Hexafluorosilicate Research Articles

Electro-deposition behavior and proof-of-concept operation in methanesulfonic acid-based crude lead electro-refining

A promising methanesulfonic acid (MSA) system, in lieu of conventional fluosilicic acid system, for green and efficient electro-refining of Pb, was proposed, due to its low volatility, low corrosivity, desired thermal stability and high conductivity. The electro-deposition behavior of the MSA-based Pb electro-refining (MPR) was explored, including its operation mechanism, reaction reversibility, nucleation, and growth mode. Based on cyclic voltammetry (CV) and chronoamperometry (CA), the diffusion-controlled and irreversible lead deposition process of MPR was revealed, and the theoretical model of MPR lead deposition nucleation and growth with transient nucleation was established. The bench-scale proof-of-concept operation of MPR achieved energy consumption of 104.22 kW·h/t Pb and current efficiency of 99.24%, which was competitive with the energy consumption of 120 kW·h/t Pb and current efficiency of 95% for H2SiF6 system. The bench-scale operation of MPR obtained a smooth and compact deposit sample with Pb purity of 99.9925%, which satisfied the standard of Pb ingot (GB/T 469—2013) of 99.97%.

Comparative Evaluation of Antimicrobial Efficacy of Fluoride-Based and Self-Assembling Peptide P11-4-based Tooth Remineralization Agents on Streptococcus mutans: A Microbiological Study.

Dental caries is a biofilm-related oral disease that continues to afflict the majority of the world's population. The disease results from an interaction between specific bacteria and dietary constituents within a biofilm known as dental plaque. Among the cariogenic microorganisms, Streptococcus mutans (S. mutans) plays pivotal role in caries-inducing processes. Evaluate and compare the antimicrobial efficacy of self-assembling peptide P11-4-based tooth remineralization agents on S. mutans. An in vitro microbiological study. The antibacterial efficacy of self-assembling peptide P11-4 gel (Group 1), fluoride enhanced hydroxyapatite gel (Group 2), acidulated phosphate fluoride gel (Group 3), chlorhexidine gluconate gel 1.0% w/w (Group 4; positive control), and normal saline (Group 5; negative control) was performed using time-kill assay over a period of 24 h and the number of S. mutans colony-forming units (CFUs) were calculated. Statistical analysis was done using Kruskal-Wallis test and Mann-Whitney post hoc Test. The level of significance was set at P < 0.05. Group 1 showed mean CFUs (× 103) of 841.33 ± 3.51, Group 2 showed 10035.33 ± 60.68, Group 3 showed 1058.00 ± 56.96, Group 4 showed 0.00 ± 0.00, and Group 5 showed mean CFUs with 15226.67 ± 96.67. The difference in the mean CFUs (× 103) between different groups was statistically significant at P < 0.001. The self-assembling peptide P11-4-based tooth remineralization agent exhibited an inhibitory influence on S. mutans and hence formation of cariogenic bacteria dominant biofilm can thus be affected by its application.

Influence of Different Conditioning Protocols on Bond Strength to Glass Ceramic

Sixteen glass ceramic blocks (IPS e.max CAD/CAM) were fabricated by a CAD/CAM machine withdimensions (6mm × 11mm x 13mm) and divided into 4 groups (n=4), according to surface treatments: (G1)Hydrofluoric acid (HF) etching and silane application, (G2) Acidulated phosphate fluoride (APF) and silaneapplication, (G3) Monobond Etch and Prime (MEP), (G4) Tetrabutylammonium dihydrogen trifluoride (TDTF) andsilane application.Composite resin blocks (Te econome) were fabricated and cemented to the treated ceramic blocksusing adhesive resin cement. All bonded specimens were kept in a water bath for three months and went through 5000thermal cycles. The bilayered specimens were sectioned into micro-bars (1 mm* 1 mm in cross-section) using adiamond-coated disc under water cooling using a cutting machine. Microtensile bond strength (μTBS) test wasperformed. Scanning Electron Microscope (SEM) was used for specimens’ examination.

Bond Strength and Failure Mode of Glass Fiber Posts with Different Surface Treatments Prior to Silanization: An In Vitro Comparative Study.

