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  Subjects -> SCIENCES: COMPREHENSIVE WORKS (Total: 428 journals)
Showing 1 - 200 of 265 Journals sorted alphabetically
AAS Open Research     Open Access   (Followers: 2)
ABC Journal of Advanced Research     Open Access  
Academic Voices : A Multidisciplinary Journal     Open Access   (Followers: 2)
Accountability in Research: Policies and Quality Assurance     Hybrid Journal   (Followers: 18)
Acta Materialia Transilvanica     Open Access  
Acta Nova     Open Access   (Followers: 1)
Acta Scientifica Malaysia     Open Access  
Acta Scientifica Naturalis     Open Access   (Followers: 3)
Adıyaman University Journal of Science     Open Access  
Advanced Science     Open Access   (Followers: 13)
Advanced Science, Engineering and Medicine     Partially Free   (Followers: 10)
Advanced Theory and Simulations     Hybrid Journal   (Followers: 5)
Advances in Research     Open Access   (Followers: 1)
Advances in Science and Technology     Full-text available via subscription   (Followers: 17)
African Journal of Science, Technology, Innovation and Development     Hybrid Journal   (Followers: 8)
Afrique Science : Revue Internationale des Sciences et Technologie     Open Access   (Followers: 2)
AFRREV STECH : An International Journal of Science and Technology     Open Access   (Followers: 4)
Akademik Platform Mühendislik ve Fen Bilimleri Dergisi     Open Access   (Followers: 2)
American Academic & Scholarly Research Journal     Open Access   (Followers: 6)
American Journal of Applied Sciences     Open Access   (Followers: 27)
American Journal of Humanities and Social Sciences     Open Access   (Followers: 15)
Anadol University Journal of Science and Technology B : Theoritical Sciences     Open Access  
Anadolu University Journal of Science and Technology A : Applied Sciences and Engineering     Open Access  
ANALES de la Universidad Central del Ecuador     Open Access   (Followers: 3)
Anales del Instituto de la Patagonia     Open Access  
Annali dell'Istituto e Museo di storia della scienza di Firenze     Hybrid Journal  
Applied Mathematics and Nonlinear Sciences     Open Access  
Apuntes de Ciencia & Sociedad     Open Access  
Arab Journal of Basic and Applied Sciences     Open Access  
Arabian Journal for Science and Engineering     Hybrid Journal   (Followers: 5)
Archives Internationales d'Histoire des Sciences     Partially Free   (Followers: 6)
Archives of Current Research International     Open Access   (Followers: 1)
ARO. The Scientific Journal of Koya University     Open Access  
ARPHA Conference Abstracts     Open Access   (Followers: 7)
ARPHA Proceedings     Open Access   (Followers: 4)
ArtefaCToS : Revista de estudios sobre la ciencia y la tecnología     Open Access   (Followers: 1)
Asia-Pacific Journal of Science and Technology     Open Access  
Asian Journal of Advanced Research and Reports     Open Access   (Followers: 2)
Asian Journal of Applied Science and Engineering     Open Access   (Followers: 2)
Asian Journal of Scientific Research     Open Access   (Followers: 3)
Asian Journal of Technology Innovation     Hybrid Journal   (Followers: 7)
Australian Field Ornithology     Full-text available via subscription   (Followers: 4)
Australian Journal of Social Issues     Hybrid Journal   (Followers: 7)
Avances en Ciencias e Ingeniería     Open Access  
Avrasya Terim Dergisi     Open Access  
AZimuth     Full-text available via subscription   (Followers: 2)
Bangladesh Journal of Scientific Research     Open Access   (Followers: 1)
Beni-Suef University Journal of Basic and Applied Sciences     Open Access   (Followers: 3)
Berichte Zur Wissenschaftsgeschichte     Hybrid Journal   (Followers: 10)
Berkeley Scientific Journal     Full-text available via subscription  
BIBECHANA     Open Access   (Followers: 2)
BibNum     Open Access  
Bilge International Journal of Science and Technology Research     Open Access   (Followers: 1)
Bioethics Research Notes     Full-text available via subscription   (Followers: 16)
Bistua : Revista de la Facultad de Ciencias Básicas     Open Access  
Bitlis Eren Üniversitesi Fen Bilimleri Dergisi     Open Access  
Bitlis Eren University Journal of Science and Technology     Open Access   (Followers: 1)
