feldspar and mica

Today the terrestrial surface drives biogeochemical cycles on Earth through chemical weathering reactions mediated by the biological influence of soils. Prior to the expansion of life on to land, abiotic weathering may have resulted in different boundary conditions affecting the composition of the biosphere. Here we show a striking difference in weathering produced minerals preserved in the Mesoproterozoic Velkerri Formation. While the bulk chemistry and mineralogy is dominated by illite similar to many modern mudstones, application of a novel microbeam technology reveals that the initial detrital minerals were composed of mica (28%) and feldspar (45%) with only a trace amount (<2%) of typical soil formed clay minerals. The majority of illite and the high Al

Topics: Aluminum Silicates; Australia; Chemical Phenomena; Chemistry, Physical; Clay; Environmental Monitoring; Geological Phenomena; Geology; Minerals; Oceans and Seas; Potassium Compounds; Soil; Trace Elements; Weather

Although brittle material behavior is often considered undesirable, a quantitative measure of "brittleness" is currently not used in assessing the clinical merits of dental materials.. To quantify and compare the brittleness of human enamel and common dental restorative materials used for crown replacement.. Specimens of human enamel were prepared from the third molars of "young" (18< or =age< or =25) and "old" (50< or =age) patients. The hardness, elastic modulus and apparent fracture toughness were characterized as a function of distance from the DEJ using indentation approaches. These properties were then used in estimating the brittleness according to a model that accounts for the competing dissipative processes of deformation and fracture. The brittleness of selected porcelain, ceramic and micaceous glass ceramic (MGC) dental materials was estimated and compared with that of the enamel.. The average brittleness of the young and old enamel increased with distance from the DEJ. For the old enamel the average brittleness increased from approximately 300 microm(-1) at the DEJ to nearly 900 microm(-1) at the occlusal surface. While there was no significant difference between the two age groups at the DEJ, the brittleness of the old enamel was significantly greater (and up to four times higher) than that of the young enamel near the occlusal surface. The brittleness numbers for the restorative materials were up to 90% lower than that of young occlusal enamel.. The brittleness index could serve as a useful scale in the design of materials used for crown replacement, as well as a quantitative tool for characterizing degradation in the mechanical behavior of enamel.

Topics: Adolescent; Age Factors; Aluminum Silicates; Biomechanical Phenomena; Crowns; Dental Enamel; Dental Porcelain; Dental Stress Analysis; Elasticity; Hardness; Humans; Materials Testing; Middle Aged; Potassium Compounds; Stress, Mechanical; Surface Properties

To examine whether the ion exchange strengthening can be achieved for several new ceramics such as glass ceramics or castable ceramics.. The ceramics selected for this study were three porcelains and three castable ceramics. 60 bend bars of the respective ceramics (1 x 5 x 10 mm) were fabricated according to the respective manufacturer's directions. Finally, the respective specimens were polished up to 0.1 microm and then divided into two groups: one was coated with an ion-exchange paste and the other was not treated as the control. Then, for the respective ceramics the hardness, flexural strength and fracture toughness were investigated and compared to the control.. Although the ion-exchange treatment significantly (P < 0.05, Scheffé's test) increased flexural strength and fracture toughness for the porcelain based ceramics, it did not increase these properties for the castable ceramics. The chemical treatment did not affect hardness for any of the specimens.

Topics: Aluminum Silicates; Apatites; Ceramics; Dental Materials; Dental Polishing; Dental Porcelain; Glass; Hardness; Humans; Ion Exchange; Materials Testing; Pliability; Potassium Compounds; Surface Properties

