Powder Heat Research Articles

Development of an electric arc furnace steel slag-based ceramic material for high temperature thermal energy storage applications

This paper details the development process of ceramics made out of 100% electric arc furnace (EAF) steel slag, to be used as a shaped homogenous thermal energy storage (TES) media in packed-bed thermocline systems for high-temperatures industrial waste heat recovery, concentrated solar power (CSP), and Carnot batteries applications, among others. The main objective of this study was to investigate the influence of different process parameters on the properties of the resulting ceramics. The samples have been characterized in terms of bulk density, apparent solid density, and water absorption to identify the best values for different process parameter. The best properties were obtained for samples prepared with heat-treated slag powders, pressed at 300 MPa and fired at 1300 °C for 8 h under a static air atmosphere. The optimal bulk density was 3.1 g/cm3, and the water absorption was 1.2%wt. The measured specific heat capacity was 1026, 1181 and 1216 J/(kg.K) at 200, 400 and 600 °C, respectively, while the thermal conductivity values were 1.53, 1.50 and 1.37 W/(m.K) at the same temperatures. This work confirms the feasibility of manufacturing TES ceramics out of EAF steel slags, using equipment and techniques well-known in the refractory industry.

Role of heat treatment of hydroxyapatite powder prior to suspension preparation on the suspension flow behavior

One of the key issues involved in successfully achieving hydroxyapatite (HA) ceramic body without defects using colloidal processing technique, is the preparation of homogeneously high solid loading HA ceramic suspension. This could be achieved via controlling the HA powder properties. The maximum achievable solid loading suspension from the as received HA powder was found to be 14 vol%. The treatment of the as received powder via heat treatment process play a very versatile role in changing the physical properties of the powder. Owing to these changes, well dispersed high solid loading HA suspensions reaching 57 and 59 vol% were successfully prepared from HA powder heat-treated at 1000 and 1100 °C, respectively. The suspensions prepared from the heat-treated powder was found to have acceptable rheological properties for casting processes in terms of low particle interaction, lower number of floc and floc network and higher fluidity.

Effect of Microwave Heat Processing on Nutritional Indices, Antinutrients, and Sensory Attributes of Potato Powder-Supplemented Flatbread

This study aims at evaluating nutritional, toxicological, and sensory attributes of microwave heat-treated potato powder-supplemented unleavened flatbread. Straight-grade wheat flour (SGF) was substituted with potato powder at the rate of 2.5–10% d.w. A comparison was made for nutritional, antinutrient, and organoleptic attributes of microwave heat-treated potato powder and SGF—potato powder composite flour-based flatbreads. The results suggest processed potato powder supplementation in SGF to significantly ( p < 0.05 ) improve ash (0.48 to 0.63 g/100 g), dietary fiber (2.15 to 2.61 g/100 g), and protein (8.33 to 9.91 g/100 g) contents of composite chapatis. Likewise, significant ( p < 0.05 ) improvement in the concentration of microelements and trace elements was observed including Ca, Na, K, Fe, and Zn contents, which were increased from 29.7 to 33.5 mg/100 g, 2.8 to 6.3 mg/100 g, 376 to 466 mg/100 g, 3.1 to 3.4 mg/100 g, and 3.17 to 3.25 mg/100 g, respectively. Microwave heating of potato powder was observed to reduce the load of alkaloids, oxalates, tannins, and phytates of the raw potato powder at the rate of 76%, 80%, 84%, and 82%, respectively, thus anticipating a promising response to minimize toxicant load in supplemented flatbread. Supplementing potato powder in SGF elucidated significant ( p < 0.05 ) improvement in color values, i.e., a∗ (1.89–2.32) and b∗ (10.95–13.22), and increased product hardness from 3.17 to 7.9 N. The study concludes that microwave heat-treated potato powder yield improved nutritional and safety concerns of the consumers when used alone or as a supplement for developing composite flours based on value-added products.

