scholarly journals Influence of Concentration and Activation on Hydrogen Peroxide Diffusion through Dental TissuesIn Vitro

2013 ◽  
Vol 2013 ◽  
pp. 1-5 ◽  
Author(s):  
Carlos R. G. Torres ◽  
Cristiane S. Souza ◽  
Alessandra B. Borges ◽  
Maria Filomena R. L. Huhtala ◽  
Taciana M. F. Caneppele
Keyword(s):  
Hydrogen Peroxide ◽  
Chemical Activation ◽  
Video Camera ◽  
Diffusion Time ◽  
Light Activation ◽  
Anova Analysis ◽  
Dental Tissues ◽  
Internal Cavities ◽  
Physical And Chemical ◽  
Bleaching Gels

This study evaluated the effect of physical and chemical activation on the diffusion time of different concentrations of hydrogen peroxide (HP) bleaching agents through enamel and dentin. One hundred and twenty bovine cylindrical specimens were divided into six groups (n=20): 20% HP ; 20% HP with light activation; 20% HP with manganese gluconate; 35% HP; 35% HP with light activation; and 35% HP with manganese gluconate. The specimens were fixed over transparent epoxy wells with internal cavities to simulate a pulpal chamber. This chamber was filled with an enzymatic reagent to simulate pulpal fluid. The bleaching gels were applied on enamel surface and the image of the pulpal fluid was captured by a video camera to monitor the time of peroxide penetration in each specimen. ANOVA analysis showed that concentration and type of activation of bleaching gel significantly influenced the diffusion time of HP (P<0.05). 35% HP showed the lowest diffusion times compared to the groups with 20% HP gel. The light activation of HP decreased significantly the diffusion time compared to chemical activation. The highest diffusion time was obtained with 20% HP chemically activated. The diffusion time of HP was dependent on activation and concentration of HP. The higher concentration of HP diffused through dental tissues more quickly.

A comparative study of physical and chemical activation of rice straw derived biochar to enhance Zn+2 adsorption

2021 ◽  
pp. 100774
Author(s):  
Anil Kumar Sakhiya ◽  
Paramjeet Baghel ◽  
Abhijeet Anand ◽  
Virendra Kumar Vijay ◽  
Priyanka Kaushal
Keyword(s):  
Comparative Study ◽  
Rice Straw ◽  
Chemical Activation ◽  
Physical And Chemical

Comparative Study of Different Activation Treatments for the Preparation of Activated Carbon: A Mini-Review

2017 ◽  
Vol 100 (3) ◽  
pp. 299-312 ◽  
Author(s):  
Muhammad Imran Din ◽  
Sania Ashraf ◽  
Azeem Intisar
Keyword(s):  
Activated Carbon ◽  
Comparative Study ◽  
Raw Materials ◽  
Chemical Activation ◽  
Comparative Approach ◽  
Adsorption Mechanisms ◽  
Temperature Activation ◽  
Activation Conditions ◽  
Physical And Chemical ◽  
Characterisation Techniques

In this review, various methods of preparation of activated carbon from agricultural and commercial waste material are reviewed. In addition, we also discuss various activation treatments using a comparative approach. The data are organised in tabulated form for ease of comparative study. A review of numerous characterisation techniques is also provided. The effect of time and temperature, activation conditions, carbonisation conditions and impregnation ratios are explained and several physical and chemical activation treatments of raw materials and their impact on the micro- and mesoporous volumes and surface area are discussed. Lastly, a review of adsorption mechanisms of activated carbon (AC) is also provided.

Influence of Hydrogen Peroxide Bleaching Gels on Color, Opacity, and Fluorescence of Composite Resins

2012 ◽  
Vol 37 (5) ◽  
pp. 526-531 ◽  
Author(s):  
CRG Torres ◽  
CF Ribeiro ◽  
E Bresciani ◽  
AB Borges
Keyword(s):  
Hydrogen Peroxide ◽  
Composite Resin ◽  
Color Change ◽  
Composite Resins ◽  
Control Group ◽  
Peroxide Bleaching ◽  
Color Changes ◽  
Tukey Test ◽  
Bleaching Gels ◽  
Bleaching Treatment

SUMMARY The aim of the present study was to evaluate the effect of 20% and 35% hydrogen peroxide bleaching gels on the color, opacity, and fluorescence of composite resins. Seven composite resin brands were tested and 30 specimens, 3-mm in diameter and 2-mm thick, of each material were fabricated, for a total of 210 specimens. The specimens of each tested material were divided into three subgroups (n=10) according to the bleaching therapy tested: 20% hydrogen peroxide gel, 35% hydroxide peroxide gel, and the control group. The baseline color, opacity, and fluorescence were assessed by spectrophotometry. Four 30-minute bleaching gel applications, two hours in total, were performed. The control group did not receive bleaching treatment and was stored in deionized water. Final assessments were performed, and data were analyzed by two-way analysis of variance and Tukey tests (p&lt;0.05). Color changes were significant for different tested bleaching therapies (p&lt;0.0001), with the greatest color change observed for 35% hydrogen peroxide gel. No difference in opacity was detected for all analyzed parameters. Fluorescence changes were influenced by composite resin brand (p&lt;0.0001) and bleaching therapy (p=0.0016) used. No significant differences in fluorescence between different bleaching gel concentrations were detected by Tukey test. The greatest fluorescence alteration was detected on the brand Z350. It was concluded that 35% hydrogen peroxide bleaching gel generated the greatest color change among all evaluated materials. No statistical opacity changes were detected for all tested variables, and significant fluorescence changes were dependent on the material and bleaching therapy, regardless of the gel concentration.

