacitance increases with graphite loading in the blend.

Screening of Lost Circulation Materials for Geothermal Applications: Experimental Study at High Temperature

Abstract This study presents a laboratory experimental research to determine the characteristics of lost circulation materials (LCMs) capable of addressing thermal degradation, providing bridging and sealing in geothermal conditions. Eleven different materials were tested: Walnut Fine, Walnut Medium, Sawdust, Altavert, Graphite Blend, Bentonite Chips, Micronized Cellulose (MICRO-C), Magma Fiber Fine, diatomaceous earth/amorphous silica powder (DEASP), Cotton Seed Hulls, and a Calcium Carbonate Blend. The filtration and sealing pressure of the LCMs were measured with HPHT equipment up to 149 °C (300 °F). Besides, the particle size distribution (PSD) of fine granular materials was measured. The results show that the performance of some LCM materials commonly used in geothermal operations is affected by high temperature. Characteristics such as shape and size made some materials more prone to thermal degradation. Also, it was found that the PSD of LCMs is a key factor in the effectiveness of bridging and sealing fractures. The results suggest that granular materials with a wide particle size distribution PSD are suitable for geothermal applications.

Microporous Graphite Composites of Tailorable Porosity, Surface Wettability, and Water Permeability for Fuel Cell Bipolar Plates

To address the water management problem in proton-exchange membrane fuel cells, porous graphite composites were prepared by incorporating sacrificial pore-forming agents in the blend of graphite and a phenolic resin formed into a flat plate using compression molding. Sucrose was found to be an effective porogen in the porous plate production process. The effects of relative amounts of graphite, polymer, and porogen in the composite were studied. Bipolar plate properties such as the water uptake by wicking and vacuum infusion, gas-breakthrough pressure across the water-infused pores, electrical conductivity, and flexural strength of the plates were measured and correlated with the plate composition. The plate porosity was evaluated by determining the masses of dry and water-infused plates in air and under water. The porosity, ε, showed a linear increase with an increase in the porogen concentration in the range of 0–10%. The permeabilities, K, of water through the graphite plates with different porosity values were calculated by measuring the water flux over a range of pressures. The water permeability increased with oxidation and hydrophilization of the pore surface. Dynamic water contact angle measurements were used to characterize the effect of chemical and thermal treatments on the water wettability of the plates. The gas-breakthrough pressure of the water-infused plates was found to be linearly correlated with the parameter, γcos⁡θ/K/ε, proportional to the capillary pressure of the gas–water interface of surface tension, γ, and contact angle, θ. Porous plates capable of a total water uptake greater than 25 wt %, with the gas-breakthrough pressure higher than 10 psi, through-plane electrical conductivity exceeding 100 S cm–1, and flexural strength exceeding 25 MPa were obtained.

Weakly Solvating Solution Enables Chemical Prelithiation of Graphite-SiOx Anodes for High-Energy Li-Ion Batteries.

Although often overlooked in anode research, the anode's initial Coulombic efficiency (ICE) is a crucial factor dictating the energy density of a practical Li-ion battery. For next-generation anodes, a blend of graphite and Si/SiOx represents the most practical way to balance capacity and cycle life, but its low ICE limits its commercial viability. Here, we develop a chemical prelithiation method to maximize the ICE of the blend anodes using a reductive Li-arene complex solution of regulated solvation power, which enables a full cell to exhibit a near-ideal energy density. To prevent structural degradation of the blend during prelithiation, we investigate a solvation rule to direct the Li+ intercalation mechanism. Combined spectroscopy and density functional theory calculations reveal that in weakly solvating solutions, where the Li+-anion interaction is enhanced, free solvated-ion formation is inhibited during Li+ desolvation, thereby mitigating solvated-ion intercalation into graphite and allowing stable prelithiation of the blend. Given the ideal ICE of the prelithiated blend anode, a full cell exhibits an energy density of 506 Wh kg-1 (98.6% of the ideal value), with a capacity retention after 250 cycles of 87.3%. This work highlights the promise of adopting chemical prelithiation for high-capacity anodes to achieve practical high-energy batteries.

