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  Subjects -> CHEMISTRY (Total: 849 journals)
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    - CHEMISTRY (598 journals)
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CHEMISTRY (598 journals)                  1 2 3 | Last

Showing 1 - 200 of 735 Journals sorted alphabetically
2D Materials     Hybrid Journal   (Followers: 8)
Accreditation and Quality Assurance: Journal for Quality, Comparability and Reliability in Chemical Measurement     Hybrid Journal   (Followers: 26)
ACS Catalysis     Full-text available via subscription   (Followers: 32)
ACS Chemical Neuroscience     Full-text available via subscription   (Followers: 17)
ACS Combinatorial Science     Full-text available via subscription   (Followers: 23)
ACS Macro Letters     Full-text available via subscription   (Followers: 23)
ACS Medicinal Chemistry Letters     Full-text available via subscription   (Followers: 39)
ACS Nano     Full-text available via subscription   (Followers: 226)
ACS Photonics     Full-text available via subscription   (Followers: 11)
ACS Synthetic Biology     Full-text available via subscription   (Followers: 21)
Acta Chemica Iasi     Open Access   (Followers: 2)
Acta Chimica Sinica     Full-text available via subscription   (Followers: 1)
Acta Chimica Slovaca     Open Access   (Followers: 1)
Acta Chromatographica     Full-text available via subscription   (Followers: 9)
Acta Facultatis Medicae Naissensis     Open Access  
Acta Metallurgica Sinica (English Letters)     Hybrid Journal   (Followers: 5)
Acta Scientifica Naturalis     Open Access   (Followers: 2)
adhäsion KLEBEN & DICHTEN     Hybrid Journal   (Followers: 5)
Adhesion Adhesives & Sealants     Hybrid Journal   (Followers: 7)
Adsorption Science & Technology     Full-text available via subscription   (Followers: 5)
Advanced Functional Materials     Hybrid Journal   (Followers: 50)
Advanced Science Focus     Free   (Followers: 3)
Advances in Chemical Engineering and Science     Open Access   (Followers: 53)
Advances in Chemical Science     Open Access   (Followers: 13)
Advances in Chemistry     Open Access   (Followers: 14)
Advances in Colloid and Interface Science     Full-text available via subscription   (Followers: 18)
Advances in Drug Research     Full-text available via subscription   (Followers: 22)
Advances in Enzyme Research     Open Access   (Followers: 9)
Advances in Fluorine Science     Full-text available via subscription   (Followers: 8)
Advances in Fuel Cells     Full-text available via subscription   (Followers: 15)
Advances in Heterocyclic Chemistry     Full-text available via subscription   (Followers: 8)
Advances in Materials Physics and Chemistry     Open Access   (Followers: 19)
Advances in Nanoparticles     Open Access   (Followers: 14)
Advances in Organometallic Chemistry     Full-text available via subscription   (Followers: 15)
Advances in Polymer Science     Hybrid Journal   (Followers: 41)
Advances in Protein Chemistry     Full-text available via subscription   (Followers: 18)
Advances in Protein Chemistry and Structural Biology     Full-text available via subscription   (Followers: 19)
Advances in Quantum Chemistry     Full-text available via subscription   (Followers: 5)
Advances in Science and Technology     Full-text available via subscription   (Followers: 12)
African Journal of Bacteriology Research     Open Access  
African Journal of Chemical Education     Open Access   (Followers: 2)
African Journal of Pure and Applied Chemistry     Open Access   (Followers: 7)
Agrokémia és Talajtan     Full-text available via subscription   (Followers: 2)
Alkaloids: Chemical and Biological Perspectives     Full-text available via subscription   (Followers: 3)
AMB Express     Open Access   (Followers: 1)
Ambix     Hybrid Journal   (Followers: 3)
American Journal of Biochemistry and Biotechnology     Open Access   (Followers: 67)
American Journal of Biochemistry and Molecular Biology     Open Access   (Followers: 14)
American Journal of Chemistry     Open Access   (Followers: 26)
American Journal of Plant Physiology     Open Access   (Followers: 13)
American Mineralogist     Hybrid Journal   (Followers: 13)
Analyst     Full-text available via subscription   (Followers: 38)
Angewandte Chemie     Hybrid Journal   (Followers: 159)
Angewandte Chemie International Edition     Hybrid Journal   (Followers: 210)
Annales UMCS, Chemia     Open Access   (Followers: 1)
Annals of Clinical Chemistry and Laboratory Medicine     Open Access   (Followers: 1)
Annual Reports in Computational Chemistry     Full-text available via subscription   (Followers: 3)
Annual Reports Section A (Inorganic Chemistry)     Full-text available via subscription   (Followers: 3)
