Al Powder Research Articles

Prediction of the Flattening Ratio and Hardness of Cold Sprayed Deposits

Cold spray technology is a solid-state deposition process where solid particles are accelerated to very high velocities by expanding a compressed gas through a supersonic nozzle. The particles impact a substrate located approximately 25 mm from the exit plane of the nozzle. Predicting the deformation and resultant properties helps in developing process parameters and tailoring coatings to get the desired properties. In this study, aluminum, copper, and nickel coatings were produced using a range of process parameters that produced different particle impact velocities. The Hollomon power law relationship and Johnson-Cook flow stress model were utilized to predict the hardness of cold spray coatings. Results showed there was good agreement between the predicted and measured hardness of the respective coatings. Additionally, a methodology was developed to measure deformation in the form of a flattening ratio of the deposited particles. There was good agreement between the predicted and measured flattening ratio, especially for the Al and Ni feedstock powders.

Thermal decomposition kinetics and combustion performance of paraffin-based fuel in the presence of CeO2 catalyst

In recent years, significant developments have been made in solid-fuel combustion. Paraffin-based fuels could be a potential solid fuel for hybrid and ramjet applications due to their high regression rate, low cost, and minimal environmental impact. This study examines the thermal and combustion performance of paraffin-based fuels loaded with CeO2 combustion catalysts and Al additive. A typical melt-cast technique was used to prepare three different fuel formulations, which are paraffin/10 wt.% of Al (S2), paraffin/10 wt.% of CeO2 (S3), and CeO2-Al (10:10 wt.%) binary composite (S4). The pure paraffin (S1) fuel was manufactured as a reference formulation. The CeO2-Al binary composite powder was prepared by ball-milling of CeO2 and Al powders. The CeO2 and Al nanoparticles were characterized by X-ray diffraction (XRD), particle size distribution (PSD), and scanning electron microscope (SEM). The PSD study revealed that the majority of CeO2, Al, and CeO2-Al binary composite particles are 29 nm, 34 nm, and 26 nm in size, respectively. The thermogravimetric analysis (TGA) was used to investigate the effect of CeO2 and Al on the thermal decomposition of paraffin. The results indicate that the paraffin decomposes faster and at a higher rate when CeO2 and CeO2-Al binary composite additives were added. The activation energy of paraffin-based fuel (S4) was reduced from 254 kJ/mol to 214 kJ/mol when a CeO2-Al combustion catalyst was added. The lab-scale ballistic tests showed that the average regression rate of paraffin-Al (S2) and paraffin-CeO2(S3) samples increased in the range of 1.1-1.4 mm/s and 1.12-1.38 mm/s, respectively, whereas, with the CeO2-Al binary composite (S4) sample, a reasonable improvement of 1.15 mm/s to 1.49 mm/s was reported.

Synthesis of cerium aluminate by the mechanical activation of aluminum and ceria precursors and firing in controlled atmospheres

AbstractSingle‐phase cerium aluminate was synthesized from mixtures of ceria and metallic aluminum by milling and firing under controlled conditions in reducing (10%H2 + 90%N2) or inert atmospheres (N2 or CO2). Firing in an inert atmosphere (CO2) did not yield conversion to cerium aluminate, and conversion was also low after firing in reducing conditions (10%H2 + 90%N2) and only improved slightly on changing from powder mixtures with coarse Al powder (15 µm) to mixtures with submicron Al (0.77 µm). High‐energy milling promoted reactivity by the combined effects of improved homogeneity, decreasing grain size of the Al precursor, increase in lattice strain and decrease in crystallite size down to 40–50 nm. Extensive oxidation of the metallic Al precursor after long‐term milling prevented complete conversion to cerium aluminate even after firing under reducing conditions at temperatures up to 1400°C. Thermodynamic modeling of the Al–Ce–O system provided interpretation for differences between firing in reducing and inert atmospheres. Controlled milling time hinders oxidation of Al to the poorly reactive α‐Al2O3 polymorph. This was supported by thermogravimetry after controlled milling and yielded phase pure CeAlO3 at T ≥ 1200°C. The high conversion was achieved even by firing at 1100°C under an inert atmosphere.

