DOCSLIB.ORG

Crystal Structures and Luminescence Properties of Aln-Deficient Eu2+

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text

Load more

Journal of the Korean Physical Society, Vol. 57, No. 4, October 2010, pp. 990∼993

Crystal Structures and Luminescence Properties of AlN-deficient
Eu2+-activated Ca-α-SiAlON Phosphor

Sung-Soon Park, Bo-Yun Jang∗ and Joo-Seok Park

Korea Institute of Energy Research, Daejeon 305-343

Sahn Nahm

Department of Materials Science and Engineering, Korea University, Seoul 136-701

(Received 15 January 2010, in final form 5 July 2010)
Eu2+-doped Ca-α-SiAlON phosphor was synthesized by normal pressure sintering with conven-

  • tional tube furnace, and its crystal structures and luminescence properties were investigated. Eu2+
  • -

doped Ca-α-SiAlON phosphor exhibited an orange light peaking at 583 nm. During the annealing, some of the raw materials evaporated, which resulted in unreacted AlN in the final product. In order to obtain a final product with a single α-phase, we prepared samples with various AlN-deficient compositions, and we studied the effects on crystal structures and luminescence properties. For the sample with 15 mol% AlN-deficient composition, 18% enhancement of the intensity was obtained with the disappearance of excess AlN. In addition, the internal quantum efficiency (IQE) was measured using a specially designed integrating sphere, and 56.82% IQE was gained from Eu2+-doped Ca-α-SiAlON phosphor.

PACS numbers: 42.70.-a Keywords: α-SiAlON, Europium, Phosphor, Luminescence, Crystal Structure DOI: 10.3938/jkps.57.990

I. INTRODUCTION

shows excellent chemical and mechanical stability [15– 17]. SiAlON is known to be stabilized structurally by doping with Y, Li, Ca and rare earth element. Krevel et al. have been reported the use of Ce3+- and Eu2+-doped M-α-SiAlON (M = Y, Ca) phosphors as green and yellow
White light emitting diodes (LEDs) have been the subjects of enormous research as next-generation illumination sources because of their high efficiency, long life time and low power consumption [1–3]. The yellow phosphor Y3Al5O12:Ce3+, so-called YAG, packaged with a blue chip (emission at around 460 nm) has been widely used for first-generation LEDs [2, 3]. However, the color rendering index (CRI) of the YAG phosphor is too low (∼75%) to be applied for general illumination sources.
There are two approaches to increase the CRI. The first one is packaging the blue chip with green and red phosphors. The other is based on an ultraviolet (UV) chip (emission at around 405 nm) packaged with blue (B), green (G), and red (R) phosphors. Especially, an UV chip with RGB phosphors has been investigated for next-generation illumination because the emission power of the UV chip is higher than that of a blue chip [4,5].
Many nitride and oxy-nitride phosphors have been reported for LED applications because these phosphors can absorb light with wavelengths of 390 ∼ 460 nm [6– 14]. As an orange phosphor, Eu2+-doped Ca-α-SiAlON is a promising phosphor because this crystal structure

  • phosphors, respectively [6]. Xie et al. synthesized Ce3+
  • -

or Eu2+-doped α-SiAlON using hot pressing (HP) and gas pressure sintering (GPS) [7–10]. Fabrication of this phosphor with a blue chip was conducted by Sakuma, and a luminous efficiency of 25.9 lm/W was achieved at room temperature with a forward-bias current of 20 mA [11]. Eu2+-doped β-SiAlON was also studied, and green light was emitted [12]. Recently, Eu2+-doped Ca, Y-stabilized α-SiAlON with an emission at over 580 nm was reported [13,14]. However, those phosphors required a relatively complex process, such as GPS or carbothermal reduction nitridation (CRN), to obtain a single α phase.
In this study, Eu2+-doped Ca-α-SiAlON phosphor was synthesized by conventional solid state reaction method with a horizontal tube furnace, and its crystal structures and luminescence properties were analyzed. Especially, the effects of nonstoichiometric compositions on the luminescence properties were investigated.

∗E-mail: [email protected]; Fax: +82-42-860-3133

-990-

  • Crystal Structures and Luminescence Properties of AlN-deficient · · · – Sung-Soon Park et al.
  • -991-

Fig. 1. Schematic diagram of the system for measuring the internal quantum efficiency.

II. EXPERIMENTS AND DISCUSSION

Ca0.8−xEuxSi9.2Al2.8O1.2N14.8 (x = 0.08, 0.12, 0.16)

Fig. 2. Excitation and emission spectra for various amounts of Eu2+ doping in samples fired at 1680 ◦C for 2 hrs in 30% H2 - 70% N2 atmosphere.

was prepared by the solid state reaction method. CaCO3 (Acros, 99.9%), AlN (Kojundo, 99.9%), α-Si3N4 (LC- 12, Starck, α content 90%, oxygen content <1.2%) and Eu2O3 (Kojundo, 99.9%) were used as the as-received raw materials. After the sample powders had been weighed in appropriate amounts, they were mixed and ground in high-purity isopropyl alcohol us◦ing ball milling for 2 hrs. After having been dried at 90 C, the sample powders were transferred into an alumina boat. Those mixtures were fired in a horizontal tube furnace at 850 ◦C for 4 hrs in N2 atmosphere to evaporate CO2 from CaCO3. Subsequently, a second annealing was carried

Ls

η =
,

Lb − Lu

=

  • R
  • R

  • where Ls
  • Is(λ)dλ, Lb
  • =

λ Ib(λ)dλ, Lu

=
Iu(λ)dλ, with λη being the internal quantum efficiency,
Isλ, Ib, and Iu being the intensities from the light emitted by the sample, the light from the base lamp and the light unabsorbed by the sample, respectively, Ls, Lb, and Lu being the photon fluxes from the light emitted by the sample, the light from the base lamp and the light unabsorbed by the sample, respectively, and λ being the wavelength.

