Ya. I. Evich

The Structure and Properties of Calcium Phosphate Ceramics Produced from Monetite and Biogenic Hydroxyapatite

It is shown that porous calcium phosphate ceramics can be produced from monetite and biogenic hydroxyapatite, the starting materials being in the ratios 25 : 75, 50 : 50, and 75 : 25 wt.%. It is established that phase transitions and solid-phase reactions take place during sintering to form polyphosphate ceramics consisting of hydroxyapatite (Ca5(PO4)3(OH)), β-pyrophosphate (β-Ca2P2O7), and β-tricalcium phosphate (β-Ca3(PO4)2), in which β-Ca2P2O7 and Ca5(PO4)3(OH) phases are predominant, depending on starting composition. When the biogenic hydroxyapatite content changes from 25 to 75 wt.%, the grain size decreases and the pore size increases. The ceramics have 40 to 42% porosity with predominant open porosity for all compositions. The ceramics show 32–55 MPa strength, which increases with the amount of biogenic hydroxyapatite in starting composition.

Synthesis and Properties of Si-Modified Biogenic Hydroxyapatite Ceramics

The paper examines the production of Si-modified biogenic hydroxyapatite ceramics. The introduction of methylsilicic acid hydrogel in amounts converted to 2 and 5 wt.% Si and subsequent sintering at 600°C increase the specific surface area by 10 times, from 6.1 to 59.8 m2/g. The porosity of ceramics increases from 43.0 to 62.3% when the modifying addition reaches up to 5 wt.%, the compressive strength being equal to 27–33 MPa. The modifying addition also influences the structure and reduces the minimum grain size of the material from 0.65 to 0.1μm

Structure and Properties of Ni3Al Intermetallic Under Vacuum Impact Sintering

The compaction, structure, and mechanical properties of Ni3Al intermetallic, corresponding to PN85Yu15 commercial powder and mainly consisting of 50–100 μm particles, are studied. The preforms were subjected to impact sintering in 0.013 Pa vacuum at 1100, 1150, 1200, 1250, and 1300°C. Isothermal holding at these temperatures lasted for 20 min. The samples were compacted at an impact energy of 1200 J/cm3 and an initial impact velocity of 6.5 m/sec. The disk samples were used to cut out rectangular bars to determine their density, resistivity, bending, tensile, and compression strength, conditional fracture toughness, and fracture energy (for notched samples). The Vickers hardness and plasticity of the samples were evaluated in different types of tests. The mechanical properties of Ni3Al intermetallic powder samples compacted at 1250°C and higher temperatures are consistent with those of the standard conventionally melted intermetallic. In particular, the average bending strength is 650–675 MPa, tensile strength 385–400 MPa, fracture toughness 14.6–18.2 MPa · m1/2, compression strength 1650 MPa, and Vickers hardness 2500–2600 MPa.