The use of chemical agents in the surface treatment of glass fiber posts can improve their bond strength to the root canal. The aim of this study was to assess the bond strength and failure mode of glass fiber posts that received different surface treatments prior to silanization. In this cross-sectional and in vitro experimental study, 50 human lower premolar roots were randomly divided into five groups and subsequently prepared to receive the cementation of a fiberglass post prior to silanization. They were distributed as group 1 (with 24% hydrogen peroxide), group 2 (with 37% phosphoric acid), group 3 (with 1.23% acidulated phosphate fluoride for 2 minutes), group 4 (with 1.23% acidulated phosphate fluoride for 6 minutes), and group 5 (without pretreatment). After cementation, the roots were sectioned into two discs for each cervical, middle, and apical region. Bond strength was assessed using the push out technique. Adhesive, mixed, and cohesive failure modes were also assessed. For data analysis, ANOVA and Tukey's post hoc tests were used, as well as Pearson's chi-square test. A significance of P < 0.05 was considered in all statistical analyses. When comparing the bond strength of root regions, significant differences were obtained in groups pretreated with phosphoric acid (P = 0.018) and acidulated phosphate fluoride for 2 and 6 minutes (P = 0.001 and P = 0.000, respectively). Furthermore, significant differences were obtained between posts treated only with silane and those that received phosphoric acid pretreatment (P = 0.006) and acidulated phosphate fluoride for 6 minutes (P = 0.001). Significant association of mixed failure mode was observed with hydrogen peroxide (P = 0.014) and phosphoric acid (P = 0.006) pretreatments. Cohesive failure was significantly associated with acidulated phosphate fluoride pretreatment for 2 minutes (P = 0.032) and with posts that did not receive treatment prior to silanization (P = 0.000). Posts treated only with silane and pretreated with hydrogen peroxide and acidulated phosphate fluoride for 2 minutes presented significantly higher bond strength with respect to those pretreated with phosphoric acid and acidulated phosphate fluoride for 6 minutes. However, acidulated phosphate fluoride for 2 minutes and silane were associated with a better bonding type.

Kinetic studies on acidic wet chemical etching of silicon in binary and ternary mixtures of HF, HNO3 and H2SiF6.

The etching of silicon with mixtures of hydrofluoric acid (HF), nitric acid (HNO3) and hexafluorosilicic acid (H2SiF6) proceeds in a complex reaction scenario consisting of interacting side reactions. Almost no other dissolution reaction is so massively dependent on the reaction conditions that influence the etching rate and the mechanism of the individual reactions. Extensive studies of the reaction rate of silicon etching in binary and ternary acid mixtures have allowed the transition point between the reaction-controlled and diffusion-controlled reaction regimes to be determined as a function of the composition of the etching mixture. It was verified that the reaction mechanism for binary and ternary mixtures does not differ and only the lower water content in ternary mixtures favours an enhanced formation of the reactive N(III) intermediate HNO2 in side reactions. Based on the exact knowledge of the point of mechanism change, determination of the reaction rate under quasi-isothermal conditions in the bulk etching range allows, for the first time, deriving formal kinetic terms from the kinetic data to describe the dissolution rate in both the reaction-controlled and diffusion-controlled regimes. The formal kinetic terms were designed both for the kinetically correct quasi-isothermal approach to the dissolution rate in the Si bulk and for the application-oriented approach that includes induction phases and temperature increases in the considered dissolution period as well as influences of the surface properties. Moreover, by using the water content of the etching mixtures as a proxy variable, uniform calculation of the etching rates in HF/HNO3 as well as in HF/HNO3/H2SiF6 mixtures in the entire composition range of the application can be formulated.

