PEMBUATAN GEL HIDROKSIAPATIT CANGKANG KERANG-SIMPING (Amusium pleuronectes) DAN PENGARUHNYA SETELAH APLIKASI DI LESI WHITE-SPOT EMAIL GIGI

Masalah kesehatan gigi tertinggi di Indonesia adalah karies yaitu rusaknya jaringan keras gigi. Pencegahan karies dapat dilakukan dengan meningkatkan remineralisasi. Cangkang kerang-simping merupakan limbah industri kaya kalsium yang dapat menjadi prekursor hidroksiapatit yaitu kristal penyusun gigi. Penelitian ini bertujuan untuk mensintesis gel hidroksiapatit dari cangkang kerang- simping dan mengetahui pengaruh gel hidroksiapatit terhadap remineralisasi email gigi. Metode penelitian merupakan eksperimental laboratoris 2 tahap. Pertama adalah sintesis hidroksiapatit dan evaluasi fisikokimia menggunakan SEM-EDX dan XRD. Hidroksiapatit kemudian dibuat menjadi sediaan gel dan diuji secara organoleptik. Tahap kedua adalah penelitian pre dan post-test control group design menggunakan 16 sampel gigi premolar satu rahang atas post ekstraksi yang terbagi menjadi 2 kelompok yaitu kelompok gel hidroksiapatit 20%, dan kelompok kontrol. Uji kekerasan email gigi menggunakan Vickers microhardness tester sebanyak 2 kali, yaitu sebelum dan setelah aplikasi gel. Hasil menunjukkan bahwa hidroksiapatit cangkang kerang simping berukuran nano, berbentuk granular dengan rasio molar Ca:P 3,22. Konsistensi gel hidroksiapatit homogen, sedikit berbau dan berwarna putih krem. Pada hasil uji kekerasan email terdapat perbedaan signifikan sebelum dan sesudah aplikasi (p0,05) dan terdapat signifikansi perbedaan peningkatan kekerasan antar kelompok (p0,05). Peningkatan kekerasan email kelompok gel hidroksiapatit lebih tinggi daripada kelompok kontrol. Kesimpulannya adalah gel hidroksiapatit cangkang kerang-simping berpotensi sebagai agen remineralisasi email gigi

Excellent Properties of Ni-15 wt.% W Alloy Electrodeposited from a Low-Temperature Pyrophosphate System

Electrodeposited Ni-W alloy coatings are considered to be one of the most suitable candidate coatings to replace carcinogenic hexavalent chromium coatings. In this work, Ni-W alloys are electrodeposited from pyrophosphate baths containing different concentrations of Na2WO4 2H2O (CW) at 40 °C. Both CW and the applied current density can affect the W content in the coatings. The effect of CW becomes weaker with the increased current density. The Ni-W alloys with 15 ± 5 wt.% W (Ni-15 wt.% W) are obtained from the bath containing 40 g L−1 CW at a high current of 8 A dm−2. The microhardness, corrosion resistance and hydrogen evolution reaction (HER) are measured with a microhardness tester and an electrochemical workstation. The modified properties are studied by heat treatment from 200 to 700 °C. The highest microhardness of 895.62 HV and the better HER property is presented after heat treatment at 400 °C, while the best corrosion resistance in 3.5 wt.% NaCl solution appears at 600 °C.

Effects of process parameters on microstructure and mechanical properties of ZL114A alloy under directional solidification

Directional solidification (DS) processing parameters have significant influence on microstructure of ZL114A alloy. Therefore, it is necessary to optimize DS processing parameters to control its properties. This work is aimed at studying the effect rule of DS processing parameters on microstructure of ZL114A alloy. The specimens of this alloy were prepared using high-vacuum DS equipment. In the process of DS, temperatures change from 700 °C to 800 °C, and pulling rates increase from 100 μm/s to 200 m/s. Microstructure of specimens was investigated using scanning electron microscope (SEM) and energy dispersive spectrometer (EDS). Mechanical properties of specimens were measured by means of universal tension tester and microhardness tester. Effects of melt temperatures and pulling rates on the microstructures and mechanical properties were studied and discussed. Experimental results show that the microstructure can be improved with the decrease in melting temperatures and the increase in pulling rates. However, the microstructure became coarser when the pulling rate is too higher. Therefore, a set of processing parameters were optimized as melting temperature of 700 °C and pulling rate of 150 μm/s to improve the microstructure of ZL114A alloy.

