• International Journal of Highway Engineering
• /
• v.14 no.3
• /
• pp.69-76
• /
• 2012

A recent shortage in Korean aggregate market leads a social demand to utilize recycled aggregate to more advanced level, such as the use in concrete structures or paving materials for surface and base layers. Government announced a recycled aggregate guideline in 2009 to provide an institutional framework for recycled aggregate in such an up-scaled use. The use of recycled aggregate in such use; however, is very minimal. This paper evaluates the validity of the impurity content criteria of recycled aggregate for lean concrete base through a series of material tests. The analysis results shows that reclaimed asphalt pavement (RAP) in recycled aggregate not only influence a strength lean concrete adversely, but also influence negatively on an absorption and abrasion characteristics of aggregate system significantly that made those two indices lower. Since absorption and abrasion characteristics are very important indices for recycled aggregate quality, RAP in recycled aggregate could significantly mislead the recycled aggregate qualification. This paper provides a suggestion to resolve these problems.

• Journal of the Korean Recycled Construction Resources Institute
• /
• v.1 no.1
• /
• pp.72-80
• /
• 2005

A recycled aggregate contains impurities that affect negative effects on physical properties of concrete. Therefore, a test method for examining impurities content in recycled aggregate is necessary before use of recycled aggregate. In this study, the test method by visual examination for separating impurities in recycled fine and coarse aggregates was developed. The results of the test are as follow: 1. The current KS F 2576 was necessary for comprehensive revision including types of tested recycled aggregate, definition of terminology, quantity of sample, and test method. 2. Visual examination is appropriate for larger than impurity panicle size of 1.2mm, and the larger panicle size the shorter time was required. 3. For the impurity content test by visual examination, the easiness and accuracy of the test can be obtained from the condition of sample weight of 30 grams with particle size of 2.5mm to 5mm for recycled fine aggregate and the condition of sample weight of 1 kilogram with panicle size of larger than 5mm for recycled coarse aggregate.

• Proceedings of the Korean Powder Metallurgy Institute Conference
• /
• 2004.04a
• /
• pp.61-62
• /
• 2004

• Resources Recycling
• /
• v.11 no.5
• /
• pp.21-23
• /
• 2002

A new process based on the co-precipitation method was developed fer removing harmful impurities during Mn-Zn ferrite production such as $SiO_2$ and P from waste pickle liquor. By this process a final result of less than 100 ppm of $SiO_2$ and less than 10 ppm of P content in the ferric oxide is easily attained. Though Ca cannot be removed by this process, water rinsing of the ferric oxide is effective fer reducing Ca content to less than 100 pm. For further purification, the origins of each impurity must be investigated and then taken away.

• Bulletin of the Korean Chemical Society
• /
• v.29 no.6
• /
• pp.1185-1189
• /
• 2008

Two HPLC methods such as cefadroxil and cefalexin methods were compared in their performance for the quantitative analysis of the content and purity of $\beta$ -lactamic antibiotic, cefradine, for six bulk drug samples. Between the two methods, the cefadroxil method prescribed by the European Pharmacopoeia (EP) for the determination of impurities in cefradoxil was superior to the cefalexin method prescribed by the EP and by the United States Pharmacopeia (USP) for the determination of cefalexin impurity in cefradine in terms of the greater stability of the chromatogram baselines and the higher precision, i.e., the lower % relative standard deviation (RSD). Based on the comparison of the two HPLC methods, the cefadroxil method was recommended to replace the TLC method, which has been prescribed by the EP as the official method for determination of extraneous impurities in cefradine.

