Evidence Of Dissolution Research Articles

The effect of colchicine on cholesterol crystal formation, expansion and morphology: a potential mechanism in atherosclerosis.

Inflammation is pivotal to the progression of atherosclerosis. Cholesterol crystals (CCs) that grow and enlarge within the plaque core can cause plaque rupture and trigger inflammation as they deposit into the atherosclerotic bed. Thus, agents that affect CC formation, expansion, and morphology may reduce cardiovascular (CV) risk independent of lipid-lowering and anti-inflammatory therapy. Because colchicine is highly concentrated in leukocytes that can enter the atherosclerotic plaque core, we tested its effect on the formation and growth of CCs in bench experiments to determine whether it may have direct effects on CCs, independent of its known anti-inflammatory actions. Different dosages of colchicine mixed with cholesterol (0.05-5 mg/ml/g of cholesterol) were used to influence the formation CCs and volume expansion in vitro. These were compared to control samples with cholesterol in ddH2O without colchicine. In an ex vivo study, fresh atherosclerotic human plaques were incubated with and without colchicine in a water bath at 37°C for 48 h to assess the impact of colchicine on CC morphology. Scanning electron microscopy (SEM) was utilized to analyze CC morphology in samples from the various treatment groups. The addition of colchicine to cholesterol caused a substantial dose-dependent reduction in volume (p < 0.05). Pairwise comparisons of volume reduction, showed a significant reduction in volume at 5 mg/ml/g when compared to control (p < 0.02) but the calculated Cohen's d effect size was large for five of the six pairwise comparisons. By SEM, CCs from both in vitro and ex vivo samples treated with colchicine had evidence of dissolution and changes in their morphology as evidenced by the loss of their sharp edges. In contrast, CCs in untreated specimens retained their typical geometric structure. Colchicine can reduce CC formation and expansion and alter CC morphology. These previously unappreciated effects of colchicine may contribute to its clinical benefit in patients with CV disease independent of its anti-inflammatory effects.

Characterization of silicification and dissolution zones by integrating borehole image logs and core samples: a case study of a well from the Brazilian pre-salt

Precise knowledge of the spatial distribution patterns of non-matrix porosity zones and the establishment of the geological factors controlling their evolution are crucial for building more accurate carbonate reservoir models and improving hydrocarbon production. The occurrence of intervals affected by significant carbonate dissolution may result in drilling fluid loss and time-consuming drawbacks during well construction. Vug or cave-rich reservoirs may exhibit excess permeability and extremely high initial flow rates. Similar situations have been reported in exploration activities in the Brazilian pre-salt plays, where evidence of dissolution and other burial diagenetic processes, such as severe silicification and dolomitization, are common. In this study, we investigate evidence of major post-depositional changes in the lacustrine carbonate reservoirs of the Barra Velha Formation, which comprises the most prolific hydrocarbon play in Brazil. Using a comprehensive database consisting of both core samples and well-log data from a vertical well in the Santos Basin, we have characterized, at multiple scales, reservoir zones affected by silicification and carbonate dissolution. In addition, we have performed a petrophysical evaluation of the reservoir to understand the impact of such processes on porosity and permeability development. The results suggested an intimate relationship between silicification and dissolution processes, which can be associated with late fluid percolation under a deep burial flow regime. The occurrence of silicified and vuggy beds, associated with specific zones and lithofacies, indicates an important degree of stratigraphic control on fluid percolation and lateral migration. Furthermore, the presence of fractures at discrete stratigraphic levels has preferentially influenced the development of high-permeability zones, including metric-scale fracture-related conduits. This study contributes to the general knowledge of carbonate reservoirs affected by silicification and dissolution while providing support for the recognition of such processes in partially- or non-cored wells.

Enhanced weathering in the seabed: Rapid olivine dissolution and iron sulfide formation in submarine volcanic ash