Manufacturing Bulk Nanocrystalline Al-3Mg Components Using Cryomilling and Spark Plasma Sintering.

In the current study, pure aluminum (Al) powders were cryomilled with and without 3 wt.% pure magnesium (Mg) dopant for varying durations followed by spark plasma sintering (SPS) of powders to prepare bulk components with superior mechanical properties. The crystallite sizes were determined for powders and the bulk components by analyzing the X-ray diffraction (XRD) spectrum. The calculations indicated a reduction in crystallite size with the increase in the cryomilling duration. The results also showed a more significant decrease in the crystallite sizes for Al-3Mg samples than that of pure Al. The changes in the surface morphology of powders were characterized using scanning electron microscopy (SEM). The elemental mapping analysis at nanoscale was carried out using Energy-dispersive X-ray spectroscopy (EDX) in Scanning transmission electron microscopy (STEM). The mechanical properties of the bulk components were assessed using a Vickers Microhardness tester. The test results demonstrated an improvement in the hardness of Mg-doped components. Higher hardness values were also reported with an increase in the cryomilling duration. This article discusses the mechanisms for the reduction in crystallite size for pure Al and Al-3Mg and its subsequent impact on improving mechanical properties.

(Digital Presentation) Spark Plasma Sintering Fabrication of α/β Interface in Mg Alloys and Analysis of Corrosion Behavior

In Mg alloys, corrosion behavior is known to be related to the microstructure. For example, AZ91D alloy contains an α matrix phase (Mg solid solution), β phases (Mg17Al12) and lamellar α+β microstructures. During the real-time in situ observation of the corrosion process under galvanostatic polarization, filiform corrosion proceeded along the outside of the β-phase (in lamellar α + β microstructure and along the α-mother phase[1]. However, the detailed mechanism of the initiation and growth of filiform corrosion is still unknown. An electrode area contains simplified α + β structure is needed to clarify the corrosion mechanism of Mg alloys. The fabrication of such specimen could be actualized by Spark Plasma Sintering (SPS).The advantage of SPS is that it can produce specimens with high efficiency and few pores. The energy from the pulsed current, self-heating of the workpiece, and particle-to-particle discharge are the combined driving force for sintering. In recent years, many experiments have been reported on the fabrication and strength evaluation of pure Mg and Mg alloys. However, only a few studies have been conducted on the fabrication and corrosion resistance of different phases.In this study, we attempted to fabricate the interface of β and α phases by SPS using pure Al powder and pure Mg powder and other materials. The characterization of different phases was carried out by XRD, EPMA and TEM. The corrosion behavior of the sintered specimens was then observed using an in-situ observation system during open circuit potential measurements. After measurements, the specimen surface was assessed using OM, AES, and FE-SEM.When a 0.25 mm thick Mg sheet was surrounded by pure Al powder, the temperature was set at 420 °C and kept for 30 minutes, a uniform white microstructure was found to form around the Mg sheet. The thickness is about 50 µm. EDS maps and point analysis show that this phase consists a β-phase (Mg17Al12) on the Mg sheet side and Mg23Al30 on the Al powder side. The thickness of the β-phase did not change obviously when the sintering time was extended to 1 hour. Finally, a β phase with a thickness of about 100 μm could be fabricated by using a specimen assembly method of outer Al powder, intermediate layer Mg powder. Analysis of corrosion behavior was done with this specimen. Z. Shao, M. Nishimoto, I. Muto, and Y. Sugawara, Corrosion Science, 192, 109834 (2021).