Black Sea Journal of Engineering and Science     Open Access  
Borneo Journal of Resource Science and Technology     Open Access  
Brazilian Journal of Science and Technology     Open Access   (Followers: 2)
Bulletin de la Société Royale des Sciences de Liège     Open Access  
Bulletin of the National Research Centre     Open Access  
Butlletí de la Institució Catalana d'Història Natural     Open Access  
Celal Bayar Üniversitesi Fen Bilimleri Dergisi     Open Access   (Followers: 1)
Central European Journal of Clinical Research     Open Access  
Chain Reaction     Full-text available via subscription  
Ciencia & Natura     Open Access   (Followers: 1)
Ciencia Amazónica (Iquitos)     Open Access   (Followers: 1)
Ciencia en Desarrollo     Open Access   (Followers: 2)
Ciencia en su PC     Open Access   (Followers: 1)
Ciencia Ergo Sum     Open Access  
Ciência ET Praxis     Open Access  
Ciencia y Tecnología     Open Access  
Ciencia, Docencia y Tecnología     Open Access  
Ciencias Holguin     Open Access   (Followers: 2)
CienciaUAT     Open Access   (Followers: 1)
Citizen Science : Theory and Practice     Open Access   (Followers: 1)
Communications Faculty of Sciences University of Ankara Series A2-A3 Physical Sciences and Engineering     Open Access  
Communications in Applied Sciences     Open Access  
Comprehensive Therapy     Hybrid Journal   (Followers: 3)
Comunicata Scientiae     Open Access   (Followers: 1)
ConCiencia     Open Access  
Conference Papers in Science     Open Access   (Followers: 2)
Configurations     Full-text available via subscription   (Followers: 10)
COSMOS     Hybrid Journal  
Crea Ciencia Revista Científica     Open Access   (Followers: 3)
Cuadernos de Investigación UNED     Open Access  
Cumhuriyet Science Journal     Open Access  
Current Issues in Criminal Justice     Hybrid Journal   (Followers: 15)
Current Research in Geoscience     Open Access   (Followers: 8)
Dalat University Journal of Science     Open Access  
Data     Open Access   (Followers: 4)
Data Curation Profiles Directory     Open Access   (Followers: 4)
Dhaka University Journal of Science     Open Access  
Dharmakarya     Open Access  
Diálogos Interdisciplinares     Open Access  
Digithum     Open Access   (Followers: 2)
Eastern Anatolian Journal of Science     Open Access  
Einstein (São Paulo)     Open Access  
Ekaia : EHUko Zientzia eta Teknologia aldizkaria     Open Access  
Elkawnie : Journal of Islamic Science and Technology     Open Access  
Emergent Scientist     Open Access  
Enhancing Learning in the Social Sciences     Open Access   (Followers: 9)
Enseñanza de las Ciencias : Revista de Investigación y Experiencias Didácticas     Open Access  
Entramado     Open Access  
Entre Ciencia e Ingeniería     Open Access   (Followers: 1)
Epiphany     Open Access   (Followers: 4)
Episteme Transversalis     Open Access  
Ergo     Open Access  
Estação Científica (UNIFAP)     Open Access   (Followers: 1)
Ethiopian Journal of Education and Sciences     Open Access   (Followers: 6)
Ethiopian Journal of Science and Technology     Open Access  
Ethiopian Journal of Sciences and Sustainable Development     Open Access   (Followers: 7)
European Online Journal of Natural and Social Sciences     Open Access   (Followers: 12)
European Scientific Journal     Open Access   (Followers: 10)
Evidência - Ciência e Biotecnologia - Interdisciplinar     Open Access  
Exchanges : the Warwick Research Journal     Open Access   (Followers: 2)
Extensionismo, Innovación y Transferencia Tecnológica     Open Access   (Followers: 5)
Facets     Open Access  
Fides et Ratio : Revista de Difusión Cultural y Científica     Open Access   (Followers: 1)
Fırat Üniversitesi Fen Bilimleri Dergisi     Open Access  
Fırat University Turkish Journal of Science & Technology     Open Access  
Fontanus     Open Access  
Forensic Science Policy & Management: An International Journal     Hybrid Journal   (Followers: 378)
Frontiers for Young Minds     Open Access  
Frontiers in Climate     Open Access   (Followers: 3)
Frontiers in Science     Open Access   (Followers: 1)
Futures & Foresight Science     Hybrid Journal   (Followers: 4)