Abstract In basaltic volcanic ash recovered from a seamount at 3000 m water depth, we discovered marcasite and pyrite precipitation within cavities that formed by partial to complete dissolution of olivine. In places, these cavities are reminiscent of negative crystal shapes; elsewhere they apparently continue along cracks. In strong contrast, adjacent volcanic glass shows little, if any, evidence for dissolution. The FeS2 precipitates were commonly found to be conjoined and planar aggregates, occurring in the center of the voids. Their maximum volume fraction in relation to the void space as determined by 2D and 3D imaging techniques corresponds to the amount of iron released by olivine dissolution. Almost all occurrences of FeS2 precipitation are related to Cr-spinel inclusions in the former olivine. We propose that rapid olivine dissolution was initiated by reduced H2S-bearing fluids at olivine grain boundaries or surfaces exposed by cracks. Many of these cracks are connected to spinel grains, where the iron liberated from olivine is mineralized as FeS2, initially facilitated by heterogeneous nucleation. Subsequent pyrite and/or marcasite precipitation occurred as overgrowths on existing FeS2 aggregates. The particular chemical environment of low-pH, hydrogen sulfide-bearing fluids may have enhanced olivine dissolution by (1) keeping Fe in solution and (2) sequestering important quantities of Fe as FeS2. The in situ oxidation of ferrous Fe and precipitation of ferric hydroxides at the olivine surface commonly observed in oxic environments were obviously impeded. It would have slowed down olivine dissolution to rates more similar to the dissolution of basaltic glass. We have no direct indication that the process of rapid olivine dissolution was aided by subseafloor life. However, the presence of fibrous structures with small sulfide particles could indicate late colonization of sulfate-reducing bacteria that may add an additional path of iron fixation.

Stromatolites and calcitized evaporite in a hypersaline playa lake: Rossport Formation (Mesoproterozoic, Ontario)

ABSTRACT The Mesoproterozoic Rossport Formation of Ontario, Canada is generally interpreted as having been deposited in an intracratonic basin, most probably a rift‐related lake. While the Rossport, overall, is dominated by sandstone and shale, the Middlebrun Bay Member, in the middle of the formation, is a carbonate unit. The Middlebrun Bay Member, in exposures on the Channel Islands and along the north Shore of Lake Superior, consists most commonly of cherty, dolomitic microbial laminites and low‐relief columnar to conical forms. In contrast to typical outcrops, the Middlebrun Bay Member on Copper Island expresses as a massive, coarsely crystalline limestone unit, devoid of stromatolites or microbial laminae. Several features suggest dissolution and replacement of a primary, soluble phase such as an evaporite mineral. The top of the unit is marked by evidence of dissolution and collapse, including large sandstone clasts let down from the overlying bed. At petrographic scale, the Copper Island Carbonate comprises millimetre‐scale anhedral spar with abundant stylolites and concentration of insoluble material at grain boundaries, indicating recrystallization from a previous phase. Geochemical data from Copper Island and from correlative stromatolitic carbonate on Channel Island and mainland Ontario are consistent with hypersaline conditions, with elevated concentrations of carbonate‐associated sulphate, V and Ba. Based on these data, the massive carbonate exposed on Copper Island is interpreted as a calcitized evaporite, probably deposited originally as gypsum, and replaced by calcite during diagenesis. These data support previous work suggesting that the Middlebrun Bay interval was deposited during a period of increased aridity and low clastic influx, and further suggest that this restricted, hypersaline lake precipitated both carbonate and gypsum, comparable to modern arid playa lakes.

Influence of aging on microstructure and hardness of lead-free solder alloys

Purpose The purpose of this paper is to carry out a study of the evolution of the microstructure and the microhardness of Sn-Cu-Ag alloys from as-cast condition and under artificial isothermal aging at different temperatures (100ºC and 180ºC) for a treatment time up to 500 h. A comparison with Sn-37% Pb eutectic solder samples was also made. Design/methodology/approach Sn-3.5%Ag, Sn-0.7%Cu and Sn-3.5%Ag-0.9%Cu were poured in two different cooling rate conditions and then aged at 100ºC (373ºK) and 180 °C (453ºK) during 500 h. Microstructural changes were observed by optical microscopy, scanning electron micrograph and energy dispersive X-ray microanalysis. Differential scanning calorimetry technique (DSC) was also used to confirm the obtained results. Findings A decrease up to 20% in microhardness respect to the value of the as-cast alloy was observed for both aging temperatures. These changes can be explained considering the coarsening and recrystallization of Sn dendrites present in the microstructures of all the systems studied. Originality/value There is no evidence of dissolution or precipitation of new phases in the range of studied temperatures that could be detected by DSC calorimetry technique. The acting mechanisms must be the result of coarsening of Sn dendrites and the residual stresses relaxation during the first stages of the isothermal aging.

