Formation of Nanocrystalline SiC Powder from Chlorine-Containing Polycarbosilane Precursors

1999 ◽  
Vol 581 ◽  
Author(s):  
Brian S. Mitchell ◽  
Haoyue Zhang ◽  
Martin Ade ◽  
Dirk Kurtenbach ◽  
Eberhard Müller

ABSTRACTNanocrystalline β-SiC particulates with a grain size range of 5-20 nm were prepared by heating a pre-pyrolyzed, chlorine-containing polysilane/polycarbosilane (PS/PCS) to 1600°C. The transformation from the pre-pyrolyzed PS/PCS to nanocrystalline SiC was investigated by differential thermal analysis (DTA), thermogravimetric analysis (TGA), X-ray diffraction (XRD), mass-spectrometry and infrared spectroscopy. The results indicated that the nanocrystalline P-SiC was formed by the crystallization of the PS/PCS random network, and crosslinking of Si-Si, Si-Cl, and Si-CH2-Si bonds. The TEM observation showed that SiC particulates consist of equiaxed, randomly oriented, ultrafine grains.

2016 ◽  
Vol 5 (1) ◽  
pp. 6
Author(s):  
Budi Setiawan ◽  
Erizal Zaini ◽  
Salman Umar

Sebuah penelitian tentang sistem dispersi padat dari asiklovir dengan poloxamer 188 telah dilakukan formulasi dengan pencampuran secara fisika dengan rasio 1 : 1, 1 : 3, 1 : 5 dan dispersi padat 1 : 1, 1 : 3, 1 : 5 dan penggilingan 1:1 sebagai pembanding. Dispersi padat dibuat menggunakan metode pencairan (fusi), yang digabung dengan poloxamer 188 pada hotplate kemudian asiklovir dimasukkan ke dalam hasil poloxamer 188 lalu di kocok hingga membentuk masa homogen. Semua formula yang terbentuk termasuk asiklovir poloxamer 188 murni dianalisis karakterisasinya dengan Differential Thermal Analysis (DTA), X-ray Diffraction, Scanning Electron Microscopy (SEM), dan Fourier Transform Infrared (FTIR), kemudian pengambilan dilakukan  (penentuan kadar) mengunakan spektrofotometer UV pada panjang gelombang 257,08 nm dan uji laju disolusi dengan aquadest bebas CO2 menggunakan metode dayung. Hasil pengambilan  (penentuan kadar) menunjukkan bahwa semua formula memenuhi persyaratan farmakope Amerika edisi 30 dan farmakope Indonesia edisi 4 yaitu 95-110%. Sedangkan hasil uji laju disolusi untuk campuran fisik 1: 1, dan dispersi padat 1: 1, dan penggilingan 1: 1 menunjukkan peningkatan yang nyata dibandingkan asiklovir murni. Hal ini juga dapat dilihat dari hasil perhitungan statistik  menggunakan analisis varian satu arah  SPSS 17.


Minerals ◽  
2021 ◽  
Vol 11 (5) ◽  
pp. 440
Author(s):  
Fabiana Pereira da Costa ◽  
Jucielle Veras Fernandes ◽  
Luiz Ronaldo Lisboa de Melo ◽  
Alisson Mendes Rodrigues ◽  
Romualdo Rodrigues Menezes ◽  
...  

Natural stones (limestones, granites, and marble) from mines located in northeastern Brazil were investigated to discover their potential for use in civil construction. The natural stones were characterized by chemical analysis, X-ray diffraction, differential thermal analysis, and optical microscopy. The physical-mechanical properties (apparent density, porosity, water absorption, compressive and flexural strength, impact, and abrasion) and chemical resistance properties were also evaluated. The results of the physical-mechanical analysis indicated that the natural stones investigated have the potential to be used in different environments (interior, exterior), taking into account factors such as people’s circulation and exposure to chemical agents.


1992 ◽  
Vol 267 ◽  
Author(s):  
Ana M De Andres ◽  
Isabel MuÑOZ

ABSTRACTNineteen roman ceramic sherds found near Salobreña (Granada, Spain), in the western coast of the Mediterranean Sea, as well as different ceramic clays from the surroundingsare studied. Both clays and ceramic sherds are characterizad by X-ray diffraction and spectrometry, differential thermal analysis, and scanning electron and optical microscopies. A good number of the ceramic pieces, among which some “Terrae Sigillatae”, have a composition similar to that of the local clays and, thus, have been probably manufactured at Salobreña. Only a few of them have a foreign origin. For most of them, the firing temperature was about 800-850 °C, although some have been produced at 900-1000 °C, and some others at 1000-1100 °C. It is concluded that Salobreña appearsto have been an important settlement just in the third century of the Christian era.