Electromagnetic shielding material based on hydrogenated natural rubber/expanded graphite blend: Preparation and characterization

Expanded graphite (EG) and hydrogenated natural rubber (HNR) latexes with the hydrogenation conversion of 60 and 95 mol% (HNR60 and HNR95, respectively) were prepared according to our proposed procedure, and they were blended in the latex stage. The characterization of EG was determined through BET surface area determination, XRD, and SEM. The investigation of HNR/EG blends was carried out through the tensile property measurement, weather resistance determination, electromagnetic shielding efficiency measurement, and TEM observations. The SEM images and the angles of X‐ray diffraction of EG showed the significant expansion of the graphite and graphitic carbon structure with the interlayer spacing (d) of 3.357 Å. The EG was porous with 91.2146 m2/g of BET‐specific surface by N2 adsorption/desorption isotherms measurements. The highest tensile property, weather resistance, and electromagnetic shielding efficiency of HNR60 were achieved when the amount of dispersed EG was 10%. In contrast, those of HNR95 were achieved when the amount of dispersed EG was 12%. EG was found to be well dispersed in HNR95 than HNR60 as being verified through TEM and FIB‐SEM observations.

(Invited) Electrolyte Design for Li Batteries

Li metal, with the lowest thermodynamically achievable negative electrochemical potential and the highest specific capacity (3860 mAh g−1), is the ultimate anode choice for Li batteries. However, the highest reported Li plating/stripping Coulombic efficiency (CE) of 99.5% after extensive efforts is still too low for the Li metal-free (all the Li metal in cycling comes from cathode, without anode pre-lithiation) Li metal batteries. The low CE is attributed to both non-uniform Li plating/stripping on the lithiophobic Cu current collector and Li dendrite growth through lithiophilic organic-inorganic solid electrolyte interphase (SEI) formed in carbonate electrolytes. Here, we use a lithiophilic Bismuth graphite blend (Bi-Gr) substrate to replace lithiophobic Cu current collector to seed a uniform Li nucleation, and form a lithiophobic LiF-rich SEI rather than lithiophilic organic-inorganic SEI to suppress Li dendrite growth. Molecular dynamics simulations reveal the preferential reduction of anions in 2 M LiPF6 in tetrahydrofuran/2-methyl tetrahydrofuran (2.0 M LiPF6-mixTHF) electrolyte to generate LiF-rich SEI on plated Li. Bi-Gr substrate and 2.0 M LiPF6-mixTHF electrolyte enable the Li anodes to achieve a record high CE of 99.83% at a high capacity of 1.0 mAh cm−2 and current of 0.5 mA cm−2. The Bi particles serve as dispersed nucleation centers that promote uniform Li deposition with strong adhesion to the substrate to avoid dead Li, while the lithiophobic LiF-rich SEI promotes lateral Li growth and suppresses the vertical Li dendrite growth even at a high current density of 3.0 mA cm−2 and high areal capacities of 3.0 mAh cm−2. The regulation of Li nucleation and growth enables the Li metal-free LiFePO4 full cells to achieve 100 cycles at a practical areal capacity of >2.0 mAh cm−2. This manuscript highlights the benefits of simultaneous substrate design to improve Li nucleation and electrolyte design to promote lithiophobic SEI growth, enabling a promising and practical route Li metal-free Li metal batteries