Microstructure modification of Y2O3 stabilized ZrO2 thermal barrier coatings by laser glazing and the effects on the hot corrosion resistance

Y2O3 stabilized ZrO2 (YSZ) thermal barrier coatings (TBCs) are prone to hot corrosion by molten salts. In this study, the microstructure of atmospheric plasma spraying YSZ TBCs is modified by laser glazing in order to improve the corrosion resistance. By optimizing the laser parameters, a ∼18 µm smooth glazed layer with some vertical cracks was produced on the coating surfaces. The as-sprayed and modified coatings were both exposed to hot corrosion tests at 700 and 1000 °C for 4 h in V2O5 molten salt, and the results revealed that the modified one had improved corrosion resistance. After hot corrosion, the glazed layer kept structural integrity, with little evidence of dissolution. However, the vertical cracks in the glazed layer acted as the paths for molten salt penetration, accelerating the corrosion of the non-modified coating. Further optimization of the glazed layer is needed in the future work.

Effects of laser glazing on CMAS corrosion behavior of Y2O3 stabilized ZrO2 thermal barrier coatings

Calcium-magnesium-alumina-silicate (CMAS) is a serious threat to thermal barrier coatings (TBCs). The goal of this study is to tailor YSZ coating microstructures by laser for alleviating CMAS attack. A smooth laser glazed layer with a columnar microstructure and some open channels is produced on the coating surface. Under molten CMAS conditions, the glazed layer remains phase stability and has little evidence of dissolution. Exposed to thermal shock tests with CMAS deposits, the glazed layer keeps structural integrity. However, the open channels also act as the paths for CMAS penetration, which brings destructive damages to the coating beneath the glazed layer.

Procesos tafonómicos en una encrinita regional pensilvánica (Atokano), Sonora, México

Taphonomic processes in a Pennsylvanian regional encrinite (Atokano), Sonora, Mexico. Crinoids have an extensive fossil record and were a major component in Paleozoic marine communities; encrinites are common crinoid accumulations where specimens are totally disarticulated from the Ordovician to the Jurassic. In Sonora, Mexico, the crinoid skeleton was altered during diagenesis and replaced by silica. The corrasion was high; the incrustation low and there is evidence of dissolution and compaction. This is a sedimentological type accumulation in a high energy environment of allochthonous organism transported in a debris flow, deposited below the storm wave base in an outer ramp. Our results can be correlated with regional encrinites prevalent in the Pennsylvanian cyclothems of North America. Rev. Biol. Trop. 65(Suppl. 1): S147-S159. Epub 2017 November 01.

The trace element chemistry and cathodoluminescence characteristics of fluorite in the Mount Pleasant Sn-W-Mo deposits: Insights into fluid character and implications for exploration

The trace element chemistry of fluorite in various mineral assemblages from the Mount Pleasant Sn-W-Mo deposits was determined using laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). These data show that fluorite chemistry correlates with both the presence and the character of associated ore mineral assemblages, in that fluorite from the W-Mo deposits has significantly higher W/Sn ratios than fluorite associated with Sn deposits. In addition, the REE content of fluorite associated with Sn-W-Mo mineralization is higher than fluorite associated with base metal sulphides and fluorite that is barren of sulphide minerals. The W/Sn ratios and REE content of fluorite can therefore be potentially used as a possible indicator of associated Sn-W-Mo mineralization. The similarities between chondrite-normalized REE patterns in fluorite and the associated granitic intrusions (i.e., flat, insignificant tetrad effect, and negative Eu anomalies) suggest that magma composition controls the composition of the associated hydrothermal fluorite, and that the trace element content of the fluorite reflects the composition of the magmatic fluid from which it was precipitated. Fluorite crystals associated with Sn and W mineralization exhibit complex cathodoluminescence (CL) character with evidence of dissolution and re-precipitation of fluorite. The complex CL nature of fluorite associated with Sn and W mineralization is interpreted to reflect interplay among fluids of different character or origin. Fluorite crystals associated with molybdenite, fluorite that is not associated with any sulphide minerals, and fluorite that is associated with base-metal sulphides showed homogeneous or simple CL zoning patterns, suggesting that Mo mineralization formed in a less complex fluid environment.

Endovascular ischemic stroke models of adult rhesus monkeys: a comparison of two endovascular methods.