Powder HIP of pure Nb and C-103 alloy: The influence of powder characteristics on mechanical properties

In this work, pure Nb processed by Powder Metallurgy Hot Isostatic Pressing (PM HIP) was investigated as a potential alternative to C-103 Nb-based alloy for the manufacture of near-net-shape thruster combustion chambers. Three Nb powders with varied particle size range (fine, mid-range and coarse) and C-103 powder were investigated to understand the differences in particle size distribution (PSD), morphology and oxygen (O) content present in the alloy chemistry. The as-HIPed microstructures of pure Nb and C-103 are characterised by a near to fully dense microstructure and the absence of PPBs. Microstructural analyses performed on pure Nb highlighted the influence of particle size on the average as-HIPed grain size. Additionally, it was observed that O content plays a crucial role in the microhardness of pure Nb. Tensile tests performed on Nb mid-range and on Nb mid-range sieved showed that a simple sieve operation was effective in increasing the strength of the material while maintaining good levels of elongation. Alternatively, it was also demonstrated that pure Nb powder heat treatment can be regarded as an effective way to increase the O levels in pure Nb powders as witnessed by the high hardness levels. On the other hand, as-HIPed C-103 powder showed superior tensile properties if compared to the minimum specifications for wrought C-103. Finally, to summarise, the work performed on pure Nb, a simple structure-property relation model was developed to predict the YS of pure Nb based on the O levels and grain size of the as-HIPed microstructure.

On some Aspects of the Refinement of the Temperature Distribution in the Developed Software Toolkit for Modeling Powder Heating by a Laser

Nowadays, the use of additive manufacturing is gaining popularity. The cost of product manufacturing with additive manufacturing (AM) in large-scale production is usually higher than the traditional technologies (for example, casting, milling), therefore AM is often used for prototyping and small-scale production. The paper presents results of powder heating by a laser beam modeling, powder melting modeling, and area-bath melt formation. The presented results are part of the work of solver development for modeling the selective laser melting (SLM) process. SLM technology makes it possible to manufacture a product with a complex shape in a fairly short time. As a material SLM provides for the use of powder metals and alloys, including titanium, aluminum, stain­less steel. In this case, the shape of the manufactured parts is often prone to deformations and cracks. The reason for the deformation is the presence of inherited stresses due to cyclic uneven heating and cooling, arising during layer-by-layer melting of powder particles. To solve this problem, it was decided to develop a software tool that would analyze the manufacturing process and correct it, reducing the occurrence of residual stresses. The article presents the results of modeling and calculating the geometric size of the melt pool in a dynamic setting. A comparison is made between the results obtained in the course of this work and the results of expe­riments. Modeling the selective fusion process entails high computational costs. The article presents a method based on mesh adaptation, which allows to reduce the computational costs of modeling. The analysis of the effectiveness of this method is carried out.

Electronic structure and physical properties of EuAuAs single crystal

High-quality single crystals of EuAuAs were studied by means of powder x-ray diffraction, magnetization, magnetic susceptibility, heat capacity, electrical resistivity and magnetoresistance measurements. The compound crystallizes with a hexagonal structure of the ZrSiBe type (space group $P6_3/mmc$). It orders antiferromagnetically below 6 K due to the magnetic moments of divalent Eu ions. The electrical resistivity exhibits metallic behavior down to 40 K, followed by a sharp increase at low temperatures. The magnetotransport isotherms show a distinct metamagnetic-like transition in concert with the magnetization data. The antiferromagnetic ground state in \mbox{EuAuAs} was corroborated in the \textit{ab initio} electronic band structure calculations. Most remarkably, the calculations revealed the presence of nodal line without spin-orbit coupling and Dirac point with inclusion of spin-orbit coupling. The \textit{Z}$_2$ invariants under the effective time reversal and inversion symmetries make this system nontrivial topological material. Our findings, combined with experimental analysis, makes EuAuAs a plausible candidate for an antiferromagnetic topological nodal-line semimetal.

Development of spinel magnesium aluminate by modified solid state process and its characterization

Spinel magnesium aluminate synthesis by modified solid state process using AR grade oxide precursors in stoichometric (1:1) ratio was used after mild activation carried by agate-mortar pestle in dry condition. Thermal analyses were carried off for the mixed activated powder to determine the zone for phase formation (spinelization) which plays a pivotal role for annealing temperature selection. Followed by phase transition studied from thermal analyses, heat treatment of powders (annealing/sintering) in air was carried at various temperatures of 900˚C, 1050˚C and 1150˚C for variable durations. Phase development was confirmed after XRD analyses while FTIR determine the bonding of compound as well as required M−O coordinations for the required phase formation. Morphological analyses of annealed powders by SEM, FESEM represent dense agglomerates with fine particulates of spherical to hexagonal shape, irregular polygon with negligible interconnected porosity. Electronic transition of the compound developed was studied by UV–VIS followed by band gap estimation using Tauc relation. Band gap of the compound evolved was noted to be varying with temperature and soaking period.

