• Tribology and Lubricants
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• v.34 no.6
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• pp.209-216
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• 2018

Sapphire is a substrate material that is widely used in optical and electronic devices. However, the processing of sapphire into a substrate takes a long time owing to its high hardness and chemical inertness. In order to process the sapphire ingot into a substrate, ingot growth, multiwire sawing, lapping, and polishing are required. The lap grinding process using pellets is known as one of the ways to improve the efficiency of sapphire substrate processing. The lap grinding process ensures high processing efficiency while utilizing two-body abrasion, unlike the lapping process which utilizes three-body abrasion by particles. However, the lap grinding process has a high material removal rate (MRR), while its weakness is in obtaining the required surface roughness for the final polishing process. In this study, we examine the effects of free abrasives in lap grinding on the material removal characteristics of sapphire substrate. Before conducting the lap grinding experiments, it was confirmed that the addition of free abrasives changed the friction force through the pin-on-disk wear test. The MRR and roughness reduction rate are experimentally studied to verify the effects of free abrasive concentration on deionized water. The addition of free abrasives (colloidal silica) in the lap grinding process can improve surface roughness by three-body abrasion along with two-body abrasion by diamond grits.

• Microbiology and Biotechnology Letters
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• v.24 no.5
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• pp.597-603
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• 1996

This study was carried out to examine degradation characteristics of microalgae Chlorella vulgaris in methane fermentation. We measured COD and VS reduction, gas and methane productivity, VFA (volatile fatty acid), respectively. Then we calculated material balance and hydrolysis rates in soluble and solid material. The substrate concentration was controlled from 14 gCOD$_{cr}$/l to 64 gCOD$_{cr}$/l in batch cultures, and HRT (hydraulic retention time) controlled from 2 days to 30 days in continuous experi- ments. The results were as follows. In batch culture, accumulated gas productivity increased with the increase of the substrate concentration. The SS and VSS was removed all about 30% increase of substrate concentration and the most of the degradable material removed during the first 10 days. The curve of gas and methane production rate straightly increased until substrate concentration is 26 gCOD$_{cr}$/l. In continuous culture experiments, the removal rates at HRT 10days were 20% for total COD and TOC, respectively. At longer HRT, there was no increase in the removal efficiency. At HRT 15 days, the removal rates were 30% for SS and VSS, respectively. Soluble organic materials were rapidly degraded, and so there was no accumulated. Soluble COD concentration was not increase regardless of HRT-increasing. That meaned the hydrolysis was one of the rate-limiting stage of methane fermentation. The first-order rate constants of hydrolysis were 0.23-0.28 day$^{-1}$ for VSS, and 0.07-0.08 day$^{-1}$ for COD.

• Tribology and Lubricants
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• v.33 no.3
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• pp.106-111
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• 2017

Sapphire is an anisotropic material with excellent physical and chemical properties and is used as a substrate material in various fields such as LED (light emitting diode), power semiconductor, superconductor, sensor, and optical devices. Sapphire is processed into the final substrate through multi-wire saw, double-side lapping, heat treatment, diamond mechanical polishing, and chemical mechanical polishing. Among these, chemical mechanical polishing is the key process that determines the final surface quality of the substrate. Recent studies have reported that the material removal characteristics during chemical mechanical polishing changes according to the crystal orientations, however, detailed analysis of this phenomenon has not reported. In this work, we carried out chemical mechanical polishing of C(0001), R($1{\bar{1}}02$), and A($11{\bar{2}}0$) substrates with different sapphire crystal planes, and analyzed the effect of crystal orientation on the material removal characteristics and their correlations. We measured the material removal rate and frictional force to determine the material removal phenomenon, and performed nano-indentation to evaluate the material characteristics before and after the reaction. Our findings show that the material removal rate and frictional force depend on the crystal orientation, and the chemical reaction between the sapphire substrate and the slurry accelerates the material removal rate during chemical mechanical polishing.