(Digital Presentation) Anodic Formation of Oxide Film on MoSi2 Containing Al or Nb in LiCl-KCl Molten Salt

Li and Mg metals are produced by electrolysis in a molten chloride bath. Currently carbon-based material is used as anode. However, carbon-based anode reacts electrochemically with oxide ions dissolved in the bath, which causes its undesirable consumption. In our laboratory, a new type of inert anode by forming a thin and dense oxide film has been studied. It was shown that a SiO2 film was formed on MoSi2 anode in molten LiCl-KCl melt with Li2O, and that the dissolution of MoSi2 was inhibited by the formation of oxide film. However, sufficient electrolytic current was hardly applied. In this study, the modification of the anodic properties of MoSi2 has been attempted by the addition of Nb or Al in MoSi2. A MoSi2 rod containing Nb(0.1~1.0mol%) or Al(0.1~0.5mol%) was prepared by sintering from MoSi2, Nb and Al powder. The prepared rod was pre-oxidized (1573K, 4h) to form a SiO2 film in advance, and then used as working electrode. An Al plate and Ag/AgCl were used as counter and reference electrode, respectively. The potential of the Ag/AgCl electrode was calibrated against the Li metal deposition potential measured by cyclic voltammetry. Electrolysis was conducted at 700K in an Ar atmosphere. Anodic behavior of MoSi2 was investigated by cyclic voltammetry, and potentio-static electrolysis was performed. The weight change in MoSi2 anode was measured, and the surface and cross section of the MoSi2 electrode were observed and analyzed by SEM-EDX and XRD.The shape of the cyclic voltammogram did not change significantly by the addition of Nb or Al in the MoSi2. Anodic peaks were seen around 2.5V (vs. Li / Li+, the same hereinafter) and around 3.6V. Above 3.6V, anodic current continued to flow with gas bubble formation. The current at 3.6V in the cyclic voltammogram changed with the added amount of Nb or Al as shown in Fig.1, which suggests the Nb or Al addition strongly influenced the anodic property of MoSi2.Current during potentio-static electrolysis at 4.2V increased with current oscillation. It was seen that a black film peeled periodically, and the current oscillation seemed to link the peeling. The quantity of electricity increased with Ni or Al addition in MoSi2. An oxide layer was observed on the MoSi2 surface after potentio-static electrolysis, and a dense layer was formed on MoSi2 containing 0.5~1.0mol% Nb. The weight of MoSi2 decreased by potentio-static electrolysis, and Nb or Al addition in MoSi2 clearly inhibited the weight change. The addition of 0.5~1.0mol%-Nb seemed suitable from the improvement of the anodic property of MoSi2.It was indicated that Nb or Al addition in MoSi2 influenced its anodic property, and that the addition inhibited its anodic consumption in molten LiCl-KCl. However, it was shown that the formation and peeling of the surface film occurred repeatedly, so the formation of a durable surface film should be necessary.The results of this research were obtained as a result of the commissioned work (JPNP 14004) of the New Energy and Industrial Technology Development Organization (NEDO). Figure 1

(Digital Presentation) Corrosion Resistance of 55%Al-Zn Alloy Fabricated By Ball Milling and Spark Plasma Sintering

Hot-dip 55mass%Al-Zn coated steels show good corrosion resistance because the 55%Al-Zn alloy coating layer acts as a sacrificial anode and protects the steel substrate from atmospheric corrosion.1 The balance between sacrificial behavior and dissolution resistance is important for improving the corrosion protection ability of the Al-Zn coating. In this study, 55%Al-Zn alloy was fabricated by ball milling and spark plasma sintering, and the effect of microstructure on the dissolution behavior of the 55%Al-Zn alloy was investigated. The 55%Al-Zn alloy specimen was fabricated by ball milling of Al and Zn powders and subsequent spark plasma sintering. The coating layer on the hot-dip 55%Al-Zn coated steel was used to compare the dissolution behavior. The dissolution behavior of 55%Al-Zn alloys was analyzed by galvanic current measurements and polarization measurements in a diluted synthetic seawater. In the sintered 55%Al-Zn alloy, Zn-rich phases with diameter less than 500 nm were dispersed in the Al matrix. The galvanic current measurements between the sintered 55%Al-Zn alloy and the steel substrate showed that the sintered 55%Al-Zn alloy acted as a sacrificial anode. In the galvanostatic polarization measurements, the potential of the sintered 55%Al-Zn alloy remained lower than that of the hot-dip 55%Al-Zn coating layer.Reference: S. Tokuda, I. Muto, Y. Sugawara, M. Takahashi, M. Matsumoto, and N. Hara, Corros. Sci., 129, 126–135 (2017).