PROPERTIES OF COMPOSITE RESIN ALKASIT AND ZIRCONIA-REINFORCED GLASS-IONOMER CEMENT IN DIFFERENT STORAGE

Background: The temperature and salivary pH in a person's mouth are highly dynamic (e.g., before, during, and after eating) and so restorations in a cavity must be resilient to these variable conditions. Temperature and immersion conditions affect the mechanical properties of a restoration. This study aimed to determine the effect of environmental conditions on diametral tensile strength (DTS) and surface microhardness of a resin composite with alkaline fillers or zirconia–reinforced glass ionomer cement (Zr-reinforced GIC). Method: Thirty specimens of a resin composite with alkaline fillers (Cention-N, Ivoclar-Vivadent, Lichtenstein) and 30 specimens with zirconia-reinforced GIC (Zirconomer, Shofu, Japan) were stored at different conditions (23°C and 37°C; with and without immersion in water) for 24 hours. DTS was tested with a Universal Testing Machine (AGS-X series, Shimadzu, Japan) and surface microhardness was tested with a Vickers Microhardness tester (HMV-G Series Micro Vickers Microhardness Tester, Shimadzu, Japan). Data were analyzed statistically using a one-way ANOVA test (and Shapiro-Wilk test. Result: The values of microhardness and DTS increased significantly both for the composite resin alkasite and zirconia-reinforced GIC with increasing temperature in the groups without immersion. However, there was a significant decrease in microhardness and DTS after immersion in distilled water at 37°C for both the composite resin alkasite and zirconia-reinforced GIC. Conclusion: It can be concluded that storage conditions affect the microhardness and DTS of resin composite Alkasite and Zirconia-reinforced GIC

Study on the Softening Behavior of Cu–Cr–In Alloy during Annealing

The softening behavior of a cold-drawn Cu–Cr–In alloy was investigated during annealing between 450 °C and 700 °C. The properties and microstructure evolution of the alloy were characterized using a microhardness tester, electron back-scatter diffraction, and transmission electron microscopy. Elemental In addition was found to hinder the dislocation movement and delay the recovery and recrystallization of the Cu–Cr–In alloy. The experimental data were analyzed using the Johnson–Mehlv–Avramiv–Kolmogorov model. The activation energy of recrystallization of the 60% cold-drawn Cu0.54Cr0.17In alloy was 188.29 ± 18.44 kJ/mol, and the recrystallization mechanism of the alloy was attributed mainly to Cu self-diffusion.

Effect of Silicon Nitride (Si3N4) Addition on the Mechanical and Tribological Performance of Al-Fe-Si Alloy (AA8011)

This research examines the effect of ceramic particulate of Si3N4 on the hardness, tensile, corrosion, and microstructure of reinforced AA8011 composites. The composites were developed by two steps stir casting process where both the particulates and the alloy matrix were preheated and melted respectively before mixing. 0%, 5%, 10%, 15%, and 20% Si3N4 particulates compositions were varied to fabricate the composites. Vickers microhardness tester was employed to study the hardness, the universal testing machine was used to analyze the ultimate tensile strength, the tribological performances of the developed composites AA8011-Si3N4 were analyzed under dry sliding condition using Universal Tribometer. The results of the experiment clearly revealed the improvement in the mechanical properties of the composites compared to the primary Al-Fe-Si alloy with excellent strength mechanism recorded at 20% reinforcement. Composites with 20% Si3N4 was found to have a better wear resistance hence, lowest wear rate.

The Effect of Thermocycling and Surface Treatments on the Surface Roughness and Microhardness of Three Heat-Pressed Ceramics Systems

Dental ceramic restorations are widely used in restorative dentistry. However, these restorations can be affected once cemented in the oral cavity by several factors. How can conventional surface treatments, such as glazing and mechanical polishing, diminish the effects of aging? The purpose of this in vitro study was to evaluate the effect of thermocycling and conventional surface treatments on the surface roughness and microhardness of three types of glass-ceramics by using a profilometer, scanning electron microscopy (SEM), atomic force microscopy (AFM), and a microhardness tester. Three types of ceramic systems (zirconia reinforced lithium silicate glass-ceramic, lithium disilicate glass-ceramic, and feldspathic glass-ceramic) (n = 48) were prepared. The samples were subjected to thermocycling for 10,000 cycles. Surface roughness was evaluated numerically using a profilometer and visually by using SEM and AFM. Microhardness was performed using a microhardness tester. The data were interpreted using the ANOVA test, and the results were correlated using Pearson’s correlation formula (r). Significant differences were found before and after thermocycling for the Ra (p < 0.01) and Rz (p < 0.05) parameters. As well, differences between glazed and polished surfaces were significant before and after thermocycling for surface roughness and microhardness (p < 0.05). A correlation was made between average surface roughness and microhardness (r = −460) and for the maximum surface roughness and microhardness (r = −606). Aging increases the roughness and decreases in time the microhardness. The tested ceramic systems behaved differently to the aging and surface treatments. Surface treatments had a significant impact on the microhardness and surface characteristics. The glazed groups were reported with higher surface roughness and lower microhardness when compared to the polished groups before and after thermocycling. The measuring roughness techniques determine the scale-dependent values for the Ra (Sa) and Rz (Sq) parameters. Thermocycling almost doubled the surface roughness for all the tested samples. Microhardness decreased only for the Celtra glazed samples. Nano-roughness increased the values for Vita and slightly for Emax. Thermocycling had little effect on Emax ceramic and a more significant impact on Celtra Press ceramic.

