Si Conversion Research Articles

Hierarchical zinc-copper oxide hollow microspheres as active Rochow reaction catalysts: The formation and effect of charge transferable interfaces

In this work, we report the preparation of nearly monodispersed and hierarchical CuxZnOy (6<x<100) hollow microspheres as catalysts for the Rochow reaction. The composites were synthesized by a facile one-pot and template-free hydrothermal method, which showed intergrowth and coexistence of the two components throughout the whole structure. The high-resolution transmission electron microscope (HRTEM) analysis confirmed the formation of intimate hetero-interfaces between CuO and ZnO in these composites. X-ray photoelectron spectroscopy (XPS), H2-temperature programmed reduction (H2-TPR) and Raman spectra results revealed the presence of a strong interaction between the two oxide components. The inclusion of Zn into the system increased electron density of Cu cores, leaving substantial holes on the surface of ZnO, thus forming the charge transferable channels between the two phases. These well-defined CuxZnOy samples were further utilized as model catalysts to investigate the relationship between structure modulation and catalytic performance. It was observed that the catalytic property can be easily tuned upon a systematic composition variation. Among CuO and various CuxZnOy samples, Cu10ZnOy exhibited the highest dimethyldichlorosilane (M2) selectivity and Si conversion in the Rochow reaction, mainly due to the formation of effective charge transfer interfaces as a result of intergrowth and coexistence effect.

Promoting effect of In2O3 on CuO for the Rochow reaction: The formation of P–N junctions at the hetero-interfaces

Here we report the first work on the synthesis of a series of xIn-CuO model catalysts for the Rochow reaction with formed P–N junctions at interfaces and with different In/Cu molar ratios. These composites were prepared by a one-pot hydrothermal method using metal nitrate salts and K2CO3 as the precursors and precipitant, respectively. Scanning electron microscopy and transmission electron microscopy characterization revealed the formation of the P–N junctions at the hetero-interfaces between CuO and In2O3, and X-ray photoelectron spectroscopy and H2 temperature-programmed reduction demonstrated a strong interaction between the CuO and In2O3 phases. The addition of In2O3 increased the electron density in the Cu nucleus, causing Cu2+ and In3+ to become less and more positively charged, respectively. When used for the Rochow reaction, the catalyst 2In–CuO (2wt.% In on CuO) exhibited a significantly higher Si conversion and dimethyldichlorosilane ((CH3)2SiCl2, M2) selectivity than CuO, which is attributed to the formation of P–N junctions that can facilitate the charge transfer. In addition, the detailed characterizations of the fresh and spent contact masses indicated that the Rochow reaction occurred on the Si surface and probably in the areas between ultrathin two-dimensional Cu–Si species and Cu doping deposits. In2O3 species promote the outward spreading of Cu∗ (intermediate species) and improve the Cu∗ diffusion rate at the reactive interfaces. This work not only deepens the fundamental understanding of the Rochow reaction, but also provides a new approach for the design of more efficient Cu-based catalysts by adding promoters such as In2O3 and by engineering the interfaces.

One-dimensional Cu-based catalysts with layered Cu–Cu2O–CuO walls for the Rochow reaction

A series of copper catalysts with a core–shell or tubular structure containing various contents of Cu, Cu2O, and CuO were prepared via controlled oxidation of Cu nanowires (NWs) and used in the synthesis of dimethyldichlorosilane (M2) via the Rochow reaction. The Cu NWs were prepared from copper (II) nitrate using a solution-based reduction method. The samples were characterized by X-ray diffraction, thermogravimetric analysis, temperature-programmed reduction, X-ray photoelectron spectroscopy, transmission electron microscopy, and scanning electron microscopy. It was found that the morphology and composition of the catalysts could be tailored by varying the oxidation temperature and time. During the gradual oxidation of Cu NWs, the oxidation reaction initiated on the outer surface and gradually developed into the bulk of the NWs, leading to the formation of catalysts with various structures and layered compositions, e.g., Cu NWs with surface Cu2O, ternary Cu–Cu2O–CuO core–shell NWs, binary Cu2O–CuO nanotubes (NTs), and single CuO NTs. Among these catalysts, ternary Cu–Cu2O–CuO core–shell NWs exhibited superior M2 selectivity and Si conversion in the Rochow reaction. The enhanced catalytic performance was mainly attributed to improved mass and heat transfer resulting from the peculiar heterostructure and the synergistic effect among layered components. Our work indicated that the catalytic property of Cu-based nanoparticles can be improved by carefully controlling their structures and compositions.

