Change in Surface Hardness of BisGMA/TEGDMA Polymer due to Enzymatic Action

1992 ◽  
Vol 71 (11) ◽  
pp. 1851-1853 ◽  
Author(s):  
I.B. Larsen ◽  
M. Freund ◽  
E.C. Munksgaard
Keyword(s):  
Wear Resistance ◽  
Surface Layer ◽  
Applied Load ◽  
Surface Hardness ◽  
Human Saliva ◽  
Surface Microhardness ◽  
Enzymatic Action ◽  
Outermost Surface ◽  
The Mean ◽  
The Difference

The surface microhardness of specimens made of a BisGMA/ TEGDMA polymer was measured before and during treatment for 60 days with phosphate buffer or phosphate-buffered esterase solution with an activity corresponding to the mean hydrolase activity of human saliva. The hardness of the buffer-treated specimens was unchanged during the incubation period, while that of the esterase-treated specimens decreased gradually. After about five days of treatment, no further change in hardness was observed for up to 60 days. Based on the difference in the calculated hardness of the specimens as a function of the applied load during measurement, it was estimated that the mean microhardness of the outermost surface layer of the esterase-treated specimens was diminished by about 15%, compared with that of the buffer-treated specimens. From these results, it was concluded that the wear resistance of a BisGMA/TEGDMA polymer is most likely diminished by hydrolases in saliva.

Stabilization of microhardness of hard alloy VK6 cutting plates modified by fast electrons by cryoprocessing

2020 ◽  
pp. 47-50
Author(s):  
V. N. Anikin ◽  
S. A. Yeremin ◽  
E. S. Potapova ◽  
A. B. Korshunov ◽  
A. M. Kolesnikova ◽  
...  
Keyword(s):  
Wear Resistance ◽  
Hard Alloy ◽  
Initial Surface ◽  
Surface Microhardness ◽  
Fast Electrons ◽  
X Ray ◽  
Microstructure Characteristics ◽  
Structure Sensitive ◽  
The Difference ◽  
Sensitive Property

The study is devoted to the effect cryoprocessing has on the stabilization of VK6 (hard alloy) after irradiation with fast electrons with energy of 5 MeV. To investigate samples with a close microstructure characteristics, a measurement of a structure-sensitive property -- co-effective force -- was held. It was shown that the treatment of VK6 hard alloy with fast electron irradiation increases its microhardness by 30 % in comparison with the original samples without any irradiation. It was found out that the microhardness of VK6 hard alloy samples after treatment with fast electrons depends on the initial surface structure, so that polished samples have higher values of microhardness than samples which surface were ground. X-ray phase analysis made it possible to establish the difference between the structures of polished and ground surfaces of the VK6 hard alloy in a stressed state. It was also shown that the treatment with fast electrons irradiation with an energy of 5 MeV does not lead to the formation of new phases. To establish the consolidation of the effect of increasing the hardness of the irradiated materials, annealing of VK6 hard alloy samples at the temperature of 30–100 °C (on air) was held. Cryoprocessing allowed us to consolidate the effect of increasing microhardness of the surface (surface microhardness) and wear resistance after irradiation of the VK6 hard alloy. Ill. 5. Ref. 10.

Effect of powder metallurgy Cu-B4C electrodes on workpiece surface characteristics and machining performance of electric discharge machining

2016 ◽  
Vol 230 (12) ◽  
pp. 2190-2203 ◽  
Author(s):  
Can Cogun ◽  
Ziya Esen ◽  
Asim Genc ◽  
Ferah Cogun ◽  
Nizami Akturk
Keyword(s):  
Wear Resistance ◽  
Surface Layer ◽  
Powder Metallurgy ◽  
Abrasive Wear ◽  
Surface Hardness ◽  
Surface Characteristics ◽  
Abrasive Wear Resistance ◽  
Machining Performance ◽  
Electric Discharge Machining ◽  
Workpiece Surface