Modelling and Optimisation of Copper Adsorption in Solution by the Response Surface Method

Copper is considered a heavy metal that can be toxic at certain concentrations and its presence in water is a potential threat to public health. These heavy metals also contribute to a remarkable degradation of the environment, hence the need for effective treatment methods to remove them. In this study, a mixture of titaniferous sand and calcium silicate was used as adsorbent material to eliminate copper in solution. The calcium silicate was synthesised from fluosilicic acid, which is a by-product of phosphoric acid manufacture. The titaniferous sand is a residue from a mining industry. Both adsorbents were characterised by infrared spectroscopy and X-ray fluorescence to determine their compositions and physicochemical properties. The response surfaces, through the Box-Behnken model, were used to model and optimise various adsorption parameters, namely initial copper concentration (A: 60 - 200 mg/L), adsorbent dose (B: 0.1 - 0.6 g) and pH (C: 4 - 10). The copper removal efficiency (98.92%), after statistical analysis, was obtained under the following optimal conditions: an adsorbent dose of 0.55 g, an initial copper concentration of 197.25 mg/L and a pH of 9.85. The study of the effects of the operating parameters showed that they had a positive effect on the copper removal efficiency.

Preventive effect of combined Er, Cr: YSGG and fluoride gel on acid resistance of the permanent tooth enamel: An in vitro study.

Increasing the resistance of enamel to acids may prevent dental erosion and diminish microhardness alterations in the enamel. This study aimed to evaluate the preventive effect of erbium, chromium: yttrium, scandium, gallium, and garnet laser combined with 1.23% acidulated phosphate fluoride gel on enamel resistance to demineralization. Thirty-four human maxillary first premolars were randomly assigned to three groups. Group I (control group), group II were treated with fluoride gel for 4-minutes and group III received ten seconds of laser treatment; then fluoride has applied. Each sample was immersed in a soft drink for 2 minutes, then washed and kept in deionized water. Four consecutive cycles were carried out at 6 hours intervals. The effects were studied utilizing the Vickers microhardness test and scanning electron microscopy. Data analyses were performed by Levene test and General Linear Model Repeated Measure Factorial ANOVA with Bonferonni post hoc test, the accepted level of significance was 0.05. Microhardness was increased statistically in groups II and III after treatment, with the highest value for group III. After demineralization, the control group had the lowest microhardness score, followed by group II and group III, which showed the least reduction in microhardness with a statistical significance (p<0.05). There was a correlation between the morphological alterations in enamel surfaces and the increased enamel resistance. Both fluoride and the combined laser fluoride treatment had an advantage in protecting the enamel and increasing enamel resistance to acids, with a more significant benefit for the combined laser fluoride group. Key words:Prevention, Er, Cr: YSGG, enamel demineralization, fluoride, microhardness.

Comparative In Vitro Study Regarding the Effect of 2% and 6% Titanium Tetrafluoride on Demineralized Human Enamel

Background: Dental caries is the most common disease of the childhood and adulthood where the mineral contents of the enamel of the teeth begin to lose due to acids attacks by demineralization process. It can be prevented by application of fluoride that increased the mineral content of the enamel and made it highly resistant to acid demineralization. Objectives: This study was conducted to investigate the effects of titanium tetrafluoride (TiF4) in different concentrations and frequencies on surface microstructure and chemical structure of artificially demineralized enamel. Materials and Methods: The sample consisted of 35 premolar teeth: seven teeth randomly selected remained sound (five for energy dispersive spectroscopy analysis and two for scan electronic microscopy, whereas the remaining 28 teeth were divided into four treatment groups (n = 7): (1) control negative (deionized water), (2) control positive (acidulated phosphate fluoride gel), (3) 6% TiF4 solution once daily, (4) 2% TiF4 solution three times daily. Chemical structure and surface microstructure analyses were made for sound, after demineralization then after treatments. Results: The fluoride content was greater in 6% TiF4, whereas the calcium content was greater in control positive followed by 6% TiF4 then 2% TiF4 groups. Surface microstructure revealed uniform, smooth, glaze-like surface with no irregularities in 6% TiF4 while localized areas of glaze-like depositions were noted in 2% TiF4. Conclusions: The TiF4 showed better minerals contents and uniform surface in its higher concentration and the frequency of applications was not important as concentration.

