Voltammetry and surface analysis of AISI 316 stainless steel in chloride-containing simulated concrete pore environment

The study of passive layers grown on AISI 316 stainless steel in solutions that simulate concrete pore environments contaminated with Cl^? is presented. Model solutions of saturated Ca(OH)₂ and cement extract (CE) with and without the addition of 5 g/L of NaCl are compared. Cyclic voltammetry (CV) shows different electrochemical responses of passive layers grown on samples immersed in these solutions under open circuit potential (ocp). A more resistive passive film was found on the samples exposed to the CE solution. The different voltammetric responses suggest differences in composition of the passive layers formed on each solution. XPS spectra confirm the dissimilarity in atomic composition. Optical microscope images and AFM images of the pits formed on the samples illustrate the differences of AISI 316 surface topography after exposure to model solutions. Because of these differences, it is recommended to use CE solution as a model solution and ocp passivation to simulate concrete environments.     

Surface alteration of human tooth enamel subjected to acidic and neutral 30% hydrogen peroxide

Objectives

To investigate the effects of acidic and neutral 30% hydrogen peroxide (HP) on human tooth enamel in terms of chemical structure, mechanical property, surface morphology and tooth colour.

Methods

Twenty-seven human dental blocks were obtained from premolars and randomly divided into three groups (n = 9): Group acidic HP (30% HP, pH ≈ 3.6), Group neutral HP (30% HP, pH ≈ 7.0) and Group DW (distilled water, pH ≈ 6.8). Attenuated total reflection-Fourier transform infrared spectroscopy (ATR-FTIR), Raman spectroscopy, atomic force microscopy (AFM) investigation, microhardness test and colour measurements were carried out before and after treatments. ATR-FTIR and Raman spectroscopy were analysed and then the carbonate:mineral ratio (C:M), Raman absolute intensity (RAI), Raman relative intensity (RRI), and laser-induced fluorescence intensity (FI) were obtained for evaluation.

Results

The C:M, percentage microhardness and percentage RRI of group acidic HP decreased more significantly than those of group neutral HP (P = 0.02, P = 0.001, P < 0.001, respectively) and group DW (P = 0.01, P = 0.008, P < 0.001, respectively). Whilst group neutral HP and group DW had no statistical difference in above terms (P = 0.818, P = 0.528, P = 0.158, respectively). Significant morphological alterations were observed in group acidic HP. Group acidic HP and neutral HP had no significant difference in percentage FI (P = 0.652) and ΔE (P = 0.906).

Conclusions

This study suggested that neutral 30% HP had the same efficiency in tooth bleaching and it caused less deleterious effects on enamel than acidic 30% HP.     

Evidence of chemisorption of maleic acid to enamel and hydroxyapatite

Maleic acid has been used as an etchant or non-rinse conditioner in adhesive dentistry. However, the inherent mechanisms of the interaction of maleic acid with hydroxyapatite/enamel have never been fully elucidated. The purpose of this study was to provide evidence for the chemisorption of maleic acid onto hydroxyapatite/enamel, and to identify the reaction products obtained following the interaction of maleic acid with hydroxyapatite. Hydroxyapatite particles were dissolved in a 15% (w/v) aqueous solution of maleic acid (pH = 0.98). Half of the solution was dried to obtain a desiccated mixture. This mixture, hydroxyapatite, maleic acid and self-prepared calcium maleate were analysed by X-ray diffraction (XRD). Acetone was added to the other half of the solution to obtain a precipitate. This precipitate, hydroxyapatite, maleic acid, unetched enamel and maleic acid-etched enamel were analysed by X-ray photoelectron spectroscopy (XPS). The precipitate was also analysed by (1)H NMR. A new binding energy, indicating carboxylate groups, was detected by XPS on the precipitate and maleic acid-etched enamel surface. XRD data indicated the formation of calcium maleate and calcium hydrogen phosphate after the reaction. NMR data revealed that one carboxylic group of maleic acid reacted with hydroxyapatite. Hence, maleic acid can chemisorb to hydroxyapatite and enamel via ionic interactions.     

用傅立叶变换红外光谱仪研究复合树脂的双键转化度

为了研究牙科复合树脂的聚合，采用傅立叶变换红外（Ｆｏｕｒｉｅｒｔｒａｎｓｆｏｒｍｉｎｆｒａｒｅｄ，ＦＴＩＲ）光谱仪测定８种牙科复合树脂的双键转化度并比较了压片制样法和薄膜制样法对转化度的影响。结果发现，树脂的双键转化度在４５％～７４％之间；可见光固化树脂的转化度高于化学固化树脂者。在光固化树脂中，混合填料树脂的转化度高于超微填料树脂者，粘接辅助剂的转化度最高。对光固化树脂而言，压片制样法所测得的转化度值高于用薄膜制样法；而在化学固化树脂，用二种制样方法所测得的转化度值相同。本研究结果可供临床应用复合树脂参考。     