Self-ignition temperature of the dust accumulations for sunflower and wood powders

Spontaneous combustion is a phenomenon that results from the heating of combustible organic powders by slow oxidation and which occurs through the air passage (created by an air depression) through the mass of dust. The oxidation phenomenon of combustible powders represents their reaction with atmospheric oxygen resulting in products of carbon dioxide, carbon oxide, water and other gases whose content depends on the temperature at which the oxidation takes place. The self-ignition of combustible dusts depends on their chemical composition, the properties of component substances, on the particle size and geometry of the material mass and, last but not least, on the temperature of the environment. Due to global worries of sustainability in construction engineering the trend is to use ecofriendly organic waste to various purposes as in construction materials. The challenge is that by using this kind of materials one should ensure the safety related to the process of such organic materials which are known to have combustible properties. The purpose of this work is to present the self-ignition behavior of combustible dusts such as sunflower and wood by means of drying tests under constant temperature conditions.

Effective Utilization of Textile Industry Waste in Mortar: Experimental Investigation of Heat-Treated Waste-Derived Pumice Powder in Mortar

Effective Utilization of Textile Industry Waste in Mortar: Experimental Investigation of Heat-Treated Waste-Derived Pumice Powder in Mortar

Characterization of opportunity for upgrading of the system based on arc plasma torch for thermal spaying of ceramic materials, by means of use of fuel vortex intensifier. Part I: Thermodynamic modeling of the system efficiency parameters

One of the main trends in the field of improving the modern technologies of thermal spraying, including plasma one, for functional ceramic coatings formation is the reducing the energy consumption of the process. In this regard, one of the important directions for improving these technologies is the development of their new versions, using the principle of adding inexpensive fuel-oxidizer mixtures based on hydrocarbons with air. This type of plasma-fuel type of spraying will be promising for application at the present time, first of all, in order to obtain refractory functional coatings. For this purpose, we investigated the opportunity for upgrading an industrial unit/system for plasma spraying of ceramic powder materials with arc plasma torch of 25–40 kW power by the use of experimental variant of a fuel gas-vortex intensifier. The thermodynamic assessment of possible parameters of the generated mixed flow after the torch with this fuel intensifier was carried out to estimate the applicability of this system to optimize the spraying of oxide and carbide coatings (based on the examples of Al2O3, Cr3C2 and other powders). The analysis of possible parameters of the produced flow after the torch with intensifier was performed for the cases of main C–H–O–N–Ar–Me (Me = Al, Cr) systems and additional C–H–O–Al-system to assess the potential of this system to modify the technology of oxide and carbide ceramic coatings formation. New regimes, which were analyzed in our research as the simulants of Al2O3 spraying, surpass on calculated energy efficiency characteristics (by 10–20 %) one of the new prospective spraying methods with (СO2+СH4)-plasma, as well as the conventional method of powder heating during the spraying with N2-plasma. The case of our proposed fuel assisted process (FA-APS) with liquefied petroleum gas (LPG) fuel for the heating of ceramic powders (especially, Al2O3) demonstrates the advantage of the process (in particular, on the energy efficiencies and energy consumption) in a comparison with the conventional regimes of APS of the powders (in N2 plasma of the standard torch). For the variants of the FA-APS with Al2O3 and Cr3C2 feedstock powders it was established to be potentially possible to obtain (at the moderate values of total electric energy consumption for the torch and auxiliary equipment, – near 1.8 and 1.0 kWh/(kg of product)) such high level of the process productivity on the final product as approximately 17 and 28 kg/h, respectively; at the values of required power of the torch:  28.2 and  22.3 kW.

