Micron Aluminum Research Articles

3‐D Printing and Development of Fluoropolymer Based Reactive Inks

Engineering reactive materials is an ever present goal in the energetics community. The desire is to have energetics configured in such a manner that performance is tailored and energy delivery can be targeted. Additive manufacturing (3‐D printing) is one area that could significantly improve our capabilities in this area, if adequate formulations are developed. In this paper, fluoropolymer based reactive inks are developed with micron (mAl) and nanoscale aluminum (nAl) serving, as the fuel at high solids loading (up to 67 wt%) and their viscosity required for 3‐D printing is detailed. For the pen‐type technique and valves used in this work, it is required to have viscosities on the order of 104–105 cP. For printed traces with apparent diameters under <500 μm, the combustion velocities for both micron and nano scale aluminum formulations, are approximately identical: 30 ± 3 versus 32 ± 2 mm s−1, respectively. Further increasing the apparent diameter is shown to increase the combustion velocity in the case of the nanoscale aluminum formulation by four‐fold over that of the micron scale aluminum formulation, but it plateaus as it approaches an apparent diameter of 2 mm. The results suggest with proper architecture that tailorable combustion rates and energy delivery are feasible.

Preparation of mono-dispersed, high energy release, core/shell structure Al nanopowders and their application in HTPB propellant as combustion enhancers

Mono-dispersed, spherical and core/shell structure aluminum nanopowders (ANPs) were produced massively by high energy ion beam evaporation (HEIBE). And the number weighted average particle size of the ANPs is 98.9 nm, with an alumina shell (3–5 nm). Benefiting from the passivation treatment, the friction, impact and electrostatic spark sensitivity of the ANPs are almost equivalent to those of aluminum micro powders. The result of TG-DSC indicates the active aluminum content of ANPs is 87.14%, the enthalpy release value is 20.37 kJ/g, the specific heat release S1/Δm1* (392–611 °C) which determined the ability of energy release is 19.95 kJ/g. And the value of S1/Δm1* is the highest compared with ANPs produced by other physical methods. Besides, the ANPs perfectly compatible with hydroxyl-terminated polybutadiene (HTPB), 3 wt. % of ANPs were used in HTPB propellant replaced micron aluminum powders, and improved the burning rate in the 3–12 MPa pressure range and reduced the pressure exponential by more than 31% in the 3–16 MPa pressure range. The production technology of ANPs with excellent properties will greatly promote the application of ANPs in the field of energetic materials such as propellant, explosive and pyrotechnics.

Shear bond strength of resin adhesive to laser treated surface of yttria tetragonal zirconia polycrystalline

Purpose: This study evaluated the effects of surface treatment of zirconia with erbium-doped yttrium aluminum garnet (Er-YAG) laser on shear bond strength to resin cement. Materials and Methods: Thirty disc-shaped zirconia specimens (10 mm in diameter and 2 mm in thickness) were fabricated, randomly assigned to 3 groups (n = 10) and treated surface with: Gr. N) no treated surface, Gr. S) sandblasted with 50 micron alumina and Gr. L) treated with an Er-YAG laser. Zirconia surface was then applied with metal/zirconia primer prior to be cemented to composite cylinder (5 mm in diameter and 4 mm in thickness) with resin cement. Shear bond strength test was performed at a crosshead speed of 0.5 mm/min. Data were analyzed by ANOVA and Tukey HSD tests. Results: The means and standard deviations of shear bond strength (MPa) were: Gr. N) 10.79 ± 1.03, Gr. S) 14.15 ± 3.07, Gr. L) 14.11 ± 1.98. The treatment of zirconia surface were significantly affected to shear bond of resin adhesive to zirconia (p 0.05). Conclusion: Pretreatment of zirconia by Er-YAG laser improved bond strength to resin cement. The study suggested that Y-TZP ceramics should be treated surface with Er-YAG laser before cementation. Keywords: Zirconia; Resin Cement; Er-YAG Laser; Shear Bond Strength

Thermal and Chemical Stability of Micron Aluminum Powders Subjected to Gaseous Water

The paper studies the impact of gaseous water on the stability of micron aluminum powders in time at room temperature using the method of gravimetric analysis. The stability was studied using methods of thermal analysis during heating up to 1200 °С in air. The composition of products was analyzed using X-ray diffraction analysis. It was found out that the stability of micron aluminum powders depends on partial pressure of water vapor: the increase of pressure results in decreased stability of powders. The work gives recommendations for storing micron aluminum powders.