Shear bond strength fissure sealant based on glass ionomer after topical fluor application: a comparison between sodium fluoride and acidulated phosphate fluoride

Background: Application of fissure sealants to young permanent teeth is one of the preventive measures for caries in the field of dentistry. Fissure sealants based on glass ionomer cement (GIC) have the advantage of releasing fluoride. Sodium fluoride and acidulated phosphate fluoride (APF) are remineralization agents because they can increase remineralization by altering hydroxyapatite to fluorapatite and this in turn makes fluorine able to increase pH. Fluoride can prevent caries by increasing remineralization of the enamel that has just been demineralized by acids produced by plaque bacteria. The aim of this study is to compare the shear bond strength fissure sealant based on glass ionomer between sodium fluoride and APF topical fluor application Method: This research applied true experimental design with post test only control group design. The 21 maxillary permanent premolars were distributed into 3 groups, namely the control group (K1), the treatment group added 5% sodium fluoride (K2), and the treatment group added 1.23% APF (K3). Result: One Way ANOVA and post hoc LSD analysis test displayed no significant difference in each group. This could be due to the material used as a conditioner prior to the GIC application. The addition of fluoride ions will inhibit the demineralization process of the enamel produced by the application of conditioner. So it does not rule out that it will interfere with the attachment of the GIC material used as a fissure sealant in this research. Conclusion: There was no significant difference in shear bond strength of fissure sealant based on glass ionomer between sodium fluoride and acidulated phosphate fluoride topical application.

Acidulated phosphate fluoride sebagai bahan pencegahan Karies gigi anak : a scoping review (Laporan Penelitian)

Background: Caries occur in the hard tissues of the teeth due to bacterial activity in plaque. Untreated dental caries can result in pain, therefore early and if caries is left over time it will cause pain so that early caries prevention is necessary. Caries prevention can be done using Acidulated Phosphate Fluoride as an effective option in preventing the process of caries development in children. Aim: To know the effectiveness of APF gel 1,23% in preventing caries in children. Method: Scoping Review with inclusion criteria using a Randomized Controlled Trial (RCT) study design was conducted according to Preferres Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) and two databases (PubMed and Google Scholar). Result: The results showed that the initial search yielded 985 documents. After eliminating duplicate studies and screening full-text articles for eligibility (n = 21), the authors identified 3 studies that met the criteria for inclusion. Conclusion: APF gel 1.23% has the effectiveness and preventing dental caries in children due to its better ability to bind calcium enamel,also does not irritate the gingiva..

Is professionally applied fluoride effective in preventing or arresting caries in older adults?

Design Systematic review of clinical trials.Case selection Clinical trials with adults 60 years of age or older who professionally received fluoride therapy for caries prevention or arrest. Controls were adults of the same age group who received another professionally applied fluoride agent, placebo, or nothing.Data analysis The expected outcomes were the mean difference in the number of new caries, caries prevented fraction and caries arrest rate. Independently, two researchers assessed the risk of bias in the included studies.Results Seven studies met the selection criteria where 5% sodium fluoride varnish, 38% sodium diamine fluoride solution and 1.23% acidulated phosphate fluoride gel were used with root caries and coronal caries. Given the nature of the studies, the three agents were effective in preventing root caries in older adults. None of the agents were particularly superior to the others.Conclusions Professionally applied fluoride is effective in preventing dental caries in older adults.

Estimation of wettability of topical fluoride gel on anterior and posterior teeth: An in vitro study.

The surface area determination has a vital role in measuring the properties of liquid and solid substances. Fluoride is a potent remineralizing agent of the teeth. The surface area is measured using a goniometer. The main aim of this study is to estimate the wettability of topical fluoride gel on the anterior and posterior teeth surfaces. Topical acidulated phosphate fluoride (APF) gel was taken in small quantities. Anterior and posterior teeth were collected, and their superficial unaltered enamel sections were used as the surface where the contact angle (CA) is determined. The surface wettability is determined using Ossila goniometer to measure CA. Each stage was mounted on a mechanical stage of the goniometer. A calibrated microsyringe was used to dispense drops of the APF gel over the surface of the specimen Group A (anterior tooth cut section) and Group B (posterior tooth cut section). This procedure is repeated for all specimen samples. The mean of CAs of the anterior teeth (88.41°) was greater when compared with the mean of posterior teeth (80.36°) CA. P value found using the paired t-test of SPSS software is found to be 0.271 (>0.05), hence statistically not significant. The greater the CA, the lower is the degree of wettability on the teeth surfaces. The mean CA of the topical fluoride APF gel on the anterior tooth surface is greater when compared to the posterior tooth surface. This signifies that greater wettability is seen on posterior tooth surfaces.