Gaudium Sciendi     Open Access   (Followers: 1)
Gazi University Journal of Science     Open Access  
Gaziosmanpaşa Bilimsel Araştırma Dergisi     Open Access  
Ghana Studies     Full-text available via subscription   (Followers: 15)
Global Journal of Pure and Applied Sciences     Full-text available via subscription  
Global Journal of Science Frontier Research     Open Access   (Followers: 2)
Globe, The     Full-text available via subscription   (Followers: 4)
HardwareX     Open Access  
Heidelberger Jahrbücher Online     Open Access  
Heliyon     Open Access  
Himalayan Journal of Science and Technology     Open Access   (Followers: 1)
Hoosier Science Teacher     Open Access  
Iğdır Üniversitesi Fen Bilimleri Enstitüsü Dergisi / Journal of the Institute of Science and Technology     Open Access  
Impact     Open Access   (Followers: 2)
Indonesian Journal of Fundamental Sciences     Open Access  
Indonesian Journal of Science and Mathematics Education     Open Access   (Followers: 3)
Indonesian Journal of Science and Technology     Open Access  
Ingenieria y Ciencia     Open Access   (Followers: 1)
Innovare : Revista de ciencia y tecnología     Open Access  
Instruments     Open Access  
Integrated Research Advances     Open Access  
Interciencia     Open Access   (Followers: 1)
Interface Focus     Full-text available via subscription  
International Annals of Science     Open Access  
International Archives of Science and Technology     Open Access  
International Journal of Academic Research in Business, Arts & Science     Open Access   (Followers: 2)
International Journal of Advanced Multidisciplinary Research and Review     Open Access  
International Journal of Advancement in Education and Social Sciences     Open Access   (Followers: 1)
International Journal of Advances in Engineering, Science and Technology     Open Access   (Followers: 3)
International Journal of Applied Science     Open Access  
International Journal of Basic and Applied Sciences     Open Access   (Followers: 4)
International Journal of Computational and Experimental Science and Engineering (IJCESEN)     Open Access  
International Journal of Engineering, Science and Technology     Open Access  
International Journal of Engineering, Technology and Natural Sciences     Open Access  
International Journal of Innovation and Applied Studies     Open Access   (Followers: 12)
International Journal of Innovative Research and Scientific Studies     Open Access   (Followers: 5)
International Journal of Innovative Research in Social and Natural Sciences     Open Access   (Followers: 1)
International Journal of Network Science     Hybrid Journal   (Followers: 3)
International Journal of Recent Contributions from Engineering, Science & IT     Open Access   (Followers: 1)
International Journal of Research in Science     Open Access   (Followers: 2)
International Journal of Science & Emerging Technologies     Open Access   (Followers: 1)
International Journal of Sciences : Basic and Applied Research     Open Access  
International Journal of Social Sciences and Management     Open Access   (Followers: 2)
International Journal of Technology Policy and Law     Hybrid Journal   (Followers: 7)
International Letters of Social and Humanistic Sciences     Open Access   (Followers: 1)
International Review of Applied Sciences     Open Access  
International Scientific and Vocational Studies Journal     Open Access   (Followers: 1)
InterSciencePlace     Open Access   (Followers: 1)
Investiga : TEC     Open Access  
Investigación Joven     Open Access  
Investigación Valdizana     Open Access  
Investigacion y Ciencia     Open Access   (Followers: 1)
Iranian Journal of Science and Technology, Transactions A : Science     Hybrid Journal  
iScience     Open Access  
Issues in Science & Technology     Free   (Followers: 7)
İstanbul Ticaret Üniversitesi Fen Bilimleri Dergisi / İstanbul Commerce University Journal of Science     Open Access  
Istituto Lombardo - Accademia di Scienze e Lettere - Rendiconti di Scienze     Open Access  
Ithaca : Viaggio nella Scienza     Open Access  
J : Multidisciplinary Scientific Journal     Open Access  
Journal de la Recherche Scientifique de l'Universite de Lome     Full-text available via subscription   (Followers: 2)
