• Transactions on Electrical and Electronic Materials
• /
• v.12 no.1
• /
• pp.32-34
• /
• 2011

A zero-shrinkage sintering process in which the shrinkage of the x-y axis is controlled to be zero is in great demand due to the high integration trend in ceramic modules. Among the zero-shrinkage sintering processes available, the glass infiltration method proposed in the preliminary study with an $Al_2O_3/Glass/Al_2O_3$ structure is one promising method. However, problems exist in regard to the glass infiltration method, including partially incomplete joining between $Al_2O_3$ and glass layers due to the precipitate of Ti-Pb rich phase during the sintering process. Therefore, we wish to solve the de-lamination problems and suggest a mechanism for delamination and the solutions in the zero-shrinkage low temperature co-fired ceramic (LTCC) layers. The de-lamination problems diminished using the Pb-BSi-O glass without $TiO_2$ in Pb-B-Ti-Si-O glass and produced a very dense zero-shrinkage LTCC.

• Transactions on Electrical and Electronic Materials
• /
• v.13 no.1
• /
• pp.23-26
• /
• 2012

A zero-shrinkage sintering process in which the shrinkage of x-y axis is controlled to be zero is in great demand due to the trend of high integration in the ceramic modules. Among the zero-shrinkage sintering processes that are available, the proposed glass infiltration method where the viscous but fluidic glass infiltrates of the $Al_2O_3$ particles in the structure of $Al_2O_3$/glass/$Al_2O_3$ during firing is one of the applicable methods. However, the above proposed glass infiltration method has the problem of the warpage-like delamination. This occurred at the outermost surface of the multiple-bundle substrate. It is thought that the decomposed gas rapidly expands in low viscous glass to create vacant space. To solve this problem, the vacant space was tamped with $Al_2O_3$ particles to lead to the actual improvement of the sintered properties. With 15 wt% of tamping $Al_2O_3$ particles in glass, most of the vacant space disappeared. Fully densified zero-shrinkage substrate without delamination can be obtained.

• Proceedings of the Materials Research Society of Korea Conference
• /
• 2007.11a
• /
• pp.103.1-103.1
• /
• 2007

• Proceedings of the Korea Concrete Institute Conference
• /
• 2005.05b
• /
• pp.9-12
• /
• 2005

In this study, to investigate shrinkage and cracking behavior of 120MPa UHSC, free and restrained drying shrinkage test were performed. Three strength levels(50MPa, 80MPa, 120MPa) were used and the effect of mineral admixtures(fly ash, slag) on free and restrained shrinkage was investigated. From comparing the result of pin -penetration test with the result of ring test, Time-Zero was determined as initial set. Shrinkage test results show that autogenous shrinkage of UHSC was much higher than that of HSC, VHSC and fly ash delayed cracking age in UHSC by decreasing autogenous shrinkage. Additional free concrete rings(with restraint removed) were also tested to check the influence of the geometry of the specimens on free shrinkage. And then the relationship between free shrinkage and restrained shrinkage was investigated.

• Ceramist
• /
• v.8 no.3
• /
• pp.48-57
• /
• 2005

• Journal of the Korean Ceramic Society
• /
• v.16 no.1
• /
• pp.31-37
• /
• 1979

The middle point of composition within the system $MgO-Al_2O_3-SiO_2$ has been studied for applicability as ceramics dielectrics. A Kyul Sung Tale of high purity, magnesia clinker of Sam-wha chemical company, C.P. aluminium oxide, calcium carbonate, red lead, barium carbonate which was made into frit were used the raw materials. A number of steatite ceramics were prepared under carefully controlled condition and the water absorption, linear shrinkage, power factor, dielectric constant and dielectric loss were measured at elevated temperature. When we used magnesia clinker as flux, the quantity of this flux was 0.05mole, sintering temperature was continued for 2 hrs. at 1, 27$0^{\circ}C$. From this conditions, we could get the data whose power factor was 0.142%, water absorption was zero, linear shrinkage was 8.76%, dielectric constant was 5.63, dielectric loss was 0.00799. When we used red lead as flux, the quantity of this flux was 0.033mole and 0.066mole, sintering temperature was continued for 2hrs. at 1, 26$0^{\circ}C$. From this conditions, we could get the data whose water absorption was zero, linear shrinkage was 8.03%, and 8.48%, power factor was 0.136% and 0.062%, dielectric loss was 0.0072 and 0.0037. When we used barium carbonate made into frit as flux, the quantity of this flux was 0.02mole, sintering temperature was continued for 2hrs. at 1, 27$0^{\circ}C$. From this conditions, we could get the data whose water absoption was zero, linear shrinkage was 8.44%, power factor was 0.138%, dielectric constant was 5.69, dielectric loss was 0.0074.