&lt;strong&gt;The effect of acidulated phosphate fluoride (APF) gel against erosion on enamel microstructure of primary teeth which soaked with Citrus aurantifolia &lt;/strong&gt;

ABSTRACTIntroduction: Erosion is a common dental problem that is especially prevalent in children due to the increasing consumption of acidic food and beverages. APF gel is believed to be effective in reducing the demineralization effect of the teeth as well as escalating the remineralization process. This research aims to determine and evaluate the effectiveness of 1.23% APF gel as a preventive agent for the erosion of tooth enamel, specifically in deciduous teeth. Methods: This type of research is true experimental research. The population of this research would be primary teeth extracted from children, using a purposive sampling technique with inclusive and exclusive criteria. A total amount of 5 maxillary primary central incisors were extracted and cleaned. APF gel was applied repetitively on the left side of the teeth for 4 minutes every hour, whereas the right side was left as it is. Samples were then analyzed using a scanning electron microscope (SEM). A qualitative and subjective analysis regarding the micromorphological features of the erosion can be done. Result: The side of teeth without APF gel application has a greater erosion rate compared with teeth with APF gel application. The tooth which is demineralized shows a honeycomb structure of the interprismatic enamel. As for the dentinal tubules, teeth without APF gel application have a bigger opening of dentinal tubules, going up to 7.868 micrometers in size compared to teeth with APF gel application (1-2 micrometers). Conclusion: The application of professional acidulated phosphate fluoride (APF) gel on deciduous teeth even when soaked in Citrus aurantifolia, is proven to be effective in preventing dental erosion.Keywords: acidulated phosphate fluoride (APF) gel; citrus aurantifolia; dental erosion; primary tooth

Development of Root Caries Prevention by Nano-Hydroxyapatite Coating and Improvement of Dentin Acid Resistance.

There is no established method for optimizing the use of dentin to prevent root caries, which are increasing in the elderly population. This study aimed to develop a new approach for root caries prevention by focusing on bioapatite (BioHap), a new biomaterial, combined with fluoride. Bovine dentin was used as a sample, and an acid challenge was performed in three groups: no fluoride (control group), acidulated phosphate fluoride treatment (APF group), and BioHap + APF treatment (BioHap group). After applying the new compound, the acid resistance of dentin was compared with that of APF alone. The BioHap group had fewer defects and an increased surface hardness than the APF group. The BioHap group had the smallest lesion depth and least mineral loss among all groups. Using a scanning electron microscope in the BioHap group showed the closure of dentinal tubules and a coating on the surface. The BioHap group maintained a coating and had higher acid resistance than the APF group. The coating prevents acid penetration, and the small particle size of BioHap and its excellent reactivity with fluoride are thought to have contributed to the improvement of acid resistance in dentin. Topical fluoride application using BioHap protects against root caries.

