Dense Tablets Research Articles

Micromechanical properties of hydroxyapatite nanocomposites reinforced with CNTs and ZrO2

This study examined the mechanical properties, wettability, and tribology of hydroxyapatite (HA)–zirconia (ZrO2)–carbon nanotube (CNTs) ceramic nanocomposites (with various CNT ratios (x): 1, 5, and 10 wt%). HA–ZrO2–CNT-x powders were hydrothermally synthesized. Hot isostatic pressing (HIP) and cold isostatic pressing were used to manufacture solid and dense tablets; consolidation was performed by sintering the nanocomposites under Ar gas at 1150 °C during HIP. The microstructure and morphology of the nanocomposites were characterized via transmission electron microscopy, energy-dispersive X-ray spectroscopy, powder X-ray diffractometry, Fourier transform infrared (FTIR), and scanning electron microscopy. The effects of ZrO2 and CNTs on the mechanical characteristics of the nanocomposites were examined via nanoindentation, reciprocating wear, and Vickers hardness tests. The microhardness of HA–ZrO2–CNT-1% and HA–ZrO2–CNT-5% increased by 36.8% and 66.67%, respectively, compared with that of pure HA. The nanohardness of the HA–ZrO2–CNT-1%, HA–ZrO2–CNT-5%, and HA–ZrO2–CNT-10% samples was 8.3, 9.65, and 8.02 Gpa, and the corresponding elastic modulus was 83.72, 114.34, and 89.27 GPa, respectively. Both of these parameters were higher than those of pure HA. However, in the nanocomposite reinforced with 10% CNT, as opposed to those with lower CNT ratios, their values were lower. Additionally, HA–ZrO2–CNT-10% was the most hydrophilic nanocomposite synthesized in this study with a contact angle of 48.8°.

The Influence of Microstructure on the Surface Charge of Sintered Hydroxyapatite Ceramics

Hydroxyapatite (HAp) has shown the ability to store a charge induced by electrical polarization a method potential for improved bone ingrowth. In this work electrical polarization was carried out on HAp ceramics with three different microstructures, obtained at three different sintering temperatures. Microstructure of the sintered HAp was evaluated from density measurements and SEM observations. Sintered HAp tablets were electrically polarized in an electric field of 5 kV/cm at 400 °C for 1h. Surface charges investigated by thermally stimulated depolarization current measurements showed 104,8 μC/cm2 for denser tablets, while charge density of 22,8 μC/cm2 was obtained for less dense tablets.

Hydrothermal synthesis and influence of later heat treatment on the structural evolution, optical and electrical properties of nanostructured α-MoO3 single crystals

In the current study, α-MoO3 nanocrystals were successfully synthesized from ammonium heptamolybdate tetrahydrate using a simple hydrothermal route. The influence of calcination temperature on the structural, optical and electrical properties was systematically investigated for the MoO3 powder products. The XRD results were analyzed for these powders, revealing the formation of a mixed phase (β- and α-MoO3) at calcination temperatures ranging from 350 °C–450 °C, and hence a residual monoclinic phase still exists in the samples at the calcination temperature of 450 °C. Subsequently, the mixed phase was completely converted to a pure single phase of α-MoO3 at a calcination temperature of 500 °C. The optical properties of the MoO3 powders were investigated using the transformed diffuse reflectance technique according to Kubelka–Munk theory. For such a powder product, the results of the optical measurements demonstrated the realization of indirect and direct allowed transitions at the spectral ranges 3.31–3.91 eV and 3.66–4.27 eV, respectively. The indirect- and direct-allowed band-gaps of the MoO3 products were found to increase from 2.69–3.12 eV and from 3.43–3.64 eV, respectively, by increasing the calcination temperature from 350 °C–600 °C. The MoO3 powders calcined at different temperatures were converted into five dense tablets for performing the electrical measurements. These measurements were carried out at different working temperatures using a system operating under high vacuum conditions. The results revealed that the dc-conductivity of such a tablet typically increases by more than five orders of magnitude with an increase in the working temperature from 77–300 K. These results also demonstrated a high dependence of dc-conductivity on the calcination temperature for the MoO3 products. The dc-conductivity as a function of the operating temperature revealed the presence of at least three different electrical conduction mechanisms for the same MoO3 tablet.

The influence of non-disintegrating tablet dimensions and density on their gastric emptying in fasted volunteers

The aim of this work was to identify the influence of tablet density on their gastric emptying in fasted subjects and to compare the findings with those of a previous study using the same subjects with tablets of a larger diameter. Tablets of 6.6 mm diameter and densities of 1.41 and 2.85 g cm-3 were labelled with 99mTc and 111In. They were coated with ethyl cellulose to ensure that they remained intact within the gastrointestinal tract. Their position within the gastrointestinal tract of fasted healthy subjects was monitored with a double-headed gamma camera at 1-min time intervals. The median gastric emptying time and the interquartile range were derived from the Bernoulli random event distribution. It was found that the dense tablets had a significantly longer gastric emptying time than the light tablets. Comparison with the results from the previous study gave a clear indication that irrespective of tablet density, the 6.6-mm tablets had longer gastric emptying times than the 12.0-mm tablets.