Annual Reports Section B (Organic Chemistry)     Full-text available via subscription   (Followers: 8)
Annual Review of Chemical and Biomolecular Engineering     Full-text available via subscription   (Followers: 12)
Annual Review of Food Science and Technology     Full-text available via subscription   (Followers: 14)
Anti-Infective Agents     Hybrid Journal   (Followers: 3)
Antiviral Chemistry and Chemotherapy     Hybrid Journal  
Applied Organometallic Chemistry     Hybrid Journal   (Followers: 7)
Applied Spectroscopy     Full-text available via subscription   (Followers: 23)
Applied Surface Science     Hybrid Journal   (Followers: 28)
Arabian Journal of Chemistry     Open Access   (Followers: 6)
ARKIVOC     Open Access   (Followers: 2)
Asian Journal of Biochemistry     Open Access   (Followers: 1)
Atomization and Sprays     Full-text available via subscription   (Followers: 3)
Australian Journal of Chemistry     Hybrid Journal   (Followers: 7)
Autophagy     Hybrid Journal   (Followers: 2)
Avances en Quimica     Open Access   (Followers: 1)
Biochemical Pharmacology     Hybrid Journal   (Followers: 10)
Biochemistry     Full-text available via subscription   (Followers: 282)
Biochemistry Insights     Open Access   (Followers: 5)
Biochemistry Research International     Open Access   (Followers: 6)
BioChip Journal     Hybrid Journal  
Bioinorganic Chemistry and Applications     Open Access   (Followers: 9)
Bioinspired Materials     Open Access   (Followers: 5)
Biointerface Research in Applied Chemistry     Open Access   (Followers: 2)
Biointerphases     Open Access   (Followers: 1)
Biology, Medicine, & Natural Product Chemistry     Open Access   (Followers: 1)
Biomacromolecules     Full-text available via subscription   (Followers: 19)
Biomass Conversion and Biorefinery     Partially Free   (Followers: 10)
Biomedical Chromatography     Hybrid Journal   (Followers: 6)
Biomolecular NMR Assignments     Hybrid Journal   (Followers: 3)
BioNanoScience     Partially Free   (Followers: 4)
Bioorganic & Medicinal Chemistry     Hybrid Journal   (Followers: 108)
Bioorganic & Medicinal Chemistry Letters     Hybrid Journal   (Followers: 93)
Bioorganic Chemistry     Hybrid Journal   (Followers: 10)
Biopolymers     Hybrid Journal   (Followers: 18)
Biosensors     Open Access   (Followers: 2)
Biotechnic and Histochemistry     Hybrid Journal   (Followers: 1)
Bitácora Digital     Open Access  
Boletin de la Sociedad Chilena de Quimica     Open Access  
Bulletin of the Chemical Society of Ethiopia     Open Access   (Followers: 2)
Bulletin of the Chemical Society of Japan     Full-text available via subscription   (Followers: 24)
Bulletin of the Korean Chemical Society     Hybrid Journal   (Followers: 1)
C - Journal of Carbon Research     Open Access   (Followers: 3)
Cakra Kimia (Indonesian E-Journal of Applied Chemistry)     Open Access  
Canadian Association of Radiologists Journal     Full-text available via subscription   (Followers: 2)
Canadian Journal of Chemistry     Hybrid Journal   (Followers: 10)
Canadian Mineralogist     Full-text available via subscription   (Followers: 3)
Carbohydrate Research     Hybrid Journal   (Followers: 26)
Carbon     Hybrid Journal   (Followers: 67)
Catalysis for Sustainable Energy     Open Access   (Followers: 6)
Catalysis Reviews: Science and Engineering     Hybrid Journal   (Followers: 8)
Catalysis Science and Technology     Free   (Followers: 6)
Catalysis Surveys from Asia     Hybrid Journal   (Followers: 3)
Catalysts     Open Access   (Followers: 7)
Cellulose     Hybrid Journal   (Followers: 7)
Cereal Chemistry     Full-text available via subscription   (Followers: 4)
ChemBioEng Reviews     Full-text available via subscription   (Followers: 1)
ChemCatChem     Hybrid Journal   (Followers: 8)
Chemical and Engineering News     Free   (Followers: 12)
Chemical Bulletin of Kazakh National University     Open Access  
Chemical Communications     Full-text available via subscription   (Followers: 70)
Chemical Engineering Research and Design     Hybrid Journal   (Followers: 23)
Chemical Research in Chinese Universities     Hybrid Journal   (Followers: 3)
Chemical Research in Toxicology     Full-text available via subscription   (Followers: 19)
Chemical Reviews     Full-text available via subscription   (Followers: 173)
Chemical Science     Open Access   (Followers: 21)
Chemical Technology     Open Access   (Followers: 16)
Chemical Vapor Deposition     Hybrid Journal   (Followers: 5)
Chemical Week     Full-text available via subscription   (Followers: 8)
Chemie in Unserer Zeit     Hybrid Journal   (Followers: 55)
Chemie-Ingenieur-Technik (Cit)     Hybrid Journal   (Followers: 25)
ChemInform     Hybrid Journal   (Followers: 8)