Novel leaflike Cu–O–Sn nanosheets as highly efficient catalysts for the Rochow reaction

In this work, we report the preparation of novel leaflike Cu–O–Sn nanosheet catalysts for the Rochow reaction. The catalysts were synthesized via a facile hydrothermal approach using CuSO4·3H2O and SnCl4·5H2O as the precursors, but without the use of any template. When used for the Rochow reaction to synthesize dimethyldichlorosilane (M2), the as-prepared 0.1wt.% Cu–O–Sn nanosheet exhibited a much higher M2 selectivity (93.3%), Si conversion (68.4%), and stability than the catalysts of CuO or SnO2 alone, the Cu–O–Sn catalysts with different compositions, and the commercial catalysts. The samples were characterized by X-ray diffraction, transmission electron microscopy, scanning electron microscopy, atomic force microscopy, Raman spectroscopy, X-ray photoelectron spectroscopy, and temperature-programmed reduction analyses. Surface segregation of Sn was observed, and the quantities of chemisorbed oxygen species and cation vacancies were well correlated with the activity of the catalysts. It is concluded that small crystal size, high chemisorbed oxygen species concentration, more cation vacancies, and strong interaction between Cu and Sn are responsible for the excellent catalytic performance of 0.1wt.% Cu–O–Sn catalyst.

Nitridation of Silicon Powders Catalyzed by Cobalt Nanoparticles

The effect of Co nanoparticles (NPs) on the nitridation of silicon (Si) was studied. Co NPs were deposited homogeneously on the surfaces of Si powders using an in situ reduction method using NaBH4 as a reducing reagent. Si powders impregnated with 0.5–2.0 wt% Co NPs were nitrided in 1200°C–1400°C for 2 h. The resultant silicon nitride powders were characterized by XRD, FE‐SEM, TEM, and EDS. The results showed that: (1) Co NPs significantly decreased the Si nitridation temperature, and the nitridation could be completed at 1300°C upon using 2 wt% Co NPs as catalysts. For comparison, the Si conversion could not be completed even at a temperature as high as 1400°C in the case without using a catalyst; (2) many Si3N4 whiskers with 80–320 nm in diameter and tens micrometers in length were generated and uniformly distributed in the final products. They were single‐crystalline α‐Si3N4 grown along the [101] direction. The enhanced nitridation in the case of using Co NPs as a catalyst was attributed two following factors, the increased bond length and weakened bond strength in N2 caused by the electron donation from the Co atoms to the N atoms.

Raman Characterization of Poly-Si Channel Materials for 3D Flash Memory Device Applications

For poly Si channel applications used in three-dimensional (3D) flash memory devices, amorphous Si films deposited on thin SiO2 on Si wafers were converted to poly Si by solid-phase crystallization in the temperature range of 600 ~ 1050oC under Ar, N2 and forming gas (N2 96% + H2 4%) ambients. Annealing temperature and process ambient gas dependence of the poly conversion process was studied. The degree of amorphous to poly conversion and grain size distribution of poly Si were investigated using Raman spectroscopy. Six different Raman excitation wavelengths, with different probing depths, were tested to observe the uniformity of amorphous to poly Si conversion in the depth direction. No significant excitation wavelength dependence of the Raman spectra was observed from the converted poly Si, implying fairy homogeneous conversion throughout the thickness of film.

Solvothermal synthesis of copper (I) chloride microcrystals with different morphologies as copper-based catalysts for dimethyldichlorosilane synthesis

CuCl microcrystals with different morphologies such as tetrahedra, etched tetrahedra, tripod dendrites, and tetrapods were synthesized using CuCl2⋅2H2O as the copper precursor in the mixed solvent of acetylacetone and ethylene glycol. The samples were characterized with X-ray diffraction, scanning electron microscopy, infrared spectroscopy, and transmission electron microscope. Cu(C5H7O2)2 was identified as the key intermediate, and the morphology and structure of the CuCl microcrystals were highly dependent on the reaction time and temperature, as well as the volume of the solvents. The catalytic properties of these CuCl microcrystals were explored in the dimethyldichlorosilane synthesis via Rochow reaction. Compared to the commercial CuCl microparticles with irregular morphology and dense internal structure, the obtained CuCl microcrystals possessed regular morphology and different exposed crystal planes and showed much higher dimethyldichlorosilane selectivity and Si conversion via the Rochow reaction because of the enhanced formation of active CuxSi phase and gas transportation within the dendritic structure, demonstrating the significance of regular morphology of the copper-based catalysts in catalytic organosilane synthesis.