Gastrointestinal transit of model mini-tablet controlled release oral dosage forms in fasted human volunteers

The aim of this study was to compare the gastrointestinal transit of multiple unit, small diameter (3.2 mm), non-disintegrating tablets of differing densities with results previously reported in the same volunteers in the fasted state for larger diameter (6.6 and 12.2 mm) tablets. The gastrointestinal transit was observed with gamma-scintigraphy at various intervals over a 9-h period to give an accurate assessment of the transit characteristics. The value for the median emptying time of the first light tablet was significantly shorter than that for the dense tablet, but the total emptying time and the time for the last tablet to empty for both sets of tablets were not statistically different. The value of the median time for initial and final emptying of the small tablets from the stomach was significantly longer than that for the larger diameter tablets. The 9-h time limit of the observations limited the estimation of the time taken to enter the caecum and consequently the small intestine transit times. There was clear evidence that for the dense tablets of all sizes, the value for the small intestine transit time was longer than the 3-4 h reported in the literature. The only tablet system to enter the caecum within the time limit of the study was the normal density 12.2-mm tablets.

Human osteoblasts adhesion and proliferation on magnesium-substituted tricalcium phosphate dense tablets

Tricalcium phosphate (TCP) is recognized as a promising bone replacement material due to its high bioactivity and resorbable properties. To mimic biological apatites, incorporation of magnesium (Mg) in TCP was proposed. Mg-substituted TCP (beta-TCMP) and beta-TCP dense tablets were obtained by pressing and sintering at 1,000 degrees C Mg-substituted calcium deficient apatite (Mg-CDA) and commercial TCP, respectively. The materials were characterized using X-ray diffraction, infrared spectroscopy and electron microscopy. Human osteoblast cells (SaOs2) were seeded onto the sintered tablets for 4 h, 24 h and 7 days. Results showed that Mg-CDA was completely transformed into beta-TCMP. Moreover, beta-TCMP stimulated adhesion and proliferation of human osteoblast cells. Consequently, the magnesium incorporation on calcium deficient apatites followed by sintering at 1,000 degrees C seems to be a useful path to obtain biocompatible and non cytotoxic dense tablets with TCP structure with potential application on bone engineering.

Fluorohalogenation of superconducting oxide YBa 2Cu 3O 7− δ with ClF 3

The low- Tc phase YBa 2Cu 3O x ( x∼6.6, Tc∼60 K) which was sintered into a dense tablet was subjected to gaseous ClF 3, in order to investigate the mechanism of fluorohalogenation of a sintered YBa 2Cu 3O x . It was found that the fluorochlorinated high- Tc phase YBa 2Cu 3O x F y Cl z ( x∼6.6, y∼0.5, z∼0.1) was formed at the outer part of sample tablet, and that the high- Tc phase with high oxygen and low halogen contents ( x∼6.8, y∼0.1, z∼0.01) was also formed at the inner part of it, despite of no oxygen in the reaction atmosphere. Rietveld analysis of neutron powder diffraction data of the fluorochlorinated high- Tc phase YBa 2Cu 3O x F y Cl z (YBa 2Cu 3O 6.10F 0.75Cl 0.49, T onset=94.5 K) revealed that fluorine preferentially occupied the oxygen defect site and/or the vacant site along the Cu–O chain. On the other hand, chlorine occupied as Cl the site at (0, 0, 1/2) which was the center of the yttrium site surrounded with oxygen because Cl − was too large to occupy the oxygen defect site and/or the vacant site along the Cu–O chain. The ClF 3-treated sample was considered to consist of at least two phases of the orthorhombic YBa 2Cu 3O 6.35F 0.65Cl 0.49 ( Pmmm) and the tetragonal YBa 2Cu 3O 6.29F 1.17Cl 0.49 ( P4/ mmm). The chemical formula estimated by the Rietveld refinement was YBa 2Cu 3O 6.33F 0.80Cl 0.49 which was very close to the analyzed composition, YBa 2Cu 3O 6.35F 0.75Cl 0.49 in which chlorine was assumed to be zero-valence.

Preparation and electrical conductivity of thin films of Rb4Cu16I7Cl13

A thin film of the copper ion conductor Rb4Cu16I7Cl13 was prepared on a glass plate by vacuum evaporation. An appropriate thin film was obtained by controlling the amount of the electrolyte mounted in a boat, the evaporation time etc. and by heating the deposited film at a temperature between 130 and 210° C. The electronic and ionic conductivities of the film measured by d.c. and a.c. techniques were nearly equal to those of a dense tablet of the solid electrolyte.