Increase Of Co Content Research Articles

Pilot Study on a New Conveyor Bed Magnetization Roasting Process for Efficient Iron Extraction from Low-Grade Siderite

Realizing the large-scale development and utilization of siderite, a difficult iron ore reserve, has great practical significance in ensuring the supply of iron ore resources. Therefore, a new in-house conveyor bed magnetization roasting–dry cooling process was pilot-tested using low-grade siderite from the Daxigou iron ore mine. A two-stage weak magnetic separation method was used for a beneficiation test to investigate the influence of temperature and CO content on the magnetization of siderite. At 600 °C and 800 °C under suspension, iron minerals were converted into magnetite with an effective 3–5 s residence time. Furthermore, at 600 °C and 750 °C, increasing the calcination temperature increased the iron grade and the concentrate recovery rate. However, calcination at temperatures >750 °C resulted in a slight decrease in the iron grade and recovery rate of the concentrate. 61.50% Fe grade and 80.30% concentrate recovery rate were obtained under 750 °C from magnetization roasting. Magnetization roasting in a reducing atmosphere provides mainly magnetite as the roasted ore, and increased CO content can efficiently promote this effect. At 700–780 °C and when the CO content was increased to more than 3 wt.%, the improvement of the roasting effect was very limited. Rapid cooling of the roasted ore using a mixture of circulating exhaust gas and air could prevent considerable oxidation of the magnetic ferrous material. Therefore, the preferred process conditions are 700–780 °C with a CO content range of 1–3%. It provided a concentrate iron grade of 59.27–61.50% and a recovery rate of 78.32–80.30%. The results of this study provide a reference for the development of conveyor bed magnetization technology, process design, and production control.

Effects of carbothermal prereduction temperature and Co content on mechanical properties of WC–Co cemented carbides

AbstractWC–Co cemented carbides were prepared via an in situ synthesis method, including the carbothermal prereduction of WO3 and Co2O3 to remove all oxygen and a subsequent carbonization‐vacuum sintering process. The experimental results revealed that as the prereduction temperature increased from 1000 to 1200°C, the grain sizes of WC in WC–6Co and WC–12Co cemented carbides increased from .91 to 1.09 and .97 to 1.19 μm, respectively. Further, the fracture toughness of the sintered WC–6Co and WC–12Co cemented carbides increased from 9.97 to 10.83 and 11.11 to 18.30 MPa m1/2, respectively. In contrast, the hardness of the WC–6Co and WC–12Co cemented carbides decreased from 1477 to 1368 and 1351 to 1184 HV30, respectively. For a given prereduction temperature, an increase in Co content can improve the fracture toughness while lowering the hardness. In addition, an increase in the prereduction temperature or Co content led to an increase in the grain size of WC, which resulted in a transgranular fracture as the dominant mode.

Simulation on shear deformation property of nano-polycrystalline Ni-Co alloy with concentration gradient

In concentration gradient (CG) nano-polycrystalline Ni-Co alloy, the deformation mechanism of each region is different with the increase of Co content. It is found that in the Co-free region, grain boundary diffusion and dislocation slip mechanisms are dominant, while in other regions, there is a synergistic effect of solid solution strengthening. Moreover, the formation of new small grains by the migration of GB atoms will assist in the deformation of large grains, and the alloy exhibits gentle and stable stress–strain curve pattern. Meantime, although the dislocation density of each region is different, the dislocation density still changes stably before and after shearing. Compared with the uniform structure, the flow stress fluctuation is small when the CG structure is plastically deformed, which proves that this kind of structure is more stable. Moreover, it is found that at different temperatures, the CG alloy also shows stable dislocation density and coordination of various mechanisms, which ensures the strength stability. It is revealed that the CG structure has important properties that make the material strength more stable. This work demonstrates the excellent properties of CG alloy and has positive guiding significance for the development of low-cost, high-performance materials in terms of theoretical and practical applications.