Comments on: “Combustion of nano-sized aluminum particles in steam: Numerical modeling”, by V.B. Storozhev and A.N. Yermakov

This comment points out the large discrepancy between the predictions of the recently published model by Storozhev and Yermakov (Storozhev and Yermakov, Combust. Flame 162 (2015) 4129–4137) and the large body of accumulated literature on aluminum combustion. Their model predicts burning times between 40-63 ms for a cloud of nanometric aluminum particles (20 or 50 nm) burning in steam at initial temperatures around 2300 K. These predictions are roughly two orders of magnitude larger than the measured combustion times of micron and submicron aluminum particles from various experiments, which are on the order or hundreds of microseconds to milliseconds. Experimentally measured flame speeds of aluminum flames in the products of hydrocarbon flames, and the burn rates of metal-water propellants, also point to much faster burning rates of aluminum particles in steam than predicted by this model. As such, the predictions of the model by Storozhev and Yermakov cannot be reconciled with the available experimental evidence.

Ignition and combustion of pyrotechnic compositions based on micro- and nanoparticles of aluminum diboride in air flow in a two-zone combustion chamber

This paper presents the experimental study of ignition and combustion of micro- and nanoparticles of aluminum diboride as part of pyrotechnic energy-saturated compositions in a gas generator with an air afterburner chamber and the thermodynamic calculations of combustion of pyrotechnic compositions based on aluminum diboride in air. The discharge of the combustion products from the afterburner chamber is recorded on video. It is shown that replacing micron aluminum diboride by powdered diboride with a mass-average diameter of particles equal to ≈270 nm in the pyrotechnic composition and increasing the pressure in the afterburner chamber cause the combustion efficiency in air to increase by 5–20%.

Effect of surface treatments on shear bond strength of resin composite bonded to CAD/CAM resin-ceramic hybrid materials.

PURPOSEThe purpose of this study was to assess the effect of surface treatments on shear bond strength of resin composite bonded to thermocycled and non-thermocycled CAD/CAM resin-ceramic hybrid materials.MATERIALS AND METHODS120 specimens (10×10×2 mm) from each material were divided into 12 groups according to different surface treatments in combination with thermal aging procedures. Surface treatment methods were airborne-particle abrasion (abraded with 50 micron alumina particles), dry grinding (grinded with 125 µm grain size bur), and hydrofluoric acid (9%) and silane application. According to the thermocycling procedure, the groups were assigned as non-thermocycled, thermocycled after packing composites, and thermocycled before packing composites. The average surface roughness of the non-thermocycled specimens were measured after surface treatments. After packing composites and thermocycling procedures, shear bond strength (SBS) of the specimens were tested. The results of surface roughness were statistically analyzed by 2-way Analysis of Variance (ANOVA), and SBS results were statistically analyzed by 3-way ANOVA.RESULTSSurface roughness of GC were significantly lower than that of LU and VE (P<.05). The highest surface roughness was observed for dry grinding group, followed by airborne particle abraded group (P<.05). Comparing the materials within the same surface treatment method revealed that untreated surfaces generally showed lower SBS values. The values of untreated LU specimens showed significantly different SBS values compared to those of other surface treatment groups (P<.05).CONCLUSIONSBS was affected by surface treatments. Thermocycling did not have any effect on the SBS of the materials except acid and silane applied GC specimens, which were subjected to thermocycling before packing of the composite resin.

金属アルミニウム粒子の連続燃焼技術の確立

Aluminum is expected to be one of candidates to store energies that has generated by renewable source such as solar and wind powers, which yields a sustainable energy cycle between aluminum and alumina. In the present paper, we developed an aluminum powder burner to extract heat and emission by the combustion for power generation. We supplied 3 micron aluminum powder with air to the cylindrical combustor with a backward step and achieved continuous combustion after ignition. We then investigated the flammable map and it was found that the limiting equivalence ratio for blow-off increased with the total air flow rate.