1992 ◽  
Vol 7 (7) ◽  
pp. 1751-1761 ◽  
Author(s):  
J. Eckert ◽  
J.C. Holzer ◽  
C.E. Krill ◽  
W.L. Johnson

Nanocrystalline fcc metals have been synthesized by mechanical attrition. The crystal refinement and the development of the microstructure have been investigated in detail by x-ray diffraction, differential scanning calorimetry, and transmission electron microscopy. The deformation process causes a decrease of the grain size of the fcc metals to 6–22 nm for the different elements. The final grain size scales with the melting point and the bulk modulus of the respective metal: the higher the melting point and the bulk modulus, the smaller the final grain size of the powder. Thus, the ultimate grain size achievable by this technique is determined by the competition between the heavy mechanical deformation introduced during milling and the recovery behavior of the metal. X-ray diffraction and thermal analysis of the nanocrystalline powders reveal that the crystal size refinement is accompanied by an increase in atomic-level strain and in the mechanically stored enthalpy in comparison to the undeformed state. The excess stored enthalpies of 10–40% of the heat of fusion exceed by far the values known for conventional deformation processes. The contributions of the atomic-level strain and the excess enthalpy of the grain boundaries to the stored enthalpies are critically assessed. The kinetics of grain growth in the nanocrystalline fcc metals are investigated by thermal analysis. The activation energy for grain boundary migration is derived from a modified Kissinger analysis, and estimates of the grain boundary enthalpy are given.


2016 ◽  
Vol 16 (3) ◽  
pp. 83-88 ◽  
Author(s):  
B.V. Omidiji ◽  
R.H. Khan ◽  
M.S. Abolarin

Abstract The influence of the refractory coating which is a mixture of silica flour and kaolin on the surface roughness of the plate castings produced using evaporative patterns had been considered in this work. The kaolin was used as a binder and ratio method was employed to form basis for the factorial design of experiment which led to nine runs of experiments. Methyl alcohol at 99% concentration was used as the carrier for the transfer of the coating to the surface of the patterns. Pouring temperature was observed as a process parameter alongside the mix ratios of the coating. Attempts were made to characterize the refractory coating by using two methods; differential thermal analysis (DTA) and X-ray diffraction. Attempt was also made to characterize the casting material. Gating system design was done for the plate casting to determine the correct proportions of the gating parameters in order to construct the gating system properly to avoid turbulence during pouring of liquid metal. A digital profilometer was used to take the measurements of the surface roughness. It was observed that the mix ratio 90% silica flour-10% kaolin produced the lowest value of the surface roughness of the plate castings and had the lowest material loss in the DTA test. The pouring temperature of 650°C produced best casting.


2021 ◽  
Vol 0 (4) ◽  
pp. 67-70
Author(s):  
Z.T. Hasanova ◽  

Differential thermal analysis and powder X-ray diffraction methods were used for phase equilibria studying in the Cu3AsSe4-GeSe2 system. It was established that wide (up to 30 mol.%) solid solutions based on Cu3AsSe4 are formed. GeSe2-rich alloys consist of various heterogeneous mixtures, including phases outside the T–x plane of this section


2005 ◽  
Vol 2 (10) ◽  
pp. 3766-3769 ◽  
Author(s):  
S. Durán ◽  
P. Grima ◽  
M. Muñoz ◽  
M. Quintero ◽  
J. Ruiz ◽  
...  

2014 ◽  
Vol 805 ◽  
pp. 486-491
Author(s):  
J.M.R. Figueirêdo ◽  
Juliana Melo Cartaxo ◽  
I.A. Silva ◽  
C.D. Silva ◽  
Gelmires Araújo Neves ◽  
...  

The State of Paraíba, Brazil, retains about 88.5% of all Brazilian bentonite, and much of this production comes from deposits in the District of Boa Vista, PB. Nevertheless, the deposits are almost depleted. Recently, new deposits were found, which will increases the reserves of the State, in the regions of Cubati and Pedra Lavrada, PB. The objective of this work is to characterize and develop purified clays, through sieving and hydrocycloning techniques, from those recently discovered bentonites for several applications. The characterization of the sample was done through granulometric analysis by laser diffraction, X-ray diffraction, chemical analysis by X-ray fluorescence, and thermogravimetric and differential thermal analysis. The results show that the samples are typical of bentonite clays, and that the purification solely by hydrocyclone presents the best results.


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