Propellant Formulations Research Articles

Environmentally safe (chlorine-free): new green propellant formulation based on 2,2,2-trinitroethyl-formate and HTPB.

A new green (chlorine-free) high energy dense oxidizer (HEDO) 2,2,2-trinitroethyl-formate (TNEF) and its propellant formulation based on the hydroxyl-terminated polybutadiene (HTPB) as a binder was prepared and studied. The new oxidizer TNEF was successfully prepared and characterized by nuclear magnetic resonance (NMR) and FTIR spectrometer. Scanning electron microscopy (SEM) was used to check the crystal morphology of the oxidizer. A high specific impulse (Is = 250.1 s) was obtained from the characteristics calculation of the new oxidizer instead of (Is = 156.9 s) for the commonly used ammonium perchlorate (AP) by using EXPLO5_V6.03 software. The burning behavior and the burning rate were determined by using a high speed camera. TNEF and the propellant formulations were studied by using nonisothermal thermogravimetric analysis (TGA) and the kinetic parameters of the studied samples were determined by using isoconversional (model-free) methods “Kissinger, Ozawa and Flynn–Wall (OFW) and Kissinger–Akahira–Sunose (KAS)”. The results proved that the new oxidizer and its formulation based on HTPB have chlorine-free decomposition products and have higher performance characteristics than the traditional propellants.

Characterization of Propellant Modulus and Rocket Motor Stress-Free Temperature Using Stress Sensors

Embedded stress sensors have previously been employed as part of health monitoring systems for solid rocket motors; however, the sensor readings were used to detect anomalies such as bore cracks and bondline delaminations. This work is unique because, instead of structural defects, the sensors are used to determine changes to both the modulus and the stress-free temperature: both of which are useful and difficult to obtain. To do this, sensors were embedded into a test motor (a small motor with a metal case, insulation, and an inert composite propellant formulation) and subjected to stepwise cooling cycles: the sensor readings at each plateau in the cooling cycle were a function of the stress-free temperature and modulus. When analyzed, the data gave both the modulus and stress-free temperature shift in the motor. The sensor and accompanying analyses were used to establish baseline readings; then, the motor was aged, and the procedures were repeated. Over an equivalent age of several years (about 4.5 years of aging at ambient temperature), the modulus changed by about 20%. Shifts in stress-free temperature were harder to detect and will be investigated in future work.

Experimental Approaches to Develop a High Thrust Ratio in a Single Chamber Dual Thrust Motor Using a Composite Propellant Formulation Based on HTPB/AP/Al

Experimental Approaches to Develop a High Thrust Ratio in a Single Chamber Dual Thrust Motor Using a Composite Propellant Formulation Based on HTPB/AP/Al

Thermal Behavior and Decomposition Kinetics of Bis(2,2,2‐trinitroethyl)‐oxalate as a High Energy Dense Oxidizer and its Mixture with Nitrocellulose

AbstractA new propellant formulation (NC‐BTNEOx) based on bis(2,2,2‐trinitroethyl)oxalate (BTNEOx) as a high energy dense oxidizer (HEDO) mixed with nitrocellulose (NC) matrix was prepared and studied. BTNEOx was prepared and characterized by nuclear magnetic resonance (NMR) and X‐ray diffraction (XRD). Photos of the prepared formulation obtained by scanning electron microscope (SEM) clarified a good mixing of the nitrocellulose (NC) matrix with BTNEOx. A smokeless burning was observed and recorded for the prepared NC‐BTNEOx by a high speed camera. The thermal behavior and decomposition kinetics of the NC matrix, BTNEOx and their mixture have been investigated nonisothermally by using thermogravimetric analysis (TGA) and Differential scanning calorimetry (DSC). Isoconversional (model‐free) methods; Kissinger, Ozawa and Flynn−Wall (OFW) and Kissinger−Akahira−Sunose (KAS), were used to determine the kinetic parameters of the studied samples. The results proved that BTNEOx has melting temperature at 104.1 °C and maximum peak temperature at 200.6 °C, also it has effective activation energy in the range of 107–110 kJ/mol. The prepared NC‐BTNEOx has no endothermic peak and has exothermic peak at 201.7 °C which means that a composite might be formed due to the mixing of BTNEOx with NC. The prepared NC‐BTNEOx has effective activation energy in the range of 172–180 kJ/mol. BTNEOx required more study to proof the possibility of replacing the nitroglycerine in a smokeless double base propellant.

