Addition Of CaF2 Research Articles

INFLUENCE OF DIFFERENT CaF₂ CONTENTS AND HEAT TREATMENT TEMPERATURES ON APATITE-MULLITE GLASS CERAMICS DERIVED FROM WASTE MATERIALS

An apatite-mullite glass ceramics composition derived from clam shell (CS) and soda lime silicate (SLS) glass has been fabricated from a heat treatment process of composition [xCaF2·(45−x)SLS·15CS·20Al2O3·20P2O5], where x is 5, 10, 15 and 20 (wt. %). The result concluded that the Ca and Si elements were found in the CS and SLS glass respectively as a major weight composition, thereby promoting the use of waste materials in the manufacture of glass ceramic samples. Besides, the CaF2 addition lowers the glass transition temperature (Tg) and crystallisation temperature (Tc) of the glass composition. The density and percentage of the linear shrinkage of the samples differs with the addition of CaF2 and various heat treatment temperatures. For the structural properties’ analysis, the formation of fluorapatite with a needle-like microstructure and mullite phase was enhanced with a higher CaF2 content, while the growth of the anorthite phase was observed to occur at a higher heat treatment temperature. Generally, the addition of ahigh CaF2 content with the help of heat treatment in apatitemullite glass ceramics composition greatly promotes the crystallisation of the fluorapatite phase, which is crucial for denture glass ceramics.

Phase chemistry of Submerged Arc Welding (SAW) fluoride based slags

Phase chemical analysis of post-weld slags from Submerged Arc Welding (SAW) is applied to explain the chemical function of flux constituent compounds in the welding process. FactSage 6.4 calculations were used to aid in the interpretation of the phase chemical analyses. Five commercial agglomerated fluxes from two suppliers were used. These fluxes cover three types of fluoride based flux classes: Fluoride Basic flux, Aluminate Basic flux and Aluminate Rulile flux. Basic fluxes are based in the SiO2–Al2O3–MgO CaF2 system. The slag liquidus lowering effect of CaF2 is 19 °C/%CaF2 in the Fluoride Basic fluxes, and 4 °C/%CaF2 in the Aluminate Basic fluxes. The Aluminate Rutile flux is based in the SiO2–Al2O3–MgO–TiO2–MnO–CaF2 system. Little CaF2 addition is used in this flux since TiO2 addition lowers its liquidus temperature sufficiently. The level of CaF2 addition sets the quantity and chemistry of fluoride gas compounds formed. The main gas fluoride gas species expected to form in welding with the five fluxes are CaF2, MgF2, NaF, KF, NaAlF4, and AlF3. In addition, TiF3 is expected to form in welding with the Aluminate Rutile flux, indicating the importance of titanium oxidation state in fluoride gas formation.

Influence Mechanisms of Additives on Coal-based Reduction of Complex Refractory Iron Ore

ABSTRACT Additives play an important role in the recycling of complex refractory iron ore by coal-based reduction to improve the self-sufficiency rate of the ore. In this work, the influence mechanisms of CaF2, Na2CO3, and MgCO3 additives on the coal-based reduction of complex refractory iron ore were studied by x-ray diffraction, thermogravimetry and differential scanning calorimetry, scanning electron microscopy, and energy dispersive spectrometry. The results indicate the three additives could greatly improve the quality of reduction and magnetic separation products. A reduction product metallization degree 93.42%, iron grade 91.23%, and iron recovery 95.48% were obtained under conditions of CaF2 dosage 6%, reduction temperature 1225 °C, and reduction time 50 min. These results were 3.38%, 8.09%, and 0.39% higher, respectively, than could be obtained without additives. The CaF2, and the Na2O and MgO produced by the decomposition of Na2CO3 and MgCO3, could not only replace the FeO from (Mg,Fe)SiO4 and FeAl2O4, but also react with SiO2 and Al2O3 in ore to form their corresponding complex compounds. Moreover, all compounds were benefitted by the increase of the FeO content. The F− ion could replace the O2- ion in the silicon oxygen tetrahedron to reduce the viscosity and surface tension of reduced ore, thus reducing the resistance of iron particle aggregation and growth. In addition, the formation of a local micro melting phase under the action of additives could promote the diffusion of crystalline particles, which is more conducive to the reduction of iron minerals and the formation and growth of iron particles.