The Influence of Anodic Alumina Coating Nanostructure Produced on EN AW-5251 Alloy on Type of Tribological Wear Process

The article presents the influence of the anodic alumina coating nanostructure produced on aluminum alloy EN AW-5251 on the type of tribological wear process of the coating. Oxide coatings were produced electrochemically in a ternary electrolyte by the DC method. Analysis of the nanostructure of the coating was performed using ImageJ 1.50i software on micrographs taken with a scanning electron microscope (SEM). Scratch tests of the coatings were carried out using a Micron-Gamma microhardness tester. The scratch marks were subjected to surface geometric structure studies with a Form TalySurf 2 50i contact profiler. Based on the studies, it was found that changes in the manufacturing process conditions (current density, electrolyte temperature) affect changes in the coating thickness and changes in the anodic alumina coating nanostructure (quantity and diameter of nanofibers), which in turn has a significant impact on the type of tribological wear. An increase in the density of the anodizing current from 1 to 4 A/dm2 causes an increase in the diameter of the nanofibers from 75.99 ± 7.7 to 124.59 ± 6.53 nm while reducing amount of fibers from 6.6 ± 0.61 to 3.8 ± 0.48 on length 1 × 103 nm. This affects on a change in the type of tribological wear from grooving to micro-cutting.

KARAKTERISASI MIKROSTRUKTUR, KEKERASAN, KOMPOSISI KIMIA DAN STRUKTUR KRISTAL LAPISAN PADA PERMUKAAN BAJA

KARAKTERISASI MIKROSTRUKTUR, KEKERASAN, KOMPOSISI KIMIA DAN STRUKTUR KRISTAL LAPISAN PADA PERMUKAAN BAJA. Baja dan paduannya digunakan sebagai bahan struktur komponen reaktor nuklir dan peralatan dukung fasilitas hot cell. Selama pengoperasian reaktor nuklir atau fasilitas hot cell, bahan struktur mengalami tegangan tarik, tekan, dan gesek dalam lingkungan radiasi tinggi sehingga dapat menurunkan umur komponen. Salah satu solusi yang digunakan adalah pelapisan permukaan baja dengan bahan pelapis yang mempunyai kekerasan, ketahanan korosi dan aus tinggi. Penelitian ini mempunyai tujuan untuk mendapatkan karakter mikrostruktur, ketebalan, kekerasan, komposisi kimia dan struktur kristal lapisan pada permukaan baja. Metode yang digunakan adalah pengamatan mikrostruktur menggunakan mikroskop optik, kekerasan dengan Vickers microhardness tester, komposisi kimia dengan spark spectrometer dan struktur lapisan permukaan baja dengan difraktometer sinar-X (XRD). Hasil penelitian menunjukkan bahwa mikrostruktur base metal terdiri dari butiran ekuiaksial halus dengan fasa ferit dan perlit, antarmuka logam-lapisan terlihat jelas, serta lapisan kompak dan homogen dengan ketebalan rerata 624,071 μm. Kekerasan lapisan adalah 943 VHN. Dari komposisi kimia diketahui base metal adalah baja karbon S45C, sedangkan lapisan permukaan berupa senyawa stabil khrom oksida (Cr2O3) dengan struktur kristal heksagonal. Kata kunci: lapisan permukaan, baja, mikrostruktur, kekerasan, komposisi kimia, struktur kristal.

EFFECT OF Cr3C2 ADDITION ON THE MICROSTRUCTURE AND PROPERTIES OF LASER CLADDING NiCrBSi COATINGS

In this paper, the enhancement of NiCrBSi coatings by adding Cr3C2 were investigated. The NiCrBSi coatings with different additions of Cr3C2 were produced by laser cladding. The microstructure, hardness and wear resistance of the coatings were studied by optical microscope (OM), scanning electron microscopy (SEM), X-ray diffraction (XRD), microhardness tester and M-200 wear tester. It is found that the main phases in the coatings are [Formula: see text]-Ni, Cr[Formula: see text]C6 and Cr7C3, and they also contain a small amount of CrB, Ni4B3 and Ni3Si2. Moreover, with the increase of Cr3C2 addition, the microhardness and wear resistance of coatings are obviously improved. When the addition of Cr3C2 is 20%, the wear resistance of the coating is the best, and the wear resistance of the coating increased by 191.2% than that of the Cr3C2-free coating. The wear resistance of coating decreases when the addition of Cr3C2 reaches 30%.