Nitride Powders Research Articles

Mechanism for the hydrolysis resistance of aluminum nitride powder modified by boric acid

Aluminum nitride (AlN) ceramics are becoming cutting-edge materials for electronic information and communication. However, raw AlN hydrolyzed rapidly, and the high storage costs of this material prevent widespread application. In this study, raw AlN was modified by boric acid (H3BO3) at 30 °C to enhance hydrolysis resistance. Transmission electron microscope (TEM), X-ray diffraction (XRD), the magic angle spinning nuclear magnetic resonance (27Al-MAS-NMR and 11B-MAS-NMR), and the fourier transform infrared spectrometer (FTIR) were used to characterize the powder before and after treatment, and the mechanism of hydrolysis resistance was determined. Modification with 0.1 M boric acid did not change the crystal phase of the AlN particles. The modified powder did not hydrolyse at 90% humidity and 70° Celsius. In the presence of boric acid, a network structure of B–O–B linkages ([BOn], n = 3 or 4) formed that was connected to the AlN core via chemical bonds of B–N–Al and B–O–Al. The protective 6 – 10 nm-thick layer that formed on the surface of the AlN crystal, prevented attack by water molecules and hindered the hydrolysis of aluminium nitride. This study provides an alternative means of preparing anti-hydrolysis AlN powders.

Mechanical Properties and Microstructure of Hot-Pressed Silica Matrix Composites.

Silica is one of the most widely used ceramics due to its excellent chemical stability and dielectric property. However, its destructive brittle nature inhabits it from wider application as a functional ceramic. An improvement in toughness is a challenging topic for silica ceramic, as well as other ceramics. In the paper, silica ceramic with different types of boron nitride powders and alumina platelets was fabricated by hot-pressing. Introduction of the additives had great influence on the composites’ mechanical properties and microstructure. The silica matrix composite containing micro-sized boron nitride powders possessed the best mechanical properties, including the bending strength (134.5 MPa) and the fracture toughness (1.85 Mpa·m1/2). Meanwhile, the introduction of alumina platelets combined with boron nitride nanosheets achieved an effective enhancement of fracture toughness while maintaining the bending strength. Compared with the monolithic silica, the composite with simultaneous addition of alumina platelets and boron nitride nanosheets had a fracture toughness of 2.23 Mpa·m1/2, increased by approximately 27% (1.75 Mpa·m1/2). The crack deflection and platelet pullout were contributing to enhancement of the fracture toughness. The improved mechanical properties, combined with the intrinsic excellent dielectric and chemical properties, make the silica matrix composites promising wave transparent and thermal protection materials.

Synthesis, crystal structure, and photoluminescence of the new nitridoboroaluminosilicate phosphor (Sr0.93Eu0.07)11B2(Al0.275Si0.725)40N59

Single crystals of a new nitride, (Sr0.93Eu0.07)11B2(Al0.275Si0.725)40N59, were synthesized by heating a mixture of binary nitride powders at 2030 ​°C under nitrogen gas at 0.85 ​MPa. The fundamental X-ray diffraction reflections from a single crystal were indexed with the monoclinic cell parameters a ​= ​5.6836(4) Å, b ​= ​46.772(3) Å, c ​= ​5.6845(4) Å, and β = 118.028(2)° and diffuse streaks were observed between the reflections. The crystal structure was analyzed based on a statistical average structural model with space group Cm. The structure was determined to comprise (Al/Si)N4 tetrahedra and BN3 planar triangles forming a three-dimensional framework by sharing nitrogen atoms with Sr/Eu atoms located in the cage portions of the framework. Stacking faults in the b-axis direction and disordered atomic arrangements along the [1 0 1] direction on the a-c plane were observed by scanning transmission electron microscopy. These single crystal grains were found to emit red light when irradiated with near ultraviolet or blue light, with a maximum emission wavelength of 616 ​nm and a full width at half-maximum value of 106 ​nm in response to 450 ​nm light.