Electrolyte design for Li metal-free Li batteries

Li metal, with the lowest thermodynamically achievable negative electrochemical potential and the highest specific capacity (3860 mAh g−1), is the ultimate anode choice for Li batteries. However, the highest reported Li plating/stripping Coulombic efficiency (CE) of 99.5% after extensive efforts is still too low for the Li metal-free (all the Li metal in cycling comes from cathode, without anode pre-lithiation) Li metal batteries. The low CE is attributed to both non-uniform Li plating/stripping on the lithiophobic Cu current collector and Li dendrite growth through lithiophilic organic–inorganic solid electrolyte interphase (SEI) formed in carbonate electrolytes. Here, we use a lithiophilic Bismuth graphite blend (Bi–Gr) substrate to replace lithiophobic Cu current collector to seed a uniform Li nucleation, and form a lithiophobic LiF-rich SEI rather than lithiophilic organic-rich SEI to suppress Li dendrite growth. Molecular dynamics simulations reveal the preferential reduction of anions in 2.0 M LiPF6 in tetrahydrofuran/2-methyl tetrahydrofuran (2.0 M LiPF6–mixTHF) electrolyte to generate LiF-rich SEI on plated Li. Bi–Gr substrate and 2.0 M LiPF6–mixTHF electrolyte enable the Li anodes to achieve a record high CE of 99.83% at a high capacity of 1.0 mAh cm−2 and current of 0.5 mA cm−2. The Bi particles serve as dispersed nucleation centers that promote uniform Li deposition with strong adhesion to the substrate to avoid dead Li, while the lithiophobic LiF-rich SEI promotes lateral Li growth and suppresses the vertical Li dendrite growth even at a high current density of 3.0 mA cm−2 and high areal capacities of 3.0 mAh cm−2. The regulation of Li nucleation and growth enables the Li metal-free LiFePO4 full cells to achieve 100 cycles at a practical areal capacity of >2.0 mAh cm−2. This manuscript highlights the benefits of simultaneous substrate design to improve Li nucleation and electrolyte design to promote lithiophobic SEI growth, enabling a promising and practical route Li metal-free Li metal batteries.

Environment-friendly novel fuel additives: Investigation of the effects of graphite nanoparticles on performance and regulated gaseous emissions of CI engine

Increased menacing engine emissions and threat to human health from metallic combustion catalysts demand a shift towards the application of non-metallic fuel additives. Therefore, the current study is an effort, conducted to introduce a new, less toxic and non-metallic graphite (G) nano diesel-fuel additive, by investigating its effects on the performance and regulated gaseous emissions of a four-cylinder, water-cooled, compression ignition (CI) engine. The experiments were also repeated with Iron oxide (Fe2O3) nanoparticles and statistical analyses were implemented to have a comparison with graphite nanoparticles. The G and Fe2O3 nanoparticles, in concentrations of 50, 100 and 150 mg per litre (mg/l), were mixed with neat diesel by magnetic stirring to prepare homogeneous fuel blends. The physicochemical properties of the fuel blends were determined. A maximum decrease of 4.9% in viscosity and an increase of 3.26% in Cetane index was observed for graphite blends. The investigated parameters include torque (T), brake power (BP), brake specific fuel consumption (bsfc), brake thermal efficiency (BTE), carbon monoxide (CO) and nitrogen oxides (NOx) emissions at engine speed varying from 1500 to 3000 rpm with an interval of 300 rpm at full load. The results revealed that at a confidence level of 95% (significance level α = 0.05), G-blends indicated a higher increase in torque, power, BTE and a greater decrease in bsfc than Fe2O3 blends. Graphite blends produced significantly lower NOx emissions than Fe2O3 treated blends. The increase in T, BP and BTE was 2.4%, 8.9% and 3.9% respectively, with 150 mg/l Fe2O3 blends and 2.9%, 9.6% and 4.1% respectively, with 150 mg/l G-blends. Graphite blends resulted in a 2.6% reduction in bsfc. The increase in NOx emissions was 34.7% with Fe2O3 and 29.2% with G at concentrations of 150 mg/l. The CO increased by 14.2% with G blends. A negative statistical correlation was observed for CO emissions between G and Fe2O3 blends. We conclude that G nanoparticles are more environmentally friendly fuel additives than Fe2O3; however, their application is more recommended for large turbocharged CI engines with improved oxygen density in inlet compressed air.

Towards 3D-lithium ion microbatteries based on silicon/graphite blend anodes using a dispenser printing technique.