R

◦

out at 1680 C under flowing 30% H2 - 70% N2 mixed gas controlled by mass flow controllers. After firing, the samples were gradually cooled down in the furnace.
X-Ray diffraction (XRD, Rigaku, DMAX 2000, Japan) pattern analysis was conducted using Cu-Kα radiation (λ = 1.5418 angstrom). For the analysis of luminescence characteristics, the excitation and emission spectra were achieved using luminescence spectrometer (Perkin-Elmer, LS50B, USA) equipped with a 200 W Xe lamp and red-sensitive photomultipliertube (Hamamatsu, R928, Japan). To evaluate the possibility of its use as an orange phosphor for a white LED light source, we measured the IQE using the system shown in Fig. 1. LED (LS395, Oceanoptics, USA) with excitation at 395 nm was used as a reference light source. A 2048 × 64 pixel CCD array detector (Maya2000pro, Oceanoptics, USA) was connected to the integrating sphere using an optical fiber. The sample was placed at the center of an integrating sphere with two baffles. At first, the base spectrum (Ib) from the LED light source was measured without the sample. Then, a quartz tube filled with the phosphor was placed into the integrating sphere, and the sample spectrum was measured. The sample spectrum was divided into two spectra, which were attributed to the light unabsorbed by the sample (Iu) and the light emitted by the sample (Is). Therefore, the internal quantum efficiency was calculated using the following equation:
Excitation and emission spectra were obtained from
Ca0.8−xEuxAl2.8Si9.2O1.2N14.8 phosphor with various amounts of doped-Eu2+ ions, as shown in Fig. 2. All the emission spectra were measured at an excitation wavelength of 405 nm, and the excitation spectra were measured with the maximum emission wavelength of each sample. As shown in the emission spectra, broad emission bands peaking from 580 to 586 nm were observed. With increasing Eu2+ doping concentration, the peak shifted toward longer wavelength. This shift stopped when x exceeded 0.16. The intensity of the emission band changed slightly with x. but that change was small. Generally, emission from the 4f - 5d transition of Eu2+ ion is known to have a very sharp and narrow peak because only line-to-line transitions between energy levels shielded by the outer 5d-electron shell [18]. The broad emission band in α-SiAlON phosphor might be attributed to the large energy level splitting due to the strong covalent bonding between the Eu2+ ions and neighboring atoms. This strong covalent bonding was one of the characteristics of nitride or oxy-nitride materials. In the case of excitation, many broad bands were detected from 300 to 550 nm. The sharp excitation

  • -992-
  • Journal of the Korean Physical Society, Vol. 57, No. 4, October 2010

Fig. 3. X-ray diffraction pattern of Eu2+-doped Ca-α-
Fig. 4. X-ray diffraction patterns of AlN-deficient Eu2+

doped Ca-α-SiAlON fired at 1680 ◦C for 2 hrs in 30% H2 70% N2 atmosphere.
--
SiAlON fired at 1680 ◦C for 2 hrs in 30% H2 - 70% N2 atmosphere.

peak at 390 nm has been reported to be a representative peak of Eu2+ ions [18]. In SiAlON phosphor, however, there were additional bands that might also be due to the strong covalent bonding of Eu2+ ion. It must be pointed out that four small peaks from 425 to 460 nm were dummy ones from the xenon light source because those peaks were detected for all phosphors. There wide excitation bands allow α-SiAlON phosphor to be applied for UV, as well as blue, LEDs.
In this study, evaporation was always observed in the raw materials during the annealing process. At the outlet of the alumina tube in the furnace, the evaporated elements, which were proven to be mainly SiO2 by SEM and XRD measurements, were deposited. Although annealing was conducted in strong a reducing atmosphere, oxidation always occurred due to the residual oxygen inside and outside the raw materials. Thus, SiO2 was formed and easily evaporated during annealing at temperatures

Fig. 5. Normalized intensities and peak emission wavelengths of AlN-deficient Eu2+-doped Ca-α-SiAlON fired at 1680 ◦C for 2 hrs in 30% H2 - 70% N2 atmosphere.