Carbon Nitride Thin Film‐Sensitized Graphene Field‐Effect Transistor: A Visible‐Blind Ultraviolet Photodetector

AbstractUltraviolet (UV) photodetectors often suffer from the lack of spectral selectivity due to strong interference from visible light. In this study, the exceptional electrical properties of graphene and the unique optical properties of carbon nitride thin films (CNTFs) are used to design visible‐blind UV photodetectors. First, polycrystalline CNTFs with different thicknesses (12–94 nm) are produced by thermal vapor condensation. Compared to the bulk carbon nitride powder, these films have a considerable sp2 nitrogen deficiency, which is thickness dependent. In addition to showing a wider bandgap than the bulk counterpart, their optical absorption profile (in the ultraviolet–visible range) is unique. Critically, the absorbance falls sharply above 400 nm, making the CNTFs suitable for ultraviolet photodetection. As a result, graphene field‐effect transistors (GFETs) sensitized with CNTFs show 103 A W−1 responsivity to UV radiation, a stark contrast to the negligible value obtained in the visible spectrum. The effect of film thickness on the photoresponse is determined, with the thinner CNTF leading to much better device performance. The CNTF/GFET photodetectors are also characterized by their fast response and recovery times, 0.5 and 2.0 s, respectively. These findings pave a simple route for the development of sensitive, visible‐blind UV photodetectors.

Assessment of the data repeatability of x-ray diffraction study for silicon nitride powders of different dispersion

X-ray diffraction methods are indispensable for studying crystalline materials and provide determination of the phase composition, internal stresses and the parameters of unit cells of crystalline phases, as well as the crystalline size, which is related to the average grain size and affects the width of the diffraction peaks. We present the results of evaluating the repeatability of the X-ray diffraction data obtained for silicon nitride powders Si 3 N 4 of different particle size and different initial phase ratios α-, β-Si 3 N 4 . The relative error of measuring the diffraction peaks was determined using the intensity detector and the absolute error of calculating the unit cell parameters was determined by the Rietveld method. The average particle size of the initial powders was analyzed using scanning electron microscopy. X-ray diffraction studies were performed according to the Bragg – Brentano scheme using CuKα radiation (λ = 1.5406 Å). A series of three experiments was performed for each powder. It is shown that the relative error of intensity measurements with a detector does not exceed 2% for peaks corresponding to 3σ criterion, and the absolute error of the determination of the unit cell phase parameters by the Rietveld method is 0.001 Å. The results obtained can be used to assess the stability of the diffractometer both for the samples based on silicon nitride and materials of different composition and structure, especially for submicron samples. In the latter case, the error of the parameters obtained by X-ray phase analysis can be taken into account without resorting to statistical estimates, as in the method of least squares.

Optimizing Hydrolysis Resistance and Dispersion Characteristics via Surface Modification of Aluminum Nitride Powder Coated with PVP-b-P(St-alt-ITA) Copolymer.

Developing new coating modification technology of aluminum nitride (AlN) powder for higher hydrolysis resistance is the key to prepare high-performance AlN ceramic substrate with water-based wet process in the future. In the this paper, The poly(vinyl pyrrolidone)-b-poly(Styrene/Itaconic anhydride) (PVP-b-P(St/ITA))block copolymer with PVP as the independent chain segment was designed and synthesized through reversible addition fragmentation chain transfer (RAFT) polymerization, which was used for the study on coating modification, hydrolysis resistance, and dispersion performance of AIN powder. The study results show that, when using PVP macromolecular chain transfer agent (PVP-CTA) for the RAFT chain extension and polymerization in St/ITA binary system, the molecular weight increases linearly and the molecular weight distribution tends to decrease with the monomer conversion rate, which is in line with the activity-controlled characteristics of RAFT polymerization. The copolymer PVP-b-P(St/ITA) was used to for surface modification treatment of submicron AlN powder to generate esterification reaction, which was absorbed and bound to the powder surface. Hydrolysis resistance and dispersion experiments were conducted for modified powder, and the crystal phase and micro structure of modified powder were analyzed and observed through XRD, SEM, and TEM. It was found that copolymer modification had no effect on the powder crystal phase. A 8–21 nm passivation layer was coated on the surface, which can exist stably for 10 h in 60 °C water. Zeta potential and laser particle analyzer tests showed that modified powder featured excellent water-based slurry dispersion performance, and certain self-dispersing characteristics. The highest Zeta potential appeared in pH 6~7, and the particle granularity was distributed uniformly with the median particle diameter of 875 nm. The powder hydrolysis resistance and dispersion performance are significantly improved.