Structural, Ferroelectric and Magnetic Properties of NiTiO3–CoTiO3 Solid Solutions Synthesized by Sol–Gel Method

The Ni[Formula: see text]CoxTiO3[Formula: see text] solid solution powders were prepared by an aqueous sol–gel method. The structural, optical, magnetic and ferroelectric properties of NiTiO3 were investigated by X-ray diffraction, scanning electron microscope, UV–Vis absorption, vibration samples magnetometer and ferroelectric test system. The X-ray diffraction analysis revealed that prepared materials were in a single phase with rhombohedral structure with [Formula: see text] up to 1. The increasing Co content resulted in decreasing of tolerance factor and increasing of the lattice constant. The crystalline size increased with an increase of Co content. The optical bandgap value of solid solution increased from 2.23[Formula: see text]eV for NiTiO3 to 2.36[Formula: see text]eV for CoTiO3. The magnetic hysteresis loop results indicate that all samples showed paramagnetic state at room temperature. A correlation between magnetization values and composition of the materials was observed with magnetization values which increased with increasing of CoTiO3 content in solid solution. Ferroelectric polarization analysis showed that the polarization of the Ni[Formula: see text]CoxTiO3 solid solution depended on x value and reached the maximum with [Formula: see text].

A Study on the Co-Content Optimization of the DD15 Single-Crystal Superalloy

The fourth-generation single-crystal superalloy DD15 with 6% Co, 9% Co and 12% Co was cast using the vacuum directionally solidified furnace, while other alloying element’s content remained unchanged. The long-term aging experiment was conducted at 1100 °C for 1000 h after standard heat treatment. The stress rupture tests of the alloy were conducted at 1100 °C/137 MPa and 1140 °C/137 Mpa. The influence of Co content on the microstructure and stress rupture properties of DD15 alloy had been investigated to optimize the Co content to obtain excellent comprehensive performance. The results showed that the primary dendrite arm spacing of the alloy decreases at first and increases afterwards, and the volume fraction of γ-γ′ eutectic decreases with the growth of Co content in the as-cast microstructures. The size, cubic degree and volume fraction of the γ′ phase of the alloy after standard heat treatment all decrease with the increase in Co content. The microstructure stability of the alloy is enhanced with the increase in Co content. No TCP phase was present in the alloy with 12% Co precipitate even after aging 1000 h. The stress rupture lives at two conditions, both reduced in different degrees with the increase in Co content. The effect of Co on the stress rupture life of the alloy improves with the increase in Co content or test temperature. The acicular TCP phase appeared in the 6% Co alloy and 9% Co alloy in the microstructure of the ruptured specimens with different Co contents. Moreover, the TCP phase content in the 6% Co alloy is much more than that in the 9% Co alloy. There is no TCP phase precipitation in the 12% Co alloy. At last, the relationship between microstructure stability, stress rupture properties and Co content of the alloy is discussed. The alloy containing 9% Co is the best choice considering the microstructure stability and stress rupture properties.

Effect of Co on Microstructure and Properties of Al-30%Si Alloys

In this paper, the effects of different Co contents on the microstructure and properties of Al-30% Si alloy were studied by means of metallographic microscope, microhardness tester, XRD, conductivity tester and DSC thermal analyzer. The results show that cobalt can effectively improve the microstructure of the alloy, the long needle eutectic silicon becomes short rod, and the coarse irregular block primary silicon particles become smaller. When 0.3% cobalt is added into the alloy, the refining effect of eutectic silicon is the most obvious. When the amount of Co is 0.6%, the refinement effect of primary silicon is the best. The addition of Co can improve the hardness of the alloy. When 0.6 ~ 0.9% cobalt is added, the hardness is the highest. With the increase of Co content, the conductivity and transformation latent heat of the alloy show the same change law. When 0.6% cobalt is added, its value is the maximum. It can be seen that when the Co content is 0.6%, the microstructure and comprehensive properties of the alloy are the best.