◦

higher than 1600 C. As a result, a secondary phase was detected in the final product. Figure 3 shows the XRD patterns of α-SiAlON phosphor (x = 0.12) fired at 1680 ◦C for 2 hrs in 30% H2 - 70% N2 atmosphere. Main peaks were matched those from Ca0.8Al2.8Si9.2O14.8 (JCPDF #33-0261). Even though the raw materials had been mixed in a stoichiometric composition, unreacted AlN was detected in the final product, which was obviously attributed to the evaporation of Si from the raw materials. Generally, unreacted elements caused a degradation of the luminescence properties. Therefore, to obtain a single α-phase, we synthesized AlN-deficient samples, and their properties were observed.
A single α-phase was achieved from the samples when the deficient amount of AlN was from 10 to 30 mol% in the starting composition. In addition, unreacted Si3N4 appeared when AlN deficiency was 35 mol%. As a result, preparing the starting materials with AlN-deficient compositions was needed to gain single-phase α-SiAlON.
To investigate the luminescence properties of the above phosphors, we measured the PL spectra. Figure 5 shows the normalized intensities and peak emission wavelengths of 0 ∼ 30 mol% AlN-deficient phosphors fired at 1680 ◦C for 2 hrs in 30% H2 - 70% N2 atmosphere. As the deficient amount of AlN increased, the PL intensity also increased. The maximum intensity was gained when the deficient amount of AlN was 15 mol%. The intensity decreased when the deficient amount of AlN exceeded 15 mol%. An intensity enhancement of 18% was obtained by preparing the sample in 15 mol% AlN-deficient com-
Figure 4 shows the XRD patterns of AlN-deficient

◦

phosphors (x = 0.12) fired at 1680 C for 2 hrs in 30% H2 -70% N2 atmosphere. There was no significant crystal structure change from that of α-SiAlON. However, a single α-phase without unreacted AlN was achieved.

  • Crystal Structures and Luminescence Properties of AlN-deficient · · · – Sung-Soon Park et al.
  • -993-

α-SiAlON was synthesized in atmosphere at normal pressure, SiO2 always evaporated from the raw materials, resulting in some AlN remaining in the final phase. Therefore, the samples with AlN-deficient compositions were sintered. From the crystal structural analysis, unreacted AlN disappeared when the deficient amount of AlN was from 10 ∼ 30 mol%. The maximum intensity was obtained from the 15 mol% AlN deficient sample. An internal quantum efficiency of 56.83% was obtained from that sample. As a consequence, high-efficiency Eu2+-doped Ca-α-SiAlON could be achieved using normal pressure sintering by preparing the starting materials in AlN- deficient composition.

  • Fig. 6. Emission spectra of 15 mol% AlN-deficient Eu2+
  • -

-

REFERENCES

doped Ca-α-SiAlON fired at 1680 ◦C for 2 hrs in 30% H2 70% N2 atmosphere: (a) peak from the source light, (b) peak from the light unabsorbed by the sample, and (c) peak from the light emitted by the sample.
[1] S. Nakamura, T. Mukai and M. Senoh, Appl. Phys. Lett.
64, 1687 (1994).
[2] S. Narukawa and G. Fasol, The Blue Laser Diode:

GaN Based Light Emitters and Lasers (Springer, Berlin,

1997), p. 216.
[3] P. Schlotter, J. Baur, Ch. Hielscher, M. Kunzer, H.
Obloh, R. Schmidt and J. Schneider, Mater. Sci. Eng., B. 59, 390 (1999).
[4] W. Tews, G. Roth and S. Tews, Advanced Silicate Phos-

phors for Improved White LED: Proceeding of the Phos-

phor Global Summit (Seoul, 2007), p. 5.

[5] Y. Fukuda, Luminescence of Eu-doped Sr-SiAlON Phosphor, Proceeding of the Phosphor Global Summit (Seoul,

2007).

position. There was no change in the emission peak’s wavelength, except for the 30 mol% AlN-deficient sample. This result indicates that no crystal field changes occurred until the deficient amount of AlN was lower than 30 mol%. According to previous research, a highpressure atmosphere is required to synthesize nitride or oxy-nitride phosphors. From the results of this research, however, an oxy-nitride phosphor of α-SiAlON could be obtained by using a normal-pressure sintering process. In addition, the raw materials needed to be prepared with AlN-deficient compositions for the synthesis of α-phase SiAlON phosphor by normal pressure sintering.

[6] J. W. H. van Krevel, J. W. T. van Rutten, H. Mandal,
H. T. Hintzen and R. Metselaar, J. Solid State Chem. 165, 19 (2002).
[7] R. J. Xie, M. Mitomo, K. Uheda, F. F. Xu and Y.
Akimune, J. Am. Ceram. Soc. 85, 1229 (2002).
[8] R. J. Xie, N. Hirosaki, M. Mitomo, Y. Yamamoto and
T. Suehiro, J. Phys. Chem. B. 108, 12027 (2004).
[9] R. J. Xie, N. Hirosaki, M. Mitomo, Y. Yamamoto, T.
Suehiro and N. Ohashi, J. Am. Ceram. Soc. 87, 1368 (2004).
[10] R. J. Xie, N. Hirosaki, K. Sakuma, Y. Yamamoto and
M. Mitomo, Appl. Phys. Lett. 84, 26 (2004).
[11] K. Sakuma, K. Omichi, N. Kimura, M. Ohashi and D.
Tanaka, Opt. Lett. 29, 17 (2004).

To evaluate α-SiAlON phosphor in this study for LED applications, we measured the internal quantum effi- ciency. Figure 6 shows the emission spectra of 15mol% AlN-deficient phosphor fired at 1680 ◦C for 2 hrs in 30% H2 - 70% N2 atmosphere. Peak (a) was from the source light, the peak (b) was from the light unabsorbed by the sample and peak (c) was from the light emitted by the sample. The measured internal quantum efficiency was 56.83%. Consequently, α-SiAlON phosphor in this research should be a good candidate for UV, as well as blue LED applications.