Effect of Process Parameters on Properties of Cold-Sprayed Zn-Al Composite Coatings.

Al–Zn composite coating can provide effective cathodic protection for E235 steel. This study aims to obtain the Al–Zn composite coating with the best anti-corrosion performance by optimizing the spraying temperature, spraying distance and powder-feeding motor speed. The Al and Zn powders were analyzed by scanning electron microscope (SEM), and the microstructure of the coatings prepared by different process parameters was observed by optical microscope. The mechanical and anticorrosive properties of the coating were evaluated using hardness, porosity, thickness and electrochemical tests. According to the experimental results, when the spraying temperature, spraying distance and powder-feeding motor speed were 500 °C, 27 mm and 1.5 r/min, respectively, the hardness of the coating was 67 HV, the porosity was 0.57% and the thickness was 0.588 mm. The EIS test results show that the coating has the maximum polarization resistance, and therefore the coating has good corrosion resistance at this parameter.

Effects of forging on the mechanical properties of B4Cp/Al composite with flaked Al and Al2O3 particles

Abstract To flake the pure aluminum powder, ball grinding and forging are used. The mechanical properties of the forged B4Cp/Al composite are tested. The results show that ball milling can flake the pure aluminum powder. The alumina layer of Al2O3 on the surface of aluminum powder are broken during the ball milling and can be dispersed in the matrix as reinforcement. The hardness of the forged aluminum with flaked Al is higher of 19.5% than that without flaked. The forging can increase ultimate tensile strength of the B4Cp/Al composite. Increasing B4C volume fraction, the average hardness of the forged B4C/Al composite with flaked Al powder gradually increases, relative density gradually decreases, ultimate tensile strength first increases and then decreases.

Structure, phase composition and mechanical characteristics of layered composite materials based on TiB/xTi-Al/α-Ti (x = 1, 1.5, 3) obtained by combustion and high-temperature shear deformation

The effect of the ratio of titanium and aluminum in the Ti–Al intermetallic layer on the microstructure, phase composition, and mechanical characteristics of layered composite materials based on TiB/xTi-Al/α-Ti (x = 1, 1.5, 3) is studied systematically. The layered composite materials are obtained by combustion and high-temperature shear deformation. The green sample is a compressed sandwich blank consisting of two Ti–B and Ti–Al powder layers and an α-Ti titanium sheet. The mechanisms of phase and structure formation that occur during synthesis and subsequent high-temperature shear deformation in ceramic and intermetallic layers are described. It is shown that the synthesis between the initial components proceeds according to the reaction-diffusion mechanism. It has been found that the structure, grain size (from 200 nm to 15 μm), phase composition, and mechanical characteristics of the composite can be tuned by changing the initial composition and the delay time before applying external pressure. It is shown that the mechanical characteristics of the resulting composites depend on the location of macrolayers relative to the applied load during high-temperature shear deformation and have the following values: composite surface hardness up to 1800 HV, elastic modulus up to 300 GPa, elastic recovery up to 43, stress intensity factor up to 25.3 MPa m1/2, bending strength up to 650 MPa. The mechanical characteristics of the obtained composites are compared with known analogs, and the advantages are revealed.

Studying the adhesion strength of plasma powder metal coatings on the surface of graphite

Coatings applied onto the surface of specimens made of UHP electrode graphite are studied. Coatings are applied by thermal spraying in two stages: spraying of a sublayer (layer I) of the powder materials being tested; spraying of the main layer of the plasma coating, consisting of a mechanical mixture of fine spherical aluminum (Al) and copper (CuCr1) powders in an equal volume ratio. The adhesion strength between the coating and the graphite surface is studied as dependent on the following factors: sublayer thickness; the type of preliminary surface preparation; the chemical composition of the powder material of the sublayer. It has been found that the highest adhesion strength between the coating and the graphite base is achieved when the sublayer thickness is 80 µm, when a thread with a depth of 1.0 mm is cut on the base surface, and when Al powder is used as a sublayer.