Journal for New Generation Sciences     Open Access   (Followers: 3)
Journal of Chromatography & Separation Techniques     Open Access   (Followers: 12)
Journal of Advanced Research     Open Access   (Followers: 3)
Journal of Al-Qadisiyah for Pure Science     Open Access   (Followers: 1)
Journal of Analytical Science & Technology     Open Access   (Followers: 6)
Journal of Applied Science and Technology     Full-text available via subscription   (Followers: 1)
Journal of Applied Sciences and Environmental Management     Open Access   (Followers: 3)
Journal of Big History     Open Access   (Followers: 3)
Journal of Composites Science     Open Access   (Followers: 3)
Journal of Critical Thought and Praxis     Open Access   (Followers: 2)
Journal of Deliberative Mechanisms in Science     Open Access  
Journal of Diversity Management     Open Access   (Followers: 4)

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Journal of Applied Science and Technology
Number of Followers: 1  
 
  Full-text available via subscription Subscription journal
ISSN (Print) 0855-2215
Published by African Journals Online Homepage  [265 journals]
  • Effect of permeability anisotropy on forced convection thermal
           –hydrodynamics of entrance and developed flow regimes in porous
           saturated circular tube
    • Authors: C Akowanou, G Degan, V Prodjinonto
      Abstract: Forced convective flow through anisotropic porous saturated circular tube was analysed to determine the entrance length to the hydrodynamic flow. The porous medium saturated with an incompressible viscous fluid was characterized by anisotropy permeability ratio, inclination angle of the principal axes and Prandtl number. The flow field was a succession of two distinct flow regions, the entrance region followed by fully developed flow regime. The boundary-layer regime prevailing at the thermal entrance region was analysed by integral relations approach, and analytical expressions of the entrance length, wall friction and heat transfer rate were obtained. Limiting cases for flow applicable to low and high porosity media were also observed. The anisotropic properties of the porous medium were significant where permeability ratio was either greater or less than 1.Keywords: Forced convection, Porous medium, Hydrodynamic flow field, Anisotropy Permeability ratio, Wall friction
      PubDate: 2017-01-23
      Issue No: Vol. 21, No. 1-2 (2017)
       
  • Theoretical analysis of hydriding reactions of ZrCo and LaNi5
           intermetallic alloys using non-isothermal shrinking core model
    • Authors: R Bhattacharyya
      Abstract: Hydriding reactions of spherical and flat plate geometries of zirconium cobalt (ZrCo) and lanthanum penta-nickel (LaNi5) intermetallic alloys were studied using kinetic data, and modified shrinking core model to account for concentration and temperature gradients in the gas film and ash layer under pseudo steady state non-isothermal conditions of 300, 310 and 320 K. The volumetric expansion of the alloy particle due to changing density was assumed during the hydriding reactions. The total hydriding time of 109 s was determined by numerical computati-on for different bulk temperatures, hydrogen concentrations and particle sizes; and the rate controlling process was identified to be diffusional. The values of the reaction times were very high, but could serve as data for predicting the length of hydriding cycle during hydrogen storage and recovery.Keywords: Hydriding reactions, Intermetallic alloys, Hydrogen storage, Shrinking core, Non-linear kinetics
      PubDate: 2017-01-23
      Issue No: Vol. 21, No. 1-2 (2017)
       
  • Thermal ageing analysis and lifetime prediction of IGBT inverter for solar
           PV-grid electricity connectivity
    • Authors: R.G. Agbokpanzo, T.K. Houngan, F.X. Fifatin, M Saleh, C Espanet