Effect of silver diamine fluoride on the surface roughness of dental ceramics

Statement of problemApplication of silver diamine fluoride (SDF) can be a straightforward and efficient way to manage recurrent caries around the margins of crowns. However, its effect on ceramic surfaces is unknown. PurposeThe purpose of this in vitro study was to evaluate and compare the effect of SDF, acidulated phosphate fluoride (APF), and distilled water on the surface roughness of dental ceramics. Material and methodsForty-five rectangles (10×10×2 mm) each of 5% yttria-stabilized tetragonal zirconia polycrystal (5Y-TZP) zirconia (Zir), lithium disilicate (LDS), overglazed feldspathic porcelain (FO), and polished feldspathic porcelain (FP) were fabricated. The specimens were treated with 38% SDF, 1.23% APF, and distilled water to simulate 3 years of topical applications. The surface roughness (Ra) of each rectangle was measured with a profilometer before and after treatment with the solutions, and the change in Ra (△Ra) was calculated. Scanning electron microscope images were obtained of each treatment group. Multiple comparison of the means among the ceramics and testing solutions was done using 2-way ANOVA followed by the Tukey Honestly Significant test (α=.05). ResultsANOVA revealed significant differences in the 2 main factors, as well as their interaction (P<.001). The surface roughness of the treated rectangles was significantly dependent on the type of ceramic and the testing solution. The greatest surface roughness increase was seen in the interaction of LDS:APF (△Ramean=0.51 ±0.13 μm), closely followed by FO:APF (△Ramean=0.49 ±0.20 μm) and FP:APF (△Ramean=0.41 ±0.17 μm) (P<.001). SDF increased the surface roughness of LDS, FO, and FP; however, the increase was not significant (△Ramean LDS=0.25 ±0.11 μm; △Ramean FO=0.17 ±0.16 μm; △Ramean FP=.1 ±0.14 μm; P >.118). None of the solutions had any effect on zirconia (P>.977). ConclusionsSDF is safe to use around zirconia restorations. Long-term and repeated application of SDF on lithium disilicate and feldspathic porcelain must be considered with caution.

Prevention of Dental Erosion Caused by Fermented Milk: An In-vitro Study.

This study aimed to assess the efficacy of three techniques for preventing dental erosion and thereby identify effective methods. The three techniques were: 1) adding calcium to fermented milk (2% Ca and 0.5% Ca); 2) topical application of fluoride to the teeth before exposure to fermented milk (acidulated phosphate fluoride [APF] gel and 0.05% NaF); and 3) a combination of the two techniques (APF gel + 0.5% Ca, 0.05% NaF + 0.5% Ca). pH cycling was performed on bovine-tooth specimens alternately immersed in experimental solutions and artificial saliva. After treatment, the microhardness and roughness of the enamel surfaces were measured, and changes in the surface morphology were observed using atomic force microscope images. Microhardness did not differ statistically significantly between the 2% Ca and mineral water (negative control) groups (2% Ca: 295.34 ± 11.50; mineral water group: 294.76 ± 10.67; p > 0.05). Surface roughness did not differ statistically significantly between the 2% Ca, 0.05% NaF + 0.5% Ca, and mineral water groups (2% Ca: 16.81 ± 7.23; 0.05% NaF + 0.5% Ca: 15.77 ± 2.86; mineral water group: 13.35 ± 5.53; p > 0.05). The surface morphology did not change in the mineral water and 2% Ca groups. Considering that 2% calcium is a high concentration, adding a low concentration of calcium to fermented milk and applying a low concentration of fluoride daily decreased the reduction of surface microhardness and reduced the increase in surface roughness without causing marked changes in surface morphology. This confirms that combining the two techniques is an effective strategy to prevent dental erosion in-vitro.

Gels containing statherin-derived peptide protect against enamel and dentin erosive tooth wear in vitro

The effect of gels containing a statherin-derived peptide (Stn) on the protection against enamel and dentin erosive tooth wear (ETW) in vitro was evaluated. Bovine enamel and dentin specimens were divided into 2 groups (n = 15 and 18/group for enamel and dentin, respectively) that were treated with Chitosan or Carboxymethylcellulose (CMC) gels containing Stn15pSpS at 1.88 × 10-5 M or 3.76 × 10-5 M. Chitosan or CMC gels without active ingredients served as negative controls, while chitosan gel containing 1.23% F (as NaF) and acidulated phosphate fluoride gel (1.23% F) served as positive controls. The gels were applied on the specimens for 4 min. Stimulated saliva was collected from 3 donors and used to form a 2-h acquired pellicle on the specimens. Then, the specimens were submitted to an erosive pH cycling protocol 4 times/day for 7 days (0.01 M HCl pH 2.0/45 s, artificial saliva/2 h, and artificial saliva overnight). The gels were applied again during pH cycling, 2 times/day for 4 min after the first and last erosive challenges. Enamel and dentin loss (μm) were assessed by contact profilometry. Scanning electron microscopy (SEM) was analyzed using a cold field emission. Data were analyzed by two-way ANOVA (for chitosan and CMC gels, separately) and Tukey's multiple comparison test. SEM images showed changes to enamel topography after application oft the gels containing Stn or F. Regarding CMC-based gels, for enamel, none of the treatments significantly reduced ETW in comparison with placebo; for dentin, however, gels containing Stn, regardless the concentration, significantly reduced the ETW. Moreover, Chitosan-based gels, regardless the Stn concentration, were able to protect enamel and dentin against ETW. Gels containing Stn might be a new approach to protect against ETW.