Partially Reduced CuO Nanoparticles as Multicomponent Cu-Based Catalysts for the Rochow Reaction

We report the application of partially reduced CuO nanoparticles as Cu-based catalysts for dimethyldichlorosilane (M2) synthesis via the Rochow reaction. The CuO nanoparticles (50–100 nm) were synthesized by a simple precipitation method and partially reduced in a H2/N2 mixture gas to obtain the Cu-based catalyst containing different Cu species of CuO, Cu2O, and Cu. It was found that the composition of the samples could be tailored by varying the volume ratio of H2/N2 at the given reduction temperature and time. Compared to the synthesized CuO and Cu nanoparticles, as well as the commercial CuO microparticles, these multicomponent Cu-based catalysts, particularly for the CuO–Cu2O–Cu catalyst, showed much higher M2 selectivity and Si conversion in the Rochow reaction. The enhanced catalytic performance is attributed to the smaller particle size and the synergistic effect among the different components. The work would help to develop novel ternary Cu-based catalysts for organosilane synthesis.

Facile Solvothermal Synthesis of Porous Cubic Cu Microparticles as Copper Catalysts for Rochow Reaction

Porous cubic Cu microparticles were synthesized by a facile solvothermal method using Cu(CH(3)COO)(2)·H(2)O as the Cu precursor and NaOH in a solution containing ethanol, ethylene glycol, and water. The synthesis conditions were investigated and a growth process of porous cubic Cu microparticles was proposed. The catalytic properties of the porous Cu microparticles as model copper catalysts for Rochow reaction were explored. The samples were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, thermogravimetric analysis, temperature-programmed reduction, and nitrogen adsorption. It was found that the morphology and structure of the porous cubic Cu microparticles are highly dependent on the reaction time and temperature as well as on the amount of reactants added. Compared to the commercial Cu microparticles with irregular morphology and dense internal structure, porous cubic Cu microparticles show much higher dimethyldichlorosilane selectivity and Si conversion via Rochow reaction, which are attributed to the enhanced formation of active Cu(x)Si phase and gas transportation in the presence of the pore system within microparticles, demonstrating the significance of the pore structure of the copper catalysts in catalytic reactions of organosilane synthesis.

Flower-like CuO microspheres with enhanced catalytic performance for dimethyldichlorosilane synthesis

Flower-like CuO microspheres synthesized by a facile hydrothermal method were found to be an effective catalyst for the Rochow reaction with a higher dimethyldichlorosilane selectivity and Si conversion because of the enhanced formation of an active CuxSi phase and mass transport.

Using Apolipoprotein B to Manage Dyslipidemic Patients: Time for a Change?