Study of Evolution Rule of Aggregates in Ceramic Suspension

Using the micron alumina powder for the study, through the analysis of the ceramic suspension rheological, the generation and evolution and its mechanism of aggregates in the ceramic suspension were studied. The results showed that the number, size and intensity of aggregates will be effected by the gravitational potential or the barrier height between the particles in suspension as varying the process conditions. Generally, the formation of aggregates was corresponded to the interaction potential between particles, that is, the second potential well. Thus, their internal bonding strength is weak. In the flowing suspension, aggregates were meta-stability under shear forces, electrostatic repulsion and van der Waals potential. The variation of the aggregates was a reversible process as decomposition then reunion again.

Investigation on high-velocity impact of micron particles using material point method

Continuous high-velocity impact of micro space debris and micro-meteroids may cause significant accumulative damages to spacecrafts. The process of high-velocity impact of micron aluminum particles on the aluminum target is investigated with the material point method (MPM). As a meshfree particle method, MPM is very suitable for solving high-velocity impact problems owing to its prominent advantages of dealing with fracture, fragmentation and moving material interface over the traditional mesh-based methods. The target plate is modeled as semi-infinite media since its thickness is much larger than the characteristic length of the projectile particles. The micron particles are projected to the target individually and in group with different angles and different velocities. The predicted impact responses and dimensions of the craters agree well with the experimental results and the empirical equations. The influences of the flux density, the projectile angle and the impact velocity are thoroughly investigated, and the morphology modes of the crater group are concluded. Finally, an empirical formula is proposed for the crater depth under impact of particle group.

Porous mullite ceramics fabricated by co-pyrolysis alumina powders filled silicone resin

Nanoporous mullite ceramics were fabricated by pyrolysis of micron alumina powders filled with silicone resin. The mixture of silicone resin and micron γ-Al2O3 began transforming to mullite at 1250°C in air, and could be entirely transformed to mullite when the pyrolysis temperature exceeded 1300°C. The effect of shaping pressure on microstructure and mechanical property of the porous mullite ceramics was investigated. The experimental results showed that the porosity and flexural strength can be easily tuned by changing shaping pressure. Both of the open porosity and average pores size of the obtained samples decreased at elevated shaping pressure. With a shaping pressure of 65 MPa, nanoporous mullite ceramics with an average pore size of 32 nm can be obtained, showing 23·5% in open porosity and 50 MPa in flexural strength. Interestingly, the microstructure of porous mullite ceramics consisted of loose region and dense region for the most possible reason that the Al2O3 powders were un-homogeneously distributed in silicone resin.

Material Characterization and Microwave Substrate Applications of Alumina‐Filled Butyl Rubber Composites

Composites of butyl rubber with micron alumina (BRAL) and nanoalumina (BRnAL) have been prepared by sigma mixing. The stress‐strain curves of both BRAL and BRnAL composites show the mechanical flexibility of the composites. The dielectric and thermal properties of both composites were studied as a function of ceramic loading. For 0.1 volume fraction of micron alumina loading, the composites have attained a relative permittivity (εr) of 2.82 and loss tangent (tanδ) of 0.0023 at 5 GHz, and for the same volume fraction of nanoalumina content, the composite showed εr of 3.15 and tanδ of 0.014 at 5 GHz.

Influence of aluminum particle size on ignition and nonstationary combustion of heterogeneous condensed systems

The results of studies of the effect of particle size of aluminum powder in condensed systems on the ignition, nonstationary combustion, and acoustic conductivity of the burning surface are presented. Analysis of the experimental data shows that the ignition delay and the temperature of burning surface of the heterogeneous condensed systems under study decrease with increasing particle size of aluminum powder, and the nature of the dependence of the nonstationary burning rate on the time of depressurization of the combustion chamber for compositions containing micron or ultrafine aluminum powders is in qualitative agreement with the phenomenological theory of nonstationary combustion. Replacement of micron aluminum powder by ultrafine powder in a heterogeneous condensed system increases acoustic conductivity.