Chemistry & Biodiversity     Hybrid Journal   (Followers: 6)
Chemistry & Biology     Full-text available via subscription   (Followers: 30)
Chemistry & Industry     Hybrid Journal   (Followers: 5)
Chemistry - A European Journal     Hybrid Journal   (Followers: 147)
Chemistry - An Asian Journal     Hybrid Journal   (Followers: 15)
Chemistry and Materials Research     Open Access   (Followers: 18)
Chemistry Central Journal     Open Access   (Followers: 4)
Chemistry Education Research and Practice     Free   (Followers: 5)
Chemistry in Education     Open Access   (Followers: 9)
Chemistry International     Hybrid Journal   (Followers: 2)
Chemistry Letters     Full-text available via subscription   (Followers: 45)
Chemistry of Materials     Full-text available via subscription   (Followers: 250)
Chemistry of Natural Compounds     Hybrid Journal   (Followers: 9)
Chemistry World     Full-text available via subscription   (Followers: 22)
Chemistry-Didactics-Ecology-Metrology     Open Access  
ChemistryOpen     Open Access   (Followers: 2)
Chemkon - Chemie Konkret, Forum Fuer Unterricht Und Didaktik     Hybrid Journal  
Chemoecology     Hybrid Journal   (Followers: 2)
Chemometrics and Intelligent Laboratory Systems     Hybrid Journal   (Followers: 15)
Chemosensors     Open Access  
ChemPhysChem     Hybrid Journal   (Followers: 9)
ChemPlusChem     Hybrid Journal   (Followers: 2)
ChemTexts     Hybrid Journal  
CHIMIA International Journal for Chemistry     Full-text available via subscription   (Followers: 2)
Chinese Journal of Chemistry     Hybrid Journal   (Followers: 6)
Chinese Journal of Polymer Science     Hybrid Journal   (Followers: 10)
Chromatographia     Hybrid Journal   (Followers: 24)
Chromatography Research International     Open Access   (Followers: 7)
Clay Minerals     Full-text available via subscription   (Followers: 9)
Cogent Chemistry     Open Access  
Colloid and Interface Science Communications     Open Access  
Colloid and Polymer Science     Hybrid Journal   (Followers: 10)
Colloids and Surfaces B: Biointerfaces     Hybrid Journal   (Followers: 8)
Combinatorial Chemistry & High Throughput Screening     Hybrid Journal   (Followers: 3)
Combustion Science and Technology     Hybrid Journal   (Followers: 18)
Comments on Inorganic Chemistry: A Journal of Critical Discussion of the Current Literature     Hybrid Journal   (Followers: 2)
Composite Interfaces     Hybrid Journal   (Followers: 6)
Comprehensive Chemical Kinetics     Full-text available via subscription   (Followers: 2)
Comptes Rendus Chimie     Full-text available via subscription  
Comptes Rendus Physique     Full-text available via subscription   (Followers: 1)
Computational and Theoretical Chemistry     Hybrid Journal   (Followers: 9)
Computational Biology and Chemistry     Hybrid Journal   (Followers: 12)
Computational Chemistry     Open Access   (Followers: 2)
Computers & Chemical Engineering     Hybrid Journal   (Followers: 9)
Coordination Chemistry Reviews     Full-text available via subscription   (Followers: 2)
Copernican Letters     Open Access  
Critical Reviews in Biochemistry and Molecular Biology     Hybrid Journal   (Followers: 5)
Crystal Structure Theory and Applications     Open Access   (Followers: 3)
CrystEngComm     Full-text available via subscription   (Followers: 11)
Current Catalysis     Hybrid Journal   (Followers: 2)
Current Metabolomics     Hybrid Journal   (Followers: 5)
Current Opinion in Colloid & Interface Science     Hybrid Journal   (Followers: 9)
Current Research in Chemistry     Open Access   (Followers: 8)
Current Science     Open Access   (Followers: 57)
Dalton Transactions     Full-text available via subscription   (Followers: 19)
Detection     Open Access   (Followers: 2)
Developments in Geochemistry     Full-text available via subscription   (Followers: 2)
Diamond and Related Materials     Hybrid Journal   (Followers: 12)
Dislocations in Solids     Full-text available via subscription  
Doklady Chemistry     Hybrid Journal  
Drying Technology: An International Journal     Hybrid Journal   (Followers: 4)
Eclética Química     Open Access   (Followers: 1)
Ecological Chemistry and Engineering S     Open Access   (Followers: 4)
Ecotoxicology and Environmental Contamination     Open Access  
Educación Química     Open Access   (Followers: 1)
Education for Chemical Engineers     Hybrid Journal   (Followers: 5)
EJNMMI Radiopharmacy and Chemistry     Open Access  
Elements     Full-text available via subscription   (Followers: 2)
Environmental Chemistry     Hybrid Journal   (Followers: 9)
Environmental Chemistry Letters     Hybrid Journal   (Followers: 4)
Environmental Science & Technology Letters     Full-text available via subscription   (Followers: 5)