Effects of structural transformation on magnetic properties of AlCoFeCr high-entropy soft magnetic powder cores by adjusting Co/Fe ratio

Al1.5(CoxFe6-x)6Cr high-entropy alloy (HEA) soft magnetic powder cores (SMPCs) were designed and prepared via gas atomization and insulation, and the effects of the Co/Fe ratio on their phase formation, microstructure evolution, and soft magnetic properties were systematically investigated. An increase in Co content promoted the precipitation of the B2 phase from the body-centered cubic (BCC) matrix, and the content of the B2 phase was greater than that of the BCC phase at x = 4, thus replacing the BCC phase as the matrix, which contributed to the optimization of the soft magnetic properties of the AlCoFeCr HEA. The SMPC composed of the BCC single phase exhibits the lowest eddy current loss (Pe) of 55.1 mW/cm3 (@100 kHz, 50 mT), excellent direct current (DC) bias performance of 80.6 % at 100 Oe, and high stable effective permeability (μe) of 49.9 up to 1 MHz. The association of magnetic domains, grain size, and particle size with Hc variation was analyzed, providing guidelines for subsequent studies to obtain HEAs with good soft magnetic properties. By comprehensively and systematically comparing the microstructural differences of diverse matrix-phase HEAs and SMPCs, the specific application of this HEA system under high-temperature conditions can be expanded.

Microstructure and mechanical properties of as-cast (CuNi)100−xCox medium-entropy alloys

Microstructure and mechanical properties of non-equiatomic (CuNi)100−xCox (x=15, 20, 25 and 30, at.%) medium-entropy alloys (MEAs) prepared by vacuum arc-melting were investigated. Results show that all the as-cast MEAs exhibit dual face-centered cubic (fcc) solid-solution phases with identical lattice constant, showing typical dendrite structure consisting of (Ni, Co)-rich phase in dendrites and Cu-rich phase in inter-dendrites. The positive enthalpy of mixing among Cu and Ni-Co elements is responsible for the segregation of Cu. With the increase of Co content, the volume fraction of (Ni, Co)-rich phase increases while the Cu-rich phase decreases, resulting in an increment of yield strength and a decrement of elongation for the (CuNi)100−xCox MEAs. Nano-indentation test results show a great difference of microhardness between the two fcc phases of the MEAs. The measured microhardness value of the (Ni, Co)-rich phase is almost twofold as compared to that of the Cu-rich phase in all the (CuNi)100−xCox MEAs. During the deformation of the MEAs, the Cu-rich phase bears the main plastic strain, whereas the (Ni, Co)-rich phase provides more pronounced strengthening.

Enhanced hydrogen evolution performance by nanoarchitectonics of Fe/Co alloy electrode beyond Fe/Co/Ni alloy electrode

With the increasing global energy demand, hydrogen production from electrolytic water became the main way to prepare efficient and clean hydrogen energy. Transition metal catalyst were promising hydrogen evolution catalyst for low cost, stable performance and high catalytic activity. In this study, Fe–Co–Ni, Co–Fe, Ni–Fe and Co–Ni alloy electrodes were prepared by electrodeposition. Among the four alloys, Co–Fe showed the best hydrogen evolution performance. The surface of Co–Fe alloy electrode coating was composed of round small particles of different sizes closely combined to form a large complex. In the alloy, Co was accounted for 62.2% and Fe was accounted for 37.8%. The increase of Co content increased the specific surface area of the electrode, provided a large number of catalytic active sites, and improved the hydrogen evolution performance. In the Co–Fe alloy electrode, Fe was existed in the form of Fe2+ and Fe3+, Co was existed in the form of Co2+. The electrochemical test results showed that Co–Fe alloy electrode had the highest electrocatalytic activity. Since the conductivity of cobalt hydroxide and iron hydroxide generated in the strong alkali environment, which was stronger than that of nickel hydroxide, the internal resistance of the Co–Fe alloy electrode in the hydrogen evolution process was reduced. Under the same conditions, the Co–Fe alloy electrode needed only 1483 mV overpotential to drive a current density of 0.1 A/cm2. The Tafel slope of Co–Fe alloy electrode was the smallest, only 144.04 mV/dec, and the electron transmission efficiency was the highest. Co–Fe alloy electrode had the lower electron conduction resistance and better electrochemical hydrogen evolution performance.

