Peter Švančárek | Alexander Dubcek University of Trencin, Slovakia (original) (raw)
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Papers by Peter Švančárek
Journal of Inorganic Biochemistry, 2000
An overview of structurally characterized alpha-hydroxycarboxylatodioxo- and alpha-hydroxycarboxy... more An overview of structurally characterized alpha-hydroxycarboxylatodioxo- and alpha-hydroxycarboxylatooxoperoxovanadates(V) is presented and the geometric parameters of the V2O2 bridging core are discussed. The first case of a stereospecific formation of oxoperoxovanadates(V) is reported: The crystal structures of the isomeric compounds (NBu4)2[V2O2(O2)2(L-lact)2] x 2H2O and (NBu4)2[V2O2(O2)2(D-lact)(L-lact)] x 2H2O (lact = C3H4O3(2-), the anion of the lactic acid) differ mainly in the arrangement of the V2O2 core and in mutual orientation of the V=O bonds. The complexes with achiral ligands adopt the same structural type as the complexes formed from a racemic mixture of a chiral ligand, while the structure obtained using an enantiopure L,L-hydroxycarboxylate is different.
Monatshefte Fur Chemie, 2000
Oxo peroxo glycolato complexes of vanadium(V) (M 2[V2O2(O2)2(C2H2O3)2]ċnH2O (n=0, 1; M=NBu4+ (1)... more Oxo peroxo glycolato complexes of vanadium(V) (M 2[V2O2(O2)2(C2H2O3)2]ċnH2O (n=0, 1; M=NBu4+ (1), K+ (2), NH4+ (3), Cs+ (4), NPr4+ (5)) as well as (NBu4)2[V2O4(C2H2O3)2]ċ H2O (6) have been prepared and characterized by spectroscopic methods. X-Ray structure analysis of 1 revealed the presence of dinuclear [V2O2(O2)2(C2H2O3)2]2− anions with a (chemical structure) bridging core and six coordinated vanadium(V) atoms in a distorted pentagonal pyramidal array.
Acta Crystallographica Section C-crystal Structure Communications, 1998
Acta Crystallographica Section C-crystal Structure Communications, 2000
Monatshefte Fur Chemie, 2000
ABSTRACT Oxo peroxo glycolato complexes of vanadium(V) (M 2[V2O2(O2)2(C2H2O3)2]ċnH2O (n=0, 1; M=... more ABSTRACT Oxo peroxo glycolato complexes of vanadium(V) (M 2[V2O2(O2)2(C2H2O3)2]ċnH2O (n=0, 1; M=NBu4 + (1), K+ (2), NH4 + (3), Cs+ (4), NPr4 + (5)) as well as (NBu4)2[V2O4(C2H2O3)2]ċ H2O (6) have been prepared and characterized by spectroscopic methods. X-Ray structure analysis of 1 revealed the presence of dinuclear [V2O2(O2)2(C2H2O3)2]2− anions with a (chemical structure) bridging core and six coordinated vanadium(V) atoms in a distorted pentagonal pyramidal array.
Journal of The American Ceramic Society, 2007
This work verifies the applicability of two-stage sintering as a means of suppressing the final s... more This work verifies the applicability of two-stage sintering as a means of suppressing the final stage grain growth of submicrometer alumina. The first heating step should be short at a relatively high-temperature (1400°–1450°C) in order to close porosity without significant grain growth. The second step at temperatures around 1150°C facilitates further densification with limited grain growth. Fine-grained alumina with a relative density of 98.8% and a grain size of 0.9 μm was prepared by two-stage sintering. A standard sintering process resulted in ceramics with identical relative density and a grain size of 1.6 μm.
Journal of The European Ceramic Society, 2004
... Peter Svancarek a , b , Dusan Galusek a , Clair Calvert b , Fiona Loughran b , Andy Brown b ,... more ... Peter Svancarek a , b , Dusan Galusek a , Clair Calvert b , Fiona Loughran b , Andy Brown b , Rik Brydson Corresponding Author Contact ... polycrystalline aluminas hot pressed with a total of 5 wt.% of liquid phase-forming sintering additives: calcium oxide (CaO) and silicon oxide ...
Acta Materialia, 2006
Hot-pressed alumina samples, with 5 wt.% additions of CaO:SiO 2 possessing molar ratios ranging b... more Hot-pressed alumina samples, with 5 wt.% additions of CaO:SiO 2 possessing molar ratios ranging between 1:5 and 10:1 were studied by electron microscopy. Marked differences in microstructure (e.g. grain size, secondary crystalline phases and grain boundary film thickness) were observed, which depended on the composition of sintering additives. The compositions of glassy phases in triple pockets and in grain boundaries varied markedly depending on sintering additives, but also within individual specimens. High residual compressive stresses were measured in alumina grains of samples which contained low thermal expansion crystalline phases such as anorthite and grossite, while gehlenite-containing samples were correspondingly less stressed.
