Particle In Binder Research Articles

Analysis of gaseous emission and particle number size distributions in metal casting processes with binder jetting moulds

The impact on indoor air quality during metal casting processes using the 3D printing (3DP) binder jetting technique to manufacture moulds is analyzed in this research. This study investigates the particle size distribution and gas concentration during the manufacturing stages of 3DP moulds, with focus on particle deposition in the human respiratory system. The goal is to understand the risks associated with particle and gas emissions in binder jetting 3D printing, and thus improve worker safety. The results indicate that particle emission rates are lowest during printing (0.01 1011particles min−1) but increase during post-processing and melting-pouring phases (3.07 1011 particles min−1). During melting and pouring, the emission of particles was mainly in the range 7.9–71 nm, with values 10 times higher than in the previous phases. The study calculates the deposition of inhaled particles in different parts of the respiratory tract and reveals a 2.39 times higher extrathoracic mass deposition during 3DP mould manufacturing stages compared to melting-pouring stages. Additionally, alveolar mass deposition is higher during melting-pouring stages due to an increase in ultrafine emission rates. The study emphasizes the importance of insulation equipment and workplace ventilation in indoor spaces, particularly during heating processes that generate ultrafine particles through nucleation, so that health risks can be mitigated.

Feasibility study of a photoconductor based dosimeter for quality assurance in radiotherapy

With the recent market entries of new types of linear accelerators (LINACs) with a multi leaf collimator (MLC) mounted on them, high-precision radiosurgery applying a LINAC to measure high-dose radiation on the target region has been gaining popularity. Systematic and accurate quality assurance (QA) is of vital important for high-precision radiosurgery because of its increased risk of side effects including life-threatening ones such as overexposure of healthy tissues to high-dose radiation beams concentrated on small areas. Therefore, accurate dose and dose-distribution measurements are crucial in the treatment procedure. The accurate measurement of the properties of beams concentrated on small areas requires high-precision dosimeters capable of high-resolution output and dose mapping as well as accurate dosimetry in penumbra regions. In general, the properties of beams concentrated on small areas are measured using thermos luminescent dosimeters (TLD), diode detectors, ion chambers, diamond detectors, or films, and many papers have presented the advantages and disadvantages of each of these detectors for dosimetry. In this study, a solid-state photoconductor dosimeter was developed, and its clinical usability was tested by comparing its relative dosimetric performance with that of a conventional ion chamber. As materials best-suited for radiation dosimeters, four candidates namely lead (II) iodide (PbI2), lead (II) oxide (PbO), mercury (II) iodide (HgI2), and HgI2/ titanium dioxide (TiO2) composite, the performances of which were proved in previous studies, were used. The electrical properties of each candidate material were examined using the sedimentation method, one of the particle-in-binder (PIB) methods, and unit-cell-type prototypes were fabricated. The unit-cell samples thus prepared were cut into specimens of area 1 × 1 cm2 with 400-μ m thickness. The electrical properties of each sample, such as sensitivity, dark current, output current, rising time, falling time, and response delay, were then measured, in addition to the consistency, reproducibility and linearity of each unit-cell. According to the measurement results, HgI2/TiO2 composite outperformed the other candidate materials. A radiation dosimeter with a chamber-type structure was fabricated in this study using a LINAC under accelerating voltages of 6, and 15 MV and compared with a commercial ion chamber. Percent depth dose (PDD) and beam profile were measured on a water phantom at a fixed area of 10 × 10 cm2 by using the fabricated chamber-type dosimeter, and the values were compared with those measured by a commercial ion chamber. Additionally, a homogeneous phantom was fabricated, and the exposure doses of the center points were measured according to a real treatment plan, followed by a comparison of the measured values as relative values. In this paper, we report that the manufactured dosimeter shows similar characteristics in terms of PDD and beam profile and results for the conventional ion chamber. Based on these results, it is demonstrated that the HgI2/TiO2-based dosimeter complies with radiotherapy QA requirements, namely Superior detection characteristics, consistency, dose linearity, reproducibility. Thus, we expect the HgI2/TiO2-based dosimeter to be used commercially in the future.

