Acid Activation Process Research Articles

Biological Behavior of Osteoblast Cell and Apatite Forming Ability of the Surface Modified Ti Alloys.

Titanium as one kind of biomaterials comes in direct contact with the body, making evaluation of biocompatibility an important aspect to biomaterials development. Surface chemistry of titanium plays an important role in osseointegration. Different surface modification alters the surface chemistry and result in different biological response. In this study, three kinds of mixed acid solutions were used to treat Ti specimens to induce Ca-P formation. Following a strong mixed acid activation process, Ca-P coating successfully formed on the Ti surfaces in simulated body fluid. Strong mixed acid increased the roughness of the metal surface, because the porous and rough surface allows better adhesion between Ca-P coatings and substrates. After modification of titanium surface by mixed acidic solution and subsequently H2O2/HCL treatment evaluation of biocompatibility was conducted from hydroxyapatite formation by biomimetic process and cell viability on modified titanium surface. Nano-scale modification of titanium surfaces can alter cellular and tissue responses, which may benefit osseointegration and dental implant therapy. Results from this study indicated that surface treatment methods affect the surface morphology, type of TiO2 layer formed and subsequent apatite deposition and biological responses. The thermo scientific alamarblue cell viability assay reagent is used to quantitatively measure the viability of mammalian cell lines, bacteria and fungi by incorporating a rapid, sensitive and reliable fluorometric/colorimetric growth indicator, without any toxic and side effect to cell line. In addition, mixed acid treatment uses a lower temperature and shorter time period than widely used alkali treatment.

Operational parameter impact and back propagation artificial neural network modeling for phosphate adsorption onto acid-activated neutralized red mud

In this research the combination of neutralization activation and acid activation processes was employed to improve the physicochemical characters of red mud. In order to better understand the phosphate adsorption behaviors and further improve the phosphate adsorption performance of acid-activated neutralized red mud (AaN-RM), for the first time the impact of operational parameters on phosphate adsorption onto AaN-RM was systematically investigated, and back propagation artificial neural network (ANN) modeling was conducted. The results demonstrated that phosphate adsorption capacity of AaN-RM decreased with the enhancement of adsorbent dosage and the concentration of the competing ion (carbonate), while it increased with the increase of initial phosphate concentration and contact time. The optimal adsorption temperature and initial solution pH for phosphate adsorption onto AaN-RM were 50°C and 4.0, respectively. Moreover, a 6-10-1 feed forward ANN structure with trainlm algorithm was successfully constructed for predicting the phosphate removal by AaN-RM. The RMSE and R2 values for two subsets (training and validation subset, and testing subset) were 3.06 and 2.61, and 0.9932 and 0.9969, respectively. Furthermore, the importance analysis showed that contact time and initial phosphate concentration were the most influential parameters on phosphate removal by AaN-RM, the importance of which reached 24.64% and 22.16%, respectively.

Effect of acid activation of Saudi local clay mineral on removal properties of basic blue 41 from an aqueous solution

Local clay mineral from Khulais area, was activated at different acid to clay mineral ratios (in mass) at 90°C. The local clay mineral contained a major phase of smectite, in addition to kaolinite and quartz as impurities. Upon acid activation, structural changes in the treated clay minerals occurred for the smectite phase. The other phases were not affected as indicated by powder x-ray diffraction and Fourier transform infrared. Decrease in contents for Al2O3, MgO, Fe2O3, and Na2O, followed by a relative increase in SiO2 occurred. The acid activated clays exhibited lower cation exchange capacity, and higher specific surface areas. These changes in chemical compositions and other properties were related to the extent of the acid activation process. The acidity of local clay mineral was enhanced up to a certain level of activation, then it decreased gradually. A maximum specific surface area of 330m2/g was achieved at an acid to clay mineral ratio of 0.5. The increase of surface area was not the main key that controlled the removal capacity of the acid activated clays for basic blue-41 dye. The acid activation has improved the removal capacity of the raw clay mineral from 50mg/g to 73mg/g. This capacity was reduced with the extent of the acid activation, and was related to the destruction of the removal sites during the acid activation and not to the specific surface areas of the clay mineral. The recycling of spent acid activated clay was achieved by the sulfate radical oxidation, and about 85% of dye removal could be still retained after six recycle runs.