• KSBB Journal
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• v.6 no.2
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• pp.115-121
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• 1991

A number of experiments were conducted in order to investigate the COD removal rate according to the biofilm thickness in a Fluidized-Bed Biofilm Reactor(FBBR). The following conditions were fixed during the experiments: superficial upflow velocity was 0.47cm/sec, operating temperature was $22{\pm}1{\circ}C$ and pH was about $7{\pm}0.1$. The synthetic wastewater based on glucose was used as a substrate. The COD removal efficiencies were shown as 73% and 95%, respectively, when organic loading rate was increased from $10kgCOD\;/\;{\textrm{m}^3}$.day to $80kgCOD\;/\;{\textrm{m}^3}$.day. Andrew's model of substrate removal rate which was commonly used in fixed-biofilm reactor was transformed and applied in this FBBR experiment to predict substrate removal rate and gave 85% agreement with the experimental values.

• Tribology and Lubricants
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• v.33 no.5
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• pp.228-233
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• 2017

Chemical Mechanical Polishing of chemically stable sapphire substrates is dominantly affected by the mechanical processing of abrasives, in terms of the material removal rate. In this study, we investigated the effect of electrostatic force between the abrasives and substrate, on the polishing. If potassium chloride (KCl) is added to slurry, water molecules are decomposed into $H^+$ and $OH^-$ ions, and the amount of ions in the slurry changes. The zeta potential of the abrasives decreases with an increase in the amount of $H^+$ ions in the stern layer; consequently, the electrostatic force between the abrasives and substrate decreases. The change in zeta potential of abrasives in the slurry is affected by the slurry pH. In acidic zones, the amount of ions bound to the abrasives increases if the amount of $H^+$ ions is increased by adding KCl. However, in basic zones, there is no change in the corresponding amount. In acidic zones, zeta potential decreases as molar concentration of potassium increases; however, it does not change significantly in basic zones. The removal rate tends to decrease with increase in molar amount of potassium in acidic zones, where zeta potential changes significantly. However, in basic zones, the removal rate does not change with zeta potential. The tendencies of zeta potential and that of the frictional force generated during polishing show strong correlation. Through experiments, it is confirmed that the contact probability of abrasives changes according to the electrostatic force generated between the abrasives and substrate, and variation in removal rate.

• Journal of Korean Society on Water Environment
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• v.22 no.3
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• pp.566-571
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• 2006

A sequencing batch biofilm reactor (SBBR) operated with a cycle of anaerobic - aerobic - anoxic - aerobic has been evaluated for the nutrient removal characteristics. The sponge-like moving media was filled to about 10% of reactor volume. The sewage was the major substrate while external synthetic carbon substrate was added to the anoxic stage to enhance the nitrogen removal. The operational results indicated that maximum T-N and T-P removal efficiencies were 97% and 94%, respectively were achieved, while COD removal of 92%. The observations of significant nitrogen removal in the first aerobic stage indicated that nitrogen removal behaviour in this SBBR was different to conventional SBR. Although the reasons for aerobic nitrogen removal has speculated to either simultaneous nitrification and denitrification or anoxic denitrification inside of the media, further researches are required to confirm the observation. The specific oxygen uptake rate (SOUR) test with biofilm and suspended growth sludge indicated that biofilm in SBBR played a major role to remove substrates.

• Laser Solutions
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• v.13 no.1
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• pp.11-15
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• 2010

Indium tin oxide (ITO) provides high electrical conductivity and transparency in the visible and near IR (infrared) wavelengths. Thus, it is widely used as a transparent electrode for the fabrication of liquid crystal displays (LCDs) and organic light emitting diode displays (OLRDs), photovoltaic devices, and other optical applications. Lasers have been used for removing coating on polymer substrate for flexible display and electronic industry. In selective removal of ITO layer, laser wavelength, pulse energy, scan speed, and the repetition rate of pulses determine conditions, which are efficient for removal of ITO coating without affecting properties of the polymer substrate. ITO coating removal with a laser is more environmentally friendly than other conventional etching methods. In this paper, pattering of ITO film from polymer substrates is described. The Yb:KGW femtosecond laser processing system with a pulse duration of 250fs, a wavelength of 1030nm and a repetition rate of 100kHz was used for removing ITO coating in air. We can remove the ITO coating using a scanner system with various pulse energies and scan speeds. We observed that the amount of debris is minimal through an optical and a confocal microscope, and femtosecond laser pulses with 1030nm wavelength are effective to remove ITO coating without the polymer substrate ablation.