      Abstract: Thermal factors contributing to the ageing of Insulated Gate Bipolar Transistor (IGBT) inverters were investigat-ed, with special reference to temperature variation as the main source of degradation of the electrical insulations and material layers. The inverter configuration was analysed in order to predict the lifetime based on thermal age-ing. Therefore, a lifetime prediction model based on NSGA-II algorithm was implemented to identify optimal design condition as a compromise between the average temperature and total mass of the inverter. The option of either choosing design configuration according to using the device during the entire lifetime or half of the lifetime of the solar panel was the major decision. The research findings would contribute to better adaptation of IGBT inverter-solar panel for grid electricity connectivity in relation to the replacement of the invertor once over the lifetime of the panel.Keywords: IGBT inverter, solar PV-Grid electricity, NSGA-II algorithm, Thermal ageing, Lifetime prediction
      PubDate: 2017-01-23
      Issue No: Vol. 21, No. 1-2 (2017)
       
  • Changes in meteorological parameters in Nigeria by different
           manifestations of solar activities
    • Authors: E.O. Falayi, J.O. Adepitan, K Giwa, J.D. Ayanda, F.O. Ogunsanwo
      Abstract: The annual mean solar indices of MgII core to core wing ratio, solar flux 10.7 cm and sunspot number over an eleven (11) year period, 2000 – 2010, were correlated with the annual mean rainfall, maximum temperature, relati-ve humidity, cloud cover and wind speed of 8 meteorological stations in Nigeria. Correlation analyses were perfo-rmed to determine relationships between the solar indices and the meteorological parameters at the same temporal scale. In general, weak correlation and significant levels were exhibited between solar indices and meteorological parameters, except Sokoto, Ilorin and Yola, where there were strong negative and positive correlations with high level of significance between solar indices and meteorological parameters. The observations indicated that increa-sed solar activities might have contributed to decrease in rainfall, cloud cover, and relative humidity; but elevated maximum temperature; implying that variability of solar indices affected galactic cosmic radiation reaching the earth’s atmosphere.Keywords: MgII core to core wing ratio, Solar flux, Sunspot number, Solar activities, Meteorological parameters, Correlation coefficient
      PubDate: 2017-01-23
      Issue No: Vol. 21, No. 1-2 (2017)
       
  • Analysis and evaluation of post construction failures of airport apron
           pavement in Ghana
    • Authors: S Bawa, R Lumor
      Abstract: A new apron pavement for parking aircrafts was constructed in 2014, but major depressions occurred when used by aircrafts soon after the construction. Failure analysis revealed structural design inconsistent with the United States Federal Aviation Administration Design Code AC 150-5320-6E. The methodologies for the technical investigations of the failures encompassed field investigation (including visual condition survey), sampling core materials for verification tests, non-destructive and destructive tests to evaluate the integrity and characteristics of the pavement layers. The sample of cores tested in an accredited laboratory were inconsistent with the site tests. Air voids and Marshall Stability for wearing course were low. Binder specification should have been PG82, instead of PG76, which was not appropriate for aprons subjected to large static loads. The low air voids in the wearing course were linked with the compaction regime adopted. Fuel resistant polymer modified bitumen was adopted for the construction, without correct application techniques, thereby affecting the pavement performance. The key factors underlying the pavement failures were binder specifications, tenderness of the mix, compaction regime and structural design, which contributed to the immediate distress and possible long term performance of the pavement.Keywords: Apron Pavement, Wearing course, Cores, Air voids, Marshall stability, Compacting regime, Polymer modified bitumen
      PubDate: 2017-01-23
      Issue No: Vol. 21, No. 1-2 (2017)
       
  • Semi-empirical model for estimating molar fraction of syngas produced by
           thermal cracking of wood tar
    • Authors: L.A. Fagbemi, D.G.F. Adamon, E.A. Sanya