Phase analysis and microstructure study of sintered Ni-Cr composites containing MoS2, Ag and CaF2 additives as solid lubricants

Ni-Cr based composites with and without the addition of solid lubricants (MoS2, Ag and CaF2) were prepared by powder metallurgy method. The samples were sintered at different temperatures (1000oC, 1100oC and 1200oC) under controlled atmosphere and various holding times. The physical properties such as sintered density, relative density and porosity were studied. The microstructures and phase studies of the Ni-Cr based composites were conducted using Scanning Electron Microscope (SEM) and X-Ray Diffraction Analysis (XRD) while the hardness of the composites was measured by the Vickers Micro Hardness Tester. The results revealed that as the sintering temperature was increased, the sintered density, relative density and hardness also increased while the porosity was reduced. At the sintering temperature of 1200oC, the relative density reached its maximum value. SEM and XRD analysis confirmed the existence of MoS2 and Ag in sintered samples. MoS2 and Ag were not mainly dissolved and/or decomposed even after sintering at 1200oC

Effects of CaF2 on the sintering and crystallisation of CaO–MgO–Al2O3–SiO2 glass-ceramics

The effects of CaF2 (1–5 wt.%) on the glass structure, crystallisation behaviour, sinterability, microstructure, and properties of a CaO–MgO–Al2O3–SiO2 glass-ceramic system were investigated. The results show that the glass transition temperature, crystallisation peak temperature and the activation energy for crystallisation decreased with the addition of CaF2. The crystallisation of diopside was initiated at the particle boundaries and followed with progressive advancing towards the centre. The enhanced crystallisation for CaF2-containing samples was observed and is likely due to the depolymerisation of the glass structure. However, the enrichment of Ca–2F complexes resulted in fluorite phase precipitation at the crystallisation front of the diopside phase when the CaF2 addition exceeded 3 wt.%. The hindered viscous flow sintering from a lower crystallisation temperature led to a decline in the sintering shrinkage, the extent of which was proportional to the amount of added CaF2. Plastic deformation was observed along with the newly-formed amorphous phase as the sintering temperature approached the glass melting point, which benefits densification. The performance analysis reveals that the fabricated glass-ceramics with the proper addition of CaF2 exhibited significant improvements in its density and bending strength. Whereas, the Vickers hardness, water absorption and chemical resistance all decreased.

Crystallisation kinetics and structural stability of transparent CaF2 glass ceramics: Dependence of light transmittance on the amount of CaF2 added

The effect of CaF2 addition (15.4, 20.4, 27.4 and 35.4 wt%) on the crystallisation ability and preparation of transparent glass ceramics (TGCs) containing CaF2 nanocrystals was studied. It was found that samples with 15.4, 20.4, and 35.4 wt% CaF2 are crystallised with multiple crystal phases, making the TGCs opaque. Only when the amount of CaF2 added is increased to 27.4 wt%, TGCs with only CaF2 nanocrystals can be successfully prepared by heat treatment at 630 and 730 °C for 2 h. The crystallisation activation energy of the sample with 27.4 wt% CaF2 is 247.07 kJ mol−1, and the crystallisation energy barrier to be overcome corresponds to the formation of CaF2 nanocrystals rather than the formation of aluminosilicates, whose size and distribution easily make the glass opaque. Similarly, the FT-IR and XPS results indicate that as the amount of CaF2 added is increased to 27.4 wt%, the polymerisation degree of the sample is more suitable for the diffusion of calcium and fluorine atoms to form only CaF2 nanocrystals; therein, the corresponding mole fractions of the bridging oxygen (Oo), non-bridging oxygen (O−), and free oxygen (O2−) are approximately about 0.12, 0.77 and 0.11, respectively.