Journal of The European Ceramic Society, 2008
The response of Al 2 O 3 , Al 2 O 3 -SiC-(C) and Al 2 O 3 -C nanocomposites to grinding was inves... more The response of Al 2 O 3 , Al 2 O 3 -SiC-(C) and Al 2 O 3 -C nanocomposites to grinding was investigated in terms of changes of quality of ground surfaces and of the weight losses with time. The study used monolithic polycrystalline aluminas as references, and alumina-based composites with nanosized SiC and C inclusions and with alumina matrix grain size varying from submicrometer to approximately 4 m. The studied materials can be roughly divided into two groups. Materials with submicrometer alumina matrix grains (Group 1) wear predominantly by plastic deformation and grooving. Coarse-grained materials (Group 2) wear by mixed wear mechanism involving crack initiation and interlinking accompanied by grain pull-out, plastic deformation and grooving. The wear rate of composites increases with increasing volume fraction of SiC. The Group 2 materials wear much faster then those with submicron microstructure. In all cases (with one exception) the wear resistance of composites was higher than that of pure aluminas of comparable grain sizes used as reference materials.
Journal of The European Ceramic Society, 2007
Al 2 O 3 -SiC nanocomposites containing 3-8 vol.% SiC were prepared from fine ␣-alumina powder an... more Al 2 O 3 -SiC nanocomposites containing 3-8 vol.% SiC were prepared from fine ␣-alumina powder and a poly(allyl)carbosilane precursor of SiC by polymer infiltration of porous alumina matrix (composites IP), or by warm pressing of polymer-coated alumina powder (composites CW). The polymer was converted to SiC by careful heating of green specimens in inert atmosphere (Ar). The residual porosity was eliminated to less than 10% by pressureless sintering (PS) at temperatures between 1700 and 1850 • C. The post-sintering hot isostatic pressing (HIP) at 1700 • C eliminated the residual porosity to less than 1%, but also resulted in coarsening of the alumina matrix grains, and the inter-and intragranular SiC inclusions. The Vickers hardness of IP specimens sintered at T < 1850 • C increased by 1-10%, which is attributed to elimination of residual porosity. The hardness and indentation fracture toughness of specimens IP sintered at 1850 • C decreased after HIP by 6 and 15%, respectively. The HIP of CW composites increased their hardness and fracture toughness by approximately 10%. The maximum fracture toughness of 5.2 ± 0.2 MPa m 1/2 was measured for the materials containing 8 vol.% of SiC. A correlation was found between the fracture toughness, and the mean size and volume fraction of intergranular SiC inclusions in composites CW.
Journal of Inorganic Biochemistry, 2000
An overview of structurally characterized alpha-hydroxycarboxylatodioxo- and alpha-hydroxycarboxy... more An overview of structurally characterized alpha-hydroxycarboxylatodioxo- and alpha-hydroxycarboxylatooxoperoxovanadates(V) is presented and the geometric parameters of the V2O2 bridging core are discussed. The first case of a stereospecific formation of oxoperoxovanadates(V) is reported: The crystal structures of the isomeric compounds (NBu4)2[V2O2(O2)2(L-lact)2] x 2H2O and (NBu4)2[V2O2(O2)2(D-lact)(L-lact)] x 2H2O (lact = C3H4O3(2-), the anion of the lactic acid) differ mainly in the arrangement of the V2O2 core and in mutual orientation of the V=O bonds. The complexes with achiral ligands adopt the same structural type as the complexes formed from a racemic mixture of a chiral ligand, while the structure obtained using an enantiopure L,L-hydroxycarboxylate is different.
Monatshefte Fur Chemie, 2000
Oxo peroxo glycolato complexes of vanadium(V) (M 2[V2O2(O2)2(C2H2O3)2]ċnH2O (n=0, 1; M=NBu4+ (1)... more Oxo peroxo glycolato complexes of vanadium(V) (M 2[V2O2(O2)2(C2H2O3)2]ċnH2O (n=0, 1; M=NBu4+ (1), K+ (2), NH4+ (3), Cs+ (4), NPr4+ (5)) as well as (NBu4)2[V2O4(C2H2O3)2]ċ H2O (6) have been prepared and characterized by spectroscopic methods. X-Ray structure analysis of 1 revealed the presence of dinuclear [V2O2(O2)2(C2H2O3)2]2− anions with a (chemical structure) bridging core and six coordinated vanadium(V) atoms in a distorted pentagonal pyramidal array.
Acta Crystallographica Section C-crystal Structure Communications, 1998
Acta Crystallographica Section C-crystal Structure Communications, 2000
Monatshefte Fur Chemie, 2000
ABSTRACT Oxo peroxo glycolato complexes of vanadium(V) (M 2[V2O2(O2)2(C2H2O3)2]ċnH2O (n=0, 1; M=... more ABSTRACT Oxo peroxo glycolato complexes of vanadium(V) (M 2[V2O2(O2)2(C2H2O3)2]ċnH2O (n=0, 1; M=NBu4 + (1), K+ (2), NH4 + (3), Cs+ (4), NPr4 + (5)) as well as (NBu4)2[V2O4(C2H2O3)2]ċ H2O (6) have been prepared and characterized by spectroscopic methods. X-Ray structure analysis of 1 revealed the presence of dinuclear [V2O2(O2)2(C2H2O3)2]2− anions with a (chemical structure) bridging core and six coordinated vanadium(V) atoms in a distorted pentagonal pyramidal array.