방사선치료기기 정도관리를 위한 광도전체 센서 제작 및 평가

최근 다엽콜리메이터를 부착한 선형가속기를 이용한 방사선수술의 빈도가 점차 높아지고 있다. 이러한 정교한 방사선 수술은 소조사면 내에 고선량의 방사선이 집중적으로 조사되기 때문에 체계적이고 정확한 정도관리가 필수적이다. 본 연구는 PIB(Particle in Binder) 방식 중 침전법을 이용하여 <TEX>$400{\mu}m$</TEX> 두께의 요오드화납(<TEX>$PbI_2$</TEX>)과 요오드화수은(<TEX>$HgI_2$</TEX>) 광도전체 센서 시편를 제작하였다. 제작된 시편의 전기적 특성은 암전류, 출력전류, 응답특성 및 선형성을 평가하였다. 평가 결과, <TEX>$HgI_2$</TEX> 가 우수한 신호발생량과 선형성을 보였다. 끝으로, 두께에 따른 <TEX>$HgI_2$</TEX> 센서의 신호반응 특성 결과, <TEX>$400{\mu}m$</TEX> 두께에서 신호발생효율이 가장 높았고, <TEX>${\pm}2.5%$</TEX> 이내의 우수한 재현성을 보였다. Recently, a use of linear accelerator with a multi-leaf collimator(MLC) for radiation therapy is increasing. The importance of quality assurance (QA) for the linear accelerator is emphasized as the side effects of the inaccurate delivery of the radiation beam has been increased according to the high dose irradiation technique. In this study, The <TEX>$HgI_2$</TEX> and <TEX>$PbI_2$</TEX> photoconductor layer samples of <TEX>$400{\mu}m$</TEX> thickness were fabricated using sedimentation method among particle-in-binder technology. From the fabricated samples, the electrical properties(dark current, output current, response properties and linearity) were investigated. From the experimental results, <TEX>$HgI_2$</TEX> has good charge signal generation and linearity. Finally, from the signal response results about various thickness of <TEX>$HgI_2$</TEX> sensor, the signal creation efficiency of <TEX>$400{\mu}m$</TEX> thickness of <TEX>$HgI_2$</TEX> sensor has the highest value and the excellent reproducibility below <TEX>${\pm}2.5%$</TEX>.

Improvement in pixel signal uniformity of polycrystalline mercuric iodide films for digital X-ray imaging

We investigated polycrystalline mercuric iodide (HgI2) that exhibits uniform pixel signals for its use in digital X-ray imaging. To fabricate thin polycrystalline HgI2 films, the particle-in-binder (PIB) method is used because it enables the fabrication of X-ray conversion films at a low temperature and a normal pressure. Moreover, it has a large-scale deposition capacity at a low cost. Although the thin layers fabricated by the PIB method have such advantages, they are chemically unstable and show poor reproducibility and nonuniform X-ray response. To solve these problems, in this study, additional physical and chemical treatments were performed along with the PIB method after taking the size confinement effect of photoconductive particles into consideration. Morphological and electrical properties were measured to investigate the effects of the physical and chemical treatments.

Study on the feasibility of the HgI2 dosimeter for quality assurance of radiotherapy

In radiotherapy, a variety of detectors such as ionization chambers, films, TLDs, diodes, and OSL, are being used for quality assurance (QA). Owing to its high sensitivity and feasibility to operate at low voltages, silicon (Si) photoconductors, which are used as detection material of a diode, are currently being used as relative dosimeters. In addition, other materials such as amorphous selenium (a-Se), cadmium telluride (CdTe), lead iodide (PbI2), and mercury iodide (HgI2) were also being investigated for their feasibility as diagnostic radiation detector. Among these materials, HgI2 has been reported to show remarkable properties including high spatial resolution and high stopping power. Hence In this study, we have verified the feasibility of HgI2 dosimeter for quality assurance of radiotherapy. In order to fabricate the detector, HgI2 was mixed with TiO2 to minimize the signal reduction. Following this, the resulting mixture was deposited onto indium tin oxide (ITO) coated glass by particle-in binder (PIB) method. Finally, the top ITO electrode was coated by magnetron sputterring system. Subsequently, we measured the electrical properties generated by high-energy radiation from linear accelerator (LINAC), and analyzed the reproducibility, linearity, and percent depth dose (PDD) of the fabricated detoctor. In addition, we have determined the build-up materials in experimental setup, since the thickness of build-up region, where the secondary electron emission equilibrium occurs, changes depending on radiation energy. It was observed that the relative variations measured as standard deviation divided by the average value among repeated measurements was approximately 1%. Deviations from linearity are smaller than 5%. Finally, we compared the experimental data of the detector fabricated in this study with those of the farmer-type ionization chamber. Base on the results obtained from this study, it could be realized that HgI2 could be used as dosimeter for QA of radiotherapy.