[12] N. hirosaki, R. J. Xie, K. Kimoto, T. Sekiguchi, Y. Yamamoto, T. Suehiro and M. Mitomo, Appl. Phys. Lett. 86, 211905 (2005).
[13] T. Suehiro, N. Hirosaki, R. J. Xie and M. Mitomo, Chem.
Mater. 17, 308 (2005).
[14] K. Sakuma, N. Hirosaki, R. J. Xie, Y. Yamamoto and T.
Suehiro, Mater. Lett. 61, 547 (2007).

III. CONCLUSION

AlN-deficient Eu2+-doped Ca-α-SiAlON was synthesized by normal pressure sintering with a conventional alumina tube furnace, and its crystal structures and luminescence properties were investigated. In the PL spectra, broad emission and excitation bands were observed, and those broad bands were due to a strong crystal field caused by highly-covalent bonding of Eu2+ ions. When

[15] J. W. T. van Rutten, H. T. Hintzen and R. Matselaar,
J. Eur. Ceram. Soc. 16, 955 (1996).
[16] H. Mandal, J. Eur. Ceram. Soc. 19, 2349 (1999). [17] C. Santos, K. Strecker, J. V. C. de Souza, O. M. M. Silva and C. R. M. da Silva, Mater. Lett. 58, 1792 (2004).
[18] G. Blasse and B. C. Grabmaier, Luminescent Materials
(Springer Verlag, Berlin, 1994), p. 25.

Recommended publications
  • Combustion Synthesis of Porous Oxynitride Materials Under Conditions of Forced filtration of Reacting Gas ⇑ Anatoly S

    Combustion Synthesis of Porous Oxynitride Materials Under Conditions of Forced filtration of Reacting Gas ⇑ Anatoly S

    International Journal of Heat and Mass Transfer 95 (2016) 264–271 Contents lists available at ScienceDirect International Journal of Heat and Mass Transfer journal homepage: www.elsevier.com/locate/ijhmt Combustion synthesis of porous oxynitride materials under conditions of forced filtration of reacting gas ⇑ Anatoly S. Maznoy a, , Alexander I. Kirdyashkin b, Ramil M. Gabbasov a a Tomsk Scientific Center SB RAS, Akademicheskiy Av., 10/4, Tomsk 634055, Russia b Far Eastern Federal University, Suhanova St., 8, Vladivostok 690950, Russia article info abstract Article history: Combustion synthesis is a promising technique for producing the oxynitride ceramics, which represent a Received 5 June 2015 new class of materials with high resistance to high temperatures and to intensive wear. The different Received in revised form 15 November 2015 experimental ways of control of combustion parameters were considered, such as sample porosity, poros- Accepted 23 November 2015 ity structure of samples, different experimental configurations (coflowing and opposite flow systems), Available online 21 December 2015 and pressure. Kinetic features of nitrogenation of reacting samples (aluminium, silicon oxide and sialon powders) were analyzed at different conditions. Forced nitrogen filtration through porous sample sub- stantially improved the process of combustion synthesis (yield with higher nitrogen content, porous structure). The application of coflowing configuration intensifies the combustion synthesis and provides the re-heating process by convective heat transfer from combustion products to the initial mixture. It was demonstrated that this process leads to super-adiabatic temperature rise in the combustion zone. Coflowing configuration allow one to synthesize porous sialon with the conversion ratio up to 0.995 with combustion rate 0.8 mm/s and maximum combustion temperature about 1900 °C.
  • SIALON CERAMIC MATRIX COMPOSITES ﻤﻭﺍﺩ�ﻤﺭﻜﺒﺔ�ﺴﻴﺭﺍﻤﻴﻜﻴﺔ�ﺫﺍﺕ� ﺃﺴﺎﺱ �ﺴﺎﻴﻠﻭﻥ �� �� Shaker J