Insights into the remediation characterization of modified bentonite in minimizing organosulphur compounds from diesel fuel

In this work, physical and chemical characteristics of the raw, treated, and acid activated bentonite were investigated using XRD, FTIR, scanning electron microscopy (SEM), and differential thermal analysis (DTA)/thermogravimetry (TG) analysis and surface area and porosity determination techniques. The organosulphur compounds (ORS) uptake was slightly affected by the particle size indicating that the removal of ORS mainly occurred on the external surface of the modified bentonite samples. The acid activation process enhanced the adsorptive efficiency of the bentonite sample through increasing both the surface area and the pore volume, in addition to the release of a considerable amount of interlayer cations of the clay.

Biomimetic Deposition of Hydroxyapatite by Mixed Acid Treatment of Titanium Surfaces.

A simple chemical method was established for inducing bioactivity of Ti metal. In the present study, two kinds of mixed acid solutions were used to treat Ti specimens to induce Ca-P formation. Following a strong mixed acid activation process, Ca-P coatings successfully formed on the Ti surfaces in the simulated body fluid. Strong mixed acid etching was used to increase the roughness of the metal surface, because the porous and rough surfaces allow better adhesion between Ca-P coatings and substrate. Nano-scale modification of titanium surfaces can alter cellular and tissue responses, which may benefit osseointegration and dental implant therapy. Some specimens were treated with a 5 M NaOH aqueous solution, and then heat treated at 600 °C in order to form an amorphous sodium titanate layer on their surface. This treated titanium metal is believed to form a dense and uniform bone-like apatite layer on its surface in a simulated body fluid (SBF). This study proved that mixed acid treatment is not only important for surface passivation but is also another bioactive treatment for titanium surfaces, an alternative to alkali treatment. In addition, mixed acid treatment uses a lower temperature and shorter time period than alkali treatment.

The Effects of Acid Activation on the Thermal Properties of Polyvinylpyrrolidone and Organoclay Composites

The thermal stabilities of polyvinylpyrrolidone-organoclays or organo-acid-activated clay composites prepared by chemical exchange reactions were assessed. The raw clay mineral was acid-activated prior to expansion by cetyltrimethylammonium surfactants. The acid activation process affected the intercalated amount of cetyltrimethylammonium cations in the resulting organoclays and, thus, the amount of polyvinylpyrrolidone in the composite. The content of cetyltrimethylammonium cations decreased with the extent of acid activation. The organophilic modification of the clay mineral was an important step in the intercalation of the polyvinylpyrrolidone molecules and, thus, in the expansion of the silicate sheets from 3.80 nm to 4.20 nm. The composites exhibited better crystalline order with intense reflections at lower angles. The thermal stability of organoclays, acid-activated clays, and composites was studied using thermogravimetric analysis andin situX-ray diffraction. The decomposition of intercalated surfactants occurred at lower temperatures relative to the neat surfactant salt, and the basal spacing of the organoclays (or acid-activated clays) shrunk to 2.0 nm at 215°C. However, the basal spacing of composites exhibited better stability and collapsed to 2.0 nm at 300°C. This type of material could offer an alternative stable product for engineering purposes in the design of new composites.

High-level expression of a manganese superoxide dismutase (PoMn-SOD) from Pleurotus ostreatus in Pichia pastoris.

The full-length cDNA of Pleurotus ostreatus superoxide dismutase (PoMn-SOD) was cloned and successfully expressed by using the pPIC9K vector under the control of alcohol oxidase 1 promoter with a secretion signal peptide (α-factor) in Pichia pastoris. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and Western blotting demonstrated that recombinant PoMn-SOD, a 21.8 kDa protein, was secreted into the culture medium. Nondenaturing PAGE experiments confirmed that recombinant PoMn-SOD was secreted in a functionally active form and the expression system did not require any acid activation process. The factors affecting the expression level were optimized in shaking flask cultures. The maximum enzyme activity (156.9 U/mg) was observed under the following conditions: Initial medium pH was 6.0, induction time point was at the 6th day, and methanol concentration was 0.7 % (v/v). This was the first report on secretory expression of recombinant PoMn-SOD in P. pastoris, which might provide a reference for further practical applications.

Metallization of Iron Powders by Autocatalytic Copper Plating Process

The metalization of iron powders was studied by autocatalytic copper plating based on copper methane sulphonic acid and new activation process uses TiB2 and chloroplatinic acid. The deposition of copper particles on iron powders was confirmed by X-ray diffraction (XRD) and scanning electron microscope (SEM) studies. Diallyl thiourea and 2-mercapto benzotriazole were found as stabilizers in autocatalytic bath to obtain copper coatings on iron powders. The stabilization effects of thio compounds were screened by weight gain, anodic, cathodic polarization, and impedance methods. The influence of adsorption of the stabilizers on iron powder was established by quantum mechanical indices like EHOMO, ELUMO, energy gap (ΔE), and dipole moment (µ).