저온동시소성세라믹 기판 위에 제작된 PZT 박막의 증착조건이 박막의 구조적 특성에 미치는 영향

Recently, low temperature co-fired ceramic (LTCC) technology is widely used in sensors, actuators and microsystems fields because of its very good electrical and mechanical properties, high reliability and stability as well as possibility of making 3D micro structures. In this study, we investigated the effects of sputtering gas ratio and annealing temperature on the crystal structure of <TEX>$Pb(ZrTi)O_3$</TEX> (PZT) thin films deposited on LTCC substrate. The LTCC substrate with thickness of <TEX>$400\;{\mu}m$</TEX> were fabricated by laminating 4 green tapes which consist of alumina and glass particle in an organic binder. The PZT thin films were deposited on Pt / Ti / LTCC substrates by RF magnetron sputtering method. The results showed that the crystallization of the films were enhanced as increasing <TEX>$O_2$</TEX> mixing ratio. At about 25% <TEX>$O_2$</TEX> mixing ratio, was well crystallized in the perovskite structure. PZT thin films was annealed at various temperatures. When the annealing temperature is lower, the PZT thin films become a phyrochlore phase. However, when the annealing temperature is higher than <TEX>$600^{\circ}C$</TEX>, the PZT thin films become a perovskite phase. At the annealing temperature of <TEX>$700^{\circ}C$</TEX>, perovskite PZT thin films with good quality structure was obtained.

LTCC 기판상에 증착한 GZO 가스 센싱 박막의 두께 의존 특성 연구

A novel design of gas sensor using Ga-doped ZnO (GZO) thin films which are deposited on low temperature co-fired ceramic (LTCC) substrates is presented. The LTCC substrates with thickness of 400 are fabricated by laminating 12 green tapes which consist of alumina and glass particle in an organic binder. The GZO thin films with different thickness are deposited on LTCC substrates, by RF magnetron sputtering method. The microstructure and sensing properties of GZO gas sensing films are analyzed as a function of the film thickness. The films are well crystallized in the hexagonal (wurzite) structure with increasing thickness. The maximum sensitivity of 3.49 is obtained at 100 nm film thickness and the fastest 90% response time of 27.2 sec is obtained at 50 nm film thickness for the operating temperature of to the gas.

Comparison of characteristics of α-PbO and β-PbO photoconductors for digital X-ray detectors

There have been recent investigations on direct conversion materials and photoconductors, which generate electron–hole pairs (EHPs), for X-ray image acquisition. In this paper, we compare the characteristics of lead oxides of specific phases. We prepared litharge, the red tetragonal lead oxide α-PbO, from massicot, the yellow orthorhombic oxide β-PbO, and fabricated films by the particle in binder (PIB) method. Structural and optical characteristics of the fabricated lead oxide films were investigated using scanning electron microscopy (SEM) and X-ray diffraction (XRD). Also, we measured electrical properties of the films and compared X-ray sensitivities, leakage currents and Signal to Noise Ratio (SNR) of tetragonal α-PbO and orthorhombic β-PbO. The electrical properties and X-ray sensitivities of tetragonal α-PbO films were similar to those of orthorhombic films, but the leakage current of α-PbO films was about 0.5 pA/mnf while the leakage current of the other films was about 3.5 pA/mnf. We therefore conclude that the electrical properties of tetragonal α-PbO films are better. In results reported here, however, we did not succeed in creating pure tetragonal α-PbO from orthorhombic β-PbO, indicating that more research is needed on the preparation of pure α-PbO material.