Microstructure and Properties of Microwave-Sintered Nd2Fe14Bp/2024 Aluminum-Alloy–Co Composites

This study aimed at the preparation of a 2024 aluminum alloy (2024Al) matrix composite with high strength, high toughness and high magnetic properties that can be used in practical applications. Therefore, Nd2Fe14Bp/2024Al–Co composites with different Co contents (wt.%) were prepared by ball milling, cold isostatic pressing and microwave sintering. The effects of the Co content on the microstructure, mechanical properties and magnetic properties of the prepared composites were studied. Under the conditions of the sintering temperature of 490 °C, heating rate of 20 min/°C and soaking time of 30 min, it was found that with the increase in Co content (0→2.5%→5%→7.5%→10%), the grain size first decreased and then increased, and reached the optimal value of about 3–5 μm when the Co content was 7.5%, with the microstructure being relatively uniform. At the same time, the compactness of the composite arrived at a maximum of 95.4%. The main particle phases in the composite were Nd2Fe14B, Nd2 (Fe, Co)14B and Co particles. In the nanoindentation test, the interface strength of the 7.5% Co sample was significantly higher than that of the Co-free sample. In addition, the microhardness, yield strength and compressive strength of the 7.5% Co sample were 152 HV, 210 MPa and 269 MPa, respectively, which increased by 67%, 78% and 75%, respectively, compared with the Co-free sample. With the increase in Co content, the remanence (Br), coercivity (Hcj) and maximum magnetic energy product ((BH) max) of the composites first increased and then decreased. When the Co content was 7.5%, the three performance indicators reached their optimum values, which were Br: 0.20 (T), Hcj: 4.6 (kOe) and (BH)max: 28.36 (kJ/m3). The expected goal of the lightweight magnetic materials was achieved, and the action mechanism of Co addition in the composites was also analyzed in detail.

Influence of Co content on the simultaneous enhancement of strength and ductility in severely drawn textured Ni-Co microwires

ABSTRACT This study examines the deformation behaviour of Ni-Co microwires exhibiting high strengths and ductility, where the addition of Co is intended to decrease the stacking fault energy. A reduction in stacking fault energy is likely to retard the recovery processes, refine grain size and enhance strain hardening by dislocation interactions at twin boundaries. Microwires were drawn to a strain of 5.88, from annealed Ni-Co alloys with Co content varying from 30 to 60 wt%. Subsequent tensile testing revealed a simultaneous increase in strength and ductility with an increase in Co content. The enhanced strength is a consequence of the finer grain size with an increase in Co, and the larger ductility is related to a combination of greater strain hardening and a higher strain rate sensitivity with an increase in Co. The textured drawn Ni-Co wires exhibited higher strengths than those obtained by severe plastic deformation with comparable grain sizes.

Microstructure and enhanced tensile properties of AlCo CrFeNi high entropy alloys with high Co content fabricated by laser melting deposition

AlCoxCrFeNi (x = 2.2, 2.8) high entropy alloys (HEAs) were successfully prepared by multi-layer and multi-channel laser melting deposition (LMD). The tensile properties of the LMD-fabricated AlCoxCrFeNi HEAs were investigated. The phase evolution of these alloys was examined by X-ray diffraction and compared with existing models. The microstructure of the alloys was characterized using scanning electron microscopy and electron backscatter diffraction. It is found that Co element can promote the phase transformation from BCC phase to FCC phase in the as-deposited AlCoxCrFeNi HEAs, and the volume fraction of FCC phase increases from 51.4% to 74.6% as the Co content increases from 36.2 at% to 40.8 at%. With the increase of Co content, the grain size of BCC phase in the alloys decreases and a larger amount of fine needle-like BCC phase appears in the FCC matrix. Tensile testing shows that higher Co content in the deposited AlCoxCrFeNi alloy can enhance its plasticity without significantly compromising its ultimate strength. As the Co content increases, the fracture strain increases from 5.9% to 15.4%, while the yield strength reduces from 450 MPa to 360 MPa and the ultimate tensile strength increases from 734 MPa to 739 MPa. The variations in tensile properties of the AlCoxCrFeNi alloy result from phase structure changes and microstructure evolution. Through this research, it is demonstrated that enhancement of the tensile properties of the LMD-fabricated AlCoCrFeNi HEAs can be realized by increasing the content of Co element.

