Tallinn University of Technology

About: Tallinn University of Technology is a education organization based out in Tallinn, Estonia. It is known for research contribution in the topics: European union & Computer science. The organization has 3688 authors who have published 10313 publications receiving 145058 citations. The organization is also known as: Tallinn Technical University & Tallinna Tehnikaülikool.

Sliding wear behaviour of alumina/nickel nanocomposites processed by a conventional sintering route

Abstract: The wear resistance of Al 2 O 3 /2.5 vol.% Ni nanocomposites sintered by a conventional route was studied under ball-on-disk dry sliding conditions and compared with the same nanocomposites but consolidated by spark plasma sintering, together with alumina obtained by the same technique and by hot pressing. The results showed an improvement of about 0.5, 1 and 2 orders of magnitude, respectively. Thus, alumina/Ni nanocomposites processed by conventional route can compete, in cost and wear performance, with nanomaterials obtained by more sophisticated techniques.

Graphene-encapsulated aluminium oxide nanofibers as a novel type of nanofillers for electroconductive ceramics

Abstract: Graphene has attracted tremendous research interest in recent years owing to its exceptional properties. We report the remarkable ability to transform an insulating material, such as Al 2 O 3 , into a highly conductive material by filling the matrix with alumina nanofibers encapsulated by multi-layered graphene. The fibers of 7 nm in diameter were covered by graphene by catalyst-free one-step CVD process for the first time. Coupling between graphene layers and Al 2 O 3 nanofibers results in the development of a novel type of fillers for ceramics, which modify the intrinsic electrical properties of the insulating materials by addition of less than 1 wt.% of graphene into the ceramic matrix. We believe that the general strategy described in this study will open new avenues in developing of graphene–ceramic composites with enhanced electrical properties that can be then suitable for high-precision electrical discharge machining.

Altered volcanic ash as an indicator of marine environment, reflecting pH and sedimentation rate : Example from the ordovician kinnekulle bed of baltoscandia

Abstract: The composition of altered volcanic ash of the Late Ordovician Kinnekulle bed was studied in geological sections of the Baltic Paleobasin. The composition of altered ash varies with paleosea depth from northern Estonia to Lithuania. The ash bed in shallow shelf limestones contains an association of illite-smectite (I-S) and K-feldspar, with the K2O content ranging from 7.5 to 15.3%. The limestone in the transition zone between shallow- and deep-shelf environments contains I-S-dominated ash with K2O content from 6.0 to 7.5%. In the deep-shelf marlstone and shale, the volcanic ash bed consists of I-S and kaolinite with a K2O content ranging from 4.1 to 6.0%. This shows that authigenic silicates from volcanic ash were formed during the early sedimentary-diagenetic processes. The composition of the altered volcanic ash can be used as a paleoenvironmental indicator showing the pH of the seawater or porewater in sediments as well as the sedimentation rate.

Asymmetric synthesis of congested spiro-cyclopentaneoxindoles via an organocatalytic cascade reaction.

Abstract: Starting from simple alkylidene oxindoles and nitroketones, a highly stereoselective methodology was developed for the synthesis of spiro-cyclopentaneoxindoles with four consecutive stereogenic centers. Using an organocatalytic cascade of Michael and aldol reactions in the presence of a chiral thiourea catalyst products were obtained in moderate to high yields and excellent enantioselectivities. Nitro, ester, and hydroxyl groups were introduced to the spiro ring, which could be used to facilitate further functionalization of the products.