The main aim of this study is to produce new powder metallurgy (PM) Cu-B4C composite electrode (PM/(Cu-B4C)) capable of alloying the recast workpiece surface layer during electric discharge machining process with boron and other hard intermetallic phases, which eventually yield high hardness and abrasive wear resistance. The surface characteristics of the workpiece machined with a PM/(Cu-B4C) electrode consisted of 20 wt% B4C powders were compared with those of solid electrolytic copper (E/Cu) and powder metallurgy pure copper (PM/Cu) electrodes. The workpiece surface hardness, surface abrasive wear resistance, depth of the alloyed surface layer and composition of alloyed layers were used as key parameters in the comparison. The workpiece materials, which were machined with PM/(Cu-B4C) electrodes, exhibited significantly higher hardness and abrasive wear resistance than those of machined with the E/Cu and PM/Cu. The main reason was the presence of hard intermetallic phases, such as FeB, B4C (formed due to the boron in the electrode) and Fe3C in the surface layer. The improvement of the surface hardness achieved for steel workpiece when using PM/(Cu-B4C) electrodes was significantly higher than that reported in the literature. Moreover, the machining performance outputs (workpiece material removal rate, electrode wear rate and workpiece average surface roughness (Ra)) of the electrodes were also considered in this study.

scholarly journals Strengthening the Surface Layer of Tools with State-of-the-Art Technologies

2021 ◽  
Vol 22 (1) ◽  
pp. 78-102
Author(s):  
K. O. Kostyk ◽  
V. O. Kostyk ◽  
V. D. Kovalev
Keyword(s):  
Wear Resistance ◽  
Surface Layer ◽  
Surface Hardening ◽  
High Speed ◽  
Cutting Tool ◽  
Surface Condition ◽  
Surface Hardness ◽  
Physical And Mechanical Properties ◽  
Boride Layer ◽  
Hard Alloys

Increasing both the service life and the wear resistance of the tool by surface hardening is an urgent issue. Its solution contributes to a significant increase in the performance of products. Available methods of surface hardening of tools, based on coating or changing the surface condition, are becoming increasingly important due to the complexity of the operation of products. Plates made of the T5K10 (85%WC–6%TiC–9%Co) and T15K6 (79%WC–15%TiC–6%Co) hard alloys as well as cylindrical samples made of the W6Mo5Cr4V2 and W18Cr4V high-speed steels are used for the study. Studies have shown that, after processing the T15K6 alloy plates with a pulsed magnetic field, the cutting tool life improved by more than 200% as compared to the untreated ones. The proposed method will increase the strength of carbide plates and stabilize the physical and mechanical properties of the cutting tool. For tools made of alloy steels, the hardening treatment is carried out by the boron method in pastes with nanodisperse powders. As shown, the thickness of the boride layer for high-speed steels increases with the duration of the process; however, its growth rate depends on the composition of the steel. An increase in the holding time of the chemical and thermal treatment leads to the growth of boride layers. The layer thickness changes quadratically (as a second-degree polynomial) with duration time. A feature of formation of diffusion layers is revealed. The dependences of both the surface hardness and the thickness of boride layer on the borating time for high-speed steels are also shown. Studies have shown that boriding in a nanodisperse medium can significantly increase the wear resistance of steels. The method of expert assessments of the maximum values of the surface properties of the studied steels is carried out. As shown, it is more rational to use W6Mo5Cr4V2 steel as a cutting tool after hardening the surface layer by boriding in a nanodisperse boron-containing powder. The proposed processing method demonstrates the prospects of using it to improve the performance of products. In addition, this method of hardening can significantly increase the wear resistance of materials (by ≈3.38–3.75 times) as compared to steels without processing.

scholarly journals The Abrasion Behaviour of X40CrMoV5-1 Steel Under Various Surface Treatments