        1 2 3 | Last

Journal Cover Chemical Technology
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  This is an Open Access Journal Open Access journal
   ISSN (Print) 1392-1231
   Published by Kaunas University of Technology Homepage  [10 journals]
  • The 7th Baltic Conference on Silicate Materials BaltSilica 2016

    • Authors: R. Šiaučiūnas, R. Kaminskas
      Abstract: This issue of ”Chemine technologija” (Chemical Technology) is actually the proceedings of the 7th Baltic Conference on Silicate Materials, hosted by the Department of Silicate Technology, Kaunas University of Technology on 26–27 May, 2016.
      PubDate: 2016-10-05
      Issue No: Vol. 67 (2016)
       
  • Leaching of phase-separated glasses in the Na2O-B2O3-SiO2-Fe2O3 system

    • Authors: M. Konon, T. Antropova, T. Kostyreva, I. Drozdova, I. Polyakova
      Abstract: The leaching behavior of heat-treated phase-separated iron-containing sodium borosilicate glasses within the range of compositions of 8Na2O·(22 – х)B2O3·70SiO2·хFe2O3, where х varies from 0.3 to 10 mol.%, and (8 – x)Na2O∙22B2O3∙70SiO2· xFe2O3, where х varies from 2 to 6 mol.%, in the 3M aqueous HCl solution at boiling, was studied. It has been shown that the introduction of Fe2O3 in these phase-separated glasses increases their chemical durability, the values of porosity and the average pore diameter, but reduces the specific surface area in the porous glasses based on them, compared with glass without Fe2O3. The compositions suitable for producing porous glasses were determined.
      DOI : http://dx.doi.org/10.5755/j01.ct.67.1.14800
      PubDate: 2016-08-01
      Issue No: Vol. 67 (2016)
       
  • Interactions among the characteristics of concretes containing a high
           portion of micro-filler

    • Authors: A. Sicakova, M. Kovac, M. Draganovska
      Abstract: Utilization of the construction and demolition waste (C&DW) for the production of building materials is discussed for a longer time worldwide, whether in the form of coarse aggregates or in the fine-grain form as a micro-filler/additive. The valorization of waste/by-products in the production of building materials can be improved by their modification using some treatment technologies. The article presents the results of testing the concretes containing a high dosage of the C&DW that were previously adjusted into fine-particle powders. Those powders were prepared by the grinding and sorting of concrete, brick and glass to specific dimensions – under 250 μm. They were intended as a micro filler substitution of natural aggregate (NA) within the 0/4 fraction to the extent permitted by technological rules. Except for environmental reasons (saving the natural sources of NA), the high dosage of micro-fillers was intended for improving the technical parameters of concrete. The main goal was to attain a concrete of high fluidity, as it is in great demand by constructors. That is why also other parameters of concrete mixtures were optimized; the amount of water as well as the dosage of plasticizer were adjusted during mixing in order to keep the standard criteria. Next, a positive impact on the properties of hardened concrete was expected due to the effect of micro-fillers in the concrete microstructure. The results of these properties are presented and discussed in the paper, namely density, compressive strength, water absorption capacity and frost resistance. The analysis of the results is focused on the effect of an individual powdered material, on the interaction of the resulting properties of concretes, as well as on the changes of those properties in time, since the data were collected at 7, 28 and 365 days of hardening. Positive effect of fine-grain form of brick, glass and concrete on the compressive strength and partially on the frost resistance was found compared to the reference concrete, while it is not the case of water absorption capacity.