FT-Raman spectroscopy of calcium hydroxide medicament in root canals

AIM: To investigate chemical changes in calcium hydroxide introduced into human root canals as a medicament using Fourier transform-(FT) Raman spectroscopy. METHODOLOGY: Ten necrotic maxillary anterior teeth were selected in 10 patients. The teeth were divided into five treatment groups, according to the survey time. Root canal instrumentation was performed with hand instruments until the master apical file was size 40. Calcium hydroxide paste, in a 1 : 1.25 mixture by weight of powder and distilled water, was introduced directly into the root canal with a lentulo-spiral filler and then condensed with a finger plugger. The access cavity was sealed with a temporary dressing. After 2 and 4 days, then 2, 4 and 6 weeks, the calcium hydroxide paste was sampled with a K-file and then analysed using FT-Raman spectroscopy. The excitation source was an Nd : YAG laser with an excitation wavelength of 1064 nm. All spectra were taken with a laser power of 200 mW, 275-1185 scans, and 4 cm(-1) resolution. The conversion of calcium hydroxide to calcium carbonate was calculated on the basis of the spectral data obtained from the mixtures of both compounds. RESULTS: The calcium hydroxide paste in the apical region showed weak bands at 1088 and 284 cm(-1), in addition to bands associated with calcium hydroxide. The weak bands, assigned to calcium carbonate, became stronger with time. Calcium carbonate content increased rapidly in the first 2 days and then tended to increase slowly. Approximately 11% of the calcium hydroxide at the apical portion of the canal was converted to calcium carbonate after 6 weeks. However, little alteration of the paste was noticed in the samples from the middle portion of the canal. CONCLUSIONS: Calcium hydroxide medicament in root canals became transformed into calcium carbonate in the apical region within 2 days. Although the transformation continued with time, approximately 90% of the calcium hydroxide remained unchanged after 6 weeks.     

Anisotropy in the anodic dissolution of silicon elucidated by in situ infrared spectroscopy

The anodic dissolution of silicon in dilute HF electrolyte exhibits some anisotropy in the region of the first electropolishing plateau. This anisotropy can plausibly be assigned to an orientation-dependent surface chemistry. The silicon|dilute fluoride electrolyte interface has been investigated by in situ infrared vibrational spectroscopy in the differential mode, in the potential region where the surface turns from hydrogenated to oxidised. Silicon surfaces of different orientations exhibit closely similar behaviour. However, careful analysis of the ν OH region reveals a significant difference in the concentration of SiOH groups at (1 0 0)- and (1 1 1)-oriented Si surfaces. This observation points to the key role of the SiOH groups in determining the anisotropic behaviour of the electrochemical dissolution of silicon.     

Vibrational study of adsorbed phosphate ions on rhodium single crystal electrodes

The adsorption of H₂PO₄^? ions was studied on low Miller index rhodium single crystal electrodes by in situ FTIR spectroscopy. It is found that for Rh(1 0 0) and Rh(1 1 0), H₂PO₄^? ions are the major species at low potentials, but at higher potentials, some of the H₂PO₄^? ions undergo a potential induced deprotonation and probably there is a mixture of H₂PO₄^? and HPO₄^2? ions. On Rh(1 1 1) the deprotonation starts at very low potentials and at higher potentials the H₂PO₄^? is fully converted to HPO₄^2?. The behavior of the band center and of the band intensity with the applied potential was also analyzed. It is found that the adsorption increases from 0.08 V vs. a Pd–H₂ electrode up to 0.5 V and then it decreases when the OH starts to be adsorbed.     

EIS study of solid-state transformations in the passivation process of bismuth in sulfide solution

Anodic oxidation of polycrystalline bismuth in alkaline medium, containing sulfide ions was investigated in situ. Cyclic voltammetry was used to define the potential regions of formation and stability of anodic Bi₂S₃ and Bi₂O₃ semiconductor films that translate bismuth to the passive state. The mechanism of elementary steps of the passivation process has been investigated using electrochemical impedance spectroscopy (EIS). The electric and dielectric properties of anodic films and structural parameters of the interfaces Bi–growing film–electrolyte in a wide region of potentials and frequencies of six decades, were determined. The EIS data have been analyzed and discussed in the frame of the point defect model (PDM) of anodic film formation and growth. The growth of passive surface films on bismuth takes place via transport of anionic vacancies generated at the metal–film interface. The slow step of the process is the layer-limited diffusion of anionic vacancies (D≈ 10^?16 cm² s^?1).Solid-state transformation of sulfide to the oxide film is a consequence of OH^? ion capture into the anionic vacancies of the sulfide film, the generation and transport of cation vacancies from the film–solution interface, their annihilation and formation of a vacancy condensate of a critical size at the metal–film interface.     

Impedance of metastable pitting corrosion

A metastable pitting corrosion impedance investigation has been performed. The shape of the dc current is connected with the shape of the impedance diagram. The corrosion rate inside an active pit is charge transfer controlled. The active surface area expansion is proportional to the double layer capacity changes. Changes of the electrolyte resistance inside the pit have been detected.     

X-ray photoelectron spectroscopic investigation and electrochemistry of polynuclear indium(III) hexacyanoferrate films

An electrochemically deposited indium(III)-hexacyanoferrate (InHCF) film on glassy carbon and platinum electrodes has been investigated by X-ray photoelectron spectroscopy (XPS). Attempts were made to characterise such a polynuclear inorganic film upon its electrochemical conditioning in both reduced and oxidised forms. The indium ions were unaffected by the oxidation state of the film and were present mainly as In(III). In the oxidised form (i.e. conditioned at +0.90 V) the InHCF is unstable during XPS analysis, with Fe being reduced from Fe^III to Fe^II. Profound alterations were also observed in the chemical form of nitrogen. Although the InHCF film was grown in potassium containing solutions, a very low amount of K⁺ ions was incorporated into the inorganic lattice. This fact, along with the iron to indium ratio of 0.76±0.06 (n=6), is consistent with a potassium-free structure of `insoluble' In₄[Fe(CN)₆]₃ · xH₂O. Yet the stability of InHCF films is not very good, and the electrochemical formation of InFe(CN)₆ and KInFe(CN)₆ is probably the main cause of the film dissolution.