In this work we present for the first time high capacity silicon/carbon–graphite blend slurries designed for application in 3D-printed lithium ion microbatteries (3D-MLIBs). The correlation between electrochemical and rheological properties of the corresponding slurries was systematically investigated with the prospect of production by an automated dispensing process. A variation of the binder content (carboxymethyl cellulose/styrene–butadiene rubber, CMC/SBR) between 6 wt%, 12 wt%, 18 wt% and 24 wt% in the anode slurry proved to be crucial for the printing process. Regarding the rheological properties increasing binder content leads to increased viscosity and yield stress values promising printed structures with high aspect ratios. Consequently, interdigital 3D-printed micro anode structures with increasing aspect ratios were printed with increasing binder content. For printed 6-layer structures aspect ratios of 6.5 were achieved with anode slurries containing 24 wt% binder. Electrochemical results from planar coin cell measurements showed that anodes containing 12 wt% CMC/SBR binder content exhibited stable cycling at the highest charge capacities of 484 mA h g−1 at a current rate of C/4. Furthermore, at 4C the cells showed high capacity retention of 89% compared to cycling at C/4. Based on this study and the given material formulation we recommend 18 wt% CMC/SBR as the best trade-off between electrochemical and rheological properties for future work with fully 3D-printed MLIBs.

Novel Recycling to Transform Automotive Waste Glass and Plastics into SiC-Bearing Resource by Silica Reduction

A significant amount of end-of-life plastics and glass are currently landfilled, incinerated, or just illegally dumped even though conventional plastic and glass recycling practices are well established. This paper describes a novel approach to synthesize silicon carbide (SiC)-bearing product by utilizing waste automotive glass and plastic. The reduction of silica in glass by blend of graphite and plastic (Bakelite) to produce SiC was established experimentally under inert condition at a temperature 1,550 °C. The results from X-ray diffraction, scanning electron microscopy, energy dispersive X-ray spectroscopy EDS confirm the formation of SiC, and the reaction kinetics and the mechanism of reduction were investigated by means of infrared gas analyzer. Rate constant, k = 12.8 × 10−4 s−1, for the initial stage was measured for overall silica reduction, and the mechanism was established to be predominantly controlled by chemical reactions. This process innovation has two significant advantages: it is a major step toward transforming nonmetallic automotive waste into valuable resources like SiC-containing refractory materials, and it reduces the industry’s reliance on conventional raw materials including quartz and coke which are typically used as silicon and carbon bearing resources.

Effect of composition, sonication and pressure on the rate capability of 5 V-LiNi0.5Mn1.5O4 composite cathodes

Positive composite electrodes having LiNi0.5Mn1.5O4 spinel as active material, a blend of graphite and carbon black for increasing the electrode electrical conductivity and either polyvinyldenefluoride (PVDF) or a blend of PVDF with a small amount of Teflon® (1wt%) for building up the electrode. They have been processed by tape casting on an aluminum foil as current collector using the doctor blade technique. Additionally, the component blends were either sonicated or not, and the processed electrodes were compacted or not under subsequent cold pressing. Composites electrodes with high weight, up to 17mg/cm2, were prepared and studied as positive electrodes for lithium-ion batteries. The addition of Teflon® and the application of the sonication treatment lead to uniform electrodes that are well-adhered to the aluminum foil. Both parameters contribute to improve the capacity drained at high rates (5C). Additional compaction of the electrode/aluminum assemblies remarkably enhances the electrode rate capabilities. At 5C rate, remarkable capacity retentions between 80% and 90% are found for electrodes with weights in the range 3–17mg/cm2, having Teflon® in their formulation, prepared after sonication of their component blends and compacted under 2tonnes/cm2.

Preparation and thermal properties of polyethylene glycol/expanded graphite blends for energy storage

Expanded graphite is a promising heat transfer promoter due to its high conductivity, which improves the thermal conductivity of organic phase change materials. Moreover, it can also serve as supporting materials to keep the shape of the blends stable during the phase transition. After various investigation, the results showed that the maximum weight percentage of polyethylene glycol was as high as 90% in this paper without any leakage during the melting period, with the latent heat of 161.2 J g −1 and the melting point of 61.46 °C. It was found that the value of the latent heat was related to the polyethylene glycol portion, increased with the increase in polyethylene glycol content. Moreover, the measured enthalpy of the composite phase change materials was proportional to the mass ratio of the polyethylene glycol component. The melting temperatures were almost the same with different ratios of composites. The conductivity of blends was improved significantly with the high value of 1.324 W m −1 K −1 compared to the pure polyethylene glycol conductivity of 0.2985 W m −1 K −1.

