Effect of Mechanical Alloying on the Microstructural Evolution of Al60Cr30Si10 Alloys Processed by Spark Plasma Sintering

Jeong‑Han Lee,Ik‑Hyun Oh,Jun‑Ho Jang,Ju‑Hun Kim,Sung‑Kil Hong,Hyun‑Kuk Park 대한금속·재료학회 2021 METALS AND MATERIALS International Vol.27 No.5

In this study, Al, Cr and Si fine powders were alloyed by planetary ball milling to investigate their microstructural evolution,following their mechanical alloying behavior. The formation of Al(Cr) supersaturated solid solution by the Cr grainsembedded in Al-matrix, which contributed substitutional structure is discussed in relation to their structural evolution inaccordance with the distortion of a crystal lattice. The compacts of Al–Cr–Si alloys were prepared by rapid sintering withina short time by dense consolidation above the density of 99.9% as the formation of intermetallics, except in the case of thedistribution of single-phases induced by the Al-melting. The formation behavior of intermetallics was dominated by dependenceon the structures of the milled-powder and subsequent sintering temperature. To estimate the consolidated behaviorsof compacts, various approaches derived from TEM and XRD analysis were taken to obtain microstructural evidences ofthe inter-diffusion, following the presence of thermally stable intermetallics.

Influence of Phase Composition in TiAlSiN Hard Coatings on the Evolution of Structure and Mechanical Properties

Jeong‑Han Lee,Ik‑Hyun Oh,Jun‑Ho Jang,Ju‑Hun Kim,Sung‑Kil Hong,Hyun‑Kuk Park 대한금속·재료학회 2021 METALS AND MATERIALS International Vol.27 No.3

The aim of this study is to investigate the structural evolution and mechanical properties of TiAlSiN coatings when processedby the arc ion plating method. To form a hard coating, Ti, Al, and Si powders were mechanically alloyed by planetary ballmilling; the powders were then densely compacted during a rapid sintering process into a ternary system coating, i.e. TiAlSi. The evolution of the structural phase from a powder to a compact material is dominated considerably by phase states suchas a supersaturated solid solution or intermetallic compounds. In the case of coating layers, the factors that determine thestructural evolution are associated with the phase stability of the nano-crystalline structure that in turn is associated withthe Ti/Al composition ratio. Motivated by this, we performed experiments to investigate the distribution of microstructures;the material’s binding energy, quantitative properties, transformation of crystal structure, and distribution of amorphous/crystalline were all recorded. In particular, the relationship between the physical and chemical properties during the coatingprocess is considered to be the dominant factor controlling the orientation and morphology of that zone (1, T, and 2). TheTiAlSiN coating layer was found to have hardness above 45 GPa and an adhesion above 100 N. In other words, understandingthe evolution and structure of TiAlSin helped us to produce a material with excellent properties that can be used as a hardcoating. Specifically, these properties were induced by a grain refinement of the nano-crystalline structure that correspondsto an increase in the silicon nitride contents.

Rapid Consolidation of WC‑ZrSiO4 Hard Materials by Spark Plasma Sintering: Microstructure, Densification, and Mechanical Properties

Jeong‑Han Lee,Ik‑Hyun Oh,Ju‑Hun Kim,Sung‑Kil Hong,Hyun‑Kuk Park 대한금속·재료학회 2021 METALS AND MATERIALS International Vol.27 No.9

Densely consolidated WC-based hard materials with 5–20 vol% ZrSiO4was fabricated by spark plasma sintering at 1400 ℃ ata constant heating rate of 70 ℃/min−1. To achieve mechanical alloying of WC-ZrSiO4, planetary ball milling was carried outfor 12 h, during which the brittle-brittle components (WC-ZrSiO4) became fragmented and their particles became refined. Itwas observed that certain, specific, non-isothermal sintering kinetics, such as apparent activation energy, sintering exponents,and densification strain, affected the densification behavior. The evolution of phase structure from powder to compact wasfound to be related the lattice distortion and micro-strain in the basal planes of WC. By examining the mechanical propertiesof the samples, it was that the added zircon content leads to enhanced fracture toughness (12.9 MPa m1/2) owing to thepresence of WC-ZrSiO4 in the cemented carbide. In fact, the microcrack propagation of the fracture passed through zirconfrom a transgranular to a ductile component (fcc) where the crack tips could be absorbed.

