scholarly journals EXCESSIVE ENERGY OF DETONATION NANODIAMONDS

Author(s):  
О.Б. Кудряшова ◽  
Е.А. Петров ◽  
А.А. Ветрова

Алмазы детонационного синтеза (ДНА) отличаются набором уникальных свойств, связанных с существенно неравновесными условиями их получения. Исследование их свойств продолжает оставаться актуальным в последние годы. Наноалмазы находят применение в полировальных составах, при модификации каучуков, резин, полимеров, металлов, создании новых композиционных материалов, в качестве добавок к топливу, адсорбентов и катализаторов, в биологии и в медицине. Интерес представляет энергетическая насыщенность наноалмазов. В данной работе проведено теоретическое и экспериментальное исследование избыточной энергии алмазов детонационного синтеза. Доказано, что ДНА обладают избыточной энергией по сравнению с природными и синтетическими алмазами. Рассмотрены возможные источники возникновения избыточной энергии. Исследованы образцы ДНА, полученные в различных условиях синтеза. На основе данных по термогравиметрическому анализу образцов ДНА представлены результаты анализа избыточной энергии образцов и ее зависимости от площади удельной поверхности частиц. Площадь удельной поверхности порошков получена методом БЭТ. Установлено, что чем больше поверхность частиц, тем больше тепла затрачено на её получение и выделилось при сжигании. Однако зависимость избыточной энергии от площади удельной поверхности частиц обратная. Экспериментально полученные нами величины плотности избыточной энергии на 1-2 порядка выше теоретически полученных значений для природных алмазов и для наноалмазов, что подтверждает наличие большой избыточной энергии ДНА. Такое свойство детонационных наноалмазов может найти применение в новых технологиях, в частности, при использовании наноалмазов в роли сорбентов. Detonation synthesis diamonds (DNDs) are distinguished by a set of unique properties associated with substantially nonequilibrium conditions for their production. The study of their properties continues to be relevant in recent years. Nanodiamonds are used in polishing compositions, in the modification of rubbers, polymers, metals, the creation of new composite materials, as additives to fuel, adsorbents and catalysts, in biology and medicine. The energy saturation of nanodiamonds is of interest. In this work, a theoretical and experimental study of the excessive energy of detonation synthesis diamonds is carried out. It has been proven that DNDs have excessive energy in comparison with natural and synthetic diamonds. Possible sources of excess energy are considered. Samples of DND obtained under various synthesis conditions have been investigated. Based on the data on thermogravimetric analysis of DND samples, the results of the analysis of the excessive energy of the samples and their dependence on the specific surface area of ​​the particles are presented. The specific surface area of ​​the powders was obtained by the BET method. It was found that the larger the surface of the particles, the more heat is spent on its production and released during combustion. However, the dependence of the excessive energy on the specific surface area of ​​the particles is inverse. The experimentally obtained values ​​of the excessive energy density are 1–2 orders of magnitude higher than the theoretically obtained values ​​for natural diamonds and for nanodiamonds, which confirms the presence of a large excess excessive of DND. This property of detonation nanodiamonds can find application in new technologies, in particular, when nanodiamonds are used as sorbents.

2020 ◽  
Vol 850 ◽  
pp. 199-206
Author(s):  
Marika Mosina ◽  
Janis Locs

The aim of this study is to summarize various synthesis routes of amorphous calcium phosphate (ACP), focusing on properties, especially Ca/P molar ratio and specific surface area (SSA) of obtained ACP. The effects of synthesis conditions on properties of final products are analysed and discussed.


2019 ◽  
Author(s):  
Dandan Fang ◽  
Xiaodong Li ◽  
Meishuai Zou ◽  
Xiaoyan Guo ◽  
Aijuan Zhang

To systematically explore the effects of the synthesis conditions on the porosity of hyper-cross-linked polymers (HCPs), a series of 9-phenylcarbazole HCPs (P1-P11) have been made by changing the dosage of cross-linker, the reaction temperature, catalyst usage and solvent dosage. Fourier transform infrared spectroscopy is utilized to characterize the structure of the obtained polymers. The TG analysis shows a high thermal stability of the HCPs. More importantly, comparative studies on the porous properties reveals that: molar ration of cross-linker and building block is the main factor of BET specific surface area; Improving reaction temperature or the usage of catalyst could increase the total pore volume greatly but sacrifice part of BET specific surface area; Fortunately changing solvent dosage could remedy this situation, that is slightly changing solvent dosage could simultaneously obtain high surface area and high total pore volume. The BET specific surface areas of P3 is up to 769 m2g-1 with narrow pore size distribution and the CO2 adsorption capacity of P11 is up to 52.4 cm3g-1 (273 K/1.00 bar).