Twinning damping interface design and synergistic internal friction behavior in FeMnCrCo high-entropy alloys

Vibration and noise reduction has always been important problem to be solved in the fields of rail transit, aerospace, marine engineering, and so on. In this paper, a novel Fe65-XMn20Cr15CoX (X = 5, 10, 15, 20) dual-phase high-entropy damping alloy with excellent properties were prepared by vacuum melting. The dependence of the alloy damping behavior on the twin interface, magnetic properties and phase interface was emphatically analysed. The effects of Co content on its microstructure, damping behavior and magnetic properties were investigated. The results show that with the increase of Co content, ε martensite gradually transforms to γ austenite, and the number of twins increases gradually. The peak damping (Q−1) increased from 0.0442 to 0.0595, an increase of 34.6%. The coupled effects of magneto-mechanical hysteresis, twin interface motion, and phase interface motion provide the alloy's excellent damping properties. The alloy has a higher damping internal friction peak of around 200 °C, which is due to the phase transition from ε to γ at the temperature. By adjusting the Co content, the phase content and twinning and other microstructures of the alloy can be regulated, and multiple damping mechanisms can be coupled to achieve higher damping performance.

Beneficial effects of Co to CoCrNiMoCB coatings obtained by laser cladding

• Coherent ceramic reinforced HEA coatings were prepared by laser cladding. • The addition of cobalt can homogenize element distribution. • The addition of cobalt increased the nanocrystalline thickness of the worn surface. Degradation by wear is a common failure mode for materials used in extreme environments. Herein, coherent ceramic-reinforced CoCrNiMoCB high-entropy alloy coatings with different cobalt content were prepared by laser cladding. The effects of cobalt on the phases, microstructures, composition and wear performance of the coatings were studied. Due to the increased fraction of M 23 (B, C) 6 , refined crystalline strengthening, and solid solution strengthening, the wear resistance was greatly improved with the increase of Co content. And the increased thickness of the nano-crystalline work hardening layer in the depth direction of the worn surfaces further improved the wear force resistant ability.

Microstructure and mechanical properties of Co-containing Ti-48Al alloys prepared from irregular pre-alloyed powder

Poor sinterability of powder metallurgy TiAl-based alloy is an important factor that restricts its industrial production. In this paper, we improve the sinterability of Ti-48Al alloy by adding Co element. In such case, the relative density of Ti–48Al based alloy sintered at 1250 ℃ increases from 82.6% to 96% with an increase of Co content from 0 to 1.5 at%. The densification improvement is caused by liquid TiAl2Co phase, which is formed at 1230 ℃. Then, uniform and fine near-γ microstructure is obtained, and the grain size increases with the increasing of Co content. More than 70% of grains in the Ti-48Al-0.5Co alloy are smaller than 2 µm. Overall, Ti-48Al-0.5Co alloy has better comprehensive performance, with compressive strength of 2533 MPa, yield strength of 683 MPa and fracture strain of 29.5%.

Microbial conversion of syngas to single cell protein: The role of carbon monoxide

Syngas has been widely utilized as substrate in microbial processes to produce various high-value products. Nevertheless, its applicability for single cell protein (SCP) production by hydrogen-oxidizing bacteria (HOB) has never been explored. Especially, the role of carbon monoxide in SCP synthesis is unknown. Thus, this study first investigated the effect of different CO and H2 ratios in syngas on Cupriavidus necator H16 growth and SCP production. The growth of C. necator H16 was significantly restrained with the increase of CO content, and it almost ceased once the CO:H2 ratios were above 1. In addition, the growth rate of C. necator H16 increased with the increase of shaking frequency and inoculum volume. Furthermore, larger gas–liquid interfacial areas and gas input amount resulted in a higher growth rate and OD value. The raw protein contents were around 50–60% regardless of CO concentration, and the amino acid profiles showed no apparent differences. The results showed that although the presence of CO led to the reduction of the growth rate of C. necator H16, it had a limited effect on the SCP quality. H2 and CO2 in syngas were the primary substrates for SCP production, while CO served more as a toxic inhibitor. The successful demonstration of SCP synthesis from syngas may provide a superior route for the valorization of waste biomass by turning it into food or feed.