Selection of inoculant additives for modifying nickel alloys

Heat-resistant nickel alloys are widely used in the production of castings for aircraft and industrial gas turbine engines. Structural factors are the main determinants of the performance properties of cast nickel alloys. The main disadvantage of castings obtained from these alloys is the coarse-crystalline structure, uneven grain size and columnar crystals in the cross-section. Therefore, the creation of an optimal alloy structure is an important condition for obtaining high properties and ensuring the increased operability of cast parts. Obtaining a fine-grained structure has a beneficial effect on the level of mechanical and operational properties of cast metal. The most promising way to create such a structure is to introduce a small number of additives into the melt that cause heterogeneous formation of crystal nuclei, i.e. modification of the melt with dispersed particles of refractory elements and inocular compounds. To select the type of inocular particles required to initiate crystallization of a particular phase, it is necessary to have a set of data that allows one to form a theoretical understanding of the principles of such a choice. The paper provides a rationale for the selection of the type of particles of inoculators capable of causing the process of artificial changes in the structure of cast metal. For a heat-resistant nickel alloy, the use of refractory particles of ultra-dispersed titanium carbo nitride powder as inoculators are the most effective. When introduced into the melt 0.025 wt. % of such particles, a fine-grained structure of the alloy is obtained, and its ductility in comparison with the unmodified one is more than doubled.

High velocity air fuel (HVAF) spraying of nickel phosphorus-coated cubic-boron nitride powders for realizing high-performance tribological coatings

High velocity air fuel (HVAF) spraying is an emergent thermal spray process, which is used in this work to realize high-performance large area tribological coatings of nickel-phosphorus cladded cubic-boron nitride (c-BN) particles. To the best of authors’ knowledge, this is the first time that HVAF has been utilized for developing Ni–P coatings reinforced with c-BN (NBN). The importance of appropriate processing was highlighted by utilizing two different nozzle configurations, for which microstructure, phase analysis and hardness results demonstrates considerable differences. Furthermore, the coatings were subjected to sliding wear tests to assess their friction and wear characteristics. Post-wear SEM analysis reveals the associated wear mechanisms. Effect of annealing on tribological performance of NBN coatings was also examined, and it is shown that optimal processing can preclude the need for post-treatment. Results ensuing from this work lay the foundation for new generation of HVAF-sprayed wear resistant metal/c-BN composite coatings for diverse applications.

Synthesis of highly purified and crystallized h‐BN using calcium‐assisted carbothermal reduction nitridation

AbstractHighly purified and crystallized hexagonal boron nitride (h‐BN) powder is suitable as thermally conductive filler in resins. To obtain h‐BN powder with large particle size, as well as high purity and crystallinity, high‐temperature heat treatment over 1800°C in a N2 gas atmosphere is effective. The carbothermal reduction nitridation (CRN) involves the carbothermic reduction of boric oxide in a N2 gas atmosphere. In CRN using a CaO promoter, h‐BN particles with high crystallinity can be obtained by a simple heat treatment process. CaO prevents the evaporation of boron oxide and aids in h‐BN particle growth at high temperatures. However, CaB6 is formed as byproduct or impurity when CRN using the CaO promoter is performed at temperatures higher than 1800°C. In this study, the relationship between the products and the reaction temperature was clarified via thermodynamic considerations and experimentation. The results clarified the ideal reaction process of CRN using a CaO promoter to obtain highly purified and crystallized h‐BN powder.