2012 ◽  
Vol 2012 ◽  
pp. 1-10 ◽  
Author(s):  
Yosep Han ◽  
Hyung-Seok Kim ◽  
Hyunjung Kim

The degradation efficiency of methylene blue by TiO2nanoparticles, which were synthesized under different synthesis conditions (i.e., molar ratio of water and titanium tetraisopropoxide (TTIP), pH, and calcination temperature) in a sol-gel process, was systematically investigated. The results showed that increasing the molar ratio of water and TTIP led to the enhanced photocatalytic activity of TiO2nanoparticles, which were likely attributed to the increased specific surface area of TiO2nanoparticles synthesized with high molar ratio. The results were supported by the relative increase in the size of interaggregated pores of the aggregated TiO2nanoparticles. The best photocatalytic activity of TiO2nanoparticles was observed at acidic synthesis conditions; however, the results were not consistent with physical properties for the crystallinity and the crystallite size of TiO2nanoparticles but rather explained by the presence of abundant hydroxyl groups and water molecules existing on the surface of TiO2under acidic synthesis environments. Furthermore, methylene blue degradation experiments revealed that the photocatalytic activity of TiO2nanoparticles was maximized at the calcination temperature of 700°C. The trend was likely due to the combined effect of the anatase crystallinity which showed the highest value at 700°C and the crystallite size/specific surface area which did not excessively increase up to 700°C.


2021 ◽  
Vol 1027 ◽  
pp. 48-57
Author(s):  
Jiao Dai ◽  
Tao Fang Zeng ◽  
Yue Hui Hu

The article presents an investigation about effects of the synthesis conditions on the performance of silica aerogels. Tetraethyl orthosilicates (TEOS) were selected as the silicon source, and two acid-base catalysts were adopted to catalyze the reaction. CO2 supercritical drying was used to drive out the solvent of alcohols in the wet gels. Semi-transparent monolithic and crack-free SiO2 aerogels were successfully obtained. The solvents were prepared with a ratio of ethyl orthosilicate: absolute ethanol: H2O:HCl:NH3·H2O=1:3:5:3×10-3:4.8×10-3.The single effects of solution pH, water volume, and aging temperature synthesized were investigated. The aerogels were characterized with SEM, specific surface area analysis, thermal constant analysis, thermogravimetric analysis, Raman spectroscopy analysis, N2 adsorption-desorption analysis, and hydrophobic angle test. The as-synthesized silica aerogels have a porosity of 95.6%, a specific surface area of 756.9m2/g, an average pore diameter of 16.22nm, a density of 96.8kg/m2, and a thermal conductivity of 0.02W/(m· K). Hydrophobic silica aerogels were also obtained.


2011 ◽  
Vol 44 (9) ◽  
pp. 1687-1701 ◽  
Author(s):  
K. Baltakys ◽  
A. Eisinas ◽  
T. Dizhbite ◽  
L. Jasina ◽  
R. Siauciunas ◽  
...  

2010 ◽  
Vol 148-149 ◽  
pp. 920-923
Author(s):  
Yue Qing Zhao ◽  
Ying Hua Liang ◽  
Feng Feng Li ◽  
Hong Ping Chen ◽  
Xin Hua Liu ◽  
...  

CuO-CoO-MnO/SiO2 nanocomposite aerogels were prepared by using tetraethyl orthosilicate (TEOS) as Si source, and aqueous solution of Cu, Co and Mn acetates as transition metal sources via sol-gel process and supercritical drying (SCD) technique. The effect of synthesis conditions on gelation was investigated. The composition of the nanocomposite aerogels was characterized by electron dispersive spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS). The specific surface area of the nanocomposite aerogels was determined by the Brunauer-Emmett-Teller (BET) method. The results show that the range of optimal temperature for gelation is 30-45 °C, and the pH is 3.0-4.5. CuO-CoO-MnO/SiO2 nanocomposite aerogels are porous with a specific surface area of 384.9-700.6 m2/g. Compared to CO2 SCD, ethanol SCD is even favorable to the formation of aerogel with high specific surface area. The transition metals content in the nanocomposite aerogels can be controlled to be 0.71-13.77 at.%.


2008 ◽  
Vol 32 ◽  
pp. 13-16 ◽  
Author(s):  
X.J. Li ◽  
Xin Ouyang ◽  
Hong Hao Yan ◽  
G.L. Sun ◽  
F. Mo

In this paper, TiO2 nanopowders are produced by gas-phase detonation method. The powders are analyzed by X-ray diffraction (XRD), transmission electron microscopy (TEM) and specific surface area determination. The results indicate that the powders are mixed crystal of rutile and anatase, and have good dispersibility and high specific surface area. Also, the particle sizes of powders are between 40 to 200 nm which are spheroid and cube. The measurement data of detonation pressures shows that the reaction took place under a deflagration to detonation transition (DDT).


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