Influence of Na2O Content and Ms (SiO2/Na2O) of Alkaline Activator on Workability and Setting of Alkali-Activated Slag Paste

The performance of alkali-activated slag (AAS) paste using activators of strong alkali components is affected by the type, composition, and dosage of the alkaline activators. Promoting the reaction of ground granulated blast furnace slag (GGBFS) by alkaline activators can produce high-strength AAS concrete, but the workability might be drastically reduced. This study is aimed to experimentally investigate the heat release, workability, and setting time of AAS pastes and the compressive strength of AAS mortars considering the Na2O content and the ratio of Na2O to SiO2 (Ms) of binary alkaline activators blended with sodium hydroxide and sodium silicate. The test results indicated that the AAS mortars exhibited a high strength of 25 MPa at 24 h, even at ambient temperature, even though the pastes with an Na2O content of ≥6% and an Ms of ≥1.0 exhibited an abrupt decrease in flowability and rapid setting.

Gemischte Erdalkalimetall-Trielide AIIM1IIIx M2 III2– x (AII = Ca, Sr, Ba; MIII = Al, Ga, In). Strukturchemische und bindungstheoretische Untersuchungen / Mixed Alkaline Earth Trielides AIIM1IIIx M2III2−x (AII = Ca, Sr, Ba; MIII=Al, Ga, In). A Structural and Theoretical Study

The binary alkaline earth trielides of the composition AIIMIII 2 exhibit a puzzling variety of structure types ranging from electron precise Zintl compounds like CaIn2 and KHg2 (both with networks of four-bonded M− entities) and the AlB2 structure type (with graphite analogue M sheets) to the cubic Laves phases e. g. of CaAl2. The examination of the phase stabilities of mixed compounds AM1IIIx M2III2−x of two trielides allows to separate the stability ranges in a structure map by taking the electronegativity differences of MIII and AII (Δ EN) and the radius ratios (RR = rM/rA) into account: The CaIn2-type is stable at comparatively large RR, for example over the whole range CaGa2 -CaIn2 and even up to CaAl0.6Ga1.4 and CaAl1.2In0.8, and in SrIn2, together with a limited substitution of In by Al or Ga. The KHg2-type is observed in a region of lower RR: In BaIn2, a substitution of In by 50% Al and 30% Ga is possible without a general structure change, in SrAl2 this holds for a content of up to 50% In. At high Δ EN and low RR values (e. g. Sr/Ba-Ga), the ideal AlB2 structure type exhibits a distinct stability range; only for small RR around CaAl2 the MgCu2-type is stable. FP-LAPWband structure calculations of the binary trielides allow to explain the structural changes qualitatively. In the case of the electron precise phases forming the CaIn2, KHg2 or AlB2 structure type, details of the bonding situation (such as M-M distances) as well as differences to other isoelectronic compounds can be rationalized taking the incomplete charge transfer from the alkaline earth towards the triel elements into account. This causes a partial depopulation of some of the bonding and a population of predominantly antibonding states.

Neue Erdalkalimetall-reiche binäre Indide: Ca2In, Sr28In11 und Sr5In3 / New Alkaline Earth Rich Binary Indides: Ca2In, Sr28In11 und Sr5In3

The new binary alkaline earth rich indides Ca2In (orthorhombic, space group Pnma, a =727.5(2), b = 537.1(2), c = 999.0(3) pm, Z = 4, R1 = 0.0252, Co2Si structure type) and Sr28In11 (orthorhombic, space group Imm2, a=582.6(3), b=6687.8(9), c=823.5(6) pm, Z =2, R1=0.0571, Ca28Ga11 structure type) have been synthesized from stoichiometric melts of the elements. Both crystal structures exhibit isolated In atoms coordinated by seven to ten alkaline earth atoms. In the crystal structure of Sr5In3 (tetragonal, space group I4/mcm, a = 874.4(3), c = 1642.9(8) pm, Z = 4, R1 = 0.0347, Cr5B3 structure type) isolated In atoms coexist with In2 dumbbells exhibiting short In-In contacts (284.4 pm). The electronic structures of the less elaborate compounds Ca2In and Sr5In3 are discussed in comparison with those of the closely related, nominally electron precise Zintl compounds Ca2Sn and Sr5Sn3.