Low-density lipoprotein cholesterol (LDL-C) concentration has been established as an independent risk factor for the development of atherosclerosis; consequently, multiple practice guidelines recognize LDL-C as the primary target of therapy.1,2 For decades, considerable effort has been committed to educating physicians and the general public about the importance of lowering LDL-C levels. Despite the extensive data relating LDL-C to atherosclerosis, some have suggested that focusing only on LDL-C may not be an optimal strategy.3 Several limitations exist for an approach that focuses only on LDL-C: (1) evidence is increasing that triglyceride-rich lipoproteins, including very low-density lipoproteins (VLDL) and intermediate-density lipoproteins (IDL) (Figure 1)4 are also atherogenic5,6; and (2) a substantial percentage of patients with atherosclerotic vascular disease have LDL-C in the optimal range.7 Furthermore, many patients who receive treatment and achieve recommended LDL-C goals even lower than 70 mg/dL (to convert to mmol/L, multiply by 0.0259) still develop the complications of atherosclerotic vascular disease, which is referred to as residual risk.8 One explanation for these discrepancies is the mismatch that has been described in many patients between the LDL-C concentration reported on a basic lipid panel and the number of atherogenic lipid particles, which is often expressed as low-density lipoprotein (LDL) particle number or the number of apolipoprotein B (apo B)–containing lipoproteins.9 The reason for this mismatch is that LDL particles are extremely heterogeneous with respect to the amount of cholesterol contained in the LDL particle core.10 Patients with a predominance of cholesterol-depleted LDL particles (also called small dense LDL-C) may have a low LDL “cholesterol” concentration as reported on the standard lipid panel but still have a large number of circulating atherogenic LDL particles.11 For example, 2 patients with the same LDL-C concentration on a basic lipid panel may have markedly different LDL particle numbers and different cardiovascular risk (Figure 2).12 Extrapolating information concerning the number of atherogenic LDL particles from the LDL-C content is an unreliable strategy. FIGURE 1. Lipoprotein subclasses and apolipoprotein (apo) B–containing lipoproteins. HDL = high-density lipoprotein; iDL = intermediate-density lipoprotein; LDL = low-density lipoprotein; VLDL = very low-density lipoprotein. FIGURE 2. Same low-density lipoprotein cholesterol (LDL-C) levels, different cardiovascular risk. apo = apolipoprotein. SI conversion factors: To convert LDL-C value to mmol/L, multiply by 0.0259. Recently, some expert panels and national organizations have proposed using apo B in conjunction with standard lipid testing to address the aforementioned limitations.13 Apo B is a key structural component of all the atherogenic lipoprotein particles, including LDL, VLDL, and IDL. Each of these atherogenic particles carries only one apo B molecule; thus, the total apo B level represents the total number of circulating atherogenic lipoprotein particles and provides the clinician a more accurate picture of a patient's risk of cardiovascular events.13 Other advantages to the measurement of apo B include the fact that it does not require a fasting specimen, its relative low cost, and the existence of a World Health Organization–approved standard. Alternatively, some experts advocate calculating and using non–high-density lipoprotein cholesterol (non–HDL-C) instead of LDL-C to improve risk prediction in certain groups of patients, particularly in those with elevated triglyceride values.1 The National Cholesterol Education Program (NCEP)/Adult Treatment Panel (ATP) III guidelines recommend that, in patients with triglyceride levels of 200 mg/dL or higher, non–HDL-C should be calculated and the goal set at 30 mg/dL higher than the LDL-C goal (Table1).1 Substantial evidence supports the idea that non–HDL-C is clearly superior to LDL-C for cardiovascular disease risk prediction. Non–HDL-C is calculated by subtracting the HDL-C from the total cholesterol, and it represents the cholesterol concentration of all atherogenic lipoproteins.14,15 Although non–HDL-C is a good surrogate measure of apo B, it does not measure the same thing. Non–HDL-C measures the “cholesterol” content of all atherogenic lipoproteins (LDL, IDL, and VLDL), whereas apo B represents the total number of circulating atherogenic particles. Although substantial evidence supports the idea that non–HDL-C is clearly superior to LDL-C for cardiovascular disease risk prediction, strong evidence shows that apo B may be superior to both LDL-C and non–HDL-C for both risk stratification and determination of goal attainment during therapy. TABLE 1. ATP III LDL-C Goals and Cutpoints for Drug Therapya In this commentary, we propose how apo B might be used by clinicians involved in the primary and secondary prevention of coronary heart disease. First, we briefly discuss the evidence that suggests the superiority of apo B as a risk predictor compared to non–HDL-C and LDL-C. Then, we suggest certain patient populations in whom clinicians may wish to target apo B because of demonstrated superiority to LDL-C, including those with diabetes and those receiving statin therapy. Finally, we discuss current recommendations for apo B goals of therapy and the evidence for these goals.

Designing the Si(100) conversion into SiC(100) by Ge

AbstractThe deposition of Germanium (Ge) prior to the conversion of Si(100) into 3C‐SiC(100) results in changes of the structure and surface morphology of the formed silicon carbide layer. First of all it reduces the thickness of the 3C‐SiC layer grown during the conversion process and therefore the probability of voids formation. Secondly, it increases the nucleation density of the formed 3C‐SiC nuclei and therefore, decreases the grain size at Ge coverages below two monolayers. These affect the roughness of the SiC surface positively by modifying the width of the SiC‐Si interface. If the Ge coverages exceed two monolayers the structural and morphological properties begin to degrade. (© 2010 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Effects of individual promoters on the Direct Synthesis of methylchlorosilanes

The industrially relevant Direct Synthesis involves the reaction of methyl chloride with silicon in the presence of a copper catalyst (promoted with Zn, Sn, and P), termed the contact mass, to form methylchlorosilanes. In situ attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR) coupled with flow reactor studies was used to help understand the relationship between the composition of the working catalytic surface and product selectivity during reaction (1 bar CH 3Cl at 300 °C). Promotion of copper–silicon contact masses with Sn and Zn increased the selectivity of the reaction for dimethyldichlorosilane compared to P-promoted and copper–silicon (unpromoted) contact masses. Results showed that the rate of Si conversion associated with the Sn-promoted contact mass was higher than the Si conversion rate associated with the Zn and unpromoted contact masses. ATR-FTIR results suggested that Sn promotion led to a stabilization and relatively high concentration of surface methyl species. In contrast to Sn or Zn promotion, P promotion led to significant methyl fragmentation on the contact mass surface, consistent with its relatively low selectivity toward dimethyldichlorosilane.

