Omar A. Al-Harbi

Sedimentology, Mineralogy and Geochemistry of Al-Awshaziyah Inland Sabkha, Central Saudi Arabia

In the Kingdom of Saudi Arabia, a rising demand of municipal, agricultural and industrial sectors require better utilization of surface and groundwater resources. Some of the wadi and low depressions in the central Saudi Arabia are covered with salt (Inland sabkha). It is also suspected that the aquifers below receive substantial amounts of recharge from the above ground salt flat. It is, therefore, important to investigate the mineralogy and geochemistry of these salt-flats to determine their impact on groundwater chemistry. Al-Awshaziyah inland sabkha is a saline dry/wet land with an area of 18 km2 in the central Saudi Arabia. The study area was divided into six transverses beginning at a permanent marker. The distance of different profiles ranged between 200–300 m. Soil, groundwater and well water samples were collected for physical and chemical composition. Additionally, different soil and salt facies were measured in each profile. Three sedimentary facies, viz., silty sand; black mud, and salt facies (from bottom to top) had been delineated. The mineralogy by X-ray diffraction analysis (XRD) for silty-sand facies composed of quartz (25–74%), halite (11–16%), dolomite (5–27%), calcite (4–21%), and gypsum (4–8%); black mud facies composed of quartz (14–16%), halite (25–33%), dolomite (18–25%), calcite (20–25%) and gypsum (8–11%); and salt facies is dominated only by halite (100%). The delineated facies led to highlight the depositional environment; mineralogy and geochemistry were studied. The elemental concentrations of CaO, MgO, K2O, Na2O, Al2O3, and SiO2 have been analyzed in order to understand the element behavior of each delineated sedimentary facie of sabkha basin. The geochemistry data reveals that SiO2 increases with the depth and CaO, MgO, Al2O3, and K2O behave in the reverse with the depth of sabkha sediments. The geochemical data has good correlation with the mineralogy of the same profile. Thus, the relationship has been established for the evolution of sabkha basin on the basis of sedimentary facies, mineralogy, and geochemistry.

Sintered Mono-Cordierite Mg2Al4−xBxSi5O18 Glass-Ceramic with B/Al Replacement at the Nano- and Micro-Scale

Sintered glass-ceramics based on cordierite modified glass with partial substitution of aluminum by boron [(Mg2Al4−xBxSi5O18 (x = 1 and 3)] were prepared mainly from natural raw materials. Mono-mineralic cordierite was formed at all the sintering temperatures. The results of infrared spectra confirmed the cordierite presence. The microcrystalline structure shows scattered hexagonal cordierite crystals, either at the micro- or nano-scale, in a glassy groundmass. The microanalysis of the hexagonal crystals indicated the incorporation of some elements in the cordierite structure. The density of the sintered samples was 2.0857 and 1.4857 g/cm 3 and the coefficient of thermal expansion, from room temperature up to 500 ∘C, was in the range from 10.46 and 25.60 × 10−7∘C−1. The microhardness value was 5.64 GPa and 5.90 GPa.

Characterization and Bioactivity in High Cristobalite-Nepheline-Apatite Glass and Glass Ceramics

Within the Na2O-CaO-Al2O3-SiO2-P2O5-F system, in the nominal binary nepheline-fluorapatite phases were prepared and investigated. Transparent glasses were obtained in a high nominal ratio of nepheline, i.e. 75, 80, 85 and 90%, whereas the low ones, i.e. 25, 50 and 70% gave devitrified glasses. The thermal behaviour of the glasses and both the crystalline phases and the microstructure of the glass ceramic were investigated. Moreover, the bioactivity of glasses and glass ceramics was also examined. Nepheline, fluorapatite and high cristobalite were the main crystalline phases developed through the heat-treatment process of the glass powders in the 800–1250°C temperature range. High cristobalite and nepheline were developed as the main phases that were treated either at high or low temperature. The microstructure shows spread crystals and flake-like crystals embedded in a glassy matrix. In vitro, the bioactivity testing of the glasses and the corresponding glass-ceramic, sintered at 900°C, showed that the sample containing 75% nominal nepheline was the best regarding in the bioactivity behaviour.

Stable Wollastonite-Cuspidine Glass-Ceramic Using Inexpensive Raw Materials

Transparent glasses within the K2O-CaO-SiO2-F composition were prepared. The influence of CaF2, TiO2, Li2O, Li2O-TiO2 and CeO2 additions on the crystallization of the parent glass has been investigated. Crystallization process gave wollastonite and cuspidine as the major phases whereas; xontolite and traces of miserite were developed as subordinate ones. Wollastonite was developed alone in the temperature range of 800 °C-1100 °C in Li2O-containing the base glass. Wollastonite and cuspidine were stable in the 800-1100 °C range in Li2O+TiO2-containing samples and within the 900 °C-1100 °C range in CaF2 and CeO2 containing samples. The microstructure of the Li2O-containing glass-ceramic showed an interlocked needle in nano-scale wollastonite crystals, while fibrous textures were developed in all other crystallized samples at 1000 °C. The thermal expansion coefficient value of the crystallized samples was between 7.596 to 8.708 X10 −6 °C−1 (20-500 °C) and the higher values reflect the increase of crystallization content of cuspidine and even the traces of miserite. This glass-ceramic is thought to be important in dental laboratories.