The elegant 2D multiquantum (MQ) MAS NMR has been applied to investigate the coordination of Al atoms in SAPO-34. The results show that the effects of the template and/or water on the coordination of Al atoms are sig...The elegant 2D multiquantum (MQ) MAS NMR has been applied to investigate the coordination of Al atoms in SAPO-34. The results show that the effects of the template and/or water on the coordination of Al atoms are significant, which lead to the formation of various Al species. Up to four kinds of Al species are distinctly resolved.展开更多
^27Al,^29Si MAS NMR studies of kaolinite and its thermal transformation products show that in the kaolinite-mullite reaction series there is an extensive segregation of Al2O3 and SiO2 and the reaction of Al2O3 with Si...^27Al,^29Si MAS NMR studies of kaolinite and its thermal transformation products show that in the kaolinite-mullite reaction series there is an extensive segregation of Al2O3 and SiO2 and the reaction of Al2O3 with SiO2 to form mullite is the main path of mullite formation.At about 850°C,the peak intensity of Al(V) reaches its maximum and with the further rise of temperature the Al(V)signal completely disappears.At about 950°C,γ-Al2O3 accounts for about 71%of the material phases containing Al atoms.In the series there is no obvious presence of Al-Si spinel.The ^27Al and ^29Si MAS NMR spectra show that there is an obvious difference between the temperature points for Al-O2(OH)4 octahedral sheet collapsing and Si-O4 tetrahedral sheet breaking down.展开更多
The IR spectrum and 11B and 27Al MAS NMR spectra of Al18B4O33 are presented and discussed in relation to the possible existence of boron atoms substituting for aluminum atoms. The IR spectrum shows that the strong vi...The IR spectrum and 11B and 27Al MAS NMR spectra of Al18B4O33 are presented and discussed in relation to the possible existence of boron atoms substituting for aluminum atoms. The IR spectrum shows that the strong vibrations of the BO3 groups are present in the 1 500-1 200 cm-1 region, and very weak bands of BO4 units are present in the region from 1 000 to 1 100 cm-1. 11B MAS NMR spectrum indicates that the strong signal for BO3 units appears in the region from δ+5 to δ+20, and the very weak signal for BO4 units is at about δ- 1, while 27Al MAS NMR spectrum shows five peaks at about δ+62, +42. 1, +14, -4. 7 and -6. 4, originating from AlO4, AlO4, AlO5, AlO6 and AlO6, respectively. These results reveal that there are minor BO4 units in Al18B4O33, indicating that a small amount of B atoms substitute for Al atoms in the 4-fold coordination.展开更多
The coordination structure of aluminum in magnesium aluminum hydroxide was studied by 27Al NMR. The result showed that tetrahedral aluminum (AlIV) existed in magnesium aluminum hydroxide, and the contents of AlIV inc...The coordination structure of aluminum in magnesium aluminum hydroxide was studied by 27Al NMR. The result showed that tetrahedral aluminum (AlIV) existed in magnesium aluminum hydroxide, and the contents of AlIV increased with the increase of the ratio of Al/Mg and with the peptizing temperature. AlIV originated from the so-called Al13 polymer with the structure of one Al tetrahedron surrounded by twelve Al octahedrons.展开更多
The microstructural study was conducted on cement and cement-slag pastes immersed in different concentrations of Mg（NO3）2 solutions utilizing ^29Si, ^27Al NMR spectroscopy and XRD techniques. The results show that t...The microstructural study was conducted on cement and cement-slag pastes immersed in different concentrations of Mg（NO3）2 solutions utilizing ^29Si, ^27Al NMR spectroscopy and XRD techniques. The results show that the hydration of both the cement and cement-slag pastes is delayed when the pastes are cured in Mg（NO3）2 solutions as compared to the pastes cured in water. Moreover, Mg^2＋ ions also exhibit an decalcifying and dealuminizing effect on the C-A-S-H in cement and cement-slag pastes, and thereby decrease Ca/Si and Al[4]/Si ratios of