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PubMed1981

[Studies on the accuracy of the castings. (Part 10) On the effects of starting time of the heat to phosphate bonded investment mold (author's transl)].

Properties of phosphate bonded investments are superior than that of plaster bonded investments in mechanical properties, expansional values for compensating to the casting shrinkage of alloys, and refractory resistance. Therefore, phosphate bonded investments have been available to casting for high fusing alloys. But, their properties are varied easily by manipulating. In this report, two commercial products of Cerami Gold (Whip--Mix Corp.) and Ceravest (G--C Dental Industrial Corp.) were used. They were studied on setting expansion, thermal expansion, compressive strength, change of pH value caused by setting reaction, decrement of weight, casting accuracy and roughness of castings in process of time. Results were follows; 1. The weight decrement of investment mold were about 1.5% on Cerami Gold and 3.5% on Ceravest at 24 hours after the mold had been prepared. 2. pH value of Cerami Gold investment mold changed to 8.5 from 7.0 at 5 hours after mixing, but that of Ceravest investment mold changed to 9.0 from 7.0 at 3 hours. 3. The setting expansion of Cerami Gold investment was caused about 0.9% at 3 hours and that of Ceravest investment was about 0.3% at 1 hour ater mixing. Since then, they were to be constant. 4. The thermal expansion of Cerami Gold investment was decreased by elapsed time until 3 hours after mixing, and then since passing at 5 hours, they were increased. But, that of Ceravest investment was decreased in process of time. 5. The compressive strength of both investments were increased as long as elapsed time after setting. Heating at 800 degrees C in the oven, it was 100--110 Kg/cm2 regardless of time on Ceravest investment, and other was 170 kg/cm2 which was increased until passing 5 hours. 6. The roughness of castings surface were similar to the mold surface and they were H3 12--16 microns which were decreased as elapsed time after investment was mixed. 7. Accurate castings were produced by the mold heated after 24 hours, using with Cerami Gold investment. On the Ceravest investment, it was 30 minutes of 5 hours after mixing.

Dental Casting Investment↗

PubMed1996

Surface reaction between titanium castings and investments.

The selection of investments suitable for titanium castings is critical because the surface-reacted layer greatly affects their mechanical properties. This study analyzed the interfacial zone of titanium castings obtained from various commercial investments and examined the relationship between the surface-reacted layer and the hardness. CP titanium disks (20 mm diameter, 1 mm thick, n = 5) were cast using eight commercial casting systems and investments for titanium casting: two alumina-based investments (T-invest, CD-titan investment), two spinel-based investments (Titanmold, Titavest MZ), three zirconia-based investments (Asahivest-D, Titaniumvest EX, Tycast investment TM), and a magnesia-based investment (Selevest CB). The Vickers hardness of cast disks in cross-section was tested at 50 microns intervals from the surface to 0.5 mm in depth. The cross-section was observed metallurgically, and an elemental mapping measurement of the reacted layer was conducted under the EPMA. The Vickers hardnesses at 50 microns from the surface of the specimens ranged 312 to 624 and were significantly different among the investments (p < 0.01). The thickness of the reacted layer, rich in O, Si, Al, Zr, Mg, and P, ranged from 10 to 60 microns. No correlation was seen between the thickness of reacted layer and the hardness (p > 0.05). However, the specimens cast with alumina-based and zirconia-based investments were harder than the spinel-based and magnesia-based investments at 500 microns. Although the free energies of metal oxide formation of alumina and zirconia were lower than titania, these data suggest that silica, alumina and zirconia were reduced by contact with molten titanium. Accordingly, silicon, aluminum and zirconium diffused to the interior of the titanium castings and changed their mechanical properties.

Aluminum Oxide↗

PubMed2005

Evaluation of the castability of a Co-Cr-Mo-W alloy varying the investing technique.