Effect of carbon materials on the graphite-diamond phase transition at high pressures and temperatures

Experimental data are used in an attempt to unravel the mechanism underlying the effect of modification of a graphite blend by fullerenes on the diamond synthesis at high pressures and temperatures in the presence of metal catalysts. Diamonds have been synthesized under different conditions in a wide range of temperatures and at different pressures, and the effects of blend modification by fullerenes and by addition of natural microcrystalline diamonds to a blend on the diamond synthesis at high pressures and temperatures have been compared.

Comparison of solid oxide fuel cell anode coatings prepared from different feedstock powders by atmospheric plasma spray method

Atmospheric plasma spray (APS) deposition of a high-performance anode coating, which is essential for obtaining high power density from a solid oxide fuel cell (SOFC), is developed. A conventional, micron-sized, nickel-coated graphite – yttria stabilized zirconia (YSZ) – graphite blend feedstock leads to a non-uniform layered coating microstructure due to the difference in the physical and thermo-physical properties of the components. In this research, new types of feedstock material received from a spray-drying method, which includes nano-components of NiO and YSZ (300 nm), are used. The microstructure and mechanical properties of a coating containing a nano composite that is prepared from spray-dried powders are evaluated and compared with those of a coating prepared from blended powder feedstock. The coating microstructures are characterized for uniformity, mechanical properties and electrical conductivity. The coatings prepared from spray-dried powders are better as they provide larger three-phase boundaries for hydrogen oxidation and are expected to have lower polarization losses in SOFC anode applications than those of coatings prepared from blended feedstock.

Electronic Conductive Microporous Polymer‐Based Structures

AbstractSummary: This study aims at developing a highly electronic conductive microporous structure from thermoplastic polymers filled with carbon black (CB) and graphite (GR). The matrix was a low viscosity poly(propylene) (PP) and the conductive additives were composed of high specific surface area CB and synthetic flake GR. Conductive blends were first developed using a corotating twin‐screw extruder. Rheological properties and conductivities of these blends were then characterized as a function of blend composition. Blends that show the best compromise between electronic conductivity and processability were subsequently extruded through a sheet die to obtain films of around 500 µm in thickness. These films were then stretched in two successive steps under controlled temperature and stretching rate to generate a film of controlled microporous structure.TEM of film made from a 50 wt.‐% PP/25 wt.‐% CB/25 wt.‐% GR blend after stretching.magnified imageTEM of film made from a 50 wt.‐% PP/25 wt.‐% CB/25 wt.‐% GR blend after stretching.

On the Behaviour of Hematite and Graphite Blend during Ball Milling and Heating Up Reduction of Milled Mixture

The effect of ball milling under argon and air atmospheres on the reaction behaviour of the mixture of sintered hematite and graphite was investigated. Thermo‐gravimetry / differential thermal analysis (TG‐DTA) was adopted to determine the effect of milling time on the reduction process during heating up under Ar atmosphere. The samples were heated at a constant heating rate of 10 °C/min from room temperature up to 1100 °C and maintained at this temperature for 30 minutes.TGL (thermo‐gravimetry loss) curves showed a decrease of onset temperature of reduction with increase of milling time. XRD patterns of milled samples at room temperature revealed that the peaks of graphite disappeared after 48 hours milling. This represents the transformation of crystalline structure of graphite to the amorphous structure. By increasing the milling time to 72 hours, magnetite peaks appeared in the XRD pattern as a result of reduction of hematite with graphite during milling. However, the amount of magnetite formed during milling process increased as milling proceeded. The powders milled under Ar atmosphere became more active than the powders milled under air and consequently the carbothermic reduction of hematite in powders milled under Ar atmosphere was observed at lower temperatures compared with air‐milled powders. It was observed that the reduction time of hematite in powder mixture was decreased with increase of sintering time of hematite prior to milling.