Potentialities of Reaction Sintering in the Fabrication of High-Strength Macroporous Ceramics Based on Substituted Calci
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ntialities of Reaction Sintering in the Fabrication of High-Strength Macroporous Ceramics Based on Substituted Calcium Phosphate N. K. Orlova, b, *, A. K. Kiselevaa, P. A. Milkina, P. V. Evdokimova, c, V. I. Putlayeva, c, and J. Günsterb aFaculty
of Materials Science, Moscow State University, Moscow, 119234 Russia Federal Institute for Materials Research and Testing (BAM), Berlin, 12203 Germany c Faculty of Chemistry, Moscow State University, Moscow, 119234 Russia *e-mail: [email protected]
b
Received March 27, 2020; revised August 6, 2020; accepted August 10, 2020
Abstract—Calcium alkali metal (potassium and sodium) double and triple phosphates have been synthesized in different ways. Was for the first time used reaction sintering to produce ceramics based on calcium alkali metal mixed phosphates and investigated the densification behavior of mixed phosphate-based multiphase materials during sintering by this method. Was presented the microstructure of polished surfaces of sintered samples differing in phase composition and determined the density of ceramics prepared using reaction mixtures differing in composition. The effect of reaction sintering on the porosity of the ceramics has been assessed. Using stereolithographic printing and reaction sintering, was produced macroporous mixed calcium phosphate-based ceramic implants. Their compressive strength has been determined to be 0.78 ± 0.21 MPa for two-phase samples and 1.02 ± 0.13 MPa for three-phase samples. Keywords: reaction sintering, calcium alkali metal double phosphates, rhenanites, bioceramics, stereolithography DOI: 10.1134/S0020168520120146
INTRODUCTION Owing to accumulation of data on the in vivo functioning of implants in the human body, a highly porous (70 to 90% porosity) scaffold is currently thought to be an optimal kind of implant. This is due to a number of requirements for bone implants, such as bioresorbability, osteoconductivity, biocompatibility, and others [1–4]. Nevertheless, the ceramic scaffold itself should have strength as high as possible and, hence, density as high as possible. Raising the density of substituted calcium phosphate-based ceramics is a rather nontrivial issue because the cation diffusion rate in calcium phosphates with calcium partially replaced by other metal ions (in particular, by potassium and/or sodium) [5– 7] is rather high. At the same time, the diffusion rate of phosphate anions remains low owing to their considerable size and large charge [8, 9]. The former factor, which at first site might be expected to be favorable for effective sintering of materials, actually leads to a reverse effect: fast cation diffusion results in activation of secondary recrystallization processes, leading to the formation of a coarse-grained structure containing low-mobility pores in the bulk of the grains.
Thus, the problem of preparing dense, highstrength phosphate ceramics can be examined through the lens of the low phosphate anion mobility in the structure of phosphates [9]. At present, there are several approaches for i
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