the C-A-S-H. The dealuminization of C-A-S-H is mitigated for cement-slag paste as compared to pure cement paste. The depolymerized calcium and aluminum ions from C-A-S-H gel mainly enter the pore solution to maintain the pH value and form Al^[6] in TAH, respectively. On the other hand, Mg^2＋ ions exert an impact on the intra-transition between Al^[6] species, from AFm and hydrogarnet to hydrotalcite-like phase. NO3^-ions are interstratified in the layered Mg-Al structure and formed nitrated hydrotalcite-like phase（Mg1-xAlx（OH）2（NO3）x·nH2O）. Results from both ^27Al NMR and XRD data show that ettringite seems not to react with Mg^2＋ ions.展开更多
Coalification temperatures are often considered to be approximately 100-170 ℃ for bituminous coal and 170-275 ℃ for anthracite. However, our micropetrographic observations, solid state ^27Al magic-angle spinning nuc...Coalification temperatures are often considered to be approximately 100-170 ℃ for bituminous coal and 170-275 ℃ for anthracite. However, our micropetrographic observations, solid state ^27Al magic-angle spinning nuclear magnetic resonance measurements, interpretation of δ^13C values for whewellite in pelosiderite concretions from Carboniferous sediments, and assessment of whewellite thermal stability show that coalification temperatures can be significantly lower. Also the temperatures of coal alteration may be substantially lower than is stated. Ordinarily, high- temperature alteration is reported, but microthermometric measurements of fluids temperatures and micropetrographic observations show that the coal alteration can take place at low temperatures. For this reason, coals from the Kladno- Rakovnik Basin, part of Late Paleozoic continental basins of the Czech Republic, were analyzed. Regarding coalification, micropetrographic characterizations of unaltered coals, the presence of thermally unstable Al complexes in the coal organic mass documented using ^27Al MAS NMR method, and proven occurrence of whewellite in pelosiderite concretions suggest a lower coalification temperature, max. -70 ℃. Regarding coal alteration, micropetrographic observations revealed （a） the weaker intensity of fluorescence of liptinite, （b） mylonitic structures and microbreccia with carbonate fluid penetration, and （c） high oxygen content in coals （37-38 wt.%）. These phenomena are typical for thermal and oxidative alteration of coal. As the temperature of carbonate fluids inferred from fluid inclusion analysis was evaluated as -100-113 ℃, the temperature of coal alteration was suggested as -113℃; the alteration was caused by hot hydrothermal fluids.展开更多
基金We are grateful to the support of the National Natural Science Foundation of China and the Ministry of Science and Technology of China. We appreciate Dr. R. Fu (NHMFL Tallahassee) for his kind help regarding the MQ MAS NMR experiments.
文摘The elegant 2D multiquantum (MQ) MAS NMR has been applied to investigate the coordination of Al atoms in SAPO-34. The results show that the effects of the template and/or water on the coordination of Al atoms are significant, which lead to the formation of various Al species. Up to four kinds of Al species are distinctly resolved.
文摘^27Al,^29Si MAS NMR studies of kaolinite and its thermal transformation products show that in the kaolinite-mullite reaction series there is an extensive segregation of Al2O3 and SiO2 and the reaction of Al2O3 with SiO2 to form mullite is the main path of mullite formation.At about 850°C,the peak intensity of Al(V) reaches its maximum and with the further rise of temperature the Al(V)signal completely disappears.At about 950°C,γ-Al2O3 accounts for about 71%of the material phases containing Al atoms.In the series there is no obvious presence of Al-Si spinel.The ^27Al and ^29Si MAS NMR spectra show that there is an obvious difference between the temperature points for Al-O2(OH)4 octahedral sheet collapsing and Si-O4 tetrahedral sheet breaking down.
基金Supported by the National Natural Science Foundation of China.