A Thermolabile Aspartic Proteinase from Mucor mucedo DSM 809: Gene Identification, Cloning, and Functional Expression in Pichia pastoris

In this study, the cDNA encoding the aspartic proteinase of Mucor mucedo DSM 809 has been identified by RNA ligased-mediated and oligo-capping rapid amplification of cDNA ends (RACE) technique. The gene contained an open reading frame of 1,200 bp and encoded for a signal peptide of 21 amino acid residues. Two N-glycosylation sites were observed within the identified sequence. The proteinase gene was cloned into the vector pGAPZαA and expressed in Pichia pastoris X-33 for the first time. The protein has been secreted in functionally active form into the culture medium. The expression system does not require any acid activation process. The factors affecting the expression level were optimized in shaking flask cultures. Maximum enzyme production was observed with an initial medium pH of 3.5 at 20 °C and 220 rpm shaking speed utilizing 4 % glucose as a carbon and energy source. The enzyme was purified with cation exchange chromatography and further studies revealed that the enzyme was secreted in glycosylated form. The purified enzyme exhibited remarkable sensitivity to thermal treatment and became completely inactivated after incubation at 55 °C for 10 min. These results indicated that the recombinant proteinase could be considered as a potential rennet candidate for the cheese-making industry.

Response Surface Optimization for Activation of Bentonite Using Microwave Irradiation

AbstractMicrowave irradiation as a means for heating bentonites during acid activation has been investigated in the past but it has never been optimized for industrial applications. The purpose of this study was to apply a factorial 23 experimental design to a Serbian bentonite in order to determine the influence of microwave heating on the acid-activation process. The effect of acid activation under microwave irradiation on the textural and structural properties of bentonite was studied as a model reaction. A mathematical, second-order response surface model (RSM) was developed with a central composite design that incorporated the relationships among various process parameters (time, acid concentration, and microwave heating power) and the selected process response of specific surface area of the bentonite. The ranges of values for the process parameters chosen were: time, 5–21 min; acid concentration, 2–7 M; and microwave heating power, 63–172 W. The effect of individual variables and their interaction effects on the textural and structural properties of the bentonite were determined. Statistical analysis showed that the duration of microwave irradiation was less significant than the other two factors. The model showed that increasing the time and acid concentration improved the textural properties of bentonites, resulting in increased specific surface area. This model is useful for setting an optimum value of the activation parameters for achieving the maximum specific surface area. An optimum specific surface area of 142 m2g−1 was achieved with an acid concentration of 5.2 M, activation time of 7.4 min, and microwave power of 117 W.

Response surface optimisation for activation of bentonite with microwave irradiation

In this study, the statistical design of the experimental method was applied on the acid activation process of bentonite with microwave irradiation. The influence of activation parameters (time, acid normality and microwave heating power) on the selected process response of the activated bentonite samples was studied. The specific surface area was chosen for the process response, because the chemical, surface and structural properties of the activated clay determine and limit its potential applications. The relationship of various process parameters with the specific surface area of bentonite was examined. A mathematical model was developed using a second-order response surface model (RSM) with a central composite design incorporating the above mentioned process parameters. The mathematical model developed helped in predicting the variation in specific surface area of activated bentonite with time (5-21 min), acid normality (2-7 N) and microwave heating power (63-172 W). The calculated regression models were found to be statistically significant at the required range and presented little variability. Furthermore, high values of R2 (0.957) and R2 (adjusted) (0.914) indicate a high dependence and correlation between the observed and the predicted values of the response. These high values also indicate that about 96% of the result of the total variation can be explained by this model. In addition, the model shows that increasing the time and acid normality improves the textural properties of bentonites, resulting in increased specific surface area. This model also can be useful for setting an optimum value of the activation parameters for achieving the maximum specific surface area. An optimum specific surface area of 142 m2g-1 was achieved with an acid normality of 5.2 N, activation time of 7.38 min and microwave power of 117 W. Acid activation of bentonite was found to occur faster with microwave irradiation than with conventional heating. Microwave-assisted processes have the potential to develop into a cost efficient route for acid activation of bentonite.