To further investigate and improve upon current stroke models in nonhuman primates, infarct size, neurologic function and survival were evaluated in two endovascular ischemic models in sixteen rhesus monkeys. The first method utilized a micro-catheter or an inflatable balloon to occlude the M1 segment in six monkeys. In the second model, an autologous clot was injected via a micro-catheter into the M1 segment in ten monkeys. MRI scanning was performed on all monkeys both at baseline and 3 hours after the onset of ischemia. Spetzler neurologic functions were assessed post-operatively, and selective perfusion deficits were confirmed by DSA and MRI in all monkeys. Animals undergoing micro-catheter or balloon occlusion demonstrated more profound hemiparesis, larger infarct sizes, lower Spetzler neurologic scores and increased mortality compared to the thrombus occlusion group. In animals injected with the clot, there was no evidence of dissolution, and the thrombus was either near the injection site (M1) or flushed into the superior division of the MCA (M2). All animals survived the M2 occlusion. M1 occlusion with thrombus generated 50% mortality. This study highlighted clinically important differences in these two models, providing a platform for further study of a translational thromboembolic model of acute ischemic stroke.

Coralline algal structure is more sensitive to rate, rather than the magnitude, of ocean acidification

Marine pCO2 enrichment via ocean acidification (OA), upwelling and release from carbon capture and storage (CCS) facilities is projected to have devastating impacts on marine biomineralisers and the services they provide. However, empirical studies using stable endpoint pCO2 concentrations find species exhibit variable biological and geochemical responses rather than the expected negative patterns. In addition, the carbonate chemistry of many marine systems is now being observed to be more variable than previously thought. To underpin more robust projections of future OA impacts on marine biomineralisers and their role in ecosystem service provision, we investigate coralline algal responses to realistically variable scenarios of marine pCO2 enrichment. Coralline algae are important in ecosystem function; providing habitats and nursery areas, hosting high biodiversity, stabilizing reef structures and contributing to the carbon cycle. Red coralline marine algae were exposed for 80 days to one of three pH treatments: (i) current pH (control); (ii) low pH (7.7) representing OA change; and (iii) an abrupt drop to low pH (7.7) representing the higher rates of pH change observed at natural vent systems, in areas of upwelling and during CCS releases. We demonstrate that red coralline algae respond differently to the rate and the magnitude of pH change induced by pCO2 enrichment. At low pH, coralline algae survived by increasing their calcification rates. However, when the change to low pH occurred at a fast rate we detected, using Raman spectroscopy, weaknesses in the calcite skeleton, with evidence of dissolution and molecular positional disorder. This suggests that, while coralline algae will continue to calcify, they may be structurally weakened, putting at risk the ecosystem services they provide. Notwithstanding evolutionary adaptation, the ability of coralline algae to cope with OA may thus be determined primarily by the rate, rather than magnitude, at which pCO2 enrichment occurs.

Field Evidence of Dissolution and Degradation Rates Enhancement During ISCR and ENA Treatments of Chlorinated Solvents

AbstractThis article presents field tests comparing two methods of treatment of chlorinated solvents undertaken at the same site. The site is an automobile factory where two chlorinated solvents (CS) plumes were identified. At the first source, in situ chemical reduction (ISCR) was applied, while at the second one, enhanced natural attenuation (ENA) was used. A set of specific multilevel sampling wells were installed approximately 20 m downgradient of the sources to estimate the efficiency of the treatments. The presence of a low‐permeability layer (source 1) or a thick oil lens (source 2) in the top part of the aquifer prevented the CS from reaching the bottom of the aquifer. These layers led to difficulties treating the contamination. At the ISCR and ENA treatment zones, the concentrations of tetrachloroethene (PCE) and trichloroethene (TCE) did not change significantly, while the concentration of metabolites (cis‐1,2‐DCE, vinyl chloride, and ethene) significantly increased 50 to 150 days after treatment. Due to high concentration of CS in the source zone, a mass balance calculation, including chlorine, was possible. It showed that around 1 to 2 percent of the injected products were used to reduce the CS. A detailed analysis and 1D analytical modeling of CS concentrations showed that the treatment led to a large (two to three times) increase in dissolution of the organic phase. This explains why, despite an efficient treatment, the PCE and TCE concentrations remained virtually unchanged. Degradation rates also increased due to the treatment. Due to some differences in the source‐zone chemistry, it was not possible to differentiate between the ISCR and ENA efficiencies. © 2013 Wiley Periodicals, Inc.