STRUCTURE AND TRIBOTECHNICAL PROPERTIES OF COMPOSITE ANTIFRICTION MATERIALS BASED ON R7M2F6 STEEL WASTE

Background. Development of the technological measures for creating new antifriction composite materials based on waste powders of steel P7M2F6 with solid lubricant CaF2, intended for operation at temperatures up to 600 °C, sliding speeds up to 1 m/s, loads up to 5.0 MPa in air.Objective. The purpose of the paper is to determine the features of structure formation and their influence on the properties of composite antifriction materials based on industrial grinding waste of steel P7M2F6 with solid lubricant CaF2 for operation at high temperature friction units in air.Methods. Methodology consisted of the development of the regeneration technological modes of the industrial grinding waste of steel P7M2F6, determination of technological manufacturing operations for new antifriction composites that include mixing of steel powders with solid lubricant, pressing and sintering of composites. The study of the structure formation processes and properties of materials was carried out using optical and electron microscopy methods, standard methods for determining mechanical properties and tests for friction and wear.Results. The influence of the developed manufacturing technology on the formation of the structure, physical mechanical and tribotechnical properties of materials based on steel P7M2F6 grinding waste with solid lubricant CaF2 additives was determined and grounded; resulting is the formation of complex heterogeneous antifriction material with high functional characteristics. The new material’s structure formation and its influence on the functional properties after using the developed manufacture modes was shown. Micro-X-ray spectral analysis confirmed the fact that CaF2, the contact pair’s chemical elements and oxygen form an antifriction film that provides a self-lubrication mode at the determined friction temperatures.Conclusions. The possibility of predicting the structure and functional properties of antifriction self-lubricating composite materials at high temperatures by purposeful choice of starting metal grinding wastes for certain operation conditions of contact pair was shown.

Experimental Study on Strengthening Carbothermic Reduction of Vanadium-Titanium-Magnetite by Adding CaF2

The effects and reduction mechanisms of carbothermic reduction of vanadium–titanium–magnetite were studied by adding various mass fractions of CaF2 ranging from 0%, 1%, 3%, 5% to 7%. The results showed that the proper CaF2 addition could strengthen the carbothermic reduction of vanadium–titanium–magnetite while the excessive amounts will weaken the promotive effect, hence the appropriate dosage was determined to be 3 mass%. The CaF2 was favorable for the carbon gasification reaction, where it increased the partial pressure of CO inside briquette and caused the lattice distortion of vanadium–titanium–magnetite. The reaction improved the reduction process and accelerated the reduction rate. The appearance of 3CaO·2SiO2·CaF2 and other complex compounds with low melting point facilitated the aggregation and growth of the slag and the iron, which increased the concentration of iron grains and the aggregation level of the slag.

Synthesis of blue‐emitting AlN:Eu2+ spherical phosphors by carbothermal reduction nitridation method

AbstractIn this study, blue‐emitting AlN:Eu2+ spherical phosphors were successfully synthesized for the first time by the carbothermal reduction nitridation (CRN) method, assisted with high nitrogen pressure, appropriate synthesis temperature, and the addition of CaF2. The influence of typical experimental parameters, such as N2 pressure, heating temperature, CaF2 content and Eu2+ concentration on the morphologies and luminescence properties of AlN phosphors were comprehensively investigated. The formation mechanism of spherical morphology were significantly proffered, indicating that sufficient liquid Ca‐aluminates during the AlN growth stage were essential for the spheroidization process under the action of surface tension. The synthesized AlN:Eu2+ spherical phosphors presented an intense blue emission band centered in the range of 427‐ 476 nm relative to the reaction temperature. The lifetime of AlN:Eu2+ phosphor was calculated to be around 1.89 μs. The temperature‐dependent PL spectra suggested that the emission band did not shift until 225°C. In addition, the spectral analysis strongly suggested that the luminescence property of AlN:Eu2+ phosphors was significantly enhanced by the large particle size, spherical morphology, reduced impurity content, and appropriate Eu2+ concentration.

Mechanism of CaF2 under Vacuum Carbothermal Conditions for Recovering Nickel, Iron, and Magnesium from Garnierite

