In this study, we intend to develop a control valve with oxidation resistance for hydrogen fluoride that can be applied to the semiconductor production process. Operated Valves currently in use is a form of assembling an air cylinder to the valve body. These valves generally have a cylinder body made of aluminum (Al), so they may corrode depending on the external environment, and the solution leaks along the rod inside the cylinder, causing damage to parts due to corrosion. To solve this problem, the valve plug shape was developed by devising and applying a plug using a valve different from the existing method, and it is possible to block the inflow of hydrogen fluoride into the valve control unit, thereby preventing damage to parts as well as maintaining stable valve operation.

The oral cavity is rich in blood flow, which can cause excessive bleeding. Excessive bleeding in oral cavity is rare, but if the cause of the bleeding is not found, the patient's life may be at risk. Therefore, in the case of excessive bleeding, the dentist should consider the cause and provide appropriate first treatment. Hydrofluoric acid is widely used as a material for pre-treatment of ceramics before oral restoration for prosthetics and conservative dentistry. Since hydrofluoric acid is very reactive, when it comes into contact with tissues, even very diluted 0.1% hydrofluoric acid can cause very painful 2-3 degree burns, which heal very slowly. Negative reactions and even deaths of hydrofluoric acid have been reported in other fields, but there are very few case reports of complications related to hydrofluoric acid in the dental field. In this article, we report a case of excessive gingival bleeding after restorative treatment and discuss the effects of hydrofluoric acid on oral soft tissues and blood vessels and its prevention

Micro-electromechanical systems (MEMS) 구조물용 고 종횡비의 외팔보 제작을 목적으로 초임계 이산화탄 소를 사용한 건식 식각 실험을 진행하였다. 건식 식각 실험은 초임계 이산화탄소에 50% 불산 (HF) 원액과 공용매 (물, 메탄올, 에탄올, 이소프로필 알콜)를 사용하여 진행되었다. 희생 실리카 층을 식각하여 드러난 MEMS 외팔보 빔 은 주사전자현미경을 이용하여 관찰하였다. HF원액을 사용한 건식 식각 실험은 종횡비 1 : 150의 외팔보 빔까지 기 판과 접착없이 단독으로 서 있는 형태로 제작되었다. 공용매로 메탄올과 에탄올을 사용한 건식 식각의 결과에서는 종 횡비 1 : 75 까지 접착없이 제작할 수 있었고, 이소프로필 알콜을 공용매로 첨가한 실험 결과에서는 종횡비 1 : 37.5 까지 접착없이 제작할 수 있었다. 본 연구의 결과 건식 식각과정에서 알콜계 공용매의 첨가는 대체로 식각 성능을 저 하시킴을 알 수 있었다.

Three activated carbons (ACs) were prepared using NaOH (N) as an activating agent. Hy-drofluoricacid pre-leached rice husk was used as a precursor. After leaching, the precursor was washed with distilled water, dried, crushed, and then sieved; a size fraction of 0.3-0.5 mm was selected for carbonization in the absence of air at 600°C. The carbonization prod-uct (LC) was mixed with NaOH at ratios of 1:2, 1:3, and 1:4 (wt of LC: wt of NaOH) and the produced ACs after activation at 800°C were designated NLC21, NLC31, and NLC41, respectively. Surface and textural properties were determined using nitrogen adsorption at -196°C, scanning electron microscopy images, thermogravimetric analysis, and Fourier transform infrared spectra . These ACs were used as adsorbents for lead(II) from aqueous solutions. The effects of the textural properties and the chemistry of the carbon surfaces were investigated and the impact of the operation conditions on the capacity for lead(II) sorption was also considered. Modificationof NLC41 with H2O2 and HNO3 gave two other adsorbents, HNLC41 and NNLC41 respectively. These two new samples exhibited the highest removal capacities for lead(II), i.e.117.5 and 128.2 mg/g, respectively. The adsorption data fittedthe Langmuir isotherm and the kinetic adsorption followed pseudo-second order kinet-ics. The thermodynamic parameters have been determined and they indicated a spontaneous endothermic process.

반도체 산업에서 발생되는 고농도 폐액은 반도체 세정액으로 초고순도의 산용액을 사용하기 때문에 폐액이라고 하여도 일반 공업용 산용액에 비해 농도가 매우 높은 편에 속한다. 특히 반도체업계를 포함한 IT산업의 급속한 발달로 인하여 불산페액 발생량이 증가하는 추세를 보이고 있다. 규모에 따른 발생량을 추정해보면 국내 반도체 업계에서 연간 15,000ton의 불산폐액이 발생되고 LCD업계와 태양광산업에서 발생되는 불산폐액을 합산하면 국내 발생량은 약 50,000ton 정도로 예상된다. 또한 성장성과 경쟁력으로 볼 때 투자/매출 증가에 따른 폐액 발생 증가분을 예측해보면 향후 5년 내 현재 발생량의 약 2배에 이르게 될 전망이다. 발생된 불산 폐액은 일반적인 생물학적 처리가 불가능하며 현재 물리화학적 처리를 통해서 처리하고 있으나 재활용이 어렵고 2차폐기물이 발생하여 실용성이 떨어진다. 본 연구는 이러한 문제점을 해결하기 위해 반도체 업체에서 발생하는 불산폐액을 분리막을 이용한 투과증발 공정을 통해 수분을 분리하고 불산의 농도를 3배(약 20%, w/w)이상으로 농축을 가능케 하여 폐수 처리에 대한 부담을 줄였으며, 불산폐액에 포함된 이물질을 제거하기 위해 전처리로써 Activation Carbon과 제올라이트를 이용한 흡착법, Struvite 결정화 공법, 암모니아 stripping, 이온교환법을 이용하여 불산폐수 내 포함된 이물질의 제거를 꾀하였다.

Even though removal of fluoride in HF wastewater by crystallization using a fluidized bed reactor (FBR) has been widely studied as an efficient alternative to the chemical precipitation method using traditional stirred tank reactor, serious problems have been encountered for the optimum design of FBR together with the determination of proper operating conditions. One problem is the proper formation of the fluidization state of the seed as a function of seed particle characteristics such as particle size and density. Because dynamics in the reactor are governed by forces such as gravity, drag, and buoyancy as a function of particle size, particle density, relative velocity together with flow characteristics, this study carefully examines the effects of these factors on the formation of fluidization via theoretical analysis and numerical calculation in fluidized bed reactors in the range of practical design and operation condition. The results of this study show the overall trend of the motion of particle behavior in terms of particle size and flow condition.