Atomistic insights on the deformation mechanisms of Cox(CrNi)100-x multicomponent alloys: The effect of Co content

CoCrNi multicomponent alloys with equiatomic and non-equiatomic concentrations are promising for achieving an excellent balance of strength and ductility. However, the correlations between elemental concentrations and deformation mechanisms of this alloy family need to be uncovered for further targeted alloy design. In this work, atomistic molecular dynamics simulations were performed to study the effects of Co concentration on the mechanical behaviors and underlying deformation mechanisms of single-crystal Cox(CrNi)100-x (x = 13, 23, 33.3, 50 at. %) alloys. Atomic-scale microstructural evolution with increasing the compressive strain was revealed in each specimen with different Co concentrations. The results suggest that the yield stress and elastic modulus are enhanced with increasing the Co content. Atomic pairs containing Cr exhibit the lowest cohesion energy among all pair types, and therefore Cr atoms participate most actively in dislocation nucleation. Although dislocation slip comes into play in all specimens, the primary deformation mechanism changes from the multilayering of stacking faults (SFs) to the formation of primary-secondary twin pairs with the increase of Co content. Further, the twinnability of these alloys was estimated using a theoretical model based on the generalized stacking fault energy (GSFE) curves. The results indicate that the Co50Cr25Ni25 alloy owns the highest twinning tendency among the probed alloy variants, which promotes the formation of secondary deformation twins and leads to high deformability. This work provides guidelines for the design of non-equiatomic CoCrNi multicomponent alloys with proper Co content for desirable mechanical properties.

Synthesis and Blue Emission Properties of Co-Doped CdS Semiconductor Nanoparticles

Background: Cadmium sulfide (CdS) based semiconductors are of great interest for different high-end applications because they pose a direct bandgap (2.42 eV). CdS are used as the main constituent material in many applications, namely solar cells, electroluminescent, and quantum dot light-emitting diodes. Transition metal-doped CdS revealed considerable influence in the bandgap, photoluminescence properties and peak energy upon increasing the metal content. Objective: In this work, we study the single-phase cubic structure of CdS. Photoluminescence spectra revealed a strong blue emission peak located at about 445 nm. Methods: We investigate the Co-doping CdS semiconductor nanoparticles prepared via the chemical co-precipitation method using thiophenol as template, 300 °C/2h in vacuum optimum temperature and period of annealing to yield nanosized particles. Morphology and structural studies of the particles were using XRD, and TEM, respectively. Results: XRD and TEM studies for the calcined samples revealed a cubic structure. The crystalline size was in the range of 10-17 nm. Thermogravimetric analysis (TGA) was employed to stabilize the temperature of annealing for the samples. The blue shift in the spectra and the band gap value of Codoped CdS nanoparticles were estimated using UV-vis absorption spectra. Photoluminescence spectra revealed a strong blue emission peak around 445 nm indicating the presence of surface states within the bandgap region, which is a characteristic feature of nanoparticles. Conclusion: XRD analysis indicated zinc blend structure and the intensity decreased with increasing Co content. TEM images show that the particles are spherical in shape with average sizes around 13 nm. Luminescence of the synthesized nanoparticles exhibited blue emission between 400 – 500 nm with the peak located at about 445 nm. The emission intensity increased with the increase in Co concentration.