Journal of The American Ceramic Society, 2007
This work verifies the applicability of two-stage sintering as a means of suppressing the final s... more This work verifies the applicability of two-stage sintering as a means of suppressing the final stage grain growth of submicrometer alumina. The first heating step should be short at a relatively high-temperature (1400°–1450°C) in order to close porosity without significant grain growth. The second step at temperatures around 1150°C facilitates further densification with limited grain growth. Fine-grained alumina with a relative density of 98.8% and a grain size of 0.9 μm was prepared by two-stage sintering. A standard sintering process resulted in ceramics with identical relative density and a grain size of 1.6 μm.
Journal of The European Ceramic Society, 2004
... Peter Svancarek a , b , Dusan Galusek a , Clair Calvert b , Fiona Loughran b , Andy Brown b ,... more ... Peter Svancarek a , b , Dusan Galusek a , Clair Calvert b , Fiona Loughran b , Andy Brown b , Rik Brydson Corresponding Author Contact ... polycrystalline aluminas hot pressed with a total of 5 wt.% of liquid phase-forming sintering additives: calcium oxide (CaO) and silicon oxide ...
Acta Materialia, 2006
Hot-pressed alumina samples, with 5 wt.% additions of CaO:SiO 2 possessing molar ratios ranging b... more Hot-pressed alumina samples, with 5 wt.% additions of CaO:SiO 2 possessing molar ratios ranging between 1:5 and 10:1 were studied by electron microscopy. Marked differences in microstructure (e.g. grain size, secondary crystalline phases and grain boundary film thickness) were observed, which depended on the composition of sintering additives. The compositions of glassy phases in triple pockets and in grain boundaries varied markedly depending on sintering additives, but also within individual specimens. High residual compressive stresses were measured in alumina grains of samples which contained low thermal expansion crystalline phases such as anorthite and grossite, while gehlenite-containing samples were correspondingly less stressed.
Journal of The European Ceramic Society, 2008
The response of Al 2 O 3 , Al 2 O 3 -SiC-(C) and Al 2 O 3 -C nanocomposites to grinding was inves... more The response of Al 2 O 3 , Al 2 O 3 -SiC-(C) and Al 2 O 3 -C nanocomposites to grinding was investigated in terms of changes of quality of ground surfaces and of the weight losses with time. The study used monolithic polycrystalline aluminas as references, and alumina-based composites with nanosized SiC and C inclusions and with alumina matrix grain size varying from submicrometer to approximately 4 m. The studied materials can be roughly divided into two groups. Materials with submicrometer alumina matrix grains (Group 1) wear predominantly by plastic deformation and grooving. Coarse-grained materials (Group 2) wear by mixed wear mechanism involving crack initiation and interlinking accompanied by grain pull-out, plastic deformation and grooving. The wear rate of composites increases with increasing volume fraction of SiC. The Group 2 materials wear much faster then those with submicron microstructure. In all cases (with one exception) the wear resistance of composites was higher than that of pure aluminas of comparable grain sizes used as reference materials.
Journal of The European Ceramic Society, 2007
Al 2 O 3 -SiC nanocomposites containing 3-8 vol.% SiC were prepared from fine ␣-alumina powder an... more Al 2 O 3 -SiC nanocomposites containing 3-8 vol.% SiC were prepared from fine ␣-alumina powder and a poly(allyl)carbosilane precursor of SiC by polymer infiltration of porous alumina matrix (composites IP), or by warm pressing of polymer-coated alumina powder (composites CW). The polymer was converted to SiC by careful heating of green specimens in inert atmosphere (Ar). The residual porosity was eliminated to less than 10% by pressureless sintering (PS) at temperatures between 1700 and 1850 • C. The post-sintering hot isostatic pressing (HIP) at 1700 • C eliminated the residual porosity to less than 1%, but also resulted in coarsening of the alumina matrix grains, and the inter-and intragranular SiC inclusions. The Vickers hardness of IP specimens sintered at T < 1850 • C increased by 1-10%, which is attributed to elimination of residual porosity. The hardness and indentation fracture toughness of specimens IP sintered at 1850 • C decreased after HIP by 6 and 15%, respectively. The HIP of CW composites increased their hardness and fracture toughness by approximately 10%. The maximum fracture toughness of 5.2 ± 0.2 MPa m 1/2 was measured for the materials containing 8 vol.% of SiC. A correlation was found between the fracture toughness, and the mean size and volume fraction of intergranular SiC inclusions in composites CW.