In Situ Determination of Speciation and Local Structure of NaCl-SrCl2 and LiF-ZrF4 Molten Salts.

Understanding the local environment of the metal atoms in salt melts is important for modeling the properties of melts and predicting their behavior and thus helping enable the development of technologies such as molten salt reactors and solar-thermal power systems and new approaches to recycling rare-earth metals. Toward that end, we have developed an in situ approach for measuring the coordination of metals in molten salt coupling X-ray absorption spectroscopy (XAS) and Raman spectroscopy. Our approach was demonstrated for two salt mixtures (1.9 and 5 mol % SrCl2 in NaCl, 0.8 and 5 mol % ZrF4 in LiF) at up to 1100 °C. Near-edge (X-ray absorption near-edge structure, XANES) and extended X-ray absorption fine structure (EXAFS) spectra were measured. The EXAFS response was modeled using ab initio FEFF calculations. Strontium's first shell is observed to be coordinated with chlorine (Sr2+-Cl-) and zirconium's first shell is coordinated by fluorine (Zr4+-F-), both having coordination numbers that decrease with increasing temperature. Multiple zirconium complexes are believed to be present in the melt, which may interfere and distort the EXAFS spectra and result in an anomalously low zirconium first shell coordination number. The use of boron nitride (BN) powder as a salt diluent for XAFS measurements was found to not interfere with measurements and thus can be used for investigations of such systems.

Additive manufacturing of complex-shaped and high-performance aluminum nitride-based components for thermal management

Improved heat dissipation performance, by way of thermal management, is critical in many engineering applications. In this study, three types of silane coupling agents were used to modify aluminum nitride (AlN) powder for vat photopolymerization. The effect of silane coupling agents on the rheology, stability, and curing behavior were systematically studied. The results showed that, compared with two other types of silane coupling agents, one silane agent (KH570) had a larger positive effect on the rheology and stability of the AlN suspension, and the absorbance of the AlN powder increased after surface modification. In addition, the effects of different solid loadings on the curing behavior and CC double-bond conversion rate were systematically investigated. It was found that a higher solid loading resulted in a lower curing depth, cure width, and CC double-bond conversion rate. For the sintered AlN components with increased solid loading, the shrinkage decreased while both the flexural strength and thermal conductivity increased. In addition, the shrinkage in the Z-direction was higher than that in the X- and Y-directions. Scanning electron microscopy analysis showed that the mean grain size decreased with increasing solid loading. Furthermore, a heat dissipation performance evaluation system was designed to illustrate the heat transmission capacity of AlN ceramics. Simulation and experimental results showed that AIN ceramic parts with complex shapes achieved better heat-dissipation performance than those with simple shapes.

Fabrication and mechanical properties of multi-walled carbon nanotubes doped AlN ceramics prepared by spark plasma sintering

In this study, multi-walled carbon nanotubes (MWCNTs) are uniformly dispersed in aluminium nitride (AlN) powders, and the MWCNTs-doped AlN ceramics are sintered at 1500 °C with a holding time of 5 min by spark plasma sintering using Y 2 O 3 as the sintering additive. The effects of the MWCNTs content on the microstructure and mechanical properties of the as-obtained ceramic composites are investigated. The results reveal that many submicron pores are generated when protecting the structure of the CNTs, thereby reducing the density of the AlN ceramic. However, the gradual filling of the grain gap may compensate for the strengthening after CNT doping. The relative density and hardness reach the maximum values of 89.6% of the theoretical density and 7.0 ± 0.3 GPa, respectively, at the doping amount of 2.5 wt%.