Binary component sorption of Cu(II) and Pb(II) with activated carbon from Eucalyptus camaldulensis Dehn bark

The objective of this work is to illustrate the potential in the use of activated carbon in the binary component sorption of copper and lead ions. Eucalyptus bark was used as a precursor for the activated carbon which was prepared through the phosphoric acid activation process. This activated carbon was then used for the sorption of copper and lead ions. The quantity of the metal ions in the solution was measured with the Flame & Graphite Furnace Atomic Adsorption Spectrophotometer. The results indicated that the optimal pH for sorption was 5. The maximum sorption capacities for Cu(II) and Pb(II) were 0.45 and 0.53 mmol g −1. Carboxylic, amine and amide groups were found to involve in the sorptions of Cu(II) and Pb(II). A major mechanism for the uptake of both heavy metals was proven not to be ion exchange but adsorption. In binary component sorptions, activated carbon still could sorb Pb(II) in a greater amount than Cu(II). However, the presence of the secondary metal ions suppressed the sorption of the primary metal ions. There seemed to have a linear inverse dependency between the sorption capacity and the concentration of the secondary metal ion.

One-step pickling-activation before magnesium alloy plating

A one-step pickling-activation process was proposed as an environmental friendly pretreatment method in phosphate-permanganate solution before electroplating on magnesium alloys. The effects of pickling-activation on qualities of coating were assessed by adhesion and porosity testing of copper plating. The interfacial reactions between specimen and solution were analyzed with SEM, EDX and XRD. The results show that the developed process of pickling-activation can equalize the potentials on substrate surface. The compacted zinc film can be obtained by zinc immersion after treating magnesium alloy in the pH 4–6 phosphate-permanganate solution for 3–5 min. The adhesion and corrosion resistance of copper plating are enhanced. The one-step pickling-activation can replace the existing two-step process of acid pickling and activation which contains a great deal of chromium and fluorine. The procedure of surface pretreatment is simplified and the production environment is improved.

Chemical and surface properties of longan seed activated charcoal

In order to study the chemical compositions and surface properties of longan seed (Daw) activated charcoal, the influences of a phosphoric acid activation process was investigated before and after carbonization. Carbonization temperatures in this study were ranged from 400 - 800°C. It was found that higher carbonization temperatures resulted in a high amount of organic carbon and ashes, while the volatile matters were reversely lowered at higher carbonization temperatures. For carbonization temperatures studied between 400 - 800°C, the activated charcoal possessed a higher iodine number in comparison to the longan seed activated charcoal. Also, the longan seed activated charcoal, being activated by phosphoric acid prior to carbonization, had a greater iodine number than the one being activated by phosphoric acid and then undergoing carbonization. The highest iodine number was obtained from longan seed activated charcoal carbonized at 500°C. Surface properties of activated charcoal showed a loss of its side chains and inherent functionalities while being run through high carbonization temperatures, however, the P-O-C remained intact, especially under carbonization temperatures lower than 700°C. The surface images of the activated charcoal showed more rough. Key words: Longan seed, carbonization, charcoal, activated charcoal, phosphoric acid.

Statistical design of experiments of acid activation of smectite clay from Serbia and its bleaching capacity

BACKGROUND: Serbian smectite clay has been activated using a response surface method with central composite design. Because, among the criteria of an edible oil, colour is the most important factor in the commercial value of the oil, and since the colour is due to the presence of pigments such as β-carotene in the crude oil, acid-activated clay was used for decolourisation of soybean oil. RESULTS: The effects of five parameters, namely, temperature, time, acid strength, solid/liquid ratio and stirring speed, on the process of acid activation of the clay and its bleaching capacity were determined using a statistical model. The results indicated that all parameters were significant factors in the bleaching capacity of acid-activated clay, and a quadratic polynomial equation for bleaching capacity was obtained by multiple regression analysis. The optimal bleaching capacity was estimated to be 96.61% for an experimental run under the following conditions: activation temperature 80 °C, HCl concentration 4.78 mol L−1, stirring speed 450 rpm, solid/liquid ratio 1:4.5 and activation time 2.81 h. CONCLUSIONS: The central composite design, regression analysis and response surface method were effective in identifying the optimal conditions for bleaching capacity of acid-activated smectite. Copyright © 2008 Society of Chemical Industry

Formation process of bright spots on surfaces of die-cast magnesium alloy components after chemical conversion treatment

A component for a mobile phone, made of AZ91D alloy, is manufactured by die cast. After chemical conversion treatment, it was found that there were some bright spots on the component surface. The formation mechanism of the bright spots was studied by means of SEM and metallgraphic microscope. The corrosion resistance of coatings was measured by potentiodynamic polarization test. The reason of bright spots formation is that the coarse primary α is dissolved into a dent during acid activation process because of little netted β and little aluminum. Besides, the coatings on bright spots are thin, the dimensions of primary α grains are large, and the surfaces are smooth relatively, so they are prone to reflecting light and become bright spots.