Feasibility Study and Demonstration of an Aluminum and Ice Solid Propellant

Aluminum-water reactions have been proposed and studied for several decades for underwater propulsion systems and applications requiring hydrogen generation. Aluminum and water have also been proposed as a frozen propellant, and there have been proposals for other refrigerated propellants that could be mixed, frozen in situ, and used as solid propellants. However, little work has been done to determine the feasibility of these concepts. With the recent availability of nanoscale aluminum, a simple binary formulation with water is now feasible. Nanosized aluminum has a lower ignition temperature than micron-sized aluminum particles, partly due to its high surface area, and burning times are much faster than micron aluminum. Frozen nanoscale aluminum and water mixtures are stable, as well as insensitive to electrostatic discharge, impact, and shock. Here we report a study of the feasibility of an nAl-ice propellant in small-scale rocket experiments. The focus here is not to develop an optimized propellant; however improved formulations are possible. Several static motor experiments have been conducted, including using a flight-weight casing. The flight weight casing was used in the first sounding rocket test of an aluminum-ice propellant, establishing a proof of concept for simple propellant mixtures making use of nanoscale particles.

COMBUSTION OF BIMODAL ALUMINUM PARTICLES AND ICE MIXTURES

The combustion of aluminum with ice is studied using various mixtures of nanoand micrometersized aluminum particles as a means to generate high-temperature hydrogen at fast rates for propulsion and power applications. Bimodal distributions are of interest in order to vary mixture packing densities and nascent alumina concentrations in the initial reactant mixture. In addition, the burning rate can be tailored by introducing various particle sizes. The effects of the bimodal distributions and equivalence ratio on ignition, combustion rates, and combustion efficiency are investigated in strand experiments at constant pressure and in small lab-scale [1.91 cm (0.75 in.) diameter] static firedrocket-motor combustion chambers with center-perforated propellant grains. The aluminum particles consisted of nanometer-sized particles with a nominal diameter of 80 nm and micron-sized particles with nominal diameters of 2 and 5 μm. The micron particle addition ranged from 0% to 80% by active mass in the mixture. Burning rates from 1.1 (160 psia) to 14.2 MPa (2060 psia) were determined. From the small scale motor experiments, thrust, C∗, Isp, and C∗ and Isp efficiencies are provided. From these results, mechanistic issues of the combustion process are discussed. In particular, overall lean equivalence ratios that produce flame temperatures near the melting point of alumina resulted in considerably lower experimental C∗ and Isp efficiencies than equivalence ratios closer to stoichiometric. The substitution of micron aluminum for nanometer aluminum had little effect on the linear burning rates of Al/ice mixtures for low-mass substitutions. However, as the mass addition of micron aluminum increased (e.g., beyond 40% 2-μm aluminum in place of 80-nm aluminum), the burning rates decreased. The effects of bimodal aluminum compositions on motor performance were minor, although the experimental results suggest longer combustion times are necessary for complete combustion.

Comparative Experimental Study on Explosion Characteristics of Nano-Aluminum Powder and Common Aluminum Powder in the Explosive Device of a Long Pipeline

In order to study the explosion characteristics of nanometer aluminum, comparative experimental studies on explosion characteristics of nanometer aluminum powder and common aluminum powder with different grain diameters have been carried out by using the horizontal pipeline explosive test device. After analyzing both the explosion process and the data of explosion characteristics of two aluminum powder during the experiment, some explosion characteristics of nanometer aluminum powder different from common aluminum powder can be concluded. Research result expressed: The maximal duration of explosion pressure of nanometer aluminum powder in its explosion process is much longer, which is about 3 to 4 times longer than non-nanometer aluminum; In the nanometer range, the scope of explosion pressure is much wider (between the 40~750kPa) than others, and as a whole, explosion pressure of the nanometer aluminum powder is much higher than the micron aluminum powder; In the process of explosion propagation of aluminum powder, flame combustion wave and explosion pressure wave show the positive feedback mechanism, which is interacting with each other and accelerating each other.