Research of plastic ice, mineral formations and air of multi-frozen karst cave Heetey in Transbaikalia

2020 ◽  
Vol 26 (7) ◽  
pp. 33-43
Author(s):  
I. Zheleznyak ◽  
◽  
S. Tsyrenzhapov ◽  
А. Gurulev ◽  
◽  
...  
Keyword(s):  
Radon Concentration ◽  
Maximum Level ◽  
Natural Environments ◽  
Geochemical Background ◽  
Karst Cave ◽  
Ice Volume ◽  
Internal Cavities ◽  
The Subject ◽  
Microwave Radiometers ◽  
Physical And Chemical

Heetey caves (“cold” and “warm”) which are located in the southern part of the permafrost in the Transbaikal Region have been chosen as the object of the research in the article. The subject is the physical and chemical parameters of the object. The results of the research in the “cold” Heetey cave are given in more detail. The following methods of this object research were chosen: study of the chemical composition of cave air using a chromatograph; radar survey of the cave grotto in the centimeter range; measurement of its own radio-thermal radiation using microwave radiometers. As a result of the research, the following results were obtained. The article provides information on the natural conditions that determine the dependence of the state of natural environments in the Heetey karst caves. The characteristics of occurrence and composition conditions of the natural environments of a karst cave (geological, cryogenic, atmospheric, groundwater) are given, taking into account the cryogenesis of their formation, transformation and influence on the cave air composition. A description of a rare low-temperature mineral, aragonite, which was first discovered in the cave and which is transformed into calcite over time is described. It is shown that the ice cover at the bottom of the cave has a layered structure, which is due to the seasonal ingress of surface water into the cave. The results of measurements of the surface air composition above the rocks’ surface and in caves, namely the content of oxygen, nitrogen, carbon dioxide, explosive gases – methane and hydrogen, mercury vapors are presented. A previously unknown fact of an increased geochemical background of radon concentration has been established. The most probable reasons for the formation and increased background of radon concentration are indicated. Microwave radiometric measurements have shown that there has been warming inside the cave over the past decade. This fact is associated with a general warming of the climate in Transbaikalia, as well as with an increase in the number of visits to caves by unorganized tourists. With the use of a 10 GHz nanosecond radar, hidden internal cavities were discovered in the roof of the cave, which can further lead to its destruction. The prints on the walls of the cave (in its lower part) show that the level of the ice sheet in 2015 is lower than its maximum level (1990) by 10 cm, which corresponds to a loss of ice volume of 12...15 m3 per year

scholarly journals Influence of chemical agents on the surface area and porosity of active carbon hollow fibers

2011 ◽  
Vol 76 (9) ◽  
pp. 1283-1294 ◽  
Author(s):  
Ljiljana Kljajevic ◽  
Vladislava Jovanovic ◽  
Sanja Stevanovic ◽  
Zarko Bogdanov ◽  
Branka Kaludjerovic
Keyword(s):  
Hydrogen Peroxide ◽  
Surface Area ◽  
Active Carbon ◽  
Chemical Activation ◽  
Hollow Fibers ◽  
Activation Process ◽  
X Ray Diffraction ◽  
Hydrogen Phosphate ◽  
Small Surface ◽  
X Ray

Active carbon hollow fibers were prepared from regenerated polysulfone hollow fibers by chemical activation using: disodium hydrogen phosphate 2-hydrate, disodium tetraborate 10-hydrate, hydrogen peroxide, and diammonium hydrogen phosphate. After chemical activation fibers were carbonized in an inert atmosphere. The specific surface area and porosity of obtained carbons were studied by nitrogen adsorption-desorption isotherms at 77 K, while the structures were examined with scanning electron microscopy and X-ray diffraction. The activation process increases these adsorption properties of fibers being more pronounced for active carbon fibers obtained with disodium tetraborate 10-hydrate and hydrogen peroxide as activator. The obtained active hollow carbons are microporous with different pore size distribution. Chemical activation with phosphates produces active carbon material with small surface area with but with both mesopores and micropores. X-ray diffraction shows that besides turbostratic structure typical for carbon materials, there are some peaks which indicate some intermediate reaction products when sodium salts were used as activating agent. Based on data from the electrochemical measurements the activity and porosity of the active fibers depend strongly on the oxidizing agent applied.