Preparation of Al‐Dy core‐shell particles by electron beam treatment of Al powder with consequent magnetron deposition of Dy film

• A new method was proposed for coating a commercial aluminum powder by Dy. • Low-energy high-current electron-beam treatment and magnetron sputtering were used. • Surface smoothing and cleaning were detected after electron-beam refinement. • The average size of powder particles increases with the number of e-beam pulses. • Rolling and shaking of powder during the treatment causes uniformity of deposition. The paper presents a new method for coating commercial metal powders with rare‐earth elements (REE). This method consists of a two‐step treatment of a metal powder in a single vacuum cycle, namely the pulsed irradiation above the melting point by a low‐energy high‐current electron beam with subsequent magnetron sputtering of REE. This research reports the preparation of Al‐Dy core‐shell powder with an average diameter of particles of 40 µm. A powder holder system, providing rotary agitation and shaking of powder, was used to guarantee the uniform processing of each particle. It was established that electron beam irradiation leads to smoothing and cleaning the Al particles from surface oxides. With an increase in the number of pulses, the uniformity of processing increases; however, an increase in the average particle size occurs. Subsequent magnetron sputtering allows completely coating the surface of processed powder with dysprosium. The proposed method can be suitable for fabricating different metal‐REE core‐shell powders with necessary changes in processing parameters.

Natural pozzolan–based green geopolymer foam for thermal insulation

The current study investigates the possibility of volcanic Tuff of Earth of Datça (ED) in Turkey to be used as an aluminosilicate source in producing a geopolymer foam for thermal insulation. An extensive evaluation of the effects of fine sand–to–pozzolan and Al powder–to–pozzolan ratios on the physical, mechanical, and thermal properties and morphology (porosity, average and maximum pore diameter, pore size distribution) of the pores were carried out. The sodium silicate and potassium hydroxide (12.5 M) solutions with an activator ratio of 2.5 were used as alkali activators, and Al powder was used as a foaming agent. Research results reveal that Earth of Datça is a suitable precursor for producing a geopolymer foam. Fine sand and aluminum powder contents are critical to the optimum foam structure. The addition of finely ground silica sand ensured the volumetric stability of the binder and prevented the collapse after swelling of the binder. The optimum Al powder–to–pozzolan ratio was determined as 0.5% because it gives higher physical, mechanical, and thermal properties due to the more homogenous microstructure with finer pore size and narrower pore size distribution lower degree of interconnectivity between the pores. Research results also show that the natural volcanic Tuff of Datça Peninsula as an aluminosilicate source gives promising results in the field of producing highly porous geopolymers with low thermal conductivity (0.087–0.134 W/mK), high porosity (72.3–82.6%) and an adequate compressive strength (0.40–2.09 MPa). This study contributes to the literature that Earth of Datça–based geopolymer foam may function well as an insulation material for building enclosures.

Natural pozzolan-based green geopolymer foam for thermal insulation

The purpose of the current study is to investigate the possibility of volcanic Tuff of Earth of Datça (ED) in Turkey to be used as an aluminosilicate source in the production of a geopolymer foam for thermal insulation. An extensive evaluation of the effects of fine sand-to-pozzolan and Al powder-to-pozzolan ratios on the physical, mechanical, and thermal properties and morphology (porosity, average and maximum pore diameter, pore size distribution) of the pores were carried out. The sodium silicate and potassium hydroxide (12.5 M) solutions with an activator ratio of 2.5 were used as alkali activators and Al powder was used as a foaming agent. Research results reveal that Earth of Datça is a suitable precursor for the production of a geopolymer foam. Fine sand and aluminum powder contents are key factors on optimum foam structure. Addition of finely ground silica sand ensured the volumetric stability of the binder and prevented the collapse after swelling of the binder. The optimum Al powder-to-pozzolan ratio was determined as 0.5 % because it gives higher physical, mechanical and thermal properties due to the more homogenous microstructure with finer pore size, narrower pore size distribution and lower degree of interconnectivity between the pores. Research results also show that natural volcanic Tuff of Datça Peninsula as aluminosilicate source gives promising results in the field of producing highly porous geopolymers with low thermal conductivity (0.087-0.134 W/mK), high porosity (72.3-82.6 %) and an acceptable compressive strength (0.40-2.09 MPa). This study contributes to the literature that Earth of Datça-based geopolymer foam may function well as an insulation material for building enclosure.