2020 ◽  
Vol 3 (1) ◽  
pp. 50-54
Author(s):  
László Tóth ◽  
Tünde Kovács ◽  
Zoltán Nyikes ◽  
Mhatre Umesh
Keyword(s):  
Heat Treatment ◽  
Wear Resistance ◽  
Surface Layer ◽  
Surface Treatment ◽  
Surface Hardness ◽  
Surface Treatments ◽  
Plasma Nitridation ◽  
Pvd Coating ◽  
Abrasion Wear ◽  
Wear Tests

AbstractFor evolving a surface layer on the X40CrMoV5-1 steel, a plasma-nitridation and PVD coating process was applied. In our experiments, the samples were heat-treated (high-temperature hardening, annealed three times) and surface treatments (plasma-nitridation, PVD coating by TiAlN, duplex surface treating by plasma nitridation and after that, PVD coating TiAlN). After the heat treatments, we performed hardness tests and surface abrasion wear tests. The abrasion wear resistance of the specimens was studied in order to understand the heat treatment effects on abrasion behaviour. It was observed that the heat treatment and surface treatment process greatly influence the tool steel surface hardness and abrasion resistance behaviour. By plasma-nitridation the surface hardness doubled compared to the quenched surface hardness while the PVD coated TiAlN surface layer hardness is more than five times that of the hardened one. There was no relevant difference between the PVD coated (TiAlN) surface hardness and the duplex surface-treated hardness. On the basis of the results of the comparative abrasive wear tests, it can be concluded that the duplex surface treatment resulted in the greatest wear resistance..

scholarly journals Влияние поверхностных эффектов на изгиб и колебания нанопленок

2019 ◽  
Vol 61 (10) ◽  
pp. 1825
Author(s):  
М.А. Ильгамов
Keyword(s):  
Surface Layer ◽  
Elastic Modulus ◽  
Film Thickness ◽  
Natural Frequencies ◽  
Cylindrical Bending ◽  
Bending Vibrations ◽  
Mean Pressure ◽  
The Mean ◽  
Linear And Nonlinear ◽  
The Difference

AbstractStatic cylindrical bending of nanofilms is considered in linear and nonlinear formulations. The frequency spectrum of bending vibrations and the parametric resonance are determined. In this case, two surface effects are taken into account. The first one is associated with different elastic properties in the surface layer and in the bulk of the material. It is manifested in stretching and bending of nanometer-thick films. The second effect is due to the difference, caused by bending, between the areas of the convex and concave surfaces subjected to gas pressure. The greater the ratio of the mean pressure to the elastic modulus of the material and the ratio of the length of the film to its thickness, the stronger this effect. The loading conditions of the end surfaces of the film are also important, as well as the strain over the film thickness under the action of the mean pressure. A positive mean pressure leads to an increase in effective stiffness, a decrease in deflection, and an increase in natural frequencies. A negative mean pressure reduces stiffness and natural frequencies. It is shown that, in this case, film bending may occur as a result of the longitudinal in stability. Oscillations of the mean pressure lead to a parametric amplification of bending vibrations. These results cannot be obtained on the basis of the classical equations of bending of plates and films.

The Effect of Vocabulary Intervention on Text Comprehension: Who Benefits?

2019 ◽  
Vol 50 (4) ◽  
pp. 562-578 ◽  
Author(s):  
Dawna Duff
Keyword(s):  
Middle School ◽  
Reading Comprehension ◽  
Text Comprehension ◽  
Classroom Instruction ◽  
Vocabulary Instruction ◽  
Clinical Intervention ◽  
Vocabulary Knowledge ◽  
Vocabulary Intervention ◽  
The Mean ◽  
The Difference