The purpose of this study was to compare the castability of Co-Cr-Mo-W (Remanium 2000), Ni-Cr (Durabond) and Co-Cr-Mo (Vera PDI) alloys invested with either conventional (phosphate- and silica-based) or mixed investing techniques. A 10 X 10 mm square-shaped nylon net containing 100 open squares served as a template for construction of wax patterns, which were invested with phosphate-based investment (Termocast), silica-based investment (Refrafil) and mixed investing technique (2-mm layer phosphate investment plus filling with silica investment). Forty-five cast specimens (5 per experimental condition) were obtained and sandblasted with aluminum oxide. The number of completely reproduced cast segments was counted to obtain a percentage designated "castability value", which indicated the accuracy of the alloy to reproduce mold details. Statistical analysis using two-way ANOVA and Tukey's test showed that, comparing the alloys, Remanium 2000 had statistically similar castability (p>0.05) to Vera PDI and lower than Durabond (p<0.05). Considering the mixed technique results, Remanium 2000 yielded lower castability value (p<0.05) than Durabond and Vera PDI alloys, which showed similar results to each other (p>0.05). In conclusion, the castability of the Co-Cr-Mo-W alloy (Remanium 2000) was comparable to that of the Co-Cr alloy (Vera PDI) and worse than that of the Ni-Cr alloy (Durabond). Except for Remanium 2000, the mixed investing technique considerably improved the accuracy of the alloys to reproduce cast details, compared to the phosphate-based investment. The mixed investing technique appears as a viable alternative to improve castability of base metal alloys without decreasing the surface quality of the metallic pieces.

Analysis of Variance↗

PubMed2005

[Study on insufficiency of government investment to the centers of disease prevention and control].

OBJECTIVE: To make clear the superaddition of government investment to the centers of disease prevention and control (CDC) which will ensure fulfillment of public functions of the center of disease prevention and control. Methods Centers of disease prevention and control had been sampled by two-stage stratified sampling method to investigate the status of government investment to the centers of disease prevention and control, which would be compared with the expected government investment to fulfill the public functions of CDC. RESULTS: According to the cost of manpower and the price in 2003, the government should give another 304.9% investment than current government investment (3.88 billions). For CDC of county level, the superaddition rate even reached 416.1%. The percentage of manpower expense would be 32.2% and the percentage of routine expense would be 67.8% of the superaddtion of government investment. The percentage of routine expense even reached 70.7% of the superaddtion of government investment. CONCLUSION: There was a big gap between the current government investment to CDC and the expected government investment to CDC. To fulfill the public function of CDC, the current government investment to CDC should increase by 3-4 times. The superaddition of government investment to CDC should be allocated more to the routine expense.

China↗

PubMed1975

Permeability and porosity of dental casting investments.

Permeability of various gypsum- and phosphate-bonded investments was measured during conventional burn-out procedures. Porosity determinations were made on specimens cooled to room temperature after burn-out. As a group, the gypsum-bonded investments were found to be more permeable than the phosphate-bonded investments. Two phosphate-bonded investments were determined to be relatively impermeable to gas flow, while another exhibited permeability comparable to that of the gypsum-bonded investments. In spite of differences in permeability, the porosity of each type of investment was nearly constant. The porosity of the phosphate-bonded investment was approximately three-fourths that of the gypsum investments. These investments were modified by the addition of varying amounts of acrylic polymer for the purpose of altering permeability. The addition of acrylic polymer increased porosity and permeability of all of the materials included in this investigation. The acrylic additives, however, had no effect on the permeability of relatively impermeable investments unless used in high concentration. The results of this investigation would tend to substantiate the need for special spruing and venting procedures.

Acrylic Resins↗

PubMed1997

Effect of burnout temperatures on strength of phosphate-bonded investments--Part II: Effect of metal temperature.

OBJECTIVES: It had previously been found that the strength of phosphate-bonded investments is temperature sensitive. However, while the effect of heat from the cast metal is expected to have some effect on continued reactions and melting, there is no published report dealing with this. It was the purpose of this study to consider further the effects of burnout temperature on strength and the contribution of metal casting temperature and investment composition. METHODS: The disc-rupture test (Luk, H. W.-K. and Darvell, B. W., Strength of phosphate-bonded investments at high temperature. Dental Materials 1991, 7, 99-102) was employed to determine the effect of burnout temperature (ranging from 400 to 1000 degrees C) on the 'actual' strength of six phosphate-bonded investments; the cast metal temperature was controlled to be the same as that of the mould. Atomic absorption was employed to investigate aspects of the composition of the investments. RESULTS: The 'actual' strength obtained in this test was always higher than the 'service' strength observed in similar testing with the metal at a fixed temperature (1460 degrees C). The 'actual' strength was also temperature sensitive, but with a different pattern of variation compared with the 'service' values. All investments tested were found to behave plastically at high temperatures. Calcium, sodium, zinc and iron were found in appreciable quantities in the investments. CONCLUSION: Heat from the high-temperature casting metal has a material effect in decreasing the strength of phosphate-bonded investments. Such heating increases the plastic behaviour of the investment and this, together with the casting pressure, may result in a distorted mould and thus inaccurate castings, a hitherto unrecognized source of error. 'Actual' strength gives no guide to the 'service' strength, emphasizing the need for tests under service conditions. Composition affects investment high-temperature strength substantially.