Metal Coating by TIG Arc Deposition Method

Metal (Aluminum) coating was prepared on stainless steel substrate by arc deposition method using TIG Welding machine. Plasma spray is a type of metal coating that is widely used in the industry and its preparation cost is expensive. It is also the most flexible method to apply a wide variety of coatings on a substrate. To reduce the cost of the set-up, the plasma will be generated by using a TIG welding machine to replace the plasma spray. The use of powder which is aluminium as a coating raw material causes almost no restrictions on the use of coating materials used in the plasma melting process. The changing parameters in this experiment are the angle nozzle powder and the flow rate of the working gas which is Argon (Ar) gas and the substrate used is SUS304 stainless steel and the feedstock powder used is Aluminium (Al) powder with an average size of 5 μm. Flow rate used in this study was 10,20 and 30 l/min of Ar and the powder nozzle spray angle was 45°, The live image, diameter, thickness, and surface roughness of the coatings were systematically analyzed using LEXT OLS5000 3D Measuring Laser Microscope.

Synthesis of substitutional hexaboride of lanthanum and cerium La1–xCexB6 via aluminothermic reduction

Rare-earth hexaborides (REB6) are vital raw materials for cathode materials and high temperature structural ceramics that are widely applied as high-frequency electron tubes and ceramics adaptive for extreme environment, respectively. In this work, single phase substitutional solid solution REB6 (LaB6, La0.75Ce0.25B6, La0.5Ce0.5B6, La0.25Ce0.75B6 and CeB6) powders were prepared with the raw materials of La2O3, CeO2, B4C and Al powders, after calcining at 1773 K for 4 h and the following alkaline leaching. All substitutional solid solution products have homogeneous distributions of La and Ce in particles. Through microscopic morphology analysis, it is discovered that the formation of solid solution is beneficial for reducing the particle size of product, relative to LaB6 and CeB6. Moreover, Al flux plays an important role in decarbonizing reaction, and C contents of all products are below 0.4 wt%.

Enhanced room-temperature reduction of graphene oxide using Al as a supplement in the liquid phase HI

Chemical reduction of graphene oxide has emerged as one of the most suitable processes for low-cost and large-scale production of graphene for potential applications. Here we report a simple, efficient, scalable, room-temperature method for enhanced reduction of graphene oxide (GO). Nowadays, hydroiodic acid (HI) is being widely used as a reducing agent for synthesizing highly conductive reduced graphene oxide. Herein, aluminum (Al) powder was used in the second step to improve the extent of reduction using HI. Al3+, which is a strong lewis acid, helps further in the reduction and enhances the one-step reduction by HI. Field Emission Scanning Electron Microscope (FESEM), Transmission Electron Microscope (TEM), X-Ray Diffraction (XRD), Raman and X-Ray Photoelectron Spectroscopy (XPS) confirmed the formation of GO and assisted in understanding the potential of HI and Al–HI as reducing agents. The comparative analysis demonstrates the enhancement in the reduction properties of the novel Al supplemented reduced GO. Additionally, an electrically conductive dip-coated film with a sheet resistance of 4.56 × 104 Ω/sq was successfully fabricated using this Al-supplemented reduction technique.