文摘The IR spectrum and 11B and 27Al MAS NMR spectra of Al18B4O33 are presented and discussed in relation to the possible existence of boron atoms substituting for aluminum atoms. The IR spectrum shows that the strong vibrations of the BO3 groups are present in the 1 500-1 200 cm-1 region, and very weak bands of BO4 units are present in the region from 1 000 to 1 100 cm-1. 11B MAS NMR spectrum indicates that the strong signal for BO3 units appears in the region from δ+5 to δ+20, and the very weak signal for BO4 units is at about δ- 1, while 27Al MAS NMR spectrum shows five peaks at about δ+62, +42. 1, +14, -4. 7 and -6. 4, originating from AlO4, AlO4, AlO5, AlO6 and AlO6, respectively. These results reveal that there are minor BO4 units in Al18B4O33, indicating that a small amount of B atoms substitute for Al atoms in the 4-fold coordination.
基金This research is supported by NNSFC No:20273041.
文摘The coordination structure of aluminum in magnesium aluminum hydroxide was studied by 27Al NMR. The result showed that tetrahedral aluminum (AlIV) existed in magnesium aluminum hydroxide, and the contents of AlIV increased with the increase of the ratio of Al/Mg and with the peptizing temperature. AlIV originated from the so-called Al13 polymer with the structure of one Al tetrahedron surrounded by twelve Al octahedrons.
基金Funded by National Natural Science Foundation of China(Nos.51778513,51402003,51578004)China Ministry of Science and Technology(No.2015CB655101)
文摘The microstructural study was conducted on cement and cement-slag pastes immersed in different concentrations of Mg（NO3）2 solutions utilizing ^29Si, ^27Al NMR spectroscopy and XRD techniques. The results show that the hydration of both the cement and cement-slag pastes is delayed when the pastes are cured in Mg（NO3）2 solutions as compared to the pastes cured in water. Moreover, Mg^2＋ ions also exhibit an decalcifying and dealuminizing effect on the C-A-S-H in cement and cement-slag pastes, and thereby decrease Ca/Si and Al[4]/Si ratios of the C-A-S-H. The dealuminization of C-A-S-H is mitigated for cement-slag paste as compared to pure cement paste. The depolymerized calcium and aluminum ions from C-A-S-H gel mainly enter the pore solution to maintain the pH value and form Al^[6] in TAH, respectively. On the other hand, Mg^2＋ ions exert an impact on the intra-transition between Al^[6] species, from AFm and hydrogarnet to hydrotalcite-like phase. NO3^-ions are interstratified in the layered Mg-Al structure and formed nitrated hydrotalcite-like phase（Mg1-xAlx（OH）2（NO3）x·nH2O）. Results from both ^27Al NMR and XRD data show that ettringite seems not to react with Mg^2＋ ions.
文摘Coalification temperatures are often considered to be approximately 100-170 ℃ for bituminous coal and 170-275 ℃ for anthracite. However, our micropetrographic observations, solid state ^27Al magic-angle spinning nuclear magnetic resonance measurements, interpretation of δ^13C values for whewellite in pelosiderite concretions from Carboniferous sediments, and assessment of whewellite thermal stability show that coalification temperatures can be significantly lower. Also the temperatures of coal alteration may be substantially lower than is stated. Ordinarily, high- temperature alteration is reported, but microthermometric measurements of fluids temperatures and micropetrographic observations show that the coal alteration can take place at low temperatures. For this reason, coals from the Kladno- Rakovnik Basin, part of Late Paleozoic continental basins of the Czech Republic, were analyzed. Regarding coalification, micropetrographic characterizations of unaltered coals, the presence of thermally unstable Al complexes in the coal organic mass documented using ^27Al MAS NMR method, and proven occurrence of whewellite in pelosiderite concretions suggest a lower coalification temperature, max. -70 ℃. Regarding coal alteration, micropetrographic observations revealed （a） the weaker intensity of fluorescence of liptinite, （b） mylonitic structures and microbreccia with carbonate fluid penetration, and （c） high oxygen content in coals （37-38 wt.%）. These phenomena are typical for thermal and oxidative alteration of coal. As the temperature of carbonate fluids inferred from fluid inclusion analysis was evaluated as -100-113 ℃, the temperature of coal alteration was suggested as -113℃; the alteration was caused by hot hydrothermal fluids.