Nickel laterite ore is divided into three layers and the garnierite examined in this study belongs to the third layer. Garnierite is characterized by high magnesium and silicon contents. The main contents of garnierite are silicates, and nickel, iron, and magnesium exist in silicates in the form of lattice exchange. Silicate minerals are difficult to destroy so are suitable for smelting using high-temperature pyrometallurgy. To solve the problem of the large amounts of slag produced and the inability to recycle the magnesium in the traditional pyrometallurgical process, we propose a vacuum carbothermal reduction and magnetic separation process to recover nickel, iron, and magnesium from garnierite, and the behavior of the additive CaF2 in the reduction process was investigated. Experiments were conducted under pressures ranging from 10 to 50 Pa with different proportions of CaF2 at different temperatures. The experimental data were obtained by various methods, such as thermogravimetry, differential scanning calorimetry, scanning electron microscopy, energy dispersive spectrometry, X-ray diffraction, and inductively coupled plasma atomic emission spectroscopy. The analysis results indicate that CaF2 directly reacted with Mg2SiO4, MgSiO3, Ni2SiO4, and Fe2SiO4, which were isolated from the bearing minerals, to produce low-melting-point compounds (FeF2, MgF2, NiF2, etc.) at 1315 and 1400 K. This promoted the conversion of the raw materials from a solid–solid reaction to a liquid–liquid reaction, accelerating the mass transfer and the heat transfer of Fe–Ni particles, and formed Si–Ni–Fe alloy particles with diameters of approximately of 20 mm. The smelting materials appeared stratified, hindering the reduction of magnesium. The results of the experiments indicate that at 1723 K, the molar ratio of ore/C was 1:1.2, the addition of CaF2 was 3%, the recovery of Fe and Ni reached 82.97% and 98.21% in the vacuum carbothermal reduction–magnetic separation process, respectively, and the enrichment ratios of Fe and Ni were maximized, reaching 3.18 and 9.35, respectively.

The effect of the addition of CaF2 and PbF2 on boro-tellurite glasses doped with chromium ions

This article presents the impact of CaF2 and PbF2 on boro-tellurite glasses, together with preparation of glass, primary experimental techniques, modern technology and progress, particularly the development of transition metal ion doped boro-tellurite glasses for optical glass related applications. Physical and structural investigations on chromium doped boro-tellurite glasses have been studied as a function of metal fluorides. Several physical and optical parameters have been obtained and their results are explained clearly. High density and refractive index values were observed for lead fluoride doped boro-tellurite glasses which are the essential properties of the materials for applications in fiber optical communication. Electron Paramagnetic Resonance (EPR) spectrum have shown two resonance signals at low and high field regions. FTIR spectra revealed that the B–O–B vibrations are due to various BO3 and BO4 units and Te–O vibrations are from different TeO3 and TeO4 units. Deconvoluted Raman spectra being used to locate the band positions in the spectra. Raman spectra confirmed that the presence of stretching vibrations of Te–O–B links, B–O links in BO4 units. The conversion of Te–O linkages to Te–F linkages by the addition of metal fluorides is observed from of Raman spectra.

Sintered glass-ceramics and foams by metallurgical slag with addition of CaF2

The possibilities for the production of self-glazed sintered glass-ceramics or/and glass-ceramic foams using metallurgical slag are discussed. The effect of CaF2 addition on the glass melting, the densification and the foaming is also studied.The sintering and the bloating trends are evaluated by hot stage microscopy and the phase formation is estimated by X-ray diffraction spectroscopy. The structure of the obtained samples is studied with scanning electron microscopy and with computed tomography.The results demonstrate a good sinter ability of the used glass powders in the interval 800–950 °C and a subsequent intensive bloating behaviour of the sintered samples in the range 1050–1150 °C.The addition of a certain amount of CaF2 in the glass batches leads to a noticeable decrease of both the melting and the sintering temperatures as well as to some increase of the crystallinity. As a result, self-glazed glass-ceramics with high percentage of CaF2 and with an improved micro-hardness and crystallinity can be obtained using finer glass powders, moderate heating rates and holding temperatures of 950–1000 °C.At the same time, glass-ceramic foams with closed porosity of about 80 vol % can be synthesized using glass powders with a modest addition of CaF2 by applying higher heating rates and holding temperatures of 1100–1150 °C.

Corrosion Behavior of Alumina Containing Refractory in Blast Furnace Hearth by CaO–SiO<sub>2</sub>–MgO–Al<sub>2</sub>O<sub>3</sub>–Cr<sub>2</sub>O<sub>3</sub> Slags

The corrosion behaviors of corundum brick and carbon composite brick used in blast furnace hearth by CaO-SiO2-MgO-Al2O3-Cr2O3(-CaF2) slags were studied in the present work. The degradation of the corundum brick in slag was a result of slag infiltration and brick dissolution, and the corrosion of the brick became more serious with the addition of CaF2 due to the decrease of slag viscosity. The disintegration of carbon composite brick in CaF2-containing slag was caused by the combination of slag penetration, brick dissolution and reaction between slag and brick. By comparing the corrosion behavior in CaF2-containing slag between the corundum brick and carbon composite brick, the corrosion degree of the corundum brick was greater than that of the carbon composite brick. To the blast furnace operation in which a low grade iron ore such as laterite ore and CaF2 containing slag (about 2 wt%) are used, it was found that the carbon composite brick with better slag corrosion resistance can be selected as a hearth refractory so as to improve the operation performance and ensure the longer campaign life of blast furnace.