scholarly journals Preparation and Characterization of Activated Carbon from Waste Rubber Tires: A Comparison between Physical and Chemical Activation

2015 ◽  
Vol 1107 ◽  
pp. 347-352 ◽  
Author(s):  
Collin Glen Joseph ◽  
Duduku Krishniah ◽  
Yun Hin Taufiq-Yap ◽  
Masnah Massuanna ◽  
Jessica William
Keyword(s):  
Activated Carbon ◽  
Automobile Industry ◽  
Chemical Activation ◽  
Waste Product ◽  
Physical Activation ◽  
Activation Process ◽  
Waste Rubber ◽  
Percentage Yield ◽  
Static Conditions ◽  
Physical And Chemical

Abstract. Waste tires, which are an abundant waste product of the automobile industry, were used to prepare activated carbon by means of physical and chemical activation. A two-stage process was used, with a semi-carbonization stage as the first stage, followed by an activation stage as the second stage.All experiments were conducted in a laboratory-scale muffle furnace under static conditions in a self-generated atmosphere. During this process, the effects of the parametric variables of semi-carbonization time (for the physical activation process), activation time and temperature and impregnation ratios (for the chemical activation process) on the percentage yield were studied and compared. Varying these parametric variables yielded interesting results, which in turn affected the adsorption process of 2,4-DCP, which was the simulated pollutant in aqueous form. The optimized percentage yields of activated carbon that were obtained were 41.55% and 44.88% ofthe physical and chemical activation treatment processes respectively.Keywords: Physical activation, chemical activation, waste rubber tires, 2,4-dichlorophenol, activated carbon.

AKTIVASI KIMIA-FISIK LIMBAH SERUTAN ROTAN MENJADI KARBON AKTIF

2014 ◽  
Vol 14 (1) ◽  
pp. 82-98
Author(s):  
Andy Mizwar
Keyword(s):  
Activated Carbon ◽  
Water Content ◽  
Iodine Number ◽  
Surface Area ◽  
Chemical Activation ◽  
Raw Material ◽  
Physical Activation ◽  
Fixed Carbon ◽  
Impregnation Time ◽  
Physical And Chemical

Limbah rotan dari industri kerajinan dan mebel berpotensi untuk dijadikan sebagai bahan baku pembuatan karbon aktif karena memiliki kandungan holoselulosa dan kadar karbon yang tinggi. Penelitian ini bertujuan untuk menganalisis efektifitas dari aktivasi kimia menggunakan larutan natrium klorida (NaCl) yang dilanjutkan dengan aktivasi fisik dalam pembuatan karbon aktif berbahan dasar  limbah serutan rotan. Pembuatan karbon aktif diawali dengan proses karbonisasi pada suhu 250°C selama 1 jam. Selanjutnya aktivasi kimia menggunakan larutan NaCl dengan variasi konsentrasi 10%, 15% dan 20% serta waktu perendaman selama 10, 15 dan 20 jam. Aktivasi fisik dilakukan dengan pembakaran pada suhu 700°C selama 30 menit. Analisis karakteristik fisik-kimia karbon aktif mengacu pada SNI 06-3730-95, meliputi kadar air, fixed carbon, dan iodine number, sedangkan perhitungan luas permukaan spesifik karbon aktif dilakukan dengan Metode Sears. Hasil penelitian ini menunjukkan bahwa kondisi optimum aktivasi kimia terjadi pada konsentrasi NaCl 10% dan lama perendaman 10 jam dengan hasil analisis kadar air 2.90%, fixed carbon 72.70%, iodine number 994.59 mg/g dan luas permukaan 1587.67 m²/g. Peningkatan fixed carbon, iodine number dan luas permukaan karbon aktif berbanding terbalik dengan peningkatan konsentrasi NaCl dan lama waktu perendaman, sedangkan peningkatan kadar air pada karbon aktif berlaku sebaliknya. Rattan waste from handicraft and furniture industry could potentially be used as raw material of activated carbon due to high content of holoselulosa and carbon. This paper investigates the effectiveness of chemical activation using sodium chloride (NaCl) followed by physical activation in the making of activated carbon-based on rattan shavings waste. Preparation of the activated carbon began with the carbonization process at 250°C for 1 hour. Furthermore chemical activation using a variation of NaCl concentrations 10%, 15% and 20% as well as the time of immersion 10, 15 and 20 hours. Physical activation was done by burning at 700°C for 30 minutes. Analysis of the physical and chemical characteristics of the activated carbon was referred to the SNI 06-3730-95, including of moisture content, fixed carbon and iodine number, while the calculation of the specific surface area was done by the Sears’s method. The results of this study showed that the optimum conditions of chemical activation occurred in impregnation by NaCl 10% for 10 hours. The water content, fixed carbon, iodine number and surface area of activated carbon was 2.90%, 72.70%, 994.59 mg/g and 1587.67 m²/g  respectively. The increase values of fixed carbon, iodine number, and surface area was inversely proportional to the increase of NaCl concentration and the length of impregnation time, while the increase of water content applied vice versa.

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