    SIALON CERAMIC MATRIX COMPOSITES ﻤﻭﺍﺩﻤﺭﻜﺒﺔﺴﻴﺭﺍﻤﻴﻜﻴﺔﺫﺍﺕ ﺃﺴﺎﺱ ﺴﺎﻴﻠﻭﻥ Shaker J

    + SIALON CERAMIC MATRIX COMPOSITES ﻤﻭﺍﺩ ﻤﺭﻜﺒﺔ ﺴﻴﺭﺍﻤﻴﻜﻴﺔ ﺫﺍﺕ ﺃﺴﺎﺱ ﺴﺎﻴﻠﻭﻥ Shaker J. Edrees * Abstract : The material under investigation is Sialon matrix reinforced with TiN. The Percentage of TiN is changed until maximum density is achieved. TiN is added to improve hardness, fracture toughness and density. ﺍﻝﻤﺴﺘﺨﻠﺹ -: ﻓﻲ ﻫﺫﻩ ﺍﻝﺩﺭﺍﺴﺔ ﻴﺘﻡ ﺘﻐﻴﺭ ﻨﺴﺒﺔ ﺍﻝــ TiN ﺍﻝﻤﻀﺎﻓﺔ ﺇﻝﻰ ﺍﻷﺭﻀﻴﺔ ﻤﻥ Sialon ﻝﻐﺭﺽ ﺍﻝﺤﺼﻭل ﻋﻠﻰ ﺍﻋﻠﻰ ﻜﺜﺎﻓﺔ ﻭﻤﻥ ﺜﻡ ﺘﺤﺴﻴﻥ ﻓﻲ ﺍﻝﺨﻭﺍﺹ ﺍﻝﻤﻴﻜﺎﻨﻴﻜﻴﺔ ﺍﻷﺨﺭﻯ . ﺃﻥ ﺍﻝﻬﺩﻑ ﻤﻥ ﻫﺫﻩ ﺍﻹﻀﺎﻓﺔ ﻫﻲ ﻝﺘﺤﺴﻴﻥ ﺍﻝﺼﻼﺩﺓ ﻭ ﻤﺘﺎﻨﺔ ﺍﻝﻜﺴﺭ ﻝﻠﻤﺎﺩﺓ ﻝﻐﺭﺽ ﻤﻼﺌﻤﺘﻬﺎ ﻝﻠﺘﻁﺒﻴﻕ ﺍﻝﻤﻌﻴﻥ Introduction: Strength and hardness are major requrrements in engineering materials and these have been recognised as characteristics which give ceramics their unique value for certain engineering material application[1] . The application of ceramic materials, however, is limited by their brittle nature and any improvement in the fracture toughness of these materials would considerably expand their range of applications . By incorporating a second phase in the structure of a material toughness can be increased[2] . The particle-reinforced composites with nitrides, carbides and borides of the transition elements (TiN, TiC, TiB2, ZrN) have found some special applications as cutting tools [3] . A group of ceramics known as “ Sialons” has been intensively investigated because of their outstanding properties as high strength refractory material ,since 1976 their use as acutting tools has been explosed and they have been very successful in several application[4,5] Sialons (Si-Al-O-N) are silicon nitride-based materials with aluminum and oxygen additions[6,7] . Silicon nitried (Si3N4) has useful properties, including high hardness, bend strength better than alumina, and low coefficient of thermal expansion, giving good resistance of thermal shock[8] .
  • Translucent Α-Sialon Ceramics Produced by Gass Pressure Sintering

    Translucent Α-Sialon Ceramics Produced by Gass Pressure Sintering

    UCTEA Chamber of Metallurgical & Materials Engineers Proceedings Book Translucent α-SiAlON Ceramics Produced by Gass Suna Avcıoğlu¹, Semra Kurama² Pressure Sintering (GPS) Method ¹Ondokuz Mayıs University, ²Anadolu University - Türkiye Abstract translucent SiAlONs by the gas pressure sintering (GPS) method. In the present work, translucent Dy3+-doped -SiAlON ceramics were successfully fabricated by gas pressure The aim of this study is to fabricate translucent Dy-- sintering (GPS) method and their microstructure were SiAlON ceramics by using GPS technique. Additionaly to tailored by controling sintering parameters to improve investigate effects of GPS parameters on optical properties transmittance of products. The transmittance of the sintered of products. Dy--SiAlON ceramics were inspected in 2000–7000 cm-1 wave number region by using FTIR. The microstructure 2. Experimental Procedure and phase characterization of the samples were also carried out by using SEM and XRD techniques, respectively. High-purity powders of Si3N4 (UBE-10, containing 1.6 Results showed that the main parameters determining the wt.% oxygen), AlN (Tokuyama, containing 1 wt.% optical features of translucent SiAlON ceramics are grain oxygen), Al2O3 (99.99 wt.%, Sumitomo AES IIC) and size/grain size distribution in the sintered product, phase Dy2O3 (99.99%, HC Starck) were used to prepare Dy0.66 variety therein, the amount and distribution of grain Si9.0 Al3.0O1.0N15.0 composition according to general formula boundary phases within the structure and density. of -SiAlON (Re(x)Si(12-m-n)Al(m + n)O(n)N(16-n)). The weighed starting powders were milled by planetary ball milling 1. Introduction (Pulverisette 6 Fritsch, Germany) by using Si3N4 balls and a Si3N4 jar in order to obtain a homogeneous mixture.
  • Development of the Microstructure of the Silicon Nitride Based Ceramics

    Development of the Microstructure of the Silicon Nitride Based Ceramics

    Materials Research, Vol. 2, No. 3, 165-172, 1999. © 1999 Development of the Microstructure of the Silicon Nitride Based Ceramics J.C. Bressiani, V. Izhevskyi*, Ana H. A. Bressiani Instituto de Pesquisas Energéticas e Nucleares, IPEN, C.P. 11049 Pinheiros 05422-970 São Paulo - SP, Brazil Received: August 15, 1998; Revised: March 30, 1999 Basic regularities of silicon nitride based materials microstructure formation and development in interrelation with processing conditions, type of sintering additives, and starting powders properties are discussed. Models of abnormal or exaggerated grain growth are critically reassessed. Results of several model experiments conducted in order to determine the most important factors directing the microstructure formation processes in RE-fluxed Si3N4 ceramics are reviewed. Existing data on the mechanisms governing the microstructure development of Si3N4-based ceramics are analyzed and several principles of microstructure tailoring are formulated. Keywords: silicon nitride, microstructure, phase transformation, liquid phase sintering 1. Introduction the Weibull modulus of the fracture strength of silicon nitride. A small transverse grain size was shown to give Mechanical properties of the Si3N4-based ceramics higher Weibull modulus than the coarse microstructures. such as strength and fracture toughness as well as Weibull The observed increase in fracture resistance was mainly modulus are strongly dependent on the microstructure. attributed to crack deflection, and crack bridging mecha- Formation of the resulting microstructure is dictated by the nism3-6. In some cases crack branching was also observed. densification mechanism, i.e., reactive liquid phase sinter- An important role in fracture resistance improvement is ing. The α-Si3N4 in the starting powder compact is trans- played also by the secondary phase.
  • Sialon/Ni Composites Synthesized by Spark Plasma Sintering