Calcium↗

PubMed2002

Investing in river health.

Rivers provide society with numerous returns. These relate to both the passive and extractive uses of the resources embodied in river environments. Some returns are manifest in the form of financial gains whilst others are non-monetary. For instance, rivers are a source of monetary income for those who harvest their fish. The water flowing in rivers is extracted for drinking and to water crops and livestock that in turn yield monetary profits. However, rivers are also the source of non-monetary values arising from biological diversity. People who use them for recreation (picnicking, swimming, boating) also receive non-monetary returns. The use of rivers to yield these returns has had negative consequences. With extraction for financial return has come diminished water quantity and quality. The result has been a diminished capacity of rivers to yield (non-extractive) environmental returns and to continue to provide extractive values. A river is like any other asset. With use, the value of an asset depreciates because its productivity declines. In order to maintain the productive capacity of their assets, managers put aside from their profits depreciation reserves that can be invested in the repair or replacement of those assets. Society now faces a situation in which its river assets have depreciated in terms of their capacity to provide monetary and non-monetary returns. An investment in river "repair" is required. But, investment means that society gives up something now in order to achieve some benefit in the future. Society thus has to grapple wih the choice between investing in river health and other investments--such as in hospitals, schools, defence etc. - as well as between investing in river health and current consumption--such as on clothes, food, cars etc. A commonly used aid for investment decision making in the public sector is benefit cost analysis. However, its usefulness in tackling the river investment problem is restricted because it requires all benefits and costs to be measured in dollar terms, and many of the benefits arising from investments in river health are non-monetary. In this paper, techniques that enable non-monetary values to be estimated in dollar terms are described. Applications of the techniques to the estimation of the environmental values of rivers are demonstrated. The values estimated are used to demonstrate the extent of returns that are possible from investing in river health.

Conservation of Natural Resources↗

PubMed1999

Investment strength as a function of time and temperature.

OBJECTIVES: The purpose of this investigation was to evaluate and compare the compressive strength characteristics of selected investments and to determine if these change as a function of time and temperature after mixing. METHODS: Two phosphate-bonded investments and one gypsum-bonded investment were selected and 288 cylindrical specimens were fabricated (n = 9). Baseline compressive strength values were determined for each material at room temperature and compressive strength measurements were made for all materials at 700 degrees C, and at 872 degrees C only for phosphate-bonded investments. Each material was tested at 2, 6, 12, and 24 h after mixing. Specimens were heated at 15 degrees C/min and heat soaked for 5 min in a burnout oven at the applicable testing temperature. They were transferred to a preheated chamber on an Instron testing machine and subjected to a compressive load at a crosshead speed of 2 mm/min until failure. The resulting strength data are presented in MN/m2. RESULTS: The gypsum-bonded investment did not exhibit marked differences in strength as a function of either time or temperature. The phosphate-bonded investments, on the other hand, demonstrated considerable changes in compressive strength and differed in compressive strength characteristics at 700 degrees C and 872 degrees C respectively. CONCLUSIONS: At elevated temperatures, all materials approximated peak strength 2 h after initial mixing. At room temperature, the phosphate-bonded investments in this study were not significantly stronger than the gypsum-bonded investment material. However, they exhibited increased compressive strength as a function of time and temperature that was considerably higher than that exhibited by the gypsum-bonded investments.

Analysis of Variance↗

PubMed2006

[Study on the expansion properties of homemade fast investment material for the IPS-Empress2 castable ceramic].

IPS-Empress2 is a successful all-ceramic restoration system. To lower its cost, and promote its application, a kind of homemade fast investment material has been developed. The aim of this study was to evaluate the expansion properties of this investment material. The setting expansion, thermal expansion and total expansion of the homemade fast investment material were tested. The same properties of the IPS special fast investment material were also tested as control. Then the SPSS statistics software was used to evaluate the differences between the homemade material and the special material. The results show that the setting expansion rate, thermal expansion rate and total expansion rate of the special investment material for IPS-Empress2 are 0.858%, 1.11% and 1.17% respectively, while the same parameters of the homemade investment material are 0.798%, 1.09% and 1.16% respectively. There is no statistically significant difference in these expansion properties between the two investment materials. In conclusion, the expansion properties of homemade fast investment material are comparable to those of the special fast investment material, so it can compensate for the cast contraction of IPS-Empress2 castable ceramic precisely.