Purpose Vocabulary intervention can improve comprehension of texts containing taught words, but it is unclear if all middle school readers get this benefit. This study tests 2 hypotheses about variables that predict response to vocabulary treatment on text comprehension: gains in vocabulary knowledge due to treatment and pretreatment reading comprehension scores. Method Students in Grade 6 ( N = 23) completed a 5-session intervention based on robust vocabulary instruction (RVI). Knowledge of the semantics of taught words was measured pre- and posttreatment. Participants then read 2 matched texts, 1 containing taught words (treated) and 1 not (untreated). Treated texts and taught word lists were counterbalanced across participants. The difference between text comprehension scores in treated and untreated conditions was taken as a measure of the effect of RVI on text comprehension. Results RVI resulted in significant gains in knowledge of taught words ( d RM = 2.26) and text comprehension ( d RM = 0.31). The extent of gains in vocabulary knowledge after vocabulary treatment did not predict the effect of RVI on comprehension of texts. However, untreated reading comprehension scores moderated the effect of the vocabulary treatment on text comprehension: Lower reading comprehension was associated with greater gains in text comprehension. Readers with comprehension scores below the mean experienced large gains in comprehension, but those with average/above average reading comprehension scores did not. Conclusion Vocabulary instruction had a larger effect on text comprehension for readers in Grade 6 who had lower untreated reading comprehension scores. In contrast, the amount that children learned about taught vocabulary did not predict the effect of vocabulary instruction on text comprehension. This has implications for the identification of 6th-grade students who would benefit from classroom instruction or clinical intervention targeting vocabulary knowledge.

Effect of silver nitrate on some mechanical properties of heat polymerizing acrylic resins

2019 ◽  
Vol 14 (1) ◽  
pp. 110
Author(s):  
Assiss. Prof. Dr. Sabiha Mahdi Mahdi ◽  
Dr. Firas Abd K. Abd K.
Keyword(s):  
Mechanical Properties ◽  
Tensile Strength ◽  
Silver Nitrate ◽  
Surface Hardness ◽  
Mechanical Tests ◽  
Hardness Tester ◽  
Acrylic Resins ◽  
The Difference

Aim: The aimed study was to evaluate the influence of silver nitrate on surfacehardness and tensile strength of acrylic resins.Materials and methods: A total of 60 specimens were made from heat polymerizingresins. Two mechanical tests were utilized (surface hardness and tensile strength)and 4 experimental groups according to the concentration of silver nitrate used.The specimens without the use of silver nitrate were considered as control. Fortensile strength, all specimens were subjected to force till fracture. For surfacehardness, the specimens were tested via a durometer hardness tester. Allspecimens data were analyzed via ANOVA and Tukey tests.Results: The addition of silver nitrate to acrylic resins reduced significantly thetensile strength. Statistically, highly significant differences were found among allgroups (P≤0.001). Also, the difference between control and experimental groupswas highly significant (P≤0.001). For surface hardness, the silver nitrate improvedthe surface hardness of acrylics. Highly significant differences were statisticallyobserved between control and 900 ppm group (P≤0.001); and among all groups(P≤0.001)with exception that no significant differences between control and150ppm; and between 150ppm and 900ppm groups(P>0.05).Conclusion: The addition of silver nitrate to acrylics reduced significantly the tensilestrength and improved slightly the surface hardness.

Efficacy and Safety of Oral Ivermectin and Topical Permethrin in the Treatment of Scabies

2020 ◽  
Vol 33 (1) ◽  
pp. 41-47
Author(s):  
Mohsena Akhter ◽  
Ishrat Bhuiyan ◽  
Zulfiqer Hossain Khan ◽  
Mahfuza Akhter ◽  
Gulam Kazem Ali Ahmad ◽  
...  
Keyword(s):  
Skin Diseases ◽  
Close Contact ◽  
Randomized Study ◽  
Sarcoptes Scabiei ◽  
Efficacy And Safety ◽  
Common Skin ◽  
Group A ◽  
The Mean ◽  
The Difference ◽  
Group B

