Iron Oxide Doped Spray Dried Aluminum Oxide Granules for Selective Laser Sintering and Melting of Ceramic Parts

Abstract

Powder bed density, flowability, and laser light absorption of the powder strongly influence the quality and performance of aluminum oxide parts processed by selective laser sintering and melting. By means of spray drying, highly dense granules with a good flowability are manufactured. An ultrasonic atomizer and a co-current droplet air mixing are used to spray aqueous slurries consisting of either bimodal or trimodal distributions of aluminum oxide. Nano-iron oxide improves the interaction with the green pulsed laser. The improved absorption of the green laser light is verified by means of an Ulbricht sphere. The appropriate amount of dispersant for consecutive water-based spray granulation is determined by Zeta Potential measurements. Dibasic ammonium citrate is found to be the most suitable dispersant. A final uniform distribution of the iron oxide within the spray dried granules is confirmed by X-ray μ-beam fluorescence tomography. The powder quality is characterized by apparent density, tapped density, Hausner ratio, moisture content, and particle size distribution. Powders with a tapped density of almost 50% of the theoretical density and an absorbance of 69% (green laser light) lead to maximum densities of the laser processed parts of around 96%.

Pre-processing of hematite-doped alumina granules for Selective Laser Melting

“…Fe 2 O 3 as a dopant in alumina granules. As already demonstrated by the authors, the presence of 1 wt% of the dopant has significant effect on the optical properties of the powder, but also on the final properties of the manufactured parts [13], [14].…”

Millisecond photonic sintering of iron oxide doped alumina ceramic coatings

“…6c) were all indexed to the Al 2 O 3 α-phase. One possible factor, which could lead to the formation of the spheres, is the balling effect due to the partial melting of the ceramic layer, which is known from laser processing to be the most favorable shape during melting of alumina ceramics 29 . However, the fact that these spheres were hollow and composed of only α-Al 2 O 3 grains is contradictory to the assumption of balling, since rapid cooling from the melt most likely leads to the γ-Al 2 O 3 formation, as described before.…”

“…www.nature.com/scientificreports/ homogeneous dispersion of all particles in Nanopure water. For the nano-α/γ-Fe 2 O 3 L2715D a BET average particle size was calculated from the absolute density and the corresponding specific surface area (SSA) assuming monomodal spherical particles according to the Sauter mean diameter 29 . BET (Brunauer-Emmett-Teller) measurements (SA 3100 Surface Area Analyzer, Beckman Coulter, Germany) provided the specific surface area (SSA) of the particles.…”

“…Table S1 summarizes the measured absolute density, SSA and calculated BET average particle size and Table S2 shows d 10 , d 50 and d 90 measured by DLS and LD. A thin and uniform coating layer was achieved by utilizing a bimodal mixture of micron-sized (µm-sized) α-Al 2 O 3 , submicron (nm-sized) α-Al 2 O 3 , and doping of 1 wt% Fe 2 O 3 nanoparticles, which was previously used for the selective laser melting (SLM) method 29,30 . Both corundum (α-Al 2 O 3 ) and hematite (Fe 2 O 3 ) belong to the same space group R3c with lattice parameters of a = 4.760 Å and c = 12.993 Å and a = 5.039 Å and c = 13.740 Å, respectively, and can form solid solutions.…”

An Innovative Selective Laser Melting Process for Hematite‐Doped Aluminum Oxide

“…The starting material consisted of granules prepared by Empa Swiss Federal Laboratories for Materials Science and Technology. The procedure for the production of granules was explained in detail in Pfeiffer . Each granule consists of aluminum oxide Sumitomo AA3 (average particle size of 3.4 μm), Sumitomo Al 2 O 3 AA03 (0.44 μm) and Al 2 O 3 Evonik AluC (13 nm) with the addition of a light‐absorbing additive, namely, iron oxide (Fe 2 O 3 ) in the form of nano‐rods (BASF L2818D).…”