Investigation of 2,2,2-trinitroethyl-nitrocarbamate as a high energy dense oxidizer and its mixture with Nitrocellulose (thermal behavior and decomposition kinetics)

Thermal behavior and decomposition kinetics of the new interesting high energy dense oxidizer (HEDO) 2,2,2-trinitroethyl-nitrocarbamate (TNENC) and its propellant formulation based on nitrocellulose (NC) as a binder was investigated using nonisothermal thermogravimetric analyzer (TGA) and differential scanning calorimetry (DSC). TNENC has been prepared and characterized by nuclear magnetic resonance (NMR). X-ray diffraction (XRD) was used to study the molecular structure of TNENC. Scanning electron microscope (SEM) was used to check the homogeneity of the new propellant formulation (NC-TNENC). The burning behavior of the prepared NC-TNENC was recorded by high speed camera to observe the smoke produced. A high specific impulse (Is=244.46s) was obtained from the characteristics calculation of the new propellant formulation by using EXPLO5_V6.03 software. The kinetic parameters of the studied samples were determined by using isoconversional (model-free) methods Kissinger, Ozawa and Flynn–Wall (OFW) and Kissinger–Akahira–Sunose (KAS). The results proved that TNENC melts at temperature of 110.5°C and has a maximum decomposition peak temperature at 166.4°C, also it has activation energy in the range of 104–106kJmol−1. The prepared NC-TNENC didn’t show any endothermic peak and its exothermic peak was at 200.8°C which means that a composite might be formed during the chemical mixing of TNENC with NC. The activation energy of the prepared NC-TNENC was in the range of 176–181kJmol−1. TNENC required experimental performance measurements to proof the possibility of replacing the nitroglycerine in a smokeless double base propellant.

Studies on Effect of Nano-MnO2 in HTPB-based Composite Propellant Formulations

Studies on Effect of Nano-MnO2 in HTPB-based Composite Propellant Formulations

HTPB/AP계 고체 추진제의 연소속도 증진 방안 연구

본 논문에서는 HTPB/AP/Al계 추진제의 성능 개선을 위한 연소속도와 압력지수를 제어하기 위하여 연소특성에 관한 AP입자 사이즈 비율과 연소촉매로 사용된 Butacene 함량의 영향을 조사하였다. 23%의 <TEX>$28{\mu}m$</TEX> Al과 3%의 Butacene을 포함하는 추진제 조성에서 연소속도와 압력지수는 <TEX>$9{\mu}m$</TEX> AP 입자의 함량이 증가함에 따라 증가하였다. 그리고 Butacene을 함유하는 추진제는 비교적 낮은 압력지수 특성을 보임으로써 Butacene의 함량이 증가함에 따라 연소속도도 증가하였다. 그러나 Butacene의 함량에 의한 압력지수의 변화는 크게 나타나지 않았다. In this paper, in order to control the burning rate and pressure exponent of HTPB/AP/Al based propellant for the improvement of performance, the effect of the size ratio of AP particles and various contents of Butacene as burning catalyst on combustion properties was investigated. In the propellant formulation with both <TEX>$28{\mu}m$</TEX> Al of 23% and Butacene of 3%, the burning rate and pressure exponent were increased with increasing the contents of <TEX>$9{\mu}m$</TEX> AP particles. And the burning rate was increased with increasing the contents of Butacene with showing the relatively low pressure exponent in the propellant containing Butacene. However, the significant variations of pressure exponent by contents of Butacene were not observed.

New directions in the area of modern energetic polymers: An overview

Energetic polymers containing nitro, nitrato, and azido groups release high energy during combustion and thereby increase the performance of the systems. A number of energetic polymers have been found suitable for use as binders in high-performance propellant and explosive formulations. This review describes the synthetic and application aspects of various modern energetic polymers for explosive formulations and propellants.