      Abstract: To optimize the efficiency of the wood gasification, tar which limits the use of syngas in thermal engines must be reduced. The quantity, quality and composition of syngas produced after thermal cracking of tar were analysed, and mathematical equations formulated based on Newton’s bivariate polynomial interpolation were used to estimate the molar fraction of the gases. The conceptual analysis of the problem was based on experimental data of temperature and residence time, and the semi-empirical model was simulated using Matlab to predict the composition of the syngas and the tar content in the gas mixture. The thermal cracking of tar increased the amount of syngas produced; in particular, the molar fraction of carbon monoxide and hydrogen. The gasification energy efficiency also improved with temperature and residence time, as the quantity of tar was reduced during cracking. The model was validated by comparing the experimental and numerical data.Keywords: Syngas, Gasification, Pyrolysis, Residence time, Thermal cracking of tar, Semi-empirical model
      PubDate: 2017-01-23
      Issue No: Vol. 21, No. 1-2 (2017)
       
  • Impact assessment of illegal small scale mining on construction of
           Tarkwa-Bogoso-Ayanfuri Highway in Ghana
    • Authors: S Bawa, A.O. Agyemang
      Abstract: Small-scale mining involves exploitation of mineral deposits using rudimentary implements and at low levels of production with minimal capital investment. South-Western Ghana has the largest concentration of mining operat-ions of both large companies and small scale miners. Illegal mining activities have impacted negatively on road constructions in the Region. A typical case is the construction of the Tarkwa-Bogoso-Ayanfuri highway, which provides very important link between Western and Central Region of Ghana. Prior to the rehabilitation, illegal small-scale miners operated in close proximity to the old road, often impacting on the structural integrity in many sections, but with the construction of the new road, the activities of the small-scale miners assumed prominence. The impact assessment presented in this paper reveals the negative effects of illegal mining on the road constructi-on project; particularly, project delivery schedule, time delays for completion, additional cost to the project and security on the project, which were critical issues of concerns. Future formulation of road projects for South-Western Ghana must take cognizance of the issues, which must be factored in the project management.Keywords: Impact assessment, Small-Scale Mining, Project Delivery, Project Cost, Project management, Alternative livelihood
      PubDate: 2017-01-23
      Issue No: Vol. 21, No. 1-2 (2017)
       
  • Assessment of cancer incidence and mortality risks associated with
           effective dose of computed tomography examinations
    • Authors: K.O. Akyea-Larbi, C Schandorf, F Hasford, S Inkoom, T.A. Sackey, G.F. Acquah
      Abstract: Advances in diagnostic medical imaging in the past few decades using procedures such as computed tomography (CT), have significantly enhanced health care delivery. The effective doses and associated cancer incidence and mortality risks were estimated for adult patients undergoing the five most common types of CT examinations, namely, head, neck, chest, abdomen and pelvis, at Sweden Ghana Medical Centre (SGMC) in Accra, Ghana. The two methods employed in the study were patients’ data collection and phantom measurements to verify the patien-ts’ data. The effective doses were estimated using the dose length product (DLP) from the control console of the CT machine and the anatomic region specific conversion factors. The lifetime attributable risks of cancer inciden-ce and cancer mortality for each patient for a particular examination were both determined from the effective dose, age and sex of each patient using the standard Biological Effects of Ionizing Radiation (BEIR) VII criteria. The effective doses were all within the range of 1 - 10 mSv recommended for CT examinations. The average risk for all the examinations was observed to be very low, i.e. 1 in 10001 to 1 in 10 000. The average lifetime attributable risk (LAR) of cancer incidence was 0.049 % (1 in 2041), while for risk of cancer mortality, the average was 0.030 % (1 in 3333).Keywords: Computed tomography, Effective dose, Dose length product, Life attributable risk, Cancer incidence, Cancer mortality
