Negative thermal expansion （NTE） ZrW2O8 powders were prepared by step-by-step solid-state reaction with ZrO2 and WO3 powders. The coefficient of thermal expansion （CTE） of the as-prepared ZrW208 was around -5.08&#...Negative thermal expansion （NTE） ZrW2O8 powders were prepared by step-by-step solid-state reaction with ZrO2 and WO3 powders. The coefficient of thermal expansion （CTE） of the as-prepared ZrW208 was around -5.08×10^-6 K^-1 at 20-700℃. Different amounts of ZrW208 powders were added in BTDA-ODA polyamic acid to form polyimide/ZrW2O8 composites （PI/ZrW2O8）. With the increment of ZrW2O8, experimental results show that ZrW2O8 powders can significantly enhance the thermal stability of the composites, and reduce the thermal expansion. A 50 wt pct ZrW2O8 addition can give rise to a 31% reduction of CTE. It is suggested that the PI/ZrW2O8 composites have potential applications in high performance microelectronic devices.展开更多
A S 2O 2- 8/ZrO 2 Al 2O 3 type solid superacid catalyst was prepared from ZrOCl 2·8H 2O, AlCl 3· 6H 2O and (NH 4) 2S 2O 8 by coprecipitation, maceration and calcination processes. Their crystal structures an...A S 2O 2- 8/ZrO 2 Al 2O 3 type solid superacid catalyst was prepared from ZrOCl 2·8H 2O, AlCl 3· 6H 2O and (NH 4) 2S 2O 8 by coprecipitation, maceration and calcination processes. Their crystal structures and acidities were determined by XRD and Hammett method, respectively. The activity of the catalyst was studied as function of Al 2O 3 content, calcination temperature and time in the esterification of acetic acid with butanol, and a conversion of 96 5% was obtained. The catalyst gave also higher yields in syntheses of ketals and acetals: cyclohexanone ethylene ketal(86 2%), acetophenone ethylene ketal(78 5%), acetylacetic ester ketal(88 5%), benzaldehyde glycol acetal(76 3%). The chemical structures of the products were confirmed by IR spectra.展开更多
Negative thermal expansion (NTE) material ZrW2O8 powders were synthesized using co-precipitation route. The precursor of ZrW2O8 was studied by Thermogravimetric and differential scanning calorimetry (TG-DSC). The stru...Negative thermal expansion (NTE) material ZrW2O8 powders were synthesized using co-precipitation route. The precursor of ZrW2O8 was studied by Thermogravimetric and differential scanning calorimetry (TG-DSC). The structure and morphology of the resulting powders were characterized by Powder X-ray diffraction (XRD) and Scanning electron microscopy (SEM), respectively. The results showed that the samples were single phase of α- ZrW2O8 with regular shape. High temperature X-ray diffraction measurement indicated that the thermal expansion coefficient of ZrW2O8 was - 10.35 ×10-6 K-1 in the temperature range from room temperature to 150 ℃, - 3.08 × 10-6 K-1 from 200 ℃ to 600 ℃ and the average value was - 5.38 ×10-6 K-1. At the same time, polyethylene glycol (PEG) was used as dispersant to primary control the size of ZrW2O8.展开更多
基金supported by the National NaturalScience Foundation of China(No.50372027)the Natural Science Foundation of Jiangsu Province(No.BK2003404)
文摘Negative thermal expansion （NTE） ZrW2O8 powders were prepared by step-by-step solid-state reaction with ZrO2 and WO3 powders. The coefficient of thermal expansion （CTE） of the as-prepared ZrW208 was around -5.08×10^-6 K^-1 at 20-700℃. Different amounts of ZrW208 powders were added in BTDA-ODA polyamic acid to form polyimide/ZrW2O8 composites （PI/ZrW2O8）. With the increment of ZrW2O8, experimental results show that ZrW2O8 powders can significantly enhance the thermal stability of the composites, and reduce the thermal expansion. A 50 wt pct ZrW2O8 addition can give rise to a 31% reduction of CTE. It is suggested that the PI/ZrW2O8 composites have potential applications in high performance microelectronic devices.
文摘A S 2O 2- 8/ZrO 2 Al 2O 3 type solid superacid catalyst was prepared from ZrOCl 2·8H 2O, AlCl 3· 6H 2O and (NH 4) 2S 2O 8 by coprecipitation, maceration and calcination processes. Their crystal structures and acidities were determined by XRD and Hammett method, respectively. The activity of the catalyst was studied as function of Al 2O 3 content, calcination temperature and time in the esterification of acetic acid with butanol, and a conversion of 96 5% was obtained. The catalyst gave also higher yields in syntheses of ketals and acetals: cyclohexanone ethylene ketal(86 2%), acetophenone ethylene ketal(78 5%), acetylacetic ester ketal(88 5%), benzaldehyde glycol acetal(76 3%). The chemical structures of the products were confirmed by IR spectra.
文摘Negative thermal expansion (NTE) material ZrW2O8 powders were synthesized using co-precipitation route. The precursor of ZrW2O8 was studied by Thermogravimetric and differential scanning calorimetry (TG-DSC). The structure and morphology of the resulting powders were characterized by Powder X-ray diffraction (XRD) and Scanning electron microscopy (SEM), respectively. The results showed that the samples were single phase of α- ZrW2O8 with regular shape. High temperature X-ray diffraction measurement indicated that the thermal expansion coefficient of ZrW2O8 was - 10.35 ×10-6 K-1 in the temperature range from room temperature to 150 ℃, - 3.08 × 10-6 K-1 from 200 ℃ to 600 ℃ and the average value was - 5.38 ×10-6 K-1. At the same time, polyethylene glycol (PEG) was used as dispersant to primary control the size of ZrW2O8.