Synthesis of CaF2 Nanoparticles Coated by SiO2 for Improved Al2O3/TiC Self-Lubricating Ceramic Composites.

In order to reduce the influence of CaF2 addition on the mechanical properties of self-lubricating ceramic tools, we applied a silicon dioxide (SiO2) coating on calcium fluoride (CaF2) nanoparticles through hydrolysis and condensation reactions using the tetraethoxysilane (TEOS) method. The powder was dried by the azeotropic method, so that it acquired a better dispersibility. The resulting composite powders were characterized using XRD (X-ray diffraction) and TEM (transmission electron microscopy), showing that the surface of CaF2 was coated with a layer of uniform and compact SiO2. SiO2 shells with different thicknesses could be obtained by changing the amount of TEOS added, and the thickness of the SiO2 shells could be controlled between 1.5 and 15 nm. At the same time, a ceramic material containing CaF2 nanoparticles and CaF2@SiO2-coated nanoparticles was prepared. It had the best mechanical properties when CaF2@SiO2-coated nanoparticles were added; its flexural strength, fracture toughness, and hardness were 562 ± 28 MPa, 5.51 ± 0.26 MPa·m1/2, and 15.26 ± 0.16 GPa, respectively. Compared with the ceramic tool containing CaF2 nanoparticles, these mechanical properties were increased by 17.57%, 12.67%, and 4.88%, respectively. The addition of CaF2@SiO2-coated nanoparticles greatly improved the antifriction and wear resistance of the ceramic material, and the antifriction and wear resistance were balanced.

Preparation of Ferrotitanium Using Ilmenite with Different Reduction Degrees

The effect of ilmenite with different reduction degrees on the production of ferrotitanium, using a self-propagation high-temperature synthesis method with aluminum as the reducing agent, was investigated. Increasing the degree of reduction not only contributed to lower consumption of aluminum, but also lowered the oxygen content and improved the grades of titanium and iron in the ferrotitanium. The aluminum content of the ferrotitanium increased with an increase in the extent of reduction of ilmenite, so the Al2O3 content formed in the slag decreased with the constant addition of CaO and CaF2 to the Al powder. This decreased relatively the content of high-melting-point CaAl12O19 and increased the contents of low-melting-point CaAl2O4 and CaF2 in the slag, thereby promoting the separation of ferrotitanium and slag. Improving the reduction degree of ilmenite is beneficial to the preparation of ferrotitanium.

Study on Phase Transformation and Desulfurization Ability during Refining with Flux Additions of B2O3 and CaF2 into CaO-Based Desulfurizer

CaF2 aids melting and desulfurization, but can also cause environmental pollution. Thus, it has become important to discuss the phase transformation and find a substitute for CaF2. A CaO-based desulfurizer with various flux additions of B2O3 and CaF2 is investigated during the refining process. The purpose of this study is to discuss the phase transformation and desulfurization ability and during refining with B2O3 and CaF2 using a high frequency furnace. Experimental results indicate that the melting temperature of CaO-Al2O3-SiO2 series desulfurizer becomes lower when more B2O3 and less CaF2 are added. On the other hand, the desulfurization ability can be affected within 15 min when various proportions of B2O3 and CaF2 areadded. The desulfurization ability is better with a high content of B2O3 desulfurizer within a 15 min period. However, the desulfurization ability is not affected by the proportion of B2O3 and CaF2 for a long melting period (30 min).

Enhanced energy-storage density in sodium-barium-niobate based glass-ceramics realized by doping CaF2 nucleating agent

The barium sodium niobate (BNN) glass-ceramics with different amount of CaF2 addition were fabricated by melting-crystallization method. Effects of CaF2 on microstructure, phase compositions, interface polarization, dielectric, energy-storage and charge–discharge properties of the BNN-glass-ceramics were comprehensively studied. Results indicate a suitable amount of CaF2 (from 1.0 to 3.0 mol%) is helpful to improve both relative permittivity and breakdown strength (BDS) of the BNN-glass-ceramics. The theoretical energy-storage density is up to 14.3 J/cm3 when the amount of CaF2 reaches 3.0 mol%. The optimal composition of 3.0 mol% CaF2 addition was further evaluated by a pulsed charged–discharged circuit and P–E hysteresis loops, from which we can conclude BNN-glass-ceramic is an excellent linear dielectric material. And the stored energy could be released within 50 ns and discharge power density reaches 75.6 MW/cm3. It’s for such results that the glass-ceremics with CaF2 addition are promising materials for pulse power applications.