Influence of Powder Heat Treatment on the Microstructure and Mechanical Properties of Cold Sprayed Ti-6Al-4V Coatings

Influence of Powder Heat Treatment on the Microstructure and Mechanical Properties of Cold Sprayed Ti-6Al-4V Coatings

Engineering of strong and hard in-situ Al-Al3Ti nanocomposite via high-energy ball milling and spark plasma sintering

Light-weight Al-Ti nanocomposites attract increasing attention due to the advancements in spacecraft and additive manufacturing. In this work, ab initio modeling, DSC, and in-situ XRD experiments were used to formulate a strategy for rapid fabrication of Al-Al3Ti nanocomposites with enhanced mechanical properties (ultimate tensile strength up to 437 MPa at room temperature and up to 109 MPa at 500 °С, ~6% elongation before failure), resulting from a mixed ductile-fragile deformation behavior. The investigated samples were produced by spark plasma sintering of high-energy ball-milled reactive composites Al-TiH2 leading to the precipitation of 0.05–0.25 µm Al3Ti particles from the nanostructured Al matrix. Samples with coarser TiH2 powder or higher TiH2 content featured a minor amount of transitional core-shell structures resulting from the incomplete conversion of the as-formed Ti particles into Al3Ti. The following phase and structure formation mechanism upon the heating of the reactive nanocomposite powders was proposed: Al+δ­TiH2→~450−500°СAl[Ti]+β­Ti[Al]+δ­TiH2−x→~550−600°СAl+Al3Ti. Tentative guidelines for the sintering of Al-TiH2 composites were proposed based on the analysis of diffusion kinetics.

Novel sustainable metallic powder production process with water used as milling medium.

Today, Fe–Al intermetallic compounds are receiving a great interest from the mechanical, aerospace, and biomedical industries. A novel production process for Fe–Al intermetallic powders based on the generation of metallic tapes by rapid solidification and disintegration by water vapor was proposed. In this research work, a comparison is made between the energy required to manufacture of Fe–Al powder using the aforementioned process and one of the most commonly used manufacturing processes within the industry such as mechanical alloying. In addition, some other benefits of the proposed manufacturing process are analyzed. To carry out this comparison, the theoretical equations that take into account the most important variables involved during the process such as the type of material and hardness, the initial and final particle size, the grinding stages and the heating of the treatment powder were considered. In the case of calculating the energy required for the new proposed process, the two main stages were considered such as (1) the production of FeAl metal tape and (2) the subsequent transformation of the tape into powder by means of injection water vapor. For the first stage, the CASTRIP process is considered, and for the second stage, the energy required for the generation steam. Although the calculations may have certain limitations, it is obvious that the energy required to Fe–Al powder production using the new process is much lower than that required by mechanical alloying, resulting in at least three orders of magnitude lower (2.75 × 106 versus 2.206 × 109 kJ/ton). This lower energy implies considerable economic savings in the production process. On the other hand, when using water as a grinding medium during the process, it results in less environmental and acoustic pollution, less manipulation risks for humans and finally, no harmful agents or additives are used, making the proposed process sustainable.Graphic abstract

Influence of calcination temperature in synthesizing eggshell-derived calcium phosphate

Hydroxyapatite (HA) has been used in the biomedical field not only due to its structural resemblance to the natural bone but also for its being bioactive and thermodynamically stable in the body fluid. Generally, the synthesis of HA particles through various available methods has been directed in controlling the growth of HA particles size as this characteristic has an implicit effect on the mechanical properties, biocompatibility and biological activity of HA in the application. Raw materials for the synthesis of HA can be obtained from commercial chemicals and natural sources. Natural source, particularly eggshell has been favoured due to the presence of other elements inherent in the eggshell that induced better cell response. In this study, a direct solid-state method was used to synthesize HA powder utilizing a Ca source in carbonated form from calcined discarded eggshells. The milled mixture of calcined eggshell powder and phosphorus precursor was subjected to heat treatment at various temperatures in studying the influence of different calcination temperatures on the HA phase stability, particle size and morphology through X-Ray Diffractometer and Scanning Electron Microscope analysis. Overall, HA powder consisted of flower-like particles was successfully obtained from eggshell through the combination of dry powder mixing and heat treatment at 800 °C.

Modelling and simulation of densification and σ-phase precipitation in PM duplex steel AISI 318LN during hot isostatic pressing