    Sialon/Ni Composites Synthesized by Spark Plasma Sintering

    nanomaterials Article The Property Characterization of α-Sialon/Ni Composites Synthesized by Spark Plasma Sintering Adedayo Sheriff Adeniyi 1, Bilal Anjum Ahmed 2, Abbas Saeed Hakeem 3,* , Faheemuddin Patel 1 , Akolade Idris Bakare 3, Anwar Ul-Hamid 4, Amir Azam Khan 5, Muhammad Ali Ehsan 3 and Tahir Irfan Khan 6 1 Mechanical Engineering Department, King Fahd University of Petroleum & Minerals, Dhahran 31261, Saudi Arabia; [email protected] (A.S.A); [email protected] (F.P.) 2 Department of Mechanical Engineering, National University of Sciences and Technology, Islamabad 44000, Pakistan; [email protected] 3 Center of Excellence in Nanotechnology, King Fahd University of Petroleum & Minerals, Dhahran 31261, Saudi Arabia; [email protected] (A.I.B.); [email protected] (M.A.E.) 4 Center of Engineering Research, Research Institute King Fahd University of Petroleum and Minerals, Dhahran 31261, Saudi Arabia; [email protected] 5 Department of Mechanical and Manufacturing Engineering, Faculty of Engineering, University Malaysia Sarawak, Sarawak 97000, Malaysia; [email protected] 6 Department of Mechanical Engineering, Faculty of Engineering & Informatics, University of Bradford, Bradford BD7 1DP, UK; [email protected] * Correspondence: [email protected]; Tel.: +00966-13-860-7834 Received: 28 October 2019; Accepted: 18 November 2019; Published: 25 November 2019 Abstract: This study investigates the effect of micron-sized nickel particle additions on the microstructural, thermal, and mechanical property changes of α-sialon ceramic composites. The α-sialon/Ni composites were synthesized with an increasing amount of Ni (10–40 wt.%) using the spark plasma sintering technique and nanosized alpha precursors at a relatively low synthesis temperature of 1500 ◦C with a holding time of 30 min in each case.
  • Nilcra® Sialon E

    Nilcra® Sialon E

    Data Sheet Nilcra® SiAlON E Description A Gas Pressure Sintered Silicon Nitride with exceptional strength and toughness. Contains interlocking grains of beta phase silicon nitride. Designed for applications requiring high strength, toughness and wear resistance. Prime Features Specifications High Strength at ambient & high temperature • Quality Assurance to ISO 9001 Excellent fracture toughness Extremely high hardness & wear resistance Low coefficient of thermal expansion Typical Applications: Good thermal shock resistance Excellent for combating wear and Excellent corrosion resistance corrosion in valves, pumps and liners Non-wetting in molten metal used in chemical processing and Low oxidation at elevated temperatures refining environments Successfully used for a wide variety of Physical Properties tooling used in metal forming and dry cell battery production Colour Black 3 o Density g/cm 20 C 3.21 Production Capabilities Flexural Strength MPa 20oC 650 Sintered components 1200oC 450 Precision ground components Weibull Modulus 20oC 15 Ceramic / Metal assemblies Compressive Strength MPa 20oC 3000 Ceramic design assistance Modulus of Elasticity GPa 20oC 320 Prototyping, batch and volume Poisson’s Ratio 20oC 0.28 production Hardness HV0.3 kg/mm2 20oC 1630 Hardness Rockwell 45N 20oC 85 Fracture Toughness MPa√m 20oC 8 Average Grain Size µm 1-10 Thermal Conductivity W/m-K 20oC 25 1000oC 15 Thermal Expansion Coefficient 25-1000oC 3.2 x10-6 mm/mm/˚C Please note that all values quoted are based on test pieces and may vary according to component design. These values are not guaranteed in anyway whatsoever and should only be treated as indicative and for guidance only. www.morganadvancedmaterials.com Morgan Advanced Materials PLC Registered in England & Wales at Quadrant, 55-57 High Street, Windsor, Berkshire SL4 1LP UK Company No.
  • Creep Behavior of Multi-Cation • -Sialon Partially Stabilized