• Carbon letters
• /
• v.6 no.1
• /
• pp.31-40
• /
• 2005

The carbon nanofibers (CNFs) were synthesized through the catalytic decomposition of hydrocarbons in a quartz tube reactor. The CNFs prepared from $C_3H_8$ at $550^{\circ}C$ was selected as the purification sample due to the higher content of impurity than that prepared from other conditions. In this study, we carried out the purification of CNFs by oxidation in air or carbon dioxide after acid treatment, and investigated the influence of purification parameters such as kind of acid, concentration, oxidation time, and oxidation temperature on the structure of CNFs. The metal catalysts could be easily eliminated from the prepared CNFs by liquid phase purification with various acids and it was verified by ICP analysis, in which, for example, Ni content decreased from 2.51% to 0.18% with 8% nitric acid. However, the particulate carbon and heterogeneous fibers were not removed from the prepared CNFs by thermal oxidation in air and carbon dioxide. This result can be explained by that the direction of graphene sheet in CNFs is vertical to the fiber axis and the CNFs are oxidized at about the similar rate with the impurity carbon.

• Korean Journal of Crystallography
• /
• v.6 no.2
• /
• pp.111-117
• /
• 1995

TiO2 thin films were prepared on a (100)silicon wafer using a chemical vapor deposition(CVD) method. The deposition experiments were performed using the TTIP in the deposition temperature ransing from 200 content. The deposition rate of TiO2 was increased with the substrate temperature and the oxygen content. The thickness of the deposited thin film and the compositional analysis of this thin films with theoxygen content were measured using Ellipsometry, SEM and ESCA, respectively. The deposited thin film was composed of a bilayer, external TiO2 and internal Ti. Carbon as a residual impurity was found to remain when zero sccm O2 was purged into a reaction chamber and the composition of the deposited thin film was found to change Ti into TiO in a deeper layer. However, when 600sccm O2 was supplied to a reaction chamber, it has been found to reside less carbon content than without O2. Finally, in the condition of 1200sccm O2, no impurity level of carbon was observed and a deeper layer consisted of the Ti composite, even though the deposited surface was composed of TiO2.

• Journal of the Korean Electrochemical Society
• /
• v.8 no.2
• /
• pp.82-87
• /
• 2005

The cathode material, $LiNi_{0.5}Mn_{1.5}O_4$, for high voltage applications of Li-ion batteries exhibits impurity phases due to oxygen deficiency during the high temperature heat treatment. The impurity phase reduces the electrochemical properties of the electrode since the deficiency spinel structure disturbs the lithium ion intercalation and deintercalation. In this study, Cr-substituted $LiNi_{0.5-x}Mn_{1.5}Cr_xO_4(0{\leq}x{\leq}0.05)$ powders are synthesized by a sol-gel method in order to reduce the amount of the impurity phases in the $LiNi_{0.5-x}Mn_{1.5}Cr_xO_4$. Thermal analysis of the cathode material shows that the $LiNi_{0.5}Mn_{1.5}O_4$ without Cr substitution looses $2\%$ of its weight due to oxygen deficiency but the amount of weight loss is diminished when Cr is substituted. XRD analysis also supports the reduction of the impurity phases in the cathode after chromium substitution, suggesting that the improvement of the electrochemical properties such as the capacity retention and electrochemical stability are attributed to the low content of impurity phases in the Cr-substituted $LiNi_{0.5-x}Mn_{1.5}Cr_xO_4.$

• Journal of the Korean Ceramic Society
• /
• v.32 no.1
• /
• pp.37-44
• /
• 1995

TiO2 fine powders were synthesized using oxygenolysis and hydrolysis reaction of TiCl4 vapor in gas phase. The TiO2 powder synthesized showed morphological differences depending on reaction system as follows: TiCl4-O2 reaction system produced the monosized particles having polyhedral shape with well-defined crystal planes and the particles did not agglomerate into secondary particles. TiCl4-H2O reaction system, whereas, produced the spherical secondary particles which consisted of fine primary particles. Other powder characteristics such as particle size, impurity content and rutile content are also reported in this study.

• Journal of the Korean Ceramic Society
• /
• v.24 no.4
• /
• pp.376-384
• /
• 1987

Kaolin was treated by HF and fired at high temperature in order to reduce silica and impurity minerals of kaolin, and eventually to increase the yield of mullite. The kaolin structure was destroyed by HF-treatment and transformed into mullite at lower temperature than those of non-treated kaolin. Not only the silica content of kaolin was reduced, but also the crystalline structure of it was destroyed by HF-treatment.