Background: Scabies is one of the most common skin diseases in our country. It is caused by the mite Sarcoptes scabiei var hominis, which is an ecto-parasite infesting the epidermis. Scabies is highly contagious. Prevalence is high in congested or densely populated areas. Individuals with close contact with an affected person should be treated with scabicidal which is available in both oral and topical formulations. The only oral but highly effective scabicidal known to date is Ivermectin. Amongst topical preparations, Permethrin 5 % cream is the treatment of choice. Objective: To evaluate the efficacy & safety of oral Ivermectin compared to topical Permethrin in the treatment of scabies. Methodology: This prospective, non-randomized study was conducted at the out-patient department of Dermatology and Venereology of Shaheed Suhrawardy Medical College & Hospital over a period of 6 months, from August 2016 to January 2017. The study population consisted of one hundred patients having scabies, enrolled according to inclusion criteria. They were divided into two groups. group A was subjected to oral Ivermectin and the group B to Permethrin 5% cream. Patients were followed up on day 7 and 14 for assessment of efficacy and safety. Result: The mean scoring with SD in group A (Ivermectin) and group B (Permethrin) were 8.26 ± 2.22 and 7.59 ± 2.01 respectively at the time of observation. The difference between the mean score of the two group is not significant (p=0.117) the mean scoring with SD in group A and group B were 4.54 ± 2.05 and 1.64 ± 1.84 respectively at 7thdays. The difference between the mean score of the two group is significant (p<0.001). The mean scoring with SD in group A and group B were 2.68± 2.35 and .36± 1.10 respectively at 14th day difference between the mean score of the group is significant (p<0.001). Conclusion: Topical application of permethrin 5% cream is more effective and safer than oral Ivermectin in the treatment of scabies. TAJ 2020; 33(1): 41-47

EFFECTS OF SYNTHETIC LH/FSH-RELEASING HORMONE (LRH) ON PLASMA LH AND FSH IN AMENORRHOEIC WOMEN

1974 ◽  
Vol 75 (4) ◽  
pp. 647-652 ◽  
Author(s):  
G. Rannevik ◽  
J. Thorell
Keyword(s):  
Urinary Excretion ◽  
Initial Response ◽  
Releasing Hormone ◽  
The Mean ◽  
The Difference ◽  
Serial Measurements

ABSTRACT Eight amenorrhoeic women were given 100 μg synthetic LRH (Hoechst) iv and im, respectively, at an interval of 2 weeks. Four of the women received the iv injection first and four the im injection. The urinary excretion of oestrogens and pregnanediol was low and unaltered throughout the test weeks. The effects of LRH were compared by serial measurements of the plasma LH and FSH during 8 h. The initial response of LH for up to 25 min and that of FSH for up to 60 min were equal whether LRH was given iv or im. The difference appeared later. Four hours after the injection the mean increase of LH to iv injection was 0.5 ng/ml (N. S.), while that to im injection was 1.9 ng/ml (P < 0.01). The corresponding values for FSH were 1.3 (P < 0.05) and 3.2 (P < 0.001). The effect of LRH administration im was thus found to be larger and more prolonged.

DILLIDUR 450V

Alloy Digest ◽  
2011 ◽  
Vol 60 (12) ◽  
Keyword(s):  
Fracture Toughness ◽  
Wear Resistance ◽  
Physical Properties ◽  
Tensile Properties ◽  
Room Temperature ◽  
Surface Hardness ◽  
Heat Treating ◽  
Hot Working ◽  
Resistant Steel ◽  
Bend Strength

Abstract Dillidur 450V is a water hardened wear-resistant steel with surface hardness at room temperature of 420-480 HB. The steel is easy to weld and bend. Hot working is not recommended. This datasheet provides information on composition, physical properties, hardness, tensile properties, and bend strength as well as fracture toughness. It also includes information on wear resistance as well as forming, heat treating, machining, and joining. Filing Code: SA-638. Producer or source: Dillinger Hütte GTS.

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