Optimal selection of appropriate fuels for a miniaturized motor and numerical simulations on its temperature distributions and thermal deformation

In this work, the energy characteristics of different propellants were thermodynamically calculated using the Minimum Gibbs free energy method. Based on such calculations and the previous experimental results using the DSC investigations on the thermal decomposition behavior, an optimized propellant formulation was selected. The numerical simulations on the temperature distributions for a prepared miniaturized motor with this formulation were conducted, and the resultant thermalstress and deformationof the thruster array were investigated. In particular, a physical micro model was established, and the effects of combustion parameters on the thermal performance were studied. The results showed thatthe highest temperature occurred at the boundary of the combustion chamber, where the thermal stress and deformation were the maximum. Furthermore, the thermal stress and deformation of silicon material was smaller than steel, and the thermal stress was the main reason for the destruction of micro-thruster stability. In addition, the maximum thermal deformation was small and had little effects on the thermalstability, whereas the thermal stress was the main reason for the poor thermal stability.

The effect of decorated graphene addition on the burning rate of ammonium perchlorate composite propellants

Catalysts are often added to solid propellant formulations to tailor burning rates. Nanocatalysts can increase propellant burning rates over standard catalyst sizes due to the increase in surface area per unit weight. However, the increased surface area that the binder must wet can be prohibitive if large amounts of nanocatalysts are used. Additionally, agglomeration of the nanocatalyst can result in micron-scale particles, reducing catalyst effectiveness. In this study a nanoscale iron oxide catalyst has been used to decorate graphene. By decorating graphene with the catalyst, nanoscale features are kept but the catalyst is stabilized to reduce agglomeration. Changes in burning rate between the catalyzed and uncatalyzed propellants are investigated. The effect on burning rate of encapsulating the catalyst inside the fine AP crystals compared to propellants where it is added to the binder is also investigated. We also compare propellants with decorated graphene and propellants with undecorated graphene catalysts. The three comparisons are made for two different graphene preparation methods. It is found that the highest burning rates occur in propellants where the graphene is decorated with catalyst and encapsulated in the fine AP. The next highest burning rates occur in propellants with decorated graphene that is physically mixed into the propellant. The lowest burning rates are found in propellants where the graphene is undecorated, where there is little difference between encapsulated or physically mixed graphene blanks, or compared to a baseline propellant. Burning rates are found to be similar between graphene preparation methods considered.

Studies on composite solid propellant with tri-modal ammonium perchlorate containing an ultrafine fraction

Abstract Composite solid propellant is prepared using tri-modal Ammonium perchlorate (AP) containing coarse, fine and ultrafine fractions of AP with average particle size (APS) 340, 40 and 5 μm respectively, in various compositions and their rheological, mechanical and burn rate characteristics are evaluated. The optimum combination of AP coarse to fine to ultrafine weight fraction was obtained by testing of series of propellant samples by varying the AP fractions at fixed solid loading. The concentration of aluminium was maintained constant throughout the experiments for ballistics requirement. The propellant formulation prepared using AP with coarse to fine to ultrafine ratio of 67:24:9 has lowest viscosity for the propellant paste and highest tensile strength due to dense packing as supported by the literature. A minimum modulus value was also observed at 9 wt. % of ultrafine AP concentration indicates the maximum solids packing density at this ratio of AP fractions. The burn rate is evaluated at different pressures to obtain pressure exponent. Incorporation of ultrafine fraction of AP in propellant increased burn rate without adversely affecting the pressure exponent. Higher solid loading propellants are prepared by increased AP concentration from 67 to 71 wt. % using AP with coarse to fine to ultrafine ratio of 67:24:9. Higher solid content up to 89 wt. % was achieved and hence increased solid motor performance. The unloading viscosity showed a trend with increased AP content and the propellant couldn't able to cast beyond 71 wt. % of AP. Mechanical properties were also studied and from the experiments noticed that % elongation decreased with increased AP content from 67 to 71 wt.%, whereas tensile strength and modulus increased. Burn rate increased with increased AP content and observed that pressure exponent also increased and it is high for the propellant containing with 71 wt.% of AP due to increased oxidiser to fuel ratio. Catalysed composite solid propellant is prepared by using burn rate modifiers Copper chromite and Iron oxide. Addition of Copper chromite and Iron oxide has enhanced the burn rate of tri-modal AP based composite solid propellant. The catalytic propensity of copper chromite is higher than that of iron oxide. The pressure exponent increased with the catalyst concentration and the values obtained are compatible for solid rocket motor applications.