Study on the effectiveness of WS2 and CaF2 on the performances of self-lubricating micro impregnated diamond bits

Self-lubricating micro impregnated diamond bits (IDBs) were manufactured for the first time via hot-pressing powder metallurgy to investigate the effectiveness of two promising solid lubricant additives, WS2 and CaF2, in improving IDBs' self-lubricating and drilling performances through laboratory drilling test and micro analyses. It was found that, with increase in lubricant concentration, the rate of penetration (ROP) of WS2 IDBs increased exponentially, while that of the CaF2 IDBs decreased monotonically from its maximum value at 6 vol% CaF2 concentration. For WS2 IDBs, the increase in ROP was at the sacrifice of substantial deterioration of IDBs' service life, while the service life of CaF2 IDBs gradually increased to surpass that of lubricant-free IDBs at 8 vol% CaF2 addition and continued to grow. Micro analyses, including measurement of diamond protrusion height and micro morphological analysis of IDBs' worn surface, were conducted using a confocal laser scanning microscopy (CLSM). The 10 vol% CaF2 IDBs were found under good protection from either matrix or diamond wear. By contrast, the surface of the 6 vol% WS2 IDBs suffered severe wear. Based on CLSM images, it was inferred that the high ROP and low service life of WS2 IDBs were a result of enhanced three-body abrasive wear by breakaway diamond grits. In general, self-lubricating IDBs with 10 vol% CaF2 addition acquired best overall performances in that they achieved longest service life while having higher ROP than lubricant-free IDBs.

Reducing Roasting of Hematite Laterite Nickel Ores with the Formation of Granulated Nickel-Containing Cast Iron

Abstract—The reducing roasting of hematite-type laterite nickel ores with flux CaCO3 (limestone) and CaF2 (fluorite) additions on a coal substrate in the temperature range 1350–1450°C, which causes the formation of granulated nickel-containing cast iron, is studied. The roasting time is 8–10 min without additional holding. The intense coalescence of metallic particles and the separation of metallic and slag phases is detected at 11–13% solid reducer (coke) in the presence of 7.5–12.5% CaCO3 and 1.5–2% CaF2 upon reducing roasting at a temperature of ≥1350°C. The yield of cast iron granules is 40–42.5% and the slag yield is 32–35% of the ore mass. 94–99% of iron and almost entire nickel are recovered into cast iron containing up 2.3% Ni and 2.1–2.5% C. The contents of the main components in the slag can change in the following ranges: 32–36% Al2O3, 17–24% CaO, 27–28% SiO2, and 2.5–3.5 Fetot. The slag can be used as a combined flux addition for the reducing roasting of magnesia–silicate nickel ores in rotary hearth furnaces with the formation of ferronickel ball (Krupp–Renn process), which makes the technology of processing of hematite ores wasteless and economically efficient.

Effects of Cr2O3 and CaF2 on the structure, crystal growth behavior, and properties of augite-based glass ceramics

Glass ceramics were synthetized using Cr2O3 and CaF2 as additives, and their structure, crystal growth behavior, and physicochemical properties were investigated. The results showed that an excessive amount of Cr2O3 leads to the formation of a spinel structure in the glass matrix and an increase in the number of Q3Si units. The addition of CaF2 promoted the decomposition of Q2Si into Q1Si and Q3Si. Compared with the sample with Cr2O3 alone, the addition of CaF2 helped reduce the glass transition and crystallization temperatures, forming sharper crystallization peaks. Although CaF2 increased the activation energy of crystallization, it increased the degree of crystallinity and Avrami parameter (2.019). In terms of the microstructure, the sample added with CaF2 formed a snowflake-like structure with a spinel core. An excessive amount of spinel reduced the strength of the samples. The samples (1.5Cr2O3-3.5CaF2) exhibited a maximum flexural strength of 149.85 MPa and a good chemical resistance.