    Creep Behavior of Multi-Cation • -Sialon Partially Stabilized

    Creep behavior of multi-cation α-SiAlON partially stabilized, produced with an yttrium- rare earth oxide mixture (CRE2O3) C. Santos1; K. Strecker1; M.J. R. Barboza1; S. A. Baldacim2; F. Piorino Neto2; O. M.M.Silva2; C.R.M.Silva2 1 Departamento de Engenharia de Materiais DEMAR-FAENQUIL, Polo Urbo-industrial, gleba AI-6, s/n, cep 12600-000, Lorena-SP Brazil. 2 Centro Técnico Aeroespacial – Divisão de Materiais AMR-CTA, Pça. Marechal do Ar Eduardo Gomes, 50, cep. 12228-904, S. J. Campos –SP Brazil Key-words: α-SiAlON, Si3N4, sintering additives, CRE2O3, compressive creep. ABSTRACT α−SiAlON (α’) is a solid solution of α−Si3N4, where Si and N are substituted by Al and O, respectively. The principal stabilizers of the α’-phase are Mg, Ca, Y and rare earth cations. In this way, the possible use of the yttrium-rare earth oxide mixture, CRE2O3, produced at FAENQUIL, in obtaining these SiAlONs was investigated. Samples were sintered by hot- pressing at 17500C, for 30 minutes, using a sintering pressure of 20 MPa. Creep behavior of the hot-pressed CRE-α-SiAlON/β-Si3N4 ceramic was investigated, using compressive creep tests, in air, at 1280 to 13400C, under stresses of 200 to 350 MPa, for 70 hours. This type of ceramic exhibited high creep and oxidation resistance. Its improved high-temperature properties are mainly due to the absence or reduced amount of intergranular phases, because of the incorporation of the metallic cations from the liquid phase formed during sintering into the Si3N4 structure, forming a α’/β composite. 1.
  • Elucidating Structure−Composition−Property Relationships of the Β

    Elucidating Structure−Composition−Property Relationships of the Β

    Article pubs.acs.org/cm Elucidating Structure−Composition−Property Relationships of the β‑SiAlON:Eu2+ Phosphor Zhenbin Wang, Weike Ye, Iek-Heng Chu, and Shyue Ping Ong* Department of NanoEngineering, University of CaliforniaSan Diego, 9500 Gilman Drive, La Jolla, California 92093-0448, United States *S Supporting Information ABSTRACT: In this work, we performed a systematic inves- tigation of structure−composition−property relationships in Eu2+- activated β-SiAlON, one of the most promising narrow-band green phosphors for high-power light-emitting diodes and liquid crystal display backlighting with wide color gamut. Using first-principles calculations, we identified and confirmed various chemical rules for Si−Al, O−N, and Eu activator ordering within the β-SiAlON structure. Through the construction of energetically favorable models based on these chemical rules, we studied the effect of oxygen content and Eu2+ activator concentrations on the local EuN9 activator environment, and its impact on important photoluminescence properties such as emission peak position (using the band gap as a proxy), bandwidth, and thermal quenching resistance. Increasing oxygen content is shown to lead to an − fi increase in Eu N bond lengths and distortion of the EuN9 coordination polyhedron, modifying the crystal eld environment of the Eu2+ activator, and resulting in red-shifting and broadening of the emission. We also show that the calculated excited band structure of β-SiAlON exhibits a large gap between the 5d levels and the conduction band of the host, indicating a large barrier toward thermal ionization (>0.5 eV) and, hence, excellent thermal quenching stability. Based on these insights, we discuss potential strategies for further composition optimization of β-SiAlON.
  • Sialon Ceramics

    Sialon Ceramics

    TECH SPOTLIGHT SiAlON Ceramics Vladimir D. Krstic new generation of silicon-aluminum-oxygen-nitrogen (SiAlON) ceramics ex- Functional Materials A hibits a unique combination of fracture toughness, hardness, and strength that Manufacturing Inc. provide the potential for applications in many industries. These SiAlON ce- Kingston, Ontario, Canada ramics provide fracture toughness of over 10 MPa-m1/2 and flexural strengths of over 1150 MPa, resulting in exceptionally high resistance to thermal shock. Efforts to further increase the reliability of these ceramics have led to process im- provements such as sintering aids and densification methods involving both pressure and pressureless sintering. The goal of these de- velopments has been to impart high fracture toughness and, at the same time, retain high hard- ness and strength. The unique feature in this new class of SiAlON ceramics is the microstructure, which consists of elongated grains of circular cross-section that re- semble fibers rather than plates (Fig. 1), and the inter-granular phase that encourages toughening by crack bridging. Researchers managed to change the morph- Fig. 1 — Transformation of - to -Si3N4 during sintering at high temperature. ology of growth of elongated grains by alloying with ions that change the valence state at high temperature and strain the SiAlON lattice, creating the conditions for growth of fiber-like grains. The key process step that controls the strength and toughness of SiAlON ceram- ics is the alpha to beta phase transforma- tion during densification at high temperature. This transformation is ac- companied by a growth of elongated β- phase at the expense of equiaxed α-phase, as shown in Fig.
  • The Densification and Photoluminescence Characteristics of Ca-Α-Sialon:Eu2+ Plate Phosphor

    The Densification and Photoluminescence Characteristics of Ca-Α-Sialon:Eu2+ Plate Phosphor