Aluminum Silicates↗

PubMed2005

Evaluation of different bonded investments for dental titanium casting.

The properties of several different investments were investigated including phosphate bonded, magnesia bonded, and alumina cement investments. Measurements included the setting expansion, thermal expansion, and compressive strength of investments, as well as the tensile strength, elongation, Vickers hardness (VHN) and surface roughness of titanium castings. For phosphate bonded investment, the setting expansion after being mixed with its own mixing solution was 2.10%, which was larger than the other investments; the thermal expansion was -0.25% at 200 degrees C, the compressive strength 14 and 5 MPa after heating. For titanium cast in phosphate bonded investment, the hardness on its top surface was 655 Hv, the tensile strength was 379 MPa, the elongation was 19.4%, and the surface roughness was 2.29 microm. Although the thermal expansion of phosphate bonded investment is small, the setting expansion is large enough to compensate for the shrinkage of titanium castings. As its thermal expansion at T > or = 600 degrees C was constant and its heating-cooling cycle was almost reversible, these two properties can reduce the thermal shock and thus avoid cracking of the investment.

Aluminum Oxide↗

PubMed1979

Surface smoothness and marginal fit with phosphate-bonded investments.

Two phosphate-bonded investments and one calcium sulfate investment were evaluated for the surface smoothness and marginal fit they impart to gold castings. A modified technique was also evaluated for each phosphate-bonded investment, where the silica sol was not diluted and the spatulation time was reduced. The results of this study lead to the following conclusions: 1. The marginal fits obtained with all four phosphate-bonded methods were comparable to each other and superior to that obtained with the calcium sulfate investment. 2. The presence of nodules on the surface of the castings was more prevalent with the phosphate-bonded investments. However, this effect was not statistically significant. 3. Clinical assessment of the roughness of the castings revealed that all the methods tested produced clinically acceptable castings. 4. Visual observation by five dentists revealed that both the recommended and modified techniques for one of the phosphate-bonded investments (Ceramigold) produced a smoother surface than any other investment tested. Rating of scanning electron microscope photographs (X600) revealed no difference in the surface roughness between any of the castings. Consequently, no definitive relation between investment type or technique and surface roughness was established. 5. No correlation was demonstrated between surface roughness, as evaluated by either clinical observation or scanning electron microscope photography, and marginal fit of the castings.

Dental Alloys↗

PubMed2005

The effect of investment material type on the contamination zone and mechanical properties of commercially pure titanium castings.

STATEMENT OF PROBLEM: Different types of investment materials affect the formation of a surface contamination zone within commercially pure titanium (cpTi) castings. This contamination zone may possibly alter the mechanical properties of cast titanium, which may be problematic for castings used in the fabrication of removable and fixed prostheses. PURPOSE: The purpose of this study was to evaluate the effect of different types of investments on the extent of contamination zone and the modulus of elasticity, yield strength, elongation, and hardness of cpTi castings. MATERIAL AND METHODS: Forty wax patterns were fabricated according to ISO 9693 for tensile testing. The patterns were divided into 2 groups of 20 patterns each, invested, and cast in pairs using cpTi. The first group (P) was invested with a phosphate-bonded silica-based investment material (Ticoat S+L), and the second group (M), with a magnesia-alumina investment material (Rematitan Ultra). Investment materials were examined by x-ray diffraction analysis (XRD). One specimen from each group was sectioned and prepared for metallographic observation. The extent of the contamination zone was determined by scanning electron microscopy, using back-scattering electron imaging and energy dispersive spectroscopy analysis, as well as microhardness testing. The tensile strength of the specimens was determined in a universal testing machine. From the derived tensile curves, the modulus of elasticity, yield strength, and percentage elongation were calculated and statistically evaluated among the groups using the Student t test (alpha=.05). Three fractured specimens from each group were examined by scanning electron microscopy to determine the mode of fracture. RESULTS: XRD analysis showed that silica and magnesia were the dominant phases of Ticoat S+L and Rematitan Ultra, respectively. The contamination zone was found to extend 50 to 80 mum for the P specimens and 15 to 20 mum for the M specimens. No significance difference was found for the modulus of elasticity (P=85 +/- 11 GPa, M=79 +/- 13 GPa), whereas significant differences were found for the yield strength (P=462 +/- 48 MPa, M=321 +/- 54 MPa; P<.001) and percentage elongation (P=12 +/- 2, M=21 +/- 7; P=.002) between the groups tested. The fracture mode was brittle externally and ductile internally for both groups. CONCLUSIONS: According to the results of this study, the extent of the contamination zone as well as the yield strength and percentage elongation of the cpTi castings were significantly affected by the type of the investment material.