Obituaries

OBITUARIES Obituaries ShareShare onFacebookTwitterWechatLinked InRedditEmail Linda WangC&EN, 2017, 95 (22), p 44May 29, 2017Cite this:C&EN 95, 22, 44Derek A. Davenport (Credit: Courtesy of Tamar Susskind)Figure1of1Derek A. Davenport, 89, died on April 4 in West Lafayette, Ind. “He touched the lives, and occasionally altered the career paths, of hundreds of undergraduate and graduate students. He served as chair of the ACS Division of Chemical Education as well as the Division of the History of Chemistry, and he was the recipient of several national awards. Derek traveled extensively, lectured in every state of the Union, and spent two sabbaticals overseas helping establish the Indian Institute of Technology in Kanpur. He was never one to turn down a good Manhattan, nor the opportunity to provide a colorful lecture (complete with slides) about his experiences in academia, his travels, or his ever-growing collection of Nigerian and Inuit art.”—family of Derek Davenport Most recent title: professor emeritus of chemistry, Purdue University Education: B.Sc., chemistry, 1947, and Ph.D., chemistry, 1950, University College LondonSurvivors: daughter, Susan; sons, Martin and Alan; two grandchildren; long-time companion, Tamar SusskindEugene Garfield Figure1of1Eugene Garfield, 91, died on Feb. 26 in Bryn Mawr, Pa. “Eugene Garfield is universally recognized as a visionary pioneer in information science. He founded the Institute for Scientific Information in 1960, ultimately creating research tools used by researchers around the world, including the Science Citation Index, Current Contents, and Current Chemical Reactions. His work not only changed how research was conducted but also changed the lives of many with whom he came in contact. He served as a role model, teacher, mentor, and friend to many within the scientific and information communities and earned their lifelong respect, admiration, and loyalty.”—Bonnie Lawlor, friend and former employee Most recent title: president and founder, Institute for Scientific Information (now Clarivate Analytics)Education: B.S., chemistry, 1949, and M.S., library science, 1954, Columbia University; Ph.D., structural linguistics, University of Pennsylvania, 1961Survivors: wife, Meher; sons, Alex, Stephen, and JoshMaurice M. Kreevoy Maurice M. Kreevoy, 87, died on March 20, 2016, in Crystal, Minn. “He was a terrific scientist and scholar in the best sense of the word, but he was also a real gentleman. Whenever people asked me about Maury, they would comment about what a kind man he was.”—Steven Kass, friend and colleague Most recent title: chemistry professor, University of MinnesotaEducation: B.S., chemistry, University of California, Los Angeles, 1950; Ph.D., chemistry, Massachusetts Institute of Technology, 1954Survivors: daughter, Edith Pang; son, William; two grandchildrenGeorge D. (Doug) Nelson (Credit: Courtesy of George Nelson Jr.)Figure1of1George D. (Doug) Nelson, 95, died on Sept. 25, 2016, in St. Louis. “Doug worked at Lehigh University from 1942 to 1947 on a National Defense Research Corp. program studying problems in small arms manufacturing related to stress/corrosion failure of brass cartridge shells. He later joined Monsanto Chemical Co., where he worked on applications for phosphoric acid as well as its sodium, potassium, and calcium salts. Some of this included the first formulations for fluoride in toothpastes. Additional contributions were made in reduced-fume acid bath compositions for aluminum brightening from 1959 to 1965. From 1965 to his retirement in 1986, Doug worked on chlorine stabilizers based on chlorinated-S-triazinetrione for sanitizers, detergents, bleaches, and disinfectants for swimming pools and spas. His pride in his profession led me to a career in chemistry.”—George D. Nelson Jr., son Most recent title: chemist, MonsantoEducation: B.S., chemistry, Randolph-Macon College, 1941; M.S., chemistry, Lehigh University, 1943Survivors: wife, Pauline; daughter, Laura Colburn; sons, Frederick and George Jr.; five grandchildrenJoseph N. Neucere Joseph N. Neucere, 83, died on Jan. 20, 2016, in San Angelo, Texas. “Joseph’s first language was Cajun French. After graduating from high school at age 16, he moved to New Orleans. At 19, he enlisted in the U.S. Air Force as a medic in the Korean zone. Later, he became an X-ray technician. He was employed by the U.S. Department of Agriculture in New Orleans as a research chemist. He retired in January 1997. He enjoyed, for many years, going fishing with work friends.”—family of Joseph Neucere Most recent title: research chemist, U.S. Department of Agriculture Education: B.S., chemistry and physics, Louisiana State University, Baton Rouge Survivors: wife, Martha; daughter, SeasonRodney L. Willer Rodney L. Willer, 67, died on Feb. 12, 2016, in Gulfport, Miss. “Rod published many significant papers and patents on synthesis, characterization, and scale-up of energetic binders, furazans, polycyclic nitramines, energetic cubyl compounds, hydroxyl ammonium nitrate, and propellant formulation. He was a sports car, powerboat, waterskiing, and rock climbing enthusiast.”—Robson F. Storey, colleague Most recent title: research scientist, University of Southern MississippiEducation: B.S., chemistry, 1970, and M.S., organic chemistry, 1972, East Carolina University; Ph.D., organic chemistry, University of North Carolina, Chapel Hill, 1976Survivors: brother, Clinton; sister, Yvonne Marion Evans