Few-layered graphene reinforced Al-10 wt% Si-2 wt% Cu matrix composites

Few-layered graphene (FLG) reinforced Al-10 wt% Si-2 wt% Cu (Al10Si2Cu) matrix composites were fabricated via a powder metallurgical route. FLG powders were produced in an originally designed DC arc reactor via arc discharge method. Al, Si, Cu and FLG powders were subjected to high-energy ball milling at different durations to produce ternary Al alloy with homogeneously dispersed FLG, and bulk composites were fabricated via subsequent uni-axial compaction and pressureless sintering. The effects of varying FLG amounts and milling duration on the properties of the powder and bulk samples were investigated. The characterization of as-blended and mechanically alloyed (MAed) powders and their sintered forms were performed in terms of microstructural, thermal, mechanical, wear and corrosion properties. According to the results, the hardness values of the 4 h MAed Al10Si2Cu-xFLG composites were determined as 102, 154, 191 and 241 HV for x = 0, 1, 2 and 5 wt%, respectively. Despite the greater hardness value of the Al10Si2Cu-5FLG-4h composite, its compressive strength was low due to its brittle structure. The highest compressive strength was shown by the Al10Si2Cu-1FLG as 463 MPa by an approximate increase of 53% compared to that of the Al10Si2Cu matrix. Moreover, the tribology tests showed that FLG addition (up to 2 wt%) improved the wear rate of the Al10Si2Cu matrix. However, a deteriorative effect of FLG on the corrosion resistance of the composites was determined.

An ultra-low infrared emissivity composite coating with outstanding mechanical properties and salt water resistance

An ultra-low infrared emissivity composite coating with outstanding mechanical properties and salt water resistance was prepared by using epoxy resin, flake Al powders, KH560 and dioctyl phthalate (DOP) as resin matrix, functional pigments, and modifiers, respectively. The effects of Al powder addition, silane coupling agent types, silane coupling agent addition, and DOP addition on the coating performance were discussed. In addition, the salt water resistance of the coating under the optimal formulation conditions was examined. The results show that when the addition amount of Al powder is 50 wt%, the coating has lowest infrared emissivity (0.025) and glossiness (20.7) properties. By adding a certain amount of KH560 and DOP to the coating formulation, the mechanical properties of the coating can be significantly improved by enhancing the bonding strength between the resin matrix and the pigment, and between the resin matrix and the substrate. When the content of KH560 and DOP in the coating are both 7 wt%, the coating has ultra-low infrared emissivity (0.053), low glossiness (17.3), and outstanding mechanical properties (adhesion strength is grade 1, flexibility is 2 mm, impact strength is 50 kg.cm) at the same time. After the coating with the best formulation was corroded by salt water for 21 days, the emissivity, glossiness, and mechanical properties of the coating had limited changes, which showed that the prepared coating had good salt water resistance.

Establishment of a NIR-based methodology for tracking the blend homogeneity of HTPB propellant slurry in the mixing process

The hydroxyl-terminated polybutadiene (HTPB) propellants with high level of solid loadings from 80 wt% to 90 wt% consist of aluminum (Al) powder, ammonium perchlorate (AP) and HTPB. The Al/AP/HTPB adhesive system full of solid grains appears high viscosity against flow. Therefore, the mixing is a crucial procedure in the production as it directly affects the structural integrity of the finished product. This work focused on the feasibility of tracking the blend homogeneity of Al/AP/HTPB adhesive system in the mixing process through using the near-infrared (NIR) spectroscopy and orthogonal partial least squares discrimination analysis (OPLS-DA). The OPLS-DA classification models were created by variable selection, spectral pretreatment and latent variables (LVs) optimization. It had been demonstrated that the developed models presented an excellent predictability with the root mean square error of cross-validation (RMSECV) for slurries in Ⅰ, Ⅱ groups of 0.1261 and 0.0789, respectively. Meanwhile, the well-fitted models for slurries in Ⅰ, Ⅱ groups with the squared correlation coefficient (R2) of 0.806 and 0.980, exhibited separately an acceptable predictive capability with the predictive squared correlation coefficient (Q2) > 0.5. Furthermore, Euclidean distance and move block standard deviation (MBSD) as reference methods were used to validate the predictive performance of the developed models with respect to the blend homogeneity of HTPB propellant slurry. The experimental results showed that the terminal time for each batch of slurry reaching to ideal uniformity predicted by Euclidean distance/MBSD and OPLS-DA were both at 26–30 min. Therefore, it had been proved that the method we proposed was a potential tool to monitor the variation of the uniform state of HTPB propellant slurry in the mixing process.