Dental Alloys↗

PubMed2006

Influence of investment type and sprue number on the casting accuracy of titanium crown margins.

STATEMENT OF PROBLEM: Titanium offers biocompatibility and adequate mechanical properties for fabricating dental prostheses; however, casting difficulties can compromise the accuracy of titanium crown margins. PURPOSE: The aim of this study was to evaluate the influence of investment type and number of sprues on accuracy of crown castings made with commercially pure titanium. MATERIAL AND METHODS: The casting accuracy was evaluated indirectly by determining the deficiency of titanium crown margins cast using the lost-wax technique. Crown margins were recorded in a silicone impression material. The degree of marginal rounding was measured and margin deficiencies were calculated. Seventy-five acrylic resin crown patterns with wax margins were prepared on a stainless steel stylized crown die having a 30-degree beveled finish line. Fifteen patterns were selected for the control group, and the degree of wax margin rounding was determined (group W, control). The remaining 60 were divided into 4 groups of 15 each, and cast using 2 different titanium investments: a monoammonium dihydrogenphosphate-bonded investment (Rematitan Plus; groups PI and PII), and a magnesium oxide-bonded investment (Rematitan Ultra; groups UI and UII). Each pattern was cast with either 1 (groups PI and UI) or 2 (groups PII and UII) sprues. Margin configurations for both wax pattern and cast specimens were measured and recorded with the same method, using silicone impressions of the margins. After polymerization, the silicone material was sectioned precisely in 8 locations through the margin area so that cross-sections of the margins could be observed. Marginal deficiency was determined using microscopic measurements from the silicone patterns and calculations. Data were subjected to 2-way analysis of variance (alpha=.05). RESULTS: Specimens from group W presented a mean marginal deficiency of 19 +/- 6 microm. The analysis of variance indicated a significant difference for the main factors, investment (P<.01) (P=91 +/- 28 microm and U=78 +/- 17 microm) and sprue number (P<.001) (I=97 +/- 23 microm and II=72 +/- 16 microm), as well as for interaction (P<.05) (PI=109 +/- 25 microm; PII=73 +/- 17 microm; UI=85 +/- 15 microm; and UII=71 +/- 16 microm). CONCLUSION: Within the limitations of this study, investment U provided better casting accuracy than investment P. Two sprues provided more accurate results than 1 sprue; however, this effect was more notable for investment P, as it produced similar results between groups PII and UII.

Analysis of Variance↗

PubMed2004

Tobacco and transition: an overview of industry investments, impact and influence in the former Soviet Union.

OBJECTIVES: To quantify the contribution the tobacco industry has made to foreign direct investment (FDI) in the former Soviet Union (FSU) as an indicator of its political and economic leverage; to explore the impact this has had on production capacity and tobacco control in the region. DESIGN: Data on industry investment and its impact on cigarette production capacity were collated from industry journals, reports, and websites. Data on total FDI were obtained from the European Bank of Reconstruction and Development. RESULTS: By the end of 2000, transnational tobacco companies (TTCs) had invested over 2.7 billion US dollars in 10 countries of the FSU. Tobacco money as a proportion of FDI varies from 1% to over 30% in Uzbekistan. Cigarette production capacity in the factories receiving investments tripled from 146 to 416 billion cigarettes per annum and the TTCs' market share has increased from nothing to between 50-100% in the markets in which they invested. Findings suggest that the effectiveness of national tobacco control measures corresponds broadly to the nature of the political and economic transition in each country and the size of industry investment, which is determined in part by the political context. Thus more effective measures tend to be seen in democratic states with smaller or no industry investments while the least effective measures are seen in highly centralised, one party states with high levels of industry investment or those with limited governmental capacity. CONCLUSIONS: The entry of the TTCs at a time of major political and economic change left the FSU particularly vulnerable to industry influence. This influence was enhanced by the industry's significant contribution to FDI, their ability to take over existing state monopolies in all but the largest countries, and the lack of democratic opposition.