• Advances in concrete construction
• /
• v.14 no.2
• /
• pp.139-151
• /
• 2022

Filling materials poured into precast member joint are subjected to restraint stress by the precast member and joint reinforcement. The induced stress will likely cause cracks at early ages and performance degradation of the entire structure. To prevent these issues and design reasonable joints, it is very important to analyze and evaluate the restrained shrinkage cracks of filling materials at various restraint conditions. In this study, a new time zero-that defines the shrinkage development time of a filling material-is proposed to calculate the accurate amount of shrinkage. The tensile stresses and strengths at different ages were compared through the ring test (AASHTO PP34) to evaluate the crack potential of the restrained filling materials at various restraint conditions. The mixture which contained an expansive additive and a shrinkage reducing agent exhibited high resistance to shrinkage cracking owing to the high-drying shrinkage compensation effect. The high-performance, fiber-reinforced cement composite, and ultra-high-performance, fiber-reinforced cement composite yielded very high resistance to shrinkage and cracking owing to the pull-out property of steel fibers. To this end, multiple nonlinear regression analyses were conducted based on the test results. Accordingly, a modified tensile stress equation that considered both the geometric shape of the specimen and the intrinsic properties of the material is proposed.

• KSCE Journal of Civil and Environmental Engineering Research
• /
• v.32 no.5A
• /
• pp.307-315
• /
• 2012

Recently, ultra high performance fiber reinforced concrete (UHPFRC) having over 180 MPa compressive strength and 10 MPa tensile strength has been developed in Korea. However, UHPFRC represents different material properties with normal concrete (NC) and conventional high performance concrete (HPC) such as a high early age autogenous shrinkage and a rapid dry on the surface, because it has a low water-binder ratio and high fineness admixtures without coarse aggregate. In this study, therefore, to propose suitable experimental methods and regulations, and to evaluate mechanical properties at a very early age for UHPFRC, setting, shrinkage and tensile tests were performed. From the setting test results, paraffin oil was an appropriate material to prevent drying effect on the surface, because if paraffin oil is applied on the surface, it can efficiently prevent the drying effect and does not disturb or catalyze the hydration of cement. From the ring-test results, it was defined that the shrinkage stress is generated at the time when the graph tendency of temperature and strain of inner steel ring is changed. By comparing with setting test result, the shrinkage stress was firstly occurred as the penetration resistance of 1.5 MPa was obtained, and it was about 0.6 and 2.1 hour faster than those of initial and final sets. So, the starting time of autogenous shrinkage measurement (time-zero) of UHPFRC was determined when the penetration resistance of 1.5 MPa was obtained. Finally, the tensile strength and elastic modulus of UHPFRC were measured from near initial setting time by using a very early age tensile test apparatus, and the prediction models for tensile strength and elastic modulus were proposed.

• Journal of the Korea Concrete Institute
• /
• v.23 no.4
• /
• pp.441-448
• /
• 2011

In this study, experimental tests of chemical and autogenous shrinkage were performed to evaluate the early age shrinkage behaviors of ultra high performance cementitious composites (UHPCC) with various replacement ratios of silica fume (SF), shrinkage reducing agent (SRA), expansive admixture (EA), and superplasticizer (SP). Starting time of self-desiccation, was analyzed by comparing the setting times and the deviated point of chemical and autogenous shrinkage strains. The test results indicated that both SF and SRA augment the early age chemical shrinkage, whereas SP delays the hydration reaction between cement particles and water, and reduces chemical shrinkage. About 49% of autogenous shrinkage was depleted by synergetic effect of SRA and EA. The hardening of UHPCC was catalyzed by containing EA. Self-desiccation of UHPCC occurred prior to the initial setting due to the high volume fraction of fibers and low water-binder ratio (W/B).

• Journal of the Korean Crystal Growth and Crystal Technology
• /
• v.25 no.6
• /
• pp.285-289
• /
• 2015

With the miniaturization with both high functionality and high integrity of the probe cards, the highly precise laser punching on the zero-shrinkage high strength substrate has attracted more attention recently. Taper occurrence during laser-punching on green sheets appears as a problem in process. The size (diameter) difference between the entrance hole and the exit hole in tapered holes appeared to be inversely proportional to the hole size itself. To suppress taper occurrence, two-stage punching was adopted as the size of second hole was varied from $70{\mu}m$ to $79{\mu}m$ when punching $80{\mu}m$ via holes on the substrate with thickness of $380{\mu}m$. The minimal taper ratio of 11.9 % appeared with second hole size between 70 to $79{\mu}m$ before sintering. Taper ratio reduced to 7 % after zero-shrinkage sintering. The size difference between first hole and second hole appeared minimal when the size of second hole was 95~97 % to that of first hole.