      PubDate: 2017-01-23
      Issue No: Vol. 21, No. 1-2 (2017)
       
  • Determination of thermal diffusivity of cement-stabilized laterite by
           transient thermal field and induced surface stress
    • Authors: H.E.A. Allognon, E Agoua, A Vianou
      Abstract: Knowledge of thermo-physical properties of local building materials are necessary for thermal comfort design and construction of residential accommodation. Thermal diffusivity of cement-stabilized laterites were measured under conditions of transient thermal field and induced surface stress, assuming constant temperature within the samples. The laterites were stabilized by 4 %, 8 % and 12 % cement content, and tested at water saturated and un-saturated states. The values of thermal diffusivity of dry and saturated samples were respectively ~ 5.01 x 10-7 m2/s and ~ 5.35 x 10-7 m2/s, and the two values indicated the suitability of stabilized laterite for providing thermal comfort in buildings.Keywords: Laterite, Cement-stabilization, Thermal diffusivity, Thermal comfort, Constant temperature bath
      PubDate: 2017-01-23
      Issue No: Vol. 21, No. 1-2 (2017)
       
  • Speciation and phase separation of water in quartz (A review)
    • Authors: A Ayensu Gyeabour I., A Owusu
      Abstract: Speciation, supersaturation and phase separation of water in hydrothermal grown (synthetic) quartz cryst-als have been examined as fundamental issues determining clustering, nucleation and bubble formation, which have profound influence on hydrolytic weakening, dislocation-bubble interactions and high temperature deformat-ion of quartz. Details of water speciation are necessary for explaining cluster dynamics and dislocation motion in quartz, and are also relevant in understanding magma evolution and eruption dynamics, since quartz and other sil-icates are important minerals of the earth crust. Infrared absorption studies strongly suggest that water bubbles in quartz contain hydrous species of hydroxyl ion (OH-) and molecular water (H2Om), originating from phase separat-ion of supersaturated water vapour after prolonged heat treatment of quartz at temperatures in excess of 500 °C. leading to decomposition of the hydrolyzed bonds. The hydrous species interconnect through a homogeneous spe-ciation reaction, condense, cluster and nucleate to form water bubbles, either homogeneously by thermal fluctuati-ons or heterogeneously on defects and other grown-in occlusions. The nucleation is a first order phase transition of creating liquid nucleus within the vapour phase, and chemical potential difference (related to the level of super-saturation) is the thermodynamic driving force.The unique properties of water that affect the mechanical deformation of quartz is due not only to the di-pole character, but even more to the geometrical structure of the molecules which form extended four coordinated networks. Incorporation of water tetrahedra in silicate framework [SiO4] produce electron-unsaturated chemical bonds. By sp3-hybridization of electron bonds, the water molecule exhibits a tetrahedral charged structure, leading to various water point defects in the form of substitution of SiO2 by two H2O substitutional defects (4H)Si, interstit-ial water molecules in channels parallel to the c-axis, hydrolyzed Si-O-Si bonds, and H-like alkali ions associated with substitutional impurities (such as Al3+ or Fe3+) to maintain charge balance. Water-related defects in quartz have complex structures and compositions, and the aqua-complexes are either bonded with different cations or are structurally bonded in the quartz matrix. The formation of combined defect [SiO4]-H2O-M+ [M3+O4] upon water speciation (M+ is metallic ion), is an indication of the presence of hydrous species.Keywords: Speciation, Supersaturation, Phase separation, Phase transition, Infrared absorption, Nucleation
      PubDate: 2017-01-22
      Issue No: Vol. 21, No. 1-2 (2017)
       
 
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