초등학생에서 인두배양과 항-OF 항체 보유율

정현주,김선주,김윤정,맹국영,정현주,김선주,김윤정,맹국영 대한임상병리학회 1998 대한임상병리학회지 Vol.18 No.3

성견의 외과적 치근이개부 골결손에 차폐막과 골이식재를 이용한 조직유도재생술시 치유양상

정은희,정현주 전남대학교 치과대학 1996 전남치대논문집 Vol.8 No.1

The present study was to evaluate the healing patterns of guided tissue regeneration(GTR) using resorbable Vicry??(polyglactin 910) mesh and nonresorbable expanded polytetrafluoroethylene(ePTFE) membrane with or without bone grafting using autogeneous bone and demineralized freeze-dried bone allograft(DFDBA) in the grade Ⅱ furcation defects. Mucoperiosteal flaps were reflected buccally in the mandibular 2nd, 3rd and 4th premolar areas and furcation defects were created surgically by removing 5 × 6mm alveolar bone in 4 dogs. Root surfaces were thoroughly debrided of periodontal ligament and cementum, and notches were placed on root sruface at the most apical bone level. In the right and left mandibular quadrant, each tooth was received Vicryl?? mesh(ACE Surgical Supply Co., USA) only, Vicryl?? mesh with DFDBA, Vicryl?? mesh with autogeneous bone grafts, ePTFE membrane(Gore-tex?? membrane, W.L. Gore & Associates Inc., USA) only, ePTFE membrane with DFDBA or ePTFE membrane with autogeneous bone grafts. For the fluorescent microscopic examination, fluorescent agents were injected at 2, 4 and 8 weeks after surgery. Four weeks after surgery, 2 dogs were sacrificed and ePTFE membranes were removed from remaining 2 dogs, which were sacrificed at 12 weeks after surgery. Undecalcified tissues were embedded in cethylmethacrylate and 10㎛ thick sections were cut in a buccolingual direction. These sections were stained with hematoxylin-eosin stain and Masson's trichrome stain, and evaluated by descriptive histology and linear measurements. The results were as follows : 1) Vicryl?? mesh group showed less connective tissue attachment than ePTFE membrane group. 2) The combination of GTR using Vicryl?? mesh and osseous grafts resulted in new attachment and new bone formation more than GTR using Vicryl?? mesh only. 3) GTR using ePTFE membrane, with or without osseous grafts, enhanced periodontal regeneration. 4) Root resorption and dentoalveolar ankylosis were observed in the areas treated with the combination of GTR and DFDBA. It was suggested that the effect of adjunctive bone grafting in GTR procedure depends on the materials and the physical properties of barrier membranes. Vicryl?? mesh performed a barrier function and the use of adjunctive bone grafting may enhance the periodontal regeneration.

치주병원균에 대한 유산균의 억제효과

정하나,김영준,정현주,오종석 전남대학교 치과대학 1999 전남치대논문집 Vol.11 No.1

This study was performed to evaluate the effect of hydrogen peroxide-producing Lactobacillus acidophilus V-20 on the replication of periodontal pathogens, Actinobacillus actinomycetemcomitans and Porphyromonas gingivalis. When A. actinomycetemcomitans and P. gingivalis were incubated alone and in the combination with L. acidophilus V-20, the viable cell numbers of A. actinomycetemcomitans and P.gingivalis were compared between those cultures. The effect of S. mutans, E. durans, and L. lactis on the replication of A. actinomycetemcomitans and P. gingivalis was also evaluated. The change of periodontal indexes(probine depth, gingival index, GCF volume) and the viable cell numbers of A. actinomycetemcomitans and black pigmented bacteroides in subgingival plaque sample were evaluated following gargling of fermented milk made from L.acidophilus V-20 for 1 month on patients with periodontal disease in maintenance phase. In the mixed culture of L. acidophilus V-20 and A. actinomycetemcomitans or P. gingivalis, the replication of A. actinomycetemcomitans or P. gingivalis was completely inhibited. But in the mixed culture of P. gingivalis and hydrogen peroxide-nonproducing Lactobacillus casei, the viable cell numbers of P. gingivalis was not decreased when compared with the numbers in the mixed culture of P. gingivalis and L. acidophilus V-20. In the mixed culture of A. actinomycetemcomitans and S. mutans, E. durans, or L. lactis, the viable cell number of A. actinomycetemcomitans was not almost changed when compared with the numbers in the culture of A. actinomycetemcomitans alone. And in the mixed culture of P. gingivalis and E. durans or L. lactis, the viable cell numbers of P. gingivalis was not almost changed compared with the counts in the culture of P. gingivalis alone. But the replication of P. gingivalis was completely inhibited in the mixed culture of P. gingivalis and S. mutans. When the change of periodontal indexes following gargling of fermented milk was compared with baseline, probing depth and gingival index were not changed, but GCF volume was significantly decreased(p<0.05). And when the viable cell numbers of microorganisms in subgingival plaque sample were compared with baseline, total viable cell number was almost unchanged and the viable cell numbers of A. actinomycetemcomitans and black pigmented bacteroides were significantly decreased(p<0.05). These results suggest that L. acidophilus V-20 inhibit the replication of A. actinomycetemcomitans and black pigmented bacteroides by the formation of hydrogen peroxide.