Characterization of Aging Behavior of Butacene® Based Composite Propellants by Loss Factor Curves

AbstractButacene® is a polymeric binder with ferrocenyl groups chemically bonded to HTPB backbone. Through incorporation in the AP−Al composite propellant formulation, it leads to high burning rates (BR) &gt;20 mm/s at 7 MPa, and low pressure exponents n&lt;0.5, allowing more flexibility to the rocket design, keeping the characteristics (process, mechanical properties, pot‐life) of HTPB binder formulations together with a lower vulnerability (IM) contribution by Butacene®. The key molecular level characteristic of such HTPB based elastomeric binder systems of solid composite rocket propellants (SCRP) is the glass‐rubber transition region, which is mainly defined by the molecular mobility of the components in the polymeric network during the transition from energy to entropy elasticity with respect to temperature. The molecular rearrangement regions or binder mobility fractions related to the glass‐rubber transition of such composite propellants during storage are important in terms of in‐service time estimations. They are detectable by dynamic mechanical analysis (DMA). Formulations with and without Butacene® were prepared and analyzed using the loss factor curves obtained by torsion DMA. A special modelling with so named Exponentially Modified Gaussian (EMG) distribution was used to define and quantify sub‐transition regions in the loss factor curve. SEM images revealed the network formation connected with AP bonding, which correlate to the tensile results. DMA loss factors revealed a strong oxidation with Butacene® containing formulations during aging. Burning rates of the formulations show slight increases with aging.

Structure and mechanical properties of fluorine-containing glycidyl azide polymer-based energetic binders

A novel energetic polymer, fluorine-containing glycidyl azide polymers (FGAP) was developed via an initial cationic copolymerization of epichlorohydrin and 1,1,1-trifluoro-2,3-epoxypropane, followed by azidation. The structure of the FGAP was confirmed by FT-IR, 1H NMR and 13C NMR. The molecular weight and the thermal behavior of FGAP were characterized by GPC, DSC and TGA respectively. The FGAP showed a molecular weight of 2845 g mol−1, and the glass transition temperature (Tg) and decomposition temperature were found to be −47.8 and 253 °C, respectively. FGAP based polyurethane networks were further prepared using triphenylmethane-4,4,4-triisocyanate as the cross-linking agent. In comparison with GAP, FGAP based polyurethane networks exhibited a better mechanical behaviors (a tensile strength of 1.5 MPa and an elongation at break of 81.6%). The results demonstrated that the FGAP might be a promising polymeric binder for future propellant formulations.

Characterization of display pyrotechnic propellants: Burning rate

The combustion of display pyrotechnic propellants utilized for producing colored light has been studied. The linear burning rates of cylindrical propellant strands were measured using high-speed videography. The experiments were conducted with air at atmospheric pressure as the surrounding medium mimicking the conditions of unconfined aerial combustion typically encountered for these propellants. Five different formulations of display pyrotechnic propellants producing red, green, blue, yellow, and silver color were tested. The flame zone was observed to be situated very close to the propellant surface and the colored flame extended beyond this point. The phenomenology of the combustion process was explained and the combustion process was also studied numerically using a methodology based on the deflagration rate law. The experimentally measured burning rates were utilized in the deflagration rate law to obtain the simulation parameters which may be utilized in hydrocodes for performance prediction and simulation pyrotechnic propellant applications.