The hypothesis under examination in this paper is that the lifetimes of dental restorations are limited by the accumulation of contact damage during oral function; and, moreover, that strengths of dental ceramics are significantly lower after multi-cycle loading than after single-cycle loading. Accordingly, indentation damage and associated strength degradation from multi-cycle contacts with spherical indenters in water are evaluated in four dental ceramics: "aesthetic" ceramics-porcelain and micaceous glass-ceramic (MGC), and "structural" ceramics-glass-infiltrated alumina and yttria-stabilized tetragonal zirconia polycrystal (Y-TZP). At large numbers of contact cycles, all materials show an abrupt transition in damage mode, consisting of strongly enhanced damage inside the contact area and attendant initiation of radial cracks outside. This transition in damage mode is not observed in comparative static loading tests, attesting to a strong mechanical component in the fatigue mechanism. Radial cracks, once formed, lead to rapid degradation in strength properties, signaling the end of the useful lifetime of the material. Strength degradation from multi-cycle contacts is examined in the test materials, after indentation at loads from 200 to 3000 N up to 10(6) cycles. Degradation occurs in the porcelain and MGC after approximately 10(4) cycles at loads as low as 200 N; comparable degradation in the alumina and Y-TZP requires loads higher than 500 N, well above the clinically significant range.

Topics: Aluminum Oxide; Aluminum Silicates; Bite Force; Ceramics; Crystallization; Dental Porcelain; Dental Restoration Wear; Dental Stress Analysis; Glass; Humans; Materials Testing; Potassium Compounds; Stress, Mechanical; Surface Properties; Time Factors; Water; Yttrium; Zirconium

The objective of this study was to test the hypothesis that industrially manufactured ceramic materials, such as Cerec Mark II and Zirconia-TZP, have a smaller range of fracture strength variation and therefore greater structural reliability than laboratory-processed dental ceramic materials.. Thirty bar specimens per material were prepared and tested. The four-point bend test was used to determine the flexure strength of all ceramic materials. The fracture stress values were analyzed by Weibull analysis to determine the Weibull modulus values (m) and the 1 and 5% probabilities of failure.. The mean strength and standard deviation values for these ceramics are as follows: (MPa+/-SD) were: Cerec Mark II, 86.3+/-4.3; Dicor, 70.3+/-12.2; In-Ceram Alumina, 429. 3+/-87.2; IPS Empress, 83.9+/-11.3; Vitadur Alpha Core, 131.0+/-9.5; Vitadur Alpha Dentin, 60.7+/-6.8; Vita VMK 68, 82.7+/-10.0; and Zirconia-TZP, 913.0+/-50.2. There was no statistically significant difference among the flexure strength of Cerec Mark II, Dicor, IPS Empress, Vitadur Alpha Dentin, and Vita VMK 68 ceramics (p>0.05). The highest Weibull moduli were associated with Cerec Mark II and Zirconia-TZP ceramics (23.6 and 18.4). Dicor glass-ceramic and In-Ceram Alumina had the lowest m values (5.5 and 5.7), whereas intermediate values were observed for IPS-Empress, Vita VMK 68, Vitadur Alpha Dentin and Vitadur Alpha Core ceramics (8.6, 8.9, 10.0 and 13.0, respectively).. Except for In-Ceram Alumina, Vitadur Alpha and Zirconia-TZP core ceramics, most of the investigated ceramic materials fabricated under the condition of a dental laboratory were not stronger or more structurally reliable than Vita VMK 68 veneering porcelain. Only Cerec Mark II and Zirconia-TZP specimens, which were prepared from an industrially optimized ceramic material, exhibited m values greater than 18. Hence, we conclude that industrially prepared ceramics are more structurally reliable materials for dental applications although CAD-CAM procedures may induce surface and subsurface flaws that may adversely affect this property.

Topics: Aluminum Oxide; Aluminum Silicates; Ceramics; Chemical Phenomena; Chemistry, Physical; Computer-Aided Design; Dental Alloys; Dental Porcelain; Dental Stress Analysis; Elasticity; Humans; Materials Testing; Pliability; Potassium Compounds; Stress, Mechanical; Zirconium