HUNTING FOR YOUNG DISPERSING STAR CLUSTERS IN IC 2574

Dissolving stellar groups are very difficult to detect using traditional surface photometry techniques. We have developed a method to find and characterize non-compact stellar systems in galaxies where the young stellar population can be spatially resolved. By carrying out photometry on individual stars, we are able to separate the luminous blue stellar population from the star field background. The locations of these stars are used to identify groups by applying the HOP algorithm, which are then characterized using color-magnitude and stellar density radial profiles to estimate age, size, density, and shape. We test the method on Hubble Space Telescope Advanced Camera for Surveys archival images of IC 2574 and find 75 dispersed stellar groups. Of these, 20 highly dispersed groups are good candidates for dissolving systems. We find few compact systems with evidence of dissolution, potentially indicating that star formation in this galaxy occurs mostly in unbound clusters or groups. These systems indicate that the dispersion rate of groups and clusters in IC 2574 is at most 0.45 pc Myr{sup -1}. The location of the groups found with HOP correlate well with H I contour map features. However, they do not coincide with H I holes, suggesting that those holesmore » were not created by star-forming regions.« less

Characterization of quaternary tufas in the Serra do André Lopes karst, southeastern Brazil

Active tufas in the form of waterfalls and dams occur along drainage channels in the Serra do Andre Lopes region (State of Sao Paulo, southeastern Brazil) and are associated with the karst system that developed on a dolomitic plateau with a superhumid subtropical climate. The predominance of autogenic waters enables the groundwater to become enriched in calcium carbonate, with low terrigenous sediment content. The tufas that were studied are composed of calcite and have high calcium contents and low magnesium contents. Eroded tufa beds that originate from changes in the position of fluvial channels or river flow rates also occur in this region. In the Sapatu deposit, phytohermal tufas with complex morphologies are arranged in levels constituting various temporally repeated sequences that were deposited between 10,570 and 4,972 cal years BP. In the Frias deposit, distal fluvial deposits of tufa are massive with a relatively greater quantity of terrigenous material and show evidence of dissolution and reprecipitation. The base of this deposit is composed of a cemented breccia dated at 25,390 years BP, which is younger than the overlying tufas (>42,000 years BP). In the two deposits, the levels of terrigenous sediments (quartz sand and lithic pebbles) and terrestrial gastropod shells are interpreted as phases of increased flow rate of rivers during intervals of higher rainfall.

Scientists observe fungi-dissolving minerals

Ectomycorrhizal fungi (EMF) live in moist dark recesses and never see daylight. They cling to the roots of trees in boreal forests, break down soil minerals and supply essential elements and nutrients to the trees. Along the way, they play a distinct but not yet well-understood role in bioweathering, a process in which water, air, and organisms interact to break down soil minerals within the first few meters of Earth's surface. In a synthetically designed and controlled laboratory environment, Gazze et al. cultured EMF; the researchers monitored the process as the fungi colonized a soil mineral on a petri dish over a period of 7 months. The authors then extracted individual grains of chlorite, a common soil-forming clay mineral, and cleaned the mineral surfaces to look at how the fungi had affected the mineral surfaces they came in contact with. Using atomic force microscopy, a specialized process that allows observations of three-dimensional features at nanometer (10–9 meter) scales, the authors found numerous primary channels, of the order of a micron (10–6 meters) in width and up to 50 nanometers in depth, from which smaller secondary channels extended outward. The network of channels resembled a herringbone-like pattern—evidence of dissolution by EMF.

Deformation of amphibolites via dissolution–precipitation creep in the middle and lower crust

AbstractContinuous compositional zoning in amphibole grains in strongly deformed and lineated amphibolites from the Eastern Blue Ridge, North Carolina indicates that most of the deformation was accommodated by dissolution–precipitation creep. Amphibole in most samples shows moderate prograde and/or retrograde zoning parallel to the long‐axis with compositions ranging between magnesiohornblende and tschermakite. In one sample, grains are zoned from actinolitic (Si = 7.9 p.f.u.) cores to tschermakitic (Si = 6.2 p.f.u) rims. Amphibole‐plagioclase thermometry suggests prograde growth temperatures as low as 400 °C, but typically range from 650 to 730 °C and retrograde growth temperatures &lt;700 °C. These estimates are corroborated quantitatively with amphibole‐garnet‐plagioclase thermobarometry and qualitatively with a positive correlation between TiO2 concentration in amphibole and calculated temperature. This growth zoning provides persuasive evidence that amphibole precipitation produced the fabric, but evidence for dissolution is less common. It is present, however in the form of truncations of complicated zoning patterns produced by healed fractures and overgrowths in low‐temperature cores by high‐temperature tschermakitic grains lacking similar internal structures. The preservation of this network of straight cracks filled with optically continuous amphibole also provides evidence against the operation of dislocation creep even to temperatures &gt;700 °C because dislocation‐creep would have deformed the fracture network. Thus, these amphibolites deformed by dissolution–precipitation creep that produced a strong linear fabric under upper amphibolite facies, middle‐to‐lower crustal conditions. The significance of this discovery is that dissolution–precipitation creep is activated at lower stresses than dislocation creep and that the strength of the lower crust, where amphibole is the dominant mineral is probably lower than that derived from experimental studies.