Performance evaluation of polycrystalline photoconductors for radiation therapy imaging

Electronic portal imaging devices based on megavoltage (MV), active matrix, flat-panel imagers (AMFPIs) are presently regarded as the gold standard in portal imaging for external beam radiation therapy. These devices, employing indirect detection of incident radiation by means of a metal plate plus phosphor screen combination, offer a quantum efficiency of only approximately 2% at 6 MV, leading to a detective quantum efficiency (DQE) of only approximately 1%. In order to significantly improve the DQE performance of MV AMFPIs, a strategy based on the development of direct detection imagers incorporating thick films of polycrystalline mercuric iodide (HgI2) photoconductor was undertaken and is reported. Two MV AMFPI prototypes, one incorporating an approximately 300 microm thick HgI2 layer created through physical vapor deposition (PVD) and a second incorporating an approximately 460 microm thick HgI2 layer created through screen-printing of particle-in-binder (PIB) material, were quantitatively evaluated using a 6 MV photon beam. The reported measurements include empirical determination of x-ray sensitivity, lag, modulation transfer function (MTF), noise power spectrum, and DQE. For both prototypes, MTF and DQE results were found to be consistent with theoretical expectations and the MTFs were also found to be higher than that measured from a conventional MV AMFPI. In addition, the DQE results exhibit input-quantum-limited behavior, even at extremely low doses. Compared to PVD, the PIB prototype exhibits much lower dark current, slightly higher lag, and similar DQE. Finally, the challenges associated with this approach, as well as strategies for achieving considerably higher DQE through thicker HgI2 layers, are discussed. The DQE of each of the prototypes is found to be comparable to that of conventional MV AMFPIs, commensurate with the modest photoconductor thicknesses of these early samples. It is anticipated that thicker layers of HgI2 based on PIB deposition can provide higher DQE while maintaining good material properties.

Fabrication and imaging characterization of high sensitive CsI(Tl) and Gd2O2S(Tb) scintillator screens for X-ray imaging detectors

Indirect-detection methods consisted of an X-ray converter and photodiode arrays are more widely used in medical diagnosis and industrial fields. Two major scintillation materials such as terbium-doped gadolinium oxysulfide(Gd 2 O 2 S:Tb, Gadox) and thallium-doped cesium iodide(CsI:Tl) are commonly used. In this work, Gadox screens were manufactured by particle in binder (PIB) layer method and CsI:Tl scintillator films with columnar structure were also fabricated by thermal evaporation method onto glass substrates. Furthermore, two sample screens were coated to increase the light collection efficiency by white TiO 2 reflective layers. The scintillation properties, such as emission spectrum and light output of these materials were measured by X-ray luminescence condition. In order to investigate the imaging performance of both Gadox and CsI:Tl scintillation screens as converters of X-ray imaging detectors, these materials were optically coupled with a 2D CCD image sensor. The light response to X-ray dose, spatial resolution and X-ray images were measured and analyzed under X-ray imaging system condition.

Ga이 첨가된 ZnO 박막의 가스센서로의 응용 연구

In this work, Ga-doped ZnO (GZO) thin films for gas sensor application were deposited on low temperature co-fired ceramics (LTCC) substrates, by RF magnetron sputtering method. The LTCC substrate is one of promising materials for this application since it has many advantages (e.g., low cost production, high manufacturing yields and easy realizing 3D structure etc.). The LTCC substrates with thickness of <TEX>$400\;{\mu}m$</TEX> were fabricated by laminating 12 green tapes which consist of alumina and glass particle in an organic binder. The structural properties of the fabricated GZO thin film with thickness of 50 nm is analyzed by X-ray diffraction method (XRD) and field emission scanning electron microscope (FESEM). The film shows good adhesion to the substrate. The GZO gas sensors are tested by gas measurement system and show fast response and recovery characteristics to <TEX>$NO_x$</TEX> gas that is 27.2 and 27.9 sec, recpectively.

Reviewing Polycrystalline Mercuric Iodide X-Ray Detectors

Polycrystalline films of HgI <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> , which are used as nuclear radiation detectors, are fabricated by two different methods, either by Physical Vapor Deposition (PVD) or glued with a polymeric binder called also "Particle in Binder" (PIB). Both types of PVD or PIB Detectors are deposited directly on Thin Film Transistor TFT technology imagers and can be used for X-ray imaging. The present review is concentrated on PVD- Polycrystalline-HgI <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> . However, the main review body is a summary of the work performed by RTR, HU, and Varian. Works by other groups are mentioned briefly. The PVD process is explained by reviewing X-ray Diffraction (XRD) and Scanning Electron Microscope (SEM) data. The charge transport properties of the PVD-Polycrystalline HgI <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> detectors as they improved with R&D efforts are shown. The response of these PVD detectors to <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">241</sup> Am and <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">57</sup> Co gamma rays and their X-ray imaging properties such as dark currents, sensitivity, imaging resolution and Detector Quantum Efficiency (DQE) are reviewed