Nanoscale structural heterogeneity and magnetic properties of Fe-based amorphous alloys via Co and Ni additions

Nanoscale structural heterogeneity is a critical parameter for understanding the structure-property relationships in amorphous alloys. Herein, the small-angle X-ray scattering and atomic force microscopy were utilized to quantitatively investigate the nanoscale structural heterogeneity of the Fe80-xMxSi9B11 (M = Co and Ni; x = 0, 2, 4) amorphous alloys. The results show that the nanoscale structural heterogeneity of the amorphous alloys increases prominently with Ni substitution, but gradually decreases with the increase of Co content. Such evolution of structural heterogeneity was further verified by the changes in mechanical behavior. The microalloying of Ni can increase the plastic deformation ability and reduce the microhardness, whereas an opposite effect is found in the Co-doped alloys. Finally, Mössbauer spectroscopy reveals an enhancement in ferromagnetic exchange interaction and magnetic anisotropy with Co substitution, while the microalloying of Ni leads to a deteriorative result. Such variations in magnetic properties can be attributed to the evolution of nanoscale structural heterogeneity with Co and Ni additions. Our observation serves as a link between the nanoscale structural heterogeneity and magnetic properties, providing a new sight into understanding the structural origin of the changes in magnetic properties of Fe-based amorphous alloys.

Spin conversion of positronium of ZIFs nanocrystalline

ZIFs crystal is composed of imidazolidyl bridging single metal ions, and its structure can be adjusted by flexibly selecting functional groups of imidazolidyl ligands, thereby possessing more new properties and functions. While, the pore structure and chemical environment of ZIFs crystals are closely related to their properties. In this work, ZIF nanocrystals are prepared by static reaction. The X-ray diffraction results confirm that the prepared crystals are typical of ZIF-8 crystals, and the regular rhomboidal structure can be observed by scanning electron microscopy. The N<sub>2</sub> adsorption-desorption test indicates that the ZIF crystal exhibits the larger specific surface area (2966.26 m<sup>2</sup>/g) and pore volume (3.01 cm<sup>3</sup>/g) . With the increase of Co content, specific surface area and pore volume of ZIFs crystal decrease, while the pore size remains nearly unchanged (around 12 Å). However, the pore size distribution calculated by N<sub>2</sub> adsorption/desorption isothermal curve does not show the ultra-micropore information of the six-membered ring composed of imidazole ligands (3.4 Å). The microstructure and surface properties of the crystal are investigated by positron annihilation lifetime and Doppler broadening. The positron lifetime spectrum has four components. The longer lifetimes <inline-formula><tex-math id="M8">\begin{document}$ {\tau }_{3} $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="15-20220305_M8.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="15-20220305_M8.png"/></alternatives></inline-formula> and <inline-formula><tex-math id="M9">\begin{document}$ {\tau }_{4} $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="15-20220305_M9.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="15-20220305_M9.png"/></alternatives></inline-formula> are the annihilation lifetimes of o-Ps in the microporous region and the regular angular gap of the crystal, respectively. With the increase of Co content, the lifetime <inline-formula><tex-math id="M10">\begin{document}$ {\tau }_{3} $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="15-20220305_M10.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="15-20220305_M10.png"/></alternatives></inline-formula> hardly changes, while the longer lifetime <inline-formula><tex-math id="M11">\begin{document}$ {\tau }_{4} $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="15-20220305_M11.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="15-20220305_M11.png"/></alternatives></inline-formula> decreases from 30.89 ns to 12.57 ns, and the corresponding intensities <inline-formula><tex-math id="M12">\begin{document}$ {I}_{3} $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="15-20220305_M12.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="15-20220305_M12.png"/></alternatives></inline-formula> and <inline-formula><tex-math id="M13">\begin{document}$ {I}_{4} $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="15-20220305_M13.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="15-20220305_M13.png"/></alternatives></inline-formula> decrease sharply from 12.93% and 8.15% to 3.68% and 0.54%, respectively. With the increase of Co content, the <i>S</i> parameter obtained by doppler broadening shows a continuous upward trend, and the p-Ps intensity also increases gradually, which is mainly due to the self-rotation effect of the electron element. Therefore, the decrease of <inline-formula><tex-math id="M14">\begin{document}$ {\tau }_{4} $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="15-20220305_M14.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="15-20220305_M14.png"/></alternatives></inline-formula> in ZIFs nanocrystal is probably due to the self-rotation effect of positronium and Co ion on the crystal surface.