Hertzian indentation testing is proposed as a protocol for evaluating the role of microstructure in the mechanical response of dental ceramics. A major advantage of Hertzian indentation over more traditional fracture-testing methodologies is that it emulates the loading conditions experienced by dental restorations: Clinical variables (masticatory force and cuspal curvature) identify closely with Hertzian variables (contact load and sphere radius). In this paper, Hertzian responses on four generic dental ceramics systems-micaceous glass-ceramics, glass-infiltrated alumina, feldspathic porcelain, and transformable zirconiaare presented as case studies. Ceramographic sectioning by means of a "bonded-interface" technique provides new information on the contact damage modes. Two distinct modes are observed: "brittle" mode, classic macroscopic fracture outside the contact (ring, or cone cracks), driven by tensile stresses; and "quasi-plastic" mode, a relatively new kind of deformation below the contact (diffuse microdamage), driven by shear stresses. A progressive transition from the first to the second mode with increasing microstructural heterogeneity is observed. The degree of quasi-plasticity is readily apparent as deviations from ideal linear elastic responses on indentation stress-strain curves. Plots of threshold loads for the initiation of both fracture and deformation modes as a function of indenter radius constitute "damage maps" for the evaluation of prospective restoration damage under typical masticatory conditions. The degree of damage in both modes evolves progressively with load above the thresholds. Strength tests on indented specimens quantify sustainable stress levels on restoration materials after damage. The most brittle responses are observed in the fine glass-ceramics and porcelain; conversely, the most quasi-plastic responses are observed in the coarse glass-ceramics and zirconia; the medium glass-ceramics and alumina exhibit intermediate responses. Implications of the results in relation to future materials characterization, selection, and design are considered in the clinical context.

Topics: Aluminum Oxide; Aluminum Silicates; Bite Force; Ceramics; Dental Porcelain; Dental Restoration, Permanent; Elasticity; Evaluation Studies as Topic; Glass; Hardness; Humans; Materials Testing; Potassium Compounds; Stress, Mechanical; Surface Properties; Tensile Strength; Tooth; Zirconium

Dental ceramics can fail through growth of microscopic surface flaws that form during processing or from surface impact during service. New restorative dental ceramic materials have been developed to improve resistance to crack propagation. Eleven of these improved materials with the common feature of a considerable amount of crystalline phase in the glassy matrix were evaluated. The ceramic materials studied included fluormica-, leucite-, alumina-, and zirconia-reinforced glasses. The relative hardness and fracture toughness were determined by indentation technique. Alumina-reinforced materials resulted in the highest fracture toughness values, whereas the fluormica- and leucite-reinfoced materials showed more moderate but statistically significant greater values compared with those of control materials. The hardness values of ceramic materials with improved fracture toughness were both substantially higher or lower than those of the control groups and suggested a lack of direct correlation between these two properties. Selection of appropriate restorative materials depends on clinical application and requires consideration of several physical properties including fracture toughness.

Topics: Aluminum Oxide; Aluminum Silicates; Analysis of Variance; Ceramics; Dental Alloys; Dental Porcelain; Dental Restoration, Permanent; Elasticity; Hardness; Materials Testing; Potassium Compounds; Zirconium

The quantitative mineralogical analysis of small samples (less than 20 mg) of china clay has been investigated using x ray diffractometry to determine kaolinite, mica, quartz, and feldspar. A method has been developed and applied to the quantitative analysis of airborne dust samples and of other small discrete samples. Determinations were made either on samples after collection on a membrane filter or on samples after deposition from aqueous suspension on to a silver substrate. Quantitative analysis was hindered by preferred orientation of the kaolinite and of the mica particles that occurs when using these methods of specimen preparation. Quartz and feldspar were determined direct from prepared calibration graphs. Preferred orientation of the mica particles leads to serious interference with the most sensitive quartz x ray diffraction peak which, if not recognised, will result in an overestimation of the quartz content. Kaolinite and mica were determined from the ratio of their most intense x ray diffraction peak areas to overcome the preferred orientation effects observed for these two minerals. During the investigation, the opportunity arose for comparative measurements of quartz contents of airborne dust samples with the Occupational Medicine and Hygiene Laboratories of the Health and Safety Executive. The mass of specimen examined varied between 0.8 mg and 20 mg and the quartz contents varied between 0.1% and 1.2%. The comparative results were in good agreement.

Topics: Air Pollutants, Occupational; Aluminum Silicates; Kaolin; Particle Size; Potassium; Potassium Compounds; Quartz; X-Ray Diffraction

Topics: Aluminum Silicates; Blood Protein Electrophoresis; Minerals; Pathology; Potassium Compounds; Pulmonary Fibrosis; Rats; Research; Silicosis; Toxicology