    Journal of the Korean Ceramic Society http://dx.doi.org/10.4191/kcers.2013.50.4.280 Vol. 50, No. 4, pp. 280~287, 2013. The Densification and Photoluminescence Characteristics of Ca-α-SiAlON:Eu2+ Plate Phosphor Young-Jo Park*,†, Jae-Wook Lee*, Jin-Myung Kim*, Brahma Raju Golla*, Chang-Bun Yoon**, and Chulsoo Yoon** *Engineering Ceramics Research Group, Korea Institute of Materials Science, Gyeongnam 641-831, Korea **Electro Materials and Device Center, Samsung LED, Gyeonggi 443-743, Korea (Received July 1, 2013; Revised July 22, 2013; Accepted July 23, 2013) ABSTRACT Plate-type phosphor is a promising substitute in overcoming the issues related to the powder phosphor paste mixed with resin. 2+ In this research, Ca-α-SiAlON:Eu plate phosphor (CaxSi12-(m+n)Alm+nOnN16-n:Euy) was investigated for the varied compositions (m,n) of the host crystal with the fixed Eu content (y). Densification was promoted for the compositions with increasing ‘m’ val- ues for the m=2n relationship. Dictated by the Eu concentration inside the phosphor crystal, photoluminescence intensity was stronger in α2 specimen (m = 3.0, n = 1.5) containing the second phases when compared to α1 specimen (m = 1.5, n = 0.75) com- prising a single-phase α-SiAlON. The concentration of Eu in the non-emitting amorphous interfacial glass phase was 2~4 times of the designed Eu concentration inside the α-SiAlON crystal. Key words : Phosphor, SiAlON, Plate, Sintering, Crystal, Amorphous 1. Introduction commercial white LEDs requires a LED chip and a phos- phor powder. Generally, the phosphor powder is mixed with n the midst of the global demand for energy savings and transparent resin and the paste is coated onto the LED Ilow-carbon green growth, the application of white LEDs chip.
  • Progress in Sialon Ceramics

    Progress in Sialon Ceramics

    Journal of the European Ceramic Society 20 (2000) 2275±2295 Progress in SiAlON ceramics V.A. Izhevskiy a,1, L.A. Genova a, J.C. Bressiani a, F. Aldinger b,* aInstituto de Pesquisas EnergeÂticas e Nucleares, IPEN/CNEN-SP, Trav. R, 400, Cidade UniversitaÂria, SaÄo Paulo, SP-05508-900, Brazil bMax-Planck-Institut fuÈr Metallforschung und UniversitaÈt Stuttgart, Institut fuÈr Nichtmetallische Anorganische Materialien, Heisenbergstrasse 5, D-70569, Stuttgart, Germany Received 9 June 1999; received in revised form 21 December 1999; accepted 30 January 2000 Abstract In view of the considerable progress that has been made over the last several years on the fundamental understanding of phase relationships, microstructural design, and tailoring of properties for speci®c applications of rare-earth doped SiAlONs, a clear review of current understanding of the basic regularities lying behind the processes that take place during sintering of SiAlONs is timely. Alternative secondary phase development, mechanism and full reversibility of the a0 to b0 transformation in relation with the phase assemblage evolution are elucidated. Reaction sintering of multicomponent SiAlONs is considered with regard of wetting behavior of silicate liquid phases formed on heating. Regularities of SiAlON's behavior and stability are tentatively explained in terms of RE element ionic radii and acid/base reaction principle. # 2000 Elsevier Science Ltd. All rights reserved. Keywords: Phase equilibria; Phase transformations; SiAlONs; Sintering Contents 1. Introduction.........................................................................................................................................................2276
  • Facile and Economical Preparation of Sialon-Based Composites Using Coal Gangue: from Fundamental to Industrial Application

    Facile and Economical Preparation of Sialon-Based Composites Using Coal Gangue: from Fundamental to Industrial Application

    Energies 2015, 8, 7428-7440; doi:10.3390/en8077428 OPEN ACCESS energies ISSN 1996-1073 www.mdpi.com/journal/energies Article Facile and Economical Preparation of SiAlON-Based Composites Using Coal Gangue: From Fundamental to Industrial Application Jinfu Li 1, Changsheng Yue 2, Mei Zhang 2, Xidong Wang 3 and Zuotai Zhang 3,* 1 Department of Materials Science and Engineering, Northwestern Polytechnical University, Xi’an 710072, China; E-Mail: [email protected] 2 School of Metallurgical and Ecological Engineering, University of Science and Technology Beijing, Beijing 100083, China; E-Mails: [email protected] (C.Y.); [email protected] (M.Z.) 3 Beijing Key Laboratory for Solid Waste Utilization and Management, College of Engineering, Peking University, Beijing 100871, China; E-Mail: [email protected] * Author to whom correspondence should be addressed; E-Mail: [email protected]; Tel.: +86-10-8252-4880; Fax: +86-10-6275-6623. Academic Editor: Mehrdad Massoudi Received: 21 May 2015 / Accepted: 13 July 2015 / Published: 22 July 2015 Abstract: The present study aims to synthesize SiAlON-based composites utilizing coal gangue. Different types of SiAlON-based composites were synthesized using coal gangue by carbothermal reduction nitridation method through control of different reaction atmospheres. The experimental results indicate that the oxygen partial pressure was an essential factor in the manufacture of SiAlON-based composites and under proper control of the atmospheres, SiAlON-based composites with different crystal structures could be synthesized. The optimum conditions of synthesis of different SiAlON-based composites were respectively determined. Based on the laboratory results, a prototype plant was proposed and constructed, and β-SiAlON composite was successfully produced using coal gangue.