      DOI : http://dx.doi.org/10.5755/j01.ct.67.1.14896
      PubDate: 2016-08-01
      Issue No: Vol. 67 (2016)
       
  • Influence of firing temperature on the chemical properties of hydraulic
           dolomitic binder

    • Authors: I. Kirilovica, I. Vitina, S. Igaune-Blumberga, L. Lindina
      Abstract: The synthesis of a binder from the mixture of dolomite flour and clay is investigated. The main anticipated usage of the binder is for the restoration of historical dolomitic Roman cement objects. During the 19th/20th century, in the territory of Latvia dolomitic Roman cement was the main hydraulic binder applied for the construction of buildings. It was processed in Riga since 1865 by firing the local raw material dolomitic marlstone below its sintering temperature (800–900 °C) and by fine milling. Because of its fast setting and good water resistance, the material was used mostly for decorative elements of facades. However, since the middle of the 20th century its production has been stopped. With the aim to provide a compatible material for restoration needs, compositions from dolomite flour and clay were investigated as a perspective raw material for the synthesis of a low-temperature hydraulic binder. Mixtures from two types of clay and dolomite flour in powder state were synthesized. Clay content in the compositions varied from 13 to 30 %. Samples were prepared by mixing the raw materials, semi-dry pressing and firing at 750–950 °C. The study gives an insight into the chemical processes that occur during the synthesis of a binder from a mixture of clay and dolomite flour. Thermochemical processes in the obtained binder depending on production temperature and clay type were compared by using the XRD analysis and a full chemical analysis.
      DOI : http://dx.doi.org/10.5755/j01.ct.67.1.14986
      PubDate: 2016-08-01
      Issue No: Vol. 67 (2016)
       
  • MgO-based cement as an inorganic binder for hemp hurds composites

    • Authors: N. Stevulova, I. Schwarzova, A. Estokova, M. Holub
      Abstract: The aim of this work is to study the suitability of the MgO-based cement as an inorganic binder instead of the traditional Portland cement into composites with an organic filler material such as hemp hurds. MgO-based cements, in contrast to Portland cement which requires high temperatures (about 1450 °C) during its production, demand less energy (the maximum temperature for the controlled calcination to obtain MgO from magnesium carbonate is 750 °C), becoming a more efficient cement from the environmental point of view. The first part of this paper summarises the results of physico-mechanical properties such as density, thermal conductivity, water absorbability and compressive strength of hardened hemp hurds composites that make this material useful and interesting mainly for its thermal insulating properties which can be improved by hemp hurds treatment processes. The second part of this work is devoted to the characterization of the MgO–cement matrix in the 28-day hardening stage. The MgO-based cement as an alternative binder appears to be suitable for the preparation of biocomposites based on hemp hurds.
      DOI : http://dx.doi.org/10.5755/j01.ct.67.1.15000
      PubDate: 2016-08-01
      Issue No: Vol. 67 (2016)
       
  • Potential utilization of recycled waste paper fibres in cement composites

    • Authors: N. Stevulova, V. Hospodarova, J. Junak
      Abstract: This paper deals with the utilization of waste paper fibres in cement composites. The characterization of  waste cellulosic fibres, their processing methods as well as the density and mechanical properties of cement-based composites with the 2 and 5 wt% fibre content of three fibre kinds compared to a composite based on 99.5 wt.% cellulosic fibre and the control sample without fibres are presented. It is shown that the density and mechanical properties of tested fibre-cement composites are affected by cellulosic fibre content and depend on the nature of fibres, their dimension and dispersion in the matrix. The density of each composite with fibre content was checked in a narrow range (1921–1968 kg/m3 at 2 % and 5 % replacement of the filler). Composites with recycled waste paper fibres had an increasing character in the values of flexural strength up to 14.9 % in comparison with the wood pulp mortar sample. The compressive strength of composites with 2 % of filler replacement reached up to 18 MPa. However, the 5 % replacement of the filler caused a reduction in the compressive strength values to 7.5 % in comparison with the sample containing wood pulp after 28 days of hardening.
      DOI : http://dx.doi.org/10.5755/j01.ct.67.1.15001
      PubDate: 2016-08-01
      Issue No: Vol. 67 (2016)
       
  • Performance of cement mortars with waste-material addition in
           microbiological sulphate environment

