Quantitative evaluation of cement paste carbonation using Raman spectroscopy

Carbonation induced corrosion is one of the major durability issues for reinforced concrete structures. To address this issue, it is essential to understand the underlying mechanism of carbonation by detecting the ingress of the CO2 and carbonation depth quantitatively. This paper demonstrates the potential of Raman spectroscopy, as a powerful technique, to implement quantification analysis of cement paste carbonation. In present work, the correlation between the content of the CO32− and the Raman peak intensity was initially established by using several standard specimens premixed with certain amount of CO32−. The established correlation was then used to investigate the carbonation of the cement paste in a CO2 diffusion scenario, and the results show a good agreement with that obtained by thermogravimetry measurements. Therefore, the feasibility of the Raman spectroscopy to quantify the carbonation degree of the cement paste can be demonstrated.

Analysis of Sildenafil in Liquor and Health Wine Using Surface Enhanced Raman Spectroscopy

The illegal adulteration of sildenafil in herbal food supplements and alcoholic drinks immensely threatens human health due to its harmful side-effects. Therefore, it is important to accurately detect and identify the presence of sildenafil in alcoholic drinks. In this study, Opto Trace Raman 202 (OTR 202) was used as surface enhanced Raman spectroscopy (SERS) active colloids to detect sildenafil. The results demonstrated that the Raman enhancement factor (EF) of OTR 202 colloids reached 1.84 × 107 and the limits of detection (LODs) of sildenafil in health wine and liquor were found to be as low as 0.1 mg/L. Moreover, the SERS peaks of 645, 814, 1235, 1401, 1530 and 1584 cm−1 could be qualitatively determined as sildenafil characteristic peaks and the relationship between Raman peak intensity and sildenafil concentration in health wine and liquor were different. There was a good linear correlation between Raman peak intensity, and sildenafil concentration in health wine ranged 0.1–1 mg/L (0.9687< R2 < 0.9891) and 1–10 mg/L (0.9701 < R2 < 0.9840), and in liquor ranged 0.1–1 mg/L (0.9662 < R2 < 0.9944) and 1–20 mg/L (0.9625 < R2 < 0.9922). The relative standard deviations (RSD) were less than 5.90% (sildenafil in health wine) and 9.16% (sildenafil in liquor). The recovery ranged 88.92–104.42% (sildenafil in health wine) and 90.09–104.55% (sildenafil in liquor). In general, the sildenafil in health wine and liquor could be rapidly and quantitatively determined using SERS technique, which offered a simple and accurate alternative for the determination of sildenafil in alcoholic drinks.

Study of surface defects and crystallinity of MWCNTs growth in FCCVD

This research investigated the structural growth of multiwalled carbon nanotubes (MWCNTs) in a double stage horizontal chemical vapor deposition (CVD) reactor. Ethylene was used as a carbon source for nucleation of nanotubes. Ferrocene catalyst weight was varied from 0.1 to 0.2 g to demonstrate the growth of MWCNTs on Si/SiO2/Al2O3 substrate. The obtained data revealed that the weight of the catalyst significantly affects the diameter, crystallinity, alignment and yield of the nanotubes. Lower inner-shell spacing and the ratio of D-Raman peak intensity and G-Raman peak intensity (ID/IG ratio) were obtained with 0.15 g of ferrocene, which was an indication of relatively pure carbon nanotubes (CNTs) growth. Raman spectra also confirmed the highly crystalline and relatively pure CNTs structures with ID/IG ratio of 0.700. TGA data revealed the formation of 97% pure nanotubes with oxidation temperature of 620°C. However, above and below the optimum (0.15 g of ferrocene), some of the grown CNTs were found defective and few black spots were also seen in TEM micrographs.

One-Pot Assembly of Cu2O Chain-Like Hollow Structures

Novel Cu2O chain-like network was assembled via a facile one-pot solution process with the assistance of poly(vinylpyrrolidone) (PVP). TEM observations showed that the chain-like structures were aggregated by hollow spheres ∼70 nm in diameter. To be worth mentioning, HRTEM image recorded from the coherent interfacial region demonstrated that the lattice fringes penetrate from one sphere into the adjacent one smoothly without apparent diffraction contrast, which indicated that the hollow spheres experienced lattice fusion and grew into each other. Based on the systematic studies, an oriented aggregation mechanism was proposed, i.e., Cu2O nanoparticles into hollow spheres and subsequently the hollow spheres into the chain-like structures. The Raman spectra of the Cu2O chain-like hollow nanostructures were also investigated. It was found that the Raman peak intensity is different from that in the previous reports, which might be originated from the structure defect resulted from the oriented attachment.

DX CENTERS IN AlGaN

In this letter, recent theoretical and experimental investigations of DX centers in Al x Ga 1-x N are reviewed. Due to the technological importance of III–V nitride semiconductors, studies of deep-level defects in AlGaN have attracted a great deal of interest. Oxygen impurities form DX centers in GaN under hydrostatic pressure and in Al x Ga 1-x N alloys. For GaN under pressures greater than 20 GPa, the DX level emerges from the conduction band, leading to a decrease in the free-electron concentration. The localization of free carriers leads to a decrease in the far-infrared absorption and an increase in the LO Raman peak intensity. In Al x Ga 1-x N alloys, Hall effect and persistent photoconductivity measurements indicate that the DX state is energetically favorable for x>0.3. The experimental data for oxygen DX centers are in excellent agreement with first-principles calculations. Experiments have shown that silicon remains a shallow donor up to at least x=0.5 and theory indicates that it may remain shallow up to x=1.

Deposition of Diamond-Like Carbon Films by PECVD

ABSTRACTWe have studied the structural properties of hydrogenated carbon films deposited by plasma enhanced chemical vapor deposition (PECVD). The substrate holder in reaction chamber could be biased and be heated. The Raman peak intensity at 1350 cm−1 was increased by reducing CH4 flow rate. The film structure changed from soft a-C:H to hard carbon with decreasing CH4 flow rate, resulted from increased self-bias. The 1520 cm−1 peak shifts to higher frequency by reducing the CH4flow rate, probably resulted from the increased internal stress.