Following the development of hot isostatic pressing (HIP) with integrated rapid cooling technology, it is now possible to combine consolidation of encapsulated powder and subsequent heat treatment in a single process step in a pressure vessel. Using this technology, a near-net-shape product with target microstructure can be achieved. However, qualified final products still require traditional expensive and time-consuming trial-and-error tests. To eliminate these costly trial-and-error tests and achieve the required final properties of the products, it is urged to develop a combined numerical model to precisely predict the geometrical changes of the component during the HIP process and the evolution of significant microstructural features. This is realised in this work exemplarily by using duplex stainless steel AISI 318LN. This steel was selected due to requirements coming from applications regarding precise complex shaped near-net-shape components combined with high strength and toughness by avoiding brittle σ-phase precipitation. In this study, an existing finite element model for the densification in the HIP process was supplemented by a model for σ-phase precipitation kinetics based on microscopical characterisation. Moreover, the temperature dependent heat transfer coefficient (HTC) was implemented in the developed model to simulate the evolution and the distribution of the σ-phase during cooling. The numerically simulated final component dimensions and σ-phase volume fractions were verified by comparing with experimental data obtained from specimens and components of various shapes produced by both conventional HIP process and HIP with integrated rapid cooling. The high consistency between experimental and numerical results validates the accuracy of the developed simulation approach.

Thermodynamic Estimation of the Parameters for the C–H–O–N–Me-Systems as Operating Fluid Simulants for New Processes of Powder Thermal Spraying and Spheroidizing

Over the past few years, a group of new processes was developed for high-temperature, including plasma electric arc spraying (at ambient pressure) and spheroidizing of some ceramic and metal powder materials with the use of gaseous hydrocarbons in the heat carriers as well as with feeding of organic additions into a high-temperature jet, in particular, polymeric ones, to control porosity of sprayed metallic functional coatings. The paper considers the possibility to modify such technological processes by introducing solid fuel additions of a polymer type into the operating fluid of an apparatus for gasthermal (plasma or other) treatment, which provides melting of metal or oxide powders. For this, with the help of thermodynamic analysis, the processes have been evaluated at temperatures (300–3000) K for the set of such reacting five component systems as C–H–O–N–Me (at ambient pressure 0.101 MPa) with five variants of Ме – aluminum, titanium, chrome, copper, nickel. This makes it possible to consider these systems as simulants for potential technologies for the treatment of oxide powders (Al2O3, TiO2, Cr2O3) as well as metallic ones (Cu, Ni and their alloys). In order to obtain high exothermic contribution to the heating of powders, the combination “air + polymeric addition (polyethylene) of LDPE grade” was chosen as mixed heat carrier (operating fluid) for the basic version of simulated process. During the analysis of equilibria for the considered multicomponent systems (17 variants), a set of following parameters has been used to characterize the energy intensity of the target powder heating process: the equivalence ratio for reacting mixture and its adiabatic temperature; the energy efficiency of material heating with and without taking into account the effect of fuel addition; specific energy consumption for the powder melting; autothermicity degree of the process during the combined heating (electrothermal heating by the arc of plasma torch and heat flux from the “air + solid fuel additions” mixture) of refractory powders. As a result of the assessment, the preferred (from thermodynamic standpoint) regimes of the considered processes have been found and the possibility to realize an energy-efficient heating of these oxide and metal materials (without oxidation of the latter to CuOx, NiO) with a reduced part of the electric channel of energy transfer, resulted from the carrying out of appreciable effect of the fuel-initiated mechanism of heating in the analyzed C–H–O–N–Mesystems, has been shown in the paper.

Heat treatment of 3D printed polyethylene terephthalate glycol in a supporting powder bed

Material extrusion 3D printing is a fabrication process that produces layered polymer parts with complex geometry but with inferior mechanical properties compared to parts made with other methods such as injection molding. Post fabrication heat treatment is a valid post-processing method that reduces the internal thermal stresses and improves layer adhesion in 3D printed polymers, resulting in superior mechanical properties. This study investigates the mechanical changes produced in 3D printed PETG (polyethylene terephthalate glycol-modified) parts after heat treatment. A novel technique is used, where the parts are embedded into a bed of sodium chloride powder in order to prevent deformation during postprocessing. Fully filled 3D printed PETG parts with various geometries are tightly packed in a bed of powder. The parts are subjected to heat treatment at a temperature above the material’s glass transition temperature but below its melting temperature. Destructive and non-destructive testing performed on the treated 3D printed samples shows a substantial improvement of mechanical properties. Tensile strength testing reveals an increase of tensile strength by 40% for parts printed horizontally and by over 100% for parts printed vertically. Increased stiffness is also observed in treated parts. Compressive strength testing shows a strength increase of 43% after treatment. Dimensional measurements made prior to and after treatment show significantly reduced deformation when using the supporting powder method versus unsupported treatment. Scanning electron microscopy (SEM) analysis is used to assess internal structural changes in the polymer after post-processing. This analysis reveals changes in internal void shape and distribution, increased interlayer adhesion and increased interface area of deposited filaments, providing insight into the mechanisms that lead to the improved properties observed in destructive testing. The supporting powder heat treatment allows the fabrication of parts with complex geometry through material extrusion 3D printing while mitigating the inherent disadvantage of the fabrication process of producing parts with inferior mechanical properties.