    • Authors: A. Estokova, M. Smolakova, A. Luptakova, J. Strigac
      Abstract: Bio-corrosion refers to the corrosion influenced by the presence of microorganisms on the surface of different concrete structures. Sulphate-reducing bacteria (SRB) and sulphur-oxidizing bacteria (SOB) belong to the best studied microorganisms causing bio-corrosion. Concrete sewer pipes, waste water collection systems and treatment plants ensure a suitable environment for the growth and activity of these microorganisms. Sulphur-oxidizing bacteria produce the biogenic sulphuric acid which may cause a significant structural damage to the sewage infrastructure by inducing the deterioration of concrete sewer pipes. This paper discusses the effects of SOB bacterial activity represented by Acidithiobacillus thiooxidans on parameters affecting the durability of cement mortar composites. Two mortar mixtures were used in the experiment: samples with a share of ground granulated blast furnace slag (65 % cement replacement) and the reference samples without any waste addition. The composites were exposed to an aggressive sulphate environment with sulphur-oxidizing bacteria for 60 days. Parameters such as the pH of liquid media and the leachability of the basic inorganic compounds from the cementitious matrix due to the aggressive environment were studied. The better durability of cement mortar samples, based on furnace slag addition, against the biogenic sulphate attack was not confirmed.
      DOI : http://dx.doi.org/10.5755/j01.ct.67.1.15002
      PubDate: 2016-08-01
      Issue No: Vol. 67 (2016)
       
  • Application of waste materials as potential biosorbents for Cu(II) and
           Zn(II) removal

    • Authors: M. Holub, M. Balintova, S. Demcak, P. Pavlikova
      Abstract: Mining is probably the most common activity that fundamentally impacts the country. The problems connected with the extraction of sulphide ores arise especially during the final stage of mining, closure and abandonment of the extraction area, when the conditions for the generation of strong acid water are most likely to occur. With respect to the diversity of compounds in acid mine drainage (AMD) and its low pH values it is hard to find an effective and inexpensive “active” treatment process. Recently, numerous approaches have been studied for the development of cheaper and more effective technologies, both to decrease the amount of heavy metals and to improve the quality of the treated effluent. Adsorption has become one of the alternative treatments; in the recent years, the search for low-cost adsorbents that have metal-binding capacities has intensified. Adsorption of heavy metals (Cu and Zn) from single-component aqueous solutions onto non-modified poplar sawdust, hemp shives and peat has been studied using the batch-adsorption techniques. For this purpose, solutions with different concentrations ranging from 10 to 150 mg/L have been used. The study was carried out to examine the adsorption capacity of the low-cost waste materials as potential biosorbents for the removal of heavy metals from acid mine drainage. The adsorption isotherms could be better fitted by the Langmuir model (values of the correlation factor range from 0.974 to 0.997). The values of the separation factor (RL) in the present study were found to be within 0.037–0.728, indicating the favorable adsorption process. From the comparison of maximum sorption capacities, it is evident that the best adsorption properties are exhibited by the hemp shives, and copper is overall better adsorbed than zinc (Qmax = 12.84 mg/g and 8.28 mg/g for copper and zinc, respectively). The results indicate that these freely abundant, low-cost waste materials can be treated as economically viable for the removal of metal ions in acidic conditions.
      DOI : http://dx.doi.org/10.5755/j01.ct.67.1.15003
      PubDate: 2016-08-01
      Issue No: Vol. 67 (2016)
       
  • Modification of cementitious building materials by treatment with CO2

    • Authors: D. Heinz, L. Urbonas
      Abstract: The aim of this study was to determine the effect of CO2 treatment conditions and cement composition (i.e. alkali and C3A content, cement fineness) on the microstructure, phases and the strength of hardened cement paste and mortar. The results show that CO2 treatment at elevated pressures produces significant changes in the microstructure of hardened cement paste. The decomposition of the hydrates and, to some extent, non-hydrated clinker minerals to form CaCO3 phases (mainly calcite) produces a dense microstructure and increases strength significantly. The strength increased with CO2 pressure and the duration of treatment. A further increase in strength occurred during the subsequent storage of carbonated specimens in water or in air at 20 °C and 65 %RH owing to the ongoing hydration of residual clinker minerals. Specimens treated with supercritical CO2 and then stored at 20 °C and 65 %RH reached a 28 d compressive strength which almost doubled the standard 28 d standard strength. The use of cements with a higher fineness (strength class) reduced the carbonation rate and therefore the gain in strength, owing to the lower porosity of the initial material made with these cements. The higher alkali contents of the cement led to a slower carbonation. The largest depth of carbonation and the highest increase in strength were obtained for cements with low C3A and alkali contents.
      DOI : http://dx.doi.org/10.5755/j01.ct.67.1.15823
      PubDate: 2016-08-01
      Issue No: Vol. 67 (2016)
       