Microstructures of Cu-Alloyed Ductile Cast Iron Treated by Two-Step Austempering

The excellent mechanical properties of austempered ductile iron are due to the unique matrix microstructure called “ausferrite”. Such microstructure is obtained from the first stage reaction during isothermal transformation of austenite into ferrite and high carbon austenite. The second stage reaction is the decomposition of high carbon austenite into ferrite and carbide. In this study, the microstructure of Cu-alloyed ductile iron treated by two-step austempering was investigated using SEM and TEM. The two-step austempering consists of 1) quenching from 900°C to 300°C and hold for 6 minutes in a salt bath, and 2) increasing the temperature of the salt bath by 30°C at the rate of 3°C per minute and holding until the total time was 120 minutes. The SEM samples were prepared by grinding to 1200 grit, polishing with 0.3 micron alumina powder and etching using 2% nital. Thin foil discs of 3 mm diameter for TEM observation were prepared by mechanical thinning to 80-100 microns and were then dimpled to 20 microns. Final thinning was carried out using Gatan precision ion polishing system (PIPSTM). The thin foils were then examined using Jeol-JEM2010 operating at 200 kV. TEM results show that the matrix microstructure is ferrite subunits interspersed with retained austenite films. The subunits and austenite films exhibit either Kudjamov-Sachs (K-S) or Nishiyama-Wasserman (N-W) orientation relationships. Occasionally, fine carbide precipitate was observed.

Reaction kinetics of nanometric aluminum and iodine pentoxide

Owing to increasing threats of biological attacks, new methods for the neutralization of spore-forming bacteria are currently being examined. Thermites may be an effective method to produce high-temperature reactions, and some compositions such as aluminum (Al) and iodine pentoxide (I2O5) also have biocidal properties. This study examines the thermal degradation behavior of I2O5 mixed with micron and nanometer scale aluminum (Al) particles. Differential scanning calorimetry (DSC) and thermogravimetric (TG) analyses were performed in an argon environment on both particle scales revealing a non-reaction for micron Al and a complex multistep reaction for the nanometer scale Al. Results show that upon I2O5 decomposition, iodine ion sorption into the alumina shell passivating Al particles is the rate-controlling step of the Al–I2O5 reaction. This pre-ignition reaction is unique to nano-Al mixtures and attributed to the significantly higher specific surface area of the nanometric Al particles which provide increased sites for I− sorption. A similar pre-ignition reaction had previously been observed with fluoride ions and the alumina shell passivating Al particles.

A comparative evaluation of shear bond strength of porcelain and composite using different bonding agents — An in vitro study

The purpose of the present in vitro study is to compare and evaluate the shear bond strength of porcelain and composite using different bonding agents. Sixty-three porcelain pellets were prepared and were divided into 9 groups. Three surface treatment and two bonding agents were evaluated. The surface treatment were: 1) sandblasting; 2) etching with 35% phosphoric acid; and 3) etching with 8% hydrofluoric acid. Applying bonding agents Scotch bond adhesive and clearfil liner bond 2V and combination of these treatments. Composite resin was condensed and light cured for 60 seconds on the porcelain specimens which were stored in distilled water at 37°C for 24 hours before mechanical testing. The bond strength were significantly different according to ANOVA F-test (F = 6.28, p < 0.01) and Duncan's Multiple Range Test. Eight percent hydrofluoric acid showed higher bond strength when compared to 35% phosphoric acid etching and sandblasting by 50 micron aluminum oxide. Highest bond strength was observed with hydrofluoric acid + clearfil. Etching with 8% hydrofluoric acid + clearfil liner bond showed higher bond strength when compared to hydrofluoric acid alone. This is indicative that effect of silane and etching can be use to improve mechanico chemical bonding. Among bonding agents used clearfil liner showed higher bond strength when compared to scotch bond adhesive.

Heat release measurements on micron and nano-scale aluminum powders

Aluminum nanoparticles are a focus of active research largely due to their attractive oxidation energetics and fast reaction kinetics compared with micron-scale or larger particles. A large number of different aluminum powders are currently available and the present study reports the results from a side-by-side comparison of several representative types of aluminum nanoparticles. Conventional oxide-passivated micron-scale and nano-scale powders, as well as organically passivated nanoparticles were studied using pyrolysis combustion flow calorimetry (PCFC) at temperatures up to 700 °C. The reaction onset temperature and extent of oxidation were observed to depend on particle size. A multi-step oxidation process was observed, with the individual steps becoming increasingly pronounced at smaller particle sizes. The results from PCFC testing gave useful insight into the oxidation behavior of these materials, especially the organic passivated particles, but, under these oxidation conditions the materials were not fully oxidized.