Drying Process Optimization and Efficiency of Aluminum Fluoride (AlF3) Plant

Aluminum Fluoride (AlF 3 ) is a substantive material used to reduce the melting point temperature of the Aluminum from 1500 o C to 600-850 o C. The production applies a wet process using raw materials of Fluosilicic Acid and Aluminum Hydroxide with a by-product of Silica Dioxide. In this case, AlF 3 products are expected to have a maximum H 2 O content of 2.6%. However, in the production process, the H 2 O content reached 3% due to the inoptimum drying process. Therefore, the optimization process was carried out by increasing the dry air temperature of the recycle from stage 2 to stage 1 in the drying process, so that the mass transfer of H 2 O from AlF 3 crystals to the air can be maximized. After the optimization, it was found that the H 2 O content has met the quality standard of 1.8%.

Improved Enamel Acid Resistance by Highly Concentrated Acidulated Phosphate Sodium Monofluorophosphate Solution.

Sodium monofluorophosphate (MFP) is a component of fluoride-containing dentifrices and is more biosafe than the conventional sodium fluoride (NaF). MFP can respond not only on the tooth surface layer but also deep into the enamel. We aim to confirm that high concentrations of acid phosphate MFP (AP-MFP, 9000 ppmF), used in professional care, could lead to a highly biosafe fluoride application method that acts through the deep enamel layers. Sample groups were respectively treated in vitro with NaF, acidulated phosphate fluoride (APF), MFP, and AP-MFP, and the samples were compared against an untreated group. Characterizations after fluoride application confirmed that MFP and AP-MFP treatments improved the acid resistance of enamel compared to that of conventional methods. Furthermore, the acid resistance of highly concentrated MFPs improved by using phosphoric acid. Although the acid resistance from the AP-MFP method is not as good as that using APF, AP-MFP can act both on the surface layer and deep into the enamel. Moreover, AP-MFP retains fluoride ions as much as APF does on the tooth surface. The proposed fluoride application method using AP-MFP introduces a dental treatment for acid resistance that is highly biosafe and penetrates deep layers of the enamel.

Effective removal of fluorine ions in phosphoric acid by silicate molecular sieve synthesized by hexafluorosilicic acid

Silicone zeolite prepared from hexafluorosilicic acid is a good adsorbent for fluoride removal. The morphology and structure of the prepared composites were characterized by XRD, FT-IR and BET. XRD images showed that fluorine was adsorbed on the surface of zeolite and the FT-IR spectra showed that there are different kinds of silicon and aluminum in silica-based zeolite. Therefore, through the studied of regeneration-adsorption cycle of zeolite, fluoride desorption and regeneration mechanism of zeolite defluorination was explained, and the adsorption performance and regeneration adsorption performance of zeolite defluorination were evaluated. The effects of phosphoric acid concentration, operating condition and specific surface area of zeolite and Si/Al ratio of zeolite on adsorption performance were investigated. Silicate molecule sieve shows strong adsorption capacity for fluoride (F-), and the adsorption capacity reached 352.46 mg/g under the optimal conditions. The Freundlich and Langmuir isotherm models for aluminosilicate MCM-41 and NaA zeolite which experimental data of F- adsorption on in phosphoric acid were fitted to investigate the adsorption mechanism. In the mechanism of anion adsorption, F- or SiF62- is bound by electrostatic adsorption of hydroxyl on the surface of adsorbent with anion adsorption. The adsorbed SiF62− ions can be regenerated when the environmental pH increases to value higher than that of zero charge point of zeolite. There is a competitive adsorption between OH– and F- with negative charge, which reduces the adsorption efficiency of adsorbent for F-. The NaA zeolite regenerated with NH3·H2O showed better fluorine re-adsorption performance.