Research on the effects of surface modification of ceramic powder on cure performance during digital light processing (DLP)

Digital light processing (DLP) is one of the most important additive manufacture technologies to fabricate ceramic parts with complex geometries. Compared with pure photosensitive resin, the cure performance of ceramic suspensions is obviously different due to the optical property change after the addition of ceramic powders. In this paper, a unique oxidation process was used to modify the optical properties of nitride powders including AlN and Si 3 N 4 . The properties of oxidized ceramics were investigated and the cure performance of ceramic suspensions was then characterized. The effect of oxidation time on cure performance was evaluated. The results showed that for AlN, oxidation process leads to the smaller cure depth and smaller excess cure width as compared with non-oxidized AlN and for Si 3 N 4 , oxidation process leads to the larger cure depth and larger excess cure width as compared with non-oxidized Si 3 N 4 , indicating that both refractive index and light absorbance of ceramic powders have obvious effects on cure behaviors. Additionally, the cure behavior of oxidized ceramic suspension in this study shows that the relationship of cure depth vs. incident energy agrees well with Beer- Lambert model, but the excess cure width vs. incident energy is not consistent with quasi Beer-Lambert model due to the nature of digital micromirror device (DMD).

Two-Dimensional Hexagonal Boron Nitride Nanosheets as Lateral Heat Spreader With High Thermal Conductivity

A highly thermally conductive heat spreader for applications in electronic devices is becoming increasingly demanding, and therefore the removal of excess heat requires an efficient heat dissipating device. Boron nitride nanosheets (BNNSs) were prepared as thermally conductive fillers using hexagonal boron nitride (h-BN) powder as raw material by a water exfoliation method. A composite film was prepared by vacuum filtration using cellulose nanofibers (CNFs) as the substrate with an in-plane thermal conductivity (TC) of 82.4 W m−1 K−1, thermal conductivity enhancement increasing by 9,486% compared to pure cellulose film. Thus, CNF/BNNS composite films are promising as effective thermal interface materials (TIMs) in electronic devices and electronic component applications.

Hydrolysis protection and sintering of aluminum nitride powders with yttria nanofilms

AbstractAluminum nitride (AlN) is a promising material for electronic substrates and heat sinks. However, AlN powders react with water that adversely affects final part properties and necessitates processing in organic solvents, increasing the cost of AlN parts. Small quantities of yttrium oxide (Y2O3) are commonly added to AlN particles to enable liquid phase sintering. To mitigate the reaction of AlN particles with water, particle atomic layer deposition (ALD) was used to coat AlN powders with conformal films of Y2O3 prior to densification and powder processing. When AlN particles were coated with 6 nm thick films of amorphous Y2O3, the hydrolysis reaction was significantly suppressed over 48 h, demonstrating that Y2O3 nanofilms on AlN powders act as a barrier coating in an aqueous solution. AlN powders with Y2O3 addition by particle ALD sintered to high relative densities (≥90% theoretical) after sintering at 1800°C for 50 min.

Phase transformations of iron nitrides at low temperatures (< 700 K) – application of mechanical mixtures of powders of nitrides and iron

Abstract Annealing at low temperatures (T < 670 K) of mixtures of iron nitride powders and iron powder is shown to induce phase transformations through nitrogen transfer between different powder particles. This nitrogen transfer occurs via loose mechanical contact points between different powder particles; nitrogen transport via the gas phase can be excluded. Unique scientific possibilities offered by this type of phase transformation studies are discussed.

Synthesizing of zirconium nitride powders by dynamic thermochemical method

In this study, zirconium nitride (ZrN) powders were prepared using zirconium oxide (ZrO2) and carbon black via the dynamic thermochemical method, called the dynamic carbothermal reduction and nitridation (DCRN) method. The effects of process temperatures on phase transformation and produced powder morphologies in a dynamic system under flowing nitrogen atmosphere were investigated by X-ray diffraction, scanning electron microscopy and energy dispersive spectroscopy. For this purpose, the various test parameters were investigated, such as reaction temperatures (1400, 1450, 1500?C), reaction time (1, 2, 3 h) and rotation rates (2, 4, 6 rpm). The results show that ZrN powders of sub-micron size can be obtained at 1500?C for 1h and 4 rpm by the dynamic thermochemical method.