  • The synthesis and characterization of nickel and cobalt ferrite
           nanopowders obtained by different methods

    • Authors: I. Zalite, G. Heidemane, L. Kuznetsova, M. Kodols, J. Grabis, M. Maiorov
      Abstract: The ferrite materials, especially of nickel and cobalt, are popular due to their unique mechanical and magnetic properties. The single phase NiFe2O4 and CoFe2O4 ferrites were synthesized by three methods: the high frequency plasma chemical synthesis, the sol-gel self-combustion, and the co-precipitation technology combined with the hydrothermal synthesis method. Magnetic properties, crystallite size, the specific surface area of synthesized products are characterized. Nanopowders synthesized in the high frequency plasma have a specific surface area in the range of 28–30 m2/g (the average particle size 38–40 nm, crystallite size ~40 nm), but a wider particle size distribution is in the range of 10–100 nm with some particles of 200 nm. The ferrite nanopowders obtained by the sol-gel self-combustion and hydrothermal synthesis method have the specific surface area of 40 ± 3 and 60 ± 5 m2/g (average particle size 25–30 nm and 19–26 nm, crystallite size 10–20 nm and 12–20 nm), respectively. Cobalt ferrites after synthesis are characterized by the saturation magnetization MS of 75 emu/g (for plasma chemical synthesis), 53 emu/g (for the self-combustion method), and 57 emu/g (hydrothermal synthesis). The saturation magnetization for nickel ferrites is 44, 29 and 30 emu/g, respectively. After the thermal treatment up to 900 ºC the particle size of all ferrites increases, but their magnetic properties are approaching those of monolithic ferrites.
      DOI : http://dx.doi.org/10.5755/j01.ct.67.1.15824
      PubDate: 2016-08-01
      Issue No: Vol. 67 (2016)
       
  • Influence of silica fume on the workability and hydration process of
           ultra-high performance concrete

    • Authors: E. Šerelis, V. Vaitkevičius, V. Kerševičius
      Abstract: The present article reviews the influence of silica fume on the workability and hydration process of ultra-high performance concrete (UHPC). Silica fume, also known as microsilica (MS) or condensed silica fume, is a by-product of the production of silicon metal or ferrosilicon alloys. Silica fume is one of the most effective pozzolanic additives which could be used for ultrahigh-performance and other types of concrete. According to the literature review, it is not entirely clear which amount of silica fume is optimal, how silica fume affects the hydration process; although the literature is rich in reporting on silica fume, however, most of the scientists are concentrated on workability and compressive strength. The purpose of this research is to extend knowledge on the workability and hydration process of ultra-high performance concrete affected by different amounts of silica fume. For investigation, slump, viscosity, qualitative and quantitative XRD analysis and compression strength tests were applied. The hydration time was reduces by 4.5 hours, and the compressive strength was increased by 30 % (from 95 MPa up to 127 MPa).
      DOI : http://dx.doi.org/10.5755/j01.ct.67.1.15825
      PubDate: 2016-08-01
      Issue No: Vol. 67 (2016)
       
  • Investigation of the use of enzyme preparations in leather manufacture

    • Authors: K. Beleška, J. Širvaitytė, R. Alaburdaitė, I. Komičiūtė, V. Valeika
      Abstract: An important component in tanning is the removal of hair from the hide (unhairing), a process which generates considerable amounts of toxic effluent characterized by a high concentration of sulphur, rich mineral compounds, a high alkalinity, and a high organic load. Herewith, the cleaning of unhairing solutions, polluted with lime, sulphides and products of protein degradation remains, is very complicate and expensive. Special attention is paid to lime and sulphides, which are used for beamhouse processes, trying to decrease their amounts or replace them by systems of other materials. Developing new and less polluting technologies of leather processing, it is supposed that components of more environmentally friendly unhairing systems may be enzymatic preparations characterized by a wide spectrum of effects, and, also, oxidizing materials. The presented research is aimed to develop an efficient unhairing system for hides, which contains the oxidation material and the enzyme. Hydrogen peroxide was chosen as a comparatively cheap and environmentally friendly material. Since the action of hydrogen peroxide in the unhairing system depends on its decomposition duration, the decomposition of hydrogen peroxide has been investigated with a modelling medium in the presence of metal ions (Mn2+, Fe2+, Cu2+). The addition of 28–56 μmol/L of Mn2+ or Fe2+ leads to a complete decomposition of hydrogen peroxide during 5–6 hours. The investigation of the unhairing process has shown that the separate use of hydrogen peroxide or the enzyme preparation does not lead to a qualitative unhairing of the hide. An environment-friendly and effective unhairing system has been prepared using hydrogen peroxide 2–4 % on hide mass, the enzyme preparation Aquaderm A 0.2 % on hide mass, and divalent manganese or iron salt in the range of concentration from 28 to 56 μmol/L. A good unhairing effect has been achieved in the following case: a full degradation of the epidermis; an easy hair removal by a slight mechanical action; no damage of the hide surface. The use of the developed unhairing system allows avoiding wastewater pollution by dangerous sulphides and lime.
      DOI : http://dx.doi.org/10.5755/j01.ct.67.1.15826
      PubDate: 2016-08-01
      Issue No: Vol. 67 (2016)
       