Formation of TiO<sub>2</sub> Coating Layer on the Surface Treated Ti Alloys

Pure Titanium alloys are superiorities of biocompatibility, mechanical properties and chemical stability. The biocompatibility of Ti alloy is related to the surface effect. In this study, Ti Alloys were treated by alkali and acid activation process. And through the sol coating layer, biocompatibility were investigated. Consequently, it appeared that the porous layer was generated on the surface of alloy by surface treatment and sol coating process. It was found that with surface treatment on Ti alloy, the formation speed of porous was much quicker compared with those ones without treatment. Therefore, the biocompatibility was improved.

Process improvement approach to the acid activation of smectite using factorial and orthogonal central composite design methods

The purpose of this study was to determine the effective operating parameters and the optimum operating conditions of an acid activation process within the framework of improvement of the process. Full two-level factorial and orthogonal central composite design methods were used successively. The examined parameters were the main and interaction effects of temperature, leaching time, acid normality, solid-to-liquid ratio and stirring rate. The selected process response was the leaching yield of the MgO content because Mg is the element most readily removed from the octahedral sheet, which affects the tendency for activation. Statistical regression analysis and analysis of variance were applied to the experimental data to develop a predictive model, which revealed that temperature, leaching time and acid normality exert the strongest influence on the specific surface area of smectite, whilst the solid-to-liquid ratio and the stirring rate have a secondary effect. Furthermore, the highest leaching yield of MgO was found to be 41.86 %, which is responsible for the increase in the specific surface area of up to 221 m2 g-1.

Evidence for 26 distinct acyl-coenzyme A synthetase genes in the human genome

Acyl-coenzyme A synthetases (ACSs) catalyze the fundamental, initial reaction in fatty acid metabolism. "Activation" of fatty acids by thioesterification to CoA allows their participation in both anabolic and catabolic pathways. The availability of the sequenced human genome has facilitated the investigation of the number of ACS genes present. Using two conserved amino acid sequence motifs to probe human DNA databases, 26 ACS family genes/proteins were identified. ACS activity in either humans or rodents was demonstrated previously for 20 proteins, but 6 remain candidate ACSs. For two candidates, cDNA was cloned, protein was expressed in COS-1 cells, and ACS activity was detected. Amino acid sequence similarities were used to assign enzymes into subfamilies, and subfamily assignments were consistent with acyl chain length preference. Four of the 26 proteins did not fit into a subfamily, and bootstrap analysis of phylograms was consistent with evolutionary divergence. Three additional conserved amino acid sequence motifs were identified that likely have functional or structural roles. The existence of many ACSs suggests that each plays a unique role, directing the acyl-CoA product to a specific metabolic fate. Knowing the full complement of ACS genes in the human genome will facilitate future studies to characterize their specific biological functions.

Characterization of products obtained by acid leaching of Fe-bentonite

AbstractThis study focused on the structure and physical properties of acid-treated bentonite L45 from the Lieskovec deposit (Slovakia). New applications of near infrared and visible spectroscopies were used to follow Fe-montmorillonite dissolution and layer-charge reduction. Progressive dissolution of L45 results in the formation of a protonated amorphous silica phase. The OH overtone at 7312 cm–1 revealed the creation of Si–OH groups in the mildly treated samples. The area of the Si–O–Moct band, as obtained by a peak-fitting procedure, is a sensitive indicator of the changes in the octahedral sheets. Ultraviolet-visible (UV-VIS) spectroscopy of the smectite dispersions with methylene blue (MB) is an efficient method for controlling the acid activation process of bentonites. The results reveal that acid treatment causes a substantial layer-charge reduction, probably due to prevailing dissolution of MgO4(OH)2 polyhedra in the octahedral sheets. The layer-charge reduction is proportional to the structural changes and to the extent of mineral decomposition upon acid treatment.