Optimal design of a composite propellant formulation using response surface methodology

Abstract There is a continuous demand for high performance composite propellant formulations to meet mission requirements. The performance of composite propellant formulations can be enhanced by optimizing propellant formulation. However, the main objective of this study is to formulate a composition for composite propellant by optimizing the specific impulse which is the measure of propellant performance. A central composite design (ccd) consisting five ingredients (ammonium nitrate, powdered aluminum, polyester resin, ammonium dichromate and powdered charcoal) at five levels was used to formulate optimum propellant formulation from composite materials of ammonium nitrate based propellant verified for propellant characteristics using propellant performance evaluation programme (propep 3). The responses evaluated are specific impulse, characteristic velocity, density, temperature and molecular weight. Response surface methodology was used to analyze the results of the ccd of the composite formulations. The optimum values for specific impulse, characteristic velocity, density, temperature and molecular weight of the mixture from the surface plot are 212.178 s, 1335.81 m/s, 1640.6 k g/m3, 1968.73 k and 21.7722 g/mol respectively. The optimum predicted specific impulse was 212.178 s at composite composition of 73.61% ammonium nitrate, 4.36% powdered aluminum, 14.39% polyester resin, 5.10% ammonium dichromate and 2.54% powdered charcoal. The propellant optimum composition validated with propep 3 are in good agreement with each other in their accompany propellant characteristics. Therefore, the optimal propellant formulation enhanced the performance of solid propellants.

Evaluation of 4‐(Dimethylsilyl) Butyl Ferrocene Grafted HTPB as a Burning Rate Modifier in Composite Propellant Formulation using Bicurative System

AbstractHigh burning rate composite propellants are achieved by incorporation of fine particles of oxidizer, transition metal oxides, and liquid ballistic modifiers. However, they pose processing problems, inertness to the composition and migration related issues. To overcome such problems, an attempt was made to incorporate ferrocenyl grafted HTPB as a burning rate modifier by partly replacing HTPB from 10 % to 50 % using TDI/ IPDI bicurative system and to study their processability in terms of viscosity, mechanical, thermal, sensitivity, and ballistic properties. The data on viscosity reveal that there is a marginal enhancement in end of mix viscosity as percentage of ferrocenyl grafted HTPB increases. The mechanical data reveal that tensile strength and elastic modulus increases, whereas percentage elongation decreases compared to base composition. The results on thermal properties infer that, as the percentage of ferrocenyl grafted HTPB increases, onset decomposition temperature decreases. The impact and friction sensitivity data also envisage that sensitivity increases in comparison to base composition. The data on ballistic properties revealed that there is ca. 53 % increase in burning rate, while decrease in “n” value from 0.39 to 0.2 was obtained compared to base composition.

Evaluation of Epoxy Terminated Polybutadiene in Ammonium Perchlorate Coated Boron Based Fuel Rich Propellant Formulations

Evaluation of Epoxy Terminated Polybutadiene in Ammonium Perchlorate Coated Boron Based Fuel Rich Propellant Formulations

Recent advances in new oxidizers for solid rocket propulsion

Recent progress in the synthesis and modification of green oxidizers and their application in solid rocket propellant formulations during these last few decades are reviewed.

The REACH Impact on Gun Propellant Formulations

AbstractREACH is the abbreviation for Registration, Evaluation, Authorisation, and Restriction of Chemicals. It is a regulation of the European Union, adopted to improve the protection of human health and the environment from the risks that can be posed by chemicals, while enhancing the competitiveness of the EU chemicals industry. Current gun propellant formulations employ environmentally unfriendly materials, like dibutyl‐phthalate (DBP). In this contribution a study was conducted, which aims to evaluate the environmental friendliness of common gun propellant ingredients and to propose environmentally acceptable substitutes for harmful substances. In the first step a simplified assessment matrix based on the REACH relevant properties of chemicals was developed. The matrix consists of the main criteria of the new European regulation, their legal limit values, and their evaluation by REACH. For a selected number of ingredients of commonly used gun propellants the toxicological and eco‐toxicological data were collected in order to carry out an initial assessment under the REACH regulation. In this context some substances show remarkable and critical properties and it was started to find suitable substitutes, which were first assessed with regard to the REACH regulation. As an example potential substitutes for nitroglycerine were experimentally introduced in gun propellant formulations and their main properties were determined and compared with the standard formulation.