  • Quality parameters of fermented kvass extract

    • Authors: I. Lidums, D. Karklina, A. Kirse
      Abstract: The aim of this research was to compare the commercially available kvass concentrate to the kvass extract which was experimentally produced from the naturally fermented kvass. Dry matter was determined according to the standard ISO 2173:2003, active acidity – ISO 10523:2012, and apparent viscosity was measured with a DV-III Ultra Brookfield rheometer, using a spindle SC4-18 with the speed 50 rpm at 26.9 °C. Sugars were determined using high-performance liquid chromatography. The sensory evaluation of kvass drinks (recombined kvass concentrate and extract) was performed according to the ISO 4121:2003. The dry matter content in the kvass concentrate (Ltd. Ilgzeem) was 69 %; it was diluted with distilled water to the dry matter content 32.4 ± 0.2 % of kvass extract (made from Ltd. Liepzeme kvass). Active acidity in the kvass concentrate was significantly (p = 0.012) lower (pH 2.86) than in the kvass extract (pH 4.18). Apparent viscosity in the kvass extract was 13.68 mPa×s and in the kvass concentrate 5.22 mPa×s. Major sugars in the kvass extract were fructose and glucose and in the commercial kvass concentrate – fructose. Hedonic evaluation showed that there were no significant differences (p > 0.05) in the preference of kvass drinks. The intensity of aroma, flavour and acidity was significantly more pronounced in the kvass drink made from the commercial kvass concentrate.
      DOI : http://dx.doi.org/10.5755/j01.ct.67.1.15828
      PubDate: 2016-08-01
      Issue No: Vol. 67 (2016)
       
  • Synthesis of {2-[1-(4-bromophenyl)-5-oxopyrrolidin-3-yl]-1H
           -benzimidazol-1-yl}acetic acid hydrazide derivatives

    • Authors: G. Toliušytė, K. Anusevičius, V. Mickevičius
      Abstract: First of all, condensation reactions of acetohydrazide with different aldehydes were carried out, 7 hydrazones were obtained. In the presence of acetic acid as a catalyst, reactions of acetohydrazide with 2,4-pentanedione and 2,5-hexanedione yielded pyrazole and pyrrole derivatives, respectively. The reaction of acetohydrazide and carbon disulphide in the presence of potassium hydroxide was carried out, and potassium dithiocarbazate was obtained. The cyclization reaction of potassium dithiocarbazate with hydrazine monohydrate gave 4-amino-1,2,4-triazole. The cyclization reaction of potassium dithiocarbazate was investigated in an acidic medium; 1,3,4-oxadiazole was formed. By the use of regular heating, in the reaction of acetohydrazide with triethyl orthoformate ethyl formohydrazonate was obtained. Triazine was prepared by heating at reflux a mixture of acetohydrazide, ammonium acetate, 1,2-diphenyl-1,2-ethanedione and using 2-propanol as a solvent.In reactions of acetohydrazide with phenyl isocyanate or phenyl thiocyanate, the N-substituted semicarbazide or thiosemicarbazide derivatives were synthesized, respectively. The cyclization reactions of semicarbazide and thiosemicarbazide were carried out in acidic medium - 1,3,4-oxadiazole and 1,3,4-thiadiazole were obtained. Also cyclization reactions of semicarbazide and thiosemicarbazide were investigated in alkaline medium – 1,2,4-triazole derivatives were forme.
      DOI : http://dx.doi.org/10.5755/j01.ct.67.1.15829
      PubDate: 2016-08-01
      Issue No: Vol. 67 (2016)
       
 
 
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