백서 대뇌피질절편에서 산소 및 포도당 결핍에 의한 [³H]Acetylcholine의 유리에 관한 연구

이정주,김기원,서만욱,김영현,김기원 대한신경과학회 1998 대한신경과학회지 Vol.16 No.4

상부소환관협착에 대한 Savary-Gilliard Dilatation의 치료효과와 안전성에 관한 관찰

정현용,육은주,임의혁,김병호,성자원,이기천,허승식,이헌영,김영건 충남대학교 의과대학 지역사회의학연구소 1992 충남의대잡지 Vol.19 No.2

For the patient with stenosis of upper digestive tract caused by either benign or malignant process, esophageal dilatation is an important therapeutic modality. We reviewed retrospectively 39 cases treated by Savary-Gilliard dilatation for upper digestive tract stenosis, and results were follows : (1) Dysphagia was improved in 95% of the patients. (2) Eight patients(20%) sufferd perforation, five of them were managed with conservative medical measures, others were managed operatively. (3) In the cases with benign stenosis dysphagia was not noticed for 8.8 months, but with malignant stenosis dysphagia was reappeared after 2.8 months despite concomitant chemoradiotherapy. In conclusion, Savary-Gilliard dilatation was an effective measure for symptome due to upper digestive tract stenosis, but more careful attention for perforation should be necessitated. Also another therapeutic modality for treatment of malignant stenosis was inevitable.

Alendronate가 백서에서 두개골 결손의 재생에 미치는 영향

정찬두,김정근,정현주 전남대학교 치의학연구소 2001 구강과학 Vol.13 No.4

Previous studies have demonstrated an increase in bone mass and density with the use of bisphosphonate in osteoporosis. This agent acts as an inhibitor of osteoclastic activity, and results in increase of net osteoblastic activity. Currently, it has been reported that bisphosphonate has direct effect on osteoblast. This study was designed to evaluate the effect of alendronate on bone regeneration in defect of rat calvaria. The animals used for these experiments were 48 male rats, over 6-8 weeks old. They were divided into three groups according to the dose of alendronate(MK-217®, Merck, USA) administered. After the calvarial defects were surgically created, the rats received a peritoneal alendronate (0.25mg/kg) in group I, a peritoneal alendronate (1.25mg/kg) in group Ⅱ, and a peritoneal normal saline injection in the control group. Three and six weeks later, blood was sampled and evaluated for alkaline phosphatase activity. the animals were sacrificed for histological observation and histometric analysis of the level of bone formation. The alkaline phosphatase activity was similar in three groups at 3 weeks of experiment. The activity at 6 weeks increased more than twice, compared to 3 weeks, and was slightly higher in group Ⅰ than the other two groups. In histological observation, all the groups at 3 weeks, osteoblast rimming and new bone formation were observed along the defect margin. At 6 weeks, the defect was almost closed with new and more mature bone, but new bone is thinner than original bone in the central portion of defect. In histometric analysis, group Ⅰ and Ⅱ at 3 weeks showed significantly greater new bone formation than the control, and all the groups at 6 weeks showed similar amount of bone formation. These result suggest that alendronate administration in the dose of 0.25mg/kg and 1.25mg/kg promote osseous regeneration.

백서 치주 골결손부에 calcium carbonate 이식 및 pulsed Nd : YAG 레이저에 의한 치은상피 제거후 접합상피 치유양상 YAG laser in rat peiodontal bone defect filled with calcium carbonate

정철웅,정현주 전남대학교 치과대학 1995 전남치대논문집 Vol.7 No.1

The purpose of this study was to evaluate whether removal of gingival epithelium with pulsed Nd : YAG laser could inhibit the downgrowth of junctional epithelium after alloplastic material grafting in periodontal bone defect. The periodontal bone defects were created surgically on the palatal aspect of the upper right and left molar teeth in 30 rats and filled with resorbable calcium carbonate(Biocoral 450?? : Inoteb, France). The control sites(right molar area) was sutured. The test side (left molar area) received controlled de-epithelization of the oral and sulcular epithelium with pulsed Nd : YAG laser(Sunrise Master?? : Sunrise Technologies, U.S.A.) under the mode of 1.75W, 15Hz, 116mJ/pulse and was sutured. The control and test sites were evaluated clinically and histologically, at 1, 3, 7, 14, and 28 days postoperation. Clinically, the gingiva showed normal color and shape at the 5th day in the control site and at the 10th day in the test sites. Histologically, the junctional epithelium was formed at the 7th day in the control sites and at the 14th day in the test sites, and the long JE attachment were observed at the 28th day in both sites. The attachment of connective tissue to root surface was observed initially at the 7th day in the control sites and at the 14th day in the test sites, and completed at the 28th day in both sites. In summary, these results showed that the removal of oral epithelium using pulsed Nd : YAG Laser could not prevent epithelial downgrowth after alloplastic material implantation in rat periodontal bone defect.