Advertising↗

PubMed2005

Exploring the impact of foreign direct investment on tobacco consumption in the former Soviet Union.

BACKGROUND: Tobacco is the single largest cause of morbidity and mortality in the developed world; in the former socialist bloc tobacco kills twice as many men as in the west. Although evidence shows that liberalisation of the cigarette trade through the elimination of import barriers leads to significant increases in consumption, far less is known about the impact of foreign direct investment on cigarette consumption. This paper seeks to explore the impact that the substantial transnational tobacco company investments have had on patterns of tobacco trade and consumption in the former Soviet Union. DESIGN: Routine data were used to explore trends in cigarette trade and consumption in the 15 countries of the former Soviet Union from the 1960s to the present day. Comparisons were made between trends in countries that have received substantial investment from the tobacco transnationals and countries that have not. RESULTS: Between 1991 and 2000 cigarette production increased by 96% in countries receiving industry investment and by 11% in countries that did not. Over the same period cigarette consumption increased by 40%; the increase was concentrated in countries receiving investments. Despite these investments, cigarette imports still outweigh exports and no trade surplus has yet to result. CONCLUSIONS: The findings suggest that liberalisation of inward investment has a significant and positive impact on cigarette consumption and that without appropriate safeguards, market liberalisation may have long term negative impacts on health. Specific trade rules are needed to govern trade and investment in this uniquely harmful product. Implementation of effective tobacco control policies should precede tobacco industry privatisation. International financial organisations pressing for privatisation should ensure this occurs.

Commerce↗

PubMed2001

Taking risks in investing in the equity market: racial and ethnic differences.

Some policy makers and policy analysts have proposed that Social Security should be privatized to enable participants to achieve higher returns through investment in the stock market. How well individual retirees would fare financially under a privatized system largely depends on their decision to invest in the equity market, rather than in other types of investment vehicles. For that reason, it is important to investigate the degree to which minority people are currently investing in this market. This article presents the findings of a study that compared the investment behavior of black and Hispanic people aged 51 to 61 with the investment behavior of their white counterparts. The major findings indicate that black and Hispanic people: (a) are less likely to invest in the equity market than are white people, and (b) tend to invest smaller percentages of their assets in the equity market. Implications for policy are discussed.

Black or African American↗

PubMed2004

Study of resin-bonded calcia investment. Part 3: Hardness of titanium castings.

The Vickers hardness of the cross-sectioned area of titanium castings made from an experimental resin-bonded calcia investment and three commercial investments was evaluated. The microstructure and element distribution of the surface zone were analyzed using an EPMA. The results showed that the high hardness of the casting surface could be decreased using the experimental investment. The hardness of the castings made from the experimental investment at a 25-50 microm depth was lower than those from the other investments, and the thickness of the hardened casting surface was 125 microm. Layered structures with fewer layers were formed on the surfaces of the castings made from the experimental investment. The layered structures were influenced by both the investment components and the mold temperature at casting. The less contaminating nature of the experimental investment components and the technology of the room temperature mold contributed to the improved surface properties of the resulting castings.

Calcium Compounds↗

PubMed2005

Recycling of used commercial phosphate-bonded investments with additional mono-ammonium phosphate.

Industrial waste is on the increase, resulting in severe environmental contamination. Against this background, this study sought to investigate the possibility of recycling used phosphate-bonded investments. Commercial phosphate-bonded investment was mixed and heated according to manufacturer's instructions, then powdered with a ball mill machine to be used as recycled investment (Code: R). Mono-ammonium phosphate (NH4H2PO4) of 2, 5, 8, 11, and 14 g were added to 100 g of R because of residual MgO, and coded as Ra, Rb, Rc, Rd, and Re respectively. Investment properties were then examined. Particle size of R was 50.66 microm and close to the original investment. It was found that more NH4H2PO4 led to larger setting expansion, smaller thermal expansion, and lower fired strength. The data of Re in these three aspects were 1.42 +/- 0.09%, 0.78 +/- 0.21%, and 8.85 +/- 0.88 MPa respectively, and differences against the original investment were significant. Ra showed significantly longer setting time than other investments. Based on the results of this study, we concluded that it was possible to set used phosphate-bonded investments by adding NH4H2PO4; in particular, Rd showed suitable expansion and acceptable mechanical properties.

Conservation of Natural Resources↗