Synthesis of cobalt aluminate spinel by sol-gel process: Investigation of starting reagents and precursors obtained after pyrolysis

In this study, cobalt aluminate was prepared by a sol-gel method. XRD and FTIR analyses of the precursors obtained at 300 °C for 12 h revealed that the type of complexing agent used in the synthesis affects the pyrolysis step. An amorphous phase was obtained by using citric acid as the complexing agent. A beginning of crystallization was observed by using complexing agents such as polyacrylic acid and glycine. The structural investigation of the starting reagents revealed that the observed lines exhibit characteristics of Co3O4 derived from cobalt nitrate. The crystallinity of the samples increased with the increase in the annealing temperature, with no effect observed by the change in the complexing agent. The appearance of the (331) reflection for the heat-treated powders was characteristic of the blue spinel compound.

On Characterizing Uncertainty Sources in Laser Powder-Bed Fusion Additive Manufacturing Models

Abstract Tremendous efforts have been made to use computational and simulation models of additive manufacturing (AM) processes. The goals of these efforts are to better understand process complexities and to realize better high-quality parts. However, understanding whether any model is a correct representation for a given scenario is a difficult proposition. For example, when using metal powders, the laser powder-bed fusion (L-PBF) process involves complex physical phenomena such as powder morphology, heat transfer, phase transformation, and fluid flow. Models based on these phenomena will possess different degrees of fidelity since they often rely on assumptions that may neglect or simplify process physics, resulting in uncertainties in their prediction accuracy. Prediction accuracy and its characterization can vary greatly between models due to their uncertainties. This paper characterizes several sources of L-PBF model uncertainty for low, medium, and high-fidelity thermal models including modeling assumptions (model-form uncertainty), numerical approximations (numerical uncertainty), and input parameters (parameter uncertainty). This paper focuses on the input uncertainty sources, which we model in terms of a probability density function (PDF), and its propagation through all other L-PBF models. We represent uncertainty sources using the webontologylanguage, which allows us to capture the relevant knowledge used for interoperability and reusability. The topology and mapping of the uncertainty sources establish fundamental requirements for measuring model fidelity and for guiding the selection of a model suitable for its intended purpose.

Purple nanometrics pigments based on cobalt-doped manganese molybdate: Synthesis, characterization, structural, thermal, optical, colorimetric and chemical properties

This work is related to the characterization of nanometrics materials of the βMnMoO4-βCoMoO4 system, prepared by co-precipitation and sol-gel routes from the corresponding metal salts. The structural, morphological and colorimetric characteristics of the obtained powders were studied using thermogravimetric and differential thermal analysis (TGA-DTA), X-ray diffraction (XRD), infrared and Raman spectroscopy, scanning electron microscopy (SEM) and colorimetry (CIE-L*a*b* system). The surface specific area was calculated using the Brunauer–Emmett–Teller analysis (BET) in the adsorption/desorption isotherm. The X-ray diffraction patterns highlighted the formation of a continuous solid solution Mn1-xCoxMoO4 (0 ≤ x ≤ 1) of monoclinic symmetry (C2/m) isotype to β-MnMoO4 and this regardless of the synthetic route adopted. FTIR and Raman spectroscopy analysis showed that the chemical bonds’ nature in the Mn1-xCoxMoO4 compounds corresponded to the strong Mo–O–Mo, Mo–O and Co–O–Mo vibrational modes. The micrographs (SEM) highlighted the form of nanorods with sizes ranging from 10 to 200 nm for compositions x = 0.3 and x = 0.6, prepared by co-precipitation. The specific surface area measurements indicated that the powders obtained by the sol-gel process present lower values than those prepared by co-precipitation, regardless the cobalt substitution rate. The specific surface area of the purple nanoscale powder (x = 0.6) obtained by co-precipitation was about 7.52 m2/g. Colorimetric parameters analysis of the powders heat treated at 1100 °C showed that the degree of the component (-b*) was significant for compositions x = 0.6, regardless of the synthesis method adopted.