Annealing Effect on the Structure and Electronic Transport Properties in La5/8Ca3/8MnO3/ErMnO3 Multilayer Thin Films

Ferromagnetic La5/8Ca3/8MnO3 (LCMO) and Ferroelectric ErMnO3 (EMO) multilayer thin films with sandwich structure (LCMO/EMO/LCMO) were grown on (LaAlO3)0.3(Sr2AlTaO6)0.7 (001) [LSAT (001)] substrates by pulsed laser deposition (PLD) method. For these films, the structural characterization was carried out by X-ray diffraction (XRD), and the temperature-dependence resistivity (p-T) showing the metal-insulator transition (Tp) also was measured. In the multilayer thin films the LCMO (002) peak move to lower Bragg angles after annealing at 900 degrees C for 30 hours under 1atm Oxygen pressure, and this condition is much different from the LCMO single layer films where the (002) peak moves to higher Bragg angle after annealing due to the lattice mismatch between the LCMO layer and the substrate. By increasing the thickness of LCMO, the multilayer samples show two MR peaks in a wide temperature range during the process of M-l transition. This phenomenon is attributed to a new (La5/8Ca3/8)xEr(1-x)MnO3 layer produced by the solubility between LCMO and EMO layers after high-temperature annealing. In this paper, we provide some evidence of dissolution between LCMO and EMO layers, and discuss the influence on structure and electronic transport properties in the composite thin films by annealing.

Recovery of ostracods in Cretaceous dolomitic carbonate: The efficiency of acetolysis

Abstract The aim of this paper was to test different reagents and reaction conditions to determine which is the most efficient and safest for the disaggregation of dolomite carbonate rocks. The ideal reagent should show the ability to recover the largest number of ostracods under conditions providing a good cleaning of the carapaces without causing damage and posing little risk to the laboratory technician and the environment. The method for the extraction of ostracods from lithified dolomitic carbonate was improved. The tests using glacial acetic acid showed the best results. The procedures carried out with acetic acid in samples without moisture, with slow rate of reaction and at room temperature, were the most effective and allowed the recovery of many specimens with no evidence of dissolution. The analysis carried out with this acid using a fast reaction on a hot plate showed good results, but there were fewer specimens recovered along with evidence of dissolution.

Sintering and Mechanical Property of Tuna Bone-Derived Hydroxyapatite

Hydroxyapatite (HA) ceramics derived from tuna bone (THA) was prepared and their mechanical property was investigated with immersion in buffered water. Tuna bones were soaked in 0.1 M of NaOH solution at 80°C for 1 h. After soaking, the bones were calcined at 800°C for 1 h to completely remove organic, and then attritor-milled for 24 h. The powders obtained were cold isostatically pressed and sintered at 1300°C with a dwell time of 1 h. Sintered densities of the THA was about 93%. After polishing, the THA were immersed in buffered water at 37 °C for 3 and 7 days. The THA ceramics consisted of HA and small amount of magnesium oxide. Immersion test revealed that there was no clear evidence of dissolution for the THA which sintered at high temperatures. Vickers hardness test showed that the hardness value of THA ceramics was not changed with immersion time indicating that dense hydroxyapatite from tuna bone was stable in liquid environment.

Dissolution Resistance of Bovine Teeth-Derived Hydroxyapatite

Dissolving behavior of hydroxyapatite ceramics prepared from bovine teeth (BTHA) was investigated. The bovine teeth were soaked in 0.1 M of NaOH at 80°C for 1 h. After soaking, the teeth were calcined at 800°C for 1 h, and then they were attritor-milled for 24 h. BTHA powder consisted of mainly HA and small amount of MgO. The powders obtained were cold isostatically pressed and sintered at 1200°C with a dwell time of 1 h. Sintered density of BTHA was about 70%. After polishing the surface of sintered specimen, BTHA was immersed in buffered water at 37°C for 3 and 7 days. After immersion period, there is no evidence of dissolution for BTHA at the end of the immersion time. In addition, there is no change of peak intensity in XRD after immersion time. It was found that hydroxyapatite from bovine teeth was more stable than commercial HA in liquid environment.