Disperse systems in calcium hydroxyapatite ceramics technology

Abstract

Hydroxyapatite ceramics technology is examined. Disperse systems and their evolution in each process state are determined. Data from gravimetric and dilatometric analysis and scanning microscopy are reported. The aggregate distribution by size in the initial powder and the grain distribution by size in the sintered ceramic are compared. The inheritance of the properties of the initial powders by the structure characteristic of ceramic materials is demonstrated.The evolution of modern materials science is related to the creation of new materials with unique properties. Production of such materials implies improvement of existing technologies or creation of new schemes. Considering different materials as disperse systems (DS) with defined properties allows applying the general principles of the existence of DS in technologies for different ceramic materials. An examination of preparation of the initial materials [1], molding [2, 3], and high-temperature treatment [4,5] in materials technology with consideration of the existence of disperse system and surface phenomena makes it possible to perfect existing technologies [6] and develop new materials [7], including nanoceramics [8,9].The basic stages in fabrication of ceramics are preparation of the initial components and molding and firing [10] or, in other words, preparation of the initial material in the form of powder or slip and consolidation [11]. Without any doubt, according to many determinations in ceramics, this concerns transforming the material from a granulated state to a monolithic state. Technology for ceramics, like many other highmelting nonmetallic and silicate materials, is a set of processes of creation, evolution, and in some cases destruction of DS consisting of disperse phase and dispersion medium. The most important distinctive features of DS are the continuity of the dispersion medium, state of comminution of the disperse phase, and presence of phase boundaries, which is due to their heterogeneity [12,13].The classification of disperse systems by the aggregate state of the substance of the disperse phase and dispersion medium is the most popular. According to this classification, most existing ceramic materials can be assigned to solid-insolid (S/S), gas-in-solid (G/S), or solid, gas-in-solid (S, G/S) disperse systems. The real materials are unconditionally more complex DS and can contain more than one disperse phase, as well as more than one dispersion medium. With respect to all formal features, many ceramic materials that are DS (S/S, G/S, or S, G/S) can be assigned to composite materials (CM) formed by bulk combination of chemically heterogeneous components with different physical and mechanical properties with a distinct interface between them. CM are characterized by properties that none of their components individually have [14,15]. In other words, such composite materials as DS can be polymatrix or polyfilled.According to the traditional approach to composite materials, one of the components, continuous in volume, is the matrix -the ba...

Powder Mixture for the Production of Microporous Ceramics Based on Hydroxyapatite

“…3Ca3(PO4)2 + CaCO3+ H2O = Ca10(PO4)6(OH)2 + CO2 (10) These reactions ( 6), ( 7) and ( 10) can explain the CO2 evolving (peak at 715 o C, Figure 4) in the third noticeable step at mass loss curve in the interval 550-750 o C (Figure 3). As one Figure 5 shows the XRD data of powder mixture after heat treatment at 200 o C and ceramic samples based on powder mixture prepared from powder of HA Ca10(PO4)6(OH)2 and oxalic acid dihydrate H2C2O4•2H2O after firing at 500 o C, 1000 o C, 1100 o C and 1200 o C. Table 1 briefly summarizes phase transformations in powder system under investigation from starting powder mixture (CaHPO4•2H2O, CaC2O4•H2O, non-identified phase quasi-amorphous phase) to final monophase HA (Ca10(PO4)6(OH)2) ceramics.…”

“…Tricalcium phosphate Ca3(PO4)2 can form due to thermal decomposition of hydrated tricalcium phosphate Ca3(PO4)2 xH2O (analog of Ca-deficient HA -Ca9(HPO4)(PO4)5(OH)) (reaction ( 8) and ( 9). Moreover, hydroxyapatite Ca10(PO4)6(OH)2 can form from tricalcium phosphate Ca3(PO4)2 and calcium carbonate CaCO3 according reaction (10).…”

“…To create microporosity one can use special thermal treatment scheduler to get undersintered ceramic material [ 10 ] or specially via sol-gel synthesis prepared powder system [ 11 ]. Another method of microporosity creation consists in using organic [ 12 , 13 ] or inorganic [ 14 , 15 ] additives in form of particles with a small dimensions as a sacrificed porogens.…”

Powder Mixture for the Production of Microporous Ceramics Based on Hydroxyapatite

“…To create microporosity, one can use a special thermal treatment scheduler to obtain undersintered ceramic material [24] or via a sol-gel synthesis-prepared powder system [25]. Another method of microporosity creation consists in using organic [26,27] or inorganic [28,29] additives in form of particles with small dimensions as sacrificed porogens.…”

Microporous Ceramics Based on β-Tricalcium Phosphate

“…Various methods can be used to achieve microporosity of ceramic materials. Among them are incomplete sintering [39], addition of small particles of sacrificial organic or inorganic components to the starting powder mixture [40,41], addition of components having the ability to release of sufficiently large volumes of gases when heated [42], using the sol-gel method of precursor preparation [43], or using a powder mixture containing columnar-like [44] or plate-like [45] particles restraining densification. Synthesized powders of dicalcium phosphate dihydrate CaHPO 4 •2H 2 O and/or dicalcium phosphate anhydrate CaHPO 4 (i.e., brushite and/or monetite) usually consist of plate-like or petal-like particles [46][47][48][49].…”