Nitriding during Powder Production and Study of the Structure of EP741NP Alloy Doped with Nitrogen

Abstract—The development of modern equipment is limited by the physical and mechanical characteristics of the produced alloys, properties of which are often determined and enhanced by introduced alloying components. One of the alloying elements that have been very actively introduced in recent years is nitrogen. As a rule, alloying with nitrogen is carried out by ferroalloys, less often by gaseous nitrogen, which has significant advantages. In the processes of special electrometallurgy, alloying with nitrogen can be performed using, for example, nitrogen-containing plasma. Such a method may be feasible in the production of powder metal by spraying the ingot with nitrogen-containing plasma. It is known that performance properties of the products made of powder metal are significantly higher than those of cast metal. This stimulated the investigation of the properties of a product obtained from nitrided EP741NP powder alloy. In this work, a study of changes in the chemical composition, microstructure and microhardness of EP741NP alloy samples was carried out. The studied material was nitrided metal powders made on a plasma centrifugal atomization unit (PCAU) and ingots from granules obtained by hot isostatic pressing (HIP). The chemical composition of the obtained samples was determined by wave dispersion X-ray fluorescence spectrometry. In order to study the microstructure of metal powders and ingots, the methods of scanning electron microscopy with EDXS were used. Microhardness of the samples was assessed using a microhardness tester by the Vickers method. The analysis of gas impurities was carried out on a gas analyzer. It is shown that nitriding of heat-resistant EP741NP nickel alloy is possible at the stage of metal powder production, without significant loss of alloying components and a sharp change in chemical composition. An increase in microhardness of the obtained nitrided samples was noted in comparison with the initial one.

INVESTIGATION OF POLYURETHANE-BASED HALLOYSITE NANOTUBE AS SOLID-SOLID PHASE CHANGE MATERIAL FOR THERMAL ENERGY STORAGE

Halloysite nanotubes (HNTs) have become one kind of promising supporting material for composite phase change materials (PCMs) owing to their nanostructure, the hollow tubule structure, and high surface area. In the present study, a novel solid-solid phase change material (SSPCM) was prepared based on polyethylene glycol as the soft segment and HNTs as the rigid segment through the two-step polymerization method. As a result, the prepared SSPCMs possess a steady crosslinking structure, and the SSPCMs own good crystallization properties. The SSPCM (PEG, 86.5 wt %) has high phase change enthalpy (tm is 56.49 ℃, ΔHendo is 149.0 J/g) and good crystallinity of 89.1%. Moreover, the TGA results reveal that the SSPCMx has good thermal reliability. Besides, hexagonal boron nitride (h-BN) and graphite powder (GP) were added into the system to optimize the thermal transfer properties, and the thermal conductivities of synthesized SSPCMs can be enhanced 59.0% as compared with that of pure PEG which is 0.196 W/(m K). It can be concluded that the SSPCMs possesses not only excellent phase change properties but also outstanding thermal reliability and a fast thermal response rate. Herein, the synthesized SSPCM displays the promising potential for thermal energy storage application.

An experimental study on friction stir processing of aluminium alloy (AA-2024) and boron nitride (BNp) surface composite

In this research, the influences of percentages of boron nitride powder (BNp) on the characteristics of friction stir Aluminium alloy (AA-2024) surface composite has been studied. Taguchi method has been used to design and investigate the effect of volume percentage of BNp, welding speed, and tool rotational speed on tensile strength and wear rate of surface composite. AA-2024 alloy has been used in aerospace and automotive industries due to its low weight-high strength. The optimum tensile strength and wear rate have been estimated and validated by confirmation experiments. The specimen made for confirmation experiments have been used to examine the fractures microstructure. The maximum tensile strength and minimum wear rate of the optimum specimen are 594 MPa and 1.37 mm3/Nm respectively. The optimum process parameters settings: 15% of BNp, 1200 rpm of tool rotation speed, and 50 mm/min welding speed. It was also observed that the volume percentage of BNp and tool rotational speed are significant FSP parameters on tensile strength and wear rate.