• Journal of Korean Society for Atmospheric Environment
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• v.22 no.6
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• pp.758-766
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• 2006

A two-stage bioreactor, which consists of a biotrickling filter module and a biofilter module in series, was investigated for the enhanced treatment of a VOC mixture, toluene and methyl ethyl ketone (MEK). Throughout the experiments, the overall inlet loading rate was maintained at approximately $43g/m^3/hr$, but the inlet ratios of the VOCs were modified. The experimental results showed that the different ratios of the VOC mixture resulted in changes of overall removal efficiencies, elimination capacities (ECs) and microbial accumulation on the surface of each packing material. The ratio of inlet toluene to MEK at 50 : 150 was found to be most effective in terms of the overall removal efficiency, because, at this condition, MEK (i.e., the hydrophilic compound) was mostly removed in the biotrickling filter module and the following biofilter module was used to remove toluene. It was also found that when the inlet loading rate of the VOC mixture was serially increased stepwise within short-term periods, the ECs for toluene dropped significantly but the ECs for MEK increased at the ratio of the VOC mixture. These results implied that substrate interaction and/or substrate preferable utilization might have an effect on the biological removal of each compound in the two-stage bioreactor; therefore, the bioreactor should be operated in the condition where the substrate interaction could be minimized in order to maximize overall performance of the two-stage bioreactor.

• Journal of Environmental Health Sciences
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• v.20 no.2
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• pp.22-27
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• 1994

This study is to discuss the factors influenced on the removal efficiency of a high-strength organic wastewaters investigated using the polypropyrene media which appropriate to attach microorganism in the tube type fixed biofilter reactor. The results obtained in the experiment were as follows: 1. The kinetics of reaction rate (k') were 0.125, 0.135, 0.155 varing initial COD 720, 1280, 1630 mg/l in batch reactor. 2. In the range of pH 4.0 ~12.0 was obtained the removal efficiency of COD higher than 85%. It was proved that variation of pH (4.0 ~12.0) was nothing to do with the removal efficiency of substrate in continuous reactor. 3. Temperature to obtain removal efficiency of COD higher than 85% was 10 ~ 40$\circ$C. Removal efficiency of COD was no less than those at high temperature. 4. In the continuous reactor, the volumetric loading of COD for removal efficiency higher than 95% had to be 0.5~1.5 kg COD/m$^3$.d below. And then the HRT was 8 hrs. 5. In comparison with the activated sludge process, the tube type fixed biofilter process was excellent in removal efficiency of substrate and sludge production rate.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.19 no.11
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• pp.985-993
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• 2006

An experiment to find out the removal mechanism of PEG(polyethyleneglycol) by using UV-enhanced $O_2$ GPC (gas phase cleaning) at low substrate temperature below $200^{\circ}C$ was executed under various process conditions, such as substrate temperature, UV exposure, and $O_2$ gas. The possibility of using $UV/O_2$ GPC as a low-temperature in-situ cleaning tool for organic removal was confirmed by the removal of a PEG film with a thickness of about 200 nm within 150 sec at a substrate temperature of $200^{\circ}C$. Synergistic effects by combining photo-dissociation and photo oxidation can only remove the entire PEG film without residues within experimental splits. In $UV/O_2$ GPC with substrate temperatures higher than the glass transition temperature, the substantial increase in the PEG removal rate can be explained by surface-wave formation. The photo-dissociation of PEG film by UV exposure results in the formation of end aldehyde by dissociation of back-bone chain and direct decomposition of light molecules. The role of oxygen is forming peroxide radicals and/or terminating the dis-proportionation reaction by forming peroxide.