High-Purity, Isotopically Enriched Bulk Silicon

The synthesis and characterization of dislocation-free, undoped, single crystals of Si enriched in all three stable isotopes is reported: (99.92%), (91.37%), and (89.8%). A silane-based process compatible with the relatively small amounts of isotopically enriched precursors that are practically available was used. The silane is decomposed to silicon on a graphite starter rod heated to in a recirculating flow reactor. A typical run produces of polycrystalline Si at a growth rate of and the silane to Si conversion efficiency exceeds 95%. Single crystals are grown by the float-zone method and characterized by electrical and optical measurements. Concentrations of shallow dopants (P and B) are as low as mid-. Concentrations of C and O can be lower than and , respectively.

The CARDS array for neutron-rich decay spectroscopy at HRIBF

An array for decay studies of neutron-rich nuclei has been commissioned for use at the UNISOR separator at Holifield Radioactive Ion Beam Facility. This array consists of three segmented clover Ge detectors, plastic scintillators, and a high-resolution (∼1 keV) Si conversion electron spectrometer. These detectors are mounted on a support that surrounds a moving tape collector. This system has been named clover array for radioactive decay studies. The detectors have been outfitted with digital flash ADCs (XIA DGFs) that fit the preamp signals, with built-in pileup rejection.

Times One: SI Units, Conversion and Measurement Skills, by Wacek Kijewski

Times One: <i>SI Units, Conversion and Measurement Skills</i>, by Wacek Kijewski

From molecule-based (super)conductors to thin films, nanowires and nanorings

Thin films of (TTF)(TCNQ) (TTF=tetrathiafulvalene, TCNQ=tetracyanoquinodimethane) are deposited on Si (001), KBr, and stainless steel conversion coatings (SSCC) using chemical vapor deposition. These films are characterized by IR, XRD, conductivity measurements, and SEM. Conducting nanowires and nanorings of (TTF)(TCNQ) and nanowires of (TTF)[Ni(dmit) 2 ] 2 (typically, 20 nm×20 μm) are prepared by successively dipping SSCC in acetonitrile solutions of TTF and TCNQ, or (TTF) 3 (BF 4 ) and (Bu 4 N)[Ni(dmit) 2 ], respectively. These nanowires are observed by SEM. The (TTF)(TCNQ) nanowires are also observed by TEM and AFM and characterized by current-voltage measurements. Nanowires of (TTF)[Ni(dmit) 2 ] 2 are also obtained on silicon conversion coatings (SiCC) and characterized by Raman spectroscopy.

136 3D-C/C複合材製ディスクの回転破壊(OS 耐熱材料)

Cold spin tests of three dimensional fiber-reinforced carbon-carbon composites were conducted for the turbine disk of the air-turbo ram jet engine (ATREX). The fly-out objects were detected at the rotation speed of 12000 r.p.m. and the fly-out behavior was caused by the delamination of the fiber bundles from the surface of the disk. The energy release rate, G, was estimated about 30 J/m2 for this 3D-C/C disk and fine fiber weave structure and large bonding strength between fiber bundle are shown to be effective to increase rotation speed. Gaseous Si conversion and Si infiltration method were examined to increase rotation speed of 3D-C/C disk.

Conversion Factors for SI and non‐SI Units

Soil Science Society of America JournalVolume 60, Issue 3 p. iv-v Conversion Factor for SI and non-SI Unit Conversion Factors for SI and non-SI Units First published: 01 May 1996 https://doi.org/10.2136/sssaj1996.03615995006000030001xAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat No abstract is available for this article. Volume60, Issue3May-June 1996Pages iv-v RelatedInformation

Conversion Factors for SI and non‐SI Units

Soil Science Society of America JournalVolume 60, Issue 2 p. iv-v Conversion Factor for SI and non-SI Unit Conversion Factors for SI and non-SI Units First published: 01 March 1996 https://doi.org/10.2136/sssaj1996.03615995006000020001xAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat No abstract is available for this article. Volume60, Issue2March-April 1996Pages iv-v RelatedInformation